--- jsr166/src/jsr166y/ForkJoinPool.java 2012/01/31 01:33:21 1.121
+++ jsr166/src/jsr166y/ForkJoinPool.java 2012/12/08 14:08:51 1.154
@@ -11,7 +11,6 @@ import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
-import java.util.Random;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
@@ -19,10 +18,6 @@ import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.RunnableFuture;
import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.locks.AbstractQueuedSynchronizer;
-import java.util.concurrent.locks.Condition;
/**
* An {@link ExecutorService} for running {@link ForkJoinTask}s.
@@ -42,14 +37,22 @@ import java.util.concurrent.locks.Condit
* ForkJoinPool}s may also be appropriate for use with event-style
* tasks that are never joined.
*
- * A {@code ForkJoinPool} is constructed with a given target
- * parallelism level; by default, equal to the number of available
- * processors. The pool attempts to maintain enough active (or
- * available) threads by dynamically adding, suspending, or resuming
- * internal worker threads, even if some tasks are stalled waiting to
- * join others. However, no such adjustments are guaranteed in the
- * face of blocked IO or other unmanaged synchronization. The nested
- * {@link ManagedBlocker} interface enables extension of the kinds of
+ *
A static {@link #commonPool()} is available and appropriate for
+ * most applications. The common pool is used by any ForkJoinTask that
+ * is not explicitly submitted to a specified pool. Using the common
+ * pool normally reduces resource usage (its threads are slowly
+ * reclaimed during periods of non-use, and reinstated upon subsequent
+ * use).
+ *
+ *
For applications that require separate or custom pools, a {@code
+ * ForkJoinPool} may be constructed with a given target parallelism
+ * level; by default, equal to the number of available processors. The
+ * pool attempts to maintain enough active (or available) threads by
+ * dynamically adding, suspending, or resuming internal worker
+ * threads, even if some tasks are stalled waiting to join
+ * others. However, no such adjustments are guaranteed in the face of
+ * blocked I/O or other unmanaged synchronization. The nested {@link
+ * ManagedBlocker} interface enables extension of the kinds of
* synchronization accommodated.
*
*
In addition to execution and lifecycle control methods, this
@@ -59,7 +62,7 @@ import java.util.concurrent.locks.Condit
* {@link #toString} returns indications of pool state in a
* convenient form for informal monitoring.
*
- *
As is the case with other ExecutorServices, there are three
+ *
As is the case with other ExecutorServices, there are three
* main task execution methods summarized in the following table.
* These are designed to be used primarily by clients not already
* engaged in fork/join computations in the current pool. The main
@@ -94,22 +97,16 @@ import java.util.concurrent.locks.Condit
*
*
*
- *
Sample Usage. Normally a single {@code ForkJoinPool} is
- * used for all parallel task execution in a program or subsystem.
- * Otherwise, use would not usually outweigh the construction and
- * bookkeeping overhead of creating a large set of threads. For
- * example, a common pool could be used for the {@code SortTasks}
- * illustrated in {@link RecursiveAction}. Because {@code
- * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
- * daemon} mode, there is typically no need to explicitly {@link
- * #shutdown} such a pool upon program exit.
- *
- *
{@code
- * static final ForkJoinPool mainPool = new ForkJoinPool();
- * ...
- * public void sort(long[] array) {
- * mainPool.invoke(new SortTask(array, 0, array.length));
- * }}
+ * The common pool is by default constructed with default
+ * parameters, but these may be controlled by setting three {@link
+ * System#getProperty system properties} with prefix {@code
+ * java.util.concurrent.ForkJoinPool.common}: {@code parallelism} --
+ * an integer greater than zero, {@code threadFactory} -- the class
+ * name of a {@link ForkJoinWorkerThreadFactory}, and {@code
+ * exceptionHandler} -- the class name of a {@link
+ * java.lang.Thread.UncaughtExceptionHandler
+ * Thread.UncaughtExceptionHandler}. Upon any error in establishing
+ * these settings, default parameters are used.
*
*
Implementation notes: This implementation restricts the
* maximum number of running threads to 32767. Attempts to create
@@ -177,7 +174,10 @@ public class ForkJoinPool extends Abstra
* If an attempted steal fails, a thief always chooses a different
* random victim target to try next. So, in order for one thief to
* progress, it suffices for any in-progress poll or new push on
- * any empty queue to complete.
+ * any empty queue to complete. (This is why we normally use
+ * method pollAt and its variants that try once at the apparent
+ * base index, else consider alternative actions, rather than
+ * method poll.)
*
* This approach also enables support of a user mode in which local
* task processing is in FIFO, not LIFO order, simply by using
@@ -194,20 +194,24 @@ public class ForkJoinPool extends Abstra
* WorkQueues are also used in a similar way for tasks submitted
* to the pool. We cannot mix these tasks in the same queues used
* for work-stealing (this would contaminate lifo/fifo
- * processing). Instead, we loosely associate submission queues
+ * processing). Instead, we randomly associate submission queues
* with submitting threads, using a form of hashing. The
* ThreadLocal Submitter class contains a value initially used as
* a hash code for choosing existing queues, but may be randomly
* repositioned upon contention with other submitters. In
- * essence, submitters act like workers except that they never
- * take tasks, and they are multiplexed on to a finite number of
- * shared work queues. However, classes are set up so that future
- * extensions could allow submitters to optionally help perform
- * tasks as well. Insertion of tasks in shared mode requires a
- * lock (mainly to protect in the case of resizing) but we use
- * only a simple spinlock (using bits in field runState), because
- * submitters encountering a busy queue move on to try or create
- * other queues, so never block.
+ * essence, submitters act like workers except that they are
+ * restricted to executing local tasks that they submitted (or in
+ * the case of CountedCompleters, others with the same root task).
+ * However, because most shared/external queue operations are more
+ * expensive than internal, and because, at steady state, external
+ * submitters will compete for CPU with workers, ForkJoinTask.join
+ * and related methods disable them from repeatedly helping to
+ * process tasks if all workers are active. Insertion of tasks in
+ * shared mode requires a lock (mainly to protect in the case of
+ * resizing) but we use only a simple spinlock (using bits in
+ * field qlock), because submitters encountering a busy queue move
+ * on to try or create other queues -- they block only when
+ * creating and registering new queues.
*
* Management
* ==========
@@ -229,31 +233,26 @@ public class ForkJoinPool extends Abstra
* and their negations (used for thresholding) to fit into 16bit
* fields.
*
- * Field "runState" contains 32 bits needed to register and
- * deregister WorkQueues, as well as to enable shutdown. It is
- * only modified under a lock (normally briefly held, but
- * occasionally protecting allocations and resizings) but even
- * when locked remains available to check consistency. An
- * auxiliary field "growHints", also only modified under lock,
- * contains a candidate index for the next WorkQueue and
- * a mask for submission queue indices.
+ * Field "plock" is a form of sequence lock with a saturating
+ * shutdown bit (similarly for per-queue "qlocks"), mainly
+ * protecting updates to the workQueues array, as well as to
+ * enable shutdown. When used as a lock, it is normally only very
+ * briefly held, so is nearly always available after at most a
+ * brief spin, but we use a monitor-based backup strategy to
+ * block when needed.
*
* Recording WorkQueues. WorkQueues are recorded in the
- * "workQueues" array that is created upon pool construction and
- * expanded if necessary. Updates to the array while recording
- * new workers and unrecording terminated ones are protected from
- * each other by a lock but the array is otherwise concurrently
- * readable, and accessed directly. To simplify index-based
- * operations, the array size is always a power of two, and all
- * readers must tolerate null slots. Shared (submission) queues
- * are at even indices, worker queues at odd indices. Grouping
- * them together in this way simplifies and speeds up task
- * scanning. To avoid flailing during start-up, the array is
- * presized to hold twice #parallelism workers (which is unlikely
- * to need further resizing during execution). But to avoid
- * dealing with so many null slots, variable runState includes a
- * mask for the nearest power of two that contains all currently
- * used indices.
+ * "workQueues" array that is created upon first use and expanded
+ * if necessary. Updates to the array while recording new workers
+ * and unrecording terminated ones are protected from each other
+ * by a lock but the array is otherwise concurrently readable, and
+ * accessed directly. To simplify index-based operations, the
+ * array size is always a power of two, and all readers must
+ * tolerate null slots. Worker queues are at odd indices. Shared
+ * (submission) queues are at even indices, up to a maximum of 64
+ * slots, to limit growth even if array needs to expand to add
+ * more workers. Grouping them together in this way simplifies and
+ * speeds up task scanning.
*
* All worker thread creation is on-demand, triggered by task
* submissions, replacement of terminated workers, and/or
@@ -314,24 +313,33 @@ public class ForkJoinPool extends Abstra
*
* Signalling. We create or wake up workers only when there
* appears to be at least one task they might be able to find and
- * execute. When a submission is added or another worker adds a
- * task to a queue that previously had fewer than two tasks, they
- * signal waiting workers (or trigger creation of new ones if
- * fewer than the given parallelism level -- see signalWork).
- * These primary signals are buttressed by signals during rescans;
- * together these cover the signals needed in cases when more
- * tasks are pushed but untaken, and improve performance compared
- * to having one thread wake up all workers.
+ * execute. However, many other threads may notice the same task
+ * and each signal to wake up a thread that might take it. So in
+ * general, pools will be over-signalled. When a submission is
+ * added or another worker adds a task to a queue that has fewer
+ * than two tasks, they signal waiting workers (or trigger
+ * creation of new ones if fewer than the given parallelism level
+ * -- signalWork), and may leave a hint to the unparked worker to
+ * help signal others upon wakeup). These primary signals are
+ * buttressed by others (see method helpSignal) whenever other
+ * threads scan for work or do not have a task to process. On
+ * most platforms, signalling (unpark) overhead time is noticeably
+ * long, and the time between signalling a thread and it actually
+ * making progress can be very noticeably long, so it is worth
+ * offloading these delays from critical paths as much as
+ * possible.
*
* Trimming workers. To release resources after periods of lack of
* use, a worker starting to wait when the pool is quiescent will
- * time out and terminate if the pool has remained quiescent for
- * SHRINK_RATE nanosecs. This will slowly propagate, eventually
- * terminating all workers after long periods of non-use.
+ * time out and terminate if the pool has remained quiescent for a
+ * given period -- a short period if there are more threads than
+ * parallelism, longer as the number of threads decreases. This
+ * will slowly propagate, eventually terminating all workers after
+ * periods of non-use.
*
* Shutdown and Termination. A call to shutdownNow atomically sets
- * a runState bit and then (non-atomically) sets each worker's
- * runState status, cancels all unprocessed tasks, and wakes up
+ * a plock bit and then (non-atomically) sets each worker's
+ * qlock status, cancels all unprocessed tasks, and wakes up
* all waiting workers. Detecting whether termination should
* commence after a non-abrupt shutdown() call requires more work
* and bookkeeping. We need consensus about quiescence (i.e., that
@@ -359,13 +367,13 @@ public class ForkJoinPool extends Abstra
* method tryCompensate() may create or re-activate a spare
* thread to compensate for blocked joiners until they unblock.
*
- * A third form (implemented in tryRemoveAndExec and
- * tryPollForAndExec) amounts to helping a hypothetical
- * compensator: If we can readily tell that a possible action of a
- * compensator is to steal and execute the task being joined, the
- * joining thread can do so directly, without the need for a
- * compensation thread (although at the expense of larger run-time
- * stacks, but the tradeoff is typically worthwhile).
+ * A third form (implemented in tryRemoveAndExec) amounts to
+ * helping a hypothetical compensator: If we can readily tell that
+ * a possible action of a compensator is to steal and execute the
+ * task being joined, the joining thread can do so directly,
+ * without the need for a compensation thread (although at the
+ * expense of larger run-time stacks, but the tradeoff is
+ * typically worthwhile).
*
* The ManagedBlocker extension API can't use helping so relies
* only on compensation in method awaitBlocker.
@@ -385,45 +393,83 @@ public class ForkJoinPool extends Abstra
* (http://portal.acm.org/citation.cfm?id=155354). It differs in
* that: (1) We only maintain dependency links across workers upon
* steals, rather than use per-task bookkeeping. This sometimes
- * requires a linear scan of workQueues array to locate stealers, but
- * often doesn't because stealers leave hints (that may become
- * stale/wrong) of where to locate them. A stealHint is only a
- * hint because a worker might have had multiple steals and the
- * hint records only one of them (usually the most current).
- * Hinting isolates cost to when it is needed, rather than adding
- * to per-task overhead. (2) It is "shallow", ignoring nesting
- * and potentially cyclic mutual steals. (3) It is intentionally
+ * requires a linear scan of workQueues array to locate stealers,
+ * but often doesn't because stealers leave hints (that may become
+ * stale/wrong) of where to locate them. It is only a hint
+ * because a worker might have had multiple steals and the hint
+ * records only one of them (usually the most current). Hinting
+ * isolates cost to when it is needed, rather than adding to
+ * per-task overhead. (2) It is "shallow", ignoring nesting and
+ * potentially cyclic mutual steals. (3) It is intentionally
* racy: field currentJoin is updated only while actively joining,
* which means that we miss links in the chain during long-lived
* tasks, GC stalls etc (which is OK since blocking in such cases
* is usually a good idea). (4) We bound the number of attempts
- * to find work (see MAX_HELP_DEPTH) and fall back to suspending
- * the worker and if necessary replacing it with another.
+ * to find work (see MAX_HELP) and fall back to suspending the
+ * worker and if necessary replacing it with another.
+ *
+ * Helping actions for CountedCompleters are much simpler: Method
+ * helpComplete can take and execute any task with the same root
+ * as the task being waited on. However, this still entails some
+ * traversal of completer chains, so is less efficient than using
+ * CountedCompleters without explicit joins.
*
* It is impossible to keep exactly the target parallelism number
* of threads running at any given time. Determining the
* existence of conservatively safe helping targets, the
* availability of already-created spares, and the apparent need
* to create new spares are all racy, so we rely on multiple
- * retries of each. Currently, in keeping with on-demand
- * signalling policy, we compensate only if blocking would leave
- * less than one active (non-waiting, non-blocked) worker.
- * Additionally, to avoid some false alarms due to GC, lagging
- * counters, system activity, etc, compensated blocking for joins
- * is only attempted after rechecks stabilize in
- * ForkJoinTask.awaitJoin. (Retries are interspersed with
- * Thread.yield, for good citizenship.)
- *
- * Style notes: There is a lot of representation-level coupling
- * among classes ForkJoinPool, ForkJoinWorkerThread, and
- * ForkJoinTask. The fields of WorkQueue maintain data structures
- * managed by ForkJoinPool, so are directly accessed. There is
- * little point trying to reduce this, since any associated future
- * changes in representations will need to be accompanied by
- * algorithmic changes anyway. Several methods intrinsically
- * sprawl because they must accumulate sets of consistent reads of
- * volatiles held in local variables. Methods signalWork() and
- * scan() are the main bottlenecks, so are especially heavily
+ * retries of each. Compensation in the apparent absence of
+ * helping opportunities is challenging to control on JVMs, where
+ * GC and other activities can stall progress of tasks that in
+ * turn stall out many other dependent tasks, without us being
+ * able to determine whether they will ever require compensation.
