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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.53 by dl, Mon Apr 5 15:52:26 2010 UTC vs.
Revision 1.63 by dl, Fri Aug 13 16:21:23 2010 UTC

#	Line 21 | Line 21 | import java.util.concurrent.CountDownLat
21		/**
22		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
23		* A {@code ForkJoinPool} provides the entry point for submissions
24	<	* from non-{@code ForkJoinTask}s, as well as management and
24	>	* from non-{@code ForkJoinTask} clients, as well as management and
25		* monitoring operations.
26		*
27		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
#	Line 30 | Line 30 | import java.util.concurrent.CountDownLat
30		* execute subtasks created by other active tasks (eventually blocking
31		* waiting for work if none exist). This enables efficient processing
32		* when most tasks spawn other subtasks (as do most {@code
33	<	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
34	<	* execution of some plain {@code Runnable}- or {@code Callable}-
35	<	* 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.
33	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
34	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
35	>	* with event-style tasks that are never joined.
36		*
37		* <p>A {@code ForkJoinPool} is constructed with a given target
38		* parallelism level; by default, equal to the number of available
39	<	* processors. Unless configured otherwise via {@link
40	<	* #setMaintainsParallelism}, the pool attempts to maintain this
41	<	* number of active (or available) threads by dynamically adding,
42	<	* suspending, or resuming internal worker threads, even if some tasks
43	<	* are stalled waiting to join others. However, no such adjustments
44	<	* are performed in the face of blocked IO or other unmanaged
45	<	* 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.
39	>	* processors. The pool attempts to maintain enough active (or
40	>	* available) threads by dynamically adding, suspending, or resuming
41	>	* internal worker threads, even if some tasks are stalled waiting to
42	>	* join others. However, no such adjustments are guaranteed in the
43	>	* face of blocked IO or other unmanaged synchronization. The nested
44	>	* {@link ManagedBlocker} interface enables extension of the kinds of
45	>	* synchronization accommodated.
46		*
47		* <p>In addition to execution and lifecycle control methods, this
48		* class provides status check methods (for example
#	Line 65 | Line 51 | import java.util.concurrent.CountDownLat
51		* {@link #toString} returns indications of pool state in a
52		* convenient form for informal monitoring.
53		*
54	+	* <p> As is the case with other ExecutorServices, there are three
55	+	* main task execution methods summarized in the following
56	+	* table. These are designed to be used by clients not already engaged
57	+	* in fork/join computations in the current pool.  The main forms of
58	+	* these methods accept instances of {@code ForkJoinTask}, but
59	+	* overloaded forms also allow mixed execution of plain {@code
60	+	* Runnable}- or {@code Callable}- based activities as well.  However,
61	+	* tasks that are already executing in a pool should normally
62	+	* <em>NOT</em> use these pool execution methods, but instead use the
63	+	* within-computation forms listed in the table.
64	+	*
65	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
66	+	*  <tr>
67	+	*    <td></td>
68	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
69	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
70	+	*  </tr>
71	+	*  <tr>
72	+	*    <td> <b>Arange async execution</td>
73	+	*    <td> {@link #execute(ForkJoinTask)}</td>
74	+	*    <td> {@link ForkJoinTask#fork}</td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Await and obtain result</td>
78	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#invoke}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Arrange exec and obtain Future</td>
83	+	*    <td> {@link #submit(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
85	+	*  </tr>
86	+	* </table>
87	+	*
88		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
89		* used for all parallel task execution in a program or subsystem.
90		* Otherwise, use would not usually outweigh the construction and
#	Line 89 | Line 109 | import java.util.concurrent.CountDownLat
109		* {@code IllegalArgumentException}.
110		*
111		* <p>This implementation rejects submitted tasks (that is, by throwing
112	<	* {@link RejectedExecutionException}) only when the pool is shut down.
112	>	* {@link RejectedExecutionException}) only when the pool is shut down
113	>	* or internal resources have been exhausted.
114		*
115		* @since 1.7
116		* @author Doug Lea
#	Line 116 | Line 137 | public class ForkJoinPool extends Abstra
137		* of tasks profit from cache affinities, but others are harmed by
138		* cache pollution effects.)
139		*
140	+	* Beyond work-stealing support and essential bookkeeping, the
141	+	* main responsibility of this framework is to take actions when
142	+	* one worker is waiting to join a task stolen (or always held by)
143	+	* another.  Becauae we are multiplexing many tasks on to a pool
144	+	* of workers, we can't just let them block (as in Thread.join).
145	+	* We also cannot just reassign the joiner's run-time stack with
146	+	* another and replace it later, which would be a form of
147	+	* "continuation", that even if possible is not necessarily a good
148	+	* idea. Given that the creation costs of most threads on most
149	+	* systems mainly surrounds setting up runtime stacks, thread
150	+	* creation and switching is usually not much more expensive than
151	+	* stack creation and switching, and is more flexible). Instead we
152	+	* combine two tactics:
153	+	*
154	+	*   Helping: Arranging for the joiner to execute some task that it
155	+	*      would be running if the steal had not occurred.  Method
156	+	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	+	*      links to try to find such a task.
158	+	*
159	+	*   Compensating: Unless there are already enough live threads,
160	+	*      method helpMaintainParallelism() may create or or
161	+	*      re-activate a spare thread to compensate for blocked
162	+	*      joiners until they unblock.
163	+	*
164	+	* Because the determining existence of conservatively safe
165	+	* helping targets, the availability of already-created spares,
166	+	* and the apparent need to create new spares are all racy and
167	+	* require heuristic guidance, we rely on multiple retries of
168	+	* each. Further, because it is impossible to keep exactly the
169	+	* target (parallelism) number of threads running at any given
170	+	* time, we allow compensation during joins to fail, and enlist
171	+	* all other threads to help out whenever they are not otherwise
172	+	* occupied (i.e., mainly in method preStep).
173	+	*
174	+	* The ManagedBlocker extension API can't use helping so relies
175	+	* only on compensation in method awaitBlocker.
176	+	*
177		* The main throughput advantages of work-stealing stem from
178		* decentralized control -- workers mostly steal tasks from each
179		* other. We do not want to negate this by creating bottlenecks
180	<	* implementing the management responsibilities of this class. So
181	<	* we use a collection of techniques that avoid, reduce, or cope
182	<	* well with contention. These entail several instances of
183	<	* bit-packing into CASable fields to maintain only the minimally
184	<	* required atomicity. To enable such packing, we restrict maximum
185	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
186	<	* bit field), which is far in excess of normal operating range.
187	<	* Even though updates to some of these bookkeeping fields do
188	<	* sometimes contend with each other, they don't normally
189	<	* cache-contend with updates to others enough to warrant memory
190	<	* padding or isolation. So they are all held as fields of
191	<	* ForkJoinPool objects.  The main capabilities are as follows:
180	>	* implementing other management responsibilities. So we use a
181	>	* collection of techniques that avoid, reduce, or cope well with
182	>	* contention. These entail several instances of bit-packing into
183	>	* CASable fields to maintain only the minimally required
184	>	* atomicity. To enable such packing, we restrict maximum
185	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
186	>	* unbalanced increments and decrements) to fit into a 16 bit
187	>	* field, which is far in excess of normal operating range.  Even
188	>	* though updates to some of these bookkeeping fields do sometimes
189	>	* contend with each other, they don't normally cache-contend with
190	>	* updates to others enough to warrant memory padding or
191	>	* isolation. So they are all held as fields of ForkJoinPool
192	>	* objects.  The main capabilities are as follows:
193		*
194		* 1. Creating and removing workers. Workers are recorded in the
195		* "workers" array. This is an array as opposed to some other data
#	Line 140 | Line 199 | public class ForkJoinPool extends Abstra
199		* (workerLock) but the array is otherwise concurrently readable,
200		* and accessed directly by workers. To simplify index-based
201		* operations, the array size is always a power of two, and all
202	<	* readers must tolerate null slots. Currently, all but the first
203	<	* worker thread creation is on-demand, triggered by task
204	<	* submissions, replacement of terminated workers, and/or
205	<	* compensation for blocked workers. However, all other support
206	<	* code is set up to work with other policies.
202	>	* readers must tolerate null slots. Currently, all worker thread
203	>	* creation is on-demand, triggered by task submissions,
204	>	* replacement of terminated workers, and/or compensation for
205	>	* blocked workers. However, all other support code is set up to
206	>	* work with other policies.
207	>	*
208	>	* To ensure that we do not hold on to worker references that
209	>	* would prevent GC, ALL accesses to workers are via indices into
210	>	* the workers array (which is one source of some of the unusual
211	>	* code constructions here). In essence, the workers array serves
212	>	* as a WeakReference mechanism. Thus for example the event queue
213	>	* stores worker indices, not worker references. Access to the
214	>	* workers in associated methods (for example releaseEventWaiters)
215	>	* must both index-check and null-check the IDs. All such accesses
216	>	* ignore bad IDs by returning out early from what they are doing,
217	>	* since this can only be associated with shutdown, in which case
218	>	* it is OK to give up. On termination, we just clobber these
219	>	* data structures without trying to use them.
