--- jsr166/src/jsr166y/ForkJoinPool.java 2012/01/27 17:27:28 1.116
+++ jsr166/src/jsr166y/ForkJoinPool.java 2012/08/13 18:25:53 1.130
@@ -5,7 +5,6 @@
*/
package jsr166y;
-
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
@@ -21,7 +20,7 @@ import java.util.concurrent.RunnableFutu
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
/**
@@ -60,17 +59,16 @@ import java.util.concurrent.locks.Condit
* convenient form for informal monitoring.
*
* 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 forms of these methods accept instances of {@code
- * ForkJoinTask}, but overloaded forms also allow mixed execution of
- * plain {@code Runnable}- or {@code Callable}- based activities as
- * well. However, tasks that are already executing in a pool should
- * normally instead use the within-computation forms listed in the
- * table unless using async event-style tasks that are not usually
- * joined, in which case there is little difference among choice of
- * methods.
+ * 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
+ * forms of these methods accept instances of {@code ForkJoinTask},
+ * but overloaded forms also allow mixed execution of plain {@code
+ * Runnable}- or {@code Callable}- based activities as well. However,
+ * tasks that are already executing in a pool should normally instead
+ * use the within-computation forms listed in the table unless using
+ * async event-style tasks that are not usually joined, in which case
+ * there is little difference among choice of methods.
*
*
*
@@ -131,14 +129,14 @@ public class ForkJoinPool extends Abstra
*
* This class and its nested classes provide the main
* functionality and control for a set of worker threads:
- * Submissions from non-FJ threads enter into submission
- * queues. Workers take these tasks and typically split them into
- * subtasks that may be stolen by other workers. Preference rules
- * give first priority to processing tasks from their own queues
- * (LIFO or FIFO, depending on mode), then to randomized FIFO
- * steals of tasks in other queues.
+ * Submissions from non-FJ threads enter into submission queues.
+ * Workers take these tasks and typically split them into subtasks
+ * that may be stolen by other workers. Preference rules give
+ * first priority to processing tasks from their own queues (LIFO
+ * or FIFO, depending on mode), then to randomized FIFO steals of
+ * tasks in other queues.
*
- * WorkQueues.
+ * WorkQueues
* ==========
*
* Most operations occur within work-stealing queues (in nested
@@ -156,7 +154,7 @@ public class ForkJoinPool extends Abstra
* (http://research.sun.com/scalable/pubs/index.html) and
* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
- * The main differences ultimately stem from gc requirements that
+ * The main differences ultimately stem from GC requirements that
* we null out taken slots as soon as we can, to maintain as small
* a footprint as possible even in programs generating huge
* numbers of tasks. To accomplish this, we shift the CAS
@@ -178,7 +176,10 @@ 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
@@ -188,9 +189,9 @@ public class ForkJoinPool extends Abstra
* rarely provide the best possible performance on a given
* machine, but portably provide good throughput by averaging over
* these factors. (Further, even if we did try to use such
- * information, we do not usually have a basis for exploiting
- * it. For example, some sets of tasks profit from cache
- * affinities, but others are harmed by cache pollution effects.)
+ * information, we do not usually have a basis for exploiting it.
+ * For example, some sets of tasks profit from cache affinities,
+ * but others are harmed by cache pollution effects.)
*
* WorkQueues are also used in a similar way for tasks submitted
* to the pool. We cannot mix these tasks in the same queues used
@@ -204,15 +205,14 @@ public class ForkJoinPool extends Abstra
* 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. Pool submissions from internal workers are also
- * allowed, but use randomized rather than thread-hashed queue
- * indices to avoid imbalance. 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 try or create
- * others so never block.
+ * 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 -- they block only when creating and registering
+ * new queues.
*
- * Management.
+ * Management
* ==========
*
* The main throughput advantages of work-stealing stem from
@@ -222,7 +222,7 @@ public class ForkJoinPool extends Abstra
* tactic for avoiding bottlenecks is packing nearly all
* essentially atomic control state into two volatile variables
* that are by far most often read (not written) as status and
- * consistency checks
+ * consistency checks.
*
* Field "ctl" contains 64 bits holding all the information needed
* to atomically decide to add, inactivate, enqueue (on an event
@@ -248,13 +248,10 @@ public class ForkJoinPool extends Abstra
* 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 current
- * workers. All worker thread creation is on-demand, triggered by
- * task submissions, replacement of terminated workers, and/or
+ * scanning.
+ *
+ * All worker thread creation is on-demand, triggered by task
+ * submissions, replacement of terminated workers, and/or
* compensation for blocked workers. However, all other support
* code is set up to work with other policies. To ensure that we
* do not hold on to worker references that would prevent GC, ALL
@@ -267,13 +264,12 @@ public class ForkJoinPool extends Abstra
* both index-check and null-check the IDs. All such accesses
* ignore bad IDs by returning out early from what they are doing,
* since this can only be associated with termination, in which
- * case it is OK to give up.
- *
- * All uses of the workQueues array check that it is non-null
- * (even if previously non-null). This allows nulling during
- * termination, which is currently not necessary, but remains an
- * option for resource-revocation-based shutdown schemes. It also
- * helps reduce JIT issuance of uncommon-trap code, which tends to
+ * case it is OK to give up. All uses of the workQueues array
+ * also check that it is non-null (even if previously
+ * non-null). This allows nulling during termination, which is
+ * currently not necessary, but remains an option for
+ * resource-revocation-based shutdown schemes. It also helps
+ * reduce JIT issuance of uncommon-trap code, which tends to
* unnecessarily complicate control flow in some methods.
*
* Event Queuing. Unlike HPC work-stealing frameworks, we cannot
@@ -301,7 +297,7 @@ public class ForkJoinPool extends Abstra
* some other queued worker rather than itself, which has the same
* net effect. Because enqueued workers may actually be rescanning
* rather than waiting, we set and clear the "parker" field of
- * Workqueues to reduce unnecessary calls to unpark. (This
+ * WorkQueues to reduce unnecessary calls to unpark. (This
* requires a secondary recheck to avoid missed signals.) Note
* the unusual conventions about Thread.interrupts surrounding
* parking and other blocking: Because interrupts are used solely
@@ -329,7 +325,7 @@ public class ForkJoinPool extends Abstra
* terminating all workers after long periods of non-use.
*
* Shutdown and Termination. A call to shutdownNow atomically sets
- * a runState bit and then (non-atomically) sets each workers
+ * a runState bit and then (non-atomically) sets each worker's
* runState 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
@@ -338,18 +334,18 @@ public class ForkJoinPool extends Abstra
* indication but non-abrupt shutdown still requires a rechecking
* scan for any workers that are inactive but not queued.
*
- * Joining Tasks.
- * ==============
+ * Joining Tasks
+ * =============
*
* Any of several actions may be taken when one worker is waiting
- * to join a task stolen (or always held by) another. Because we
+ * to join a task stolen (or always held) by another. Because we
* are multiplexing many tasks on to a pool of workers, we can't
* just let them block (as in Thread.join). We also cannot just
* reassign the joiner's run-time stack with another and replace
* it later, which would be a form of "continuation", that even if
* possible is not necessarily a good idea since we sometimes need
- * both an unblocked task and its continuation to
- * progress. Instead we combine two tactics:
+ * both an unblocked task and its continuation to progress.
+ * Instead we combine two tactics:
*
* Helping: Arranging for the joiner to execute some task that it
* would be running if the steal had not occurred.
@@ -384,8 +380,8 @@ 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 workers array to locate stealers, but
- * often doesn't because stealers leave hints (that may become
+ * 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).
@@ -396,22 +392,43 @@ public class ForkJoinPool extends Abstra
* 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.
*
* 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.)
+ * 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: (1) We only try
+ * compensation after attempting enough helping steps (measured
+ * via counting and timing) that we have already consumed the
+ * estimated cost of creating and activating a new thread. (2) We
+ * allow up to 50% of threads to be blocked before initially
+ * adding any others, and unless completely saturated, check that
+ * some work is available for a new worker before adding. Also, we
+ * create up to only 50% more threads until entering a mode that
+ * only adds a thread if all others are possibly blocked. All
+ * together, this means that we might be half as fast to react,
+ * and create half as many threads as possible in the ideal case,
+ * but present vastly fewer anomalies in all other cases compared
+ * to both more aggressive and more conservative alternatives.
*
* Style notes: There is a lot of representation-level coupling
* among classes ForkJoinPool, ForkJoinWorkerThread, and
@@ -419,34 +436,46 @@ public class ForkJoinPool extends Abstra
* 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. All together, these low-level
- * implementation choices produce as much as a factor of 4
- * performance improvement compared to naive implementations, and
- * enable the processing of billions of tasks per second, at the
- * expense of some ugliness.
