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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.54 by dl, Sun Apr 18 12:51:18 2010 UTC vs.
Revision 1.84 by dl, Sat Nov 13 13:11:51 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	+	import java.util.concurrent.AbstractExecutorService;
15	+	import java.util.concurrent.Callable;
16	+	import java.util.concurrent.ExecutorService;
17	+	import java.util.concurrent.Future;
18	+	import java.util.concurrent.RejectedExecutionException;
19	+	import java.util.concurrent.RunnableFuture;
20	+	import java.util.concurrent.TimeUnit;
21	+	import java.util.concurrent.TimeoutException;
22	+	import java.util.concurrent.atomic.AtomicInteger;
23		import java.util.concurrent.locks.LockSupport;
24		import java.util.concurrent.locks.ReentrantLock;
18	–	import java.util.concurrent.atomic.AtomicInteger;
19	–	import java.util.concurrent.CountDownLatch;
25
26		/**
27		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
28		* A {@code ForkJoinPool} provides the entry point for submissions
29	<	* from non-{@code ForkJoinTask}s, as well as management and
29	>	* from non-{@code ForkJoinTask} clients, as well as management and
30		* monitoring operations.
31		*
32		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
#	Line 30 | Line 35 | import java.util.concurrent.CountDownLat
35		* execute subtasks created by other active tasks (eventually blocking
36		* waiting for work if none exist). This enables efficient processing
37		* when most tasks spawn other subtasks (as do most {@code
38	<	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
39	<	* execution of some plain {@code Runnable}- or {@code Callable}-
40	<	* based activities along with {@code ForkJoinTask}s. When setting
36	<	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
37	<	* also be appropriate for use with fine-grained tasks of any form
38	<	* that are never joined. Otherwise, other {@code ExecutorService}
39	<	* implementations are typically more appropriate choices.
38	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
39	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
40	>	* with event-style tasks that are never joined.
41		*
42		* <p>A {@code ForkJoinPool} is constructed with a given target
43		* parallelism level; by default, equal to the number of available
44	<	* processors. Unless configured otherwise via {@link
45	<	* #setMaintainsParallelism}, the pool attempts to maintain this
46	<	* number of active (or available) threads by dynamically adding,
47	<	* suspending, or resuming internal worker threads, even if some tasks
48	<	* are stalled waiting to join others. However, no such adjustments
49	<	* are performed in the face of blocked IO or other unmanaged
50	<	* synchronization. The nested {@link ManagedBlocker} interface
50	<	* enables extension of the kinds of synchronization accommodated.
51	<	* The target parallelism level may also be changed dynamically
52	<	* ({@link #setParallelism}). The total number of threads may be
53	<	* limited using method {@link #setMaximumPoolSize}, in which case it
54	<	* may become possible for the activities of a pool to stall due to
55	<	* the lack of available threads to process new tasks. When the pool
56	<	* is executing tasks, these and other configuration setting methods
57	<	* may only gradually affect actual pool sizes. It is normally best
58	<	* practice to invoke these methods only when the pool is known to be
59	<	* quiescent.
44	>	* processors. The pool attempts to maintain enough active (or
45	>	* available) threads by dynamically adding, suspending, or resuming
46	>	* internal worker threads, even if some tasks are stalled waiting to
47	>	* join others. However, no such adjustments are guaranteed in the
48	>	* face of blocked IO or other unmanaged synchronization. The nested
49	>	* {@link ManagedBlocker} interface enables extension of the kinds of
50	>	* synchronization accommodated.
51		*
52		* <p>In addition to execution and lifecycle control methods, this
53		* class provides status check methods (for example
#	Line 65 | Line 56 | import java.util.concurrent.CountDownLat
56		* {@link #toString} returns indications of pool state in a
57		* convenient form for informal monitoring.
58		*
59	+	* <p> As is the case with other ExecutorServices, there are three
60	+	* main task execution methods summarized in the following
61	+	* table. These are designed to be used by clients not already engaged
62	+	* in fork/join computations in the current pool.  The main forms of
63	+	* these methods accept instances of {@code ForkJoinTask}, but
64	+	* overloaded forms also allow mixed execution of plain {@code
65	+	* Runnable}- or {@code Callable}- based activities as well.  However,
66	+	* tasks that are already executing in a pool should normally
67	+	* <em>NOT</em> use these pool execution methods, but instead use the
68	+	* within-computation forms listed in the table.
69	+	*
70	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
71	+	*  <tr>
72	+	*    <td></td>
73	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
74	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Arrange async execution</td>
78	+	*    <td> {@link #execute(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#fork}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Await and obtain result</td>
83	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#invoke}</td>
85	+	*  </tr>
86	+	*  <tr>
87	+	*    <td> <b>Arrange exec and obtain Future</td>
88	+	*    <td> {@link #submit(ForkJoinTask)}</td>
89	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
90	+	*  </tr>
91	+	* </table>
92	+	*
93		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
94		* used for all parallel task execution in a program or subsystem.
95		* Otherwise, use would not usually outweigh the construction and
#	Line 89 | Line 114 | import java.util.concurrent.CountDownLat
114		* {@code IllegalArgumentException}.
115		*
116		* <p>This implementation rejects submitted tasks (that is, by throwing
117	<	* {@link RejectedExecutionException}) only when the pool is shut down.
117	>	* {@link RejectedExecutionException}) only when the pool is shut down
118	>	* or internal resources have been exhausted.
119		*
120		* @since 1.7
121		* @author Doug Lea
#	Line 116 | Line 142 | public class ForkJoinPool extends Abstra
142		* of tasks profit from cache affinities, but others are harmed by
143		* cache pollution effects.)
144		*
145	+	* Beyond work-stealing support and essential bookkeeping, the
146	+	* main responsibility of this framework is to take actions when
147	+	* one worker is waiting to join a task stolen (or always held by)
148	+	* another.  Because we are multiplexing many tasks on to a pool
149	+	* of workers, we can't just let them block (as in Thread.join).
150	+	* We also cannot just reassign the joiner's run-time stack with
151	+	* another and replace it later, which would be a form of
152	+	* "continuation", that even if possible is not necessarily a good
153	+	* idea. Given that the creation costs of most threads on most
154	+	* systems mainly surrounds setting up runtime stacks, thread
155	+	* creation and switching is usually not much more expensive than
156	+	* stack creation and switching, and is more flexible). Instead we
157	+	* combine two tactics:
158	+	*
159	+	*   Helping: Arranging for the joiner to execute some task that it
160	+	*      would be running if the steal had not occurred.  Method
161	+	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
162	+	*      links to try to find such a task.
163	+	*
164	+	*   Compensating: Unless there are already enough live threads,
165	+	*      method helpMaintainParallelism() may create or
166	+	*      re-activate a spare thread to compensate for blocked
167	+	*      joiners until they unblock.
168	+	*
169	+	* It is impossible to keep exactly the target (parallelism)
170	+	* number of threads running at any given time.  Determining
171	+	* existence of conservatively safe helping targets, the
172	+	* availability of already-created spares, and the apparent need
173	+	* to create new spares are all racy and require heuristic
174	+	* guidance, so we rely on multiple retries of each.  Compensation
175	+	* occurs in slow-motion. It is triggered only upon timeouts of
176	+	* Object.wait used for joins. This reduces poor decisions that
177	+	* would otherwise be made when threads are waiting for others
178	+	* that are stalled because of unrelated activities such as
179	+	* garbage collection.
180	+	*
181	+	* The ManagedBlocker extension API can't use helping so relies
182	+	* only on compensation in method awaitBlocker.
183	+	*
184		* The main throughput advantages of work-stealing stem from
185		* decentralized control -- workers mostly steal tasks from each
186		* other. We do not want to negate this by creating bottlenecks
187	<	* implementing the management responsibilities of this class. So
188	<	* we use a collection of techniques that avoid, reduce, or cope
189	<	* well with contention. These entail several instances of
190	<	* bit-packing into CASable fields to maintain only the minimally
191	<	* required atomicity. To enable such packing, we restrict maximum
192	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
193	<	* bit field), which is far in excess of normal operating range.
194	<	* Even though updates to some of these bookkeeping fields do
195	<	* sometimes contend with each other, they don't normally
196	<	* cache-contend with updates to others enough to warrant memory
197	<	* padding or isolation. So they are all held as fields of
198	<	* ForkJoinPool objects.  The main capabilities are as follows:
187	>	* implementing other management responsibilities. So we use a
188	>	* collection of techniques that avoid, reduce, or cope well with
189	>	* contention. These entail several instances of bit-packing into
190	>	* CASable fields to maintain only the minimally required
191	>	* atomicity. To enable such packing, we restrict maximum
192	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
193	>	* unbalanced increments and decrements) to fit into a 16 bit
194	>	* field, which is far in excess of normal operating range.  Even
195	>	* though updates to some of these bookkeeping fields do sometimes
196	>	* contend with each other, they don't normally cache-contend with
197	>	* updates to others enough to warrant memory padding or
198	>	* isolation. So they are all held as fields of ForkJoinPool
199	>	* objects.  The main capabilities are as follows:
200		*
201		* 1. Creating and removing workers. Workers are recorded in the
202		* "workers" array. This is an array as opposed to some other data
#	Line 140 | Line 206 | public class ForkJoinPool extends Abstra
206		* (workerLock) but the array is otherwise concurrently readable,
207		* and accessed directly by workers. To simplify index-based
208		* operations, the array size is always a power of two, and all
209	<	* readers must tolerate null slots. Currently, all but the first
210	<	* worker thread creation is on-demand, triggered by task
211	<	* submissions, replacement of terminated workers, and/or
212	<	* compensation for blocked workers. However, all other support
213	<	* code is set up to work with other policies.
209	>	* readers must tolerate null slots. Currently, all worker thread
210	>	* creation is on-demand, triggered by task submissions,
211	>	* replacement of terminated workers, and/or compensation for
212	>	* blocked workers. However, all other support code is set up to
213	>	* work with other policies.
214	>	*
215	>	* To ensure that we do not hold on to worker references that
216	>	* would prevent GC, ALL accesses to workers are via indices into
217	>	* the workers array (which is one source of some of the unusual
218	>	* code constructions here). In essence, the workers array serves
219	>	* as a WeakReference mechanism. Thus for example the event queue
220	>	* stores worker indices, not worker references. Access to the
221	>	* workers in associated methods (for example releaseEventWaiters)
222	>	* must both index-check and null-check the IDs. All such accesses
223	>	* ignore bad IDs by returning out early from what they are doing,
224	>	* since this can only be associated with shutdown, in which case
225	>	* it is OK to give up. On termination, we just clobber these
226	>	* data structures without trying to use them.
227		*
228		* 2. Bookkeeping for dynamically adding and removing workers. We
229	<	* maintain a given level of parallelism (or, if
230	<	* maintainsParallelism is false, at least avoid starvation). When
152	<	* some workers are known to be blocked (on joins or via
229	>	* aim to approximately maintain the given level of parallelism.