+ * Even though work-stealing otherwise encounters little
+ * degradation in the presence of more threads than cores,
+ * aggressively adding new threads in such cases entails risk of
+ * unwanted positive feedback control loops in which more threads
+ * cause more dependent stalls (as well as delayed progress of
+ * unblocked threads to the point that we know they are available)
+ * leading to more situations requiring more threads, and so
+ * on. This aspect of control can be seen as an (analytically
+ * intractable) game with an opponent that may choose the worst
+ * (for us) active thread to stall at any time. We take several
+ * precautions to bound losses (and thus bound gains), mainly in
+ * methods tryCompensate and awaitJoin.
+ *
+ * Common Pool
+ * ===========
+ *
+ * The static commonPool always exists after static
+ * initialization. Since it (or any other created pool) need
+ * never be used, we minimize initial construction overhead and
+ * footprint to the setup of about a dozen fields, with no nested
+ * allocation. Most bootstrapping occurs within method
+ * fullExternalPush during the first submission to the pool.
+ *
+ * When external threads submit to the common pool, they can
+ * perform some subtask processing (see externalHelpJoin and
+ * related methods). We do not need to record whether these
+ * submissions are to the common pool -- if not, externalHelpJoin
+ * returns quickly (at the most helping to signal some common pool
+ * workers). These submitters would otherwise be blocked waiting
+ * for completion, so the extra effort (with liberally sprinkled
+ * task status checks) in inapplicable cases amounts to an odd
+ * form of limited spin-wait before blocking in ForkJoinTask.join.
+ *
+ * Style notes
+ * ===========
+ *
+ * There is a lot of representation-level coupling among classes
+ * ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask. The
+ * fields of WorkQueue maintain data structures managed by
+ * ForkJoinPool, so are directly accessed. There is little point
+ * trying to reduce this, since any associated future changes in
+ * representations will need to be accompanied by algorithmic
+ * changes anyway. Several methods intrinsically sprawl because
+ * they must accumulate sets of consistent reads of volatiles held
+ * in local variables. Methods signalWork() and scan() are the
+ * main bottlenecks, so are especially heavily
* micro-optimized/mangled. There are lots of inline assignments
* (of form "while ((local = field) != 0)") which are usually the
* simplest way to ensure the required read orderings (which are
@@ -431,7 +477,8 @@ public class ForkJoinPool extends Abstra
* declarations of these locals at the heads of methods or blocks.
* There are several occurrences of the unusual "do {} while
* (!cas...)" which is the simplest way to force an update of a
- * CAS'ed variable. There are also other coding oddities that help
+ * CAS'ed variable. There are also other coding oddities (including
+ * several unnecessary-looking hoisted null checks) that help
* some methods perform reasonably even when interpreted (not
* compiled).
*
@@ -449,19 +496,6 @@ public class ForkJoinPool extends Abstra
// Static utilities
/**
- * Computes an initial hash code (also serving as a non-zero
- * random seed) for a thread id. This method is expected to
- * provide higher-quality hash codes than using method hashCode().
- */
- static final int hashId(long id) {
- int h = (int)id ^ (int)(id >>> 32); // Use MurmurHash of thread id
- h ^= h >>> 16; h *= 0x85ebca6b;
- h ^= h >>> 13; h *= 0xc2b2ae35;
- h ^= h >>> 16;
- return (h == 0) ? 1 : h; // ensure nonzero
- }
-
- /**
* If there is a security manager, makes sure caller has
* permission to modify threads.
*/
@@ -493,34 +527,31 @@ public class ForkJoinPool extends Abstra
* Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
- static class DefaultForkJoinWorkerThreadFactory
+ static final class DefaultForkJoinWorkerThreadFactory
implements ForkJoinWorkerThreadFactory {
- public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+ public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
return new ForkJoinWorkerThread(pool);
}
}
/**
- * A simple non-reentrant lock used for exclusion when managing
- * queues and workers. We use a custom lock so that we can readily
- * probe lock state in constructions that check among alternative
- * actions. The lock is normally only very briefly held, and
- * sometimes treated as a spinlock, but other usages block to
- * reduce overall contention in those cases where locked code
- * bodies perform allocation/resizing.
- */
- static final class Mutex extends AbstractQueuedSynchronizer {
- public final boolean tryAcquire(int ignore) {
- return compareAndSetState(0, 1);
- }
- public final boolean tryRelease(int ignore) {
- setState(0);
- return true;
- }
- public final void lock() { acquire(0); }
- public final void unlock() { release(0); }
- public final boolean isHeldExclusively() { return getState() == 1; }
- public final Condition newCondition() { return new ConditionObject(); }
+ * Per-thread records for threads that submit to pools. Currently
+ * holds only pseudo-random seed / index that is used to choose
+ * submission queues in method externalPush. In the future, this may
+ * also incorporate a means to implement different task rejection
+ * and resubmission policies.
+ *
+ * Seeds for submitters and workers/workQueues work in basically
+ * the same way but are initialized and updated using slightly
+ * different mechanics. Both are initialized using the same
+ * approach as in class ThreadLocal, where successive values are
+ * unlikely to collide with previous values. Seeds are then
+ * randomly modified upon collisions using xorshifts, which
+ * requires a non-zero seed.
+ */
+ static final class Submitter {
+ int seed;
+ Submitter(int s) { seed = s; }
}
/**
@@ -530,6 +561,7 @@ public class ForkJoinPool extends Abstra
* actually do anything beyond having a unique identity.
*/
static final class EmptyTask extends ForkJoinTask {
+ private static final long serialVersionUID = -7721805057305804111L;
EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
public final Void getRawResult() { return null; }
public final void setRawResult(Void x) {}
@@ -550,27 +582,31 @@ public class ForkJoinPool extends Abstra
*
* Field "top" is the index (mod array.length) of the next queue
* slot to push to or pop from. It is written only by owner thread
- * for push, or under lock for trySharedPush, and accessed by
- * other threads only after reading (volatile) base. Both top and
- * base are allowed to wrap around on overflow, but (top - base)
- * (or more commonly -(base - top) to force volatile read of base
- * before top) still estimates size.
+ * for push, or under lock for external/shared push, and accessed
+ * by other threads only after reading (volatile) base. Both top
+ * and base are allowed to wrap around on overflow, but (top -
+ * base) (or more commonly -(base - top) to force volatile read of
+ * base before top) still estimates size. The lock ("qlock") is
+ * forced to -1 on termination, causing all further lock attempts
+ * to fail. (Note: we don't need CAS for termination state because
+ * upon pool shutdown, all shared-queues will stop being used
+ * anyway.) Nearly all lock bodies are set up so that exceptions
+ * within lock bodies are "impossible" (modulo JVM errors that
+ * would cause failure anyway.)
*
* The array slots are read and written using the emulation of
* volatiles/atomics provided by Unsafe. Insertions must in
* general use putOrderedObject as a form of releasing store to
* ensure that all writes to the task object are ordered before
- * its publication in the queue. (Although we can avoid one case
- * of this when locked in trySharedPush.) All removals entail a
- * CAS to null. The array is always a power of two. To ensure
- * safety of Unsafe array operations, all accesses perform
- * explicit null checks and implicit bounds checks via
- * power-of-two masking.
+ * its publication in the queue. All removals entail a CAS to
+ * null. The array is always a power of two. To ensure safety of
+ * Unsafe array operations, all accesses perform explicit null
+ * checks and implicit bounds checks via power-of-two masking.
*
* In addition to basic queuing support, this class contains
* fields described elsewhere to control execution. It turns out
- * to work better memory-layout-wise to include them in this
- * class rather than a separate class.
+ * to work better memory-layout-wise to include them in this class
+ * rather than a separate class.
*
* Performance on most platforms is very sensitive to placement of
* instances of both WorkQueues and their arrays -- we absolutely
@@ -584,18 +620,22 @@ public class ForkJoinPool extends Abstra
* trades off slightly slower average field access for the sake of
* avoiding really bad worst-case access. (Until better JVM
* support is in place, this padding is dependent on transient
- * properties of JVM field layout rules.) We also take care in
+ * properties of JVM field layout rules.) We also take care in
* allocating, sizing and resizing the array. Non-shared queue
- * arrays are initialized (via method growArray) by workers before
- * use. Others are allocated on first use.
+ * arrays are initialized by workers before use. Others are
+ * allocated on first use.
*/
static final class WorkQueue {
/**
* Capacity of work-stealing queue array upon initialization.
- * Must be a power of two; at least 4, but set larger to
- * reduce cacheline sharing among queues.
+ * Must be a power of two; at least 4, but should be larger to
+ * reduce or eliminate cacheline sharing among queues.
+ * Currently, it is much larger, as a partial workaround for
+ * the fact that JVMs often place arrays in locations that
+ * share GC bookkeeping (especially cardmarks) such that
+ * per-write accesses encounter serious memory contention.
*/
- static final int INITIAL_QUEUE_CAPACITY = 1 << 8;
+ static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
/**
* Maximum size for queue arrays. Must be a power of two less
@@ -606,96 +646,141 @@ public class ForkJoinPool extends Abstra
*/
static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
- volatile long totalSteals; // cumulative number of steals
+ // Heuristic padding to ameliorate unfortunate memory placements
+ volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
+
int seed; // for random scanning; initialize nonzero
volatile int eventCount; // encoded inactivation count; < 0 if inactive
int nextWait; // encoded record of next event waiter
- int rescans; // remaining scans until block
- int nsteals; // top-level task executions since last idle
- final int mode; // lifo, fifo, or shared
+ int hint; // steal or signal hint (index)
int poolIndex; // index of this queue in pool (or 0)
- int stealHint; // index of most recent known stealer
- volatile int runState; // 1: locked, -1: terminate; else 0
+ final int mode; // 0: lifo, > 0: fifo, < 0: shared
+ int nsteals; // number of steals
+ volatile int qlock; // 1: locked, -1: terminate; else 0
volatile int base; // index of next slot for poll
int top; // index of next slot for push
ForkJoinTask[] array; // the elements (initially unallocated)
+ final ForkJoinPool pool; // the containing pool (may be null)
final ForkJoinWorkerThread owner; // owning thread or null if shared
volatile Thread parker; // == owner during call to park; else null
- ForkJoinTask currentJoin; // task being joined in awaitJoin
+ volatile ForkJoinTask currentJoin; // task being joined in awaitJoin
ForkJoinTask currentSteal; // current non-local task being executed
- // Heuristic padding to ameliorate unfortunate memory placements
- Object p00, p01, p02, p03, p04, p05, p06, p07, p08, p09, p0a;
- WorkQueue(ForkJoinWorkerThread owner, int mode) {
+ volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
+ volatile Object pad18, pad19, pad1a, pad1b, pad1c, pad1d;
+
+ WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode,
+ int seed) {
+ this.pool = pool;
this.owner = owner;
this.mode = mode;
+ this.seed = seed;
// Place indices in the center of array (that is not yet allocated)
base = top = INITIAL_QUEUE_CAPACITY >>> 1;
}
/**
- * Returns number of tasks in the queue.
+ * Returns the approximate number of tasks in the queue.
*/
final int queueSize() {
- int n = base - top; // non-owner callers must read base first
- return (n >= 0) ? 0 : -n;
+ int n = base - top; // non-owner callers must read base first
+ return (n >= 0) ? 0 : -n; // ignore transient negative
+ }
+
+ /**
+ * Provides a more accurate estimate of whether this queue has
+ * any tasks than does queueSize, by checking whether a
+ * near-empty queue has at least one unclaimed task.
+ */
+ final boolean isEmpty() {
+ ForkJoinTask[] a; int m, s;
+ int n = base - (s = top);
+ return (n >= 0 ||
+ (n == -1 &&
+ ((a = array) == null ||
+ (m = a.length - 1) < 0 ||
+ U.getObject
+ (a, (long)((m & (s - 1)) << ASHIFT) + ABASE) == null)));
}
/**
- * Pushes a task. Call only by owner in unshared queues.
+ * Pushes a task. Call only by owner in unshared queues. (The
+ * shared-queue version is embedded in method externalPush.)
*
* @param task the task. Caller must ensure non-null.
- * @param p if non-null, pool to signal if necessary
* @throw RejectedExecutionException if array cannot be resized
*/
- final void push(ForkJoinTask task, ForkJoinPool p) {
- ForkJoinTask[] a;
+ final void push(ForkJoinTask task) {
+ ForkJoinTask[] a; ForkJoinPool p;
int s = top, m, n;
if ((a = array) != null) { // ignore if queue removed
- U.putOrderedObject
- (a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
+ int j = (((m = a.length - 1) & s) << ASHIFT) + ABASE;
+ U.putOrderedObject(a, j, task);
if ((n = (top = s + 1) - base) <= 2) {
- if (p != null)
- p.signalWork();
+ if ((p = pool) != null)
+ p.signalWork(this);
}
else if (n >= m)
- growArray(true);
+ growArray();
+ }
+ }
+
+ /**
+ * Initializes or doubles the capacity of array. Call either
+ * by owner or with lock held -- it is OK for base, but not
+ * top, to move while resizings are in progress.
+ */
+ final ForkJoinTask[] growArray() {
+ ForkJoinTask[] oldA = array;
+ int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
+ if (size > MAXIMUM_QUEUE_CAPACITY)
+ throw new RejectedExecutionException("Queue capacity exceeded");
+ int oldMask, t, b;
+ ForkJoinTask[] a = array = new ForkJoinTask[size];
+ if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
+ (t = top) - (b = base) > 0) {
+ int mask = size - 1;
+ do {
+ ForkJoinTask x;
+ int oldj = ((b & oldMask) << ASHIFT) + ABASE;
+ int j = ((b & mask) << ASHIFT) + ABASE;
+ x = (ForkJoinTask)U.getObjectVolatile(oldA, oldj);
+ if (x != null &&
+ U.compareAndSwapObject(oldA, oldj, x, null))
+ U.putObjectVolatile(a, j, x);
+ } while (++b != t);
}
+ return a;
}
/**
- * Pushes a task if lock is free and array is either big
- * enough or can be resized to be big enough.
- *
- * @param task the task. Caller must ensure non-null.
- * @return true if submitted
+ * Takes next task, if one exists, in LIFO order. Call only
+ * by owner in unshared queues.