- *
- * 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 sometimes critical). This leads to a
- * "C"-like style of listing 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 some methods perform reasonably even
- * when interpreted (not compiled).
- *
- * The order of declarations in this file is: (1) declarations of
- * statics (2) fields (along with constants used when unpacking
- * some of them), listed in an order that tends to reduce
- * contention among them a bit under most JVMs; (3) nested
- * classes; (4) internal control methods; (5) callbacks and other
- * support for ForkJoinTask methods; (6) exported methods (plus a
- * few little helpers); (7) static block initializing all statics
- * in a minimally dependent order.
+ * 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
+ * sometimes critical). This leads to a "C"-like style of listing
+ * 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
+ * some methods perform reasonably even when interpreted (not
+ * compiled).
+ *
+ * The order of declarations in this file is:
+ * (1) Static utility functions
+ * (2) Nested (static) classes
+ * (3) Static fields
+ * (4) Fields, along with constants used when unpacking some of them
+ * (5) Internal control methods
+ * (6) Callbacks and other support for ForkJoinTask methods
+ * (7) Exported methods
+ * (8) Static block initializing statics in minimally dependent order
*/
+ // Static utilities
+
+ /**
+ * If there is a security manager, makes sure caller has
+ * permission to modify threads.
+ */
+ private static void checkPermission() {
+ SecurityManager security = System.getSecurityManager();
+ if (security != null)
+ security.checkPermission(modifyThreadPermission);
+ }
+
+ // Nested classes
+
/**
* Factory for creating new {@link ForkJoinWorkerThread}s.
* A {@code ForkJoinWorkerThreadFactory} must be defined and used
@@ -475,164 +504,40 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a new ForkJoinWorkerThread. This factory is used unless
- * overridden in ForkJoinPool constructors.
- */
- public static final ForkJoinWorkerThreadFactory
- defaultForkJoinWorkerThreadFactory;
-
- /**
- * Permission required for callers of methods that may start or
- * kill threads.
- */
- private static final RuntimePermission modifyThreadPermission;
-
- /**
- * If there is a security manager, makes sure caller has
- * permission to modify threads.
- */
- private static void checkPermission() {
- SecurityManager security = System.getSecurityManager();
- if (security != null)
- security.checkPermission(modifyThreadPermission);
+ * 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(); }
}
/**
- * Generator for assigning sequence numbers as pool names.
- */
- private static final AtomicInteger poolNumberGenerator;
-
- /**
- * Bits and masks for control variables
- *
- * Field ctl is a long packed with:
- * AC: Number of active running workers minus target parallelism (16 bits)
- * TC: Number of total workers minus target parallelism (16 bits)
- * ST: true if pool is terminating (1 bit)
- * EC: the wait count of top waiting thread (15 bits)
- * ID: ~(poolIndex >>> 1) of top of Treiber stack of waiters (16 bits)
- *
- * When convenient, we can extract the upper 32 bits of counts and
- * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
- * (int)ctl. The ec field is never accessed alone, but always
- * together with id and st. The offsets of counts by the target
- * parallelism and the positionings of fields makes it possible to
- * perform the most common checks via sign tests of fields: When
- * ac is negative, there are not enough active workers, when tc is
- * negative, there are not enough total workers, when id is
- * negative, there is at least one waiting worker, and when e is
- * negative, the pool is terminating. To deal with these possibly
- * negative fields, we use casts in and out of "short" and/or
- * signed shifts to maintain signedness.
- *
- * When a thread is queued (inactivated), its eventCount field is
- * negative, which is the only way to tell if a worker is
- * prevented from executing tasks, even though it must continue to
- * scan for them to avoid queuing races.
- *
- * Field runState 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)
- *
- * The combination of mask and sequence number enables simple
- * consistency checks: Staleness of read-only operations on the
- * workers and queues arrays 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 worker
- * indices, minus one. The mask for queues (vs workers) is twice
- * this value plus 1.
- */
-
- // bit positions/shifts for fields
- private static final int AC_SHIFT = 48;
- private static final int TC_SHIFT = 32;
- private static final int ST_SHIFT = 31;
- private static final int EC_SHIFT = 16;
-
- // bounds
- private static final int MAX_ID = 0x7fff; // max poolIndex
- private static final int SMASK = 0xffff; // mask short bits
- private static final int SHORT_SIGN = 1 << 15;
- private static final int INT_SIGN = 1 << 31;
-
- // masks
- private static final long STOP_BIT = 0x0001L << ST_SHIFT;
- private static final long AC_MASK = ((long)SMASK) << AC_SHIFT;
- private static final long TC_MASK = ((long)SMASK) << TC_SHIFT;
-
- // units for incrementing and decrementing
- private static final long TC_UNIT = 1L << TC_SHIFT;
- private static final long AC_UNIT = 1L << AC_SHIFT;
-
- // masks and units for dealing with u = (int)(ctl >>> 32)
- private static final int UAC_SHIFT = AC_SHIFT - 32;
- private static final int UTC_SHIFT = TC_SHIFT - 32;
- private static final int UAC_MASK = SMASK << UAC_SHIFT;
- private static final int UTC_MASK = SMASK << UTC_SHIFT;
- private static final int UAC_UNIT = 1 << UAC_SHIFT;
- private static final int UTC_UNIT = 1 << UTC_SHIFT;
-
- // masks and units for dealing with e = (int)ctl
- private static final int E_MASK = 0x7fffffff; // no STOP_BIT
- private static final int E_SEQ = 1 << EC_SHIFT;
-
- // runState bits
- private static final int SHUTDOWN = 1 << 31;
- private static final int RS_SEQ = 1 << 16;
- private static final int RS_SEQ_MASK = 0x7fff0000;
-
- // access mode for WorkQueue
- static final int LIFO_QUEUE = 0;
- static final int FIFO_QUEUE = 1;
- static final int SHARED_QUEUE = -1;
-
- /**
- * 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.
- */
- private static final long SHRINK_RATE =
- 4L * 1000L * 1000L * 1000L; // 4 seconds
-
- /**
- * The timeout value for attempted shrinkage, includes
- * some slop to cope with system timer imprecision.
- */
- private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
-
- /**
- * 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.
- */
- private static final int MAX_HELP_DEPTH = 16;
-
- /*
- * Field layout order in 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.
+ * Class for artificial tasks that are used to replace the target
+ * of local joins if they are removed from an interior queue slot
+ * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
+ * actually do anything beyond having a unique identity.
*/
-
- volatile long ctl; // main pool control
- final int parallelism; // parallelism level
- final int localMode; // per-worker scheduling mode
- int nextPoolIndex; // hint used in registerWorker
- volatile int runState; // shutdown status, seq, and mask
- WorkQueue[] workQueues; // main registry
- final ReentrantLock lock; // for registration
- final Condition termination; // for awaitTermination
- final ForkJoinWorkerThreadFactory factory; // factory for new workers
- 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; // Prefix for assigning worker names
+ static final class EmptyTask extends ForkJoinTask {
+ EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
+ public final Void getRawResult() { return null; }
+ public final void setRawResult(Void x) {}
+ public final boolean exec() { return true; }
+ }
/**
* Queues supporting work-stealing as well as external task
@@ -683,17 +588,21 @@ public class ForkJoinPool extends Abstra
* 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
- * allocating and sizing and resizing the array. Non-shared queue
+ * 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.
*/
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
@@ -717,44 +626,61 @@ public class ForkJoinPool extends Abstra
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;
+ Object p00, p01, p02, p03, p04, p05, p06, p07;
+ Object p08, p09, p0a, p0b, p0c, p0d, p0e;
- WorkQueue(ForkJoinWorkerThread owner, int mode) {
- this.owner = owner;
+ WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
this.mode = mode;
+ this.pool = pool;
+ this.owner = owner;
// 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.getObjectVolatile
+ (a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
}
/**
* Pushes a task. Call only by owner in unshared queues.
*
* @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
+ * @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);
if ((n = (top = s + 1) - base) <= 2) {
- if (p != null)
+ if ((p = pool) != null)
p.signalWork();
}
else if (n >= m)
@@ -773,9 +699,9 @@ public class ForkJoinPool extends Abstra
boolean submitted = false;
if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
ForkJoinTask[] a = array;
- int s = top, n = s - base;
+ int s = top;
try {
- if ((a != null && n < a.length - 1) ||
+ 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"
@@ -790,15 +716,37 @@ public class ForkJoinPool extends Abstra
}
/**
- * Takes next task, if one exists, in FIFO order.
+ * 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.)
