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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.57 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.91 by dl, Tue Feb 22 00:39:31 2011 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	+	import java.util.Random;
15	+	import java.util.concurrent.AbstractExecutorService;
16	+	import java.util.concurrent.Callable;
17	+	import java.util.concurrent.ExecutorService;
18	+	import java.util.concurrent.Future;
19	+	import java.util.concurrent.RejectedExecutionException;
20	+	import java.util.concurrent.RunnableFuture;
21	+	import java.util.concurrent.TimeUnit;
22	+	import java.util.concurrent.TimeoutException;
23	+	import java.util.concurrent.atomic.AtomicInteger;
24		import java.util.concurrent.locks.LockSupport;
25		import java.util.concurrent.locks.ReentrantLock;
26	<	import java.util.concurrent.atomic.AtomicInteger;
19	<	import java.util.concurrent.CountDownLatch;
26	>	import java.util.concurrent.locks.Condition;
27
28		/**
29		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
#	Line 52 | Line 59 | import java.util.concurrent.CountDownLat
59		* convenient form for informal monitoring.
60		*
61		* <p> As is the case with other ExecutorServices, there are three
62	<	* main task execution methods summarized in the follwoing
62	>	* main task execution methods summarized in the following
63		* table. These are designed to be used by clients not already engaged
64		* in fork/join computations in the current pool.  The main forms of
65		* these methods accept instances of {@code ForkJoinTask}, but
#	Line 60 | Line 67 | import java.util.concurrent.CountDownLat
67		* Runnable}- or {@code Callable}- based activities as well.  However,
68		* tasks that are already executing in a pool should normally
69		* <em>NOT</em> use these pool execution methods, but instead use the
70	<	* within-computation forms listed in the table. To avoid inadvertant
64	<	* cyclic task dependencies and to improve performance, task
65	<	* submissions to the current pool by an ongoing fork/join
66	<	* computations may be implicitly translated to the corresponding
67	<	* ForkJoinTask forms.
70	>	* within-computation forms listed in the table.
71		*
72		* <table BORDER CELLPADDING=3 CELLSPACING=1>
73		*  <tr>
#	Line 73 | Line 76 | import java.util.concurrent.CountDownLat
76		*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
77		*  </tr>
78		*  <tr>
79	<	*    <td> <b>Arange async execution</td>
79	>	*    <td> <b>Arrange async execution</td>
80		*    <td> {@link #execute(ForkJoinTask)}</td>
81		*    <td> {@link ForkJoinTask#fork}</td>
82		*  </tr>
#	Line 88 | Line 91 | import java.util.concurrent.CountDownLat
91		*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
92		*  </tr>
93		* </table>
94	<	*
94	>	*
95		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
96		* used for all parallel task execution in a program or subsystem.
97		* Otherwise, use would not usually outweigh the construction and
#	Line 113 | Line 116 | import java.util.concurrent.CountDownLat
116		* {@code IllegalArgumentException}.
117		*
118		* <p>This implementation rejects submitted tasks (that is, by throwing
119	<	* {@link RejectedExecutionException}) only when the pool is shut down.
119	>	* {@link RejectedExecutionException}) only when the pool is shut down
120	>	* or internal resources have been exhausted.
121		*
122		* @since 1.7
123		* @author Doug Lea
#	Line 127 | Line 131 | public class ForkJoinPool extends Abstra
131		* set of worker threads: Submissions from non-FJ threads enter
132		* into a submission queue. Workers take these tasks and typically
133		* split them into subtasks that may be stolen by other workers.
134	<	* The main work-stealing mechanics implemented in class
135	<	* ForkJoinWorkerThread give first priority to processing tasks
136	<	* from their own queues (LIFO or FIFO, depending on mode), then
137	<	* to randomized FIFO steals of tasks in other worker queues, and
134	<	* lastly to new submissions. These mechanics do not consider
135	<	* affinities, loads, cache localities, etc, so rarely provide the
136	<	* best possible performance on a given machine, but portably
137	<	* provide good throughput by averaging over these factors.
138	<	* (Further, even if we did try to use such information, we do not
139	<	* usually have a basis for exploiting it. For example, some sets
140	<	* of tasks profit from cache affinities, but others are harmed by
141	<	* cache pollution effects.)
134	>	* Preference rules give first priority to processing tasks from
135	>	* their own queues (LIFO or FIFO, depending on mode), then to
136	>	* randomized FIFO steals of tasks in other worker queues, and
137	>	* lastly to new submissions.
138		*
139		* The main throughput advantages of work-stealing stem from
140	<	* decentralized control -- workers mostly steal tasks from each
141	<	* other. We do not want to negate this by creating bottlenecks
142	<	* implementing the management responsibilities of this class. So
143	<	* we use a collection of techniques that avoid, reduce, or cope
144	<	* well with contention. These entail several instances of
145	<	* bit-packing into CASable fields to maintain only the minimally
146	<	* required atomicity. To enable such packing, we restrict maximum
147	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
148	<	* bit field), which is far in excess of normal operating range.
