[ViewVC] Diff of: jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.56 by dl, Thu May 27 16:46:48 2010 UTC vs.
Revision 1.61 by dl, Wed Aug 11 18:45:12 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 exhuasted.
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 146 \| Line 205 \| public class ForkJoinPool extends Abstra
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 to spare counts must be prospective (not
232	<	* retrospective). For example, the running count is decremented
233	<	* before blocking by a thread about to block as a spare, but
163	<	* incremented by the thread about to unblock it. Updates upon
164	<	* resumption ofr threads blocking in awaitJoin or awaitBlocker
165	<	* cannot usually be prospective, so the running count is in
166	<	* general an upper bound of the number of productively running
167	<	* threads Updates to the workerCounts field sometimes transiently
168	<	* encounter a fair amount of contention when join dependencies
169	<	* are such that many threads block or unblock at about the same
170	<	* time. We alleviate this by sometimes bundling updates (for
171	<	* example blocking one thread on join and resuming a spare cancel
172	<	* each other out), and in most other cases performing an
173	<	* alternative action like releasing waiters or locating spares.
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 199 \| 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 228 \| 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 awaitJoin and awaitBlocker look
300	<	* for suspended threads to resume before considering creating a
301	<	* new replacement. We don't need a special data structure to
302	<	* maintain spares; simply scanning the workers array looking for
303	<	* worker.isSuspended() is fine because the calling thread is
244	<	* otherwise not doing anything useful anyway; we are at least as
245	<	* happy if after locating a spare, the caller doesn't actually
246	<	* block because the join is ready before we try to adjust and
247	<	* compensate. Note that this is intrinsically racy. One thread
299	>	* so, suspends itself. Method helpMaintainParallelism looks for
300	>	* suspended threads to resume before considering creating a new
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 awaitJoin and awaitBlocker. We always
318	<	* need to create one when the number of running threads becomes
319	<	* zero. But because blocked joins are typically dependent, we
320	<	* don't necessarily need or want one-to-one replacement. Using a
321	<	* one-to-one compensation rule often leads to enough useless
322	<	* overhead creating, suspending, resuming, and/or killing threads
323	<	* to signficantly degrade throughput. We use a rule reflecting
324	<	* the idea that, the more spare threads you already have, the
325	<	* more evidence you need to create another one. The "evidence"
326	<	* here takes two forms: (1) Using a creation threshold expressed
327	<	* in terms of the current deficit -- target minus running
328	<	* threads. To reduce flickering and drift around target values,
329	<	* the relation is quadratic: adding a spare if (dcdc)>=(scpc)
330	<	* (where dc is deficit, sc is number of spare threads and pc is
331	<	* target parallelism.) (2) Using a form of adaptive
332	<	* spionning. requiring a number of threshold checks proportional
333	<	* to the number of spare threads. This effectively reduces churn
334	<	* at the price of systematically undershooting target parallelism
279	<	* when many threads are blocked. However, biasing toward
280	<	* undeshooting partially compensates for the above mechanics to
281	<	* suspend extra threads, that normally lead to overshoot because
282	<	* we can only suspend workers in-between top-level actions. It
283	<	* also better copes with the fact that some of the methods in
284	<	* this class tend to never become compiled (but are interpreted),
285	<	* so some components of the entire set of controls might execute
286	<	* many times faster than others. And similarly for cases where
287	<	* the apparent lack of work is just due to GC stalls and other
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		*
290	–	* 7. Maintaining other configuration parameters and monitoring
291	–	* statistics. Updates to fields controlling parallelism level,
292	–	* max size, etc can only meaningfully take effect for individual
293	–	* threads upon their next top-level actions; i.e., between
294	–	* stealing/running tasks/submission, which are separated by calls
295	–	* to preStep. Memory ordering for these (assumed infrequent)
296	–	* reconfiguration calls is ensured by using reads and writes to
297	–	* volatile field workerCounts (that must be read in preStep anyway)
298	–	* as "fences" -- user-level reads are preceded by reads of
299	–	* workCounts, and writes are followed by no-op CAS to
300	–	* workerCounts. The values reported by other management and
301	–	* monitoring methods are either computed on demand, or are kept
302	–	* in fields that are only updated when threads are otherwise
303	–	* idle.
304	–	*
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 313 \| 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 346 \| 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 385 \| 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 414 \| 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 428 \| 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 475 \| 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
479	<	* configuration parameters.
535	>	* running state.
536		*/
537		private volatile int workerCounts;
538
#	Line 485 \| 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
488	–	/*
489	–	* Fields parallelism. maxPoolSize, and maintainsParallelism are
490	–	* non-volatile, but external reads/writes use workerCount fences
491	–	* to ensure visability.
492	–	*/
493	–
544		/**
545		* The target parallelism level.
546	+	* Accessed directly by ForkJoinWorkerThreads.
547		*/
548	<	private int parallelism;
498	<
499	<	/**
500	<	* The maximum allowed pool size.
501	<	*/
502	<	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
552	>	* Read by, and replicated by ForkJoinWorkerThreads
553		*/
554	<	private volatile boolean locallyFifo;
554	>	final boolean locallyFifo;
555
556		/**
557	<	* Controls whether to add spares to maintain parallelism
557	>	* The uncaught exception handler used when any worker abruptly
558	>	* terminates.