*/
- final boolean trySharedPush(ForkJoinTask task) {
- boolean submitted = false;
- if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
- ForkJoinTask[] a = array;
- int s = top;
- try {
- if ((a != null && a.length > s + 1 - base) ||
- (a = growArray(false)) != null) { // must presize
- int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
- U.putObject(a, (long)j, task); // don't need "ordered"
- top = s + 1;
- submitted = true;
+ final ForkJoinTask pop() {
+ ForkJoinTask[] a; ForkJoinTask t; int m;
+ if ((a = array) != null && (m = a.length - 1) >= 0) {
+ for (int s; (s = top - 1) - base >= 0;) {
+ long j = ((m & s) << ASHIFT) + ABASE;
+ if ((t = (ForkJoinTask)U.getObject(a, j)) == null)
+ break;
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s;
+ return t;
}
- } finally {
- runState = 0; // unlock
}
}
- return submitted;
+ return null;
}
/**
- * Takes next task, if one exists, in FIFO order.
+ * Takes a task in FIFO order if b is base of queue and a task
+ * can be claimed without contention. Specialized versions
+ * appear in ForkJoinPool methods scan and tryHelpStealer.
*/
- final ForkJoinTask poll() {
- ForkJoinTask[] a; int b; ForkJoinTask t;
- while ((b = base) - top < 0 && (a = array) != null) {
+ final ForkJoinTask pollAt(int b) {
+ ForkJoinTask t; ForkJoinTask[] a;
+ if ((a = array) != null) {
int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
if ((t = (ForkJoinTask)U.getObjectVolatile(a, j)) != null &&
base == b &&
@@ -708,23 +793,25 @@ public class ForkJoinPool extends Abstra
}
/**
- * Takes next task, if one exists, in LIFO order. Call only
- * by owner in unshared queues. (We do not have a shared
- * version of this method because it is never needed.)
+ * Takes next task, if one exists, in FIFO order.
*/
- final ForkJoinTask pop() {
- ForkJoinTask t; int m;
- ForkJoinTask[] a = array;
- if (a != null && (m = a.length - 1) >= 0) {
- for (int s; (s = top - 1) - base >= 0;) {
- int j = ((m & s) << ASHIFT) + ABASE;
- if ((t = (ForkJoinTask)U.getObjectVolatile(a, j)) == null)
- break;
- if (U.compareAndSwapObject(a, j, t, null)) {
- top = s;
+ final ForkJoinTask poll() {
+ ForkJoinTask[] a; int b; ForkJoinTask t;
+ while ((b = base) - top < 0 && (a = array) != null) {
+ int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ t = (ForkJoinTask)U.getObjectVolatile(a, j);
+ if (t != null) {
+ if (base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ base = b + 1;
return t;
}
}
+ else if (base == b) {
+ if (b + 1 == top)
+ break;
+ Thread.yield(); // wait for lagging update (very rare)
+ }
}
return null;
}
@@ -749,24 +836,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns task at index b if b is current base of queue.
- */
- final ForkJoinTask pollAt(int b) {
- ForkJoinTask t; ForkJoinTask[] a;
- if ((a = array) != null) {
- int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
- if ((t = (ForkJoinTask)U.getObjectVolatile(a, j)) != null &&
- base == b &&
- U.compareAndSwapObject(a, j, t, null)) {
- base = b + 1;
- return t;
- }
- }
- return null;
- }
-
- /**
* Pops the given task only if it is at the current top.
+ * (A shared version is available only via FJP.tryExternalUnpush)
*/
final boolean tryUnpush(ForkJoinTask t) {
ForkJoinTask[] a; int s;
@@ -780,30 +851,66 @@ public class ForkJoinPool extends Abstra
}
/**
- * Polls the given task only if it is at the current base.
+ * Removes and cancels all known tasks, ignoring any exceptions.
*/
- final boolean pollFor(ForkJoinTask task) {
- ForkJoinTask[] a; int b;
- if ((b = base) - top < 0 && (a = array) != null) {
- int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
- if (U.getObjectVolatile(a, j) == task && base == b &&
- U.compareAndSwapObject(a, j, task, null)) {
- base = b + 1;
- return true;
+ final void cancelAll() {
+ ForkJoinTask.cancelIgnoringExceptions(currentJoin);
+ ForkJoinTask.cancelIgnoringExceptions(currentSteal);
+ for (ForkJoinTask t; (t = poll()) != null; )
+ ForkJoinTask.cancelIgnoringExceptions(t);
+ }
+
+ /**
+ * Computes next value for random probes. Scans don't require
+ * a very high quality generator, but also not a crummy one.
+ * Marsaglia xor-shift is cheap and works well enough. Note:
+ * This is manually inlined in its usages in ForkJoinPool to
+ * avoid writes inside busy scan loops.
+ */
+ final int nextSeed() {
+ int r = seed;
+ r ^= r << 13;
+ r ^= r >>> 17;
+ return seed = r ^= r << 5;
+ }
+
+ // Specialized execution methods
+
+ /**
+ * Pops and runs tasks until empty.
+ */
+ private void popAndExecAll() {
+ // A bit faster than repeated pop calls
+ ForkJoinTask[] a; int m, s; long j; ForkJoinTask t;
+ while ((a = array) != null && (m = a.length - 1) >= 0 &&
+ (s = top - 1) - base >= 0 &&
+ (t = ((ForkJoinTask)
+ U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
+ != null) {
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s;
+ t.doExec();
}
}
- return false;
}
/**
- * If present, removes from queue and executes the given task, or
- * any other cancelled task. Returns (true) immediately on any CAS
+ * Polls and runs tasks until empty.
+ */
+ private void pollAndExecAll() {
+ for (ForkJoinTask t; (t = poll()) != null;)
+ t.doExec();
+ }
+
+ /**
+ * If present, removes from queue and executes the given task,
+ * or any other cancelled task. Returns (true) on any CAS
* or consistency check failure so caller can retry.
*
- * @return false if no progress can be made
+ * @return false if no progress can be made, else true;
*/
final boolean tryRemoveAndExec(ForkJoinTask task) {
- boolean removed = false, empty = true, progress = true;
+ boolean stat = true, removed = false, empty = true;
ForkJoinTask[] a; int m, s, b, n;
if ((a = array) != null && (m = a.length - 1) >= 0 &&
(n = (s = top) - (b = base)) > 0) {
@@ -833,106 +940,62 @@ public class ForkJoinPool extends Abstra
}
if (--n == 0) {
if (!empty && base == b)
- progress = false;
+ stat = false;
break;
}
}
}
if (removed)
task.doExec();
- return progress;
+ return stat;
}
/**
- * Initializes or doubles the capacity of array. Call either
- * by owner or with lock held -- it is OK for base, but not
- * top, to move while resizings are in progress.
- *
- * @param rejectOnFailure if true, throw exception if capacity
- * exceeded (relayed ultimately to user); else return null.
+ * Polls for and executes the given task or any other task in
+ * its CountedCompleter computation
*/
- final ForkJoinTask[] growArray(boolean rejectOnFailure) {
- ForkJoinTask[] oldA = array;
- int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
- if (size <= MAXIMUM_QUEUE_CAPACITY) {
- int oldMask, t, b;
- ForkJoinTask[] a = array = new ForkJoinTask[size];
- if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
- (t = top) - (b = base) > 0) {
- int mask = size - 1;
- do {
- ForkJoinTask x;
- int oldj = ((b & oldMask) << ASHIFT) + ABASE;
- int j = ((b & mask) << ASHIFT) + ABASE;
- x = (ForkJoinTask)U.getObjectVolatile(oldA, oldj);
- if (x != null &&
- U.compareAndSwapObject(oldA, oldj, x, null))
- U.putObjectVolatile(a, j, x);
- } while (++b != t);
+ final boolean pollAndExecCC(ForkJoinTask root) {
+ ForkJoinTask[] a; int b; Object o;
+ outer: while ((b = base) - top < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) == null ||
+ !(o instanceof CountedCompleter))
+ break;
+ for (CountedCompleter t = (CountedCompleter)o, r = t;;) {
+ if (r == root) {
+ if (base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ base = b + 1;
+ t.doExec();
+ return true;
+ }
+ else
+ break; // restart
+ }
+ if ((r = r.completer) == null)
+ break outer; // not part of root computation
}
- return a;
- }
- else if (!rejectOnFailure)
- return null;
- else
- throw new RejectedExecutionException("Queue capacity exceeded");
- }
-
- /**
- * Removes and cancels all known tasks, ignoring any exceptions.
- */
- final void cancelAll() {
- ForkJoinTask.cancelIgnoringExceptions(currentJoin);
- ForkJoinTask.cancelIgnoringExceptions(currentSteal);
- for (ForkJoinTask t; (t = poll()) != null; )
- ForkJoinTask.cancelIgnoringExceptions(t);
- }
-
- /**
- * Computes next value for random probes. Scans don't require
- * a very high quality generator, but also not a crummy one.
- * Marsaglia xor-shift is cheap and works well enough. Note:
- * This is manually inlined in several usages in ForkJoinPool
- * to avoid writes inside busy scan loops.
- */
- final int nextSeed() {
- int r = seed;
- r ^= r << 13;
- r ^= r >>> 17;
- return seed = r ^= r << 5;
- }
-
- // Execution methods
-
- /**
- * Removes and runs tasks until empty, using local mode
- * ordering.
- */
- final void runLocalTasks() {
- if (base - top < 0) {
- for (ForkJoinTask t; (t = nextLocalTask()) != null; )
- t.doExec();
}
+ return false;
}
/**
* Executes a top-level task and any local tasks remaining
* after execution.
- *
- * @return true unless terminating
*/
- final boolean runTask(ForkJoinTask t) {
- boolean alive = true;
+ final void runTask(ForkJoinTask t) {
if (t != null) {
- currentSteal = t;
- t.doExec();
- runLocalTasks();
- ++nsteals;
+ (currentSteal = t).doExec();
currentSteal = null;
+ if (base - top < 0) { // process remaining local tasks
+ if (mode == 0)
+ popAndExecAll();
+ else
+ pollAndExecAll();
+ }
+ ++nsteals;
+ hint = -1;
}
- else if (runState < 0) // terminating
- alive = false;
- return alive;
}
/**
@@ -941,8 +1004,7 @@ public class ForkJoinPool extends Abstra
final void runSubtask(ForkJoinTask t) {
if (t != null) {
ForkJoinTask ps = currentSteal;
- currentSteal = t;
- t.doExec();
+ (currentSteal = t).doExec();
currentSteal = ps;
}
}
@@ -977,7 +1039,7 @@ public class ForkJoinPool extends Abstra
// Unsafe mechanics
private static final sun.misc.Unsafe U;
- private static final long RUNSTATE;
+ private static final long QLOCK;
private static final int ABASE;
private static final int ASHIFT;
static {
@@ -986,8 +1048,8 @@ public class ForkJoinPool extends Abstra
U = getUnsafe();
Class k = WorkQueue.class;
Class ak = ForkJoinTask[].class;
- RUNSTATE = U.objectFieldOffset
- (k.getDeclaredField("runState"));
+ QLOCK = U.objectFieldOffset
+ (k.getDeclaredField("qlock"));
ABASE = U.arrayBaseOffset(ak);
s = U.arrayIndexScale(ak);
} catch (Exception e) {
@@ -999,23 +1061,6 @@ public class ForkJoinPool extends Abstra
}
}
- /**
- * Per-thread records for threads that submit to pools. Currently
- * holds only pseudo-random seed / index that is used to choose
- * submission queues in method doSubmit. In the future, this may
- * also incorporate a means to implement different task rejection
- * and resubmission policies.
- */
- static final class Submitter {
- int seed;
- Submitter() { seed = hashId(Thread.currentThread().getId()); }
- }
-
- /** ThreadLocal class for Submitters */
- static final class ThreadSubmitter extends ThreadLocal {
- public Submitter initialValue() { return new Submitter(); }
- }
-
// static fields (initialized in static initializer below)
/**
@@ -1026,9 +1071,13 @@ public class ForkJoinPool extends Abstra
defaultForkJoinWorkerThreadFactory;
/**
- * Generator for assigning sequence numbers as pool names.
+ * Per-thread submission bookkeeping. Shared across all pools
+ * to reduce ThreadLocal pollution and because random motion
+ * to avoid contention in one pool is likely to hold for others.
+ * Lazily initialized on first submission (but null-checked
+ * in other contexts to avoid unnecessary initialization).
*/
- private static final AtomicInteger poolNumberGenerator;
+ static final ThreadLocal submitters;
/**
* Permission required for callers of methods that may start or
@@ -1037,39 +1086,68 @@ public class ForkJoinPool extends Abstra
private static final RuntimePermission modifyThreadPermission;
/**
- * Per-thread submission bookeeping. Shared across all pools
- * to reduce ThreadLocal pollution and because random motion
- * to avoid contention in one pool is likely to hold for others.
+ * Common (static) pool. Non-null for public use unless a static
+ * construction exception, but internal usages null-check on use
+ * to paranoically avoid potential initialization circularities
+ * as well as to simplify generated code.
+ */
+ static final ForkJoinPool commonPool;
+
+ /**
+ * Common pool parallelism. Must equal commonPool.parallelism.
+ */
+ static final int commonPoolParallelism;
+
+ /**
+ * Sequence number for creating workerNamePrefix.
+ */
+ private static int poolNumberSequence;
+
+ /**
+ * Return the next sequence number. We don't expect this to
+ * ever contend so use simple builtin sync.
*/
- private static final ThreadSubmitter submitters;
+ private static final synchronized int nextPoolId() {
+ return ++poolNumberSequence;
+ }
// static constants
/**
- * The wakeup interval (in nanoseconds) for a worker waiting for a
- * task when the pool is quiescent to instead try to shrink the
- * number of workers. The exact value does not matter too
- * much. It must be short enough to release resources during
- * sustained periods of idleness, but not so short that threads
- * are continually re-created.
+ * Initial timeout value (in nanoseconds) for the thread
+ * triggering quiescence to park waiting for new work. On timeout,
+ * the thread will instead try to shrink the number of
+ * workers. The value should be large enough to avoid overly
+ * aggressive shrinkage during most transient stalls (long GCs
+ * etc).
*/
- private static final long SHRINK_RATE =
- 4L * 1000L * 1000L * 1000L; // 4 seconds
+ private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec
/**
- * The timeout value for attempted shrinkage, includes
- * some slop to cope with system timer imprecision.
+ * Timeout value when there are more threads than parallelism level
*/
- private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
+ private static final long FAST_IDLE_TIMEOUT = 200L * 1000L * 1000L;
/**
- * The maximum stolen->joining link depth allowed in tryHelpStealer.
- * Depths for legitimate chains are unbounded, but we use a fixed
- * constant to avoid (otherwise unchecked) cycles and to bound
- * staleness of traversal parameters at the expense of sometimes
- * blocking when we could be helping.