220		*
221		* 2. Bookkeeping for dynamically adding and removing workers. We
222	<	* maintain a given level of parallelism (or, if
223	<	* maintainsParallelism is false, at least avoid starvation). When
152	<	* some workers are known to be blocked (on joins or via
222	>	* aim to approximately maintain the given level of parallelism.
223	>	* When some workers are known to be blocked (on joins or via
224		* ManagedBlocker), we may create or resume others to take their
225		* place until they unblock (see below). Implementing this
226		* requires counts of the number of "running" threads (i.e., those
227		* that are neither blocked nor artifically suspended) as well as
228		* the total number.  These two values are packed into one field,
229		* "workerCounts" because we need accurate snapshots when deciding
230	<	* to create, resume or suspend.  To support these decisions,
231	<	* updates must be prospective (not retrospective).  For example,
232	<	* the running count is decremented before blocking by a thread
233	<	* 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.
230	>	* to create, resume or suspend.  Note however that the
231	>	* correspondance of these counts to reality is not guaranteed. In
232	>	* particular updates for unblocked threads may lag until they
233	>	* actually wake up.
234		*
235		* 3. Maintaining global run state. The run state of the pool
236		* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
#	Line 201 | Line 259 | public class ForkJoinPool extends Abstra
259		* workers that previously could not find a task to now find one:
260		* Submission of a new task to the pool, or another worker pushing
261		* a task onto a previously empty queue.  (We also use this
262	<	* mechanism for termination and reconfiguration actions that
263	<	* require wakeups of idle workers).  Each worker maintains its
264	<	* last known event count, and blocks when a scan for work did not
265	<	* find a task AND its lastEventCount matches the current
266	<	* eventCount. Waiting idle workers are recorded in a variant of
267	<	* Treiber stack headed by field eventWaiters which, when nonzero,
268	<	* encodes the thread index and count awaited for by the worker
269	<	* thread most recently calling eventSync. This thread in turn has
270	<	* a record (field nextEventWaiter) for the next waiting worker.
271	<	* In addition to allowing simpler decisions about need for
272	<	* wakeup, the event count bits in eventWaiters serve the role of
273	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
274	<	* in task diffusion, workers not otherwise occupied may invoke
275	<	* method releaseWaiters, that removes and signals (unparks)
276	<	* workers not waiting on current count. To minimize task
277	<	* production stalls associate with signalling, any worker pushing
278	<	* a task on an empty queue invokes the weaker method signalWork,
279	<	* that only releases idle workers until it detects interference
280	<	* by other threads trying to release, and lets them take
281	<	* over. The net effect is a tree-like diffusion of signals, where
282	<	* released threads and possibly others) help with unparks.  To
283	<	* further reduce contention effects a bit, failed CASes to
262	>	* mechanism for termination actions that require wakeups of idle
263	>	* workers).  Each worker maintains its last known event count,
264	>	* and blocks when a scan for work did not find a task AND its
265	>	* lastEventCount matches the current eventCount. Waiting idle
266	>	* workers are recorded in a variant of Treiber stack headed by
267	>	* field eventWaiters which, when nonzero, encodes the thread
268	>	* index and count awaited for by the worker thread most recently
269	>	* calling eventSync. This thread in turn has a record (field
270	>	* nextEventWaiter) for the next waiting worker.  In addition to
271	>	* allowing simpler decisions about need for wakeup, the event
272	>	* count bits in eventWaiters serve the role of tags to avoid ABA
273	>	* errors in Treiber stacks.  To reduce delays in task diffusion,
274	>	* workers not otherwise occupied may invoke method
275	>	* releaseEventWaiters, that removes and signals (unparks) workers
276	>	* not waiting on current count. To reduce stalls, To minimize
277	>	* task production stalls associate with signalling, any worker
278	>	* pushing a task on an empty queue invokes the weaker method
279	>	* signalWork, that only releases idle workers until it detects
280	>	* interference by other threads trying to release, and lets them
281	>	* take over.  The net effect is a tree-like diffusion of signals,
282	>	* where released threads (and possibly others) help with unparks.
283	>	* To further reduce contention effects a bit, failed CASes to
284		* increment field eventCount are tolerated without retries.
285		* Conceptually they are merged into the same event, which is OK
286		* when their only purpose is to enable workers to scan for work.
#	Line 230 | Line 288 | public class ForkJoinPool extends Abstra
288		* 5. Managing suspension of extra workers. When a worker is about
289		* to block waiting for a join (or via ManagedBlockers), we may
290		* create a new thread to maintain parallelism level, or at least
291	<	* avoid starvation (see below). Usually, extra threads are needed
292	<	* for only very short periods, yet join dependencies are such
293	<	* that we sometimes need them in bursts. Rather than create new
294	<	* threads each time this happens, we suspend no-longer-needed
295	<	* extra ones as "spares". For most purposes, we don't distinguish
296	<	* "extra" spare threads from normal "core" threads: On each call
297	<	* to preStep (the only point at which we can do this) a worker
291	>	* avoid starvation. Usually, extra threads are needed for only
292	>	* very short periods, yet join dependencies are such that we
293	>	* sometimes need them in bursts. Rather than create new threads
294	>	* each time this happens, we suspend no-longer-needed extra ones
295	>	* as "spares". For most purposes, we don't distinguish "extra"
296	>	* spare threads from normal "core" threads: On each call to
297	>	* preStep (the only point at which we can do this) a worker
298		* checks to see if there are now too many running workers, and if
299	<	* so, suspends itself.  Methods preJoin and doBlock look for
299	>	* so, suspends itself.  Method helpMaintainParallelism looks for
300		* suspended threads to resume before considering creating a new
301	<	* replacement. We don't need a special data structure to maintain
302	<	* spares; simply scanning the workers array looking for
303	<	* worker.isSuspended() is fine because the calling thread is
246	<	* otherwise not doing anything useful anyway; we are at least as
247	<	* happy if after locating a spare, the caller doesn't actually
248	<	* block because the join is ready before we try to adjust and
249	<	* compensate.  Note that this is intrinsically racy.  One thread
301	>	* replacement. The spares themselves are encoded on another
302	>	* variant of a Treiber Stack, headed at field "spareWaiters".
303	>	* Note that the use of spares is intrinsically racy.  One thread
304		* may become a spare at about the same time as another is
305		* needlessly being created. We counteract this and related slop
306		* in part by requiring resumed spares to immediately recheck (in
307	<	* preStep) to see whether they they should re-suspend. The only
308	<	* effective difference between "extra" and "core" threads is that
309	<	* we allow the "extra" ones to time out and die if they are not
310	<	* resumed within a keep-alive interval of a few seconds. This is
311	<	* implemented mainly within ForkJoinWorkerThread, but requires
312	<	* some coordination (isTrimmed() -- meaning killed while
313	<	* suspended) to correctly maintain pool counts.
307	>	* preStep) to see whether they they should re-suspend.  To avoid
308	>	* long-term build-up of spares, the oldest spare (see
309	>	* ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if
310	>	* not signalled and calls tryTrimSpare, which uses two different
311	>	* thresholds: Always killing if the number of spares is greater
312	>	* that 25% of total, and killing others only at a slower rate
313	>	* (UNUSED_SPARE_TRIM_RATE_NANOS).
314		*
315		* 6. Deciding when to create new workers. The main dynamic
316	<	* control in this class is deciding when to create extra threads,
317	<	* in methods preJoin and doBlock. We always need to create one
318	<	* when the number of running threads becomes zero. But because
319	<	* blocked joins are typically dependent, we don't necessarily
320	<	* need or want one-to-one replacement. Using a one-to-one
321	<	* compensation rule often leads to enough useless overhead
322	<	* creating, suspending, resuming, and/or killing threads to
323	<	* signficantly degrade throughput.  We use a rule reflecting the
324	<	* idea that, the more spare threads you already have, the more
325	<	* evidence you need to create another one; where "evidence" is
326	<	* expressed as the current deficit -- target minus running
327	<	* threads. To reduce flickering and drift around target values,
328	<	* the relation is quadratic: adding a spare if (dc*dc)>=(sc*pc)
329	<	* (where dc is deficit, sc is number of spare threads and pc is
330	<	* target parallelism.)  This effectively reduces churn at the
331	<	* price of systematically undershooting target parallelism when
332	<	* many threads are blocked.  However, biasing toward undeshooting
279	<	* partially compensates for the above mechanics to suspend extra
280	<	* 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
316	>	* control in this class is deciding when to create extra threads
317	>	* in method helpMaintainParallelism. We would like to keep
318	>	* exactly #parallelism threads running, which is an impossble
319	>	* task. We always need to create one when the number of running
320	>	* threads would become zero and all workers are busy. Beyond
321	>	* this, we must rely on heuristics that work well in the the
322	>	* presence of transients phenomena such as GC stalls, dynamic
323	>	* compilation, and wake-up lags. These transients are extremely
324	>	* common -- we are normally trying to fully saturate the CPUs on
325	>	* a machine, so almost any activity other than running tasks
326	>	* impedes accuracy. Our main defense is to allow some slack in
327	>	* creation thresholds, using rules that reflect the fact that the
328	>	* more threads we have running, the more likely that we are
329	>	* underestimating the number running threads. The rules also
330	>	* better cope with the fact that some of the methods in this
331	>	* class tend to never become compiled (but are interpreted), so
332	>	* some components of the entire set of controls might execute 100
333		* times faster than others. And similarly for cases where the
334		* apparent lack of work is just due to GC stalls and other
335		* transient system activity.