559		*/
560	<	private boolean maintainsParallelism;
514	<
515	<	/**
516	<	* The uncaught exception handler used when any worker
517	<	* abruptly terminates
518	<	*/
519	<	private volatile 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.
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	<	* Decrements running count unless already zero
582	>	* Tries to decrement running count unless already zero
583		*/
584		final boolean tryDecrementRunningCount() {
585		int wc = workerCounts;
#	Line 547 \| Line 590 \| public class ForkJoinPool extends Abstra
590		}
591
592		/**
593	<	* Write fence for user modifications of pool parameters
594	<	* (parallelism. etc). Note that it doesn't matter if CAS fails.
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 workerCountWriteFence() {
600	<	int wc;
601	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
602	<	wc = workerCounts, wc);
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	<	* Read fence for external reads of pool parameters
561	<	* (parallelism. maxPoolSize, etc).
614	>	* Increments event count
615		*/
616	<	private void workerCountReadFence() {
617	<	int ignore = workerCounts;
616	>	private void advanceEventCount() {
617	>	int c;
618	>	do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
619	>	c = eventCount, c+1));
620		}
621
622		/**
#	Line 612 \| Line 667 \| public class ForkJoinPool extends Abstra
667		lock.lock();
668		try {
669		ForkJoinWorkerThread[] ws = workers;
670	<	int nws = ws.length;
671	<	if (k < 0 \|\| k >= nws \|\| ws[k] != null) {
672	<	for (k = 0; k < nws && 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 == nws)
675	<	ws = Arrays.copyOf(ws, nws << 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 650 \| 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.
653	–	*
654	–	* @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;
668	<	}
669	<
670	<	/**
671	<	* Adjusts counts upon failure to create worker
672	<	*/
673	<	private void onWorkerCreationFailure() {
674	<	for (;;) {
675	<	int wc = workerCounts;
676	<	if ((wc >>> TOTAL_COUNT_SHIFT) > 0 &&
677	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
678	<	wc, wc - (ONE_RUNNING\|ONE_TOTAL)))
679	<	break;
680	<	}
681	<	tryTerminate(false); // in case of failure during shutdown
682	<	}
683	<
684	<	/**
685	<	* Create enough total workers to establish target parallelism,
686	<	* giving up if terminating or addWorker fails
687	<	*/
688	<	private void ensureEnoughTotalWorkers() {
689	<	int wc;
690	<	while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism &&
691	<	runState < TERMINATING) {
692	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
693	<	wc, wc + (ONE_RUNNING\|ONE_TOTAL)) &&
694	<	addWorker() == null))
695	<	break;
696	<	}
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
703	<	* the worker.
726	>	* down, tries to complete terminatation.
727		*
728		* @param w the worker
729		*/
730		final void workerTerminated(ForkJoinWorkerThread w) {
708	–	if (w.active) { // force inactive
709	–	w.active = false;
710	–	do {} while (!tryDecrementActiveCount());
711	–	}
731		forgetWorker(w);
732	<
733	<	// Decrement total count, and if was running, running count
734	<	// Spin (waiting for other updates) if either would be negative
735	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
717	<	int unit = ONE_TOTAL + nr;
718	<	for (;;) {
719	<	int wc = workerCounts;
720	<	int rc = wc & RUNNING_COUNT_MASK;
721	<	if (rc - nr < 0 \|\| (wc >>> TOTAL_COUNT_SHIFT) == 0)
722	<	Thread.yield(); // back off if waiting for other updates
723	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
724	<	wc, wc - unit))
725	<	break;
726	<	}
727	<
728	<	accumulateStealCount(w); // collect final count
729	<	if (!tryTerminate(false))
730	<	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		/**
736	–	* Ensures eventCount on exit is different (mod 2^32) than on
737	–	* entry. CAS failures are OK -- any change in count suffices.
738	–	*/
739	–	private void advanceEventCount() {
740	–	int c;
741	–	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
742	–	}
743	–
744	–	/**
741		* Releases workers blocked on a count not equal to current count.
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	<	final void releaseWaiters() {
750	<	long top;
751	<	int id;
752	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
753	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
754	<	ForkJoinWorkerThread[] ws = workers;
755	<	ForkJoinWorkerThread w;
756	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
757	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
758	<	top, w.nextWaiter))
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;
770	<	ec = eventCount;
771	<	for (;;) {
772	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
773	<	int id = (int)(top & WAITER_INDEX_MASK);
774	<	if (id <= 0 \|\| (int)(top >>> EVENT_COUNT_SHIFT) == ec)
775	<	return;
776	<	if ((ws = workers).length < id \|\| (w = ws[id - 1]) == null \|\|
777	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
778	<	top, top = w.nextWaiter))
779	<	continue outer; // possibly stale; reread
780	<	LockSupport.unpark(w);
781	<	if (top != eventWaiters) // let someone else take over
782	<	return;
783	<	}
784	<	}
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
790	<	* 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		}
813	–	w.lastEventCount = eventCount;
802		}
803	<	releaseWaiters();
803	>	w.lastEventCount = eventCount;
804		}
805
806	+	// Maintaining spares
807	+
808		/**
809	<	* Callback from workers invoked upon each top-level action (i.e.,
820	<	* stealing a task or taking a submission and running
821	<	* it). Performs one or both of the following:
822	<	*
823	<	* * If the worker cannot find work, updates its active status to
824	<	* inactive and updates activeCount unless there is contention, in
825	<	* which case it may try again (either in this or a subsequent
826	<	* call). Additionally, awaits the next task event and/or helps
827	<	* wake up other releasable waiters.