230	>	* When some workers are known to be blocked (on joins or via
231		* ManagedBlocker), we may create or resume others to take their
232		* place until they unblock (see below). Implementing this
233		* requires counts of the number of "running" threads (i.e., those
234	<	* that are neither blocked nor artifically suspended) as well as
234	>	* that are neither blocked nor artificially suspended) as well as
235		* the total number.  These two values are packed into one field,
236		* "workerCounts" because we need accurate snapshots when deciding
237	<	* to create, resume or suspend.  To support these decisions,
238	<	* updates must be prospective (not retrospective).  For example,
239	<	* the running count is decremented before blocking by a thread
240	<	* about to block, but incremented by the thread about to unblock
163	<	* it. (In a few cases, these prospective updates may need to be
164	<	* rolled back, for example when deciding to create a new worker
165	<	* but the thread factory fails or returns null. In these cases,
166	<	* we are no worse off wrt other decisions than we would be
167	<	* otherwise.)  Updates to the workerCounts field sometimes
168	<	* transiently encounter a fair amount of contention when join
169	<	* dependencies are such that many threads block or unblock at
170	<	* about the same time. We alleviate this by sometimes bundling
171	<	* updates (for example blocking one thread on join and resuming a
172	<	* spare cancel each other out), and in most other cases
173	<	* performing an alternative action (like releasing waiters and
174	<	* finding spares; see below) as a more productive form of
175	<	* backoff.
237	>	* to create, resume or suspend.  Note however that the
238	>	* correspondence of these counts to reality is not guaranteed. In
239	>	* particular updates for unblocked threads may lag until they
240	>	* actually wake up.
241		*
242		* 3. Maintaining global run state. The run state of the pool
243		* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
#	Line 201 | Line 266 | public class ForkJoinPool extends Abstra
266		* workers that previously could not find a task to now find one:
267		* Submission of a new task to the pool, or another worker pushing
268		* a task onto a previously empty queue.  (We also use this
269	<	* mechanism for termination and reconfiguration actions that
269	>	* mechanism for configuration and termination actions that
270		* require wakeups of idle workers).  Each worker maintains its
271		* last known event count, and blocks when a scan for work did not
272		* find a task AND its lastEventCount matches the current
#	Line 212 | Line 277 | public class ForkJoinPool extends Abstra
277		* a record (field nextEventWaiter) for the next waiting worker.
278		* In addition to allowing simpler decisions about need for
279		* wakeup, the event count bits in eventWaiters serve the role of
280	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
281	<	* in task diffusion, workers not otherwise occupied may invoke
282	<	* method releaseWaiters, that removes and signals (unparks)
283	<	* workers not waiting on current count. To minimize task
284	<	* production stalls associate with signalling, any worker pushing
285	<	* a task on an empty queue invokes the weaker method signalWork,
221	<	* that only releases idle workers until it detects interference
222	<	* by other threads trying to release, and lets them take
223	<	* over. The net effect is a tree-like diffusion of signals, where
224	<	* released threads and possibly others) help with unparks.  To
225	<	* further reduce contention effects a bit, failed CASes to
226	<	* increment field eventCount are tolerated without retries.
280	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
281	>	* released threads also try to release at most two others.  The
282	>	* net effect is a tree-like diffusion of signals, where released
283	>	* threads (and possibly others) help with unparks.  To further
284	>	* reduce contention effects a bit, failed CASes to increment
285	>	* field eventCount are tolerated without retries in signalWork.
286		* Conceptually they are merged into the same event, which is OK
287		* when their only purpose is to enable workers to scan for work.
288		*
289	<	* 5. Managing suspension of extra workers. When a worker is about
290	<	* to block waiting for a join (or via ManagedBlockers), we may
291	<	* create a new thread to maintain parallelism level, or at least
292	<	* avoid starvation (see below). Usually, extra threads are needed
293	<	* for only very short periods, yet join dependencies are such
294	<	* that we sometimes need them in bursts. Rather than create new
295	<	* threads each time this happens, we suspend no-longer-needed
296	<	* extra ones as "spares". For most purposes, we don't distinguish
297	<	* "extra" spare threads from normal "core" threads: On each call
298	<	* to preStep (the only point at which we can do this) a worker
299	<	* checks to see if there are now too many running workers, and if
300	<	* so, suspends itself.  Methods preJoin and doBlock look for
301	<	* suspended threads to resume before considering creating a new
302	<	* replacement. We don't need a special data structure to maintain
303	<	* spares; simply scanning the workers array looking for
304	<	* worker.isSuspended() is fine because the calling thread is
305	<	* otherwise not doing anything useful anyway; we are at least as
306	<	* happy if after locating a spare, the caller doesn't actually
307	<	* block because the join is ready before we try to adjust and
308	<	* compensate.  Note that this is intrinsically racy.  One thread
309	<	* may become a spare at about the same time as another is
310	<	* needlessly being created. We counteract this and related slop
311	<	* in part by requiring resumed spares to immediately recheck (in
312	<	* preStep) to see whether they they should re-suspend. The only
313	<	* effective difference between "extra" and "core" threads is that
314	<	* we allow the "extra" ones to time out and die if they are not
315	<	* resumed within a keep-alive interval of a few seconds. This is
316	<	* implemented mainly within ForkJoinWorkerThread, but requires
317	<	* some coordination (isTrimmed() -- meaning killed while
318	<	* suspended) to correctly maintain pool counts.
319	<	*
320	<	* 6. Deciding when to create new workers. The main dynamic
321	<	* control in this class is deciding when to create extra threads,
322	<	* in methods preJoin and doBlock. We always need to create one
323	<	* when the number of running threads becomes zero. But because
324	<	* blocked joins are typically dependent, we don't necessarily
325	<	* need or want one-to-one replacement. Using a one-to-one
326	<	* compensation rule often leads to enough useless overhead
327	<	* creating, suspending, resuming, and/or killing threads to
328	<	* signficantly degrade throughput.  We use a rule reflecting the
329	<	* idea that, the more spare threads you already have, the more
330	<	* evidence you need to create another one; where "evidence" is
331	<	* expressed as the current deficit -- target minus running
332	<	* threads. To reduce flickering and drift around target values,
333	<	* the relation is quadratic: adding a spare if (dc*dc)>=(sc*pc)
334	<	* (where dc is deficit, sc is number of spare threads and pc is
335	<	* target parallelism.)  This effectively reduces churn at the
336	<	* price of systematically undershooting target parallelism when
337	<	* many threads are blocked.  However, biasing toward undeshooting
338	<	* partially compensates for the above mechanics to suspend extra
339	<	* threads, that normally lead to overshoot because we can only
281	<	* suspend workers in-between top-level actions. It also better
282	<	* copes with the fact that some of the methods in this class tend
283	<	* to never become compiled (but are interpreted), so some
284	<	* components of the entire set of controls might execute many
285	<	* times faster than others. And similarly for cases where the
286	<	* apparent lack of work is just due to GC stalls and other
287	<	* transient system activity.
288	<	*
289	<	* 7. Maintaining other configuration parameters and monitoring
290	<	* statistics. Updates to fields controlling parallelism level,
291	<	* max size, etc can only meaningfully take effect for individual
292	<	* threads upon their next top-level actions; i.e., between
293	<	* stealing/running tasks/submission, which are separated by calls
294	<	* to preStep.  Memory ordering for these (assumed infrequent)
295	<	* reconfiguration calls is ensured by using reads and writes to
296	<	* volatile field workerCounts (that must be read in preStep anyway)
297	<	* as "fences" -- user-level reads are preceded by reads of
298	<	* workCounts, and writes are followed by no-op CAS to
299	<	* workerCounts. The values reported by other management and
300	<	* monitoring methods are either computed on demand, or are kept
301	<	* in fields that are only updated when threads are otherwise
302	<	* idle.
289	>	* 5. Managing suspension of extra workers. When a worker notices
290	>	* (usually upon timeout of a wait()) that there are too few
291	>	* running threads, we may create a new thread to maintain
292	>	* parallelism level, or at least avoid starvation. Usually, extra
293	>	* threads are needed for only very short periods, yet join
294	>	* dependencies are such that we sometimes need them in
295	>	* bursts. Rather than create new threads each time this happens,
296	>	* we suspend no-longer-needed extra ones as "spares". For most
297	>	* purposes, we don't distinguish "extra" spare threads from
298	>	* normal "core" threads: On each call to preStep (the only point
299	>	* at which we can do this) a worker checks to see if there are
300	>	* now too many running workers, and if so, suspends itself.
301	>	* Method helpMaintainParallelism looks for suspended threads to
302	>	* resume before considering creating a new replacement. The
303	>	* spares themselves are encoded on another variant of a Treiber
304	>	* Stack, headed at field "spareWaiters".  Note that the use of
305	>	* spares is intrinsically racy.  One thread may become a spare at
306	>	* about the same time as another is needlessly being created. We
307	>	* counteract this and related slop in part by requiring resumed
308	>	* spares to immediately recheck (in preStep) to see whether they
309	>	* should re-suspend.
310	>	*
311	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
312	>	* shed unused workers: The oldest (first) event queue waiter uses
313	>	* a timed rather than hard wait. When this wait times out without
314	>	* a normal wakeup, it tries to shutdown any one (for convenience
315	>	* the newest) other spare or event waiter via
316	>	* tryShutdownUnusedWorker. This eventually reduces the number of
317	>	* worker threads to a minimum of one after a long enough period
318	>	* without use.
319	>	*
320	>	* 7. Deciding when to create new workers. The main dynamic
321	>	* control in this class is deciding when to create extra threads
322	>	* in method helpMaintainParallelism. We would like to keep
323	>	* exactly #parallelism threads running, which is an impossible
324	>	* task. We always need to create one when the number of running
325	>	* threads would become zero and all workers are busy. Beyond
326	>	* this, we must rely on heuristics that work well in the
327	>	* presence of transient phenomena such as GC stalls, dynamic
328	>	* compilation, and wake-up lags. These transients are extremely
329	>	* common -- we are normally trying to fully saturate the CPUs on
330	>	* a machine, so almost any activity other than running tasks
331	>	* impedes accuracy. Our main defense is to allow parallelism to
332	>	* lapse for a while during joins, and use a timeout to see if,
333	>	* after the resulting settling, there is still a need for
334	>	* additional workers.  This also better copes with the fact that
335	>	* some of the methods in this class tend to never become compiled
336	>	* (but are interpreted), so some components of the entire set of
337	>	* controls might execute 100 times faster than others. And
338	>	* similarly for cases where the apparent lack of work is just due
339	>	* to GC stalls and other transient system activity.
340		*
341		* Beware that there is a lot of representation-level coupling
342		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 312 | Line 349 | public class ForkJoinPool extends Abstra
349		*
350		* Style notes: There are lots of inline assignments (of form
351		* "while ((local = field) != 0)") which are usually the simplest
352	<	* way to ensure read orderings. Also several occurrences of the
353	<	* unusual "do {} while(!cas...)" which is the simplest way to
354	<	* force an update of a CAS'ed variable. There are also a few
355	<	* other coding oddities that help some methods perform reasonably
356	<	* even when interpreted (not compiled).