+ * Tolerance for idle timeouts, to cope with timer undershoots
*/
- private static final int MAX_HELP_DEPTH = 16;
+ private static final long TIMEOUT_SLOP = 2000000L; // 20ms
+
+ /**
+ * The maximum stolen->joining link depth allowed in method
+ * tryHelpStealer. Must be a power of two. Depths for legitimate
+ * chains are unbounded, but we use a fixed constant to avoid
+ * (otherwise unchecked) cycles and to bound staleness of
+ * traversal parameters at the expense of sometimes blocking when
+ * we could be helping.
+ */
+ private static final int MAX_HELP = 64;
+
+ /**
+ * Increment for seed generators. See class ThreadLocal for
+ * explanation.
+ */
+ private static final int SEED_INCREMENT = 0x61c88647;
/**
* Bits and masks for control variables
@@ -1099,17 +1177,14 @@ public class ForkJoinPool extends Abstra
* scan for them to avoid queuing races. Note however that
* eventCount updates lag releases so usage requires care.
*
- * Field runState is an int packed with:
+ * Field plock is an int packed with:
* SHUTDOWN: true if shutdown is enabled (1 bit)
- * SEQ: a sequence number updated upon (de)registering workers (15 bits)
- * MASK: mask (power of 2 - 1) covering all registered poolIndexes (16 bits)
+ * SEQ: a sequence lock, with PL_LOCK bit set if locked (30 bits)
+ * SIGNAL: set when threads may be waiting on the lock (1 bit)
*
- * The combination of mask and sequence number enables simple
- * consistency checks: Staleness of read-only operations on the
- * workQueues array can be checked by comparing runState before vs
- * after the reads. The low 16 bits (i.e, anding with SMASK) hold
- * the smallest power of two covering all indices, minus
- * one.
+ * The sequence number enables simple consistency checks:
+ * Staleness of read-only operations on the workQueues array can
+ * be checked by comparing plock before vs after the reads.
*/
// bit positions/shifts for fields
@@ -1119,9 +1194,10 @@ public class ForkJoinPool extends Abstra
private static final int EC_SHIFT = 16;
// bounds
- private static final int POOL_MAX = 0x7fff; // max #workers - 1
private static final int SMASK = 0xffff; // short bits
- private static final int SQMASK = 0xfffe; // even short bits
+ private static final int MAX_CAP = 0x7fff; // max #workers - 1
+ private static final int EVENMASK = 0xfffe; // even short bits
+ private static final int SQMASK = 0x007e; // max 64 (even) slots
private static final int SHORT_SIGN = 1 << 15;
private static final int INT_SIGN = 1 << 31;
@@ -1146,129 +1222,247 @@ public class ForkJoinPool extends Abstra
private static final int E_MASK = 0x7fffffff; // no STOP_BIT
private static final int E_SEQ = 1 << EC_SHIFT;
- // runState bits
+ // plock bits
private static final int SHUTDOWN = 1 << 31;
- private static final int RS_SEQ = 1 << 16;
- private static final int RS_SEQ_MASK = 0x7fff0000;
+ private static final int PL_LOCK = 2;
+ private static final int PL_SIGNAL = 1;
+ private static final int PL_SPINS = 1 << 8;
// access mode for WorkQueue
static final int LIFO_QUEUE = 0;
static final int FIFO_QUEUE = 1;
static final int SHARED_QUEUE = -1;
+ // bounds for #steps in scan loop -- must be power 2 minus 1
+ private static final int MIN_SCAN = 0x1ff; // cover estimation slop
+ private static final int MAX_SCAN = 0x1ffff; // 4 * max workers
+
// Instance fields
/*
- * Field layout order in this class tends to matter more than one
- * would like. Runtime layout order is only loosely related to
+ * Field layout of this class tends to matter more than one would
+ * like. Runtime layout order is only loosely related to
* declaration order and may differ across JVMs, but the following
* empirically works OK on current JVMs.
*/
+ // Heuristic padding to ameliorate unfortunate memory placements
+ volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
+
+ volatile long stealCount; // collects worker counts
volatile long ctl; // main pool control
- final int parallelism; // parallelism level
- final int localMode; // per-worker scheduling mode
- int growHints; // for expanding indices/ranges
- volatile int runState; // shutdown status, seq, and mask
+ volatile int plock; // shutdown status and seqLock
+ volatile int indexSeed; // worker/submitter index seed
+ final int config; // mode and parallelism level
WorkQueue[] workQueues; // main registry
- final Mutex lock; // for registration
- final Condition termination; // for awaitTermination
- final ForkJoinWorkerThreadFactory factory; // factory for new workers
+ final ForkJoinWorkerThreadFactory factory;
final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
- final AtomicLong stealCount; // collect counts when terminated
- final AtomicInteger nextWorkerNumber; // to create worker name string
final String workerNamePrefix; // to create worker name string
- // Creating, registering, deregistering and running workers
+ volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
+ volatile Object pad18, pad19, pad1a, pad1b;
- /**
- * Tries to create and start a worker
- */
- private void addWorker() {
- Throwable ex = null;
- ForkJoinWorkerThread wt = null;
- try {
- if ((wt = factory.newThread(this)) != null) {
- wt.start();
- return;
+ /*
+ * Acquires the plock lock to protect worker array and related
+ * updates. This method is called only if an initial CAS on plock
+ * fails. This acts as a spinLock for normal cases, but falls back
+ * to builtin monitor to block when (rarely) needed. This would be
+ * a terrible idea for a highly contended lock, but works fine as
+ * a more conservative alternative to a pure spinlock. See
+ * internal ConcurrentHashMap documentation for further
+ * explanation of nearly the same construction.
+ */
+ private int acquirePlock() {
+ int spins = PL_SPINS, r = 0, ps, nps;
+ for (;;) {
+ if (((ps = plock) & PL_LOCK) == 0 &&
+ U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
+ return nps;
+ else if (r == 0) { // randomize spins if possible
+ Thread t = Thread.currentThread(); WorkQueue w; Submitter z;
+ if ((t instanceof ForkJoinWorkerThread) &&
+ (w = ((ForkJoinWorkerThread)t).workQueue) != null)
+ r = w.seed;
+ else if ((z = submitters.get()) != null)
+ r = z.seed;
+ else
+ r = 1;
+ }
+ else if (spins >= 0) {
+ r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
+ if (r >= 0)
+ --spins;
+ }
+ else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
+ synchronized (this) {
+ if ((plock & PL_SIGNAL) != 0) {
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ try {
+ Thread.currentThread().interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ }
+ else
+ notifyAll();
+ }
}
- } catch (Throwable e) {
- ex = e;
}
- deregisterWorker(wt, ex); // adjust counts etc on failure
}
/**
- * Callback from ForkJoinWorkerThread constructor to assign a
- * public name. This must be separate from registerWorker because
- * it is called during the "super" constructor call in
- * ForkJoinWorkerThread.
+ * Unlocks and signals any thread waiting for plock. Called only
+ * when CAS of seq value for unlock fails.
*/
- final String nextWorkerName() {
- return workerNamePrefix.concat
- (Integer.toString(nextWorkerNumber.addAndGet(1)));
+ private void releasePlock(int ps) {
+ plock = ps;
+ synchronized (this) { notifyAll(); }
}
/**
- * Callback from ForkJoinWorkerThread constructor to establish and
- * record its WorkQueue.
+ * Performs secondary initialization, called when plock is zero.
+ * Creates workQueue array and sets plock to a valid value. The
+ * lock body must be exception-free (so no try/finally) so we
+ * optimistically allocate new array outside the lock and throw
+ * away if (very rarely) not needed. (A similar tactic is used in
+ * fullExternalPush.) Because the plock seq value can eventually
+ * wrap around zero, this method harmlessly fails to reinitialize
+ * if workQueues exists, while still advancing plock.
+ *
+ * Additionally tries to create the first worker.
+ */
+ private void initWorkers() {
+ WorkQueue[] ws, nws; int ps;
+ int p = config & SMASK; // find power of two table size
+ int n = (p > 1) ? p - 1 : 1; // ensure at least 2 slots
+ n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
+ n = (n + 1) << 1;
+ if ((ws = workQueues) == null || ws.length == 0)
+ nws = new WorkQueue[n];
+ else
+ nws = null;
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if (((ws = workQueues) == null || ws.length == 0) && nws != null)
+ workQueues = nws;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ tryAddWorker();
+ }
+
+ /**
+ * Tries to create and start one worker if fewer than target
+ * parallelism level exist. Adjusts counts etc on failure.
+ */
+ private void tryAddWorker() {
+ long c; int u;
+ while ((u = (int)((c = ctl) >>> 32)) < 0 &&
+ (u & SHORT_SIGN) != 0 && (int)c == 0) {
+ long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
+ ((u + UAC_UNIT) & UAC_MASK)) << 32;
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ ForkJoinWorkerThreadFactory fac;
+ Throwable ex = null;
+ ForkJoinWorkerThread wt = null;
+ try {
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
+ break;
+ }
+ } catch (Throwable e) {
+ ex = e;
+ }
+ deregisterWorker(wt, ex);
+ break;
+ }
+ }
+ }
+
+ // Registering and deregistering workers
+
+ /**
+ * Callback from ForkJoinWorkerThread to establish and record its
+ * WorkQueue. To avoid scanning bias due to packing entries in
+ * front of the workQueues array, we treat the array as a simple
+ * power-of-two hash table using per-thread seed as hash,
+ * expanding as needed.
*
* @param wt the worker thread
+ * @return the worker's queue
*/
- final void registerWorker(ForkJoinWorkerThread wt) {
- WorkQueue w = wt.workQueue;
- Mutex lock = this.lock;
- lock.lock();
+ final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
+ Thread.UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
+ wt.setDaemon(true);
+ if ((handler = ueh) != null)
+ wt.setUncaughtExceptionHandler(handler);
+ do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed,
+ s += SEED_INCREMENT) ||
+ s == 0); // skip 0
+ WorkQueue w = new WorkQueue(this, wt, config >>> 16, s);
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
try {
- int g = growHints, k = g & SMASK;
- WorkQueue[] ws = workQueues;
- if (ws != null) { // ignore on shutdown
- int n = ws.length;
- if ((k & 1) == 0 || k >= n || ws[k] != null) {
- for (k = 1; k < n && ws[k] != null; k += 2)
- ; // workers are at odd indices
- if (k >= n) // resize
- workQueues = ws = Arrays.copyOf(ws, n << 1);
- }
- w.eventCount = w.poolIndex = k; // establish before recording
- ws[k] = w;
- growHints = (g & ~SMASK) | ((k + 2) & SMASK);
- int rs = runState;
- int m = rs & SMASK; // recalculate runState mask
- if (k > m)
- m = (m << 1) + 1;
- runState = (rs & SHUTDOWN) | ((rs + RS_SEQ) & RS_SEQ_MASK) | m;
+ if ((ws = workQueues) != null) { // skip if shutting down
+ int n = ws.length, m = n - 1;
+ int r = (s << 1) | 1; // use odd-numbered indices
+ if (ws[r &= m] != null) { // collision
+ int probes = 0; // step by approx half size
+ int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2;
+ while (ws[r = (r + step) & m] != null) {
+ if (++probes >= n) {
+ workQueues = ws = Arrays.copyOf(ws, n <<= 1);
+ m = n - 1;
+ probes = 0;
+ }
+ }
+ }
+ w.eventCount = w.poolIndex = r; // volatile write orders
+ ws[r] = w;
}
} finally {
- lock.unlock();
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
+ wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex)));
+ return w;
}
/**
* Final callback from terminating worker, as well as upon failure
- * to construct or start a worker in addWorker. Removes record of
- * worker from array, and adjusts counts. If pool is shutting
- * down, tries to complete termination.
+ * to construct or start a worker. Removes record of worker from
+ * array, and adjusts counts. If pool is shutting down, tries to
+ * complete termination.
*
- * @param wt the worker thread or null if addWorker failed
+ * @param wt the worker thread or null if construction failed
* @param ex the exception causing failure, or null if none
*/
final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
WorkQueue w = null;
if (wt != null && (w = wt.workQueue) != null) {
- w.runState = -1; // ensure runState is set
- stealCount.getAndAdd(w.totalSteals + w.nsteals);
- int idx = w.poolIndex;
- Mutex lock = this.lock;
- lock.lock();
- try { // remove record from array
+ int ps;
+ w.qlock = -1; // ensure set
+ long ns = w.nsteals, sc; // collect steal count
+ do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
+ sc = stealCount, sc + ns));
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ try {
+ int idx = w.poolIndex;
WorkQueue[] ws = workQueues;
- if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w) {
+ if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
ws[idx] = null;
- growHints = (growHints & ~SMASK) | idx;
- }
} finally {
- lock.unlock();
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
}
@@ -1278,28 +1472,37 @@ public class ForkJoinPool extends Abstra
((c - TC_UNIT) & TC_MASK) |
(c & ~(AC_MASK|TC_MASK)))));
- if (!tryTerminate(false, false) && w != null) {
+ if (!tryTerminate(false, false) && w != null && w.array != null) {
w.cancelAll(); // cancel remaining tasks
- if (w.array != null) // suppress signal if never ran
- signalWork(); // wake up or create replacement
- if (ex == null) // help clean refs on way out
- ForkJoinTask.helpExpungeStaleExceptions();
+ int e, u, i, n; WorkQueue[] ws; WorkQueue v; Thread p;
+ while ((u = (int)((c = ctl) >>> 32)) < 0) {
+ if ((e = (int)c) > 0) { // activate or create replacement
+ if ((ws = workQueues) != null &&
+ ws.length > (i = e & SMASK) &&
+ (v = ws[i]) != null && v.eventCount == (e | INT_SIGN)) {
+ long nc = (((long)(v.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ break;
+ }
+ }
+ else
+ break;
+ }
+ else {
+ if ((short)u < 0)
+ tryAddWorker();
+ break;
+ }
+ }
}
-
- if (ex != null) // rethrow
- U.throwException(ex);
- }
-
- /**
- * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
- */
- final void runWorker(ForkJoinWorkerThread wt) {
- // Initialize queue array and seed in this thread
- WorkQueue w = wt.workQueue;
- w.growArray(false);
- w.seed = hashId(Thread.currentThread().getId());
-
- do {} while (w.runTask(scan(w)));
+ if (ex == null) // help clean refs on way out
+ ForkJoinTask.helpExpungeStaleExceptions();
+ else // rethrow
+ ForkJoinTask.rethrow(ex);
}
// Submissions
@@ -1307,56 +1510,99 @@ public class ForkJoinPool extends Abstra
/**
* Unless shutting down, adds the given task to a submission queue
* at submitter's current queue index (modulo submission
- * range). If no queue exists at the index, one is created unless
- * pool lock is busy. If the queue and/or lock are busy, another
- * index is randomly chosen. The mask in growHints controls the
- * effective index range of queues considered. The mask is
- * expanded, up to the current workerQueue mask, upon any detected
- * contention but otherwise remains small to avoid needlessly
- * creating queues when there is no contention.
+ * range). Only the most common path is directly handled in this
+ * method. All others are relayed to fullExternalPush.