149	<	* Even though updates to some of these bookkeeping fields do
150	<	* sometimes contend with each other, they don't normally
151	<	* cache-contend with updates to others enough to warrant memory
152	<	* padding or isolation. So they are all held as fields of
153	<	* ForkJoinPool objects.  The main capabilities are as follows:
154	<	*
155	<	* 1. Creating and removing workers. Workers are recorded in the
156	<	* "workers" array. This is an array as opposed to some other data
140	>	* decentralized control -- workers mostly take tasks from
141	>	* themselves or each other. We cannot negate this in the
142	>	* implementation of other management responsibilities. The main
143	>	* tactic for avoiding bottlenecks is packing nearly all
144	>	* essentially atomic control state into a single 64bit volatile
145	>	* variable ("ctl"). This variable is read on the order of 10-100
146	>	* times as often as it is modified (always via CAS). (There is
147	>	* some additional control state, for example variable "shutdown"
148	>	* for which we can cope with uncoordinated updates.)  This
149	>	* streamlines synchronization and control at the expense of messy
150	>	* constructions needed to repack status bits upon updates.
151	>	* Updates tend not to contend with each other except during
152	>	* bursts while submitted tasks begin or end.  In some cases when
153	>	* they do contend, threads can instead do something else
154	>	* (usually, scan for tesks) until contention subsides.
155	>	*
156	>	* To enable packing, we restrict maximum parallelism to (1<<15)-1
157	>	* (which is far in excess of normal operating range) to allow
158	>	* ids, counts, and their negations (used for thresholding) to fit
159	>	* into 16bit fields.
160	>	*
161	>	* Recording Workers.  Workers are recorded in the "workers" array
162	>	* that is created upon pool construction and expanded if (rarely)
163	>	* necessary.  This is an array as opposed to some other data
164		* structure to support index-based random steals by workers.
165		* Updates to the array recording new workers and unrecording
166	<	* terminated ones are protected from each other by a lock
167	<	* (workerLock) but the array is otherwise concurrently readable,
166	>	* terminated ones are protected from each other by a seqLock
167	>	* (scanGuard) but the array is otherwise concurrently readable,
168		* and accessed directly by workers. To simplify index-based
169		* operations, the array size is always a power of two, and all
170	<	* readers must tolerate null slots. Currently, all worker thread
171	<	* creation is on-demand, triggered by task submissions,
172	<	* replacement of terminated workers, and/or compensation for
173	<	* blocked workers. However, all other support code is set up to
174	<	* work with other policies.
175	<	*
176	<	* 2. Bookkeeping for dynamically adding and removing workers. We
177	<	* aim to approximately maintain the given level of parallelism.
178	<	* When some workers are known to be blocked (on joins or via
179	<	* ManagedBlocker), we may create or resume others to take their
180	<	* place until they unblock (see below). Implementing this
181	<	* requires counts of the number of "running" threads (i.e., those
182	<	* that are neither blocked nor artifically suspended) as well as
183	<	* the total number.  These two values are packed into one field,
184	<	* "workerCounts" because we need accurate snapshots when deciding
185	<	* to create, resume or suspend.  To support these decisions,
186	<	* updates to spare counts must be prospective (not
187	<	* retrospective).  For example, the running count is decremented
188	<	* before blocking by a thread about to block as a spare, but
189	<	* incremented by the thread about to unblock it. Updates upon
190	<	* resumption ofr threads blocking in awaitJoin or awaitBlocker
191	<	* cannot usually be prospective, so the running count is in
192	<	* general an upper bound of the number of productively running
193	<	* threads Updates to the workerCounts field sometimes transiently
194	<	* encounter a fair amount of contention when join dependencies
195	<	* are such that many threads block or unblock at about the same
196	<	* time. We alleviate this by sometimes performing an alternative
197	<	* action on contention like releasing waiters or locating spares.
198	<	*
199	<	* 3. Maintaining global run state. The run state of the pool
200	<	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
201	<	* those in other Executor implementations, as well as a count of
202	<	* "active" workers -- those that are, or soon will be, or
203	<	* recently were executing tasks. The runLevel and active count
204	<	* are packed together in order to correctly trigger shutdown and
205	<	* termination. Without care, active counts can be subject to very
206	<	* high contention.  We substantially reduce this contention by
207	<	* relaxing update rules.  A worker must claim active status
208	<	* prospectively, by activating if it sees that a submitted or
209	<	* stealable task exists (it may find after activating that the
210	<	* task no longer exists). It stays active while processing this
211	<	* task (if it exists) and any other local subtasks it produces,
212	<	* until it cannot find any other tasks. It then tries
213	<	* inactivating (see method preStep), but upon update contention
214	<	* instead scans for more tasks, later retrying inactivation if it
215	<	* doesn't find any.
216	<	*
217	<	* 4. Managing idle workers waiting for tasks. We cannot let
218	<	* workers spin indefinitely scanning for tasks when none are
219	<	* available. On the other hand, we must quickly prod them into
220	<	* action when new tasks are submitted or generated.  We
221	<	* park/unpark these idle workers using an event-count scheme.
222	<	* Field eventCount is incremented upon events that may enable
223	<	* workers that previously could not find a task to now find one:
224	<	* Submission of a new task to the pool, or another worker pushing
225	<	* a task onto a previously empty queue.  (We also use this
226	<	* mechanism for termination and reconfiguration actions that
227	<	* require wakeups of idle workers).  Each worker maintains its
228	<	* last known event count, and blocks when a scan for work did not
229	<	* find a task AND its lastEventCount matches the current
230	<	* eventCount. Waiting idle workers are recorded in a variant of
231	<	* Treiber stack headed by field eventWaiters which, when nonzero,
232	<	* encodes the thread index and count awaited for by the worker
233	<	* thread most recently calling eventSync. This thread in turn has
234	<	* a record (field nextEventWaiter) for the next waiting worker.