352	>	* way to ensure the required read orderings (which are sometimes
353	>	* critical). Also several occurrences of the unusual "do {}
354	>	* while (!cas...)" which is the simplest way to force an update of
355	>	* a CAS'ed variable. There are also other coding oddities that
356	>	* help some methods perform reasonably even when interpreted (not
357	>	* compiled), at the expense of some messy constructions that
358	>	* reduce byte code counts.
359		*
360		* The order of declarations in this file is: (1) statics (2)
361		* fields (along with constants used when unpacking some of them)
#	Line 345 | Line 384 | public class ForkJoinPool extends Abstra
384		* Default ForkJoinWorkerThreadFactory implementation; creates a
385		* new ForkJoinWorkerThread.
386		*/
387	<	static class  DefaultForkJoinWorkerThreadFactory
387	>	static class DefaultForkJoinWorkerThreadFactory
388		implements ForkJoinWorkerThreadFactory {
389		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
390		return new ForkJoinWorkerThread(pool);
#	Line 384 | Line 423 | public class ForkJoinPool extends Abstra
423		new AtomicInteger();
424
425		/**
426	<	* Absolute bound for parallelism level. Twice this number must
427	<	* fit into a 16bit field to enable word-packing for some counts.
426	>	* The time to block in a join (see awaitJoin) before checking if
427	>	* a new worker should be (re)started to maintain parallelism
428	>	* level. The value should be short enough to maintain global
429	>	* responsiveness and progress but long enough to avoid
430	>	* counterproductive firings during GC stalls or unrelated system
431	>	* activity, and to not bog down systems with continual re-firings
432	>	* on GCs or legitimately long waits.
433	>	*/
434	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
435	>
436	>	/**
437	>	* The wakeup interval (in nanoseconds) for the oldest worker
438	>	* waiting for an event to invoke tryShutdownUnusedWorker to
439	>	* shrink the number of workers.  The exact value does not matter
440	>	* too much. It must be short enough to release resources during
441	>	* sustained periods of idleness, but not so short that threads
442	>	* are continually re-created.
443		*/
444	<	private static final int MAX_THREADS = 0x7fff;
444	>	private static final long SHRINK_RATE_NANOS =
445	>	30L * 1000L * 1000L * 1000L; // 2 per minute
446	>
447	>	/**
448	>	* Absolute bound for parallelism level. Twice this number plus
449	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
450	>	* word-packing for some counts and indices.
451	>	*/
452	>	private static final int MAX_WORKERS   = 0x7fff;
453
454		/**
455		* Array holding all worker threads in the pool.  Array size must
#	Line 413 | Line 475 | public class ForkJoinPool extends Abstra
475		/**
476		* Latch released upon termination.
477		*/
478	<	private final CountDownLatch terminationLatch;
478	>	private final Phaser termination;
479
480		/**
481		* Creation factory for worker threads.
#	Line 427 | Line 489 | public class ForkJoinPool extends Abstra
489		private volatile long stealCount;
490
491		/**
492	<	* Encoded record of top of treiber stack of threads waiting for
492	>	* Encoded record of top of Treiber stack of threads waiting for
493		* events. The top 32 bits contain the count being waited for. The
494	<	* bottom word contains one plus the pool index of waiting worker
495	<	* thread.
494	>	* bottom 16 bits contains one plus the pool index of waiting
495	>	* worker thread. (Bits 16-31 are unused.)
496		*/
497		private volatile long eventWaiters;
498
499		private static final int  EVENT_COUNT_SHIFT = 32;
500	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
500	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
501
502		/**
503		* A counter for events that may wake up worker threads:
504		*   - Submission of a new task to the pool
505		*   - A worker pushing a task on an empty queue
506	<	*   - termination and reconfiguration
506	>	*   - termination
507		*/
508		private volatile int eventCount;
509
510		/**
511	+	* Encoded record of top of Treiber stack of spare threads waiting
512	+	* for resumption. The top 16 bits contain an arbitrary count to
513	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
514	+	* index of waiting worker thread.
515	+	*/
516	+	private volatile int spareWaiters;
517	+
518	+	private static final int SPARE_COUNT_SHIFT = 16;
519	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
520	+
521	+	/**
522		* Lifecycle control. The low word contains the number of workers
523		* that are (probably) executing tasks. This value is atomically
524		* incremented before a worker gets a task to run, and decremented
525	<	* when worker has no tasks and cannot find any.  Bits 16-18
525	>	* when a worker has no tasks and cannot find any.  Bits 16-18
526		* contain runLevel value. When all are zero, the pool is
527		* running. Level transitions are monotonic (running -> shutdown
528		* -> terminating -> terminated) so each transition adds a bit.
529		* These are bundled together to ensure consistent read for
530		* termination checks (i.e., that runLevel is at least SHUTDOWN
531		* and active threads is zero).
532	+	*
533	+	* Notes: Most direct CASes are dependent on these bitfield
534	+	* positions.  Also, this field is non-private to enable direct
535	+	* performance-sensitive CASes in ForkJoinWorkerThread.
536		*/
537	<	private volatile int runState;
537	>	volatile int runState;
538
539		// Note: The order among run level values matters.
540		private static final int RUNLEVEL_SHIFT     = 16;
#	Line 465 | Line 542 | public class ForkJoinPool extends Abstra
542		private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
543		private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
544		private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
468	–	private static final int ONE_ACTIVE         = 1; // active update delta
545
546		/**
547		* Holds number of total (i.e., created and not yet terminated)
#	Line 474 | Line 550 | public class ForkJoinPool extends Abstra
550		* making decisions about creating and suspending spare
551		* threads. Updated only by CAS. Note that adding a new worker
552		* requires incrementing both counts, since workers start off in
553	<	* running state.  This field is also used for memory-fencing
478	<	* configuration parameters.
553	>	* running state.
554		*/
555		private volatile int workerCounts;
556
#	Line 484 | Line 559 | public class ForkJoinPool extends Abstra
559		private static final int ONE_RUNNING        = 1;
560		private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
561
487	–	/*
488	–	* Fields parallelism. maxPoolSize, locallyFifo,
489	–	* maintainsParallelism, and ueh are non-volatile, but external
490	–	* reads/writes use workerCount fences to ensure visability.
491	–	*/
492	–
562		/**
563		* The target parallelism level.
564	+	* Accessed directly by ForkJoinWorkerThreads.
565		*/
566	<	private int parallelism;
497	<
498	<	/**
499	<	* The maximum allowed pool size.
500	<	*/
501	<	private int maxPoolSize;
566	>	final int parallelism;
567
568		/**
569		* True if use local fifo, not default lifo, for local polling
570	<	* Replicated by ForkJoinWorkerThreads
506	<	*/
507	<	private boolean locallyFifo;
508	<
509	<	/**
510	<	* Controls whether to add spares to maintain parallelism
570	>	* Read by, and replicated by ForkJoinWorkerThreads
571		*/
572	<	private boolean maintainsParallelism;
572	>	final boolean locallyFifo;
573
574		/**
575	<	* The uncaught exception handler used when any worker
576	<	* abruptly terminates
575	>	* The uncaught exception handler used when any worker abruptly
576	>	* terminates.
577		*/
578	<	private Thread.UncaughtExceptionHandler ueh;
578	>	private final Thread.UncaughtExceptionHandler ueh;
579
580		/**
581		* Pool number, just for assigning useful names to worker threads
582		*/
583		private final int poolNumber;
584
585	<	// utilities for updating fields
585	>	// Utilities for CASing fields. Note that most of these
586	>	// are usually manually inlined by callers
587
588		/**
589	<	* Adds delta to running count.  Used mainly by ForkJoinTask.
529	<	*
530	<	* @param delta the number to add
589	>	* Increments running count part of workerCounts
590		*/
591	<	final void updateRunningCount(int delta) {
592	<	int wc;
591	>	final void incrementRunningCount() {
592	>	int c;
593		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
594	<	wc = workerCounts,
595	<	wc + delta));
537	<	}
538	<
539	<	/**
540	<	* Write fence for user modifications of pool parameters
541	<	* (parallelism. etc).  Note that it doesn't matter if CAS fails.
542	<	*/
543	<	private void workerCountWriteFence() {
544	<	int wc;
545	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
546	<	wc = workerCounts, wc);
594	>	c = workerCounts,
595	>	c + ONE_RUNNING));
596		}
597
598		/**
599	<	* Read fence for external reads of pool parameters
551	<	* (parallelism. maxPoolSize, etc).
599	>	* Tries to decrement running count unless already zero
600		*/
601	<	private void workerCountReadFence() {
602	<	int ignore = workerCounts;
601	>	final boolean tryDecrementRunningCount() {
602	>	int wc = workerCounts;
603	>	if ((wc & RUNNING_COUNT_MASK) == 0)
604	>	return false;
605	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
606	>	wc, wc - ONE_RUNNING);
607		}
608
609		/**
610	<	* Tries incrementing active count; fails on contention.
611	<	* Called by workers before executing tasks.
610	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
611	>	* (rarely) necessary when other count updates lag.
612		*
613	<	* @return true on success
613	>	* @param dr -- either zero or ONE_RUNNING
614	>	* @param dt -- either zero or ONE_TOTAL
615		*/
616	<	final boolean tryIncrementActiveCount() {
617	<	int c;
618	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
619	<	c = runState, c + ONE_ACTIVE);
616	>	private void decrementWorkerCounts(int dr, int dt) {
617	>	for (;;) {
618	>	int wc = workerCounts;
619	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
620	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
621	>	if ((runState & TERMINATED) != 0)
622	>	return; // lagging termination on a backout
623	>	Thread.yield();
624	>	}
625	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
626	>	wc, wc - (dr + dt)))
627	>	return;
628	>	}
629		}
630
631		/**
#	Line 573 | Line 635 | public class ForkJoinPool extends Abstra
635		final boolean tryDecrementActiveCount() {
636		int c;
637		return UNSAFE.compareAndSwapInt(this, runStateOffset,
638	<	c = runState, c - ONE_ACTIVE);
638	>	c = runState, c - 1);
639		}
640
641		/**
#	Line 602 | Line 664 | public class ForkJoinPool extends Abstra
664		lock.lock();
665		try {
666		ForkJoinWorkerThread[] ws = workers;
667	<	int len = ws.length;
668	<	if (k < 0 || k >= len || ws[k] != null) {
669	<	for (k = 0; k < len && ws[k] != null; ++k)
667	>	int n = ws.length;
668	>	if (k < 0 || k >= n || ws[k] != null) {
669	>	for (k = 0; k < n && ws[k] != null; ++k)
670		;
671	<	if (k == len)
672	<	ws = Arrays.copyOf(ws, len << 1);
671	>	if (k == n)
672	>	ws = Arrays.copyOf(ws, n << 1);
673		}
674		ws[k] = w;
675		workers = ws; // volatile array write ensures slot visibility
#	Line 618 | Line 680 | public class ForkJoinPool extends Abstra
680		}
681
682		/**
683	<	* Nulls out record of worker in workers array
683	>	* Nulls out record of worker in workers array.
