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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.54 by dl, Sun Apr 18 12:51:18 2010 UTC vs.
Revision 1.66 by dl, Sun Aug 29 23:34:46 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	+	* It is impossible to keep exactly the target (parallelism)
165	+	* number of threads running at any given time. Determining
166	+	* existence of conservatively safe helping targets, the
167	+	* availability of already-created spares, and the apparent need
168	+	* to create new spares are all racy and require heuristic
169	+	* guidance, so we rely on multiple retries of each. Compensation
170	+	* occurs in slow-motion. It is triggered only upon timeouts of
171	+	* Object.wait used for joins. This reduces poor decisions that
172	+	* would otherwise be made when threads are waiting for others
173	+	* that are stalled because of unrelated activities such as
174	+	* garbage collection.
175	+	*
176	+	* The ManagedBlocker extension API can't use helping so relies
177	+	* only on compensation in method awaitBlocker.
178	+	*
179		* The main throughput advantages of work-stealing stem from
180		* decentralized control -- workers mostly steal tasks from each
181		* other. We do not want to negate this by creating bottlenecks
182	<	* implementing the management responsibilities of this class. So
183	<	* we use a collection of techniques that avoid, reduce, or cope
184	<	* well with contention. These entail several instances of
185	<	* bit-packing into CASable fields to maintain only the minimally
186	<	* required atomicity. To enable such packing, we restrict maximum
187	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
188	<	* bit field), which is far in excess of normal operating range.
189	<	* Even though updates to some of these bookkeeping fields do
190	<	* sometimes contend with each other, they don't normally
191	<	* cache-contend with updates to others enough to warrant memory
192	<	* padding or isolation. So they are all held as fields of
193	<	* ForkJoinPool objects. The main capabilities are as follows:
182	>	* implementing other management responsibilities. So we use a
183	>	* collection of techniques that avoid, reduce, or cope well with
184	>	* contention. These entail several instances of bit-packing into
185	>	* CASable fields to maintain only the minimally required
186	>	* atomicity. To enable such packing, we restrict maximum
187	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
188	>	* unbalanced increments and decrements) to fit into a 16 bit
189	>	* field, which is far in excess of normal operating range. Even
190	>	* though updates to some of these bookkeeping fields do sometimes
191	>	* contend with each other, they don't normally cache-contend with
192	>	* updates to others enough to warrant memory padding or
193	>	* isolation. So they are all held as fields of ForkJoinPool
194	>	* objects. The main capabilities are as follows:
195		*
196		* 1. Creating and removing workers. Workers are recorded in the
197		* "workers" array. This is an array as opposed to some other data
#	Line 140 \| Line 201 \| public class ForkJoinPool extends Abstra
201		* (workerLock) but the array is otherwise concurrently readable,
202		* and accessed directly by workers. To simplify index-based
203		* operations, the array size is always a power of two, and all
204	<	* readers must tolerate null slots. Currently, all but the first
205	<	* worker thread creation is on-demand, triggered by task
206	<	* submissions, replacement of terminated workers, and/or
207	<	* compensation for blocked workers. However, all other support
208	<	* code is set up to work with other policies.
204	>	* readers must tolerate null slots. Currently, all worker thread
205	>	* creation is on-demand, triggered by task submissions,
206	>	* replacement of terminated workers, and/or compensation for
207	>	* blocked workers. However, all other support code is set up to
208	>	* work with other policies.
209	>	*
210	>	* To ensure that we do not hold on to worker references that
211	>	* would prevent GC, ALL accesses to workers are via indices into
212	>	* the workers array (which is one source of some of the unusual
213	>	* code constructions here). In essence, the workers array serves
214	>	* as a WeakReference mechanism. Thus for example the event queue
215	>	* stores worker indices, not worker references. Access to the
216	>	* workers in associated methods (for example releaseEventWaiters)
217	>	* must both index-check and null-check the IDs. All such accesses
218	>	* ignore bad IDs by returning out early from what they are doing,
219	>	* since this can only be associated with shutdown, in which case
220	>	* it is OK to give up. On termination, we just clobber these
221	>	* data structures without trying to use them.
222		*
223		* 2. Bookkeeping for dynamically adding and removing workers. We
224	<	* maintain a given level of parallelism (or, if
225	<	* maintainsParallelism is false, at least avoid starvation). When
152	<	* some workers are known to be blocked (on joins or via
224	>	* aim to approximately maintain the given level of parallelism.
225	>	* When some workers are known to be blocked (on joins or via
226		* ManagedBlocker), we may create or resume others to take their
227		* place until they unblock (see below). Implementing this
228		* requires counts of the number of "running" threads (i.e., those
229		* that are neither blocked nor artifically suspended) as well as
230		* the total number. These two values are packed into one field,
231		* "workerCounts" because we need accurate snapshots when deciding
232	<	* to create, resume or suspend. To support these decisions,
233	<	* updates must be prospective (not retrospective). For example,
234	<	* the running count is decremented before blocking by a thread
235	<	* 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.
232	>	* to create, resume or suspend. Note however that the
233	>	* correspondance of these counts to reality is not guaranteed. In
234	>	* particular updates for unblocked threads may lag until they
235	>	* actually wake up.
236		*
237		* 3. Maintaining global run state. The run state of the pool
238		* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
#	Line 201 \| Line 261 \| public class ForkJoinPool extends Abstra
261		* workers that previously could not find a task to now find one:
262		* Submission of a new task to the pool, or another worker pushing
263		* a task onto a previously empty queue. (We also use this
264	<	* mechanism for termination and reconfiguration actions that
264	>	* mechanism for configuration and termination actions that
265		* require wakeups of idle workers). Each worker maintains its
266		* last known event count, and blocks when a scan for work did not
267		* find a task AND its lastEventCount matches the current
#	Line 212 \| Line 272 \| public class ForkJoinPool extends Abstra
272		* a record (field nextEventWaiter) for the next waiting worker.
273		* In addition to allowing simpler decisions about need for
274		* wakeup, the event count bits in eventWaiters serve the role of
275	<	* tags to avoid ABA errors in Treiber stacks. To reduce delays
276	<	* in task diffusion, workers not otherwise occupied may invoke
277	<	* method releaseWaiters, that removes and signals (unparks)
278	<	* workers not waiting on current count. To minimize task
279	<	* production stalls associate with signalling, any worker pushing
280	<	* a task on an empty queue invokes the weaker method signalWork,
221	<	* that only releases idle workers until it detects interference
222	<	* by other threads trying to release, and lets them take
223	<	* over. The net effect is a tree-like diffusion of signals, where
224	<	* released threads and possibly others) help with unparks. To
225	<	* further reduce contention effects a bit, failed CASes to
226	<	* increment field eventCount are tolerated without retries.
275	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
276	>	* released threads also try to release at most two others. The
277	>	* net effect is a tree-like diffusion of signals, where released
278	>	* threads (and possibly others) help with unparks. To further
279	>	* reduce contention effects a bit, failed CASes to increment
280	>	* field eventCount are tolerated without retries in signalWork.
281		* Conceptually they are merged into the same event, which is OK
282		* when their only purpose is to enable workers to scan for work.
283		*
284	<	* 5. Managing suspension of extra workers. When a worker is about
285	<	* to block waiting for a join (or via ManagedBlockers), we may
286	<	* create a new thread to maintain parallelism level, or at least
287	<	* avoid starvation (see below). Usually, extra threads are needed
288	<	* for only very short periods, yet join dependencies are such
289	<	* that we sometimes need them in bursts. Rather than create new
290	<	* threads each time this happens, we suspend no-longer-needed
291	<	* extra ones as "spares". For most purposes, we don't distinguish
292	<	* "extra" spare threads from normal "core" threads: On each call
293	<	* to preStep (the only point at which we can do this) a worker
294	<	* checks to see if there are now too many running workers, and if
295	<	* so, suspends itself. Methods preJoin and doBlock look for
296	<	* suspended threads to resume before considering creating a new
297	<	* replacement. We don't need a special data structure to maintain
298	<	* spares; simply scanning the workers array looking for
299	<	* worker.isSuspended() is fine because the calling thread is
300	<	* otherwise not doing anything useful anyway; we are at least as
301	<	* happy if after locating a spare, the caller doesn't actually
302	<	* block because the join is ready before we try to adjust and
303	<	* compensate. Note that this 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.
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 (dcdc)>=(scpc)
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
333	<	* partially compensates for the above mechanics to suspend extra
334	<	* threads, that normally lead to overshoot because we can only
281	<	* suspend workers in-between top-level actions. It also better
282	<	* copes with the fact that some of the methods in this class tend
283	<	* to never become compiled (but are interpreted), so some
284	<	* components of the entire set of controls might execute many
285	<	* times faster than others. And similarly for cases where the
286	<	* apparent lack of work is just due to GC stalls and other
287	<	* transient system activity.