235	<	* In addition to allowing simpler decisions about need for
236	<	* wakeup, the event count bits in eventWaiters serve the role of
237	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
238	<	* in task diffusion, workers not otherwise occupied may invoke
239	<	* method releaseWaiters, that removes and signals (unparks)
240	<	* workers not waiting on current count. To minimize task
241	<	* production stalls associate with signalling, any worker pushing
242	<	* a task on an empty queue invokes the weaker method signalWork,
243	<	* that only releases idle workers until it detects interference
244	<	* by other threads trying to release, and lets them take
245	<	* over. The net effect is a tree-like diffusion of signals, where
246	<	* released threads (and possibly others) help with unparks.  To
247	<	* further reduce contention effects a bit, failed CASes to
248	<	* increment field eventCount are tolerated without retries.
249	<	* Conceptually they are merged into the same event, which is OK
250	<	* when their only purpose is to enable workers to scan for work.
251	<	*
252	<	* 5. Managing suspension of extra workers. When a worker is about
253	<	* to block waiting for a join (or via ManagedBlockers), we may
254	<	* create a new thread to maintain parallelism level, or at least
255	<	* avoid starvation (see below). Usually, extra threads are needed
256	<	* for only very short periods, yet join dependencies are such
257	<	* that we sometimes need them in bursts. Rather than create new
258	<	* threads each time this happens, we suspend no-longer-needed
259	<	* extra ones as "spares". For most purposes, we don't distinguish
260	<	* "extra" spare threads from normal "core" threads: On each call
261	<	* to preStep (the only point at which we can do this) a worker
262	<	* checks to see if there are now too many running workers, and if
263	<	* so, suspends itself.  Methods awaitJoin and awaitBlocker look
264	<	* for suspended threads to resume before considering creating a
265	<	* new replacement. We don't need a special data structure to
266	<	* maintain spares; simply scanning the workers array looking for
267	<	* worker.isSuspended() is fine because the calling thread is
268	<	* otherwise not doing anything useful anyway; we are at least as
269	<	* happy if after locating a spare, the caller doesn't actually
270	<	* block because the join is ready before we try to adjust and
271	<	* compensate.  Note that this is intrinsically racy.  One thread
272	<	* may become a spare at about the same time as another is
273	<	* needlessly being created. We counteract this and related slop
274	<	* in part by requiring resumed spares to immediately recheck (in
275	<	* preStep) to see whether they they should re-suspend. The only
276	<	* effective difference between "extra" and "core" threads is that
277	<	* we allow the "extra" ones to time out and die if they are not
278	<	* resumed within a keep-alive interval of a few seconds. This is
279	<	* implemented mainly within ForkJoinWorkerThread, but requires
280	<	* some coordination (isTrimmed() -- meaning killed while
281	<	* suspended) to correctly maintain pool counts.
282	<	*
283	<	* 6. Deciding when to create new workers. The main dynamic
284	<	* control in this class is deciding when to create extra threads,
285	<	* in methods awaitJoin and awaitBlocker. We always need to create
286	<	* one when the number of running threads becomes zero. But
287	<	* because blocked joins are typically dependent, we don't
288	<	* necessarily need or want one-to-one replacement. Instead, we
289	<	* use a combination of heuristics that adds threads only when the
290	<	* pool appears to be approaching starvation.  These effectively
291	<	* reduce churn at the price of systematically undershooting
292	<	* target parallelism when many threads are blocked.  However,
293	<	* biasing toward undeshooting partially compensates for the above
294	<	* mechanics to suspend extra threads, that normally lead to
292	<	* overshoot because we can only suspend workers in-between
293	<	* top-level actions. It also better copes with the fact that some
294	<	* of the methods in this class tend to never become compiled (but
295	<	* are interpreted), so some components of the entire set of
296	<	* controls might execute many times faster than others. And
297	<	* similarly for cases where the apparent lack of work is just due
298	<	* to GC stalls and other transient system activity.
170	>	* readers must tolerate null slots. To avoid flailing during
171	>	* start-up, the array is presized to hold twice #parallelism
172	>	* workers (which is unlikely to need further resizing during
173	>	* execution). But to avoid dealing with so many null slots,
174	>	* variable scanGuard includes a mask for the nearest power of two
175	>	* that contains all current workers.  All worker thread creation
176	>	* is on-demand, triggered by task submissions, replacement of
177	>	* terminated workers, and/or compensation for blocked
178	>	* workers. However, all other support code is set up to work with
179	>	* other policies.  To ensure that we do not hold on to worker
180	>	* references that would prevent GC, ALL accesses to workers are
181	>	* via indices into the workers array (which is one source of some
182	>	* of the messy code constructions here). In essence, the workers
183	>	* array serves as a weak reference mechanism. Thus for example
184	>	* the wait queue field of ctl stores worker indices, not worker
185	>	* references.  Access to the workers in associated methods (for
186	>	* example signalWork) must both index-check and null-check the
187	>	* IDs. All such accesses ignore bad IDs by returning out early
188	>	* from what they are doing, since this can only be associated
189	>	* with termination, in which case it is OK to give up.