+ *
+ * @param task the task. Caller must ensure non-null.
*/
- private void doSubmit(ForkJoinTask task) {
- if (task == null)
- throw new NullPointerException();
- Submitter s = submitters.get();
- for (int r = s.seed, m = growHints >>> 16;;) {
- WorkQueue[] ws; WorkQueue q; Mutex lk;
- int k = r & m & SQMASK; // use only even indices
- if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
- throw new RejectedExecutionException(); // shutting down
- if ((q = ws[k]) == null && (lk = lock).tryAcquire(0)) {
- try { // try to create new queue
- if (ws == workQueues && (q = ws[k]) == null) {
- int rs; // update runState seq
- ws[k] = q = new WorkQueue(null, SHARED_QUEUE);
- runState = (((rs = runState) & SHUTDOWN) |
- ((rs + RS_SEQ) & ~SHUTDOWN));
+ final void externalPush(ForkJoinTask task) {
+ WorkQueue[] ws; WorkQueue q; Submitter z; int m; ForkJoinTask[] a;
+ if ((z = submitters.get()) != null && plock > 0 &&
+ (ws = workQueues) != null && (m = (ws.length - 1)) >= 0 &&
+ (q = ws[m & z.seed & SQMASK]) != null &&
+ U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
+ int b = q.base, s = q.top, n, an;
+ if ((a = q.array) != null && (an = a.length) > (n = s + 1 - b)) {
+ int j = (((an - 1) & s) << ASHIFT) + ABASE;
+ U.putOrderedObject(a, j, task);
+ q.top = s + 1; // push on to deque
+ q.qlock = 0;
+ if (n <= 2)
+ signalWork(q);
+ return;
+ }
+ q.qlock = 0;
+ }
+ fullExternalPush(task);
+ }
+
+ /**
+ * Full version of externalPush. This method is called, among
+ * other times, upon the first submission of the first task to the
+ * pool, so must perform secondary initialization (via
+ * initWorkers). It also detects first submission by an external
+ * thread by looking up its ThreadLocal, and creates a new shared
+ * queue if the one at index if empty or contended. The plock lock
+ * body must be exception-free (so no try/finally) so we
+ * optimistically allocate new queues outside the lock and throw
+ * them away if (very rarely) not needed.
+ */
+ private void fullExternalPush(ForkJoinTask task) {
+ int r = 0; // random index seed
+ for (Submitter z = submitters.get();;) {
+ WorkQueue[] ws; WorkQueue q; int ps, m, k;
+ if (z == null) {
+ if (U.compareAndSwapInt(this, INDEXSEED, r = indexSeed,
+ r += SEED_INCREMENT) && r != 0)
+ submitters.set(z = new Submitter(r));
+ }
+ else if (r == 0) { // move to a different index
+ r = z.seed;
+ r ^= r << 13; // same xorshift as WorkQueues
+ r ^= r >>> 17;
+ z.seed = r ^ (r << 5);
+ }
+ else if ((ps = plock) < 0)
+ throw new RejectedExecutionException();
+ else if (ps == 0 || (ws = workQueues) == null ||
+ (m = ws.length - 1) < 0)
+ initWorkers();
+ else if ((q = ws[k = r & m & SQMASK]) != null) {
+ if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+ ForkJoinTask[] a = q.array;
+ int s = q.top;
+ boolean submitted = false;
+ try { // locked version of push
+ if ((a != null && a.length > s + 1 - q.base) ||
+ (a = q.growArray()) != null) { // must presize
+ int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
+ U.putOrderedObject(a, j, task);
+ q.top = s + 1;
+ submitted = true;
+ }
+ } finally {
+ q.qlock = 0; // unlock
+ }
+ if (submitted) {
+ signalWork(q);
+ return;
}
- } finally {
- lk.unlock();
}
+ r = 0; // move on failure
}
- if (q != null) {
- if (q.trySharedPush(task)) {
- signalWork();
- return;
- }
- else if (m < parallelism - 1 && m < (runState & SMASK)) {
- Mutex lock = this.lock;
- lock.lock(); // block until lock free
- int g = growHints;
- if (g >>> 16 == m) // expand range
- growHints = (((m << 1) + 1) << 16) | (g & SMASK);
- lock.unlock(); // no need for try/finally
- }
- else if ((r & m) == 0)
- Thread.yield(); // occasionally yield if busy
- }
- if (m == (m = growHints >>> 16)) {
- r ^= r << 13; // update seed unless new range
- r ^= r >>> 17; // same xorshift as WorkQueues
- s.seed = r ^= r << 5;
+ else if (((ps = plock) & PL_LOCK) == 0) { // create new queue
+ q = new WorkQueue(this, null, SHARED_QUEUE, r);
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if ((ws = workQueues) != null && k < ws.length && ws[k] == null)
+ ws[k] = q;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
+ else
+ r = 0; // try elsewhere while lock held
}
}
@@ -1371,240 +1617,182 @@ public class ForkJoinPool extends Abstra
}
/**
- * Tries to activate or create a worker if too few are active.
+ * Tries to create or activate a worker if too few are active.
+ *
+ * @param q the (non-null) queue holding tasks to be signalled
*/
- final void signalWork() {
- long c; int u;
- while ((u = (int)((c = ctl) >>> 32)) < 0) { // too few active
- WorkQueue[] ws = workQueues; int e, i; WorkQueue w; Thread p;
- if ((e = (int)c) > 0) { // at least one waiting
- if (ws != null && (i = e & SMASK) < ws.length &&
+ final void signalWork(WorkQueue q) {
+ int hint = q.poolIndex;
+ long c; int e, u, i, n; WorkQueue[] ws; WorkQueue w; Thread p;
+ while ((u = (int)((c = ctl) >>> 32)) < 0) {
+ if ((e = (int)c) > 0) {
+ if ((ws = workQueues) != null && ws.length > (i = e & SMASK) &&
(w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
long nc = (((long)(w.nextWait & E_MASK)) |
((long)(u + UAC_UNIT) << 32));
if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.hint = hint;
w.eventCount = (e + E_SEQ) & E_MASK;
if ((p = w.parker) != null)
- U.unpark(p); // activate and release
+ U.unpark(p);
break;
}
+ if (q.top - q.base <= 0)
+ break;
}
else
break;
}
- else if (e == 0 && (u & SHORT_SIGN) != 0) { // too few total
- long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
- ((u + UAC_UNIT) & UAC_MASK)) << 32;
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- addWorker();
- break;
- }
- }
- else
+ else {
+ if ((short)u < 0)
+ tryAddWorker();
break;
+ }
}
}
+ // Scanning for tasks
+
/**
- * Tries to decrement active count (sometimes implicitly) and
- * possibly release or create a compensating worker in preparation
- * for blocking. Fails on contention or termination.
- *
- * @return true if the caller can block, else should recheck and retry
+ * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
*/
- final boolean tryCompensate() {
- WorkQueue w; Thread p;
- int pc = parallelism, e, u, ac, tc, i;
- long c = ctl;
- WorkQueue[] ws = workQueues;
- if ((e = (int)c) >= 0) {
- if ((ac = ((u = (int)(c >>> 32)) >> UAC_SHIFT)) <= 0 &&
- e != 0 && ws != null && (i = e & SMASK) < ws.length &&
- (w = ws[i]) != null) {
- long nc = (long)(w.nextWait & E_MASK) | (c & (AC_MASK|TC_MASK));
- if (w.eventCount == (e | INT_SIGN) &&
- U.compareAndSwapLong(this, CTL, c, nc)) {
- w.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = w.parker) != null)
- U.unpark(p);
- return true; // release an idle worker
- }
- }
- else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
- long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
- if (U.compareAndSwapLong(this, CTL, c, nc))
- return true; // no compensation needed
- }
- else if (tc + pc < POOL_MAX) {
- long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- addWorker();
- return true; // create replacement
- }
- }
- }
- return false;
+ final void runWorker(WorkQueue w) {
+ w.growArray(); // allocate queue
+ do { w.runTask(scan(w)); } while (w.qlock >= 0);
}
- // Scanning for tasks
-
/**
* Scans for and, if found, returns one task, else possibly
* inactivates the worker. This method operates on single reads of
- * volatile state and is designed to be re-invoked continuously in
- * part because it returns upon detecting inconsistencies,
+ * volatile state and is designed to be re-invoked continuously,
+ * in part because it returns upon detecting inconsistencies,
* contention, or state changes that indicate possible success on
* re-invocation.
*
- * The scan searches for tasks across queues, randomly selecting
- * the first #queues probes, favoring steals over submissions
- * (by exploiting even/odd indexing), and then performing a
- * circular sweep of all queues. The scan terminates upon either
- * finding a non-empty queue, or completing a full sweep. If the
- * worker is not inactivated, it takes and returns a task from
- * this queue. On failure to find a task, we take one of the
- * following actions, after which the caller will retry calling
- * this method unless terminated.
+ * The scan searches for tasks across queues (starting at a random
+ * index, and relying on registerWorker to irregularly scatter
+ * them within array to avoid bias), checking each at least twice.
+ * The scan terminates upon either finding a non-empty queue, or
+ * completing the sweep. If the worker is not inactivated, it
+ * takes and returns a task from this queue. Otherwise, if not
+ * activated, it signals workers (that may include itself) and
+ * returns so caller can retry. Also returns for true if the
+ * worker array may have changed during an empty scan. On failure
+ * to find a task, we take one of the following actions, after
+ * which the caller will retry calling this method unless
+ * terminated.
*
* * If pool is terminating, terminate the worker.
*
- * * If not a complete sweep, try to release a waiting worker. If
- * the scan terminated because the worker is inactivated, then the
- * released worker will often be the calling worker, and it can
- * succeed obtaining a task on the next call. Or maybe it is
- * another worker, but with same net effect. Releasing in other
- * cases as well ensures that we have enough workers running.
- *
- * * If the caller has run a task since the last empty scan,
- * return (to allow rescan) if other workers are not also yet
- * enqueued. Field WorkQueue.rescans counts down on each scan to
- * ensure eventual inactivation and blocking.
- *
* * If not already enqueued, try to inactivate and enqueue the
- * worker on wait queue.
- *
- * * If already enqueued and none of the above apply, either park
- * awaiting signal, or if this is the most recent waiter and pool
- * is quiescent, relay to idleAwaitWork to check for termination
- * and possibly shrink pool.
+ * worker on wait queue. Or, if inactivating has caused the pool
+ * to be quiescent, relay to idleAwaitWork to check for
+ * termination and possibly shrink pool.
+ *
+ * * If already enqueued and none of the above apply, possibly
+ * (with 1/2 probability) park awaiting signal, else lingering to
+ * help scan and signal.
*
* @param w the worker (via its WorkQueue)
- * @return a task or null of none found
+ * @return a task or null if none found
*/
private final ForkJoinTask scan(WorkQueue w) {
- boolean swept = false; // true after full empty scan
- WorkQueue[] ws; // volatile read order matters
- int r = w.seed, ec = w.eventCount; // ec is negative if inactive
- int rs = runState, m = rs & SMASK;
- if ((ws = workQueues) != null && ws.length > m) { // consistency check
- for (int k = 0, j = -1 - m; ; ++j) {
- WorkQueue q; int b;
- if (j < 0) { // random probes while j negative
- r ^= r << 13; r ^= r >>> 17; k = (r ^= r << 5) | (j & 1);
- } // worker (not submit) for odd j
- else // cyclic scan when j >= 0
- k += 7; // step 7 reduces array packing bias
- if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
- ForkJoinTask t = (ec >= 0) ? q.pollAt(b) : null;
- w.seed = r; // save seed for next scan
- if (t != null)
- return t;
- break;
- }
- else if (j - m > m) {
- if (rs == runState) // staleness check
- swept = true;
- break;
- }
- }
-
- // Decode ctl on empty scan
- long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
- if (e < 0) // pool is terminating
- w.runState = -1;
- else if (!swept) { // try to release a waiter
- WorkQueue v; Thread p;
- if (e > 0 && a < 0 && (v = ws[e & m]) != null &&
- v.eventCount == (e | INT_SIGN)) {
- long nc = ((long)(v.nextWait & E_MASK) |
- ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- v.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = v.parker) != null)
- U.unpark(p);
+ WorkQueue[] ws; int m;
+ int ps = plock; // read plock before ws
+ if (w != null && (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+ int ec = w.eventCount; // ec is negative if inactive
+ int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+ int j = ((m + m + 1) | MIN_SCAN) & MAX_SCAN;
+ do {
+ WorkQueue q; ForkJoinTask[] a; int b;
+ if ((q = ws[(r + j) & m]) != null && (b = q.base) - q.top < 0 &&
+ (a = q.array) != null) { // probably nonempty
+ int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ ForkJoinTask t = (ForkJoinTask)
+ U.getObjectVolatile(a, i);
+ if (q.base == b && ec >= 0 && t != null &&
+ U.compareAndSwapObject(a, i, t, null)) {
+ if ((q.base = b + 1) - q.top < 0)
+ signalWork(q);
+ return t; // taken
+ }
+ else if ((ec < 0 || j < m) && (int)(ctl >> AC_SHIFT) <= 0) {
+ w.hint = (r + j) & m; // help signal below
+ break; // cannot take
}
}
- }
- else if ((nr = w.rescans) > 0) { // continue rescanning
- int ac = a + parallelism;
- if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0 &&
- w.eventCount == ec)
- Thread.yield(); // occasionally yield
- }
- else if (ec >= 0) { // try to enqueue
- long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
- w.nextWait = e;
- w.eventCount = ec | INT_SIGN;// mark as inactive
- if (!U.compareAndSwapLong(this, CTL, c, nc))
- w.eventCount = ec; // unmark on CAS failure
- else if ((ns = w.nsteals) != 0) {
- w.nsteals = 0; // set rescans if ran task
- w.rescans = a + parallelism;
- w.totalSteals += ns;
- }
- }
- else{ // already queued
- if (parallelism == -a)
- idleAwaitWork(w); // quiescent
- if (w.eventCount == ec) {
- Thread.interrupted(); // clear status
- ForkJoinWorkerThread wt = w.owner;
+ } while (--j >= 0);
+
+ long c, sc; int e, ns, h;
+ if ((h = w.hint) < 0) {
+ if ((ns = w.nsteals) != 0) {
+ if (U.compareAndSwapLong(this, STEALCOUNT,
+ sc = stealCount, sc + ns))
+ w.nsteals = 0; // collect steals
+ }
+ else if (plock != ps) // consistency check
+ ; // skip
+ else if ((e = (int)(c = ctl)) < 0)
+ w.qlock = -1; // pool is terminating
+ else if (ec >= 0) { // try to enqueue/inactivate
+ long nc = ((long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK)));
+ w.nextWait = e; // link and mark inactive
+ w.eventCount = ec | INT_SIGN;
+ if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
+ w.eventCount = ec; // unmark on CAS failure
+ else if ((int)(c >> AC_SHIFT) == 1 - (config & SMASK))
+ idleAwaitWork(w, nc, c);
+ }
+ else if (w.eventCount < 0) { // block
+ Thread wt = Thread.currentThread();
+ Thread.interrupted(); // clear status
U.putObject(wt, PARKBLOCKER, this);
- w.parker = wt; // emulate LockSupport.park
- if (w.eventCount == ec) // recheck
- U.park(false, 0L); // block
+ w.parker = wt; // emulate LockSupport.park
+ if (w.eventCount < 0) // recheck
+ U.park(false, 0L);
w.parker = null;
U.putObject(wt, PARKBLOCKER, null);
}
}
+ if (h >= 0 || w.hint >= 0) // signal others before retry
+ helpSignalHint(w);
}
return null;
}
/**
- * If inactivating worker w has caused pool to become quiescent,
- * checks for pool termination, and, so long as this is not the
- * only worker, waits for event for up to SHRINK_RATE nanosecs.