288	<	*
289	<	* 7. Maintaining other configuration parameters and monitoring
290	<	* statistics. Updates to fields controlling parallelism level,
291	<	* max size, etc can only meaningfully take effect for individual
292	<	* threads upon their next top-level actions; i.e., between
293	<	* stealing/running tasks/submission, which are separated by calls
294	<	* to preStep. Memory ordering for these (assumed infrequent)
295	<	* reconfiguration calls is ensured by using reads and writes to
296	<	* volatile field workerCounts (that must be read in preStep anyway)
297	<	* as "fences" -- user-level reads are preceded by reads of
298	<	* workCounts, and writes are followed by no-op CAS to
299	<	* workerCounts. The values reported by other management and
300	<	* monitoring methods are either computed on demand, or are kept
301	<	* in fields that are only updated when threads are otherwise
302	<	* idle.
284	>	* 5. Managing suspension of extra workers. When a worker notices
285	>	* (usually upon timeout of a wait()) that there are too few
286	>	* running threads, we may create a new thread to maintain
287	>	* parallelism level, or at least avoid starvation. Usually, extra
288	>	* threads are needed for only very short periods, yet join
289	>	* dependencies are such that we sometimes need them in
290	>	* bursts. Rather than create new threads each time this happens,
291	>	* we suspend no-longer-needed extra ones as "spares". For most
292	>	* purposes, we don't distinguish "extra" spare threads from
293	>	* normal "core" threads: On each call to preStep (the only point
294	>	* at which we can do this) a worker checks to see if there are
295	>	* now too many running workers, and if so, suspends itself.
296	>	* Method helpMaintainParallelism looks for suspended threads to
297	>	* resume before considering creating a new replacement. The
298	>	* spares themselves are encoded on another variant of a Treiber
299	>	* Stack, headed at field "spareWaiters". Note that the use of
300	>	* spares is intrinsically racy. One thread may become a spare at
301	>	* about the same time as another is needlessly being created. We
302	>	* counteract this and related slop in part by requiring resumed
303	>	* spares to immediately recheck (in preStep) to see whether they
304	>	* they should re-suspend.
305	>	*
306	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
307	>	* shed unused workers: The oldest (first) event queue waiter uses
308	>	* a timed rather than hard wait. When this wait times out without
309	>	* a normal wakeup, it tries to shutdown any one (for convenience
310	>	* the newest) other spare or event waiter via
311	>	* tryShutdownUnusedWorker. This eventually reduces the number of
312	>	* worker threads to a minimum of one after a long enough period
313	>	* without use.
314	>	*
315	>	* 7. Deciding when to create new workers. The main dynamic
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 parallelism to
327	>	* lapse for a while during joins, and use a timeout to see if,
328	>	* after the resulting settling, there is still a need for
329	>	* additional workers. This also better copes with the fact that
330	>	* some of the methods in this class tend to never become compiled
331	>	* (but are interpreted), so some components of the entire set of
332	>	* controls might execute 100 times faster than others. And
333	>	* similarly for cases where the apparent lack of work is just due
334	>	* to GC stalls and other transient system activity.
335		*
336		* Beware that there is a lot of representation-level coupling
337		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 312 \| Line 344 \| public class ForkJoinPool extends Abstra
344		*
345		* Style notes: There are lots of inline assignments (of form
346		* "while ((local = field) != 0)") which are usually the simplest
347	<	* way to ensure read orderings. Also several occurrences of the
348	<	* unusual "do {} while(!cas...)" which is the simplest way to
349	<	* force an update of a CAS'ed variable. There are also a few
350	<	* other coding oddities that help some methods perform reasonably
351	<	* even when interpreted (not compiled).
347	>	* way to ensure the required read orderings (which are sometimes
348	>	* critical). Also several occurrences of the unusual "do {}
349	>	* while(!cas...)" which is the simplest way to force an update of
350	>	* a CAS'ed variable. There are also other coding oddities that
351	>	* help some methods perform reasonably even when interpreted (not
352	>	* compiled), at the expense of some messy constructions that
353	>	* reduce byte code counts.
354		*
355		* The order of declarations in this file is: (1) statics (2)
356		* fields (along with constants used when unpacking some of them)
#	Line 345 \| Line 379 \| public class ForkJoinPool extends Abstra
379		* Default ForkJoinWorkerThreadFactory implementation; creates a
380		* new ForkJoinWorkerThread.
381		*/
382	<	static class DefaultForkJoinWorkerThreadFactory
382	>	static class DefaultForkJoinWorkerThreadFactory
383		implements ForkJoinWorkerThreadFactory {
384		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
385		return new ForkJoinWorkerThread(pool);
#	Line 384 \| Line 418 \| public class ForkJoinPool extends Abstra
418		new AtomicInteger();
419
420		/**
421	<	* Absolute bound for parallelism level. Twice this number must
422	<	* fit into a 16bit field to enable word-packing for some counts.
421	>	* The time to block in a join (see awaitJoin) before checking if
422	>	* a new worker should be (re)started to maintain parallelism
423	>	* level. The value should be short enough to maintain gloabal
424	>	* responsiveness and progress but long enough to avoid
425	>	* counterproductive firings during GC stalls or unrelated system
426	>	* activity, and to not bog down systems with continual re-firings
427	>	* on GCs or legitimately long waits.
428	>	*/
429	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
430	>
431	>	/**
432	>	* The wakeup interval (in nanoseconds) for the oldest worker
433	>	* worker waiting for an event invokes tryShutdownUnusedWorker to shrink
434	>	* the number of workers. The exact value does not matter too
435	>	* much, but should be long enough to slowly release resources
436	>	* during long periods without use without disrupting normal use.
437	>	*/
438	>	private static final long SHRINK_RATE_NANOS =
439	>	30L * 1000L * 1000L * 1000L; // 2 per minute
440	>
441	>	/**
442	>	* Absolute bound for parallelism level. Twice this number plus
443	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
444	>	* word-packing for some counts and indices.
445		*/
446	<	private static final int MAX_THREADS = 0x7fff;
446	>	private static final int MAX_WORKERS = 0x7fff;
447
448		/**
449		* Array holding all worker threads in the pool. Array size must
#	Line 413 \| Line 469 \| public class ForkJoinPool extends Abstra
469		/**
470		* Latch released upon termination.
471		*/
472	<	private final CountDownLatch terminationLatch;
472	>	private final Phaser termination;
473
474		/**
475		* Creation factory for worker threads.
#	Line 429 \| Line 485 \| public class ForkJoinPool extends Abstra
485		/**
486		* Encoded record of top of treiber stack of threads waiting for
487		* events. The top 32 bits contain the count being waited for. The
488	<	* bottom word contains one plus the pool index of waiting worker
489	<	* thread.
488	>	* bottom 16 bits contains one plus the pool index of waiting
489	>	* worker thread. (Bits 16-31 are unused.)
490		*/
491		private volatile long eventWaiters;
492
493		private static final int EVENT_COUNT_SHIFT = 32;
494	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
494	>	private static final long WAITER_ID_MASK = (1L << 16) - 1L;
495
496		/**
497		* A counter for events that may wake up worker threads:
498		* - Submission of a new task to the pool
499		* - A worker pushing a task on an empty queue
500	<	* - termination and reconfiguration
500	>	* - termination
501		*/
502		private volatile int eventCount;
503
504		/**
505	+	* Encoded record of top of treiber stack of spare threads waiting
506	+	* for resumption. The top 16 bits contain an arbitrary count to
507	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
508	+	* index of waiting worker thread.
509	+	*/
510	+	private volatile int spareWaiters;
511	+
512	+	private static final int SPARE_COUNT_SHIFT = 16;
513	+	private static final int SPARE_ID_MASK = (1 << 16) - 1;
514	+
515	+	/**
516		* Lifecycle control. The low word contains the number of workers
517		* that are (probably) executing tasks. This value is atomically
518		* incremented before a worker gets a task to run, and decremented
#	Line 456 \| Line 523 \| public class ForkJoinPool extends Abstra
523		* These are bundled together to ensure consistent read for
524		* termination checks (i.e., that runLevel is at least SHUTDOWN
525		* and active threads is zero).
526	+	*
527	+	* Notes: Most direct CASes are dependent on these bitfield
528	+	* positions. Also, this field is non-private to enable direct
529	+	* performance-sensitive CASes in ForkJoinWorkerThread.
530		*/
531	<	private volatile int runState;
531	>	volatile int runState;
532
533		// Note: The order among run level values matters.
534		private static final int RUNLEVEL_SHIFT = 16;
#	Line 465 \| Line 536 \| public class ForkJoinPool extends Abstra
536		private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1);
537		private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2);
538		private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1;
468	–	private static final int ONE_ACTIVE = 1; // active update delta
539
540		/**
541		* Holds number of total (i.e., created and not yet terminated)
#	Line 474 \| Line 544 \| public class ForkJoinPool extends Abstra
544		* making decisions about creating and suspending spare
545		* threads. Updated only by CAS. Note that adding a new worker
546		* requires incrementing both counts, since workers start off in
547	<	* running state. This field is also used for memory-fencing
478	<	* configuration parameters.
547	>	* running state.
548		*/
549		private volatile int workerCounts;
550
#	Line 484 \| Line 553 \| public class ForkJoinPool extends Abstra
553		private static final int ONE_RUNNING = 1;
554		private static final int ONE_TOTAL = 1 << TOTAL_COUNT_SHIFT;
555
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	–
556		/**
557		* The target parallelism level.
558	+	* Accessed directly by ForkJoinWorkerThreads.
559		*/
560	<	private int parallelism;
497	<
498	<	/**
499	<	* The maximum allowed pool size.