190	>	*
191	>	* All uses of the workers array, as well as queue arrays, check
192	>	* that the array is non-null (even if previously non-null). This
193	>	* allows nulling during termination, which is currently not
194	>	* necessary, but remains an option for resource-revocation-based
195	>	* shutdown schemes.
196	>	*
197	>	* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
198	>	* let workers spin indefinitely scanning for tasks when none are
199	>	* can be immediately found, and we cannot start/resume workers
200	>	* unless there appear to be tasks available.  On the other hand,
201	>	* we must quickly prod them into action when new tasks are
202	>	* submitted or generated.  We park/unpark workers after placing
203	>	* in an event wait queue when they cannot find work. This "queue"
204	>	* is actually a simple Treiber stack, headed by the "id" field of
205	>	* ctl, plus a 15bit counter value to both wake up waiters (by
206	>	* advancing their count) and avoid ABA effects. Successors are
207	>	* held in worker field "nextWait".  Queuing deals with several
208	>	* intrinsic races, mainly that a task-producing thread can miss
209	>	* seeing (and signalling) another thread that gave up looking for
210	>	* work but has not yet entered the wait queue. We solve this by
211	>	* requiring a full sweep of all workers both before (in scan())
212	>	* and after (in awaitWork()) a newly waiting worker is added to
213	>	* the wait queue. During a rescan, the worker might release some
214	>	* other queued worker rather than itself, which has the same net
215	>	* effect.
216	>	*
217	>	* Signalling.  We create or wake up workers only when there
218	>	* appears to be at least one task they might be able to find and
219	>	* execute.  When a submission is added or another worker adds a
220	>	* task to a queue that previously had two or fewer tasks, they
221	>	* signal waiting workers (or trigger creation of new ones if
222	>	* fewer than the given parallelism level -- see signalWork).
223	>	* These primary signals are buttressed by signals during rescans
224	>	* as well as those performed when a worker steals a task and
225	>	* notices that there are more tasks too; together these cover the
226	>	* signals needed in cases when more than two tasks are pushed
227	>	* but untaken.
228	>	*
229	>	* Trimming workers. To release resources after periods of lack of
230	>	* use, a worker starting to wait when the pool is quiescent will
231	>	* time out and terminate if the pool has remained quiescent for
232	>	* SHRINK_RATE nanosecs.
233	>	*
234	>	* Submissions. External submissions are maintained in an
235	>	* array-based queue that is structured identically to
236	>	* ForkJoinWorkerThread queues (which see) except for the use of
237	>	* submissionLock in method addSubmission. Unlike worker queues,
238	>	* multiple external threads can add new submissions.
239	>	*
240	>	* Compensation. Beyond work-stealing support and lifecycle
241	>	* control, the main responsibility of this framework is to take
242	>	* actions when one worker is waiting to join a task stolen (or
243	>	* always held by) another.  Because we are multiplexing many
244	>	* tasks on to a pool of workers, we can't just let them block (as
245	>	* in Thread.join).  We also cannot just reassign the joiner's
246	>	* run-time stack with another and replace it later, which would
247	>	* be a form of "continuation", that even if possible is not
248	>	* necessarily a good idea since we sometimes need both an
249	>	* unblocked task and its continuation to progress. Instead we
250	>	* combine two tactics:
251	>	*
252	>	*   Helping: Arranging for the joiner to execute some task that it
253	>	*      would be running if the steal had not occurred.  Method
254	>	*      ForkJoinWorkerThread.joinTask tracks joining->stealing
255	>	*      links to try to find such a task.
256	>	*
257	>	*   Compensating: Unless there are already enough live threads,
258	>	*      method tryPreBlock() may create or re-activate a spare
259	>	*      thread to compensate for blocked joiners until they
260	>	*      unblock.
261	>	*
262	>	* The ManagedBlocker extension API can't use helping so relies
263	>	* only on compensation in method awaitBlocker.
264	>	*
265	>	* It is impossible to keep exactly the target parallelism number
266	>	* of threads running at any given time.  Determining the
267	>	* existence of conservatively safe helping targets, the
268	>	* availability of already-created spares, and the apparent need
269	>	* to create new spares are all racy and require heuristic
270	>	* guidance, so we rely on multiple retries of each.  Currently,
271	>	* in keeping with on-demand signalling policy, we compensate only
272	>	* if blocking would leave less than one active (non-waiting,
273	>	* non-blocked) worker. Additionally, to avoid some false alarms
274	>	* due to GC, lagging counters, system activity, etc, compensated
275	>	* blocking for joins is only attempted after a number of rechecks
276	>	* proportional to the current apparent deficit (where retries are
277	>	* interspersed with Thread.yield, for good citizenship).  The
278	>	* variable blockedCount, incremented before blocking and
279	>	* decremented after, is sometimes needed to distinguish cases of
280	>	* waiting for work vs blocking on joins or other managed sync,
281	>	* but both the cases are equivalent for most pool control, so we
282	>	* can update non-atomically. (Additionally, contention on
283	>	* blockedCount alleviates some contention on ctl).
284	>	*
285	>	* Shutdown and Termination. A call to shutdownNow atomically sets
286	>	* the ctl stop bit and then (non-atomically) sets each workers
287	>	* "terminate" status, cancels all unprocessed tasks, and wakes up
288	>	* all waiting workers.  Detecting whether termination should
289	>	* commence after a non-abrupt shutdown() call requires more work
290	>	* and bookkeeping. We need consensus about quiesence (i.e., that
291	>	* there is no more work) which is reflected in active counts so
292	>	* long as there are no current blockers, as well as possible
293	>	* re-evaluations during independent changes in blocking or
294	>	* quiescing workers.