828	<	*
829	<	* * If there are too many running threads, suspends this worker
830	<	* (first forcing inactivation if necessary). If it is not
831	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
832	<	* -- killed while suspended within suspendAsSpare. Otherwise,
833	<	* upon resume it rechecks to make sure that it is still needed.
834	<	*
835	<	* @param w the worker
836	<	* @param worked false if the worker scanned for work but didn't
837	<	* find any (in which case it may block waiting for work).
809	>	* Pushes worker onto the spare stack
810		*/
811	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
812	<	boolean active = w.active;
813	<	boolean inactivate = !worked & active;
814	<	for (;;) {
815	<	if (inactivate) {
816	<	int c = runState;
817	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
818	<	c, c - ONE_ACTIVE))
819	<	inactivate = active = w.active = false;
820	<	}
821	<	int wc = workerCounts;
822	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
823	<	if (!worked)
824	<	eventSync(w);
825	<	return;
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		}
855	–	if (!(inactivate \|= active) && // must inactivate to suspend
856	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
857	–	wc, wc - ONE_RUNNING) &&
858	–	!w.suspendAsSpare()) // false if trimmed
859	–	return;
843		}
844		}
845
846		/**
847	<	* Adjusts counts and creates or resumes compensating threads for
848	<	* a worker blocking on task joinMe. First tries resuming an
849	<	* existing spare (which usually also avoids any count
850	<	* adjustment), but must then decrement running count to determine
851	<	* whether a new thread is needed. See above for fuller
852	<	* explanation. This code is sprawled out non-modularly mainly
853	<	* because adaptive spinning works best if the entire method is
854	<	* either interpreted or compiled vs having only some pieces of it
855	<	* compiled.
856	<	*
857	<	* @param joinMe the task to join
858	<	* @return task status on exit (to simplify usage by callers)
859	<	*/
860	<	final int awaitJoin(ForkJoinTask<?> joinMe) {
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	<	boolean adj = false; // true when running count adjusted
865	<	int scans = 0;
866	<
867	<	while (joinMe.status >= 0) {
868	<	ForkJoinWorkerThread spare = null;
869	<	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
870	<	ForkJoinWorkerThread[] ws = workers;
871	<	int nws = ws.length;
872	<	for (int i = 0; i < nws; ++i) {
873	<	ForkJoinWorkerThread w = ws[i];
889	<	if (w != null && w.isSuspended()) {
890	<	spare = w;
891	<	break;
892	<	}
893	<	}
894	<	if (joinMe.status < 0)
895	<	break;
896	<	}
897	<	int wc = workerCounts;
898	<	int rc = wc & RUNNING_COUNT_MASK;
899	<	int dc = pc - rc;
900	<	if (dc > 0 && spare != null && spare.tryUnsuspend()) {
901	<	if (adj) {
902	<	int c;
903	<	do {} while (!UNSAFE.compareAndSwapInt
904	<	(this, workerCountsOffset,
905	<	c = workerCounts, c + ONE_RUNNING));
906	<	}
907	<	adj = true;
908	<	LockSupport.unpark(spare);
909	<	}
910	<	else if (adj) {
911	<	if (dc <= 0)
912	<	break;
913	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
914	<	if (scans > tc) {
915	<	int ts = (tc - pc) * pc;
916	<	if (rc != 0 && (dc * dc < ts \|\| !maintainsParallelism))
917	<	break;
918	<	if (scans > ts && tc < maxPoolSize &&
919	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
920	<	wc+(ONE_RUNNING\|ONE_TOTAL))){
921	<	addWorker();
922	<	break;
923	<	}
924	<	}
925	<	}
926	<	else if (rc != 0)
927	<	adj = UNSAFE.compareAndSwapInt (this, workerCountsOffset,
928	<	wc, wc - ONE_RUNNING);
929	<	if ((scans++ & 1) == 0)
930	<	releaseWaiters(); // help others progress
931	<	else
932	<	Thread.yield(); // avoid starving productive threads
933	<	}
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	<	if (adj) {
876	<	joinMe.internalAwaitDone();
877	<	int c;
878	<	do {} while (!UNSAFE.compareAndSwapInt
879	<	(this, workerCountsOffset,
880	<	c = workerCounts, c + ONE_RUNNING));
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		}
942	–	return joinMe.status;
912		}
913
914		/**
915	<	* Same idea as awaitJoin
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 more of the following:
918	>	*
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 misses the number of scans by caller failing to find work
939	>	* (saturating at 2 just to avoid wraparound)
940		*/
941	<	final void awaitBlocker(ManagedBlocker blocker, boolean maintainPar)
942	<	throws InterruptedException {
950	<	maintainPar &= maintainsParallelism;
941	>	final void preStep(ForkJoinWorkerThread w, int misses) {
942	>	boolean active = w.active;
943		int pc = parallelism;
952	–	boolean adj = false; // true when running count adjusted
953	–	int scans = 0;
954	–	boolean done;
955	–
944		for (;;) {
957	–	if (done = blocker.isReleasable())