684		*/
685		private void forgetWorker(ForkJoinWorkerThread w) {
686		int idx = w.poolIndex;
687	<	// Locking helps method recordWorker avoid unecessary expansion
687	>	// Locking helps method recordWorker avoid unnecessary expansion
688		final ReentrantLock lock = this.workerLock;
689		lock.lock();
690		try {
#	Line 634 | Line 696 | public class ForkJoinPool extends Abstra
696		}
697		}
698
637	–	// adding and removing workers
638	–
699		/**
700	<	* Tries to create and add new worker. Assumes that worker counts
701	<	* are already updated to accommodate the worker, so adjusts on
702	<	* failure.
700	>	* Final callback from terminating worker.  Removes record of
701	>	* worker from array, and adjusts counts. If pool is shutting
702	>	* down, tries to complete termination.
703		*
704	<	* @return new worker or null if creation failed
704	>	* @param w the worker
705		*/
706	<	private ForkJoinWorkerThread addWorker() {
707	<	ForkJoinWorkerThread w = null;
708	<	try {
709	<	w = factory.newThread(this);
710	<	} finally { // Adjust on either null or exceptional factory return
711	<	if (w == null) {
712	<	onWorkerCreationFailure();
713	<	return null;
706	>	final void workerTerminated(ForkJoinWorkerThread w) {
707	>	forgetWorker(w);
708	>	decrementWorkerCounts(w.isTrimmed() ? 0 : ONE_RUNNING, ONE_TOTAL);
709	>	while (w.stealCount != 0) // collect final count
710	>	tryAccumulateStealCount(w);
711	>	tryTerminate(false);
712	>	}
713	>
714	>	// Waiting for and signalling events
715	>
716	>	/**
717	>	* Releases workers blocked on a count not equal to current count.
718	>	* Normally called after precheck that eventWaiters isn't zero to
719	>	* avoid wasted array checks. Gives up upon a change in count or
720	>	* upon releasing two workers, letting others take over.
721	>	*/
722	>	private void releaseEventWaiters() {
723	>	ForkJoinWorkerThread[] ws = workers;
724	>	int n = ws.length;
725	>	long h = eventWaiters;
726	>	int ec = eventCount;
727	>	boolean releasedOne = false;
728	>	ForkJoinWorkerThread w; int id;
729	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
730	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
731	>	id < n && (w = ws[id]) != null) {
732	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
733	>	h,  w.nextWaiter)) {
734	>	LockSupport.unpark(w);
735	>	if (releasedOne) // exit on second release
736	>	break;
737	>	releasedOne = true;
738		}
739	+	if (eventCount != ec)
740	+	break;
741	+	h = eventWaiters;
742		}
656	–	w.start(recordWorker(w), locallyFifo, ueh);
657	–	return w;
743		}
744
745		/**
746	<	* Adjusts counts upon failure to create worker
746	>	* Tries to advance eventCount and releases waiters. Called only
747	>	* from workers.
748		*/
749	<	private void onWorkerCreationFailure() {
750	<	int c;
751	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
752	<	c = workerCounts,
753	<	c - (ONE_RUNNING|ONE_TOTAL)));
668	<	tryTerminate(false); // in case of failure during shutdown
749	>	final void signalWork() {
750	>	int c; // try to increment event count -- CAS failure OK
751	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
752	>	if (eventWaiters != 0L)
753	>	releaseEventWaiters();
754		}
755
756		/**
757	<	* Create enough total workers to establish target parallelism,
758	<	* giving up if terminating or addWorker fails
757	>	* Adds the given worker to event queue and blocks until
758	>	* terminating or event count advances from the given value
759	>	*
760	>	* @param w the calling worker thread
761	>	* @param ec the count
762		*/
763	<	private void ensureEnoughTotalWorkers() {
764	<	int wc;
765	<	while (runState < TERMINATING &&
766	<	((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism) {
767	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
768	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
769	<	addWorker() == null))
763	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
764	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
765	>	long h;
766	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
767	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
768	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
769	>	eventCount == ec) {
770	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
771	>	w.nextWaiter = h, nh)) {
772	>	awaitEvent(w, ec);
773		break;
774	+	}
775		}
776		}
777
778		/**
779	<	* Final callback from terminating worker.  Removes record of
780	<	* worker from array, and adjusts counts. If pool is shutting
781	<	* down, tries to complete terminatation, else possibly replaces
782	<	* the worker.
779	>	* Blocks the given worker (that has already been entered as an
780	>	* event waiter) until terminating or event count advances from
781	>	* the given value. The oldest (first) waiter uses a timed wait to
782	>	* occasionally one-by-one shrink the number of workers (to a
783	>	* minimum of one) if the pool has not been used for extended
784	>	* periods.
785		*
786	<	* @param w the worker
786	>	* @param w the calling worker thread
787	>	* @param ec the count
788		*/
789	<	final void workerTerminated(ForkJoinWorkerThread w) {
790	<	if (w.active) { // force inactive
791	<	w.active = false;
792	<	do {} while (!tryDecrementActiveCount());
789	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
790	>	while (eventCount == ec) {
791	>	if (tryAccumulateStealCount(w)) { // transfer while idle
792	>	boolean untimed = (w.nextWaiter != 0L ||
793	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
794	>	long startTime = untimed ? 0 : System.nanoTime();
795	>	Thread.interrupted();         // clear/ignore interrupt
796	>	if (eventCount != ec || w.isTerminating())
797	>	break;                    // recheck after clear
798	>	if (untimed)
799	>	LockSupport.park(w);
800	>	else {
801	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
802	>	if (eventCount != ec || w.isTerminating())
803	>	break;
804	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
805	>	tryShutdownUnusedWorker(ec);
806	>	}
807	>	}
808		}
699	–	forgetWorker(w);
700	–
701	–	// decrement total count, and if was running, running count
702	–	int unit = w.isTrimmed()? ONE_TOTAL : (ONE_RUNNING|ONE_TOTAL);
703	–	int wc;
704	–	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
705	–	wc = workerCounts, wc - unit));
706	–
707	–	accumulateStealCount(w); // collect final count
708	–	if (!tryTerminate(false))
709	–	ensureEnoughTotalWorkers();
809		}
810
811	<	// Waiting for and signalling events
811	>	// Maintaining parallelism
812
813		/**
814	<	* Ensures eventCount on exit is different (mod 2^32) than on
716	<	* entry.  CAS failures are OK -- any change in count suffices.
814	>	* Pushes worker onto the spare stack.
815		*/
816	<	private void advanceEventCount() {
817	<	int c;
818	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
816	>	final void pushSpare(ForkJoinWorkerThread w) {
817	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
818	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
819	>	w.nextSpare = spareWaiters,ns));
820		}
821
822		/**
823	<	* Releases workers blocked on a count not equal to current count.
824	<	*/
825	<	final void releaseWaiters() {
826	<	long top;
827	<	int id;
828	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
829	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
830	<	ForkJoinWorkerThread[] ws = workers;
831	<	ForkJoinWorkerThread w;
832	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
833	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
834	<	top, w.nextWaiter))
823	>	* Tries (once) to resume a spare if the number of running
824	>	* threads is less than target.
825	>	*/
826	>	private void tryResumeSpare() {
827	>	int sw, id;
828	>	ForkJoinWorkerThread[] ws = workers;
829	>	int n = ws.length;
830	>	ForkJoinWorkerThread w;
831	>	if ((sw = spareWaiters) != 0 &&
832	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
833	>	id < n && (w = ws[id]) != null &&
834	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
835	>	spareWaiters == sw &&
836	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
837	>	sw, w.nextSpare)) {
838	>	int c; // increment running count before resume
839	>	do {} while (!UNSAFE.compareAndSwapInt
840	>	(this, workerCountsOffset,
841	>	c = workerCounts, c + ONE_RUNNING));
842	>	if (w.tryUnsuspend())
843		LockSupport.unpark(w);
844	+	else   // back out if w was shutdown
845	+	decrementWorkerCounts(ONE_RUNNING, 0);
846		}
847		}
848
849		/**
850	<	* Advances eventCount and releases waiters until interference by
851	<	* other releasing threads is detected.
850	>	* Tries to increase the number of running workers if below target
851	>	* parallelism: If a spare exists tries to resume it via
852	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
853	>	* existing workers are busy, adds a new worker. In all cases also
854	>	* helps wake up releasable workers waiting for work.
855		*/
856	<	final void signalWork() {
857	<	int ec;
858	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
859	<	outer:for (;;) {
860	<	long top = eventWaiters;
861	<	ec = eventCount;
862	<	for (;;) {
863	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
864	<	int id = (int)(top & WAITER_INDEX_MASK);
865	<	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
866	<	return;
867	<	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
868	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
869	<	top, top = w.nextWaiter))
870	<	continue outer;      // possibly stale; reread
871	<	LockSupport.unpark(w);
872	<	if (top != eventWaiters) // let someone else take over
873	<	return;
856	>	private void helpMaintainParallelism() {
857	>	int pc = parallelism;
858	>	int wc, rs, tc;
859	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
860	>	(rs = runState) < TERMINATING) {
861	>	if (spareWaiters != 0)
862	>	tryResumeSpare();
863	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
864	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
865	>	break;   // enough total
866	>	else if (runState == rs && workerCounts == wc &&
867	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
868	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
869	>	ForkJoinWorkerThread w = null;
870	>	Throwable fail = null;
871	>	try {
872	>	w = factory.newThread(this);
873	>	} catch (Throwable ex) {
874	>	fail = ex;
875	>	}
876	>	if (w == null) { // null or exceptional factory return
877	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
878	>	tryTerminate(false); // handle failure during shutdown
879	>	// If originating from an external caller,
880	>	// propagate exception, else ignore
881	>	if (fail != null && runState < TERMINATING &&
882	>	!(Thread.currentThread() instanceof
883	>	ForkJoinWorkerThread))
884	>	UNSAFE.throwException(fail);
885	>	break;
886	>	}
887	>	w.start(recordWorker(w), ueh);
888	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
889	>	int c; // advance event count
890	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
891	>	c = eventCount, c+1);
892	>	break; // add at most one unless total below target
893	>	}
894		}
895		}
896	+	if (eventWaiters != 0L)
897	+	releaseEventWaiters();
898		}
899
900		/**
901	<	* If worker is inactive, blocks until terminating or event count
902	<	* advances from last value held by worker; in any case helps
903	<	* release others.
901	>	* Callback from the oldest waiter in awaitEvent waking up after a
902	>	* period of non-use. If all workers are idle, tries (once) to
903	>	* shutdown an event waiter or a spare, if one exists. Note that
904	>	* we don't need CAS or locks here because the method is called
905	>	* only from one thread occasionally waking (and even misfires are
906	>	* OK). Note that until the shutdown worker fully terminates,
907	>	* workerCounts will overestimate total count, which is tolerable.
908		*
909	<	* @param w the calling worker thread
909	>	* @param ec the event count waited on by caller (to abort
910	>	* attempt if count has since changed).