295		*
296	<	* Beware that there is a lot of representation-level coupling
296	>	* Style notes: There is a lot of representation-level coupling
297		* among classes ForkJoinPool, ForkJoinWorkerThread, and
298	<	* ForkJoinTask.  For example, direct access to "workers" array by
298	>	* ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
299	>	* data structures managed by ForkJoinPool, so are directly
300	>	* accessed.  Conversely we allow access to "workers" array by
301		* workers, and direct access to ForkJoinTask.status by both
302		* ForkJoinPool and ForkJoinWorkerThread.  There is little point
303		* trying to reduce this, since any associated future changes in
304		* representations will need to be accompanied by algorithmic
305	<	* changes anyway.
306	<	*
307	<	* Style notes: There are lots of inline assignments (of form
308	<	* "while ((local = field) != 0)") which are usually the simplest
309	<	* way to ensure read orderings. Also several occurrences of the
310	<	* unusual "do {} while(!cas...)" which is the simplest way to
311	<	* force an update of a CAS'ed variable. There are also a few
312	<	* other coding oddities that help some methods perform reasonably
313	<	* even when interpreted (not compiled).
314	<	*
315	<	* The order of declarations in this file is: (1) statics (2)
316	<	* fields (along with constants used when unpacking some of them)
317	<	* (3) internal control methods (4) callbacks and other support
318	<	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
319	<	* methods (plus a few little helpers).
305	>	* changes anyway. All together, these low-level implementation
306	>	* choices produce as much as a factor of 4 performance
307	>	* improvement compared to naive implementations, and enable the
308	>	* processing of billions of tasks per second, at the expense of
309	>	* some ugliness.
310	>	*
311	>	* Methods signalWork() and scan() are the main bottlenecks so are
312	>	* especially heavily micro-optimized/mangled.  There are lots of
313	>	* inline assignments (of form "while ((local = field) != 0)")
314	>	* which are usually the simplest way to ensure the required read
315	>	* orderings (which are sometimes critical). This leads to a
316	>	* "C"-like style of listing declarations of these locals at the
317	>	* heads of methods or blocks.  There are several occurrences of
318	>	* the unusual "do {} while (!cas...)"  which is the simplest way
319	>	* to force an update of a CAS'ed variable. There are also other
320	>	* coding oddities that help some methods perform reasonably even
321	>	* when interpreted (not compiled).
322	>	*
323	>	* The order of declarations in this file is: (1) declarations of
324	>	* statics (2) fields (along with constants used when unpacking
325	>	* some of them), listed in an order that tends to reduce
326	>	* contention among them a bit under most JVMs.  (3) internal
327	>	* control methods (4) callbacks and other support for
328	>	* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
329	>	* methods (plus a few little helpers). (6) static block
330	>	* initializing all statics in a minimally dependent order.
331		*/
332
333		/**
#	Line 353 | Line 362 | public class ForkJoinPool extends Abstra
362		* overridden in ForkJoinPool constructors.
363		*/
364		public static final ForkJoinWorkerThreadFactory
365	<	defaultForkJoinWorkerThreadFactory =
357	<	new DefaultForkJoinWorkerThreadFactory();
365	>	defaultForkJoinWorkerThreadFactory;
366
367		/**
368		* Permission required for callers of methods that may start or
369		* kill threads.
370		*/
371	<	private static final RuntimePermission modifyThreadPermission =
364	<	new RuntimePermission("modifyThread");
371	>	private static final RuntimePermission modifyThreadPermission;
372
373		/**
374		* If there is a security manager, makes sure caller has
#	Line 376 | Line 383 | public class ForkJoinPool extends Abstra
383		/**
384		* Generator for assigning sequence numbers as pool names.
385		*/
386	<	private static final AtomicInteger poolNumberGenerator =
387	<	new AtomicInteger();
386	>	private static final AtomicInteger poolNumberGenerator;
387	>
388	>	/**
389	>	* Generator for initial random seeds for worker victim
390	>	* selection. This is used only to create initial seeds. Random
391	>	* steals use a cheaper xorshift generator per steal attempt. We
392	>	* don't expect much contention on seedGenerator, so just use a
393	>	* plain Random.
394	>	*/
395	>	static final Random workerSeedGenerator;
396
397		/**
398	<	* Absolute bound for parallelism level. Twice this number must
399	<	* fit into a 16bit field to enable word-packing for some counts.
398	>	* Array holding all worker threads in the pool.  Initialized upon
399	>	* construction. Array size must be a power of two.  Updates and
400	>	* replacements are protected by scanGuard, but the array is
401	>	* always kept in a consistent enough state to be randomly
402	>	* accessed without locking by workers performing work-stealing,
403	>	* as well as other traversal-based methods in this class, so long
404	>	* as reads memory-acquire by first reading ctl. All readers must
405	>	* tolerate that some array slots may be null.