500	<	*/
501	<	private int maxPoolSize;
560	>	final int parallelism;
561
562		/**
563		* True if use local fifo, not default lifo, for local polling
564	<	* Replicated by ForkJoinWorkerThreads
564	>	* Read by, and replicated by ForkJoinWorkerThreads
565		*/
566	<	private boolean locallyFifo;
566	>	final boolean locallyFifo;
567
568		/**
569	<	* Controls whether to add spares to maintain parallelism
569	>	* The uncaught exception handler used when any worker abruptly
570	>	* terminates.
571		*/
572	<	private boolean maintainsParallelism;
513	<
514	<	/**
515	<	* The uncaught exception handler used when any worker
516	<	* abruptly terminates
517	<	*/
518	<	private Thread.UncaughtExceptionHandler ueh;
572	>	private final Thread.UncaughtExceptionHandler ueh;
573
574		/**
575		* Pool number, just for assigning useful names to worker threads
576		*/
577		private final int poolNumber;
578
579	<	// utilities for updating fields
579	>	// Utilities for CASing fields. Note that most of these
580	>	// are usually manually inlined by callers
581
582		/**
583	<	* Adds delta to running count. Used mainly by ForkJoinTask.
529	<	*
530	<	* @param delta the number to add
583	>	* Increments running count part of workerCounts
584		*/
585	<	final void updateRunningCount(int delta) {
586	<	int wc;
585	>	final void incrementRunningCount() {
586	>	int c;
587		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
588	<	wc = workerCounts,
589	<	wc + delta));
537	<	}
538	<
539	<	/**
540	<	* Write fence for user modifications of pool parameters
541	<	* (parallelism. etc). Note that it doesn't matter if CAS fails.
542	<	*/
543	<	private void workerCountWriteFence() {
544	<	int wc;
545	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
546	<	wc = workerCounts, wc);
588	>	c = workerCounts,
589	>	c + ONE_RUNNING));
590		}
591
592		/**
593	<	* Read fence for external reads of pool parameters
551	<	* (parallelism. maxPoolSize, etc).
593	>	* Tries to decrement running count unless already zero
594		*/
595	<	private void workerCountReadFence() {
596	<	int ignore = workerCounts;
595	>	final boolean tryDecrementRunningCount() {
596	>	int wc = workerCounts;
597	>	if ((wc & RUNNING_COUNT_MASK) == 0)
598	>	return false;
599	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
600	>	wc, wc - ONE_RUNNING);
601		}
602
603		/**
604	<	* Tries incrementing active count; fails on contention.
605	<	* Called by workers before executing tasks.
604	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
605	>	* (rarely) necessary when other count updates lag.
606		*
607	<	* @return true on success
607	>	* @param dr -- either zero or ONE_RUNNING
608	>	* @param dt == either zero or ONE_TOTAL
609		*/
610	<	final boolean tryIncrementActiveCount() {
611	<	int c;
612	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
613	<	c = runState, c + ONE_ACTIVE);
610	>	private void decrementWorkerCounts(int dr, int dt) {
611	>	for (;;) {
612	>	int wc = workerCounts;
613	>	if ((wc & RUNNING_COUNT_MASK) - dr < 0 \|\|
614	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
615	>	if ((runState & TERMINATED) != 0)
616	>	return; // lagging termination on a backout
617	>	Thread.yield();
618	>	}
619	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
620	>	wc, wc - (dr + dt)))
621	>	return;
622	>	}
623		}
624
625		/**
#	Line 573 \| Line 629 \| public class ForkJoinPool extends Abstra
629		final boolean tryDecrementActiveCount() {
630		int c;
631		return UNSAFE.compareAndSwapInt(this, runStateOffset,
632	<	c = runState, c - ONE_ACTIVE);
632	>	c = runState, c - 1);
633		}
634
635		/**
#	Line 602 \| Line 658 \| public class ForkJoinPool extends Abstra
658		lock.lock();
659		try {
660		ForkJoinWorkerThread[] ws = workers;
661	<	int len = ws.length;
662	<	if (k < 0 \|\| k >= len \|\| ws[k] != null) {
663	<	for (k = 0; k < len && ws[k] != null; ++k)
661	>	int n = ws.length;
662	>	if (k < 0 \|\| k >= n \|\| ws[k] != null) {
663	>	for (k = 0; k < n && ws[k] != null; ++k)
664		;
665	<	if (k == len)
666	<	ws = Arrays.copyOf(ws, len << 1);
665	>	if (k == n)
666	>	ws = Arrays.copyOf(ws, n << 1);
667		}
668		ws[k] = w;
669		workers = ws; // volatile array write ensures slot visibility
#	Line 634 \| Line 690 \| public class ForkJoinPool extends Abstra
690		}
691		}
692
637	–	// adding and removing workers
638	–
693		/**
694	<	* Tries to create and add new worker. Assumes that worker counts
695	<	* are already updated to accommodate the worker, so adjusts on
696	<	* failure.
694	>	* Final callback from terminating worker. Removes record of
695	>	* worker from array, and adjusts counts. If pool is shutting
696	>	* down, tries to complete terminatation.
697		*
698	<	* @return new worker or null if creation failed
698	>	* @param w the worker
699		*/
700	<	private ForkJoinWorkerThread addWorker() {
701	<	ForkJoinWorkerThread w = null;
702	<	try {
703	<	w = factory.newThread(this);
704	<	} finally { // Adjust on either null or exceptional factory return
705	<	if (w == null) {
706	<	onWorkerCreationFailure();
707	<	return null;
700	>	final void workerTerminated(ForkJoinWorkerThread w) {
701	>	forgetWorker(w);
702	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
703	>	while (w.stealCount != 0) // collect final count
704	>	tryAccumulateStealCount(w);
705	>	tryTerminate(false);
706	>	}
707	>
708	>	// Waiting for and signalling events
709	>
710	>	/**
711	>	* Releases workers blocked on a count not equal to current count.
712	>	* Normally called after precheck that eventWaiters isn't zero to
713	>	* avoid wasted array checks. Gives up upon a change in count or
714	>	* upon releasing two workers, letting others take over.
715	>	*/
716	>	private void releaseEventWaiters() {
717	>	ForkJoinWorkerThread[] ws = workers;
718	>	int n = ws.length;
719	>	long h = eventWaiters;
720	>	int ec = eventCount;
721	>	boolean releasedOne = false;
722	>	ForkJoinWorkerThread w; int id;
723	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
724	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
725	>	id < n && (w = ws[id]) != null) {
726	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
727	>	h, w.nextWaiter)) {
728	>	LockSupport.unpark(w);
729	>	if (releasedOne) // exit on second release
730	>	break;
731	>	releasedOne = true;
732		}
733	+	if (eventCount != ec)
734	+	break;
735	+	h = eventWaiters;
736		}
656	–	w.start(recordWorker(w), locallyFifo, ueh);
657	–	return w;
737		}
738
739		/**
740	<	* Adjusts counts upon failure to create worker
740	>	* Tries to advance eventCount and releases waiters. Called only
741	>	* from workers.
742		*/
743	<	private void onWorkerCreationFailure() {
744	<	int c;
745	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
746	<	c = workerCounts,
747	<	c - (ONE_RUNNING\|ONE_TOTAL)));
668	<	tryTerminate(false); // in case of failure during shutdown
743	>	final void signalWork() {
744	>	int c; // try to increment event count -- CAS failure OK
745	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
746	>	if (eventWaiters != 0L)
747	>	releaseEventWaiters();
748		}
749
750		/**
751	<	* Create enough total workers to establish target parallelism,
752	<	* giving up if terminating or addWorker fails
751	>	* Adds the given worker to event queue and blocks until
752	>	* terminating or event count advances from the given value
753	>	*
754	>	* @param w the calling worker thread
755	>	* @param ec the count
756		*/
757	<	private void ensureEnoughTotalWorkers() {
758	<	int wc;
759	<	while (runState < TERMINATING &&
760	<	((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism) {
761	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
762	<	wc, wc + (ONE_RUNNING\|ONE_TOTAL)) &&
763	<	addWorker() == null))
757	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
758	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) \| ((long)(w.poolIndex+1));
759	>	long h;
760	>	while ((runState < SHUTDOWN \|\| !tryTerminate(false)) &&
761	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 \|\|
762	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
763	>	eventCount == ec) {
764	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
765	>	w.nextWaiter = h, nh)) {
766	>	awaitEvent(w, ec);
767		break;
768	+	}
769		}
770		}
771
772		/**
773	<	* Final callback from terminating worker. Removes record of
774	<	* worker from array, and adjusts counts. If pool is shutting
775	<	* down, tries to complete terminatation, else possibly replaces
776	<	* the worker.
773	>	* Blocks the given worker (that has already been entered as an
774	>	* event waiter) until terminating or event count advances from
775	>	* the given value. The oldest (first) waiter uses a timed wait to
776	>	* occasionally one-by-one shrink the number of workers (to a
777	>	* minimum of one) if the pool has not been used for extended
778	>	* periods.