958	–	break;
959	–	ForkJoinWorkerThread spare = null;
960	–	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
961	–	ForkJoinWorkerThread[] ws = workers;
962	–	int nws = ws.length;
963	–	for (int i = 0; i < nws; ++i) {
964	–	ForkJoinWorkerThread w = ws[i];
965	–	if (w != null && w.isSuspended()) {
966	–	spare = w;
967	–	break;
968	–	}
969	–	}
970	–	if (done = blocker.isReleasable())
971	–	break;
972	–	}
945		int wc = workerCounts;
946		int rc = wc & RUNNING_COUNT_MASK;
947	<	int dc = pc - rc;
948	<	if (dc > 0 && spare != null && spare.tryUnsuspend()) {
949	<	if (adj) {
950	<	int c;
951	<	do {} while (!UNSAFE.compareAndSwapInt
952	<	(this, workerCountsOffset,
953	<	c = workerCounts, c + ONE_RUNNING));
954	<	}
983	<	adj = true;
984	<	LockSupport.unpark(spare);
947	>	if (active && (misses > 0 \|\| rc > pc)) {
948	>	int rs; // try inactivate
949	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
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	<	else if (adj) {
957	<	if (dc <= 0)
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;
989	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
990	–	if (scans > tc) {
991	–	int ts = (tc - pc) * pc;
992	–	if (rc != 0 && (dc * dc < ts \|\| !maintainPar))
993	–	break;
994	–	if (scans > ts && tc < maxPoolSize &&
995	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
996	–	wc+(ONE_RUNNING\|ONE_TOTAL))){
997	–	addWorker();
998	–	break;
999	–	}
1000	–	}
966		}
967	<	else if (rc != 0)
968	<	adj = UNSAFE.compareAndSwapInt (this, workerCountsOffset,
969	<	wc, wc - ONE_RUNNING);
970	<	if ((++scans & 1) == 0)
971	<	releaseWaiters(); // help others progress
1007	<	else
1008	<	Thread.yield(); // avoid starving productive threads
967	>	else {
968	>	if (rc < pc \|\| eventWaiters != 0L)
969	>	helpMaintainParallelism();
970	>	break;
971	>	}
972		}
973	+	}
974
975	<	try {
976	<	if (!done)
977	<	do {} while (!blocker.isReleasable() && !blocker.block());
978	<	} finally {
979	<	if (adj) {
975	>	/**
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	>	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	>	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	<	* Unless there are not enough other running threads, adjusts
1026	<	* counts and blocks a worker performing helpJoin that cannot find
1027	<	* any work.
1028	<	*
1029	<	* @return true if joinMe now done
1014	>	* Same idea as awaitJoin, but no helping
1015		*/
1016	<	final boolean tryAwaitBusyJoin(ForkJoinTask<?> joinMe) {
1017	<	int pc = parallelism;
1018	<	outer:for (;;) {
1019	<	releaseWaiters();
1020	<	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
1021	<	ForkJoinWorkerThread[] ws = workers;
1022	<	int nws = ws.length;
1023	<	for (int i = 0; i < nws; ++i) {
1024	<	ForkJoinWorkerThread w = ws[i];
1025	<	if (w != null && w.isSuspended()) {
1026	<	if (joinMe.status < 0)
1042	<	return true;
1043	<	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
1044	<	break;
1045	<	if (w.tryUnsuspend()) {
1046	<	LockSupport.unpark(w);
1047	<	break outer;
1048	<	}
1049	<	continue outer;
1050	<	}
1051	<	}
1016	>	final void awaitBlocker(ManagedBlocker blocker)
1017	>	throws InterruptedException {
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 (joinMe.status < 0)
1029	<	return true;
1030	<	int wc = workerCounts;
1031	<	if ((wc & RUNNING_COUNT_MASK) <= 2 \|\|
1032	<	(wc >>> TOTAL_COUNT_SHIFT) < pc)
1033	<	return false; // keep this thread alive
1034	<	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1035	<	wc, wc - ONE_RUNNING))
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
1038	>	(this, workerCountsOffset,
1039	>	c = workerCounts, c + ONE_RUNNING));
1040	>	}
1041		break;
1042	+	}
1043		}
1063	–
1064	–	joinMe.internalAwaitDone();
1065	–	int c;
1066	–	do {} while (!UNSAFE.compareAndSwapInt
1067	–	(this, workerCountsOffset,
1068	–	c = workerCounts, c + ONE_RUNNING));
1069	–	return true;
1044		}
1045
1046		/**
#	Line 1090 \| 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	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1083	<	cancelSubmissions();
1104	<	shutdownWorkers();
1105	<	cancelWorkerTasks();
1082	>	cancelSubmissions();
1083	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1084		advanceEventCount();
1085	<	releaseWaiters();
1086	<	interruptWorkers();
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
#	Line 1122 \| Line 1118 \| public class ForkJoinPool extends Abstra
1118		}
1119		}
1120
1125	–	/**
1126	–	* Sets all worker run states to at least shutdown,
1127	–	* also resuming suspended workers
1128	–	*/
1129	–	private void shutdownWorkers() {
1130	–	ForkJoinWorkerThread[] ws = workers;
1131	–	int nws = ws.length;
1132	–	for (int i = 0; i < nws; ++i) {
1133	–	ForkJoinWorkerThread w = ws[i];
1134	–	if (w != null)
1135	–	w.shutdown();
1136	–	}
1137	–	}