406		*/
407	<	private static final int MAX_THREADS = 0x7fff;
407	>	ForkJoinWorkerThread[] workers;
408
409		/**
410	<	* Array holding all worker threads in the pool.  Array size must
411	<	* be a power of two.  Updates and replacements are protected by
412	<	* workerLock, but the array is always kept in a consistent enough
392	<	* state to be randomly accessed without locking by workers
393	<	* performing work-stealing, as well as other traversal-based
394	<	* methods in this class. All readers must tolerate that some
395	<	* array slots may be null.
410	>	* Initial size for submission queue array. Must be a power of
411	>	* two.  In many applications, these always stay small so we use a
412	>	* small initial cap.
413		*/
414	<	volatile ForkJoinWorkerThread[] workers;
414	>	private static final int INITIAL_QUEUE_CAPACITY = 8;
415
416		/**
417	<	* Queue for external submissions.
417	>	* Maximum size for submission queue array. Must be a power of two
418	>	* less than or equal to 1 << (31 - width of array entry) to
419	>	* ensure lack of index wraparound, but is capped at a lower
420	>	* value to help users trap runaway computations.
421		*/
422	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
422	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
423
424		/**
425	<	* Lock protecting updates to workers array.
425	>	* Array serving as submission queue. Initialized upon construction.
426		*/
427	<	private final ReentrantLock workerLock;
427	>	private ForkJoinTask<?>[] submissionQueue;
428
429		/**
430	<	* Latch released upon termination.
430	>	* Lock protecting submissions array for addSubmission
431		*/
432	<	private final Phaser termination;
432	>	private final ReentrantLock submissionLock;
433	>
434	>	/**
435	>	* Condition for awaitTermination, using submissionLock for
436	>	* convenience.
437	>	*/
438	>	private final Condition termination;
439
440		/**
441		* Creation factory for worker threads.
#	Line 417 | Line 443 | public class ForkJoinPool extends Abstra
443		private final ForkJoinWorkerThreadFactory factory;
444
445		/**
446	+	* The uncaught exception handler used when any worker abruptly
447	+	* terminates.
448	+	*/
449	+	final Thread.UncaughtExceptionHandler ueh;
450	+
451	+	/**
452	+	* Prefix for assigning names to worker threads
453	+	*/
454	+	private final String workerNamePrefix;
455	+
456	+	/**
457		* Sum of per-thread steal counts, updated only when threads are
458		* idle or terminating.
459		*/
460		private volatile long stealCount;
461
462		/**
463	<	* Encoded record of top of treiber stack of threads waiting for
464	<	* events. The top 32 bits contain the count being waited for. The
465	<	* bottom word contains one plus the pool index of waiting worker
466	<	* thread.
467	<	*/
468	<	private volatile long eventWaiters;
469	<
470	<	private static final int  EVENT_COUNT_SHIFT = 32;
471	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
472	<
473	<	/**
474	<	* A counter for events that may wake up worker threads:
475	<	*   - Submission of a new task to the pool
476	<	*   - A worker pushing a task on an empty queue
477	<	*   - termination and reconfiguration
478	<	*/
479	<	private volatile int eventCount;
480	<
481	<	/**
482	<	* Lifecycle control. The low word contains the number of workers
483	<	* that are (probably) executing tasks. This value is atomically
484	<	* incremented before a worker gets a task to run, and decremented
485	<	* when worker has no tasks and cannot find any.  Bits 16-18
486	<	* contain runLevel value. When all are zero, the pool is
487	<	* running. Level transitions are monotonic (running -> shutdown
488	<	* -> terminating -> terminated) so each transition adds a bit.
489	<	* These are bundled together to ensure consistent read for
490	<	* termination checks (i.e., that runLevel is at least SHUTDOWN
491	<	* and active threads is zero).
492	<	*/
493	<	private volatile int runState;
494	<
495	<	// Note: The order among run level values matters.
496	<	private static final int RUNLEVEL_SHIFT     = 16;
497	<	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
498	<	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
499	<	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
500	<	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
501	<	private static final int ONE_ACTIVE         = 1; // active update delta
502	<
503	<	/**
504	<	* Holds number of total (i.e., created and not yet terminated)
505	<	* and running (i.e., not blocked on joins or other managed sync)
506	<	* threads, packed together to ensure consistent snapshot when
507	<	* making decisions about creating and suspending spare
508	<	* threads. Updated only by CAS. Note that adding a new worker
509	<	* requires incrementing both counts, since workers start off in
510	<	* running state.  This field is also used for memory-fencing
511	<	* configuration parameters.
512	<	*/
513	<	private volatile int workerCounts;
514	<
515	<	private static final int TOTAL_COUNT_SHIFT  = 16;
516	<	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
517	<	private static final int ONE_RUNNING        = 1;
518	<	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
463	>	* Main pool control -- a long packed with:
464	>	* AC: Number of active running workers minus target parallelism (16 bits)
465	>	* TC: Number of total workers minus target parallelism (16bits)
466	>	* ST: true if pool is terminating (1 bit)
467	>	* EC: the wait count of top waiting thread (15 bits)
468	>	* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
469	>	*
470	>	* When convenient, we can extract the upper 32 bits of counts and
471	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
472	>	* (int)ctl.  The ec field is never accessed alone, but always
473	>	* together with id and st. The offsets of counts by the target
474	>	* parallelism and the positionings of fields makes it possible to
475	>	* perform the most common checks via sign tests of fields: When
476	>	* ac is negative, there are not enough active workers, when tc is
477	>	* negative, there are not enough total workers, when id is
478	>	* negative, there is at least one waiting worker, and when e is
479	>	* negative, the pool is terminating.  To deal with these possibly
480	>	* negative fields, we use casts in and out of "short" and/or
481	>	* signed shifts to maintain signedness.  Note: AC_SHIFT is
482	>	* redundantly declared in ForkJoinWorkerThread in order to
483	>	* integrate a surplus-threads check.