*/
- final ForkJoinTask poll() {
- ForkJoinTask[] a; int b, i;
- while ((b = base) - top < 0 && (a = array) != null &&
- (i = (a.length - 1) & b) >= 0) {
- int j = (i << ASHIFT) + ABASE;
- ForkJoinTask t = (ForkJoinTask)U.getObjectVolatile(a, j);
- if (t != null && base == b &&
+ 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;
+ }
+ }
+ }
+ return null;
+ }
+
+ /**
+ * 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 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;
@@ -808,22 +756,25 @@ public class ForkJoinPool extends Abstra
}
/**
- * Takes next task, if one exists, in LIFO order.
- * Call only by owner in unshared queues.
+ * 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
+ }
}
return null;
}
@@ -848,24 +799,6 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns task at index b if b is current base of queue.
- */
- final ForkJoinTask pollAt(int b) {
- ForkJoinTask[] a; int i;
- ForkJoinTask task = null;
- if ((a = array) != null && (i = ((a.length - 1) & b)) >= 0) {
- int j = (i << ASHIFT) + ABASE;
- ForkJoinTask t = (ForkJoinTask)U.getObjectVolatile(a, j);
- if (t != null && base == b &&
- U.compareAndSwapObject(a, j, t, null)) {
- base = b + 1;
- task = t;
- }
- }
- return task;
- }
-
- /**
* Pops the given task only if it is at the current top.
*/
final boolean tryUnpush(ForkJoinTask t) {
@@ -883,10 +816,9 @@ public class ForkJoinPool extends Abstra
* Polls the given task only if it is at the current base.
*/
final boolean pollFor(ForkJoinTask task) {
- ForkJoinTask[] a; int b, i;
- if ((b = base) - top < 0 && (a = array) != null &&
- (i = (a.length - 1) & b) >= 0) {
- int j = (i << ASHIFT) + ABASE;
+ 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;
@@ -897,54 +829,6 @@ public class ForkJoinPool extends Abstra
}
/**
- * If present, removes from queue and executes the given task, or
- * any other cancelled task. Returns (true) immediately on any CAS
- * or consistency check failure so caller can retry.
- *
- * @return false if no progress can be made
- */
- final boolean tryRemoveAndExec(ForkJoinTask task) {
- boolean removed = false, empty = true, progress = true;
- ForkJoinTask[] a; int m, s, b, n;
- if ((a = array) != null && (m = a.length - 1) >= 0 &&
- (n = (s = top) - (b = base)) > 0) {
- for (ForkJoinTask t;;) { // traverse from s to b
- int j = ((--s & m) << ASHIFT) + ABASE;
- t = (ForkJoinTask)U.getObjectVolatile(a, j);
- if (t == null) // inconsistent length
- break;
- else if (t == task) {
- if (s + 1 == top) { // pop
- if (!U.compareAndSwapObject(a, j, task, null))
- break;
- top = s;
- removed = true;
- }
- else if (base == b) // replace with proxy
- removed = U.compareAndSwapObject(a, j, task,
- new EmptyTask());
- break;
- }
- else if (t.status >= 0)
- empty = false;
- else if (s + 1 == top) { // pop and throw away
- if (U.compareAndSwapObject(a, j, t, null))
- top = s;
- break;
- }
- if (--n == 0) {
- if (!empty && base == b)
- progress = false;
- break;
- }
- }
- }
- if (removed)
- task.doExec();
- return progress;
- }
-
- /**
* 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.
@@ -980,7 +864,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Removes and cancels all known tasks, ignoring any exceptions
+ * Removes and cancels all known tasks, ignoring any exceptions.
*/
final void cancelAll() {
ForkJoinTask.cancelIgnoringExceptions(currentJoin);
@@ -989,41 +873,119 @@ public class ForkJoinPool extends Abstra
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;
+ }
+
// Execution methods
/**
- * Removes and runs tasks until empty, using local mode
- * ordering.
+ * Pops and runs tasks until empty.
*/
- final void runLocalTasks() {
- if (base - top < 0) {
- for (ForkJoinTask t; (t = nextLocalTask()) != null; )
+ 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();
+ }
}
}
/**
+ * 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) immediately on any CAS
+ * or consistency check failure so caller can retry.
+ *
+ * @return 0 if no progress can be made, else positive
+ * (this unusual convention simplifies use with tryHelpStealer.)
+ */
+ final int tryRemoveAndExec(ForkJoinTask task) {
+ int stat = 1;
+ boolean 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) {
+ for (ForkJoinTask t;;) { // traverse from s to b
+ int j = ((--s & m) << ASHIFT) + ABASE;
+ t = (ForkJoinTask)U.getObjectVolatile(a, j);
+ if (t == null) // inconsistent length
+ break;
+ else if (t == task) {
+ if (s + 1 == top) { // pop
+ if (!U.compareAndSwapObject(a, j, task, null))
+ break;
+ top = s;
+ removed = true;
+ }
+ else if (base == b) // replace with proxy
+ removed = U.compareAndSwapObject(a, j, task,
+ new EmptyTask());
+ break;
+ }
+ else if (t.status >= 0)
+ empty = false;
+ else if (s + 1 == top) { // pop and throw away
+ if (U.compareAndSwapObject(a, j, t, null))
+ top = s;
+ break;
+ }
+ if (--n == 0) {
+ if (!empty && base == b)
+ stat = 0;
+ break;
+ }
+ }
+ }
+ if (removed)
+ task.doExec();
+ return stat;
+ }
+
+ /**
* 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();
+ if (top != base) { // process remaining local tasks
+ if (mode == 0)
+ popAndExecAll();
+ else
+ pollAndExecAll();
+ }
++nsteals;
currentSteal = null;
}
- else if (runState < 0) // terminating
- alive = false;
- return alive;
}
/**
- * Executes a non-top-level (stolen) task
+ * Executes a non-top-level (stolen) task.
*/
final void runSubtask(ForkJoinTask t) {
if (t != null) {
@@ -1035,18 +997,31 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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.
+ * Returns true if owned and not known to be blocked.
*/
- final int nextSeed() {
- int r = seed;
- r ^= r << 13;
- r ^= r >>> 17;
- r ^= r << 5;
- return seed = r;
+ final boolean isApparentlyUnblocked() {
+ Thread wt; Thread.State s;
+ return (eventCount >= 0 &&
+ (wt = owner) != null &&
+ (s = wt.getState()) != Thread.State.BLOCKED &&
+ s != Thread.State.WAITING &&
+ s != Thread.State.TIMED_WAITING);
+ }
+
+ /**
+ * If this owned and is not already interrupted, try to
+ * interrupt and/or unpark, ignoring exceptions.
+ */
+ final void interruptOwner() {
+ Thread wt, p;
+ if ((wt = owner) != null && !wt.isInterrupted()) {
+ try {
+ wt.interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ if ((p = parker) != null)
+ U.unpark(p);
}
// Unsafe mechanics
@@ -1072,49 +1047,27 @@ public class ForkJoinPool extends Abstra
ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
}
}
-
/**
- * Class for artificial tasks that are used to replace the target
- * of local joins if they are removed from an interior queue slot
- * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
- * actually do anything beyond having a unique identity.
- */
- static final class EmptyTask extends ForkJoinTask {
- EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
- public Void getRawResult() { return null; }
- public void setRawResult(Void x) {}
- public boolean exec() { return true; }
- }
-
- /**
-<<<<<<< ForkJoinPool.java
- * Per-thread records for (typically non-FJ) threads that submit
- * to pools. Cureently holds only psuedo-random seed / index that
- * is used to chose submission queues in method doSubmit. In the
- * future, this may incorporate a means to implement different
- * task rejection and resubmission policies.
+ * 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.
+ *
+ * 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. This is done during
+ * registration for workers, but requires a separate AtomicInteger
+ * for submitters. Seeds are then randomly modified upon
+ * collisions using xorshifts, which requires a non-zero seed.
*/
static final class Submitter {
- int seed; // seed for random submission queue selection
-
- // Heuristic padding to ameliorate unfortunate memory placements
- int p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe;
-
+ int seed;
Submitter() {
- // Use identityHashCode, forced negative, for seed
- seed = System.identityHashCode(Thread.currentThread()) | (1 << 31);
- }
-
- /**
- * Computes next value for random probes. Like method
- * WorkQueue.nextSeed, this is manually inlined in several
- * usages to avoid writes inside busy loops.