1138	–
1139	–	/**
1140	–	* Clears out and cancels all locally queued tasks
1141	–	*/
1142	–	private void cancelWorkerTasks() {
1143	–	ForkJoinWorkerThread[] ws = workers;
1144	–	int nws = ws.length;
1145	–	for (int i = 0; i < nws; ++i) {
1146	–	ForkJoinWorkerThread w = ws[i];
1147	–	if (w != null)
1148	–	w.cancelTasks();
1149	–	}
1150	–	}
1151	–
1152	–	/**
1153	–	* Unsticks all workers blocked on joins etc
1154	–	*/
1155	–	private void interruptWorkers() {
1156	–	ForkJoinWorkerThread[] ws = workers;
1157	–	int nws = ws.length;
1158	–	for (int i = 0; i < nws; ++i) {
1159	–	ForkJoinWorkerThread w = ws[i];
1160	–	if (w != null && !w.isTerminated()) {
1161	–	try {
1162	–	w.interrupt();
1163	–	} catch (SecurityException ignore) {
1164	–	}
1165	–	}
1166	–	}
1167	–	}
1168	–
1121		// misc support for ForkJoinWorkerThread
1122
1123		/**
#	Line 1176 \| 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 1194 \| 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
1198	–	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		}
#	Line 1206 \| Line 1162 \| public class ForkJoinPool extends Abstra
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 1216 \| 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 1233 \| Line 1191 \| public class ForkJoinPool extends Abstra
1191		* java.lang.RuntimePermission}{@code ("modifyThread")}
1192		*/
1193		public ForkJoinPool(int parallelism) {
1194	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1237	<	}
1238	<
1239	<	/**
1240	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1241	<	* java.lang.Runtime#availableProcessors}, and using the given
1242	<	* thread factory.
1243	<	*
1244	<	* @param factory the factory for creating new threads
1245	<	* @throws NullPointerException if the factory is null
1246	<	* @throws SecurityException if a security manager exists and
1247	<	* the caller is not permitted to modify threads
1248	<	* because it does not hold {@link
1249	<	* java.lang.RuntimePermission}{@code ("modifyThread")}
1250	<	*/
1251	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1252	<	this(Runtime.getRuntime().availableProcessors(), factory);
1194	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1195		}
1196
1197		/**
1198	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1257	<	* 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 1266 \| 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();
1275	–	this.poolNumber = poolNumberGenerator.incrementAndGet();
1276	–	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);
1238	>	this.termination = new Phaser(1);
1239	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1240	>	this.trimTime = System.nanoTime();
1241		}
1242
1243		/**
#	Line 1289 \| 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 1310 \| Line 1266 \| public class ForkJoinPool extends Abstra
1266		throw new RejectedExecutionException();
1267		submissionQueue.offer(task);
1268		advanceEventCount();
1269	<	releaseWaiters();
1314	<	ensureEnoughTotalWorkers();
1269	>	helpMaintainParallelism(); // start or wake up workers
1270		}
1271
1272		/**
1273		* Performs the given task, returning its result upon completion.
1274	+	* If the caller is already engaged in a fork/join computation in
1275	+	* the current pool, this method is equivalent in effect to
1276	+	* {@link ForkJoinTask#invoke}.
1277		*
1278		* @param task the task
1279		* @return the task's result
#	Line 1330 \| Line 1288 \| public class ForkJoinPool extends Abstra
1288
1289		/**
1290		* Arranges for (asynchronous) execution of the given task.
1291	+	* If the caller is already engaged in a fork/join computation in
1292	+	* the current pool, this method is equivalent in effect to
1293	+	* {@link ForkJoinTask#fork}.
1294		*
1295		* @param task the task
1296		* @throws NullPointerException if the task is null
#	Line 1357 \| Line 1318 \| public class ForkJoinPool extends Abstra
1318		}
1319
1320		/**
1321	+	* Submits a ForkJoinTask for execution.
1322	+	* If the caller is already engaged in a fork/join computation in
1323	+	* the current pool, this method is equivalent in effect to
1324	+	* {@link ForkJoinTask#fork}.
1325	+	*
1326	+	* @param task the task to submit
1327	+	* @return the task
1328	+	* @throws NullPointerException if the task is null
1329	+	* @throws RejectedExecutionException if the task cannot be
1330	+	* scheduled for execution
1331	+	*/
1332	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1333	+	doSubmit(task);
1334	+	return task;
1335	+	}
1336	+
1337	+	/**
1338		* @throws NullPointerException if the task is null
1339		* @throws RejectedExecutionException if the task cannot be
1340		* scheduled for execution
#	Line 1394 \| Line 1372 \| public class ForkJoinPool extends Abstra
1372		}
1373
1374		/**
1397	–	* Submits a ForkJoinTask for execution.