779		*
780	<	* @param w the worker
780	>	* @param w the calling worker thread
781	>	* @param ec the count
782		*/
783	<	final void workerTerminated(ForkJoinWorkerThread w) {
784	<	if (w.active) { // force inactive
785	<	w.active = false;
786	<	do {} while (!tryDecrementActiveCount());
783	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
784	>	while (eventCount == ec) {
785	>	if (tryAccumulateStealCount(w)) { // transfer while idle
786	>	boolean untimed = (w.nextWaiter != 0L \|\|
787	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
788	>	long startTime = untimed? 0 : System.nanoTime();
789	>	Thread.interrupted(); // clear/ignore interrupt
790	>	if (eventCount != ec \|\| w.runState != 0 \|\|
791	>	runState >= TERMINATING) // recheck after clear
792	>	break;
793	>	if (untimed)
794	>	LockSupport.park(w);
795	>	else {
796	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
797	>	if (eventCount != ec \|\| w.runState != 0 \|\|
798	>	runState >= TERMINATING)
799	>	break;
800	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
801	>	tryShutdownUnusedWorker(ec);
802	>	}
803	>	}
804		}
699	–	forgetWorker(w);
700	–
701	–	// decrement total count, and if was running, running count
702	–	int unit = w.isTrimmed()? ONE_TOTAL : (ONE_RUNNING\|ONE_TOTAL);
703	–	int wc;
704	–	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
705	–	wc = workerCounts, wc - unit));
706	–
707	–	accumulateStealCount(w); // collect final count
708	–	if (!tryTerminate(false))
709	–	ensureEnoughTotalWorkers();
805		}
806
807	<	// Waiting for and signalling events
807	>	// Maintaining parallelism
808
809		/**
810	<	* Ensures eventCount on exit is different (mod 2^32) than on
716	<	* entry. CAS failures are OK -- any change in count suffices.
810	>	* Pushes worker onto the spare stack
811		*/
812	<	private void advanceEventCount() {
813	<	int c;
814	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
812	>	final void pushSpare(ForkJoinWorkerThread w) {
813	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) \| (w.poolIndex + 1);
814	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
815	>	w.nextSpare = spareWaiters,ns));
816		}
817
818		/**
819	<	* Releases workers blocked on a count not equal to current count.
820	<	*/
821	<	final void releaseWaiters() {
822	<	long top;
823	<	int id;
824	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
825	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
826	<	ForkJoinWorkerThread[] ws = workers;
827	<	ForkJoinWorkerThread w;
828	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
829	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
830	<	top, w.nextWaiter))
819	>	* Tries (once) to resume a spare if the number of running
820	>	* threads is less than target.
821	>	*/
822	>	private void tryResumeSpare() {
823	>	int sw, id;
824	>	ForkJoinWorkerThread[] ws = workers;
825	>	int n = ws.length;
826	>	ForkJoinWorkerThread w;
827	>	if ((sw = spareWaiters) != 0 &&
828	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
829	>	id < n && (w = ws[id]) != null &&
830	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
831	>	spareWaiters == sw &&
832	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
833	>	sw, w.nextSpare)) {
834	>	int c; // increment running count before resume
835	>	do {} while(!UNSAFE.compareAndSwapInt
836	>	(this, workerCountsOffset,
837	>	c = workerCounts, c + ONE_RUNNING));
838	>	if (w.tryUnsuspend())
839		LockSupport.unpark(w);
840	+	else // back out if w was shutdown
841	+	decrementWorkerCounts(ONE_RUNNING, 0);
842		}
843		}
844
845		/**
846	<	* Advances eventCount and releases waiters until interference by
847	<	* other releasing threads is detected.
846	>	* Tries to increase the number of running workers if below target
847	>	* parallelism: If a spare exists tries to resume it via
848	>	* tryResumeSpare. Otherwise, if not enough total workers or all
849	>	* existing workers are busy, adds a new worker. In all casses also
850	>	* helps wake up releasable workers waiting for work.
851		*/
852	<	final void signalWork() {
853	<	int ec;
854	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
855	<	outer:for (;;) {
856	<	long top = eventWaiters;
857	<	ec = eventCount;
858	<	for (;;) {
859	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
860	<	int id = (int)(top & WAITER_INDEX_MASK);
861	<	if (id <= 0 \|\| (int)(top >>> EVENT_COUNT_SHIFT) == ec)
862	<	return;
863	<	if ((ws = workers).length < id \|\| (w = ws[id - 1]) == null \|\|
864	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
865	<	top, top = w.nextWaiter))
866	<	continue outer; // possibly stale; reread
867	<	LockSupport.unpark(w);
868	<	if (top != eventWaiters) // let someone else take over
869	<	return;
852	>	private void helpMaintainParallelism() {
853	>	int pc = parallelism;
854	>	int wc, rs, tc;
855	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
856	>	(rs = runState) < TERMINATING) {
857	>	if (spareWaiters != 0)
858	>	tryResumeSpare();
859	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS \|\|
860	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
861	>	break; // enough total
862	>	else if (runState == rs && workerCounts == wc &&
863	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
864	>	wc + (ONE_RUNNING\|ONE_TOTAL))) {
865	>	ForkJoinWorkerThread w = null;
866	>	try {
867	>	w = factory.newThread(this);
868	>	} finally { // adjust on null or exceptional factory return
869	>	if (w == null) {
870	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
871	>	tryTerminate(false); // handle failure during shutdown
872	>	}
873	>	}
874	>	if (w == null)
875	>	break;
876	>	w.start(recordWorker(w), ueh);
877	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
878	>	int c; // advance event count
879	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
880	>	c = eventCount, c+1);
881	>	break; // add at most one unless total below target
882	>	}
883		}
884		}
885	+	if (eventWaiters != 0L)
886	+	releaseEventWaiters();
887		}
888
889		/**
890	<	* If worker is inactive, blocks until terminating or event count
891	<	* advances from last value held by worker; in any case helps
892	<	* release others.
890	>	* Callback from the oldest waiter in awaitEvent waking up after a
891	>	* period of non-use. If all workers are idle, tries (once) to
892	>	* shutdown an event waiter or a spare, if one exists. Note that
893	>	* we don't need CAS or locks here because the method is called
894	>	* only from one thread occasionally waking (and even misfires are
895	>	* OK). Note that until the shutdown worker fully terminates,
896	>	* workerCounts will overestimate total count, which is tolerable.
897		*
898	<	* @param w the calling worker thread
898	>	* @param ec the event count waited on by caller (to abort
899	>	* attempt if count has since changed).
900		*/
901	<	private void eventSync(ForkJoinWorkerThread w) {
902	<	if (!w.active) {
903	<	int prev = w.lastEventCount;
904	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) \|
905	<	((long)(w.poolIndex + 1)));
906	<	long top;
907	<	while ((runState < SHUTDOWN \|\| !tryTerminate(false)) &&
908	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 \|\|
909	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
910	<	eventCount == prev) {
911	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
912	<	w.nextWaiter = top, nextTop)) {
913	<	accumulateStealCount(w); // transfer steals while idle
914	<	Thread.interrupted(); // clear/ignore interrupt
915	<	while (eventCount == prev)
916	<	w.doPark();
917	<	break;
918	<	}
901	>	private void tryShutdownUnusedWorker(int ec) {
902	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
903	>	ForkJoinWorkerThread[] ws = workers;
904	>	int n = ws.length;
905	>	ForkJoinWorkerThread w = null;
906	>	boolean shutdown = false;
907	>	int sw;
908	>	long h;
909	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
910	>	int id = (sw & SPARE_ID_MASK) - 1;
911	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
912	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
913	>	sw, w.nextSpare))
914	>	shutdown = true;
915	>	}
916	>	else if ((h = eventWaiters) != 0L) {
917	>	long nh;
918	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
919	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
920	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
921	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
922	>	shutdown = true;
923	>	}
924	>	if (w != null && shutdown) {
925	>	w.shutdown();
926	>	LockSupport.unpark(w);
927		}
792	–	w.lastEventCount = eventCount;
928		}
929	<	releaseWaiters();
929	>	releaseEventWaiters(); // in case of interference
930		}
931
932		/**
933		* Callback from workers invoked upon each top-level action (i.e.,
934	<	* stealing a task or taking a submission and running
935	<	* it). Performs one or both of the following:
934	>	* stealing a task or taking a submission and running it).
935	>	* Performs one or more of the following:
936		*
937	<	* * If the worker cannot find work, updates its active status to
938	<	* inactive and updates activeCount unless there is contention, in
939	<	* which case it may try again (either in this or a subsequent
940	<	* call). Additionally, awaits the next task event and/or helps
941	<	* wake up other releasable waiters.
942	<	*
943	<	* * If there are too many running threads, suspends this worker
944	<	* (first forcing inactivation if necessary). If it is not
945	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
946	<	* -- killed while suspended within suspendAsSpare. Otherwise,
947	<	* upon resume it rechecks to make sure that it is still needed.
937	>	* 1. If the worker is active and either did not run a task
938	>	* or there are too many workers, try to set its active status
939	>	* to inactive and update activeCount. On contention, we may
940	>	* try again in this or a subsequent call.
941	>	*
942	>	* 2. If not enough total workers, help create some.
943	>	*
944	>	* 3. If there are too many running workers, suspend this worker
945	>	* (first forcing inactive if necessary). If it is not needed,
946	>	* it may be shutdown while suspended (via
947	>	* tryShutdownUnusedWorker). Otherwise, upon resume it
948	>	* rechecks running thread count and need for event sync.