336		*
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.
303	–	*
337		* Beware that there is a lot of representation-level coupling
338		* among classes ForkJoinPool, ForkJoinWorkerThread, and
339		* ForkJoinTask.  For example, direct access to "workers" array by
#	Line 312 | Line 345 | public class ForkJoinPool extends Abstra
345		*
346		* Style notes: There are lots of inline assignments (of form
347		* "while ((local = field) != 0)") which are usually the simplest
348	<	* way to ensure read orderings. Also several occurrences of the
349	<	* unusual "do {} while(!cas...)" which is the simplest way to
350	<	* force an update of a CAS'ed variable. There are also a few
351	<	* other coding oddities that help some methods perform reasonably
352	<	* even when interpreted (not compiled).
348	>	* way to ensure the required read orderings (which are sometimes
349	>	* critical). Also several occurrences of the unusual "do {}
350	>	* while(!cas...)" which is the simplest way to force an update of
351	>	* a CAS'ed variable. There are also other coding oddities that
352	>	* help some methods perform reasonably even when interpreted (not
353	>	* compiled), at the expense of some messy constructions that
354	>	* reduce byte code counts.
355		*
356		* The order of declarations in this file is: (1) statics (2)
357		* fields (along with constants used when unpacking some of them)
#	Line 345 | Line 380 | public class ForkJoinPool extends Abstra
380		* Default ForkJoinWorkerThreadFactory implementation; creates a
381		* new ForkJoinWorkerThread.
382		*/
383	<	static class  DefaultForkJoinWorkerThreadFactory
383	>	static class DefaultForkJoinWorkerThreadFactory
384		implements ForkJoinWorkerThreadFactory {
385		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
386		return new ForkJoinWorkerThread(pool);
#	Line 384 | Line 419 | public class ForkJoinPool extends Abstra
419		new AtomicInteger();
420
421		/**
422	<	* Absolute bound for parallelism level. Twice this number must
423	<	* fit into a 16bit field to enable word-packing for some counts.
422	>	* Absolute bound for parallelism level. Twice this number plus
423	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
424	>	* word-packing for some counts and indices.
425		*/
426	<	private static final int MAX_THREADS = 0x7fff;
426	>	private static final int MAX_WORKERS   = 0x7fff;
427
428		/**
429		* Array holding all worker threads in the pool.  Array size must
#	Line 413 | Line 449 | public class ForkJoinPool extends Abstra
449		/**
450		* Latch released upon termination.
451		*/
452	<	private final CountDownLatch terminationLatch;
452	>	private final Phaser termination;
453
454		/**
455		* Creation factory for worker threads.
#	Line 427 | Line 463 | public class ForkJoinPool extends Abstra
463		private volatile long stealCount;
464
465		/**
466	+	* The last nanoTime that a spare thread was trimmed
467	+	*/
468	+	private volatile long trimTime;
469	+
470	+	/**
471	+	* The rate at which to trim unused spares
472	+	*/
473	+	static final long UNUSED_SPARE_TRIM_RATE_NANOS =
474	+	1000L * 1000L * 1000L; // 1 sec
475	+
476	+	/**
477		* Encoded record of top of treiber stack of threads waiting for
478		* events. The top 32 bits contain the count being waited for. The
479	<	* bottom word contains one plus the pool index of waiting worker
480	<	* thread.
479	>	* bottom 16 bits contains one plus the pool index of waiting
480	>	* worker thread. (Bits 16-31 are unused.)
481		*/
482		private volatile long eventWaiters;
483
484		private static final int  EVENT_COUNT_SHIFT = 32;
485	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
485	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
486
487		/**
488		* A counter for events that may wake up worker threads:
489		*   - Submission of a new task to the pool
490		*   - A worker pushing a task on an empty queue
491	<	*   - termination and reconfiguration
491	>	*   - termination
492		*/
493		private volatile int eventCount;
494
495		/**
496	+	* Encoded record of top of treiber stack of spare threads waiting
497	+	* for resumption. The top 16 bits contain an arbitrary count to
498	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
499	+	* index of waiting worker thread.
500	+	*/
501	+	private volatile int spareWaiters;
502	+
503	+	private static final int SPARE_COUNT_SHIFT = 16;
504	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
505	+
506	+	/**
507		* Lifecycle control. The low word contains the number of workers
508		* that are (probably) executing tasks. This value is atomically
509		* incremented before a worker gets a task to run, and decremented
#	Line 474 | Line 532 | public class ForkJoinPool extends Abstra
532		* making decisions about creating and suspending spare
533		* threads. Updated only by CAS. Note that adding a new worker
534		* requires incrementing both counts, since workers start off in
535	<	* running state.  This field is also used for memory-fencing
478	<	* configuration parameters.
535	>	* running state.
536		*/
537		private volatile int workerCounts;
538
#	Line 484 | Line 541 | public class ForkJoinPool extends Abstra
541		private static final int ONE_RUNNING        = 1;
542		private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
543
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	–
544		/**
545		* The target parallelism level.
546	+	* Accessed directly by ForkJoinWorkerThreads.
547		*/
548	<	private int parallelism;
497	<
498	<	/**
499	<	* The maximum allowed pool size.
500	<	*/
501	<	private int maxPoolSize;
548	>	final int parallelism;
549
550		/**
551		* True if use local fifo, not default lifo, for local polling
552	<	* Replicated by ForkJoinWorkerThreads
506	<	*/
507	<	private boolean locallyFifo;
508	<
509	<	/**
510	<	* Controls whether to add spares to maintain parallelism
552	>	* Read by, and replicated by ForkJoinWorkerThreads
553		*/
554	<	private boolean maintainsParallelism;
554	>	final boolean locallyFifo;
555
556		/**
557	<	* The uncaught exception handler used when any worker
558	<	* abruptly terminates
557	>	* The uncaught exception handler used when any worker abruptly
558	>	* terminates.
559		*/
560	<	private Thread.UncaughtExceptionHandler ueh;
560	>	private final Thread.UncaughtExceptionHandler ueh;
561
562		/**
563		* Pool number, just for assigning useful names to worker threads
564		*/
565		private final int poolNumber;
566
567	<	// utilities for updating fields
567	>
568	>	// Utilities for CASing fields. Note that several of these
569	>	// are manually inlined by callers
570
571		/**
572	<	* Adds delta to running count.  Used mainly by ForkJoinTask.
529	<	*
530	<	* @param delta the number to add
572	>	* Increments running count part of workerCounts
573		*/
574	<	final void updateRunningCount(int delta) {
575	<	int wc;
574	>	final void incrementRunningCount() {
575	>	int c;
576		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
577	<	wc = workerCounts,
578	<	wc + delta));
577	>	c = workerCounts,
578	>	c + ONE_RUNNING));
579		}
580
581		/**
582	<	* Write fence for user modifications of pool parameters
541	<	* (parallelism. etc).  Note that it doesn't matter if CAS fails.
582	>	* Tries to decrement running count unless already zero
583		*/
584	<	private void workerCountWriteFence() {
585	<	int wc;
586	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
587	<	wc = workerCounts, wc);
584	>	final boolean tryDecrementRunningCount() {
585	>	int wc = workerCounts;
586	>	if ((wc & RUNNING_COUNT_MASK) == 0)
587	>	return false;
588	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
589	>	wc, wc - ONE_RUNNING);
590		}
591
592		/**
593	<	* Read fence for external reads of pool parameters
594	<	* (parallelism. maxPoolSize, etc).
593	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
594	>	* (rarely) necessary when other count updates lag.
595	>	*
596	>	* @param dr -- either zero or ONE_RUNNING
597	>	* @param dt == either zero or ONE_TOTAL
598		*/
599	<	private void workerCountReadFence() {
600	<	int ignore = workerCounts;
599	>	private void decrementWorkerCounts(int dr, int dt) {
600	>	for (;;) {
601	>	int wc = workerCounts;
602	>	if (wc == 0 && (runState & TERMINATED) != 0)
603	>	return; // lagging termination on a backout
604	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
605	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0)
606	>	Thread.yield();
607	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
608	>	wc, wc - (dr + dt)))
609	>	return;
610	>	}
611	>	}
612	>
613	>	/**
614	>	* Increments event count
615	>	*/
616	>	private void advanceEventCount() {
617	>	int c;
618	>	do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
619	>	c = eventCount, c+1));
620		}
621
622		/**
#	Line 602 | Line 667 | public class ForkJoinPool extends Abstra
667		lock.lock();
668		try {
669		ForkJoinWorkerThread[] ws = workers;
670	<	int len = ws.length;
671	<	if (k < 0 || k >= len || ws[k] != null) {
672	<	for (k = 0; k < len && ws[k] != null; ++k)
670	>	int n = ws.length;
671	>	if (k < 0 || k >= n || ws[k] != null) {
672	>	for (k = 0; k < n && ws[k] != null; ++k)
673		;
674	<	if (k == len)
675	<	ws = Arrays.copyOf(ws, len << 1);
674	>	if (k == n)
675	>	ws = Arrays.copyOf(ws, n << 1);
676		}
677		ws[k] = w;
678		workers = ws; // volatile array write ensures slot visibility
#	Line 640 | Line 705 | public class ForkJoinPool extends Abstra
705		* Tries to create and add new worker. Assumes that worker counts
706		* are already updated to accommodate the worker, so adjusts on
707		* failure.