1398	–	*
1399	–	* @param task the task to submit
1400	–	* @return the task
1401	–	* @throws NullPointerException if the task is null
1402	–	* @throws RejectedExecutionException if the task cannot be
1403	–	* scheduled for execution
1404	–	*/
1405	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1406	–	doSubmit(task);
1407	–	return task;
1408	–	}
1409	–
1410	–	/**
1375		* @throws NullPointerException {@inheritDoc}
1376		* @throws RejectedExecutionException {@inheritDoc}
1377		*/
#	Line 1449 \| Line 1413 \| public class ForkJoinPool extends Abstra
1413		* @return the handler, or {@code null} if none
1414		*/
1415		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1452	–	workerCountReadFence();
1416		return ueh;
1417		}
1418
1419		/**
1457	–	* Sets the handler for internal worker threads that terminate due
1458	–	* to unrecoverable errors encountered while executing tasks.
1459	–	* Unless set, the current default or ThreadGroup handler is used
1460	–	* as handler.
1461	–	*
1462	–	* @param h the new handler
1463	–	* @return the old handler, or {@code null} if none
1464	–	* @throws SecurityException if a security manager exists and
1465	–	* the caller is not permitted to modify threads
1466	–	* because it does not hold {@link
1467	–	* java.lang.RuntimePermission}{@code ("modifyThread")}
1468	–	*/
1469	–	public Thread.UncaughtExceptionHandler
1470	–	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1471	–	checkPermission();
1472	–	Thread.UncaughtExceptionHandler old = ueh;
1473	–	if (h != old) {
1474	–	ueh = h;
1475	–	ForkJoinWorkerThread[] ws = workers;
1476	–	int nws = ws.length;
1477	–	for (int i = 0; i < nws; ++i) {
1478	–	ForkJoinWorkerThread w = ws[i];
1479	–	if (w != null)
1480	–	w.setUncaughtExceptionHandler(h);
1481	–	}
1482	–	}
1483	–	return old;
1484	–	}
1485	–
1486	–	/**
1487	–	* Sets the target parallelism level of this pool.
1488	–	*
1489	–	* @param parallelism the target parallelism
1490	–	* @throws IllegalArgumentException if parallelism less than or
1491	–	* equal to zero or greater than maximum size bounds
1492	–	* @throws SecurityException if a security manager exists and
1493	–	* the caller is not permitted to modify threads
1494	–	* because it does not hold {@link
1495	–	* java.lang.RuntimePermission}{@code ("modifyThread")}
1496	–	*/
1497	–	public void setParallelism(int parallelism) {
1498	–	checkPermission();
1499	–	if (parallelism <= 0 \|\| parallelism > maxPoolSize)
1500	–	throw new IllegalArgumentException();
1501	–	workerCountReadFence();
1502	–	int pc = this.parallelism;
1503	–	if (pc != parallelism) {
1504	–	this.parallelism = parallelism;
1505	–	workerCountWriteFence();
1506	–	// Release spares. If too many, some will die after re-suspend
1507	–	ForkJoinWorkerThread[] ws = workers;
1508	–	int nws = ws.length;
1509	–	for (int i = 0; i < nws; ++i) {
1510	–	ForkJoinWorkerThread w = ws[i];
1511	–	if (w != null && w.tryUnsuspend()) {
1512	–	int c;
1513	–	do {} while (!UNSAFE.compareAndSwapInt
1514	–	(this, workerCountsOffset,
1515	–	c = workerCounts, c + ONE_RUNNING));
1516	–	LockSupport.unpark(w);
1517	–	}
1518	–	}
1519	–	ensureEnoughTotalWorkers();
1520	–	advanceEventCount();
1521	–	releaseWaiters(); // force config recheck by existing workers
1522	–	}
1523	–	}
1524	–
1525	–	/**
1420		* Returns the targeted parallelism level of this pool.
1421		*
1422		* @return the targeted parallelism level of this pool
1423		*/
1424		public int getParallelism() {
1531	–	// workerCountReadFence(); // inlined below
1532	–	int ignore = workerCounts;
1425		return parallelism;
1426		}
1427
#	Line 1546 \| Line 1438 \| public class ForkJoinPool extends Abstra
1438		}
1439
1440		/**
1549	–	* Returns the maximum number of threads allowed to exist in the
1550	–	* pool. Unless set using {@link #setMaximumPoolSize}, the
1551	–	* maximum is an implementation-defined value designed only to
1552	–	* prevent runaway growth.
1553	–	*
1554	–	* @return the maximum
1555	–	*/
1556	–	public int getMaximumPoolSize() {
1557	–	workerCountReadFence();
1558	–	return maxPoolSize;
1559	–	}
1560	–
1561	–	/**
1562	–	* Sets the maximum number of threads allowed to exist in the
1563	–	* pool. The given value should normally be greater than or equal
1564	–	* to the {@link #getParallelism parallelism} level. Setting this
1565	–	* value has no effect on current pool size. It controls
1566	–	* construction of new threads. The use of this method may cause
1567	–	* tasks that intrinsically require extra threads for dependent
1568	–	* computations to indefinitely stall. If you are instead trying
1569	–	* to minimize internal thread creation, consider setting {@link
1570	–	* #setMaintainsParallelism} as false.