- * On timeout, if ctl has not changed, terminates the worker,
- * which will in turn wake up another worker to possibly repeat
- * this process.
+ * If inactivating worker w has caused the pool to become
+ * quiescent, checks for pool termination, and, so long as this is
+ * not the only worker, waits for event for up to a given
+ * duration. On timeout, if ctl has not changed, terminates the
+ * worker, which will in turn wake up another worker to possibly
+ * repeat this process.
*
* @param w the calling worker
+ * @param currentCtl the ctl value triggering possible quiescence
+ * @param prevCtl the ctl value to restore if thread is terminated
*/
- private void idleAwaitWork(WorkQueue w) {
- long c; int nw, ec;
- if (!tryTerminate(false, false) &&
- (int)((c = ctl) >> AC_SHIFT) + parallelism == 0 &&
- (ec = w.eventCount) == ((int)c | INT_SIGN) &&
- (nw = w.nextWait) != 0) {
- long nc = ((long)(nw & E_MASK) | // ctl to restore on timeout
- ((c + AC_UNIT) & AC_MASK) | (c & TC_MASK));
- ForkJoinWorkerThread wt = w.owner;
- while (ctl == c) {
- long startTime = System.nanoTime();
+ private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
+ if (w != null && w.eventCount < 0 &&
+ !tryTerminate(false, false) && (int)prevCtl != 0) {
+ int dc = -(short)(currentCtl >>> TC_SHIFT);
+ long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
+ long deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
+ Thread wt = Thread.currentThread();
+ while (ctl == currentCtl) {
Thread.interrupted(); // timed variant of version in scan()
U.putObject(wt, PARKBLOCKER, this);
w.parker = wt;
- if (ctl == c)
- U.park(false, SHRINK_RATE);
+ if (ctl == currentCtl)
+ U.park(false, parkTime);
w.parker = null;
U.putObject(wt, PARKBLOCKER, null);
- if (ctl != c)
+ if (ctl != currentCtl)
break;
- if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
- U.compareAndSwapLong(this, CTL, c, nc)) {
- w.eventCount = (ec + E_SEQ) | E_MASK;
- w.runState = -1; // shrink
+ if (deadline - System.nanoTime() <= 0L &&
+ U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
+ w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
+ w.qlock = -1; // shrink
break;
}
}
@@ -1612,6 +1800,80 @@ public class ForkJoinPool extends Abstra
}
/**
+ * Scans through queues looking for work while joining a task; if
+ * any present, signals. May return early if more signalling is
+ * detectably unneeded.
+ *
+ * @param task return early if done
+ * @param origin an index to start scan
+ */
+ private void helpSignal(ForkJoinTask task, int origin) {
+ WorkQueue[] ws; WorkQueue w; Thread p; long c; int m, u, e, i, s;
+ if (task != null && task.status >= 0 &&
+ (u = (int)(ctl >>> 32)) < 0 && (u >> UAC_SHIFT) < 0 &&
+ (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+ outer: for (int k = origin, j = m; j >= 0; --j) {
+ WorkQueue q = ws[k++ & m];
+ for (int n = m;;) { // limit to at most m signals
+ if (task.status < 0)
+ break outer;
+ if (q == null ||
+ ((s = -q.base + q.top) <= n && (n = s) <= 0))
+ break;
+ if ((u = (int)((c = ctl) >>> 32)) >= 0 ||
+ (e = (int)c) <= 0 || m < (i = e & SMASK) ||
+ (w = ws[i]) == null)
+ break outer;
+ long nc = (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ if (--n <= 0)
+ break;
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Signals other workers if tasks are present in hinted queue.
+ *
+ * @param caller the worker with the hint
+ */
+ private void helpSignalHint(WorkQueue caller) {
+ WorkQueue[] ws; WorkQueue q, w; Thread p; long c; int h, m, u, e, i, s;
+ if (caller != null && (h = caller.hint) >= 0 &&
+ (u = (int)(ctl >>> 32)) < 0 && (u >> UAC_SHIFT) < 0 &&
+ (ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+ (q = ws[h & m]) != null) {
+ caller.hint = -1;
+ for (int n = 2;;) { // limit to at most 2 signals
+ int idleCount = (caller.eventCount < 0)? 0 : -1;
+ if (((s = idleCount - q.base + q.top) <= n && (n = s) <= 0) ||
+ (u = (int)((c = ctl) >>> 32)) >= 0 ||
+ (e = (int)c) <= 0 || m < (i = e & SMASK) ||
+ (w = ws[i]) == null)
+ break;
+ long nc = (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.hint = h;
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ if (--n <= 0)
+ break;
+ }
+ }
+ }
+ }
+
+ /**
* Tries to locate and execute tasks for a stealer of the given
* task, or in turn one of its stealers, Traces currentSteal ->
* currentJoin links looking for a thread working on a descendant
@@ -1622,112 +1884,261 @@ public class ForkJoinPool extends Abstra
* leaves hints in workers to speed up subsequent calls. The
* implementation is very branchy to cope with potential
* inconsistencies or loops encountering chains that are stale,
- * unknown, or of length greater than MAX_HELP_DEPTH links. All
- * of these cases are dealt with by just retrying by caller.
+ * unknown, or so long that they are likely cyclic.
*
* @param joiner the joining worker
* @param task the task to join
- * @return true if found or ran a task (and so is immediately retryable)
+ * @return 0 if no progress can be made, negative if task
+ * known complete, else positive
*/
- final boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask task) {
- ForkJoinTask subtask; // current target
- boolean progress = false;
- int depth = 0; // current chain depth
- int m = runState & SMASK;
- WorkQueue[] ws = workQueues;
-
- if (ws != null && ws.length > m && (subtask = task).status >= 0) {
- outer:for (WorkQueue j = joiner;;) {
- // Try to find the stealer of subtask, by first using hint
- WorkQueue stealer = null;
- WorkQueue v = ws[j.stealHint & m];
- if (v != null && v.currentSteal == subtask)
- stealer = v;
- else {
- for (int i = 1; i <= m; i += 2) {
- if ((v = ws[i]) != null && v.currentSteal == subtask) {
- stealer = v;
- j.stealHint = i; // save hint
- break;
+ private int tryHelpStealer(WorkQueue joiner, ForkJoinTask task) {
+ int stat = 0, steps = 0; // bound to avoid cycles
+ if (joiner != null && task != null) { // hoist null checks
+ restart: for (;;) {
+ ForkJoinTask subtask = task; // current target
+ for (WorkQueue j = joiner, v;;) { // v is stealer of subtask
+ WorkQueue[] ws; int m, s, h;
+ if ((s = task.status) < 0) {
+ stat = s;
+ break restart;
+ }
+ if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
+ break restart; // shutting down
+ if ((v = ws[h = (j.hint | 1) & m]) == null ||
+ v.currentSteal != subtask) {
+ for (int origin = h;;) { // find stealer
+ if (((h = (h + 2) & m) & 15) == 1 &&
+ (subtask.status < 0 || j.currentJoin != subtask))
+ continue restart; // occasional staleness check
+ if ((v = ws[h]) != null &&
+ v.currentSteal == subtask) {
+ j.hint = h; // save hint
+ break;
+ }
+ if (h == origin)
+ break restart; // cannot find stealer
+ }
+ }
+ for (;;) { // help stealer or descend to its stealer
+ ForkJoinTask[] a; int b;
+ if (subtask.status < 0) // surround probes with
+ continue restart; // consistency checks
+ if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
+ int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ ForkJoinTask t =
+ (ForkJoinTask)U.getObjectVolatile(a, i);
+ if (subtask.status < 0 || j.currentJoin != subtask ||
+ v.currentSteal != subtask)
+ continue restart; // stale
+ stat = 1; // apparent progress
+ if (t != null && v.base == b &&
+ U.compareAndSwapObject(a, i, t, null)) {
+ v.base = b + 1; // help stealer
+ joiner.runSubtask(t);
+ }
+ else if (v.base == b && ++steps == MAX_HELP)
+ break restart; // v apparently stalled
+ }
+ else { // empty -- try to descend
+ ForkJoinTask next = v.currentJoin;
+ if (subtask.status < 0 || j.currentJoin != subtask ||
+ v.currentSteal != subtask)
+ continue restart; // stale
+ else if (next == null || ++steps == MAX_HELP)
+ break restart; // dead-end or maybe cyclic
+ else {
+ subtask = next;
+ j = v;
+ break;
+ }
}
}
- if (stealer == null)
+ }
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Analog of tryHelpStealer for CountedCompleters. Tries to steal
+ * and run tasks within the target's computation.
+ *
+ * @param task the task to join
+ * @param mode if shared, exit upon completing any task
+ * if all workers are active
+ *
+ */
+ private int helpComplete(ForkJoinTask task, int mode) {
+ WorkQueue[] ws; WorkQueue q; int m, n, s, u;
+ if (task != null && (ws = workQueues) != null &&
+ (m = ws.length - 1) >= 0) {
+ for (int j = 1, origin = j;;) {
+ if ((s = task.status) < 0)
+ return s;
+ if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
+ origin = j;
+ if (mode == SHARED_QUEUE &&
+ ((u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0))
break;
}
+ else if ((j = (j + 2) & m) == origin)
+ break;
+ }
+ }
+ return 0;
+ }
- for (WorkQueue q = stealer;;) { // Try to help stealer
- ForkJoinTask t; int b;
- if (task.status < 0)
- break outer;
- if ((b = q.base) - q.top < 0) {
- progress = true;
- if (subtask.status < 0)
- break outer; // stale
- if ((t = q.pollAt(b)) != null) {
- stealer.stealHint = joiner.poolIndex;
- joiner.runSubtask(t);
+ /**
+ * Tries to decrement active count (sometimes implicitly) and
+ * possibly release or create a compensating worker in preparation
+ * for blocking. Fails on contention or termination. Otherwise,
+ * adds a new thread if no idle workers are available and pool
+ * may become starved.
+ */
+ final boolean tryCompensate() {
+ int pc = config & SMASK, e, i, tc; long c;
+ WorkQueue[] ws; WorkQueue w; Thread p;
+ if ((ws = workQueues) != null && (e = (int)(c = ctl)) >= 0) {
+ if (e != 0 && (i = e & SMASK) < ws.length &&
+ (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ (c & (AC_MASK|TC_MASK)));
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ return true; // replace with idle worker
+ }
+ }
+ else if ((tc = (short)(c >>> TC_SHIFT)) >= 0 &&
+ (int)(c >> AC_SHIFT) + pc > 1) {
+ long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ return true; // no compensation
+ }
+ else if (tc + pc < MAX_CAP) {
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ ForkJoinWorkerThreadFactory fac;
+ Throwable ex = null;
+ ForkJoinWorkerThread wt = null;
+ try {
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
+ return true;
}
+ } catch (Throwable rex) {
+ ex = rex;
}
- else { // empty - try to descend to find stealer's stealer
- ForkJoinTask next = stealer.currentJoin;
- if (++depth == MAX_HELP_DEPTH || subtask.status < 0 ||
- next == null || next == subtask)
- break outer; // max depth, stale, dead-end, cyclic
- subtask = next;
- j = stealer;
- break;
- }
+ deregisterWorker(wt, ex); // clean up and return false
}
}
}
- return progress;
+ return false;
}
/**
- * If task is at base of some steal queue, steals and executes it.
+ * Helps and/or blocks until the given task is done.
*
* @param joiner the joining worker
* @param task the task
+ * @return task status on exit
*/
- final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask task) {
- WorkQueue[] ws;
- int m = runState & SMASK;
- if ((ws = workQueues) != null && ws.length > m) {
- for (int j = 1; j <= m && task.status >= 0; j += 2) {
- WorkQueue q = ws[j];
- if (q != null && q.pollFor(task)) {
- joiner.runSubtask(task);
- break;
+ final int awaitJoin(WorkQueue joiner, ForkJoinTask task) {
+ int s = 0;
+ if (joiner != null && task != null && (s = task.status) >= 0) {
+ ForkJoinTask prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
+ joiner.tryRemoveAndExec(task)); // process local tasks
+ if (s >= 0 && (s = task.status) >= 0) {
+ helpSignal(task, joiner.poolIndex);
+ if ((s = task.status) >= 0 &&
+ (task instanceof CountedCompleter))
+ s = helpComplete(task, LIFO_QUEUE);
+ }
+ while (s >= 0 && (s = task.status) >= 0) {
+ if ((!joiner.isEmpty() || // try helping
+ (s = tryHelpStealer(joiner, task)) == 0) &&
+ (s = task.status) >= 0) {
+ helpSignal(task, joiner.poolIndex);
+ if ((s = task.status) >= 0 && tryCompensate()) {
+ if (task.trySetSignal() && (s = task.status) >= 0) {
+ synchronized (task) {
+ if (task.status >= 0) {
+ try { // see ForkJoinTask
+ task.wait(); // for explanation
+ } catch (InterruptedException ie) {
+ }
+ }
+ else
+ task.notifyAll();
+ }
+ }
+ long c; // re-activate
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, c + AC_UNIT));
+ }
}
}
+ joiner.currentJoin = prevJoin;
+ }
+ return s;
+ }
+
+ /**
+ * Stripped-down variant of awaitJoin used by timed joins. Tries
+ * to help join only while there is continuous progress. (Caller
+ * will then enter a timed wait.)
+ *
+ * @param joiner the joining worker
+ * @param task the task
+ */
+ final void helpJoinOnce(WorkQueue joiner, ForkJoinTask task) {
+ int s;
+ if (joiner != null && task != null && (s = task.status) >= 0) {
+ ForkJoinTask prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
+ joiner.tryRemoveAndExec(task));
+ if (s >= 0 && (s = task.status) >= 0) {
+ helpSignal(task, joiner.poolIndex);
+ if ((s = task.status) >= 0 &&
+ (task instanceof CountedCompleter))
+ s = helpComplete(task, LIFO_QUEUE);
+ }
+ if (s >= 0 && joiner.isEmpty()) {
+ do {} while (task.status >= 0 &&
+ tryHelpStealer(joiner, task) > 0);
+ }
+ joiner.currentJoin = prevJoin;
}
}
/**
- * Returns a non-empty steal queue, if one is found during a random,
- * then cyclic scan, else null. This method must be retried by
- * caller if, by the time it tries to use the queue, it is empty.