643	–	*
644	–	* @return new worker or null if creation failed
708		*/
709	<	private ForkJoinWorkerThread addWorker() {
709	>	private void addWorker() {
710		ForkJoinWorkerThread w = null;
711		try {
712		w = factory.newThread(this);
713		} finally { // Adjust on either null or exceptional factory return
714		if (w == null) {
715	<	onWorkerCreationFailure();
716	<	return null;
715	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
716	>	tryTerminate(false); // in case of failure during shutdown
717		}
718		}
719	<	w.start(recordWorker(w), locallyFifo, ueh);
720	<	return w;
658	<	}
659	<
660	<	/**
661	<	* Adjusts counts upon failure to create worker
662	<	*/
663	<	private void onWorkerCreationFailure() {
664	<	int c;
665	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
666	<	c = workerCounts,
667	<	c - (ONE_RUNNING|ONE_TOTAL)));
668	<	tryTerminate(false); // in case of failure during shutdown
669	<	}
670	<
671	<	/**
672	<	* Create enough total workers to establish target parallelism,
673	<	* giving up if terminating or addWorker fails
674	<	*/
675	<	private void ensureEnoughTotalWorkers() {
676	<	int wc;
677	<	while (runState < TERMINATING &&
678	<	((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism) {
679	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
680	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
681	<	addWorker() == null))
682	<	break;
683	<	}
719	>	if (w != null)
720	>	w.start(recordWorker(w), ueh);
721		}
722
723		/**
724		* Final callback from terminating worker.  Removes record of
725		* worker from array, and adjusts counts. If pool is shutting
726	<	* down, tries to complete terminatation, else possibly replaces
690	<	* the worker.
726	>	* down, tries to complete terminatation.
727		*
728		* @param w the worker
729		*/
730		final void workerTerminated(ForkJoinWorkerThread w) {
695	–	if (w.active) { // force inactive
696	–	w.active = false;
697	–	do {} while (!tryDecrementActiveCount());
698	–	}
731		forgetWorker(w);
732	<
733	<	// decrement total count, and if was running, running count
734	<	int unit = w.isTrimmed()? ONE_TOTAL : (ONE_RUNNING|ONE_TOTAL);
735	<	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();
732	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
733	>	while (w.stealCount != 0) // collect final count
734	>	tryAccumulateStealCount(w);
735	>	tryTerminate(false);
736		}
737
738		// Waiting for and signalling events
739
740		/**
715	–	* Ensures eventCount on exit is different (mod 2^32) than on
716	–	* entry.  CAS failures are OK -- any change in count suffices.
717	–	*/
718	–	private void advanceEventCount() {
719	–	int c;
720	–	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
721	–	}
722	–
723	–	/**
741		* Releases workers blocked on a count not equal to current count.
742	<	*/
743	<	final void releaseWaiters() {
744	<	long top;
745	<	int id;
746	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
747	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
748	<	ForkJoinWorkerThread[] ws = workers;
749	<	ForkJoinWorkerThread w;
750	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
751	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
752	<	top, w.nextWaiter))
742	>	* Normally called after precheck that eventWaiters isn't zero to
743	>	* avoid wasted array checks.
744	>	*
745	>	* @param signalling true if caller is a signalling worker so can
746	>	* exit upon (conservatively) detected contention by other threads
747	>	* who will continue to release
748	>	*/
749	>	private void releaseEventWaiters(boolean signalling) {
750	>	ForkJoinWorkerThread[] ws = workers;
751	>	int n = ws.length;
752	>	long h; // head of stack
753	>	ForkJoinWorkerThread w; int id, ec;
754	>	while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 &&
755	>	(int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) &&
756	>	id < n && (w = ws[id]) != null) {
757	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
758	>	h, h = w.nextWaiter))
759		LockSupport.unpark(w);
760	+	if (signalling && (eventCount != ec || eventWaiters != h))
761	+	break;
762		}
763		}
764
765		/**
766	<	* Advances eventCount and releases waiters until interference by
767	<	* other releasing threads is detected.
766	>	* Tries to advance eventCount and releases waiters. Called only
767	>	* from workers.
768		*/
769		final void signalWork() {
770	<	int ec;
771	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
772	<	outer:for (;;) {
773	<	long top = eventWaiters;
749	<	ec = eventCount;
750	<	for (;;) {
751	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
752	<	int id = (int)(top & WAITER_INDEX_MASK);
753	<	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
754	<	return;
755	<	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
756	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
757	<	top, top = w.nextWaiter))
758	<	continue outer;      // possibly stale; reread
759	<	LockSupport.unpark(w);
760	<	if (top != eventWaiters) // let someone else take over
761	<	return;
762	<	}
763	<	}
770	>	int c; // try to increment event count -- CAS failure OK
771	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
772	>	if (eventWaiters != 0L)
773	>	releaseEventWaiters(true);
774		}
775
776		/**
777	<	* If worker is inactive, blocks until terminating or event count
778	<	* advances from last value held by worker; in any case helps
769	<	* release others.
777	>	* Blocks worker until terminating or event count
778	>	* advances from last value held by worker
779		*
780		* @param w the calling worker thread
781		*/
782		private void eventSync(ForkJoinWorkerThread w) {
783	<	if (!w.active) {
784	<	int prev = w.lastEventCount;
785	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
786	<	((long)(w.poolIndex + 1)));
787	<	long top;
788	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
789	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
790	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
791	<	eventCount == prev) {
792	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
793	<	w.nextWaiter = top, nextTop)) {
794	<	accumulateStealCount(w); // transfer steals while idle
795	<	Thread.interrupted();    // clear/ignore interrupt
796	<	while (eventCount == prev)
797	<	w.doPark();
798	<	break;
783	>	int wec = w.lastEventCount;
784	>	long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
785	>	long h;
786	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
787	>	((h = eventWaiters) == 0L ||
788	>	(int)(h >>> EVENT_COUNT_SHIFT) == wec) &&
789	>	eventCount == wec) {
790	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
791	>	w.nextWaiter = h, nh)) {
792	>	while (runState < TERMINATING && eventCount == wec) {
793	>	if (!tryAccumulateStealCount(w))  // transfer while idle
794	>	continue;
795	>	Thread.interrupted();             // clear/ignore interrupt
796	>	if (eventCount != wec)
797	>	break;
798	>	LockSupport.park(w);
799		}
800	+	break;
801	+	}
802	+	}
803	+	w.lastEventCount = eventCount;
804	+	}
805	+
806	+	// Maintaining spares
807	+
808	+	/**
809	+	* Pushes worker onto the spare stack
810	+	*/
811	+	final void pushSpare(ForkJoinWorkerThread w) {
812	+	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1);
813	+	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
814	+	w.nextSpare = spareWaiters,ns));
815	+	}
816	+
817	+	/**
818	+	* Tries (once) to resume a spare if running count is less than
819	+	* target parallelism. Fails on contention or stale workers.
820	+	*/
821	+	private void tryResumeSpare() {
822	+	int sw, id;
823	+	ForkJoinWorkerThread w;
824	+	ForkJoinWorkerThread[] ws;
825	+	if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
826	+	id < (ws = workers).length && (w = ws[id]) != null &&
827	+	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
828	+	eventWaiters == 0L &&
829	+	spareWaiters == sw &&
830	+	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
831	+	sw, w.nextSpare) &&
832	+	w.tryUnsuspend()) {
833	+	int c; // try increment; if contended, finish after unpark
834	+	boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
835	+	c = workerCounts,
836	+	c + ONE_RUNNING);
837	+	LockSupport.unpark(w);
838	+	if (!inc) {
839	+	do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
840	+	c = workerCounts,
841	+	c + ONE_RUNNING));
842		}
792	–	w.lastEventCount = eventCount;
843		}
844	<	releaseWaiters();
844	>	}
845	>
846	>	/**
847	>	* Callback from oldest spare occasionally waking up.  Tries
848	>	* (once) to shutdown a spare if more than 25% spare overage, or
849	>	* if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at
850	>	* least #parallelism running threads. Note that we don't need CAS
851	>	* or locks here because the method is called only from the oldest
852	>	* suspended spare occasionally waking (and even misfires are OK).