1571	–	*
1572	–	* @throws IllegalArgumentException if negative or greater than
1573	–	* internal implementation limit
1574	–	*/
1575	–	public void setMaximumPoolSize(int newMax) {
1576	–	if (newMax < 0 \|\| newMax > MAX_THREADS)
1577	–	throw new IllegalArgumentException();
1578	–	maxPoolSize = newMax;
1579	–	workerCountWriteFence();
1580	–	}
1581	–
1582	–	/**
1583	–	* Returns {@code true} if this pool dynamically maintains its
1584	–	* target parallelism level. If false, new threads are added only
1585	–	* to avoid possible starvation. This setting is by default true.
1586	–	*
1587	–	* @return {@code true} if maintains parallelism
1588	–	*/
1589	–	public boolean getMaintainsParallelism() {
1590	–	workerCountReadFence();
1591	–	return maintainsParallelism;
1592	–	}
1593	–
1594	–	/**
1595	–	* Sets whether this pool dynamically maintains its target
1596	–	* parallelism level. If false, new threads are added only to
1597	–	* avoid possible starvation.
1598	–	*
1599	–	* @param enable {@code true} to maintain parallelism
1600	–	*/
1601	–	public void setMaintainsParallelism(boolean enable) {
1602	–	maintainsParallelism = enable;
1603	–	workerCountWriteFence();
1604	–	}
1605	–
1606	–	/**
1607	–	* Establishes local first-in-first-out scheduling mode for forked
1608	–	* tasks that are never joined. This mode may be more appropriate
1609	–	* than default locally stack-based mode in applications in which
1610	–	* worker threads only process asynchronous tasks. This method is
1611	–	* designed to be invoked only when the pool is quiescent, and
1612	–	* typically only before any tasks are submitted. The effects of
1613	–	* invocations at other times may be unpredictable.
1614	–	*
1615	–	* @param async if {@code true}, use locally FIFO scheduling
1616	–	* @return the previous mode
1617	–	* @see #getAsyncMode
1618	–	*/
1619	–	public boolean setAsyncMode(boolean async) {
1620	–	workerCountReadFence();
1621	–	boolean oldMode = locallyFifo;
1622	–	if (oldMode != async) {
1623	–	locallyFifo = async;
1624	–	workerCountWriteFence();
1625	–	ForkJoinWorkerThread[] ws = workers;
1626	–	int nws = ws.length;
1627	–	for (int i = 0; i < nws; ++i) {
1628	–	ForkJoinWorkerThread w = ws[i];
1629	–	if (w != null)
1630	–	w.setAsyncMode(async);
1631	–	}
1632	–	}
1633	–	return oldMode;
1634	–	}
1635	–
1636	–	/**
1441		* Returns {@code true} if this pool uses local first-in-first-out
1442		* scheduling mode for forked tasks that are never joined.
1443		*
1444		* @return {@code true} if this pool uses async mode
1641	–	* @see #setAsyncMode
1445		*/
1446		public boolean getAsyncMode() {
1644	–	workerCountReadFence();
1447		return locallyFifo;
1448		}
1449
#	Line 1711 \| Line 1513 \| public class ForkJoinPool extends Abstra
1513		public long getQueuedTaskCount() {
1514		long count = 0;
1515		ForkJoinWorkerThread[] ws = workers;
1516	<	int nws = ws.length;
1517	<	for (int i = 0; i < nws; ++i) {
1516	>	int n = ws.length;
1517	>	for (int i = 0; i < n; ++i) {
1518		ForkJoinWorkerThread w = ws[i];
1519		if (w != null)
1520		count += w.getQueueSize();
#	Line 1770 \| Line 1572 \| public class ForkJoinPool extends Abstra
1572		* @return the number of elements transferred
1573		*/
1574		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1575	<	int n = submissionQueue.drainTo(c);
1575	>	int count = submissionQueue.drainTo(c);
1576		ForkJoinWorkerThread[] ws = workers;
1577	<	int nws = ws.length;
1578	<	for (int i = 0; i < nws; ++i) {
1577	>	int n = ws.length;
1578	>	for (int i = 0; i < n; ++i) {
1579		ForkJoinWorkerThread w = ws[i];
1580		if (w != null)
1581	<	n += w.drainTasksTo(c);
1581	>	count += w.drainTasksTo(c);
1582		}
1583	<	return n;
1583	>	return count;
1584		}
1585
1586		/**
#	Line 1902 \| Line 1704 \| public class ForkJoinPool extends Abstra
1704		*/
1705		public boolean awaitTermination(long timeout, TimeUnit unit)
1706		throws InterruptedException {
1707	<	return terminationLatch.await(timeout, unit);
1707	>	try {
1708	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1709	>	} catch(TimeoutException ex) {
1710	>	return false;
1711	>	}
1712		}
1713
1714		/**
1715		* Interface for extending managed parallelism for tasks running
1716		* in {@link ForkJoinPool}s.
1717		*
1718	<	* <p>A {@code ManagedBlocker} provides two methods.
1719	<	* Method {@code isReleasable} must return {@code true} if
1720	<	* blocking is not necessary. Method {@code block} blocks the
1721	<	* current thread if necessary (perhaps internally invoking
1722	<	* {@code isReleasable} before actually blocking).