949	>	*
950	>	* 4. If worker did not run a task, await the next task event via
951	>	* eventSync if necessary (first forcing inactivation), upon
952	>	* which the worker may be shutdown via
953	>	* tryShutdownUnusedWorker. Otherwise, help release any
954	>	* existing event waiters that are now releasable,
955		*
956		* @param w the worker
957	<	* @param worked false if the worker scanned for work but didn't
816	<	* find any (in which case it may block waiting for work).
957	>	* @param ran true if worker ran a task since last call to this method
958		*/
959	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
959	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
960	>	int wec = w.lastEventCount;
961		boolean active = w.active;
962	<	boolean inactivate = !worked & active;
963	<	for (;;) {
964	<	if (inactivate) {
965	<	int c = runState;
966	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
967	<	c, c - ONE_ACTIVE))
968	<	inactivate = active = w.active = false;
827	<	}
962	>	boolean inactivate = false;
963	>	int pc = parallelism;
964	>	int rs;
965	>	while (w.runState == 0 && (rs = runState) < TERMINATING) {
966	>	if ((inactivate \|\| (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
967	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
968	>	inactivate = active = w.active = false;
969		int wc = workerCounts;
970	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
971	<	if (!worked)
972	<	eventSync(w);
973	<	return;
974	<	}
975	<	if (!(inactivate \|= active) && // must inactivate to suspend
976	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
977	<	wc, wc - ONE_RUNNING) &&
978	<	!w.suspendAsSpare()) // false if trimmed
979	<	return;
980	<	}
981	<	}
982	<
983	<	/**
984	<	* Adjusts counts and creates or resumes compensating threads for
985	<	* a worker about to block on task joinMe, returning early if
845	<	* joinMe becomes ready. First tries resuming an existing spare
846	<	* (which usually also avoids any count adjustment), but must then
847	<	* decrement running count to determine whether a new thread is
848	<	* needed. See above for fuller explanation.
849	<	*/
850	<	final void preJoin(ForkJoinTask<?> joinMe) {
851	<	boolean dec = false; // true when running count decremented
852	<	for (;;) {
853	<	releaseWaiters(); // help other threads progress
854	<
855	<	if (joinMe.status < 0) // surround spare search with done checks
856	<	return;
857	<	ForkJoinWorkerThread spare = null;
858	<	for (ForkJoinWorkerThread w : workers) {
859	<	if (w != null && w.isSuspended()) {
860	<	spare = w;
970	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
971	>	if (!(inactivate \|= active) && // must inactivate to suspend
972	>	workerCounts == wc && // try to suspend as spare
973	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
974	>	wc, wc - ONE_RUNNING))
975	>	w.suspendAsSpare();
976	>	}
977	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
978	>	helpMaintainParallelism(); // not enough workers
979	>	else if (!ran) {
980	>	long h = eventWaiters;
981	>	int ec = eventCount;
982	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
983	>	releaseEventWaiters(); // release others before waiting
984	>	else if (ec != wec) {
985	>	w.lastEventCount = ec; // no need to wait
986		break;
987		}
988	+	else if (!(inactivate \|= active))
989	+	eventSync(w, wec); // must inactivate before sync
990		}
991	<	if (joinMe.status < 0)
992	<	return;
866	<
867	<	if (spare != null && spare.tryUnsuspend()) {
868	<	if (dec \|\| joinMe.requestSignal() < 0) {
869	<	int c;
870	<	do {} while (!UNSAFE.compareAndSwapInt(this,
871	<	workerCountsOffset,
872	<	c = workerCounts,
873	<	c + ONE_RUNNING));
874	<	} // else no net count change
875	<	LockSupport.unpark(spare);
876	<	return;
877	<	}
878	<
879	<	int wc = workerCounts; // decrement running count
880	<	if (!dec && (wc & RUNNING_COUNT_MASK) != 0 &&
881	<	(dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
882	<	wc, wc -= ONE_RUNNING)) &&
883	<	joinMe.requestSignal() < 0) { // cannot block
884	<	int c; // back out
885	<	do {} while (!UNSAFE.compareAndSwapInt(this,
886	<	workerCountsOffset,
887	<	c = workerCounts,
888	<	c + ONE_RUNNING));
889	<	return;
890	<	}
891	<
892	<	if (dec) {
893	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
894	<	int pc = parallelism;
895	<	int dc = pc - (wc & RUNNING_COUNT_MASK); // deficit count
896	<	if ((dc < pc && (dc <= 0 \|\| (dc * dc < (tc - pc) * pc) \|\|
897	<	!maintainsParallelism)) \|\|
898	<	tc >= maxPoolSize) // cannot add
899	<	return;
900	<	if (spare == null &&
901	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
902	<	wc + (ONE_RUNNING\|ONE_TOTAL))) {
903	<	addWorker();
904	<	return;
905	<	}
906	<	}
991	>	else
992	>	break;
993		}
994		}
995
996		/**
997	<	* Same idea as preJoin but with too many differing details to
998	<	* integrate: There are no task-based signal counts, and only one
999	<	* way to do the actual blocking. So for simplicity it is directly
1000	<	* incorporated into this method.
997	>	* Helps and/or blocks awaiting join of the given task.
998	>	* See above for explanation.
999	>	*
1000	>	* @param joinMe the task to join
1001	>	* @param worker the current worker thread
1002		*/
1003	<	final void doBlock(ManagedBlocker blocker, boolean maintainPar)
1004	<	throws InterruptedException {
1005	<	maintainPar &= maintainsParallelism; // override
1006	<	boolean dec = false;
1007	<	boolean done = false;
1008	<	for (;;) {
922	<	releaseWaiters();
923	<	if (done = blocker.isReleasable())
924	<	break;
925	<	ForkJoinWorkerThread spare = null;
926	<	for (ForkJoinWorkerThread w : workers) {
927	<	if (w != null && w.isSuspended()) {
928	<	spare = w;
929	<	break;
930	<	}
931	<	}
932	<	if (done = blocker.isReleasable())
933	<	break;
934	<	if (spare != null && spare.tryUnsuspend()) {
935	<	if (dec) {
936	<	int c;
937	<	do {} while (!UNSAFE.compareAndSwapInt(this,
938	<	workerCountsOffset,
939	<	c = workerCounts,
940	<	c + ONE_RUNNING));
941	<	}
942	<	LockSupport.unpark(spare);
1003	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1004	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1005	>	while (joinMe.status >= 0) {
1006	>	int wc;
1007	>	worker.helpJoinTask(joinMe);
1008	>	if (joinMe.status < 0)
1009		break;
1010	<	}
1011	<	int wc = workerCounts;
1012	<	if (!dec && (wc & RUNNING_COUNT_MASK) != 0)
1013	<	dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1014	<	wc, wc -= ONE_RUNNING);
1015	<	if (dec) {
1016	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1017	<	int pc = parallelism;
1018	<	int dc = pc - (wc & RUNNING_COUNT_MASK);
1019	<	if ((dc < pc && (dc <= 0 \|\| (dc * dc < (tc - pc) * pc) \|\|
1020	<	!maintainPar)) \|\|
1021	<	tc >= maxPoolSize)
1022	<	break;
1023	<	if (spare == null &&
1024	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1025	<	wc + (ONE_RUNNING\|ONE_TOTAL))){
1026	<	addWorker();
1027	<	break;
1028	<	}
1029	<	}
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));
1010	>	else if (retries > 0)
1011	>	--retries;
1012	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1013	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1014	>	wc, wc - ONE_RUNNING)) {
1015	>	int stat, c; long h;
1016	>	while ((stat = joinMe.status) >= 0 &&
1017	>	(h = eventWaiters) != 0L && // help release others
1018	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1019	>	releaseEventWaiters();
1020	>	if (stat >= 0 &&
1021	>	((workerCounts & RUNNING_COUNT_MASK) == 0 \|\|
1022	>	(stat =
1023	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1024	>	helpMaintainParallelism(); // timeout or no running workers
1025	>	do {} while (!UNSAFE.compareAndSwapInt
1026	>	(this, workerCountsOffset,
1027	>	c = workerCounts, c + ONE_RUNNING));
1028	>	if (stat < 0)
1029	>	break; // else restart
1030		}
1031		}
1032		}
1033
1034		/**
1035	<	* Unless there are not enough other running threads, adjusts
982	<	* counts for a a worker in performing helpJoin that cannot find
983	<	* any work, so that this worker can now block.