853	>	*
854	>	* @param now the wake up nanoTime of caller
855	>	*/
856	>	final void tryTrimSpare(long now) {
857	>	long lastTrim = trimTime;
858	>	trimTime = now;
859	>	helpMaintainParallelism(); // first, help wake up any needed spares
860	>	int sw, id;
861	>	ForkJoinWorkerThread w;
862	>	ForkJoinWorkerThread[] ws;
863	>	int pc = parallelism;
864	>	int wc = workerCounts;
865	>	if ((wc & RUNNING_COUNT_MASK) >= pc &&
866	>	(((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25%
867	>	now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) &&
868	>	(id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
869	>	id < (ws = workers).length && (w = ws[id]) != null &&
870	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
871	>	sw, w.nextSpare))
872	>	w.shutdown(false);
873	>	}
874	>
875	>	/**
876	>	* Does at most one of:
877	>	*
878	>	* 1. Help wake up existing workers waiting for work via
879	>	*    releaseEventWaiters. (If any exist, then it probably doesn't
880	>	*    matter right now if under target parallelism level.)
881	>	*
882	>	* 2. If below parallelism level and a spare exists, try (once)
883	>	*    to resume it via tryResumeSpare.
884	>	*
885	>	* 3. If neither of the above, tries (once) to add a new
886	>	*    worker if either there are not enough total, or if all
887	>	*    existing workers are busy, there are either no running
888	>	*    workers or the deficit is at least twice the surplus.
889	>	*/
890	>	private void helpMaintainParallelism() {
891	>	// uglified to work better when not compiled
892	>	int pc, wc, rc, tc, rs; long h;
893	>	if ((h = eventWaiters) != 0L) {
894	>	if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
895	>	releaseEventWaiters(false); // avoid useless call
896	>	}
897	>	else if ((pc = parallelism) >
898	>	(rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) {
899	>	if (spareWaiters != 0)
900	>	tryResumeSpare();
901	>	else if ((rs = runState) < TERMINATING &&
902	>	((tc = wc >>> TOTAL_COUNT_SHIFT) < pc ||
903	>	(tc == (rs & ACTIVE_COUNT_MASK) && // all busy
904	>	(rc == 0 ||                       // must add
905	>	rc < pc - ((tc - pc) << 1)) &&   // within slack
906	>	tc < MAX_WORKERS && runState == rs)) && // recheck busy
907	>	workerCounts == wc &&
908	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
909	>	wc + (ONE_RUNNING|ONE_TOTAL)))
910	>	addWorker();
911	>	}
912		}
913
914		/**
915		* Callback from workers invoked upon each top-level action (i.e.,
916		* stealing a task or taking a submission and running
917	<	* it). Performs one or both of the following:
917	>	* it). Performs one or more of the following:
918		*
919	<	* * If the worker cannot find work, updates its active status to
920	<	* inactive and updates activeCount unless there is contention, in
921	<	* which case it may try again (either in this or a subsequent
922	<	* call).  Additionally, awaits the next task event and/or helps
923	<	* wake up other releasable waiters.
924	<	*
925	<	* * If there are too many running threads, suspends this worker
926	<	* (first forcing inactivation if necessary).  If it is not
927	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
928	<	* -- killed while suspended within suspendAsSpare. Otherwise,
929	<	* upon resume it rechecks to make sure that it is still needed.
919	>	* 1. If the worker cannot find work (misses > 0), updates its
920	>	*    active status to inactive and updates activeCount unless
921	>	*    this is the first miss and there is contention, in which
922	>	*    case it may try again (either in this or a subsequent
923	>	*    call).
924	>	*
925	>	* 2. If there are at least 2 misses, awaits the next task event
926	>	*    via eventSync
927	>	*
928	>	* 3. If there are too many running threads, suspends this worker
929	>	*    (first forcing inactivation if necessary).  If it is not
930	>	*    needed, it may be killed while suspended via
931	>	*    tryTrimSpare. Otherwise, upon resume it rechecks to make
932	>	*    sure that it is still needed.
933	>	*
934	>	* 4. Helps release and/or reactivate other workers via
935	>	*    helpMaintainParallelism
936		*
937		* @param w the worker
938	<	* @param worked false if the worker scanned for work but didn't
939	<	* find any (in which case it may block waiting for work).
938	>	* @param misses the number of scans by caller failing to find work
939	>	* (saturating at 2 just to avoid wraparound)
940		*/
941	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
941	>	final void preStep(ForkJoinWorkerThread w, int misses) {
942		boolean active = w.active;
943	<	boolean inactivate = !worked & active;
943	>	int pc = parallelism;
944		for (;;) {
945	<	if (inactivate) {
946	<	int c = runState;
945	>	int wc = workerCounts;
946	>	int rc = wc & RUNNING_COUNT_MASK;
947	>	if (active && (misses > 0 || rc > pc)) {
948	>	int rs;                      // try inactivate
949		if (UNSAFE.compareAndSwapInt(this, runStateOffset,
950	<	c, c - ONE_ACTIVE))
951	<	inactivate = active = w.active = false;
950	>	rs = runState, rs - ONE_ACTIVE))
951	>	active = w.active = false;
952	>	else if (misses > 1 || rc > pc ||
953	>	(rs & ACTIVE_COUNT_MASK) >= pc)
954	>	continue;                // force inactivate
955		}
956	<	int wc = workerCounts;
957	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
958	<	if (!worked)
959	<	eventSync(w);
960	<	return;
956	>	if (misses > 1) {
957	>	misses = 0;                  // don't re-sync
958	>	eventSync(w);                // continue loop to recheck rc
959	>	}
960	>	else if (rc > pc) {
961	>	if (workerCounts == wc &&   // try to suspend as spare
962	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
963	>	wc, wc - ONE_RUNNING) &&
964	>	!w.suspendAsSpare())    // false if killed
965	>	break;
966	>	}
967	>	else {
968	>	if (rc < pc || eventWaiters != 0L)
969	>	helpMaintainParallelism();
970	>	break;
971		}
834	–	if (!(inactivate |= active) &&  // must inactivate to suspend
835	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
836	–	wc, wc - ONE_RUNNING) &&
837	–	!w.suspendAsSpare())        // false if trimmed
838	–	return;
972		}
973		}
974
975		/**
976	<	* Adjusts counts and creates or resumes compensating threads for
977	<	* a worker about to block on task joinMe, returning early if
978	<	* joinMe becomes ready. First tries resuming an existing spare
979	<	* (which usually also avoids any count adjustment), but must then
980	<	* decrement running count to determine whether a new thread is
981	<	* needed. See above for fuller explanation.
982	<	*/
983	<	final void preJoin(ForkJoinTask<?> joinMe) {
984	<	boolean dec = false;       // true when running count decremented
985	<	for (;;) {
986	<	releaseWaiters();      // help other threads progress
987	<
988	<	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;
861	<	break;
862	<	}
863	<	}
976	>	* Helps and/or blocks awaiting join of the given task.
977	>	* Alternates between helpJoinTask() and helpMaintainParallelism()
978	>	* as many times as there is a deficit in running count (or longer
979	>	* if running count would become zero), then blocks if task still
980	>	* not done.
981	>	*
982	>	* @param joinMe the task to join
983	>	*/
984	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
985	>	int threshold = parallelism;         // descend blocking thresholds
986	>	while (joinMe.status >= 0) {
987	>	boolean block; int wc;
988	>	worker.helpJoinTask(joinMe);
989		if (joinMe.status < 0)
990	<	return;
991	<
992	<	if (spare != null && spare.tryUnsuspend()) {
993	<	if (dec || joinMe.requestSignal() < 0) {
994	<	int c;
995	<	do {} while (!UNSAFE.compareAndSwapInt(this,
996	<	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;
990	>	break;
991	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
992	>	if (threshold > 0)
993	>	--threshold;
994	>	else
995	>	advanceEventCount(); // force release
996	>	block = false;
997		}
998	<
999	<	if (dec) {
1000	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1001	<	int pc = parallelism;
1002	<	int dc = pc - (wc & RUNNING_COUNT_MASK); // deficit count
1003	<	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
1004	<	!maintainsParallelism)) ||
1005	<	tc >= maxPoolSize) // cannot add
1006	<	return;
1007	<	if (spare == null &&
1008	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
902	<	wc + (ONE_RUNNING|ONE_TOTAL))) {
903	<	addWorker();
904	<	return;
905	<	}
998	>	else
999	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1000	>	wc, wc - ONE_RUNNING);
1001	>	helpMaintainParallelism();
1002	>	if (block) {
1003	>	int c;
1004	>	joinMe.internalAwaitDone();
1005	>	do {} while (!UNSAFE.compareAndSwapInt
1006	>	(this, workerCountsOffset,
1007	>	c = workerCounts, c + ONE_RUNNING));
1008	>	break;
1009		}
1010		}
1011		}
1012
1013		/**
1014	<	* Same idea as preJoin but with too many differing details to
912	<	* integrate: There are no task-based signal counts, and only one
913	<	* way to do the actual blocking. So for simplicity it is directly
914	<	* incorporated into this method.