911		*/
912	<	private void eventSync(ForkJoinWorkerThread w) {
913	<	if (!w.active) {
914	<	int prev = w.lastEventCount;
915	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
916	<	((long)(w.poolIndex + 1)));
917	<	long top;
918	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
919	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
920	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
921	<	eventCount == prev) {
922	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
923	<	w.nextWaiter = top, nextTop)) {
924	<	accumulateStealCount(w); // transfer steals while idle
925	<	Thread.interrupted();    // clear/ignore interrupt
926	<	while (eventCount == prev)
927	<	w.doPark();
928	<	break;
929	<	}
912	>	private void tryShutdownUnusedWorker(int ec) {
913	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
914	>	ForkJoinWorkerThread[] ws = workers;
915	>	int n = ws.length;
916	>	ForkJoinWorkerThread w = null;
917	>	boolean shutdown = false;
918	>	int sw;
919	>	long h;
920	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
921	>	int id = (sw & SPARE_ID_MASK) - 1;
922	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
923	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
924	>	sw, w.nextSpare))
925	>	shutdown = true;
926	>	}
927	>	else if ((h = eventWaiters) != 0L) {
928	>	long nh;
929	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
930	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
931	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
932	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
933	>	shutdown = true;
934	>	}
935	>	if (w != null && shutdown) {
936	>	w.shutdown();
937	>	LockSupport.unpark(w);
938		}
792	–	w.lastEventCount = eventCount;
939		}
940	<	releaseWaiters();
940	>	releaseEventWaiters(); // in case of interference
941		}
942
943		/**
944		* Callback from workers invoked upon each top-level action (i.e.,
945	<	* stealing a task or taking a submission and running
946	<	* it). Performs one or both of the following:
945	>	* stealing a task or taking a submission and running it).
946	>	* Performs one or more of the following:
947		*
948	<	* * If the worker cannot find work, updates its active status to
949	<	* inactive and updates activeCount unless there is contention, in
950	<	* which case it may try again (either in this or a subsequent
951	<	* call).  Additionally, awaits the next task event and/or helps
952	<	* wake up other releasable waiters.
953	<	*
954	<	* * If there are too many running threads, suspends this worker
955	<	* (first forcing inactivation if necessary).  If it is not
956	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
957	<	* -- killed while suspended within suspendAsSpare. Otherwise,
958	<	* upon resume it rechecks to make sure that it is still needed.
948	>	* 1. If the worker is active and either did not run a task
949	>	*    or there are too many workers, try to set its active status
950	>	*    to inactive and update activeCount. On contention, we may
951	>	*    try again in this or a subsequent call.
952	>	*
953	>	* 2. If not enough total workers, help create some.
954	>	*
955	>	* 3. If there are too many running workers, suspend this worker
956	>	*    (first forcing inactive if necessary).  If it is not needed,
957	>	*    it may be shutdown while suspended (via
958	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
959	>	*    rechecks running thread count and need for event sync.
960	>	*
961	>	* 4. If worker did not run a task, await the next task event via
962	>	*    eventSync if necessary (first forcing inactivation), upon
963	>	*    which the worker may be shutdown via
964	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
965	>	*    existing event waiters that are now releasable,
966		*
967		* @param w the worker
968	<	* @param worked false if the worker scanned for work but didn't
816	<	* find any (in which case it may block waiting for work).
968	>	* @param ran true if worker ran a task since last call to this method
969		*/
970	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
970	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
971	>	int wec = w.lastEventCount;
972		boolean active = w.active;
973	<	boolean inactivate = !worked & active;
974	<	for (;;) {
975	<	if (inactivate) {
976	<	int c = runState;
977	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
978	<	c, c - ONE_ACTIVE))
979	<	inactivate = active = w.active = false;
973	>	boolean inactivate = false;
974	>	int pc = parallelism;
975	>	while (w.runState == 0) {
976	>	int rs = runState;
977	>	if (rs >= TERMINATING) { // propagate shutdown
978	>	w.shutdown();
979	>	break;
980		}
981	+	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
982	+	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
983	+	inactivate = active = w.active = false;
984		int wc = workerCounts;
985	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
986	<	if (!worked)
987	<	eventSync(w);
988	<	return;
989	<	}
990	<	if (!(inactivate |= active) &&  // must inactivate to suspend
991	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
992	<	wc, wc - ONE_RUNNING) &&
993	<	!w.suspendAsSpare())        // false if trimmed
994	<	return;
995	<	}
996	<	}
997	<
998	<	/**
999	<	* Adjusts counts and creates or resumes compensating threads for
1000	<	* a worker about to block on task joinMe, returning early if
845	<	* joinMe becomes ready. First tries resuming an existing spare
846	<	* (which usually also avoids any count adjustment), but must then
847	<	* decrement running count to determine whether a new thread is
848	<	* needed. See above for fuller explanation.
849	<	*/
850	<	final void preJoin(ForkJoinTask<?> joinMe) {
851	<	boolean dec = false;       // true when running count decremented
852	<	for (;;) {
853	<	releaseWaiters();      // help other threads progress
854	<
855	<	if (joinMe.status < 0) // surround spare search with done checks
856	<	return;
857	<	ForkJoinWorkerThread spare = null;
858	<	for (ForkJoinWorkerThread w : workers) {
859	<	if (w != null && w.isSuspended()) {
860	<	spare = w;
985	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
986	>	if (!(inactivate |= active) && // must inactivate to suspend
987	>	workerCounts == wc &&      // try to suspend as spare
988	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
989	>	wc, wc - ONE_RUNNING))
990	>	w.suspendAsSpare();
991	>	}
992	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
993	>	helpMaintainParallelism();     // not enough workers
994	>	else if (!ran) {
995	>	long h = eventWaiters;
996	>	int ec = eventCount;
997	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
998	>	releaseEventWaiters();     // release others before waiting
999	>	else if (ec != wec) {
1000	>	w.lastEventCount = ec;     // no need to wait
1001		break;
1002		}
1003	+	else if (!(inactivate |= active))
1004	+	eventSync(w, wec);         // must inactivate before sync
1005		}
1006	<	if (joinMe.status < 0)
1007	<	return;
866	<
867	<	if (spare != null && spare.tryUnsuspend()) {
868	<	if (dec || joinMe.requestSignal() < 0) {
869	<	int c;
870	<	do {} while (!UNSAFE.compareAndSwapInt(this,
871	<	workerCountsOffset,
872	<	c = workerCounts,
873	<	c + ONE_RUNNING));
874	<	} // else no net count change
875	<	LockSupport.unpark(spare);
876	<	return;
877	<	}
878	<
879	<	int wc = workerCounts; // decrement running count
880	<	if (!dec && (wc & RUNNING_COUNT_MASK) != 0 &&
881	<	(dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
882	<	wc, wc -= ONE_RUNNING)) &&
883	<	joinMe.requestSignal() < 0) { // cannot block
884	<	int c;                        // back out
885	<	do {} while (!UNSAFE.compareAndSwapInt(this,
886	<	workerCountsOffset,
887	<	c = workerCounts,
888	<	c + ONE_RUNNING));
889	<	return;
890	<	}
891	<
892	<	if (dec) {
893	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
894	<	int pc = parallelism;
895	<	int dc = pc - (wc & RUNNING_COUNT_MASK); // deficit count
896	<	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
897	<	!maintainsParallelism)) ||
898	<	tc >= maxPoolSize) // cannot add
899	<	return;
900	<	if (spare == null &&
901	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
902	<	wc + (ONE_RUNNING|ONE_TOTAL))) {
903	<	addWorker();
904	<	return;
905	<	}
906	<	}
1006	>	else
1007	>	break;
1008		}
1009		}
1010
1011		/**
1012	<	* Same idea as preJoin but with too many differing details to
1013	<	* integrate: There are no task-based signal counts, and only one
1014	<	* way to do the actual blocking. So for simplicity it is directly
1015	<	* incorporated into this method.
1016	<	*/
1017	<	final void doBlock(ManagedBlocker blocker, boolean maintainPar)
1018	<	throws InterruptedException {
1019	<	maintainPar &= maintainsParallelism; // override
1020	<	boolean dec = false;
1021	<	boolean done = false;
1022	<	for (;;) {
1023	<	releaseWaiters();
1024	<	if (done = blocker.isReleasable())
1012	>	* Helps and/or blocks awaiting join of the given task.
1013	>	* See above for explanation.
1014	>	*
1015	>	* @param joinMe the task to join
1016	>	* @param worker the current worker thread
1017	>	* @param timed true if wait should time out
1018	>	* @param nanos timeout value if timed
1019	>	*/
1020	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker,
1021	>	boolean timed, long nanos) {
1022	>	long startTime = timed? System.nanoTime() : 0L;
1023	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1024	>	while (joinMe.status >= 0) {
1025	>	int wc;
1026	>	long nt = 0L;
1027	>	if (runState >= TERMINATING) {
1028	>	joinMe.cancelIgnoringExceptions();
1029		break;
925	–	ForkJoinWorkerThread spare = null;
926	–	for (ForkJoinWorkerThread w : workers) {
927	–	if (w != null && w.isSuspended()) {
928	–	spare = w;
929	–	break;
930	–	}
1030		}
1031	<	if (done = blocker.isReleasable())
1031	>	worker.helpJoinTask(joinMe);
1032	>	if (joinMe.status < 0)
1033		break;
1034	<	if (spare != null && spare.tryUnsuspend()) {
1035	<	if (dec) {
1036	<	int c;
1037	<	do {} while (!UNSAFE.compareAndSwapInt(this,
938	<	workerCountsOffset,
939	<	c = workerCounts,
940	<	c + ONE_RUNNING));
941	<	}
942	<	LockSupport.unpark(spare);
1034	>	else if (retries > 0)
1035	>	--retries;
1036	>	else if (timed &&
1037	>	(nt = nanos - (System.nanoTime() - startTime)) <= 0L)
1038		break;
1039	<	}
1040	<	int wc = workerCounts;
1041	<	if (!dec && (wc & RUNNING_COUNT_MASK) != 0)
1042	<	dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1043	<	wc, wc -= ONE_RUNNING);
1044	<	if (dec) {
1045	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1046	<	int pc = parallelism;
1047	<	int dc = pc - (wc & RUNNING_COUNT_MASK);
1048	<	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
1049	<	!maintainPar)) ||
1050	<	tc >= maxPoolSize)
1051	<	break;
1052	<	if (spare == null &&
1053	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1054	<	wc + (ONE_RUNNING|ONE_TOTAL))){
1055	<	addWorker();
1056	<	break;
1039	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1040	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1041	>	wc, wc - ONE_RUNNING)) {
1042	>	int stat, c; long h;
1043	>	while ((stat = joinMe.status) >= 0 &&
1044	>	(h = eventWaiters) != 0L && // help release others
1045	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1046	>	releaseEventWaiters();
1047	>	if (stat >= 0) {
1048	>	if ((workerCounts & RUNNING_COUNT_MASK) != 0) {
1049	>	long ms; int ns;
1050	>	if (!timed) {
1051	>	ms = JOIN_TIMEOUT_MILLIS;
1052	>	ns = 0;
1053	>	}
1054	>	else { // at most JOIN_TIMEOUT_MILLIS per wait
1055	>	ms = nt / 1000000;
1056	>	if (ms > JOIN_TIMEOUT_MILLIS) {
1057	>	ms = JOIN_TIMEOUT_MILLIS;
1058	>	ns = 0;
1059	>	}
1060	>	else
1061	>	ns = (int) (nt % 1000000);
1062	>	}
1063	>	stat = joinMe.internalAwaitDone(ms, ns);
1064	>	}
1065	>	if (stat >= 0) // timeout or no running workers
1066	>	helpMaintainParallelism();
1067		}
1068	<	}
1069	<	}
1070	<
1071	<	try {
1072	<	if (!done)
968	<	do {} while (!blocker.isReleasable() && !blocker.block());
969	<	} finally {
970	<	if (dec) {
971	<	int c;
972	<	do {} while (!UNSAFE.compareAndSwapInt(this,
973	<	workerCountsOffset,
974	<	c = workerCounts,
975	<	c + ONE_RUNNING));
1068	>	do {} while (!UNSAFE.compareAndSwapInt
1069	>	(this, workerCountsOffset,
1070	>	c = workerCounts, c + ONE_RUNNING));
1071	>	if (stat < 0)
1072	>	break;   // else restart
1073		}
1074		}
1075		}
1076
1077		/**
1078	<	* Unless there are not enough other running threads, adjusts
982	<	* counts for a a worker in performing helpJoin that cannot find
983	<	* any work, so that this worker can now block.