984	<	*
985	<	* @return true if worker may block
1035	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1036		*/
1037	<	final boolean preBlockHelpingJoin(ForkJoinTask<?> joinMe) {
1038	<	while (joinMe.status >= 0) {
1039	<	releaseWaiters(); // help other threads progress
1040	<
1041	<	// if a spare exists, resume it to maintain parallelism level
1042	<	if ((workerCounts & RUNNING_COUNT_MASK) <= parallelism) {
1043	<	ForkJoinWorkerThread spare = null;
1044	<	for (ForkJoinWorkerThread w : workers) {
1045	<	if (w != null && w.isSuspended()) {
1046	<	spare = w;
1047	<	break;
1048	<	}
1049	<	}
1050	<	if (joinMe.status < 0)
1051	<	break;
1052	<	if (spare != null) {
1053	<	if (spare.tryUnsuspend()) {
1054	<	boolean canBlock = true;
1005	<	if (joinMe.requestSignal() < 0) {
1006	<	canBlock = false; // already done
1007	<	int c;
1008	<	do {} while (!UNSAFE.compareAndSwapInt
1009	<	(this, workerCountsOffset,
1010	<	c = workerCounts, c + ONE_RUNNING));
1011	<	}
1012	<	LockSupport.unpark(spare);
1013	<	return canBlock;
1037	>	final void awaitBlocker(ManagedBlocker blocker)
1038	>	throws InterruptedException {
1039	>	while (!blocker.isReleasable()) {
1040	>	int wc = workerCounts;
1041	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1042	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1043	>	wc, wc - ONE_RUNNING)) {
1044	>	try {
1045	>	while (!blocker.isReleasable()) {
1046	>	long h = eventWaiters;
1047	>	if (h != 0L &&
1048	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1049	>	releaseEventWaiters();
1050	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1051	>	runState < TERMINATING)
1052	>	helpMaintainParallelism();
1053	>	else if (blocker.block())
1054	>	break;
1055		}
1056	<	continue; // recheck -- another spare may exist
1056	>	} finally {
1057	>	int c;
1058	>	do {} while (!UNSAFE.compareAndSwapInt
1059	>	(this, workerCountsOffset,
1060	>	c = workerCounts, c + ONE_RUNNING));
1061		}
1017	–	}
1018	–
1019	–	int wc = workerCounts; // reread to shorten CAS window
1020	–	int rc = wc & RUNNING_COUNT_MASK;
1021	–	if (rc <= 2) // keep this and at most one other thread alive
1022	–	break;
1023	–
1024	–	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1025	–	wc, wc - ONE_RUNNING)) {
1026	–	if (joinMe.requestSignal() >= 0)
1027	–	return true;
1028	–	int c; // back out
1029	–	do {} while (!UNSAFE.compareAndSwapInt
1030	–	(this, workerCountsOffset,
1031	–	c = workerCounts, c + ONE_RUNNING));
1062		break;
1063		}
1064		}
1035	–	return false;
1065		}
1066
1067		/**
#	Line 1056 \| Line 1085 \| public class ForkJoinPool extends Abstra
1085		// Finish now if all threads terminated; else in some subsequent call
1086		if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1087		advanceRunLevel(TERMINATED);
1088	<	terminationLatch.countDown();
1088	>	termination.arrive();
1089		}
1090		return true;
1091		}
1092
1093		/**
1094		* Actions on transition to TERMINATING
1095	+	*
1096	+	* Runs up to four passes through workers: (0) shutting down each
1097	+	* (without waking up if parked) to quickly spread notifications
1098	+	* without unnecessary bouncing around event queues etc (1) wake
1099	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1100	+	* interrupted workers
1101		*/
1102		private void startTerminating() {
1103	<	// Clear out and cancel submissions, ignoring exceptions
1103	>	cancelSubmissions();
1104	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1105	>	int c; // advance event count
1106	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1107	>	c = eventCount, c+1);
1108	>	eventWaiters = 0L; // clobber lists
1109	>	spareWaiters = 0;
1110	>	ForkJoinWorkerThread[] ws = workers;
1111	>	int n = ws.length;
1112	>	for (int i = 0; i < n; ++i) {
1113	>	ForkJoinWorkerThread w = ws[i];
1114	>	if (w != null) {
1115	>	w.shutdown();
1116	>	if (passes > 0 && !w.isTerminated()) {
1117	>	w.cancelTasks();
1118	>	LockSupport.unpark(w);
1119	>	if (passes > 1) {
1120	>	try {
1121	>	w.interrupt();
1122	>	} catch (SecurityException ignore) {
1123	>	}
1124	>	}
1125	>	}
1126	>	}
1127	>	}
1128	>	}
1129	>	}
1130	>
1131	>	/**
1132	>	* Clear out and cancel submissions, ignoring exceptions
1133	>	*/
1134	>	private void cancelSubmissions() {
1135		ForkJoinTask<?> task;
1136		while ((task = submissionQueue.poll()) != null) {
1137		try {
#	Line 1073 \| Line 1139 \| public class ForkJoinPool extends Abstra
1139		} catch (Throwable ignore) {
1140		}
1141		}
1076	–	// Propagate run level
1077	–	for (ForkJoinWorkerThread w : workers) {
1078	–	if (w != null)
1079	–	w.shutdown(); // also resumes suspended workers
1080	–	}
1081	–	// Ensure no straggling local tasks
1082	–	for (ForkJoinWorkerThread w : workers) {
1083	–	if (w != null)
1084	–	w.cancelTasks();
1085	–	}
1086	–	// Wake up idle workers
1087	–	advanceEventCount();
1088	–	releaseWaiters();
1089	–	// Unstick pending joins
1090	–	for (ForkJoinWorkerThread w : workers) {
1091	–	if (w != null && !w.isTerminated()) {
1092	–	try {
1093	–	w.interrupt();
1094	–	} catch (SecurityException ignore) {
1095	–	}
1096	–	}
1097	–	}
1142		}
1143
1144		// misc support for ForkJoinWorkerThread
#	Line 1107 \| Line 1151 \| public class ForkJoinPool extends Abstra
1151		}
1152
1153		/**
1154	<	* Accumulates steal count from a worker, clearing
1155	<	* the worker's value
1154	>	* Tries to accumulates steal count from a worker, clearing
1155	>	* the worker's value.
1156	>	*
1157	>	* @return true if worker steal count now zero
1158		*/
1159	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1159	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1160		int sc = w.stealCount;
1161	<	if (sc != 0) {
1162	<	long c;
1163	<	w.stealCount = 0;
1164	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1165	<	c = stealCount, c + sc));
1161	>	long c = stealCount;
1162	>	// CAS even if zero, for fence effects
1163	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1164	>	if (sc != 0)
1165	>	w.stealCount = 0;
1166	>	return true;
1167		}
1168	+	return sc == 0;
1169		}
1170
1171		/**
#	Line 1125 \| Line 1173 \| public class ForkJoinPool extends Abstra
1173		* active thread.
1174		*/
1175		final int idlePerActive() {
1176	+	int pc = parallelism; // use parallelism, not rc
1177		int ac = runState; // no mask -- artifically boosts during shutdown
1129	–	int pc = parallelism; // use targeted parallelism, not rc
1178		// Use exact results for small values, saturate past 4
1179		return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1180		}
#	Line 1137 \| Line 1185 \| public class ForkJoinPool extends Abstra
1185
1186		/**
1187		* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1188	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1189	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1188	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1189	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1190	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1191		*
1192		* @throws SecurityException if a security manager exists and
1193		* the caller is not permitted to modify threads
#	Line 1147 \| Line 1196 \| public class ForkJoinPool extends Abstra
1196		*/
1197		public ForkJoinPool() {
1198		this(Runtime.getRuntime().availableProcessors(),
1199	<	defaultForkJoinWorkerThreadFactory);
1199	>	defaultForkJoinWorkerThreadFactory, null, false);
1200		}
1201
1202		/**
1203		* Creates a {@code ForkJoinPool} with the indicated parallelism
1204	<	* level and using the {@linkplain
1205	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1204	>	* level, the {@linkplain
1205	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1206	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1207		*
1208		* @param parallelism the parallelism level
1209		* @throws IllegalArgumentException if parallelism less than or
#	Line 1164 \| Line 1214 \| public class ForkJoinPool extends Abstra
1214		* java.lang.RuntimePermission}{@code ("modifyThread")}
1215		*/
1216		public ForkJoinPool(int parallelism) {
1217	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1217	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1218		}
1219
1220		/**
1221	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1172	<	* java.lang.Runtime#availableProcessors}, and using the given
1173	<	* thread factory.
1221	>	* Creates a {@code ForkJoinPool} with the given parameters.
1222		*
1223	<	* @param factory the factory for creating new threads
1224	<	* @throws NullPointerException if the factory is null
1225	<	* @throws SecurityException if a security manager exists and
1226	<	* the caller is not permitted to modify threads
1227	<	* because it does not hold {@link
1228	<	* java.lang.RuntimePermission}{@code ("modifyThread")}
1229	<	*/
1230	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1231	<	this(Runtime.getRuntime().availableProcessors(), factory);
1232	<	}
1233	<
1234	<	/**
1235	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1188	<	* thread factory.
1189	<	*
1190	<	* @param parallelism the parallelism level
1191	<	* @param factory the factory for creating new threads
1223	>	* @param parallelism the parallelism level. For default value,
1224	>	* use {@link java.lang.Runtime#availableProcessors}.
1225	>	* @param factory the factory for creating new threads. For default value,
1226	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1227	>	* @param handler the handler for internal worker threads that
1228	>	* terminate due to unrecoverable errors encountered while executing
1229	>	* tasks. For default value, use <code>null</code>.
1230	>	* @param asyncMode if true,
1231	>	* establishes local first-in-first-out scheduling mode for forked
1232	>	* tasks that are never joined. This mode may be more appropriate
1233	>	* than default locally stack-based mode in applications in which
1234	>	* worker threads only process event-style asynchronous tasks.
1235	>	* For default value, use <code>false</code>.