+ * Returns a (probably) non-empty steal queue, if one is found
+ * during a random, then cyclic scan, else null. This method must
+ * be retried by caller if, by the time it tries to use the queue,
+ * it is empty.
+ * @param r a (random) seed for scanning
*/
- private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
- int r = w.seed; // Same idea as scan(), but ignoring submissions
+ private WorkQueue findNonEmptyStealQueue(int r) {
for (WorkQueue[] ws;;) {
- int m = runState & SMASK;
- if ((ws = workQueues) == null)
+ int ps = plock, m, n;
+ if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
return null;
- if (ws.length > m) {
- WorkQueue q;
- for (int k = 0, j = -1 - m;; ++j) {
- if (j < 0) {
- r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
- }
- else
- k += 7;
- if ((q = ws[(k | 1) & m]) != null && q.base - q.top < 0) {
- w.seed = r;
- return q;
- }
- else if (j - m > m)
+ for (int j = (m + 1) << 2; ;) {
+ WorkQueue q = ws[(((r + j) << 1) | 1) & m];
+ if (q != null && (n = q.base - q.top) < 0) {
+ if (n < -1)
+ signalWork(q);
+ return q;
+ }
+ else if (--j < 0) {
+ if (plock == ps)
return null;
+ break;
}
}
}
@@ -1741,17 +2152,20 @@ public class ForkJoinPool extends Abstra
*/
final void helpQuiescePool(WorkQueue w) {
for (boolean active = true;;) {
- w.runLocalTasks(); // exhaust local queue
- WorkQueue q = findNonEmptyStealQueue(w);
+ ForkJoinTask localTask; // exhaust local queue
+ while ((localTask = w.nextLocalTask()) != null)
+ localTask.doExec();
+ // Similar to loop in scan(), but ignoring submissions
+ WorkQueue q = findNonEmptyStealQueue(w.nextSeed());
if (q != null) {
- ForkJoinTask t;
+ ForkJoinTask t; int b;
if (!active) { // re-establish active count
long c;
active = true;
do {} while (!U.compareAndSwapLong
(this, CTL, c = ctl, c + AC_UNIT));
}
- if ((t = q.poll()) != null)
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
w.runSubtask(t);
}
else {
@@ -1763,7 +2177,7 @@ public class ForkJoinPool extends Abstra
}
else
c = ctl; // re-increment on exit
- if ((int)(c >> AC_SHIFT) + parallelism == 0) {
+ if ((int)(c >> AC_SHIFT) + (config & SMASK) == 0) {
do {} while (!U.compareAndSwapLong
(this, CTL, c = ctl, c + AC_UNIT));
break;
@@ -1779,30 +2193,75 @@ public class ForkJoinPool extends Abstra
*/
final ForkJoinTask nextTaskFor(WorkQueue w) {
for (ForkJoinTask t;;) {
- WorkQueue q;
+ WorkQueue q; int b;
if ((t = w.nextLocalTask()) != null)
return t;
- if ((q = findNonEmptyStealQueue(w)) == null)
+ if ((q = findNonEmptyStealQueue(w.nextSeed())) == null)
return null;
- if ((t = q.poll()) != null)
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
return t;
}
}
/**
- * Returns the approximate (non-atomic) number of idle threads per
- * active thread to offset steal queue size for method
- * ForkJoinTask.getSurplusQueuedTaskCount().
- */
- final int idlePerActive() {
- // Approximate at powers of two for small values, saturate past 4
- int p = parallelism;
- int a = p + (int)(ctl >> AC_SHIFT);
- return (a > (p >>>= 1) ? 0 :
- a > (p >>>= 1) ? 1 :
- a > (p >>>= 1) ? 2 :
- a > (p >>>= 1) ? 4 :
- 8);
+ * Returns a cheap heuristic guide for task partitioning when
+ * programmers, frameworks, tools, or languages have little or no
+ * idea about task granularity. In essence by offering this
+ * method, we ask users only about tradeoffs in overhead vs
+ * expected throughput and its variance, rather than how finely to
+ * partition tasks.
+ *
+ * In a steady state strict (tree-structured) computation, each
+ * thread makes available for stealing enough tasks for other
+ * threads to remain active. Inductively, if all threads play by
+ * the same rules, each thread should make available only a
+ * constant number of tasks.
+ *
+ * The minimum useful constant is just 1. But using a value of 1
+ * would require immediate replenishment upon each steal to
+ * maintain enough tasks, which is infeasible. Further,
+ * partitionings/granularities of offered tasks should minimize
+ * steal rates, which in general means that threads nearer the top
+ * of computation tree should generate more than those nearer the
+ * bottom. In perfect steady state, each thread is at
+ * approximately the same level of computation tree. However,
+ * producing extra tasks amortizes the uncertainty of progress and
+ * diffusion assumptions.
+ *
+ * So, users will want to use values larger, but not much larger
+ * than 1 to both smooth over transient shortages and hedge
+ * against uneven progress; as traded off against the cost of
+ * extra task overhead. We leave the user to pick a threshold
+ * value to compare with the results of this call to guide
+ * decisions, but recommend values such as 3.
+ *
+ * When all threads are active, it is on average OK to estimate
+ * surplus strictly locally. In steady-state, if one thread is
+ * maintaining say 2 surplus tasks, then so are others. So we can
+ * just use estimated queue length. However, this strategy alone
+ * leads to serious mis-estimates in some non-steady-state
+ * conditions (ramp-up, ramp-down, other stalls). We can detect
+ * many of these by further considering the number of "idle"
+ * threads, that are known to have zero queued tasks, so
+ * compensate by a factor of (#idle/#active) threads.
+ *
+ * Note: The approximation of #busy workers as #active workers is
+ * not very good under current signalling scheme, and should be
+ * improved.
+ */
+ static int getSurplusQueuedTaskCount() {
+ Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
+ if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
+ int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).config & SMASK;
+ int n = (q = wt.workQueue).top - q.base;
+ int a = (int)(pool.ctl >> AC_SHIFT) + p;
+ return n - (a > (p >>>= 1) ? 0 :
+ a > (p >>>= 1) ? 1 :
+ a > (p >>>= 1) ? 2 :
+ a > (p >>>= 1) ? 4 :
+ 8);
+ }
+ return 0;
}
// Termination
@@ -1822,25 +2281,30 @@ public class ForkJoinPool extends Abstra
* @return true if now terminating or terminated
*/
private boolean tryTerminate(boolean now, boolean enable) {
- Mutex lock = this.lock;
+ if (this == commonPool) // cannot shut down
+ return false;
for (long c;;) {
if (((c = ctl) & STOP_BIT) != 0) { // already terminating
- if ((short)(c >>> TC_SHIFT) == -parallelism) {
- lock.lock(); // don't need try/finally
- termination.signalAll(); // signal when 0 workers
- lock.unlock();
+ if ((short)(c >>> TC_SHIFT) == -(config & SMASK)) {
+ synchronized (this) {
+ notifyAll(); // signal when 0 workers
+ }
}
return true;
}
- if (runState >= 0) { // not yet enabled
+ if (plock >= 0) { // not yet enabled
+ int ps;
if (!enable)
return false;
- lock.lock();
- runState |= SHUTDOWN;
- lock.unlock();
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = SHUTDOWN;
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
if (!now) { // check if idle & no tasks
- if ((int)(c >> AC_SHIFT) != -parallelism ||
+ if ((int)(c >> AC_SHIFT) != -(config & SMASK) ||
hasQueuedSubmissions())
return false;
// Check for unqueued inactive workers. One pass suffices.
@@ -1860,7 +2324,7 @@ public class ForkJoinPool extends Abstra
int n = ws.length;
for (int i = 0; i < n; ++i) {
if ((w = ws[i]) != null) {
- w.runState = -1;
+ w.qlock = -1;
if (pass > 0) {
w.cancelAll();
if (pass > 1)
@@ -1879,7 +2343,7 @@ public class ForkJoinPool extends Abstra
if (w.eventCount == (e | INT_SIGN) &&
U.compareAndSwapLong(this, CTL, cc, nc)) {
w.eventCount = (e + E_SEQ) & E_MASK;
- w.runState = -1;
+ w.qlock = -1;
if ((p = w.parker) != null)
U.unpark(p);
}
@@ -1890,6 +2354,147 @@ public class ForkJoinPool extends Abstra
}
}
+ // external operations on common pool
+
+ /**
+ * Returns common pool queue for a thread that has submitted at
+ * least one task.
+ */
+ static WorkQueue commonSubmitterQueue() {
+ ForkJoinPool p; WorkQueue[] ws; int m; Submitter z;
+ return ((z = submitters.get()) != null &&
+ (p = commonPool) != null &&
+ (ws = p.workQueues) != null &&
+ (m = ws.length - 1) >= 0) ?
+ ws[m & z.seed & SQMASK] : null;
+ }
+
+ /**
+ * Tries to pop the given task from submitter's queue in common pool.
+ */
+ static boolean tryExternalUnpush(ForkJoinTask t) {
+ ForkJoinPool p; WorkQueue[] ws; WorkQueue q; Submitter z;
+ ForkJoinTask[] a; int m, s;
+ if (t != null &&
+ (z = submitters.get()) != null &&
+ (p = commonPool) != null &&
+ (ws = p.workQueues) != null &&
+ (m = ws.length - 1) >= 0 &&
+ (q = ws[m & z.seed & SQMASK]) != null &&
+ (s = q.top) != q.base &&
+ (a = q.array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if (U.getObject(a, j) == t &&
+ U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+ if (q.array == a && q.top == s && // recheck
+ U.compareAndSwapObject(a, j, t, null)) {
+ q.top = s - 1;
+ q.qlock = 0;
+ return true;
+ }
+ q.qlock = 0;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Tries to pop and run local tasks within the same computation
+ * as the given root. On failure, tries to help complete from
+ * other queues via helpComplete.
+ */
+ private void externalHelpComplete(WorkQueue q, ForkJoinTask root) {
+ ForkJoinTask[] a; int m;
+ if (q != null && (a = q.array) != null && (m = (a.length - 1)) >= 0 &&
+ root != null && root.status >= 0) {
+ for (;;) {
+ int s, u; Object o; CountedCompleter task = null;
+ if ((s = q.top) - q.base > 0) {
+ long j = ((m & (s - 1)) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) != null &&
+ (o instanceof CountedCompleter)) {
+ CountedCompleter t = (CountedCompleter)o, r = t;
+ do {
+ if (r == root) {
+ if (U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+ if (q.array == a && q.top == s &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ q.top = s - 1;
+ task = t;
+ }
+ q.qlock = 0;
+ }
+ break;
+ }
+ } while ((r = r.completer) != null);
+ }
+ }
+ if (task != null)
+ task.doExec();
+ if (root.status < 0 ||
+ (u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0)
+ break;
+ if (task == null) {
+ helpSignal(root, q.poolIndex);
+ if (root.status >= 0)
+ helpComplete(root, SHARED_QUEUE);
+ break;
+ }
+ }
+ }
+ }
+
+ /**
+ * Tries to help execute or signal availability of the given task
+ * from submitter's queue in common pool.
+ */
+ static void externalHelpJoin(ForkJoinTask t) {
+ // Some hard-to-avoid overlap with tryExternalUnpush
+ ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; Submitter z;
+ ForkJoinTask[] a; int m, s, n;
+ if (t != null &&
+ (z = submitters.get()) != null &&
+ (p = commonPool) != null &&
+ (ws = p.workQueues) != null &&
+ (m = ws.length - 1) >= 0 &&
+ (q = ws[m & z.seed & SQMASK]) != null &&
+ (a = q.array) != null) {
+ int am = a.length - 1;
+ if ((s = q.top) != q.base) {
+ long j = ((am & (s - 1)) << ASHIFT) + ABASE;
+ if (U.getObject(a, j) == t &&
+ U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+ if (q.array == a && q.top == s &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ q.top = s - 1;
+ q.qlock = 0;
+ t.doExec();
+ }
+ else
+ q.qlock = 0;
+ }
+ }
+ if (t.status >= 0) {
+ if (t instanceof CountedCompleter)
+ p.externalHelpComplete(q, t);
+ else
+ p.helpSignal(t, q.poolIndex);
+ }
+ }
+ }
+
+ /**
+ * Restricted version of helpQuiescePool for external callers
+ */
+ static void externalHelpQuiescePool() {
+ ForkJoinPool p; ForkJoinTask t; WorkQueue q; int b;
+ if ((p = commonPool) != null &&
+ (q = p.findNonEmptyStealQueue(1)) != null &&
+ (b = q.base) - q.top < 0 &&
+ (t = q.pollAt(b)) != null)
+ t.doExec();
+ }
+
// Exported methods
// Constructors
@@ -1959,32 +2564,44 @@ public class ForkJoinPool extends Abstra
checkPermission();
if (factory == null)
throw new NullPointerException();
- if (parallelism <= 0 || parallelism > POOL_MAX)
+ if (parallelism <= 0 || parallelism > MAX_CAP)
throw new IllegalArgumentException();
- this.parallelism = parallelism;
this.factory = factory;
this.ueh = handler;
- this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
- this.growHints = 1;
+ this.config = parallelism | (asyncMode ? (FIFO_QUEUE << 16) : 0);
long np = (long)(-parallelism); // offset ctl counts
this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
- // initialize workQueues array with room for 2*parallelism if possible
- int n = parallelism << 1;
- if (n >= POOL_MAX)
- n = POOL_MAX;
- else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
- n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
- }
- this.workQueues = new WorkQueue[(n + 1) << 1]; // #slots = 2 * #workers
- this.termination = (this.lock = new Mutex()).newCondition();
- this.stealCount = new AtomicLong();
- this.nextWorkerNumber = new AtomicInteger();
+ int pn = nextPoolId();
StringBuilder sb = new StringBuilder("ForkJoinPool-");
- sb.append(poolNumberGenerator.incrementAndGet());
+ sb.append(Integer.toString(pn));
sb.append("-worker-");
this.workerNamePrefix = sb.toString();
}
+ /**
+ * Constructor for common pool, suitable only for static initialization.
+ * Basically the same as above, but uses smallest possible initial footprint.
+ */
+ ForkJoinPool(int parallelism, long ctl,
+ ForkJoinWorkerThreadFactory factory,
+ Thread.UncaughtExceptionHandler handler) {
+ this.config = parallelism;
+ this.ctl = ctl;
+ this.factory = factory;
+ this.ueh = handler;
+ this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
+ }
+
+ /**
+ * Returns the common pool instance.