984	<	*
985	<	* @return true if worker may block
1078	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1079		*/
1080	<	final boolean preBlockHelpingJoin(ForkJoinTask<?> joinMe) {
1081	<	while (joinMe.status >= 0) {
1082	<	releaseWaiters(); // help other threads progress
1083	<
1084	<	// if a spare exists, resume it to maintain parallelism level
1085	<	if ((workerCounts & RUNNING_COUNT_MASK) <= parallelism) {
1086	<	ForkJoinWorkerThread spare = null;
1087	<	for (ForkJoinWorkerThread w : workers) {
1088	<	if (w != null && w.isSuspended()) {
1089	<	spare = w;
1090	<	break;
1091	<	}
1092	<	}
1093	<	if (joinMe.status < 0)
1094	<	break;
1095	<	if (spare != null) {
1096	<	if (spare.tryUnsuspend()) {
1097	<	boolean canBlock = true;
1005	<	if (joinMe.requestSignal() < 0) {
1006	<	canBlock = false; // already done
1007	<	int c;
1008	<	do {} while (!UNSAFE.compareAndSwapInt
1009	<	(this, workerCountsOffset,
1010	<	c = workerCounts, c + ONE_RUNNING));
1011	<	}
1012	<	LockSupport.unpark(spare);
1013	<	return canBlock;
1080	>	final void awaitBlocker(ManagedBlocker blocker)
1081	>	throws InterruptedException {
1082	>	while (!blocker.isReleasable()) {
1083	>	int wc = workerCounts;
1084	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1085	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1086	>	wc, wc - ONE_RUNNING)) {
1087	>	try {
1088	>	while (!blocker.isReleasable()) {
1089	>	long h = eventWaiters;
1090	>	if (h != 0L &&
1091	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1092	>	releaseEventWaiters();
1093	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1094	>	runState < TERMINATING)
1095	>	helpMaintainParallelism();
1096	>	else if (blocker.block())
1097	>	break;
1098		}
1099	<	continue; // recheck -- another spare may exist
1099	>	} finally {
1100	>	int c;
1101	>	do {} while (!UNSAFE.compareAndSwapInt
1102	>	(this, workerCountsOffset,
1103	>	c = workerCounts, c + ONE_RUNNING));
1104		}
1017	–	}
1018	–
1019	–	int wc = workerCounts; // reread to shorten CAS window
1020	–	int rc = wc & RUNNING_COUNT_MASK;
1021	–	if (rc <= 2) // keep this and at most one other thread alive
1022	–	break;
1023	–
1024	–	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1025	–	wc, wc - ONE_RUNNING)) {
1026	–	if (joinMe.requestSignal() >= 0)
1027	–	return true;
1028	–	int c;                        // back out
1029	–	do {} while (!UNSAFE.compareAndSwapInt
1030	–	(this, workerCountsOffset,
1031	–	c = workerCounts, c + ONE_RUNNING));
1105		break;
1106		}
1107		}
1035	–	return false;
1108		}
1109
1110		/**
#	Line 1056 | Line 1128 | public class ForkJoinPool extends Abstra
1128		// Finish now if all threads terminated; else in some subsequent call
1129		if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1130		advanceRunLevel(TERMINATED);
1131	<	terminationLatch.countDown();
1131	>	termination.forceTermination();
1132		}
1133		return true;
1134		}
1135
1136	+
1137		/**
1138		* Actions on transition to TERMINATING
1139	+	*
1140	+	* Runs up to four passes through workers: (0) shutting down each
1141	+	* (without waking up if parked) to quickly spread notifications
1142	+	* without unnecessary bouncing around event queues etc (1) wake
1143	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1144	+	* interrupted workers
1145		*/
1146		private void startTerminating() {
1147	<	// Clear out and cancel submissions, ignoring exceptions
1147	>	cancelSubmissions();
1148	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1149	>	int c; // advance event count
1150	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1151	>	c = eventCount, c+1);
1152	>	eventWaiters = 0L; // clobber lists
1153	>	spareWaiters = 0;
1154	>	for (ForkJoinWorkerThread w : workers) {
1155	>	if (w != null) {
1156	>	w.shutdown();
1157	>	if (passes > 0 && !w.isTerminated()) {
1158	>	w.cancelTasks();
1159	>	LockSupport.unpark(w);
1160	>	if (passes > 1 && !w.isInterrupted()) {
1161	>	try {
1162	>	w.interrupt();
1163	>	} catch (SecurityException ignore) {
1164	>	}
1165	>	}
1166	>	}
1167	>	}
1168	>	}
1169	>	}
1170	>	}
1171	>
1172	>	/**
1173	>	* Clears out and cancels submissions, ignoring exceptions.
1174	>	*/
1175	>	private void cancelSubmissions() {
1176		ForkJoinTask<?> task;
1177		while ((task = submissionQueue.poll()) != null) {
1178		try {
#	Line 1073 | Line 1180 | public class ForkJoinPool extends Abstra
1180		} catch (Throwable ignore) {
1181		}
1182		}
1076	–	// Propagate run level
1077	–	for (ForkJoinWorkerThread w : workers) {
1078	–	if (w != null)
1079	–	w.shutdown();    // also resumes suspended workers
1080	–	}
1081	–	// Ensure no straggling local tasks
1082	–	for (ForkJoinWorkerThread w : workers) {
1083	–	if (w != null)
1084	–	w.cancelTasks();
1085	–	}
1086	–	// Wake up idle workers
1087	–	advanceEventCount();
1088	–	releaseWaiters();
1089	–	// Unstick pending joins
1090	–	for (ForkJoinWorkerThread w : workers) {
1091	–	if (w != null && !w.isTerminated()) {
1092	–	try {
1093	–	w.interrupt();
1094	–	} catch (SecurityException ignore) {
1095	–	}
1096	–	}
1097	–	}
1183		}
1184
1185		// misc support for ForkJoinWorkerThread
1186
1187		/**
1188	<	* Returns pool number
1188	>	* Returns pool number.
1189		*/
1190		final int getPoolNumber() {
1191		return poolNumber;
1192		}
1193
1194		/**
1195	<	* Accumulates steal count from a worker, clearing
1196	<	* the worker's value
1195	>	* Tries to accumulate steal count from a worker, clearing
1196	>	* the worker's value if successful.
1197	>	*
1198	>	* @return true if worker steal count now zero
1199		*/
1200	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1200	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1201		int sc = w.stealCount;
1202	<	if (sc != 0) {
1203	<	long c;
1204	<	w.stealCount = 0;
1205	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1206	<	c = stealCount, c + sc));
1202	>	long c = stealCount;
1203	>	// CAS even if zero, for fence effects
1204	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1205	>	if (sc != 0)
1206	>	w.stealCount = 0;
1207	>	return true;
1208		}
1209	+	return sc == 0;
1210		}
1211
1212		/**
#	Line 1125 | Line 1214 | public class ForkJoinPool extends Abstra
1214		* active thread.
1215		*/
1216		final int idlePerActive() {
1217	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1218	<	int pc = parallelism; // use targeted parallelism, not rc
1217	>	int pc = parallelism; // use parallelism, not rc
1218	>	int ac = runState;    // no mask -- artificially boosts during shutdown
1219		// Use exact results for small values, saturate past 4
1220	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1220	>	return ((pc <= ac) ? 0 :
1221	>	(pc >>> 1 <= ac) ? 1 :
1222	>	(pc >>> 2 <= ac) ? 3 :
1223	>	pc >>> 3);
1224		}
1225
1226		// Public and protected methods
#	Line 1137 | Line 1229 | public class ForkJoinPool extends Abstra
1229
1230		/**
1231		* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1232	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1233	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1232	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1233	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1234	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1235		*
1236		* @throws SecurityException if a security manager exists and
1237		*         the caller is not permitted to modify threads
#	Line 1147 | Line 1240 | public class ForkJoinPool extends Abstra
1240		*/
1241		public ForkJoinPool() {
1242		this(Runtime.getRuntime().availableProcessors(),
1243	<	defaultForkJoinWorkerThreadFactory);
1243	>	defaultForkJoinWorkerThreadFactory, null, false);
1244		}
1245
1246		/**
1247		* Creates a {@code ForkJoinPool} with the indicated parallelism
1248	<	* level and using the {@linkplain
1249	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1248	>	* level, the {@linkplain
1249	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1250	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1251		*
1252		* @param parallelism the parallelism level
1253		* @throws IllegalArgumentException if parallelism less than or
#	Line 1164 | Line 1258 | public class ForkJoinPool extends Abstra
1258		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1259		*/
1260		public ForkJoinPool(int parallelism) {
1261	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1261	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1262		}
1263
1264		/**
1265	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1172	<	* java.lang.Runtime#availableProcessors}, and using the given
1173	<	* thread factory.
1265	>	* Creates a {@code ForkJoinPool} with the given parameters.
1266		*
1267	<	* @param factory the factory for creating new threads
1268	<	* @throws NullPointerException if the factory is null
1269	<	* @throws SecurityException if a security manager exists and
1270	<	*         the caller is not permitted to modify threads
1271	<	*         because it does not hold {@link
1272	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1273	<	*/
1274	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1275	<	this(Runtime.getRuntime().availableProcessors(), factory);
1276	<	}
1277	<
1278	<	/**
1279	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1188	<	* thread factory.
1189	<	*
1190	<	* @param parallelism the parallelism level
1191	<	* @param factory the factory for creating new threads
1267	>	* @param parallelism the parallelism level. For default value,
1268	>	* use {@link java.lang.Runtime#availableProcessors}.
1269	>	* @param factory the factory for creating new threads. For default value,
1270	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1271	>	* @param handler the handler for internal worker threads that
1272	>	* terminate due to unrecoverable errors encountered while executing
1273	>	* tasks. For default value, use {@code null}.