- */
- final int nextSeed() {
- int r = seed;
- r ^= r << 13;
- r ^= r >>> 17;
- return seed = r ^= r << 5;
+ int s = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
+ seed = (s == 0) ? 1 : s; // ensure non-zero
}
}
@@ -1123,43 +1076,208 @@ public class ForkJoinPool extends Abstra
public Submitter initialValue() { return new Submitter(); }
}
+ // static fields (initialized in static initializer below)
+
+ /**
+ * Creates a new ForkJoinWorkerThread. This factory is used unless
+ * overridden in ForkJoinPool constructors.
+ */
+ public static final ForkJoinWorkerThreadFactory
+ defaultForkJoinWorkerThreadFactory;
+
/**
- * Per-thread submission bookeeping. Shared across all pools
+ * Generator for assigning sequence numbers as pool names.
+ */
+ private static final AtomicInteger poolNumberGenerator;
+
+ /**
+ * Generator for initial hashes/seeds for submitters. Accessed by
+ * Submitter class constructor.
+ */
+ static final AtomicInteger nextSubmitterSeed;
+
+ /**
+ * Permission required for callers of methods that may start or
+ * kill threads.
+ */
+ private static final RuntimePermission modifyThreadPermission;
+
+ /**
+ * 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.
*/
- static final ThreadSubmitter submitters = new ThreadSubmitter();
+ private static final ThreadSubmitter submitters;
+
+ // 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.
+ */
+ private static final long SHRINK_RATE =
+ 4L * 1000L * 1000L * 1000L; // 4 seconds
/**
- * Top-level runloop for workers
+ * The timeout value for attempted shrinkage, includes
+ * some slop to cope with system timer imprecision.
*/
- final void runWorker(ForkJoinWorkerThread wt) {
- // Initialize queue array and seed in this thread
- WorkQueue w = wt.workQueue;
- w.growArray(false);
- // Same initial hash as Submitters
- w.seed = System.identityHashCode(Thread.currentThread()) | (1 << 31);
+ private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
- do {} while (w.runTask(scan(w)));
- }
+ /**
+ * The maximum stolen->joining link depth allowed in method
+ * tryHelpStealer. Must be a power of two. This value also
+ * controls the maximum number of times to try to help join a task
+ * without any apparent progress or change in pool state before
+ * giving up and blocking (see awaitJoin). 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;
+
+ /**
+ * Secondary time-based bound (in nanosecs) for helping attempts
+ * before trying compensated blocking in awaitJoin. Used in
+ * conjunction with MAX_HELP to reduce variance due to different
+ * polling rates associated with different helping options. The
+ * value should roughly approximate the time required to create
+ * and/or activate a worker thread.
+ */
+ private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
- // Creating, registering and deregistering workers
+ /**
+ * Increment for seed generators. See class ThreadLocal for
+ * explanation.
+ */
+ private static final int SEED_INCREMENT = 0x61c88647;
+
+ /**
+ * Bits and masks for control variables
+ *
+ * Field ctl is a long packed with:
+ * AC: Number of active running workers minus target parallelism (16 bits)
+ * TC: Number of total workers minus target parallelism (16 bits)
+ * ST: true if pool is terminating (1 bit)
+ * EC: the wait count of top waiting thread (15 bits)
+ * ID: poolIndex of top of Treiber stack of waiters (16 bits)
+ *
+ * When convenient, we can extract the upper 32 bits of counts and
+ * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
+ * (int)ctl. The ec field is never accessed alone, but always
+ * together with id and st. The offsets of counts by the target
+ * parallelism and the positionings of fields makes it possible to
+ * perform the most common checks via sign tests of fields: When
+ * ac is negative, there are not enough active workers, when tc is
+ * negative, there are not enough total workers, and when e is
+ * negative, the pool is terminating. To deal with these possibly
+ * negative fields, we use casts in and out of "short" and/or
+ * signed shifts to maintain signedness.
+ *
+ * When a thread is queued (inactivated), its eventCount field is
+ * set negative, which is the only way to tell if a worker is
+ * prevented from executing tasks, even though it must continue to
+ * 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:
+ * SHUTDOWN: true if shutdown is enabled (1 bit)
+ * SEQ: a sequence number updated upon (de)registering workers (30 bits)
+ * INIT: set true after workQueues array construction (1 bit)
+ *
+ * The 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.
+ */
+
+ // bit positions/shifts for fields
+ private static final int AC_SHIFT = 48;
+ private static final int TC_SHIFT = 32;
+ private static final int ST_SHIFT = 31;
+ private static final int EC_SHIFT = 16;
+
+ // bounds
+ private static final int SMASK = 0xffff; // short bits
+ private static final int MAX_CAP = 0x7fff; // max #workers - 1
+ private static final int SQMASK = 0xfffe; // even short bits
+ private static final int SHORT_SIGN = 1 << 15;
+ private static final int INT_SIGN = 1 << 31;
+
+ // masks
+ private static final long STOP_BIT = 0x0001L << ST_SHIFT;
+ private static final long AC_MASK = ((long)SMASK) << AC_SHIFT;
+ private static final long TC_MASK = ((long)SMASK) << TC_SHIFT;
+
+ // units for incrementing and decrementing
+ private static final long TC_UNIT = 1L << TC_SHIFT;
+ private static final long AC_UNIT = 1L << AC_SHIFT;
+
+ // masks and units for dealing with u = (int)(ctl >>> 32)
+ private static final int UAC_SHIFT = AC_SHIFT - 32;
+ private static final int UTC_SHIFT = TC_SHIFT - 32;
+ private static final int UAC_MASK = SMASK << UAC_SHIFT;
+ private static final int UTC_MASK = SMASK << UTC_SHIFT;
+ private static final int UAC_UNIT = 1 << UAC_SHIFT;
+ private static final int UTC_UNIT = 1 << UTC_SHIFT;
+
+ // masks and units for dealing with e = (int)ctl
+ private static final int E_MASK = 0x7fffffff; // no STOP_BIT
+ private static final int E_SEQ = 1 << EC_SHIFT;
+
+ // runState bits
+ private static final int SHUTDOWN = 1 << 31;
+
+ // access mode for WorkQueue
+ static final int LIFO_QUEUE = 0;
+ static final int FIFO_QUEUE = 1;
+ static final int SHARED_QUEUE = -1;
+
+ // Instance fields
+
+ /*
+ * Field layout order in 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.
+ */
+
+ volatile long ctl; // main pool control
+ final int parallelism; // parallelism level
+ final int localMode; // per-worker scheduling mode
+ final int submitMask; // submit queue index bound
+ int nextSeed; // for initializing worker seeds
+ volatile int runState; // shutdown status and seq
+ WorkQueue[] workQueues; // main registry
+ final Mutex lock; // for registration
+ final Condition termination; // for awaitTermination
+ final ForkJoinWorkerThreadFactory factory; // factory for new workers
+ 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, and deregistering workers
/**
* Tries to create and start a worker
*/
private void addWorker() {
Throwable ex = null;
- ForkJoinWorkerThread w = null;
+ ForkJoinWorkerThread wt = null;
try {
- if ((w = factory.newThread(this)) != null) {
- w.start();
+ if ((wt = factory.newThread(this)) != null) {
+ wt.start();
return;
}
} catch (Throwable e) {
ex = e;
}
- deregisterWorker(w, ex);
+ deregisterWorker(wt, ex); // adjust counts etc on failure
}
/**
@@ -1174,35 +1292,39 @@ public class ForkJoinPool extends Abstra
}
/**
- * Callback from ForkJoinWorkerThread constructor to establish and
- * record its WorkQueue
+ * Callback from ForkJoinWorkerThread constructor to establish its
+ * poolIndex 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
+ * @param w the worker's queue
*/
- final void registerWorker(ForkJoinWorkerThread wt) {
- WorkQueue w = wt.workQueue;
- ReentrantLock lock = this.lock;
+
+ final void registerWorker(WorkQueue w) {
+ Mutex lock = this.lock;
lock.lock();
try {
- int k = nextPoolIndex;
WorkQueue[] ws = workQueues;
- if (ws != null) { // ignore on shutdown
- int n = ws.length;
- if (k < 0 || (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.poolIndex = k;
- w.eventCount = ~(k >>> 1) & SMASK; // Set up wait count
- ws[k] = w; // record worker
- nextPoolIndex = k + 2;
- 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 (w != null && ws != null) { // skip on shutdown/failure
+ int rs, n = ws.length, m = n - 1;
+ int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
+ w.seed = (s == 0) ? 1 : s; // ensure non-zero seed
+ 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) & SQMASK) + 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; // establish before recording
+ ws[r] = w; // also update seq
+ runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
}
} finally {
lock.unlock();
@@ -1210,8 +1332,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Final callback from terminating worker, as well as failure to
- * construct or start a worker in addWorker. Removes record of
+ * 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.