1718	>	* <p>A {@code ManagedBlocker} provides two methods. Method
1719	>	* {@code isReleasable} must return {@code true} if blocking is
1720	>	* not necessary. Method {@code block} blocks the current thread
1721	>	* if necessary (perhaps internally invoking {@code isReleasable}
1722	>	* before actually blocking). The unusual methods in this API
1723	>	* accommodate synchronizers that may, but don't usually, block
1724	>	* for long periods. Similarly, they allow more efficient internal
1725	>	* handling of cases in which additional workers may be, but
1726	>	* usually are not, needed to ensure sufficient parallelism.
1727	>	* Toward this end, implementations of method {@code isReleasable}
1728	>	* must be amenable to repeated invocation.
1729		*
1730		* <p>For example, here is a ManagedBlocker based on a
1731		* ReentrantLock:
#	Line 1931 \| Line 1743 \| public class ForkJoinPool extends Abstra
1743		* return hasLock \|\| (hasLock = lock.tryLock());
1744		* }
1745		* }}</pre>
1746	+	*
1747	+	* <p>Here is a class that possibly blocks waiting for an
1748	+	* item on a given queue:
1749	+	* <pre> {@code
1750	+	* class QueueTaker<E> implements ManagedBlocker {
1751	+	* final BlockingQueue<E> queue;
1752	+	* volatile E item = null;
1753	+	* QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1754	+	* public boolean block() throws InterruptedException {
1755	+	* if (item == null)
1756	+	* item = queue.take
1757	+	* return true;
1758	+	* }
1759	+	* public boolean isReleasable() {
1760	+	* return item != null \|\| (item = queue.poll) != null;
1761	+	* }
1762	+	* public E getItem() { // call after pool.managedBlock completes
1763	+	* return item;
1764	+	* }
1765	+	* }}</pre>
1766		*/
1767		public static interface ManagedBlocker {
1768		/**
#	Line 1954 \| Line 1786 \| public class ForkJoinPool extends Abstra
1786		* Blocks in accord with the given blocker. If the current thread
1787		* is a {@link ForkJoinWorkerThread}, this method possibly
1788		* arranges for a spare thread to be activated if necessary to
1789	<	* ensure parallelism while the current thread is blocked.
1958	<	*
1959	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1960	<	* supports it ({@link #getMaintainsParallelism}), this method
1961	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1962	<	* it activates a thread only if necessary to avoid complete
1963	<	* starvation. This option may be preferable when blockages use
1964	<	* timeouts, or are almost always brief.
1789	>	* ensure sufficient parallelism while the current thread is blocked.
1790		*
1791		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1792		* behaviorally equivalent to
#	Line 1975 \| Line 1800 \| public class ForkJoinPool extends Abstra
1800		* first be expanded to ensure parallelism, and later adjusted.
1801		*
1802		* @param blocker the blocker
1978	–	* @param maintainParallelism if {@code true} and supported by
1979	–	* this pool, attempt to maintain the pool's nominal parallelism;
1980	–	* otherwise activate a thread only if necessary to avoid
1981	–	* complete starvation.
1803		* @throws InterruptedException if blocker.block did so
1804		*/
1805	<	public static void managedBlock(ManagedBlocker blocker,
1985	<	boolean maintainParallelism)
1805	>	public static void managedBlock(ManagedBlocker blocker)
1806		throws InterruptedException {
1807		Thread t = Thread.currentThread();
1808	<	if (t instanceof ForkJoinWorkerThread)
1809	<	((ForkJoinWorkerThread) t).pool.
1810	<	awaitBlocker(blocker, maintainParallelism);
1811	<	else
1812	<	awaitBlocker(blocker);
1813	<	}
1814	<
1995	<	/**
1996	<	* Performs Non-FJ blocking
1997	<	*/
1998	<	private static void awaitBlocker(ManagedBlocker blocker)
1999	<	throws InterruptedException {
2000	<	do {} while (!blocker.isReleasable() && !blocker.block());
1808	>	if (t instanceof ForkJoinWorkerThread) {
1809	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1810	>	w.pool.awaitBlocker(blocker);
1811	>	}
1812	>	else {
1813	>	do {} while (!blocker.isReleasable() && !blocker.block());
1814	>	}
1815		}
1816
1817		// AbstractExecutorService overrides. These rely on undocumented
#	Line 2025 \| Line 1839 \| public class ForkJoinPool extends Abstra
1839		objectFieldOffset("eventWaiters",ForkJoinPool.class);
1840		private static final long stealCountOffset =
1841		objectFieldOffset("stealCount",ForkJoinPool.class);
1842	<
1842	>	private static final long spareWaitersOffset =
1843	>	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1844
1845		private static long objectFieldOffset(String field, Class<?> klazz) {
1846		try {

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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents): Revision 1.56 by dl, Thu May 27 16:46:48 2010 UTC vs. Revision 1.61 by dl, Wed Aug 11 18:45:12 2010 UTC

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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.56 by dl, Thu May 27 16:46:48 2010 UTC vs.
Revision 1.61 by dl, Wed Aug 11 18:45:12 2010 UTC