1274	>	* @param asyncMode if true,
1275	>	* establishes local first-in-first-out scheduling mode for forked
1276	>	* tasks that are never joined. This mode may be more appropriate
1277	>	* than default locally stack-based mode in applications in which
1278	>	* worker threads only process event-style asynchronous tasks.
1279	>	* For default value, use {@code false}.
1280		* @throws IllegalArgumentException if parallelism less than or
1281		*         equal to zero, or greater than implementation limit
1282		* @throws NullPointerException if the factory is null
#	Line 1197 | Line 1285 | public class ForkJoinPool extends Abstra
1285		*         because it does not hold {@link
1286		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1287		*/
1288	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1288	>	public ForkJoinPool(int parallelism,
1289	>	ForkJoinWorkerThreadFactory factory,
1290	>	Thread.UncaughtExceptionHandler handler,
1291	>	boolean asyncMode) {
1292		checkPermission();
1293		if (factory == null)
1294		throw new NullPointerException();
1295	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1295	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1296		throw new IllegalArgumentException();
1206	–	this.poolNumber = poolNumberGenerator.incrementAndGet();
1207	–	int arraySize = initialArraySizeFor(parallelism);
1297		this.parallelism = parallelism;
1298		this.factory = factory;
1299	<	this.maxPoolSize = MAX_THREADS;
1300	<	this.maintainsParallelism = true;
1299	>	this.ueh = handler;
1300	>	this.locallyFifo = asyncMode;
1301	>	int arraySize = initialArraySizeFor(parallelism);
1302		this.workers = new ForkJoinWorkerThread[arraySize];
1303		this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1304		this.workerLock = new ReentrantLock();
1305	<	this.terminationLatch = new CountDownLatch(1);
1306	<	// Start first worker; remaining workers added upon first submission
1217	<	workerCounts = ONE_RUNNING | ONE_TOTAL;
1218	<	addWorker();
1305	>	this.termination = new Phaser(1);
1306	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1307		}
1308
1309		/**
#	Line 1223 | Line 1311 | public class ForkJoinPool extends Abstra
1311		* @param pc the initial parallelism level
1312		*/
1313		private static int initialArraySizeFor(int pc) {
1314	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1315	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1314	>	// If possible, initially allocate enough space for one spare
1315	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1316	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1317		size |= size >>> 1;
1318		size |= size >>> 2;
1319		size |= size >>> 4;
#	Line 1235 | Line 1324 | public class ForkJoinPool extends Abstra
1324		// Execution methods
1325
1326		/**
1327	<	* Common code for execute, invoke and submit
1327	>	* Submits task and creates, starts, or resumes some workers if necessary
1328		*/
1329		private <T> void doSubmit(ForkJoinTask<T> task) {
1241	–	if (task == null)
1242	–	throw new NullPointerException();
1243	–	if (runState >= SHUTDOWN)
1244	–	throw new RejectedExecutionException();
1330		submissionQueue.offer(task);
1331	<	advanceEventCount();
1332	<	releaseWaiters();
1333	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism)
1249	<	ensureEnoughTotalWorkers();
1331	>	int c; // try to increment event count -- CAS failure OK
1332	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1333	>	helpMaintainParallelism();
1334		}
1335
1336		/**
#	Line 1259 | Line 1343 | public class ForkJoinPool extends Abstra
1343		*         scheduled for execution
1344		*/
1345		public <T> T invoke(ForkJoinTask<T> task) {
1346	<	doSubmit(task);
1347	<	return task.join();
1346	>	if (task == null)
1347	>	throw new NullPointerException();
1348	>	if (runState >= SHUTDOWN)
1349	>	throw new RejectedExecutionException();
1350	>	Thread t = Thread.currentThread();
1351	>	if ((t instanceof ForkJoinWorkerThread) &&
1352	>	((ForkJoinWorkerThread)t).pool == this)
1353	>	return task.invoke();  // bypass submit if in same pool
1354	>	else {
1355	>	doSubmit(task);
1356	>	return task.join();
1357	>	}
1358	>	}
1359	>
1360	>	/**
1361	>	* Unless terminating, forks task if within an ongoing FJ
1362	>	* computation in the current pool, else submits as external task.
1363	>	*/
1364	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1365	>	if (runState >= SHUTDOWN)
1366	>	throw new RejectedExecutionException();
1367	>	Thread t = Thread.currentThread();
1368	>	if ((t instanceof ForkJoinWorkerThread) &&
1369	>	((ForkJoinWorkerThread)t).pool == this)
1370	>	task.fork();
1371	>	else
1372	>	doSubmit(task);
1373		}
1374
1375		/**
#	Line 1272 | Line 1381 | public class ForkJoinPool extends Abstra
1381		*         scheduled for execution
1382		*/
1383		public void execute(ForkJoinTask<?> task) {
1384	<	doSubmit(task);
1384	>	if (task == null)
1385	>	throw new NullPointerException();
1386	>	forkOrSubmit(task);
1387		}
1388
1389		// AbstractExecutorService methods
#	Line 1283 | Line 1394 | public class ForkJoinPool extends Abstra
1394		*         scheduled for execution
1395		*/
1396		public void execute(Runnable task) {
1397	+	if (task == null)
1398	+	throw new NullPointerException();
1399		ForkJoinTask<?> job;
1400		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1401		job = (ForkJoinTask<?>) task;
1402		else
1403		job = ForkJoinTask.adapt(task, null);
1404	<	doSubmit(job);
1404	>	forkOrSubmit(job);
1405	>	}
1406	>
1407	>	/**
1408	>	* Submits a ForkJoinTask for execution.
1409	>	*
1410	>	* @param task the task to submit
1411	>	* @return the task
1412	>	* @throws NullPointerException if the task is null
1413	>	* @throws RejectedExecutionException if the task cannot be
1414	>	*         scheduled for execution
1415	>	*/
1416	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1417	>	if (task == null)
1418	>	throw new NullPointerException();
1419	>	forkOrSubmit(task);
1420	>	return task;
1421		}
1422
1423		/**
#	Line 1297 | Line 1426 | public class ForkJoinPool extends Abstra
1426		*         scheduled for execution
1427		*/
1428		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1429	+	if (task == null)
1430	+	throw new NullPointerException();
1431		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1432	<	doSubmit(job);
1432	>	forkOrSubmit(job);
1433		return job;
1434		}
1435
#	Line 1308 | Line 1439 | public class ForkJoinPool extends Abstra
1439		*         scheduled for execution
1440		*/
1441		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1442	+	if (task == null)
1443	+	throw new NullPointerException();
1444		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1445	<	doSubmit(job);
1445	>	forkOrSubmit(job);
1446		return job;
1447		}
1448
#	Line 1319 | Line 1452 | public class ForkJoinPool extends Abstra
1452		*         scheduled for execution
1453		*/
1454		public ForkJoinTask<?> submit(Runnable task) {
1455	+	if (task == null)
1456	+	throw new NullPointerException();
1457		ForkJoinTask<?> job;
1458		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1459		job = (ForkJoinTask<?>) task;
1460		else
1461		job = ForkJoinTask.adapt(task, null);
1462	<	doSubmit(job);
1462	>	forkOrSubmit(job);
1463		return job;
1464		}
1465
1466		/**
1332	–	* Submits a ForkJoinTask for execution.
1333	–	*
1334	–	* @param task the task to submit
1335	–	* @return the task
1336	–	* @throws NullPointerException if the task is null
1337	–	* @throws RejectedExecutionException if the task cannot be
1338	–	*         scheduled for execution
1339	–	*/
1340	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1341	–	doSubmit(task);
1342	–	return task;
1343	–	}
1344	–
1345	–	/**
1467		* @throws NullPointerException       {@inheritDoc}
1468		* @throws RejectedExecutionException {@inheritDoc}
1469		*/
#	Line 1384 | Line 1505 | public class ForkJoinPool extends Abstra
1505		* @return the handler, or {@code null} if none
1506		*/
1507		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1387	–	workerCountReadFence();
1508		return ueh;
1509		}
1510
1511		/**
1392	–	* Sets the handler for internal worker threads that terminate due
1393	–	* to unrecoverable errors encountered while executing tasks.
1394	–	* Unless set, the current default or ThreadGroup handler is used
1395	–	* as handler.
1396	–	*
1397	–	* @param h the new handler
1398	–	* @return the old handler, or {@code null} if none
1399	–	* @throws SecurityException if a security manager exists and
1400	–	*         the caller is not permitted to modify threads
1401	–	*         because it does not hold {@link
1402	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1403	–	*/
1404	–	public Thread.UncaughtExceptionHandler
1405	–	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1406	–	checkPermission();
1407	–	workerCountReadFence();
1408	–	Thread.UncaughtExceptionHandler old = ueh;
1409	–	if (h != old) {
1410	–	ueh = h;
1411	–	workerCountWriteFence();
1412	–	for (ForkJoinWorkerThread w : workers) {
1413	–	if (w != null)
1414	–	w.setUncaughtExceptionHandler(h);
1415	–	}
1416	–	}
1417	–	return old;
1418	–	}
1419	–
1420	–	/**
1421	–	* Sets the target parallelism level of this pool.
1422	–	*
1423	–	* @param parallelism the target parallelism
1424	–	* @throws IllegalArgumentException if parallelism less than or
1425	–	* equal to zero or greater than maximum size bounds
1426	–	* @throws SecurityException if a security manager exists and
1427	–	*         the caller is not permitted to modify threads
1428	–	*         because it does not hold {@link
1429	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1430	–	*/
1431	–	public void setParallelism(int parallelism) {
1432	–	checkPermission();
1433	–	if (parallelism <= 0 || parallelism > maxPoolSize)
1434	–	throw new IllegalArgumentException();
1435	–	workerCountReadFence();
1436	–	int pc = this.parallelism;
1437	–	if (pc != parallelism) {
1438	–	this.parallelism = parallelism;
1439	–	workerCountWriteFence();
1440	–	// Release spares. If too many, some will die after re-suspend
1441	–	for (ForkJoinWorkerThread w : workers) {
1442	–	if (w != null && w.tryUnsuspend()) {
1443	–	updateRunningCount(1);
1444	–	LockSupport.unpark(w);
1445	–	}
1446	–	}
1447	–	ensureEnoughTotalWorkers();
1448	–	advanceEventCount();
1449	–	releaseWaiters(); // force config recheck by existing workers
1450	–	}
1451	–	}
1452	–
1453	–	/**
1512		* Returns the targeted parallelism level of this pool.
1513		*
1514		* @return the targeted parallelism level of this pool
1515		*/
1516		public int getParallelism() {
1459	–	//        workerCountReadFence(); // inlined below
1460	–	int ignore = workerCounts;
1517		return parallelism;
1518		}
1519
1520		/**
1521		* Returns the number of worker threads that have started but not
1522	<	* yet terminated.  This result returned by this method may differ
1522	>	* yet terminated.  The result returned by this method may differ
1523		* from {@link #getParallelism} when threads are created to
1524		* maintain parallelism when others are cooperatively blocked.