1236		* @throws IllegalArgumentException if parallelism less than or
1237		* equal to zero, or greater than implementation limit
1238		* @throws NullPointerException if the factory is null
#	Line 1197 \| Line 1241 \| public class ForkJoinPool extends Abstra
1241		* because it does not hold {@link
1242		* java.lang.RuntimePermission}{@code ("modifyThread")}
1243		*/
1244	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1244	>	public ForkJoinPool(int parallelism,
1245	>	ForkJoinWorkerThreadFactory factory,
1246	>	Thread.UncaughtExceptionHandler handler,
1247	>	boolean asyncMode) {
1248		checkPermission();
1249		if (factory == null)
1250		throw new NullPointerException();
1251	<	if (parallelism <= 0 \|\| parallelism > MAX_THREADS)
1251	>	if (parallelism <= 0 \|\| parallelism > MAX_WORKERS)
1252		throw new IllegalArgumentException();
1206	–	this.poolNumber = poolNumberGenerator.incrementAndGet();
1207	–	int arraySize = initialArraySizeFor(parallelism);
1253		this.parallelism = parallelism;
1254		this.factory = factory;
1255	<	this.maxPoolSize = MAX_THREADS;
1256	<	this.maintainsParallelism = true;
1255	>	this.ueh = handler;
1256	>	this.locallyFifo = asyncMode;
1257	>	int arraySize = initialArraySizeFor(parallelism);
1258		this.workers = new ForkJoinWorkerThread[arraySize];
1259		this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1260		this.workerLock = new ReentrantLock();
1261	<	this.terminationLatch = new CountDownLatch(1);
1262	<	// Start first worker; remaining workers added upon first submission
1217	<	workerCounts = ONE_RUNNING \| ONE_TOTAL;
1218	<	addWorker();
1261	>	this.termination = new Phaser(1);
1262	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1263		}
1264
1265		/**
#	Line 1223 \| Line 1267 \| public class ForkJoinPool extends Abstra
1267		* @param pc the initial parallelism level
1268		*/
1269		private static int initialArraySizeFor(int pc) {
1270	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1271	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1270	>	// If possible, initially allocate enough space for one spare
1271	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1272	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1273		size \|= size >>> 1;
1274		size \|= size >>> 2;
1275		size \|= size >>> 4;
#	Line 1243 \| Line 1288 \| public class ForkJoinPool extends Abstra
1288		if (runState >= SHUTDOWN)
1289		throw new RejectedExecutionException();
1290		submissionQueue.offer(task);
1291	<	advanceEventCount();
1292	<	releaseWaiters();
1293	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism)
1249	<	ensureEnoughTotalWorkers();
1291	>	int c; // try to increment event count -- CAS failure OK
1292	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1293	>	helpMaintainParallelism(); // create, start, or resume some workers
1294		}
1295
1296		/**
#	Line 1292 \| Line 1336 \| public class ForkJoinPool extends Abstra
1336		}
1337
1338		/**
1339	+	* Submits a ForkJoinTask for execution.
1340	+	*
1341	+	* @param task the task to submit
1342	+	* @return the task
1343	+	* @throws NullPointerException if the task is null
1344	+	* @throws RejectedExecutionException if the task cannot be
1345	+	* scheduled for execution
1346	+	*/
1347	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1348	+	doSubmit(task);
1349	+	return task;
1350	+	}
1351	+
1352	+	/**
1353		* @throws NullPointerException if the task is null
1354		* @throws RejectedExecutionException if the task cannot be
1355		* scheduled for execution
#	Line 1329 \| Line 1387 \| public class ForkJoinPool extends Abstra
1387		}
1388
1389		/**
1332	–	* Submits a ForkJoinTask for execution.
1333	–	*
1334	–	* @param task the task to submit
1335	–	* @return the task
1336	–	* @throws NullPointerException if the task is null
1337	–	* @throws RejectedExecutionException if the task cannot be
1338	–	* scheduled for execution
1339	–	*/
1340	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1341	–	doSubmit(task);
1342	–	return task;
1343	–	}
1344	–
1345	–	/**
1390		* @throws NullPointerException {@inheritDoc}
1391		* @throws RejectedExecutionException {@inheritDoc}
1392		*/
#	Line 1384 \| Line 1428 \| public class ForkJoinPool extends Abstra
1428		* @return the handler, or {@code null} if none
1429		*/
1430		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1387	–	workerCountReadFence();
1431		return ueh;
1432		}
1433
1434		/**
1392	–	* Sets the handler for internal worker threads that terminate due
1393	–	* to unrecoverable errors encountered while executing tasks.
1394	–	* Unless set, the current default or ThreadGroup handler is used
1395	–	* as handler.
1396	–	*
1397	–	* @param h the new handler
1398	–	* @return the old handler, or {@code null} if none
1399	–	* @throws SecurityException if a security manager exists and
1400	–	* the caller is not permitted to modify threads
1401	–	* because it does not hold {@link
1402	–	* java.lang.RuntimePermission}{@code ("modifyThread")}
1403	–	*/
1404	–	public Thread.UncaughtExceptionHandler
1405	–	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1406	–	checkPermission();
1407	–	workerCountReadFence();
1408	–	Thread.UncaughtExceptionHandler old = ueh;
1409	–	if (h != old) {
1410	–	ueh = h;
1411	–	workerCountWriteFence();
1412	–	for (ForkJoinWorkerThread w : workers) {
1413	–	if (w != null)
1414	–	w.setUncaughtExceptionHandler(h);
1415	–	}
1416	–	}
1417	–	return old;
1418	–	}
1419	–
1420	–	/**
1421	–	* Sets the target parallelism level of this pool.
1422	–	*
1423	–	* @param parallelism the target parallelism
1424	–	* @throws IllegalArgumentException if parallelism less than or
1425	–	* equal to zero or greater than maximum size bounds
1426	–	* @throws SecurityException if a security manager exists and
1427	–	* the caller is not permitted to modify threads
1428	–	* because it does not hold {@link
1429	–	* java.lang.RuntimePermission}{@code ("modifyThread")}
1430	–	*/
1431	–	public void setParallelism(int parallelism) {
1432	–	checkPermission();
1433	–	if (parallelism <= 0 \|\| parallelism > maxPoolSize)
1434	–	throw new IllegalArgumentException();
1435	–	workerCountReadFence();
1436	–	int pc = this.parallelism;
1437	–	if (pc != parallelism) {
1438	–	this.parallelism = parallelism;
1439	–	workerCountWriteFence();
1440	–	// Release spares. If too many, some will die after re-suspend
1441	–	for (ForkJoinWorkerThread w : workers) {
1442	–	if (w != null && w.tryUnsuspend()) {
1443	–	updateRunningCount(1);
1444	–	LockSupport.unpark(w);
1445	–	}
1446	–	}
1447	–	ensureEnoughTotalWorkers();
1448	–	advanceEventCount();
1449	–	releaseWaiters(); // force config recheck by existing workers
1450	–	}
1451	–	}
1452	–
1453	–	/**
1435		* Returns the targeted parallelism level of this pool.
1436		*
1437		* @return the targeted parallelism level of this pool
1438		*/
1439		public int getParallelism() {
1459	–	// workerCountReadFence(); // inlined below
1460	–	int ignore = workerCounts;
1440		return parallelism;
1441		}
1442
#	Line 1474 \| Line 1453 \| public class ForkJoinPool extends Abstra
1453		}
1454
1455		/**
1477	–	* Returns the maximum number of threads allowed to exist in the
1478	–	* pool. Unless set using {@link #setMaximumPoolSize}, the
1479	–	* maximum is an implementation-defined value designed only to
1480	–	* prevent runaway growth.
1481	–	*
1482	–	* @return the maximum
1483	–	*/
1484	–	public int getMaximumPoolSize() {
1485	–	workerCountReadFence();
1486	–	return maxPoolSize;
1487	–	}
1488	–
1489	–	/**
1490	–	* Sets the maximum number of threads allowed to exist in the
1491	–	* pool. The given value should normally be greater than or equal
1492	–	* to the {@link #getParallelism parallelism} level. Setting this
1493	–	* value has no effect on current pool size. It controls
1494	–	* construction of new threads. The use of this method may cause
1495	–	* tasks that intrinsically require extra threads for dependent
1496	–	* computations to indefinitely stall. If you are instead trying
1497	–	* to minimize internal thread creation, consider setting {link
1498	–	* #setMaintainsParallelism} as false.
1499	–	*
1500	–	* @throws IllegalArgumentException if negative or greater than
1501	–	* internal implementation limit
1502	–	*/
1503	–	public void setMaximumPoolSize(int newMax) {
1504	–	if (newMax < 0 \|\| newMax > MAX_THREADS)
1505	–	throw new IllegalArgumentException();
1506	–	maxPoolSize = newMax;
1507	–	workerCountWriteFence();
1508	–	}
1509	–
1510	–	/**
1511	–	* Returns {@code true} if this pool dynamically maintains its
1512	–	* target parallelism level. If false, new threads are added only
1513	–	* to avoid possible starvation. This setting is by default true.