484	>	*/
485	>	volatile long ctl;
486	>
487	>	// bit positions/shifts for fields
488	>	private static final int  AC_SHIFT   = 48;
489	>	private static final int  TC_SHIFT   = 32;
490	>	private static final int  ST_SHIFT   = 31;
491	>	private static final int  EC_SHIFT   = 16;
492	>
493	>	// bounds
494	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
495	>	private static final int  SMASK      = 0xffff;  // mask short bits
496	>	private static final int  SHORT_SIGN = 1 << 15;
497	>	private static final int  INT_SIGN   = 1 << 31;
498	>
499	>	// masks
500	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
501	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
502	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
503	>
504	>	// units for incrementing and decrementing
505	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
506	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
507	>
508	>	// masks and units for dealing with u = (int)(ctl >>> 32)
509	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
510	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
511	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
512	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
513	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
514	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
515	>
516	>	// masks and units for dealing with e = (int)ctl
517	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
518	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
519
520		/**
521		* The target parallelism level.
485	–	* Accessed directly by ForkJoinWorkerThreads.
522		*/
523		final int parallelism;
524
525		/**
526	+	* Index (mod submission queue length) of next element to take
527	+	* from submission queue.
528	+	*/
529	+	volatile int queueBase;
530	+
531	+	/**
532	+	* Index (mod submission queue length) of next element to add
533	+	* in submission queue.
534	+	*/
535	+	int queueTop;
536	+
537	+	/**
538	+	* True when shutdown() has been called.
539	+	*/
540	+	volatile boolean shutdown;
541	+
542	+	/**
543		* True if use local fifo, not default lifo, for local polling
544		* Read by, and replicated by ForkJoinWorkerThreads
545		*/
546		final boolean locallyFifo;
547
548		/**
549	<	* The uncaught exception handler used when any worker abruptly
550	<	* terminates.
549	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
550	>	* When non-zero, suppresses automatic shutdown when active
551	>	* counts become zero.
552		*/
553	<	private final Thread.UncaughtExceptionHandler ueh;
553	>	volatile int quiescerCount;
554
555		/**
556	<	* Pool number, just for assigning useful names to worker threads
556	>	* The number of threads blocked in join.
557		*/
558	<	private final int poolNumber;
505	<
506	<	// utilities for updating fields
558	>	volatile int blockedCount;
559
560		/**
561	<	* Increments running count.  Also used by ForkJoinTask.
561	>	* Counter for worker Thread names (unrelated to their poolIndex)
562		*/
563	<	final void incrementRunningCount() {
564	<	int c;
513	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
514	<	c = workerCounts,
515	<	c + ONE_RUNNING));
516	<	}
517	<
563	>	private volatile int nextWorkerNumber;
564	>
565		/**
566	<	* Tries to decrement running count unless already zero
566	>	* The index for the next created worker. Accessed under scanGuard.
567		*/
568	<	final boolean tryDecrementRunningCount() {
522	<	int wc = workerCounts;
523	<	if ((wc & RUNNING_COUNT_MASK) == 0)
524	<	return false;
525	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
526	<	wc, wc - ONE_RUNNING);
527	<	}
568	>	private int nextWorkerIndex;
569
570		/**
571	<	* Tries incrementing active count; fails on contention.
572	<	* Called by workers before executing tasks.
573	<	*
574	<	* @return true on success
571	>	* SeqLock and index masking for for updates to workers array.
572	>	* Locked when SG_UNIT is set. Unlocking clears bit by adding
573	>	* SG_UNIT. Staleness of read-only operations can be checked by
574	>	* comparing scanGuard to value before the reads. The low 16 bits
575	>	* (i.e, anding with SMASK) hold (the smallest power of two
576	>	* covering all worker indices, minus one, and is used to avoid
577	>	* dealing with large numbers of null slots when the workers array
578	>	* is overallocated.
579		*/
580	<	final boolean tryIncrementActiveCount() {
581	<	int c;
582	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
538	<	c = runState, c + ONE_ACTIVE);
539	<	}
580	>	volatile int scanGuard;
581	>
582	>	private static final int SG_UNIT = 1 << 16;
583
584		/**
585	<	* Tries decrementing active count; fails on contention.
586	<	* Called when workers cannot find tasks to run.
585	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
586	>	* task when the pool is quiescent to instead try to shrink the
587	>	* number of workers.  The exact value does not matter too
588	>	* much. It must be short enough to release resources during
589	>	* sustained periods of idleness, but not so short that threads
590	>	* are continually re-created.
591		*/
592	<	final boolean tryDecrementActiveCount() {
593	<	int c;
547	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
548	<	c = runState, c - ONE_ACTIVE);
549	<	}
592	>	private static final long SHRINK_RATE =
593	>	4L * 1000L * 1000L * 1000L; // 4 seconds
594
595		/**
596	<	* Advances to at least the given level. Returns true if not
597	<	* already in at least the given level.