1014	>	* Same idea as awaitJoin, but no helping
1015		*/
1016	<	final void doBlock(ManagedBlocker blocker, boolean maintainPar)
1016	>	final void awaitBlocker(ManagedBlocker blocker)
1017		throws InterruptedException {
1018	<	maintainPar &= maintainsParallelism; // override
1019	<	boolean dec = false;
1020	<	boolean done = false;
1021	<	for (;;) {
1022	<	releaseWaiters();
1023	<	if (done = blocker.isReleasable())
1024	<	break;
1025	<	ForkJoinWorkerThread spare = null;
1026	<	for (ForkJoinWorkerThread w : workers) {
927	<	if (w != null && w.isSuspended()) {
928	<	spare = w;
929	<	break;
930	<	}
1018	>	int threshold = parallelism;
1019	>	while (!blocker.isReleasable()) {
1020	>	boolean block; int wc;
1021	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
1022	>	if (threshold > 0)
1023	>	--threshold;
1024	>	else
1025	>	advanceEventCount();
1026	>	block = false;
1027		}
1028	<	if (done = blocker.isReleasable())
1029	<	break;
1030	<	if (spare != null && spare.tryUnsuspend()) {
1031	<	if (dec) {
1028	>	else
1029	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1030	>	wc, wc - ONE_RUNNING);
1031	>	helpMaintainParallelism();
1032	>	if (block) {
1033	>	try {
1034	>	do {} while (!blocker.isReleasable() && !blocker.block());
1035	>	} finally {
1036		int c;
1037	<	do {} while (!UNSAFE.compareAndSwapInt(this,
1038	<	workerCountsOffset,
1039	<	c = workerCounts,
940	<	c + ONE_RUNNING));
1037	>	do {} while (!UNSAFE.compareAndSwapInt
1038	>	(this, workerCountsOffset,
1039	>	c = workerCounts, c + ONE_RUNNING));
1040		}
942	–	LockSupport.unpark(spare);
1041		break;
1042		}
945	–	int wc = workerCounts;
946	–	if (!dec && (wc & RUNNING_COUNT_MASK) != 0)
947	–	dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
948	–	wc, wc -= ONE_RUNNING);
949	–	if (dec) {
950	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
951	–	int pc = parallelism;
952	–	int dc = pc - (wc & RUNNING_COUNT_MASK);
953	–	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
954	–	!maintainPar)) ||
955	–	tc >= maxPoolSize)
956	–	break;
957	–	if (spare == null &&
958	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
959	–	wc + (ONE_RUNNING|ONE_TOTAL))){
960	–	addWorker();
961	–	break;
962	–	}
963	–	}
964	–	}
965	–
966	–	try {
967	–	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));
976	–	}
1043		}
1044		}
1045
#	Line 998 | Line 1064 | public class ForkJoinPool extends Abstra
1064		// Finish now if all threads terminated; else in some subsequent call
1065		if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1066		advanceRunLevel(TERMINATED);
1067	<	terminationLatch.countDown();
1067	>	termination.arrive();
1068		}
1069		return true;
1070		}
1071
1072		/**
1073		* Actions on transition to TERMINATING
1074	+	*
1075	+	* Runs up to four passes through workers: (0) shutting down each
1076	+	* quietly (without waking up if parked) to quickly spread
1077	+	* notifications without unnecessary bouncing around event queues
1078	+	* etc (1) wake up and help cancel tasks (2) interrupt (3) mop up
1079	+	* races with interrupted workers
1080		*/
1081		private void startTerminating() {
1082	<	// Clear out and cancel submissions, ignoring exceptions
1082	>	cancelSubmissions();
1083	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1084	>	advanceEventCount();
1085	>	eventWaiters = 0L; // clobber lists
1086	>	spareWaiters = 0;
1087	>	ForkJoinWorkerThread[] ws = workers;
1088	>	int n = ws.length;
1089	>	for (int i = 0; i < n; ++i) {
1090	>	ForkJoinWorkerThread w = ws[i];
1091	>	if (w != null) {
1092	>	w.shutdown(true);
1093	>	if (passes > 0 && !w.isTerminated()) {
1094	>	w.cancelTasks();
1095	>	LockSupport.unpark(w);
1096	>	if (passes > 1) {
1097	>	try {
1098	>	w.interrupt();
1099	>	} catch (SecurityException ignore) {
1100	>	}
1101	>	}
1102	>	}
1103	>	}
1104	>	}
1105	>	}
1106	>	}
1107	>
1108	>	/**
1109	>	* Clear out and cancel submissions, ignoring exceptions
1110	>	*/
1111	>	private void cancelSubmissions() {
1112		ForkJoinTask<?> task;
1113		while ((task = submissionQueue.poll()) != null) {
1114		try {
#	Line 1015 | Line 1116 | public class ForkJoinPool extends Abstra
1116		} catch (Throwable ignore) {
1117		}
1118		}
1018	–	// Propagate run level
1019	–	for (ForkJoinWorkerThread w : workers) {
1020	–	if (w != null)
1021	–	w.shutdown();    // also resumes suspended workers
1022	–	}
1023	–	// Ensure no straggling local tasks
1024	–	for (ForkJoinWorkerThread w : workers) {
1025	–	if (w != null)
1026	–	w.cancelTasks();
1027	–	}
1028	–	// Wake up idle workers
1029	–	advanceEventCount();
1030	–	releaseWaiters();
1031	–	// Unstick pending joins
1032	–	for (ForkJoinWorkerThread w : workers) {
1033	–	if (w != null && !w.isTerminated()) {
1034	–	try {
1035	–	w.interrupt();
1036	–	} catch (SecurityException ignore) {
1037	–	}
1038	–	}
1039	–	}
1119		}
1120
1121		// misc support for ForkJoinWorkerThread
#	Line 1049 | Line 1128 | public class ForkJoinPool extends Abstra
1128		}
1129
1130		/**
1131	<	* Accumulates steal count from a worker, clearing
1132	<	* the worker's value
1131	>	* Tries to accumulates steal count from a worker, clearing
1132	>	* the worker's value.
1133	>	*
1134	>	* @return true if worker steal count now zero
1135		*/
1136	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1136	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1137		int sc = w.stealCount;
1138	<	if (sc != 0) {
1139	<	long c;
1140	<	w.stealCount = 0;
1141	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1142	<	c = stealCount, c + sc));
1138	>	long c = stealCount;
1139	>	// CAS even if zero, for fence effects
1140	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1141	>	if (sc != 0)
1142	>	w.stealCount = 0;
1143	>	return true;
1144		}
1145	+	return sc == 0;
1146		}
1147
1148		/**
#	Line 1067 | Line 1150 | public class ForkJoinPool extends Abstra
1150		* active thread.
1151		*/
1152		final int idlePerActive() {
1153	+	int pc = parallelism; // use parallelism, not rc
1154		int ac = runState;    // no mask -- artifically boosts during shutdown
1071	–	int pc = parallelism; // use targeted parallelism, not rc
1155		// Use exact results for small values, saturate past 4
1156		return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1157		}
1158
1076	–	/**
1077	–	* Returns the approximate (non-atomic) difference between running
1078	–	* and active counts.
1079	–	*/
1080	–	final int inactiveCount() {
1081	–	return (workerCounts & RUNNING_COUNT_MASK) -
1082	–	(runState & ACTIVE_COUNT_MASK);
1083	–	}
1084	–
1159		// Public and protected methods
1160
1161		// Constructors
1162
1163		/**
1164		* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1165	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1166	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1165	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1166	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1167	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1168		*
1169		* @throws SecurityException if a security manager exists and
1170		*         the caller is not permitted to modify threads
#	Line 1098 | Line 1173 | public class ForkJoinPool extends Abstra
1173		*/
1174		public ForkJoinPool() {
1175		this(Runtime.getRuntime().availableProcessors(),
1176	<	defaultForkJoinWorkerThreadFactory);
1176	>	defaultForkJoinWorkerThreadFactory, null, false);
1177		}
1178
1179		/**
1180		* Creates a {@code ForkJoinPool} with the indicated parallelism
1181	<	* level and using the {@linkplain
1182	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1181	>	* level, the {@linkplain
1182	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1183	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1184		*
1185		* @param parallelism the parallelism level
1186		* @throws IllegalArgumentException if parallelism less than or
#	Line 1115 | Line 1191 | public class ForkJoinPool extends Abstra
1191		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1192		*/
1193		public ForkJoinPool(int parallelism) {
1194	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1119	<	}
1120	<
1121	<	/**
1122	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1123	<	* java.lang.Runtime#availableProcessors}, and using the given
1124	<	* thread factory.
1125	<	*
1126	<	* @param factory the factory for creating new threads
1127	<	* @throws NullPointerException if the factory is null
1128	<	* @throws SecurityException if a security manager exists and
1129	<	*         the caller is not permitted to modify threads
1130	<	*         because it does not hold {@link
1131	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1132	<	*/
1133	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1134	<	this(Runtime.getRuntime().availableProcessors(), factory);
1194	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1195		}
1196
1197		/**
1198	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1139	<	* thread factory.
1198	>	* Creates a {@code ForkJoinPool} with the given parameters.
1199		*
1200	<	* @param parallelism the parallelism level
1201	<	* @param factory the factory for creating new threads
1200	>	* @param parallelism the parallelism level. For default value,
1201	>	* use {@link java.lang.Runtime#availableProcessors}.
1202	>	* @param factory the factory for creating new threads. For default value,
1203	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1204	>	* @param handler the handler for internal worker threads that
1205	>	* terminate due to unrecoverable errors encountered while executing
1206	>	* tasks. For default value, use <code>null</code>.