*
@@ -1219,17 +1341,17 @@ public class ForkJoinPool extends Abstra
* @param ex the exception causing failure, or null if none
*/
final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
+ Mutex lock = this.lock;
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;
- ReentrantLock lock = this.lock;
lock.lock();
try { // remove record from array
WorkQueue[] ws = workQueues;
if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
- ws[nextPoolIndex = idx] = null;
+ ws[idx] = null;
} finally {
lock.unlock();
}
@@ -1241,52 +1363,70 @@ public class ForkJoinPool extends Abstra
((c - TC_UNIT) & TC_MASK) |
(c & ~(AC_MASK|TC_MASK)))));
- if (!tryTerminate(false) && w != null) {
+ if (!tryTerminate(false, false) && w != 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();
}
if (ex != null) // rethrow
U.throwException(ex);
}
+
+ // Submissions
+
/**
- * Tries to add and register a new queue at the given index.
+ * 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. If
+ * the queue is busy, another index is randomly chosen. The
+ * submitMask bounds the effective number of queues to the
+ * (nearest power of two for) parallelism level.
*
- * @param idx the workQueues array index to register the queue
- * @return the queue, or null if could not add because could
- * not acquire lock or idx is unusable
- */
- private WorkQueue tryAddSharedQueue(int idx) {
- WorkQueue q = null;
- ReentrantLock lock = this.lock;
- if (idx >= 0 && (idx & 1) == 0 && !lock.isLocked()) {
- // create queue outside of lock but only if apparently free
- WorkQueue nq = new WorkQueue(null, SHARED_QUEUE);
- if (lock.tryLock()) {
- try {
- WorkQueue[] ws = workQueues;
- if (ws != null && idx < ws.length) {
- if ((q = ws[idx]) == null) {
- int rs; // update runState seq
- ws[idx] = q = nq;
- runState = (((rs = runState) & SHUTDOWN) |
- ((rs + RS_SEQ) & ~SHUTDOWN));
- }
+ * @param task the task. Caller must ensure non-null.
+ */
+ private void doSubmit(ForkJoinTask task) {
+ Submitter s = submitters.get();
+ for (int r = s.seed, m = submitMask;;) {
+ WorkQueue[] ws; WorkQueue q;
+ int k = r & m & SQMASK; // use only even indices
+ if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
+ throw new RejectedExecutionException(); // shutting down
+ else if ((q = ws[k]) == null) { // create new queue
+ WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
+ Mutex lock = this.lock; // construct outside lock
+ lock.lock();
+ try { // recheck under lock
+ int rs = runState; // to update seq
+ if (ws == workQueues && ws[k] == null) {
+ ws[k] = nq;
+ runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
}
} finally {
lock.unlock();
}
}
+ else if (q.trySharedPush(task)) {
+ signalWork();
+ return;
+ }
+ else if (m > 1) { // move to a different index
+ r ^= r << 13; // same xorshift as WorkQueues
+ r ^= r >>> 17;
+ s.seed = r ^= r << 5;
+ }
+ else
+ Thread.yield(); // yield if no alternatives
}
- return q;
}
// Maintaining ctl counts
/**
- * Increments active count; mainly called upon return from blocking
+ * Increments active count; mainly called upon return from blocking.
*/
final void incrementActiveCount() {
long c;
@@ -1294,145 +1434,68 @@ public class ForkJoinPool extends Abstra
}
/**
- * Activates or creates a worker
+ * Tries to activate or create a worker if too few are active.
*/
final void signalWork() {
- /*
- * The while condition is true if: (there is are too few total
- * workers OR there is at least one waiter) AND (there are too
- * few active workers OR the pool is terminating). The value
- * of e distinguishes the remaining cases: zero (no waiters)
- * for create, negative if terminating (in which case do
- * nothing), else release a waiter. The secondary checks for
- * release (non-null array etc) can fail if the pool begins
- * terminating after the test, and don't impose any added cost
- * because JVMs must perform null and bounds checks anyway.
- */
- long c; int e, u;
- while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
- (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN)) {
- WorkQueue[] ws = workQueues; int i; WorkQueue w; Thread p;
- if (e == 0) { // add a new worker
- if (U.compareAndSwapLong
- (this, CTL, c, (long)(((u + UTC_UNIT) & UTC_MASK) |
- ((u + UAC_UNIT) & UAC_MASK)) << 32)) {
- addWorker();
- break;
+ 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 &&
+ (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.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p); // activate and release
+ break;
+ }
}
- }
- else if (e > 0 && ws != null &&
- (i = ((~e << 1) | 1) & SMASK) < ws.length &&
- (w = ws[i]) != null &&
- w.eventCount == (e | INT_SIGN)) {
- if (U.compareAndSwapLong
- (this, CTL, c, (((long)(w.nextWait & E_MASK)) |
- ((long)(u + UAC_UNIT) << 32)))) {
- w.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = w.parker) != null)
- U.unpark(p); // release a waiting worker
+ else
break;
- }
}
- else
- break;
- }
- }
-
- /**
- * 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
- */
- final boolean tryCompensate() {
- WorkQueue[] ws; WorkQueue w; Thread p;
- int pc = parallelism, e, u, ac, tc, i;
- long c = ctl;
-
- if ((e = (int)c) >= 0) {
- if ((ac = ((u = (int)(c >>> 32)) >> UAC_SHIFT)) <= 0 &&
- e != 0 && (ws = workQueues) != null &&
- (i = ((~e << 1) | 1) & SMASK) < ws.length &&
- (w = ws[i]) != null) {
- if (w.eventCount == (e | INT_SIGN) &&
- U.compareAndSwapLong
- (this, CTL, c, ((long)(w.nextWait & E_MASK) |
- (c & (AC_MASK|TC_MASK))))) {
- 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 < MAX_ID) {
- long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ 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();
- return true; // create replacement
+ break;
}
}
+ else
+ break;
}
- return false;
}
- // Submissions
+ // Scanning for tasks
/**
- * Unless shutting down, adds the given task to a submission queue
- * at submitter's current queue index. 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.
+ * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
*/
- private void doSubmit(ForkJoinTask task) {
- if (task == null)
- throw new NullPointerException();
- Submitter s = submitters.get();
- for (int r = s.seed;;) {
- WorkQueue q; int k;
- int rs = runState, m = rs & SMASK;
- WorkQueue[] ws = workQueues;
- if (rs < 0 || ws == null) // shutting down
- throw new RejectedExecutionException();
- if (ws.length > m && // k must be at index
- ((q = ws[k = (r << 1) & m]) != null ||
- (q = tryAddSharedQueue(k)) != null) &&
- q.trySharedPush(task)) {
- signalWork();
- return;
- }
- r ^= r << 13; // xorshift seed to new position
- r ^= r >>> 17;
- if (((s.seed = r ^= r << 5) & m) == 0)
- Thread.yield(); // occasionally yield if busy
- }
+ final void runWorker(WorkQueue w) {
+ w.growArray(false); // initialize queue array in this thread
+ do { w.runTask(scan(w)); } while (w.runState >= 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 2:1 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 a random permutation of
+ * queues (starting at a random index and stepping by a random
+ * relative prime, checking each at least once). 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. 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
@@ -1441,144 +1504,135 @@ public class ForkJoinPool extends Abstra
* 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 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 occasional calls to
- * Thread.yield to help avoid interference with more useful
- * activities on the system.
- *
- * * If pool is terminating, terminate the worker
- *
* * If not already enqueued, try to inactivate and enqueue the
- * worker on wait queue.
+ * 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 inactive, and the caller has run a task since the
+ * last empty scan, return (to allow rescan) unless others are
+ * also inactivated. Field WorkQueue.rescans counts down on each
+ * scan to ensure eventual inactivation and blocking.
*
- * * 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.