1525		*
#	Line 1474 | Line 1530 | public class ForkJoinPool extends Abstra
1530		}
1531
1532		/**
1477	–	* Returns the maximum number of threads allowed to exist in the
1478	–	* pool. Unless set using {@link #setMaximumPoolSize}, the
1479	–	* maximum is an implementation-defined value designed only to
1480	–	* prevent runaway growth.
1481	–	*
1482	–	* @return the maximum
1483	–	*/
1484	–	public int getMaximumPoolSize() {
1485	–	workerCountReadFence();
1486	–	return maxPoolSize;
1487	–	}
1488	–
1489	–	/**
1490	–	* Sets the maximum number of threads allowed to exist in the
1491	–	* pool. The given value should normally be greater than or equal
1492	–	* to the {@link #getParallelism parallelism} level. Setting this
1493	–	* value has no effect on current pool size. It controls
1494	–	* construction of new threads. The use of this method may cause
1495	–	* tasks that intrinsically require extra threads for dependent
1496	–	* computations to indefinitely stall. If you are instead trying
1497	–	* to minimize internal thread creation, consider setting {link
1498	–	* #setMaintainsParallelism} as false.
1499	–	*
1500	–	* @throws IllegalArgumentException if negative or greater than
1501	–	* internal implementation limit
1502	–	*/
1503	–	public void setMaximumPoolSize(int newMax) {
1504	–	if (newMax < 0 || newMax > MAX_THREADS)
1505	–	throw new IllegalArgumentException();
1506	–	maxPoolSize = newMax;
1507	–	workerCountWriteFence();
1508	–	}
1509	–
1510	–	/**
1511	–	* Returns {@code true} if this pool dynamically maintains its
1512	–	* target parallelism level. If false, new threads are added only
1513	–	* to avoid possible starvation.  This setting is by default true.
1514	–	*
1515	–	* @return {@code true} if maintains parallelism
1516	–	*/
1517	–	public boolean getMaintainsParallelism() {
1518	–	workerCountReadFence();
1519	–	return maintainsParallelism;
1520	–	}
1521	–
1522	–	/**
1523	–	* Sets whether this pool dynamically maintains its target
1524	–	* parallelism level. If false, new threads are added only to
1525	–	* avoid possible starvation.
1526	–	*
1527	–	* @param enable {@code true} to maintain parallelism
1528	–	*/
1529	–	public void setMaintainsParallelism(boolean enable) {
1530	–	maintainsParallelism = enable;
1531	–	workerCountWriteFence();
1532	–	}
1533	–
1534	–	/**
1535	–	* Establishes local first-in-first-out scheduling mode for forked
1536	–	* tasks that are never joined. This mode may be more appropriate
1537	–	* than default locally stack-based mode in applications in which
1538	–	* worker threads only process asynchronous tasks.  This method is
1539	–	* designed to be invoked only when the pool is quiescent, and
1540	–	* typically only before any tasks are submitted. The effects of
1541	–	* invocations at other times may be unpredictable.
1542	–	*
1543	–	* @param async if {@code true}, use locally FIFO scheduling
1544	–	* @return the previous mode
1545	–	* @see #getAsyncMode
1546	–	*/
1547	–	public boolean setAsyncMode(boolean async) {
1548	–	workerCountReadFence();
1549	–	boolean oldMode = locallyFifo;
1550	–	if (oldMode != async) {
1551	–	locallyFifo = async;
1552	–	workerCountWriteFence();
1553	–	for (ForkJoinWorkerThread w : workers) {
1554	–	if (w != null)
1555	–	w.setAsyncMode(async);
1556	–	}
1557	–	}
1558	–	return oldMode;
1559	–	}
1560	–
1561	–	/**
1533		* Returns {@code true} if this pool uses local first-in-first-out
1534		* scheduling mode for forked tasks that are never joined.
1535		*
1536		* @return {@code true} if this pool uses async mode
1566	–	* @see #setAsyncMode
1537		*/
1538		public boolean getAsyncMode() {
1569	–	workerCountReadFence();
1539		return locallyFifo;
1540		}
1541
#	Line 1635 | Line 1604 | public class ForkJoinPool extends Abstra
1604		*/
1605		public long getQueuedTaskCount() {
1606		long count = 0;
1607	<	for (ForkJoinWorkerThread w : workers) {
1607	>	for (ForkJoinWorkerThread w : workers)
1608		if (w != null)
1609		count += w.getQueueSize();
1641	–	}
1610		return count;
1611		}
1612
#	Line 1692 | Line 1660 | public class ForkJoinPool extends Abstra
1660		* @return the number of elements transferred
1661		*/
1662		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1663	<	int n = submissionQueue.drainTo(c);
1664	<	for (ForkJoinWorkerThread w : workers) {
1663	>	int count = submissionQueue.drainTo(c);
1664	>	for (ForkJoinWorkerThread w : workers)
1665		if (w != null)
1666	<	n += w.drainTasksTo(c);
1667	<	}
1700	<	return n;
1666	>	count += w.drainTasksTo(c);
1667	>	return count;
1668		}
1669
1670		/**
#	Line 1800 | Line 1767 | public class ForkJoinPool extends Abstra
1767		}
1768
1769		/**
1770	+	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1771	+	*/
1772	+	final boolean isAtLeastTerminating() {
1773	+	return runState >= TERMINATING;
1774	+	}
1775	+
1776	+	/**
1777		* Returns {@code true} if this pool has been shut down.
1778		*
1779		* @return {@code true} if this pool has been shut down
#	Line 1821 | Line 1795 | public class ForkJoinPool extends Abstra
1795		*/
1796		public boolean awaitTermination(long timeout, TimeUnit unit)
1797		throws InterruptedException {
1798	<	return terminationLatch.await(timeout, unit);
1798	>	try {
1799	>	termination.awaitAdvanceInterruptibly(0, timeout, unit);
1800	>	} catch (TimeoutException ex) {
1801	>	return false;
1802	>	}
1803	>	return true;
1804		}
1805
1806		/**
1807		* Interface for extending managed parallelism for tasks running
1808		* in {@link ForkJoinPool}s.
1809		*
1810	<	* <p>A {@code ManagedBlocker} provides two methods.
1811	<	* Method {@code isReleasable} must return {@code true} if
1812	<	* blocking is not necessary. Method {@code block} blocks the
1813	<	* current thread if necessary (perhaps internally invoking
1814	<	* {@code isReleasable} before actually blocking).
1810	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1811	>	* {@code isReleasable} must return {@code true} if blocking is
1812	>	* not necessary. Method {@code block} blocks the current thread
1813	>	* if necessary (perhaps internally invoking {@code isReleasable}
1814	>	* before actually blocking). The unusual methods in this API
1815	>	* accommodate synchronizers that may, but don't usually, block
1816	>	* for long periods. Similarly, they allow more efficient internal
1817	>	* handling of cases in which additional workers may be, but
1818	>	* usually are not, needed to ensure sufficient parallelism.
1819	>	* Toward this end, implementations of method {@code isReleasable}
1820	>	* must be amenable to repeated invocation.
1821		*
1822		* <p>For example, here is a ManagedBlocker based on a
1823		* ReentrantLock:
#	Line 1850 | Line 1835 | public class ForkJoinPool extends Abstra
1835		*     return hasLock || (hasLock = lock.tryLock());
1836		*   }
1837		* }}</pre>
1838	+	*
1839	+	* <p>Here is a class that possibly blocks waiting for an
1840	+	* item on a given queue:
1841	+	*  <pre> {@code
1842	+	* class QueueTaker<E> implements ManagedBlocker {
1843	+	*   final BlockingQueue<E> queue;
1844	+	*   volatile E item = null;
1845	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1846	+	*   public boolean block() throws InterruptedException {
1847	+	*     if (item == null)
1848	+	*       item = queue.take();
1849	+	*     return true;
1850	+	*   }
1851	+	*   public boolean isReleasable() {
1852	+	*     return item != null || (item = queue.poll()) != null;
1853	+	*   }
1854	+	*   public E getItem() { // call after pool.managedBlock completes
1855	+	*     return item;
1856	+	*   }
1857	+	* }}</pre>
1858		*/
1859		public static interface ManagedBlocker {
1860		/**
#	Line 1873 | Line 1878 | public class ForkJoinPool extends Abstra
1878		* Blocks in accord with the given blocker.  If the current thread
1879		* is a {@link ForkJoinWorkerThread}, this method possibly
1880		* arranges for a spare thread to be activated if necessary to
1881	<	* ensure parallelism while the current thread is blocked.
1877	<	*
1878	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1879	<	* supports it ({@link #getMaintainsParallelism}), this method
1880	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1881	<	* it activates a thread only if necessary to avoid complete
1882	<	* starvation. This option may be preferable when blockages use
1883	<	* timeouts, or are almost always brief.
1881	>	* ensure sufficient parallelism while the current thread is blocked.
1882		*
1883		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1884		* behaviorally equivalent to
#	Line 1894 | Line 1892 | public class ForkJoinPool extends Abstra
1892		* first be expanded to ensure parallelism, and later adjusted.
1893		*
1894		* @param blocker the blocker
1897	–	* @param maintainParallelism if {@code true} and supported by
1898	–	* this pool, attempt to maintain the pool's nominal parallelism;
1899	–	* otherwise activate a thread only if necessary to avoid
1900	–	* complete starvation.
1895		* @throws InterruptedException if blocker.block did so
1896		*/
1897	<	public static void managedBlock(ManagedBlocker blocker,
1904	<	boolean maintainParallelism)
1897	>	public static void managedBlock(ManagedBlocker blocker)
1898		throws InterruptedException {
1899		Thread t = Thread.currentThread();
1900	<	if (t instanceof ForkJoinWorkerThread)
1901	<	((ForkJoinWorkerThread) t).pool.
1902	<	doBlock(blocker, maintainParallelism);
1903	<	else
1904	<	awaitBlocker(blocker);
1905	<	}
1906	<
1914	<	/**
1915	<	* Performs Non-FJ blocking
1916	<	*/
1917	<	private static void awaitBlocker(ManagedBlocker blocker)
1918	<	throws InterruptedException {
1919	<	do {} while (!blocker.isReleasable() && !blocker.block());
1900	>	if (t instanceof ForkJoinWorkerThread) {
1901	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1902	>	w.pool.awaitBlocker(blocker);
1903	>	}
1904	>	else {
1905	>	do {} while (!blocker.isReleasable() && !blocker.block());
1906	>	}
1907		}
1908
1909		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 1941 | Line 1928 | public class ForkJoinPool extends Abstra
1928		private static final long eventCountOffset =
1929		objectFieldOffset("eventCount", ForkJoinPool.class);
1930		private static final long eventWaitersOffset =
1931	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1931	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1932		private static final long stealCountOffset =
1933	<	objectFieldOffset("stealCount",ForkJoinPool.class);
1934	<
1933	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1934	>	private static final long spareWaitersOffset =
1935	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1936
1937		private static long objectFieldOffset(String field, Class<?> klazz) {
1938		try {

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