1207	>	* @param asyncMode if true,
1208	>	* establishes local first-in-first-out scheduling mode for forked
1209	>	* tasks that are never joined. This mode may be more appropriate
1210	>	* than default locally stack-based mode in applications in which
1211	>	* worker threads only process event-style asynchronous tasks.
1212	>	* For default value, use <code>false</code>.
1213		* @throws IllegalArgumentException if parallelism less than or
1214		*         equal to zero, or greater than implementation limit
1215		* @throws NullPointerException if the factory is null
#	Line 1148 | Line 1218 | public class ForkJoinPool extends Abstra
1218		*         because it does not hold {@link
1219		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1220		*/
1221	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1221	>	public ForkJoinPool(int parallelism,
1222	>	ForkJoinWorkerThreadFactory factory,
1223	>	Thread.UncaughtExceptionHandler handler,
1224	>	boolean asyncMode) {
1225		checkPermission();
1226		if (factory == null)
1227		throw new NullPointerException();
1228	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1228	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1229		throw new IllegalArgumentException();
1157	–	this.poolNumber = poolNumberGenerator.incrementAndGet();
1158	–	int arraySize = initialArraySizeFor(parallelism);
1230		this.parallelism = parallelism;
1231		this.factory = factory;
1232	<	this.maxPoolSize = MAX_THREADS;
1233	<	this.maintainsParallelism = true;
1232	>	this.ueh = handler;
1233	>	this.locallyFifo = asyncMode;
1234	>	int arraySize = initialArraySizeFor(parallelism);
1235		this.workers = new ForkJoinWorkerThread[arraySize];
1236		this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1237		this.workerLock = new ReentrantLock();
1238	<	this.terminationLatch = new CountDownLatch(1);
1239	<	// Start first worker; remaining workers added upon first submission
1240	<	workerCounts = ONE_RUNNING | ONE_TOTAL;
1169	<	addWorker();
1238	>	this.termination = new Phaser(1);
1239	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1240	>	this.trimTime = System.nanoTime();
1241		}
1242
1243		/**
#	Line 1174 | Line 1245 | public class ForkJoinPool extends Abstra
1245		* @param pc the initial parallelism level
1246		*/
1247		private static int initialArraySizeFor(int pc) {
1248	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1249	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1248	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1249	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1250		size |= size >>> 1;
1251		size |= size >>> 2;
1252		size |= size >>> 4;
#	Line 1195 | Line 1266 | public class ForkJoinPool extends Abstra
1266		throw new RejectedExecutionException();
1267		submissionQueue.offer(task);
1268		advanceEventCount();
1269	<	releaseWaiters();
1199	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism)
1200	<	ensureEnoughTotalWorkers();
1269	>	helpMaintainParallelism();         // start or wake up workers
1270		}
1271
1272		/**
#	Line 1216 | Line 1285 | public class ForkJoinPool extends Abstra
1285
1286		/**
1287		* Arranges for (asynchronous) execution of the given task.
1288	+	* If the caller is already engaged in a fork/join computation in
1289	+	* the current pool, this method is equivalent in effect to
1290	+	* {@link ForkJoinTask#fork}.
1291		*
1292		* @param task the task
1293		* @throws NullPointerException if the task is null
#	Line 1243 | Line 1315 | public class ForkJoinPool extends Abstra
1315		}
1316
1317		/**
1318	+	* Submits a ForkJoinTask for execution.
1319	+	* If the caller is already engaged in a fork/join computation in
1320	+	* the current pool, this method is equivalent in effect to
1321	+	* {@link ForkJoinTask#fork}.
1322	+	*
1323	+	* @param task the task to submit
1324	+	* @return the task
1325	+	* @throws NullPointerException if the task is null
1326	+	* @throws RejectedExecutionException if the task cannot be
1327	+	*         scheduled for execution
1328	+	*/
1329	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1330	+	doSubmit(task);
1331	+	return task;
1332	+	}
1333	+
1334	+	/**
1335		* @throws NullPointerException if the task is null
1336		* @throws RejectedExecutionException if the task cannot be
1337		*         scheduled for execution
#	Line 1280 | Line 1369 | public class ForkJoinPool extends Abstra
1369		}
1370
1371		/**
1283	–	* Submits a ForkJoinTask for execution.
1284	–	*
1285	–	* @param task the task to submit
1286	–	* @return the task
1287	–	* @throws NullPointerException if the task is null
1288	–	* @throws RejectedExecutionException if the task cannot be
1289	–	*         scheduled for execution
1290	–	*/
1291	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1292	–	doSubmit(task);
1293	–	return task;
1294	–	}
1295	–
1296	–	/**
1372		* @throws NullPointerException       {@inheritDoc}
1373		* @throws RejectedExecutionException {@inheritDoc}
1374		*/
#	Line 1305 | Line 1380 | public class ForkJoinPool extends Abstra
1380		invoke(new InvokeAll<T>(forkJoinTasks));
1381
1382		@SuppressWarnings({"unchecked", "rawtypes"})
1383	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1383	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1384		return futures;
1385		}
1386
#	Line 1335 | Line 1410 | public class ForkJoinPool extends Abstra
1410		* @return the handler, or {@code null} if none
1411		*/
1412		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1338	–	workerCountReadFence();
1413		return ueh;
1414		}
1415
1416		/**
1343	–	* Sets the handler for internal worker threads that terminate due
1344	–	* to unrecoverable errors encountered while executing tasks.
1345	–	* Unless set, the current default or ThreadGroup handler is used
1346	–	* as handler.
1347	–	*
1348	–	* @param h the new handler
1349	–	* @return the old handler, or {@code null} if none
1350	–	* @throws SecurityException if a security manager exists and
1351	–	*         the caller is not permitted to modify threads
1352	–	*         because it does not hold {@link
1353	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1354	–	*/
1355	–	public Thread.UncaughtExceptionHandler
1356	–	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1357	–	checkPermission();
1358	–	workerCountReadFence();
1359	–	Thread.UncaughtExceptionHandler old = ueh;
1360	–	if (h != old) {
1361	–	ueh = h;
1362	–	workerCountWriteFence();
1363	–	for (ForkJoinWorkerThread w : workers) {
1364	–	if (w != null)
1365	–	w.setUncaughtExceptionHandler(h);
1366	–	}
1367	–	}
1368	–	return old;
1369	–	}
1370	–
1371	–	/**
1372	–	* Sets the target parallelism level of this pool.
1373	–	*
1374	–	* @param parallelism the target parallelism
1375	–	* @throws IllegalArgumentException if parallelism less than or
1376	–	* equal to zero or greater than maximum size bounds
1377	–	* @throws SecurityException if a security manager exists and
1378	–	*         the caller is not permitted to modify threads
1379	–	*         because it does not hold {@link
1380	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1381	–	*/
1382	–	public void setParallelism(int parallelism) {
1383	–	checkPermission();
1384	–	if (parallelism <= 0 || parallelism > maxPoolSize)
1385	–	throw new IllegalArgumentException();
1386	–	workerCountReadFence();
1387	–	int pc = this.parallelism;
1388	–	if (pc != parallelism) {
1389	–	this.parallelism = parallelism;
1390	–	workerCountWriteFence();
1391	–	// Release spares. If too many, some will die after re-suspend
1392	–	for (ForkJoinWorkerThread w : workers) {
1393	–	if (w != null && w.tryUnsuspend()) {
1394	–	updateRunningCount(1);
1395	–	LockSupport.unpark(w);
1396	–	}
1397	–	}
1398	–	ensureEnoughTotalWorkers();
1399	–	advanceEventCount();
1400	–	releaseWaiters(); // force config recheck by existing workers
1401	–	}
1402	–	}
1403	–
1404	–	/**
1417		* Returns the targeted parallelism level of this pool.
1418		*
1419		* @return the targeted parallelism level of this pool
1420		*/
1421		public int getParallelism() {
1410	–	//        workerCountReadFence(); // inlined below
1411	–	int ignore = workerCounts;
1422		return parallelism;
1423		}
1424
#	Line 1425 | Line 1435 | public class ForkJoinPool extends Abstra
1435		}
1436
1437		/**
1428	–	* Returns the maximum number of threads allowed to exist in the
1429	–	* pool. Unless set using {@link #setMaximumPoolSize}, the
1430	–	* maximum is an implementation-defined value designed only to
1431	–	* prevent runaway growth.
1432	–	*
1433	–	* @return the maximum
1434	–	*/
1435	–	public int getMaximumPoolSize() {
1436	–	workerCountReadFence();
1437	–	return maxPoolSize;
1438	–	}
1439	–
1440	–	/**
1441	–	* Sets the maximum number of threads allowed to exist in the
1442	–	* pool. The given value should normally be greater than or equal
1443	–	* to the {@link #getParallelism parallelism} level. Setting this
1444	–	* value has no effect on current pool size. It controls
1445	–	* construction of new threads.
1446	–	*
1447	–	* @throws IllegalArgumentException if negative or greater than
1448	–	* internal implementation limit
1449	–	*/
1450	–	public void setMaximumPoolSize(int newMax) {
1451	–	if (newMax < 0 || newMax > MAX_THREADS)
1452	–	throw new IllegalArgumentException();
1453	–	maxPoolSize = newMax;
1454	–	workerCountWriteFence();
1455	–	}
1456	–
1457	–	/**
1458	–	* Returns {@code true} if this pool dynamically maintains its
1459	–	* target parallelism level. If false, new threads are added only
1460	–	* to avoid possible starvation.  This setting is by default true.