+ * * If already enqueued and none of the above apply, park
+ * awaiting signal,
*
* @param w the worker (via its WorkQueue)
* @return a task or null of 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) {
- ForkJoinTask task = null;
- for (int k = 0, j = -2 - 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 += (m >>> 1) | 1; // step by half to reduce bias
-
- if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
- if (ec >= 0)
- task = q.pollAt(b); // steal
- break;
+ WorkQueue[] ws; // first update random seed
+ int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+ int rs = runState, m; // volatile read order matters
+ if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
+ int ec = w.eventCount; // ec is negative if inactive
+ int step = (r >>> 16) | 1; // relative prime
+ for (int j = (m + 1) << 2; ; r += step) {
+ WorkQueue q; ForkJoinTask t; ForkJoinTask[] a; int b;
+ if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
+ (a = q.array) != null) { // probably nonempty
+ int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ t = (ForkJoinTask)U.getObjectVolatile(a, i);
+ if (q.base == b && ec >= 0 && t != null &&
+ U.compareAndSwapObject(a, i, t, null)) {
+ if (q.top - (q.base = b + 1) > 1)
+ signalWork(); // help pushes signal
+ return t;
+ }
+ else if (ec < 0 || j <= m) {
+ rs = 0; // mark scan as imcomplete
+ break; // caller can retry after release
+ }
}
- else if (j > m) {
- if (rs == runState) // staleness check
- swept = true;
+ if (--j < 0)
break;
+ }
+
+ long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
+ if (e < 0) // decode ctl on empty scan
+ w.runState = -1; // pool is terminating
+ else if (rs == 0 || rs != runState) { // incomplete scan
+ WorkQueue v; Thread p; // try to release a waiter
+ if (e > 0 && a < 0 && w.eventCount == ec &&
+ (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 (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ }
}
}
- w.seed = r; // save seed for next scan
- if (task != null)
- return task;
- }
-
- // Decode ctl on empty scan
- long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
- if (!swept) { // try to release a waiter
- WorkQueue v; Thread p;
- if (e > 0 && a < 0 && ws != null &&
- (v = ws[((~e << 1) | 1) & m]) != null &&
- v.eventCount == (e | INT_SIGN) && U.compareAndSwapLong
- (this, CTL, c, ((long)(v.nextWait & E_MASK) |
- ((c + AC_UNIT) & (AC_MASK|TC_MASK))))) {
- v.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = v.parker) != null)
- U.unpark(p);
- }
- }
- else if ((nr = w.rescans) > 0) { // continue rescanning
- int ac = a + parallelism;
- if ((w.rescans = (ac < nr) ? ac : nr - 1) > 0 && w.seed < 0 &&
- w.eventCount == ec)
- Thread.yield(); // 1 bit randomness for yield call
- }
- else if (e < 0) // pool is terminating
- w.runState = -1;
- 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; // back out on CAS failure
- else if ((ns = w.nsteals) != 0) { // set rescans if ran task
- if (a <= 0) // ... unless too many active
- w.rescans = a + parallelism;
- w.nsteals = 0;
- w.totalSteals += ns;
- }
- }
- else{ // already queued
- if (parallelism == -a)
- idleAwaitWork(w); // quiescent
- if (w.eventCount == ec) {
- Thread.interrupted(); // clear status
- ForkJoinWorkerThread wt = w.owner;
- U.putObject(wt, PARKBLOCKER, this);
- w.parker = wt; // emulate LockSupport.park
- if (w.eventCount == ec) // recheck
- U.park(false, 0L); // block
- w.parker = null;
- U.putObject(wt, PARKBLOCKER, null);
+ else if (ec >= 0) { // try to enqueue/inactivate
+ long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+ w.nextWait = e;
+ w.eventCount = ec | INT_SIGN; // mark as inactive
+ if (ctl != c || !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 > 0) ? 0 : a + parallelism;
+ w.totalSteals += ns;
+ }
+ if (a == 1 - parallelism) // quiescent
+ idleAwaitWork(w, nc, c);
+ }
+ }
+ else if (w.eventCount < 0) { // already queued
+ if ((nr = w.rescans) > 0) { // continue rescanning
+ int ac = a + parallelism;
+ if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0)
+ Thread.yield(); // yield before block
+ }
+ else {
+ Thread.interrupted(); // clear status
+ Thread wt = Thread.currentThread();
+ U.putObject(wt, PARKBLOCKER, this);
+ w.parker = wt; // emulate LockSupport.park
+ if (w.eventCount < 0) // recheck
+ U.park(false, 0L);
+ w.parker = null;
+ U.putObject(wt, PARKBLOCKER, null);
+ }
}
}
return null;
}
/**
- * If inactivating worker w has caused pool to become quiescent,
- * check for pool termination, and, so long as this is not the
- * only worker, wait for event for up to SHRINK_RATE nanosecs On
- * timeout, if ctl has not changed, terminate 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 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.
*
* @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) &&
- (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));
- ForkJoinTask.helpExpungeStaleExceptions(); // help clean
- ForkJoinWorkerThread wt = w.owner;
- while (ctl == c) {
+ private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
+ if (w.eventCount < 0 && !tryTerminate(false, false) &&
+ (int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
+ Thread wt = Thread.currentThread();
+ Thread.yield(); // yield before block
+ while (ctl == currentCtl) {
long startTime = System.nanoTime();
Thread.interrupted(); // timed variant of version in scan()
U.putObject(wt, PARKBLOCKER, this);
w.parker = wt;
- if (ctl == c)
+ if (ctl == currentCtl)
U.park(false, SHRINK_RATE);
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.runState = -1; // shrink
- w.eventCount = (ec + E_SEQ) | E_MASK;
+ U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
+ w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
+ w.runState = -1; // shrink
break;
}
}
@@ -1596,65 +1650,79 @@ 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 (stealer == null)
- break;
- }
-
- 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);
+ if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
+ break restart; // shutting down
+ if ((v = ws[h = (j.stealHint | 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.stealHint = h; // save hint
+ break;
+ }
+ if (h == origin)
+ break restart; // cannot find stealer
}
}
- 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;
+ 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;
+ }
+ }
}
}
}
}
- return progress;
+ return stat;
}
/**
@@ -1663,11 +1731,10 @@ public class ForkJoinPool extends Abstra
* @param joiner the joining worker
* @param task the task
*/
- final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask task) {
+ private 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) {
+ if ((ws = workQueues) != null) {
+ for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
WorkQueue q = ws[j];
if (q != null && q.pollFor(task)) {
joiner.runSubtask(task);
@@ -1678,34 +1745,176 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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.
+ * 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 either
+ * pool would become completely starved or: (at least half
+ * starved, and fewer than 50% spares exist, and there is at least
+ * one task apparently available). Even though the availability
+ * check requires a full scan, it is worthwhile in reducing false
+ * alarms.
+ *
+ * @param task if non-null, a task being waited for
+ * @param blocker if non-null, a blocker being waited for
+ * @return true if the caller can block, else should recheck and retry
+ */
+ final boolean tryCompensate(ForkJoinTask task, ManagedBlocker blocker) {
+ int pc = parallelism, e;
+ long c = ctl;
+ WorkQueue[] ws = workQueues;
+ if ((e = (int)c) >= 0 && ws != null) {
+ int u, a, ac, hc;
+ int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
+ boolean replace = false;
+ if ((a = u >> UAC_SHIFT) <= 0) {
+ if ((ac = a + pc) <= 1)
+ replace = true;
+ else if ((e > 0 || (task != null &&
+ ac <= (hc = pc >>> 1) && tc < pc + hc))) {
+ WorkQueue w;
+ for (int j = 0; j < ws.length; ++j) {
+ if ((w = ws[j]) != null && !w.isEmpty()) {
+ replace = true;
+ break; // in compensation range and tasks available
+ }
+ }
+ }
+ }
+ if ((task == null || task.status >= 0) && // recheck need to block
+ (blocker == null || !blocker.isReleasable()) && ctl == c) {
+ if (!replace) { // no compensation
+ long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ return true;
+ }
+ else if (e != 0) { // release an idle worker
+ WorkQueue w; Thread p; int i;
+ if ((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;
+ }
+ }
+ }
+ else if (tc < MAX_CAP) { // create replacement
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ addWorker();
+ return true;
+ }
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * 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 int awaitJoin(WorkQueue joiner, ForkJoinTask task) {
+ int s;
+ if ((s = task.status) >= 0) {
+ ForkJoinTask prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ long startTime = 0L;
+ for (int k = 0;;) {
+ if ((s = (joiner.isEmpty() ? // try to help
+ tryHelpStealer(joiner, task) :
+ joiner.tryRemoveAndExec(task))) == 0 &&
+ (s = task.status) >= 0) {
+ if (k == 0) {
+ startTime = System.nanoTime();
+ tryPollForAndExec(joiner, task); // check uncommon case
+ }
+ else if ((k & (MAX_HELP - 1)) == 0 &&
+ System.nanoTime() - startTime >=
+ COMPENSATION_DELAY &&
+ tryCompensate(task, null)) {
+ if (task.trySetSignal()) {
+ 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));
+ }
+ }
+ if (s < 0 || (s = task.status) < 0) {
+ joiner.currentJoin = prevJoin;
+ break;
+ }
+ else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
+ Thread.yield(); // for politeness
+ }
+ }
+ 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
+ * @return task status on exit
+ */
+ final int helpJoinOnce(WorkQueue joiner, ForkJoinTask task) {
+ int s;
+ while ((s = task.status) >= 0 &&
+ (joiner.isEmpty() ?