+ *
+ * @return the common pool instance
+ */
+ public static ForkJoinPool commonPool() {
+ // assert commonPool != null : "static init error";
+ return commonPool;
+ }
+
// Execution methods
/**
@@ -2004,7 +2621,9 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public T invoke(ForkJoinTask task) {
- doSubmit(task);
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
return task.join();
}
@@ -2017,7 +2636,9 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public void execute(ForkJoinTask task) {
- doSubmit(task);
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
}
// AbstractExecutorService methods
@@ -2034,8 +2655,8 @@ public class ForkJoinPool extends Abstra
if (task instanceof ForkJoinTask) // avoid re-wrap
job = (ForkJoinTask) task;
else
- job = ForkJoinTask.adapt(task, null);
- doSubmit(job);
+ job = new ForkJoinTask.AdaptedRunnableAction(task);
+ externalPush(job);
}
/**
@@ -2048,7 +2669,9 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public ForkJoinTask submit(ForkJoinTask task) {
- doSubmit(task);
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
return task;
}
@@ -2058,10 +2681,8 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public ForkJoinTask submit(Callable task) {
- if (task == null)
- throw new NullPointerException();
- ForkJoinTask job = ForkJoinTask.adapt(task);
- doSubmit(job);
+ ForkJoinTask job = new ForkJoinTask.AdaptedCallable(task);
+ externalPush(job);
return job;
}
@@ -2071,10 +2692,8 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public ForkJoinTask submit(Runnable task, T result) {
- if (task == null)
- throw new NullPointerException();
- ForkJoinTask job = ForkJoinTask.adapt(task, result);
- doSubmit(job);
+ ForkJoinTask job = new ForkJoinTask.AdaptedRunnable(task, result);
+ externalPush(job);
return job;
}
@@ -2090,8 +2709,8 @@ public class ForkJoinPool extends Abstra
if (task instanceof ForkJoinTask) // avoid re-wrap
job = (ForkJoinTask) task;
else
- job = ForkJoinTask.adapt(task, null);
- doSubmit(job);
+ job = new ForkJoinTask.AdaptedRunnableAction(task);
+ externalPush(job);
return job;
}
@@ -2112,8 +2731,8 @@ public class ForkJoinPool extends Abstra
boolean done = false;
try {
for (Callable t : tasks) {
- ForkJoinTask f = ForkJoinTask.adapt(t);
- doSubmit(f);
+ ForkJoinTask f = new ForkJoinTask.AdaptedCallable(t);
+ externalPush(f);
fs.add(f);
}
for (ForkJoinTask f : fs)
@@ -2152,7 +2771,16 @@ public class ForkJoinPool extends Abstra
* @return the targeted parallelism level of this pool
*/
public int getParallelism() {
- return parallelism;
+ return config & SMASK;
+ }
+
+ /**
+ * Returns the targeted parallelism level of the common pool.
+ *
+ * @return the targeted parallelism level of the common pool
+ */
+ public static int getCommonPoolParallelism() {
+ return commonPoolParallelism;
}
/**
@@ -2164,7 +2792,7 @@ public class ForkJoinPool extends Abstra
* @return the number of worker threads
*/
public int getPoolSize() {
- return parallelism + (short)(ctl >>> TC_SHIFT);
+ return (config & SMASK) + (short)(ctl >>> TC_SHIFT);
}
/**
@@ -2174,7 +2802,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool uses async mode
*/
public boolean getAsyncMode() {
- return localMode != 0;
+ return (config >>> 16) == FIFO_QUEUE;
}
/**
@@ -2205,7 +2833,7 @@ public class ForkJoinPool extends Abstra
* @return the number of active threads
*/
public int getActiveThreadCount() {
- int r = parallelism + (int)(ctl >> AC_SHIFT);
+ int r = (config & SMASK) + (int)(ctl >> AC_SHIFT);
return (r <= 0) ? 0 : r; // suppress momentarily negative values
}
@@ -2221,7 +2849,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
- return (int)(ctl >> AC_SHIFT) + parallelism == 0;
+ return (int)(ctl >> AC_SHIFT) + (config & SMASK) == 0;
}
/**
@@ -2236,12 +2864,12 @@ public class ForkJoinPool extends Abstra
* @return the number of steals
*/
public long getStealCount() {
- long count = stealCount.get();
+ long count = stealCount;
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
for (int i = 1; i < ws.length; i += 2) {
if ((w = ws[i]) != null)
- count += w.totalSteals;
+ count += w.nsteals;
}
}
return count;
@@ -2298,7 +2926,7 @@ public class ForkJoinPool extends Abstra
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
for (int i = 0; i < ws.length; i += 2) {
- if ((w = ws[i]) != null && w.queueSize() != 0)
+ if ((w = ws[i]) != null && !w.isEmpty())
return true;
}
}
@@ -2366,7 +2994,7 @@ public class ForkJoinPool extends Abstra
public String toString() {
// Use a single pass through workQueues to collect counts
long qt = 0L, qs = 0L; int rc = 0;
- long st = stealCount.get();
+ long st = stealCount;
long c = ctl;
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
@@ -2377,14 +3005,14 @@ public class ForkJoinPool extends Abstra
qs += size;
else {
qt += size;
- st += w.totalSteals;
+ st += w.nsteals;
if (w.isApparentlyUnblocked())
++rc;
}
}
}
}
- int pc = parallelism;
+ int pc = (config & SMASK);
int tc = pc + (short)(c >>> TC_SHIFT);
int ac = pc + (int)(c >> AC_SHIFT);
if (ac < 0) // ignore transient negative
@@ -2393,7 +3021,7 @@ public class ForkJoinPool extends Abstra
if ((c & STOP_BIT) != 0)
level = (tc == 0) ? "Terminated" : "Terminating";
else
- level = runState < 0 ? "Shutting down" : "Running";
+ level = plock < 0 ? "Shutting down" : "Running";
return super.toString() +
"[" + level +
", parallelism = " + pc +
@@ -2407,11 +3035,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initiates an orderly shutdown in which previously submitted
- * tasks are executed, but no new tasks will be accepted.
- * Invocation has no additional effect if already shut down.
- * Tasks that are in the process of being submitted concurrently
- * during the course of this method may or may not be rejected.
+ * Possibly initiates an orderly shutdown in which previously
+ * submitted tasks are executed, but no new tasks will be
+ * accepted. Invocation has no effect on execution state if this
+ * is the {@link #commonPool}, and no additional effect if
+ * already shut down. Tasks that are in the process of being
+ * submitted concurrently during the course of this method may or
+ * may not be rejected.
*
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
@@ -2424,14 +3054,16 @@ public class ForkJoinPool extends Abstra
}
/**
- * Attempts to cancel and/or stop all tasks, and reject all
- * subsequently submitted tasks. Tasks that are in the process of
- * being submitted or executed concurrently during the course of
- * this method may or may not be rejected. This method cancels
- * both existing and unexecuted tasks, in order to permit
- * termination in the presence of task dependencies. So the method
- * always returns an empty list (unlike the case for some other
- * Executors).
+ * Possibly attempts to cancel and/or stop all tasks, and reject
+ * all subsequently submitted tasks. Invocation has no effect on
+ * execution state if this is the {@link #commonPool}, and no
+ * additional effect if already shut down. Otherwise, tasks that
+ * are in the process of being submitted or executed concurrently
+ * during the course of this method may or may not be
+ * rejected. This method cancels both existing and unexecuted
+ * tasks, in order to permit termination in the presence of task
+ * dependencies. So the method always returns an empty list
+ * (unlike the case for some other Executors).
*
* @return an empty list
* @throws SecurityException if a security manager exists and
@@ -2453,7 +3085,7 @@ public class ForkJoinPool extends Abstra
public boolean isTerminated() {
long c = ctl;
return ((c & STOP_BIT) != 0L &&
- (short)(c >>> TC_SHIFT) == -parallelism);
+ (short)(c >>> TC_SHIFT) == -(config & SMASK));
}
/**
@@ -2461,7 +3093,7 @@ public class ForkJoinPool extends Abstra
* commenced but not yet completed. This method may be useful for
* debugging. A return of {@code true} reported a sufficient
* period after shutdown may indicate that submitted tasks have
- * ignored or suppressed interruption, or are waiting for IO,
+ * ignored or suppressed interruption, or are waiting for I/O,
* causing this executor not to properly terminate. (See the
* advisory notes for class {@link ForkJoinTask} stating that
* tasks should not normally entail blocking operations. But if
@@ -2472,7 +3104,7 @@ public class ForkJoinPool extends Abstra
public boolean isTerminating() {
long c = ctl;
return ((c & STOP_BIT) != 0L &&
- (short)(c >>> TC_SHIFT) != -parallelism);
+ (short)(c >>> TC_SHIFT) != -(config & SMASK));
}
/**
@@ -2481,13 +3113,15 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
- return runState < 0;
+ return plock < 0;
}
/**
- * Blocks until all tasks have completed execution after a shutdown
- * request, or the timeout occurs, or the current thread is
- * interrupted, whichever happens first.
+ * Blocks until all tasks have completed execution after a
+ * shutdown request, or the timeout occurs, or the current thread
+ * is interrupted, whichever happens first. Note that the {@link
+ * #commonPool()} never terminates until program shutdown so
+ * this method will always time out.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
@@ -2498,19 +3132,21 @@ public class ForkJoinPool extends Abstra
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
- final Mutex lock = this.lock;
- lock.lock();
- try {
- for (;;) {
- if (isTerminated())
- return true;
- if (nanos <= 0)
- return false;
- nanos = termination.awaitNanos(nanos);
+ if (isTerminated())
+ return true;
+ long startTime = System.nanoTime();
+ boolean terminated = false;
+ synchronized (this) {
+ for (long waitTime = nanos, millis = 0L;;) {
+ if (terminated = isTerminated() ||
+ waitTime <= 0L ||
+ (millis = unit.toMillis(waitTime)) <= 0L)
+ break;
+ wait(millis);
+ waitTime = nanos - (System.nanoTime() - startTime);
}
- } finally {
- lock.unlock();
}
+ return terminated;
}
/**
@@ -2609,19 +3245,37 @@ public class ForkJoinPool extends Abstra
public static void managedBlock(ManagedBlocker blocker)
throws InterruptedException {
Thread t = Thread.currentThread();
- ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
- ((ForkJoinWorkerThread)t).pool : null);
- while (!blocker.isReleasable()) {
- if (p == null || p.tryCompensate()) {
- try {
- do {} while (!blocker.isReleasable() && !blocker.block());
- } finally {
- if (p != null)
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
+ while (!blocker.isReleasable()) { // variant of helpSignal
+ WorkQueue[] ws; WorkQueue q; int m, u;
+ if ((ws = p.workQueues) != null && (m = ws.length - 1) >= 0) {
+ for (int i = 0; i <= m; ++i) {
+ if (blocker.isReleasable())
+ return;
+ if ((q = ws[i]) != null && q.base - q.top < 0) {
+ p.signalWork(q);
+ if ((u = (int)(p.ctl >>> 32)) >= 0 ||
+ (u >> UAC_SHIFT) >= 0)
+ break;
+ }
+ }
+ }
+ if (p.tryCompensate()) {
+ try {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ } finally {
p.incrementActiveCount();
+ }
+ break;
}
- break;
}
}
+ else {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ }
}
// AbstractExecutorService overrides. These rely on undocumented
@@ -2629,35 +3283,93 @@ public class ForkJoinPool extends Abstra
// implement RunnableFuture.
protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return (RunnableFuture) ForkJoinTask.adapt(runnable, value);
+ return new ForkJoinTask.AdaptedRunnable(runnable, value);
}
protected RunnableFuture newTaskFor(Callable callable) {
- return (RunnableFuture) ForkJoinTask.adapt(callable);
+ return new ForkJoinTask.AdaptedCallable(callable);
}
// Unsafe mechanics
private static final sun.misc.Unsafe U;
private static final long CTL;
private static final long PARKBLOCKER;
+ private static final int ABASE;
+ private static final int ASHIFT;
+ private static final long STEALCOUNT;
+ private static final long PLOCK;
+ private static final long INDEXSEED;
+ private static final long QLOCK;
static {
- poolNumberGenerator = new AtomicInteger();
- modifyThreadPermission = new RuntimePermission("modifyThread");
- defaultForkJoinWorkerThreadFactory =
- new DefaultForkJoinWorkerThreadFactory();
- submitters = new ThreadSubmitter();
+ int s; // initialize field offsets for CAS etc
try {
U = getUnsafe();
Class k = ForkJoinPool.class;
CTL = U.objectFieldOffset
(k.getDeclaredField("ctl"));
+ STEALCOUNT = U.objectFieldOffset
+ (k.getDeclaredField("stealCount"));
+ PLOCK = U.objectFieldOffset
+ (k.getDeclaredField("plock"));
+ INDEXSEED = U.objectFieldOffset
+ (k.getDeclaredField("indexSeed"));
Class tk = Thread.class;
PARKBLOCKER = U.objectFieldOffset
(tk.getDeclaredField("parkBlocker"));
+ Class wk = WorkQueue.class;
+ QLOCK = U.objectFieldOffset
+ (wk.getDeclaredField("qlock"));
+ Class ak = ForkJoinTask[].class;
+ ABASE = U.arrayBaseOffset(ak);
+ s = U.arrayIndexScale(ak);
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
} catch (Exception e) {
throw new Error(e);
}
+ if ((s & (s-1)) != 0)
+ throw new Error("data type scale not a power of two");
+
+ submitters = new ThreadLocal();
+ ForkJoinWorkerThreadFactory fac = defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+ modifyThreadPermission = new RuntimePermission("modifyThread");
+
+ /*
+ * Establish common pool parameters. For extra caution,
+ * computations to set up common pool state are here; the
+ * constructor just assigns these values to fields.
+ */
+
+ int par = 0;
+ Thread.UncaughtExceptionHandler handler = null;
+ try { // TBD: limit or report ignored exceptions?
+ String pp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.parallelism");
+ String hp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
+ String fp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.threadFactory");
+ if (fp != null)
+ fac = ((ForkJoinWorkerThreadFactory)ClassLoader.
+ getSystemClassLoader().loadClass(fp).newInstance());
+ if (hp != null)
+ handler = ((Thread.UncaughtExceptionHandler)ClassLoader.
+ getSystemClassLoader().loadClass(hp).newInstance());
+ if (pp != null)
+ par = Integer.parseInt(pp);
+ } catch (Exception ignore) {
+ }
+
+ if (par <= 0)
+ par = Runtime.getRuntime().availableProcessors();
+ if (par > MAX_CAP)
+ par = MAX_CAP;
+ commonPoolParallelism = par;
+ long np = (long)(-par); // precompute initial ctl value
+ long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
+
+ commonPool = new ForkJoinPool(par, ct, fac, handler);
}
/**