1461	–	*
1462	–	* @return {@code true} if maintains parallelism
1463	–	*/
1464	–	public boolean getMaintainsParallelism() {
1465	–	workerCountReadFence();
1466	–	return maintainsParallelism;
1467	–	}
1468	–
1469	–	/**
1470	–	* Sets whether this pool dynamically maintains its target
1471	–	* parallelism level. If false, new threads are added only to
1472	–	* avoid possible starvation.
1473	–	*
1474	–	* @param enable {@code true} to maintain parallelism
1475	–	*/
1476	–	public void setMaintainsParallelism(boolean enable) {
1477	–	maintainsParallelism = enable;
1478	–	workerCountWriteFence();
1479	–	}
1480	–
1481	–	/**
1482	–	* Establishes local first-in-first-out scheduling mode for forked
1483	–	* tasks that are never joined. This mode may be more appropriate
1484	–	* than default locally stack-based mode in applications in which
1485	–	* worker threads only process asynchronous tasks.  This method is
1486	–	* designed to be invoked only when the pool is quiescent, and
1487	–	* typically only before any tasks are submitted. The effects of
1488	–	* invocations at other times may be unpredictable.
1489	–	*
1490	–	* @param async if {@code true}, use locally FIFO scheduling
1491	–	* @return the previous mode
1492	–	* @see #getAsyncMode
1493	–	*/
1494	–	public boolean setAsyncMode(boolean async) {
1495	–	workerCountReadFence();
1496	–	boolean oldMode = locallyFifo;
1497	–	if (oldMode != async) {
1498	–	locallyFifo = async;
1499	–	workerCountWriteFence();
1500	–	for (ForkJoinWorkerThread w : workers) {
1501	–	if (w != null)
1502	–	w.setAsyncMode(async);
1503	–	}
1504	–	}
1505	–	return oldMode;
1506	–	}
1507	–
1508	–	/**
1438		* Returns {@code true} if this pool uses local first-in-first-out
1439		* scheduling mode for forked tasks that are never joined.
1440		*
1441		* @return {@code true} if this pool uses async mode
1513	–	* @see #setAsyncMode
1442		*/
1443		public boolean getAsyncMode() {
1516	–	workerCountReadFence();
1444		return locallyFifo;
1445		}
1446
#	Line 1582 | Line 1509 | public class ForkJoinPool extends Abstra
1509		*/
1510		public long getQueuedTaskCount() {
1511		long count = 0;
1512	<	for (ForkJoinWorkerThread w : workers) {
1512	>	ForkJoinWorkerThread[] ws = workers;
1513	>	int n = ws.length;
1514	>	for (int i = 0; i < n; ++i) {
1515	>	ForkJoinWorkerThread w = ws[i];
1516		if (w != null)
1517		count += w.getQueueSize();
1518		}
#	Line 1639 | Line 1569 | public class ForkJoinPool extends Abstra
1569		* @return the number of elements transferred
1570		*/
1571		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1572	<	int n = submissionQueue.drainTo(c);
1573	<	for (ForkJoinWorkerThread w : workers) {
1572	>	int count = submissionQueue.drainTo(c);
1573	>	ForkJoinWorkerThread[] ws = workers;
1574	>	int n = ws.length;
1575	>	for (int i = 0; i < n; ++i) {
1576	>	ForkJoinWorkerThread w = ws[i];
1577		if (w != null)
1578	<	n += w.drainTasksTo(c);
1578	>	count += w.drainTasksTo(c);
1579		}
1580	<	return n;
1580	>	return count;
1581		}
1582
1583		/**
#	Line 1768 | Line 1701 | public class ForkJoinPool extends Abstra
1701		*/
1702		public boolean awaitTermination(long timeout, TimeUnit unit)
1703		throws InterruptedException {
1704	<	return terminationLatch.await(timeout, unit);
1704	>	try {
1705	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1706	>	} catch(TimeoutException ex) {
1707	>	return false;
1708	>	}
1709		}
1710
1711		/**
1712		* Interface for extending managed parallelism for tasks running
1713		* in {@link ForkJoinPool}s.
1714		*
1715	<	* <p>A {@code ManagedBlocker} provides two methods.
1716	<	* Method {@code isReleasable} must return {@code true} if
1717	<	* blocking is not necessary. Method {@code block} blocks the
1718	<	* current thread if necessary (perhaps internally invoking
1719	<	* {@code isReleasable} before actually blocking).
1715	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1716	>	* {@code isReleasable} must return {@code true} if blocking is
1717	>	* not necessary. Method {@code block} blocks the current thread
1718	>	* if necessary (perhaps internally invoking {@code isReleasable}
1719	>	* before actually blocking). The unusual methods in this API
1720	>	* accommodate synchronizers that may, but don't usually, block
1721	>	* for long periods. Similarly, they allow more efficient internal
1722	>	* handling of cases in which additional workers may be, but
1723	>	* usually are not, needed to ensure sufficient parallelism.
1724	>	* Toward this end, implementations of method {@code isReleasable}
1725	>	* must be amenable to repeated invocation.
1726		*
1727		* <p>For example, here is a ManagedBlocker based on a
1728		* ReentrantLock:
#	Line 1797 | Line 1740 | public class ForkJoinPool extends Abstra
1740		*     return hasLock || (hasLock = lock.tryLock());
1741		*   }
1742		* }}</pre>
1743	+	*
1744	+	* <p>Here is a class that possibly blocks waiting for an
1745	+	* item on a given queue:
1746	+	*  <pre> {@code
1747	+	* class QueueTaker<E> implements ManagedBlocker {
1748	+	*   final BlockingQueue<E> queue;
1749	+	*   volatile E item = null;
1750	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1751	+	*   public boolean block() throws InterruptedException {
1752	+	*     if (item == null)
1753	+	*       item = queue.take
1754	+	*     return true;
1755	+	*   }
1756	+	*   public boolean isReleasable() {
1757	+	*     return item != null || (item = queue.poll) != null;
1758	+	*   }
1759	+	*   public E getItem() { // call after pool.managedBlock completes
1760	+	*     return item;
1761	+	*   }
1762	+	* }}</pre>
1763		*/
1764		public static interface ManagedBlocker {
1765		/**
#	Line 1820 | Line 1783 | public class ForkJoinPool extends Abstra
1783		* Blocks in accord with the given blocker.  If the current thread
1784		* is a {@link ForkJoinWorkerThread}, this method possibly
1785		* arranges for a spare thread to be activated if necessary to
1786	<	* ensure parallelism while the current thread is blocked.
1824	<	*
1825	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1826	<	* supports it ({@link #getMaintainsParallelism}), this method
1827	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1828	<	* it activates a thread only if necessary to avoid complete
1829	<	* starvation. This option may be preferable when blockages use
1830	<	* timeouts, or are almost always brief.
1786	>	* ensure sufficient parallelism while the current thread is blocked.
1787		*
1788		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1789		* behaviorally equivalent to
#	Line 1841 | Line 1797 | public class ForkJoinPool extends Abstra
1797		* first be expanded to ensure parallelism, and later adjusted.
1798		*
1799		* @param blocker the blocker
1844	–	* @param maintainParallelism if {@code true} and supported by
1845	–	* this pool, attempt to maintain the pool's nominal parallelism;
1846	–	* otherwise activate a thread only if necessary to avoid
1847	–	* complete starvation.
1800		* @throws InterruptedException if blocker.block did so
1801		*/
1802	<	public static void managedBlock(ManagedBlocker blocker,
1851	<	boolean maintainParallelism)
1802	>	public static void managedBlock(ManagedBlocker blocker)
1803		throws InterruptedException {
1804		Thread t = Thread.currentThread();
1805	<	if (t instanceof ForkJoinWorkerThread)
1806	<	((ForkJoinWorkerThread) t).pool.
1807	<	doBlock(blocker, maintainParallelism);
1808	<	else
1809	<	awaitBlocker(blocker);
1810	<	}
1811	<
1861	<	/**
1862	<	* Performs Non-FJ blocking
1863	<	*/
1864	<	private static void awaitBlocker(ManagedBlocker blocker)
1865	<	throws InterruptedException {
1866	<	do {} while (!blocker.isReleasable() && !blocker.block());
1805	>	if (t instanceof ForkJoinWorkerThread) {
1806	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1807	>	w.pool.awaitBlocker(blocker);
1808	>	}
1809	>	else {
1810	>	do {} while (!blocker.isReleasable() && !blocker.block());
1811	>	}
1812		}
1813
1814		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 1891 | Line 1836 | public class ForkJoinPool extends Abstra
1836		objectFieldOffset("eventWaiters",ForkJoinPool.class);
1837		private static final long stealCountOffset =
1838		objectFieldOffset("stealCount",ForkJoinPool.class);
1839	<
1839	>	private static final long spareWaitersOffset =
1840	>	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1841
1842		private static long objectFieldOffset(String field, Class<?> klazz) {
1843		try {

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