+ tryHelpStealer(joiner, task) :
+ joiner.tryRemoveAndExec(task)) != 0)
+ ;
+ return s;
+ }
+
+ /**
+ * 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.
*/
private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
- int r = w.seed; // Same idea as scan(), but ignoring submissions
+ // Similar to loop in scan(), but ignoring submissions
+ int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+ int step = (r >>> 16) | 1;
for (WorkQueue[] ws;;) {
- int m = runState & SMASK;
- if ((ws = workQueues) == null)
+ int rs = runState, m;
+ if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
return null;
- if (ws.length > m) {
- WorkQueue q;
- for (int n = m << 2, k = r, j = -n;;) {
- r ^= r << 13; r ^= r >>> 17; r ^= r << 5;
- if ((q = ws[(k | 1) & m]) != null && q.base - q.top < 0) {
- w.seed = r;
- return q;
- }
- else if (j > n)
+ for (int j = (m + 1) << 2; ; r += step) {
+ WorkQueue q = ws[((r << 1) | 1) & m];
+ if (q != null && !q.isEmpty())
+ return q;
+ else if (--j < 0) {
+ if (runState == rs)
return null;
- else
- k = (j++ < 0) ? r : k + ((m >>> 1) | 1);
-
+ break;
}
}
}
}
+
/**
* Runs tasks until {@code isQuiescent()}. We piggyback on
* active count ctl maintenance, but rather than blocking
@@ -1714,17 +1923,19 @@ public class ForkJoinPool extends Abstra
*/
final void helpQuiescePool(WorkQueue w) {
for (boolean active = true;;) {
- w.runLocalTasks(); // exhaust local queue
+ ForkJoinTask localTask; // exhaust local queue
+ while ((localTask = w.nextLocalTask()) != null)
+ localTask.doExec();
WorkQueue q = findNonEmptyStealQueue(w);
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 {
@@ -1746,18 +1957,18 @@ public class ForkJoinPool extends Abstra
}
/**
- * Gets and removes a local or stolen task for the given worker
+ * Gets and removes a local or stolen task for the given worker.
*
* @return a task, if available
*/
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)
return null;
- if ((t = q.poll()) != null)
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
return t;
}
}
@@ -1778,99 +1989,85 @@ public class ForkJoinPool extends Abstra
8);
}
- // Termination
+ // Termination
/**
- * Sets SHUTDOWN bit of runState under lock
- */
- private void enableShutdown() {
- ReentrantLock lock = this.lock;
- if (runState >= 0) {
- lock.lock(); // don't need try/finally
- runState |= SHUTDOWN;
- lock.unlock();
- }
- }
-
- /**
- * Possibly initiates and/or completes termination. Upon
- * termination, cancels all queued tasks and then
+ * Possibly initiates and/or completes termination. The caller
+ * triggering termination runs three passes through workQueues:
+ * (0) Setting termination status, followed by wakeups of queued
+ * workers; (1) cancelling all tasks; (2) interrupting lagging
+ * threads (likely in external tasks, but possibly also blocked in
+ * joins). Each pass repeats previous steps because of potential
+ * lagging thread creation.
*
* @param now if true, unconditionally terminate, else only
* if no work and no active workers
+ * @param enable if true, enable shutdown when next possible
* @return true if now terminating or terminated
*/
- private boolean tryTerminate(boolean now) {
+ private boolean tryTerminate(boolean now, boolean enable) {
+ Mutex lock = this.lock;
for (long c;;) {
if (((c = ctl) & STOP_BIT) != 0) { // already terminating
if ((short)(c >>> TC_SHIFT) == -parallelism) {
- ReentrantLock lock = this.lock; // signal when no workers
lock.lock(); // don't need try/finally
termination.signalAll(); // signal when 0 workers
lock.unlock();
}
return true;
}
- if (!now) {
- if ((int)(c >> AC_SHIFT) != -parallelism || runState >= 0 ||
+ if (runState >= 0) { // not yet enabled
+ if (!enable)
+ return false;
+ lock.lock();
+ runState |= SHUTDOWN;
+ lock.unlock();
+ }
+ if (!now) { // check if idle & no tasks
+ if ((int)(c >> AC_SHIFT) != -parallelism ||
hasQueuedSubmissions())
return false;
// Check for unqueued inactive workers. One pass suffices.
WorkQueue[] ws = workQueues; WorkQueue w;
if (ws != null) {
- int n = ws.length;
- for (int i = 1; i < n; i += 2) {
+ for (int i = 1; i < ws.length; i += 2) {
if ((w = ws[i]) != null && w.eventCount >= 0)
return false;
}
}
}
- if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT))
- startTerminating();
- }
- }
-
- /**
- * Initiates termination: Runs three passes through workQueues:
- * (0) Setting termination status, followed by wakeups of queued
- * workers; (1) cancelling all tasks; (2) interrupting lagging
- * threads (likely in external tasks, but possibly also blocked in
- * joins). Each pass repeats previous steps because of potential
- * lagging thread creation.
- */
- private void startTerminating() {
- for (int pass = 0; pass < 3; ++pass) {
- WorkQueue[] ws = workQueues;
- if (ws != null) {
- WorkQueue w; Thread wt;
- int n = ws.length;
- for (int j = 0; j < n; ++j) {
- if ((w = ws[j]) != null) {
- w.runState = -1;
- if (pass > 0) {
- w.cancelAll();
- if (pass > 1 && (wt = w.owner) != null &&
- !wt.isInterrupted()) {
- try {
- wt.interrupt();
- } catch (SecurityException ignore) {
+ if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
+ for (int pass = 0; pass < 3; ++pass) {
+ WorkQueue[] ws = workQueues;
+ if (ws != null) {
+ WorkQueue w;
+ int n = ws.length;
+ for (int i = 0; i < n; ++i) {
+ if ((w = ws[i]) != null) {
+ w.runState = -1;
+ if (pass > 0) {
+ w.cancelAll();
+ if (pass > 1)
+ w.interruptOwner();
}
}
}
- }
- }
- // Wake up workers parked on event queue
- int i, e; long c; Thread p;
- while ((i = ((~(e = (int)(c = ctl)) << 1) | 1) & SMASK) < n &&
- (w = ws[i]) != null &&
- w.eventCount == (e | INT_SIGN)) {
- long nc = ((long)(w.nextWait & E_MASK) |
- ((c + AC_UNIT) & AC_MASK) |
- (c & (TC_MASK|STOP_BIT)));
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- w.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = w.parker) != null)
- U.unpark(p);
+ // Wake up workers parked on event queue
+ int i, e; long cc; Thread p;
+ while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
+ (i = e & SMASK) < n &&
+ (w = ws[i]) != null) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ ((cc + AC_UNIT) & AC_MASK) |
+ (cc & (TC_MASK|STOP_BIT)));
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, cc, nc)) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ w.runState = -1;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ }
+ }
}
}
}
@@ -1946,35 +2143,31 @@ public class ForkJoinPool extends Abstra
checkPermission();
if (factory == null)
throw new NullPointerException();
- if (parallelism <= 0 || parallelism > MAX_ID)
+ 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.nextPoolIndex = 1;
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 >= MAX_ID)
- n = MAX_ID;
- 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];
- ReentrantLock lck = this.lock = new ReentrantLock();
- this.termination = lck.newCondition();
+ // Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
+ int n = parallelism - 1;
+ n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
+ int size = (n + 1) << 1; // #slots = 2*#workers
+ this.submitMask = size - 1; // room for max # of submit queues
+ this.workQueues = new WorkQueue[size];
+ this.termination = (this.lock = new Mutex()).newCondition();
this.stealCount = new AtomicLong();
this.nextWorkerNumber = new AtomicInteger();
+ int pn = poolNumberGenerator.incrementAndGet();
StringBuilder sb = new StringBuilder("ForkJoinPool-");
- sb.append(poolNumberGenerator.incrementAndGet());
+ sb.append(Integer.toString(pn));
sb.append("-worker-");
this.workerNamePrefix = sb.toString();
- // Create initial submission queue
- WorkQueue sq = tryAddSharedQueue(0);
- if (sq != null)
- sq.growArray(false);
+ lock.lock();
+ this.runState = 1; // set init flag
+ lock.unlock();
}
// Execution methods
@@ -1996,6 +2189,8 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public T invoke(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
doSubmit(task);
return task.join();
}
@@ -2009,6 +2204,8 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public void execute(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
doSubmit(task);
}
@@ -2026,7 +2223,7 @@ public class ForkJoinPool extends Abstra
if (task instanceof ForkJoinTask) // avoid re-wrap
job = (ForkJoinTask) task;
else
- job = ForkJoinTask.adapt(task, null);
+ job = new ForkJoinTask.AdaptedRunnableAction(task);
doSubmit(job);
}
@@ -2040,6 +2237,8 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public ForkJoinTask submit(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
doSubmit(task);
return task;
}
@@ -2050,9 +2249,7 @@ public class ForkJoinPool extends Abstra
* scheduled for execution
*/
public ForkJoinTask submit(Callable task) {
- if (task == null)
- throw new NullPointerException();
- ForkJoinTask job = ForkJoinTask.adapt(task);
+ ForkJoinTask job = new ForkJoinTask.AdaptedCallable(task);
doSubmit(job);
return job;
}
@@ -2063,9 +2260,7 @@ 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);
+ ForkJoinTask job = new ForkJoinTask.AdaptedRunnable(task, result);
doSubmit(job);
return job;
}
@@ -2082,7 +2277,7 @@ public class ForkJoinPool extends Abstra
if (task instanceof ForkJoinTask) // avoid re-wrap
job = (ForkJoinTask) task;
else
- job = ForkJoinTask.adapt(task, null);
+ job = new ForkJoinTask.AdaptedRunnableAction(task);
doSubmit(job);
return job;
}
@@ -2092,25 +2287,31 @@ public class ForkJoinPool extends Abstra
* @throws RejectedExecutionException {@inheritDoc}
*/
public List> invokeAll(Collection> tasks) {
- ArrayList> forkJoinTasks =
- new ArrayList>(tasks.size());
- for (Callable task : tasks)
- forkJoinTasks.add(ForkJoinTask.adapt(task));
- invoke(new InvokeAll(forkJoinTasks));
-
+ // In previous versions of this class, this method constructed
+ // a task to run ForkJoinTask.invokeAll, but now external
+ // invocation of multiple tasks is at least as efficient.