1514	–	*
1515	–	* @return {@code true} if maintains parallelism
1516	–	*/
1517	–	public boolean getMaintainsParallelism() {
1518	–	workerCountReadFence();
1519	–	return maintainsParallelism;
1520	–	}
1521	–
1522	–	/**
1523	–	* Sets whether this pool dynamically maintains its target
1524	–	* parallelism level. If false, new threads are added only to
1525	–	* avoid possible starvation.
1526	–	*
1527	–	* @param enable {@code true} to maintain parallelism
1528	–	*/
1529	–	public void setMaintainsParallelism(boolean enable) {
1530	–	maintainsParallelism = enable;
1531	–	workerCountWriteFence();
1532	–	}
1533	–
1534	–	/**
1535	–	* Establishes local first-in-first-out scheduling mode for forked
1536	–	* tasks that are never joined. This mode may be more appropriate
1537	–	* than default locally stack-based mode in applications in which
1538	–	* worker threads only process asynchronous tasks. This method is
1539	–	* designed to be invoked only when the pool is quiescent, and
1540	–	* typically only before any tasks are submitted. The effects of
1541	–	* invocations at other times may be unpredictable.
1542	–	*
1543	–	* @param async if {@code true}, use locally FIFO scheduling
1544	–	* @return the previous mode
1545	–	* @see #getAsyncMode
1546	–	*/
1547	–	public boolean setAsyncMode(boolean async) {
1548	–	workerCountReadFence();
1549	–	boolean oldMode = locallyFifo;
1550	–	if (oldMode != async) {
1551	–	locallyFifo = async;
1552	–	workerCountWriteFence();
1553	–	for (ForkJoinWorkerThread w : workers) {
1554	–	if (w != null)
1555	–	w.setAsyncMode(async);
1556	–	}
1557	–	}
1558	–	return oldMode;
1559	–	}
1560	–
1561	–	/**
1456		* Returns {@code true} if this pool uses local first-in-first-out
1457		* scheduling mode for forked tasks that are never joined.
1458		*
1459		* @return {@code true} if this pool uses async mode
1566	–	* @see #setAsyncMode
1460		*/
1461		public boolean getAsyncMode() {
1569	–	workerCountReadFence();
1462		return locallyFifo;
1463		}
1464
#	Line 1635 \| Line 1527 \| public class ForkJoinPool extends Abstra
1527		*/
1528		public long getQueuedTaskCount() {
1529		long count = 0;
1530	<	for (ForkJoinWorkerThread w : workers) {
1530	>	ForkJoinWorkerThread[] ws = workers;
1531	>	int n = ws.length;
1532	>	for (int i = 0; i < n; ++i) {
1533	>	ForkJoinWorkerThread w = ws[i];
1534		if (w != null)
1535		count += w.getQueueSize();
1536		}
#	Line 1692 \| Line 1587 \| public class ForkJoinPool extends Abstra
1587		* @return the number of elements transferred
1588		*/
1589		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1590	<	int n = submissionQueue.drainTo(c);
1591	<	for (ForkJoinWorkerThread w : workers) {
1590	>	int count = submissionQueue.drainTo(c);
1591	>	ForkJoinWorkerThread[] ws = workers;
1592	>	int n = ws.length;
1593	>	for (int i = 0; i < n; ++i) {
1594	>	ForkJoinWorkerThread w = ws[i];
1595		if (w != null)
1596	<	n += w.drainTasksTo(c);
1596	>	count += w.drainTasksTo(c);
1597		}
1598	<	return n;
1598	>	return count;
1599		}
1600
1601		/**
#	Line 1821 \| Line 1719 \| public class ForkJoinPool extends Abstra
1719		*/
1720		public boolean awaitTermination(long timeout, TimeUnit unit)
1721		throws InterruptedException {
1722	<	return terminationLatch.await(timeout, unit);
1722	>	try {
1723	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1724	>	} catch(TimeoutException ex) {
1725	>	return false;
1726	>	}
1727		}
1728
1729		/**
1730		* Interface for extending managed parallelism for tasks running
1731		* in {@link ForkJoinPool}s.
1732		*
1733	<	* <p>A {@code ManagedBlocker} provides two methods.
1734	<	* Method {@code isReleasable} must return {@code true} if
1735	<	* blocking is not necessary. Method {@code block} blocks the
1736	<	* current thread if necessary (perhaps internally invoking
1737	<	* {@code isReleasable} before actually blocking).
1733	>	* <p>A {@code ManagedBlocker} provides two methods. Method
1734	>	* {@code isReleasable} must return {@code true} if blocking is
1735	>	* not necessary. Method {@code block} blocks the current thread
1736	>	* if necessary (perhaps internally invoking {@code isReleasable}
1737	>	* before actually blocking). The unusual methods in this API
1738	>	* accommodate synchronizers that may, but don't usually, block
1739	>	* for long periods. Similarly, they allow more efficient internal
1740	>	* handling of cases in which additional workers may be, but
1741	>	* usually are not, needed to ensure sufficient parallelism.
1742	>	* Toward this end, implementations of method {@code isReleasable}
1743	>	* must be amenable to repeated invocation.
1744		*
1745		* <p>For example, here is a ManagedBlocker based on a
1746		* ReentrantLock:
#	Line 1850 \| Line 1758 \| public class ForkJoinPool extends Abstra
1758		* return hasLock \|\| (hasLock = lock.tryLock());
1759		* }
1760		* }}</pre>
1761	+	*
1762	+	* <p>Here is a class that possibly blocks waiting for an
1763	+	* item on a given queue:
1764	+	* <pre> {@code
1765	+	* class QueueTaker<E> implements ManagedBlocker {
1766	+	* final BlockingQueue<E> queue;
1767	+	* volatile E item = null;
1768	+	* QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1769	+	* public boolean block() throws InterruptedException {
1770	+	* if (item == null)
1771	+	* item = queue.take();
1772	+	* return true;
1773	+	* }
1774	+	* public boolean isReleasable() {
1775	+	* return item != null \|\| (item = queue.poll()) != null;
1776	+	* }
1777	+	* public E getItem() { // call after pool.managedBlock completes
1778	+	* return item;
1779	+	* }
1780	+	* }}</pre>
1781		*/
1782		public static interface ManagedBlocker {
1783		/**
#	Line 1873 \| Line 1801 \| public class ForkJoinPool extends Abstra
1801		* Blocks in accord with the given blocker. If the current thread
1802		* is a {@link ForkJoinWorkerThread}, this method possibly
1803		* arranges for a spare thread to be activated if necessary to
1804	<	* ensure parallelism while the current thread is blocked.
1877	<	*
1878	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1879	<	* supports it ({@link #getMaintainsParallelism}), this method
1880	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1881	<	* it activates a thread only if necessary to avoid complete
1882	<	* starvation. This option may be preferable when blockages use
1883	<	* timeouts, or are almost always brief.
1804	>	* ensure sufficient parallelism while the current thread is blocked.
1805		*
1806		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1807		* behaviorally equivalent to
#	Line 1894 \| Line 1815 \| public class ForkJoinPool extends Abstra
1815		* first be expanded to ensure parallelism, and later adjusted.
1816		*
1817		* @param blocker the blocker
1897	–	* @param maintainParallelism if {@code true} and supported by
1898	–	* this pool, attempt to maintain the pool's nominal parallelism;
1899	–	* otherwise activate a thread only if necessary to avoid
1900	–	* complete starvation.
1818		* @throws InterruptedException if blocker.block did so
1819		*/
1820	<	public static void managedBlock(ManagedBlocker blocker,
1904	<	boolean maintainParallelism)
1820	>	public static void managedBlock(ManagedBlocker blocker)
1821		throws InterruptedException {
1822		Thread t = Thread.currentThread();
1823	<	if (t instanceof ForkJoinWorkerThread)
1824	<	((ForkJoinWorkerThread) t).pool.
1825	<	doBlock(blocker, maintainParallelism);
1826	<	else
1827	<	awaitBlocker(blocker);
1828	<	}
1829	<
1914	<	/**
1915	<	* Performs Non-FJ blocking
1916	<	*/
1917	<	private static void awaitBlocker(ManagedBlocker blocker)
1918	<	throws InterruptedException {
1919	<	do {} while (!blocker.isReleasable() && !blocker.block());
1823	>	if (t instanceof ForkJoinWorkerThread) {
1824	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1825	>	w.pool.awaitBlocker(blocker);
1826	>	}
1827	>	else {
1828	>	do {} while (!blocker.isReleasable() && !blocker.block());
1829	>	}
1830		}
1831
1832		// AbstractExecutorService overrides. These rely on undocumented
#	Line 1944 \| Line 1854 \| public class ForkJoinPool extends Abstra
1854		objectFieldOffset("eventWaiters",ForkJoinPool.class);
1855		private static final long stealCountOffset =
1856		objectFieldOffset("stealCount",ForkJoinPool.class);
1857	<
1857	>	private static final long spareWaitersOffset =
1858	>	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1859
1860		private static long objectFieldOffset(String field, Class<?> klazz) {
1861		try {

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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents): Revision 1.54 by dl, Sun Apr 18 12:51:18 2010 UTC vs. Revision 1.66 by dl, Sun Aug 29 23:34:46 2010 UTC

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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.54 by dl, Sun Apr 18 12:51:18 2010 UTC vs.
Revision 1.66 by dl, Sun Aug 29 23:34:46 2010 UTC