+ List> fs = new ArrayList>(tasks.size());
+ // Workaround needed because method wasn't declared with
+ // wildcards in return type but should have been.
@SuppressWarnings({"unchecked", "rawtypes"})
- List> futures = (List>) (List) forkJoinTasks;
- return futures;
- }
+ List> futures = (List>) (List) fs;
- static final class InvokeAll extends RecursiveAction {
- final ArrayList> tasks;
- InvokeAll(ArrayList> tasks) { this.tasks = tasks; }
- public void compute() {
- try { invokeAll(tasks); }
- catch (Exception ignore) {}
+ boolean done = false;
+ try {
+ for (Callable t : tasks) {
+ ForkJoinTask f = new ForkJoinTask.AdaptedCallable(t);
+ doSubmit(f);
+ fs.add(f);
+ }
+ for (ForkJoinTask f : fs)
+ f.quietlyJoin();
+ done = true;
+ return futures;
+ } finally {
+ if (!done)
+ for (ForkJoinTask f : fs)
+ f.cancel(false);
}
- private static final long serialVersionUID = -7914297376763021607L;
}
/**
@@ -2175,14 +2376,8 @@ public class ForkJoinPool extends Abstra
int rc = 0;
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 1; i < n; i += 2) {
- Thread.State s; ForkJoinWorkerThread wt;
- if ((w = ws[i]) != null && (wt = w.owner) != null &&
- w.eventCount >= 0 &&
- (s = wt.getState()) != Thread.State.BLOCKED &&
- s != Thread.State.WAITING &&
- s != Thread.State.TIMED_WAITING)
+ for (int i = 1; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null && w.isApparentlyUnblocked())
++rc;
}
}
@@ -2231,8 +2426,7 @@ public class ForkJoinPool extends Abstra
long count = stealCount.get();
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 1; i < n; i += 2) {
+ for (int i = 1; i < ws.length; i += 2) {
if ((w = ws[i]) != null)
count += w.totalSteals;
}
@@ -2254,8 +2448,7 @@ public class ForkJoinPool extends Abstra
long count = 0;
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 1; i < n; i += 2) {
+ for (int i = 1; i < ws.length; i += 2) {
if ((w = ws[i]) != null)
count += w.queueSize();
}
@@ -2274,8 +2467,7 @@ public class ForkJoinPool extends Abstra
int count = 0;
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 0; i < n; i += 2) {
+ for (int i = 0; i < ws.length; i += 2) {
if ((w = ws[i]) != null)
count += w.queueSize();
}
@@ -2292,9 +2484,8 @@ public class ForkJoinPool extends Abstra
public boolean hasQueuedSubmissions() {
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 0; i < n; i += 2) {
- if ((w = ws[i]) != null && w.queueSize() != 0)
+ for (int i = 0; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null && !w.isEmpty())
return true;
}
}
@@ -2311,8 +2502,7 @@ public class ForkJoinPool extends Abstra
protected ForkJoinTask pollSubmission() {
WorkQueue[] ws; WorkQueue w; ForkJoinTask t;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 0; i < n; i += 2) {
+ for (int i = 0; i < ws.length; i += 2) {
if ((w = ws[i]) != null && (t = w.poll()) != null)
return t;
}
@@ -2341,8 +2531,7 @@ public class ForkJoinPool extends Abstra
int count = 0;
WorkQueue[] ws; WorkQueue w; ForkJoinTask t;
if ((ws = workQueues) != null) {
- int n = ws.length;
- for (int i = 0; i < n; ++i) {
+ for (int i = 0; i < ws.length; ++i) {
if ((w = ws[i]) != null) {
while ((t = w.poll()) != null) {
c.add(t);
@@ -2362,12 +2551,27 @@ public class ForkJoinPool extends Abstra
* @return a string identifying this pool, as well as its state
*/
public String toString() {
- long st = getStealCount();
- long qt = getQueuedTaskCount();
- long qs = getQueuedSubmissionCount();
- int rc = getRunningThreadCount();
- int pc = parallelism;
+ // Use a single pass through workQueues to collect counts
+ long qt = 0L, qs = 0L; int rc = 0;
+ long st = stealCount.get();
long c = ctl;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ if ((w = ws[i]) != null) {
+ int size = w.queueSize();
+ if ((i & 1) == 0)
+ qs += size;
+ else {
+ qt += size;
+ st += w.totalSteals;
+ if (w.isApparentlyUnblocked())
+ ++rc;
+ }
+ }
+ }
+ }
+ int pc = parallelism;
int tc = pc + (short)(c >>> TC_SHIFT);
int ac = pc + (int)(c >> AC_SHIFT);
if (ac < 0) // ignore transient negative
@@ -2403,8 +2607,7 @@ public class ForkJoinPool extends Abstra
*/
public void shutdown() {
checkPermission();
- enableShutdown();
- tryTerminate(false);
+ tryTerminate(false, true);
}
/**
@@ -2425,8 +2628,7 @@ public class ForkJoinPool extends Abstra
*/
public List shutdownNow() {
checkPermission();
- enableShutdown();
- tryTerminate(true);
+ tryTerminate(true, true);
return Collections.emptyList();
}
@@ -2483,7 +2685,7 @@ public class ForkJoinPool extends Abstra
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
- final ReentrantLock lock = this.lock;
+ final Mutex lock = this.lock;
lock.lock();
try {
for (;;) {
@@ -2597,7 +2799,7 @@ public class ForkJoinPool extends Abstra
ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
((ForkJoinWorkerThread)t).pool : null);
while (!blocker.isReleasable()) {
- if (p == null || p.tryCompensate()) {
+ if (p == null || p.tryCompensate(null, blocker)) {
try {
do {} while (!blocker.isReleasable() && !blocker.block());
} finally {
@@ -2614,38 +2816,45 @@ 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 RUNSTATE;
private static final long PARKBLOCKER;
+ private static final int ABASE;
+ private static final int ASHIFT;
static {
poolNumberGenerator = new AtomicInteger();
+ nextSubmitterSeed = new AtomicInteger(0x55555555);
modifyThreadPermission = new RuntimePermission("modifyThread");
defaultForkJoinWorkerThreadFactory =
new DefaultForkJoinWorkerThreadFactory();
+ submitters = new ThreadSubmitter();
int s;
try {
U = getUnsafe();
Class k = ForkJoinPool.class;
- Class tk = Thread.class;
+ Class ak = ForkJoinTask[].class;
CTL = U.objectFieldOffset
(k.getDeclaredField("ctl"));
- RUNSTATE = U.objectFieldOffset
- (k.getDeclaredField("runState"));
+ Class tk = Thread.class;
PARKBLOCKER = U.objectFieldOffset
(tk.getDeclaredField("parkBlocker"));
+ ABASE = U.arrayBaseOffset(ak);
+ s = U.arrayIndexScale(ak);
} catch (Exception e) {
throw new Error(e);
}
+ if ((s & (s-1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
}
/**