596	>	* Top-level loop for worker threads: On each step: if the
597	>	* previous step swept through all queues and found no tasks, or
598	>	* there are excess threads, then possibly blocks. Otherwise,
599	>	* scans for and, if found, executes a task. Returns when pool
600	>	* and/or worker terminate.
601	>	*
602	>	* @param w the worker
603		*/
604	<	private boolean advanceRunLevel(int level) {
605	<	for (;;) {
606	<	int s = runState;
607	<	if ((s & level) != 0)
608	<	return false;
609	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
610	<	return true;
604	>	final void work(ForkJoinWorkerThread w) {
605	>	boolean swept = false;                // true on empty scans
606	>	long c;
607	>	while (!w.terminate && (int)(c = ctl) >= 0) {
608	>	int a;                            // active count
609	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
610	>	swept = scan(w, a);
611	>	else if (tryAwaitWork(w, c))
612	>	swept = false;
613		}
614		}
615
616	<	// workers array maintenance
616	>	// Signalling
617
618		/**
619	<	* Records and returns a workers array index for new worker.
619	>	* Wakes up or creates a worker.
620		*/
621	<	private int recordWorker(ForkJoinWorkerThread w) {
622	<	// Try using slot totalCount-1. If not available, scan and/or resize
623	<	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
624	<	final ReentrantLock lock = this.workerLock;
625	<	lock.lock();
626	<	try {
627	<	ForkJoinWorkerThread[] ws = workers;
628	<	int nws = ws.length;
629	<	if (k < 0 || k >= nws || ws[k] != null) {
630	<	for (k = 0; k < nws && ws[k] != null; ++k)
631	<	;
632	<	if (k == nws)
633	<	ws = Arrays.copyOf(ws, nws << 1);
621	>	final void signalWork() {
622	>	/*
623	>	* The while condition is true if: (there is are too few total
624	>	* workers OR there is at least one waiter) AND (there are too
625	>	* few active workers OR the pool is terminating).  The value
626	>	* of e distinguishes the remaining cases: zero (no waiters)
627	>	* for create, negative if terminating (in which case do
628	>	* nothing), else release a waiter. The secondary checks for
629	>	* release (non-null array etc) can fail if the pool begins
630	>	* terminating after the test, and don't impose any added cost
631	>	* because JVMs must perform null and bounds checks anyway.
632	>	*/
633	>	long c; int e, u;
634	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
635	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
636	>	if (e > 0) {                         // release a waiting worker
637	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
638	>	if ((ws = workers) == null ||
639	>	(i = ~e & SMASK) >= ws.length ||
640	>	(w = ws[i]) == null)
641	>	break;
642	>	long nc = (((long)(w.nextWait & E_MASK)) |
643	>	((long)(u + UAC_UNIT) << 32));
644	>	if (w.eventCount == e &&
645	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
646	>	w.eventCount = (e + EC_UNIT) & E_MASK;
647	>	if (w.parked)
648	>	UNSAFE.unpark(w);
649	>	break;
650	>	}
651	>	}
652	>	else if (UNSAFE.compareAndSwapLong
653	>	(this, ctlOffset, c,
654	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
655	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
656	>	addWorker();
657	>	break;
658		}
584	–	ws[k] = w;
585	–	workers = ws; // volatile array write ensures slot visibility
586	–	} finally {
587	–	lock.unlock();
659		}
589	–	return k;
660		}
661
662		/**
663	<	* Nulls out record of worker in workers array
663	>	* Variant of signalWork to help release waiters on rescans.
664	>	* Tries once to release a waiter if active count < 0.
665	>	*
666	>	* @return false if failed due to contention, else true
667		*/
668	<	private void forgetWorker(ForkJoinWorkerThread w) {
669	<	int idx = w.poolIndex;
670	<	// Locking helps method recordWorker avoid unecessary expansion
671	<	final ReentrantLock lock = this.workerLock;
672	<	lock.lock();
673	<	try {
674	<	ForkJoinWorkerThread[] ws = workers;
675	<	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
676	<	ws[idx] = null;
677	<	} finally {
678	<	lock.unlock();
668	>	private boolean tryReleaseWaiter() {
669	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
670	>	if ((e = (int)(c = ctl)) > 0 &&
671	>	(int)(c >> AC_SHIFT) < 0 &&
672	>	(ws = workers) != null &&
673	>	(i = ~e & SMASK) < ws.length &&
674	>	(w = ws[i]) != null) {
675	>	long nc = ((long)(w.nextWait & E_MASK) |
676	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
677	>	if (w.eventCount != e ||
678	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
679	>	return false;
680	>	w.eventCount = (e + EC_UNIT) & E_MASK;
681	>	if (w.parked)
682	>	UNSAFE.unpark(w);
683		}
684	+	return true;
685		}
686
687	<	// adding and removing workers
687	>	// Scanning for tasks
688
689		/**
690	<	* Tries to create and add new worker. Assumes that worker counts
691	<	* are already updated to accommodate the worker, so adjusts on
692	<	* failure.
690	>	* Scans for and, if found, executes one task. Scans start at a
691	>	* random index of workers array, and randomly select the first
692	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
693	>	* circular sweeps, which is necessary to check quiescence. and
694	>	* taking a submission only if no stealable tasks were found.  The
695	>	* steal code inside the loop is a specialized form of
696	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
697	>	* helpJoinTask and signal propagation. The code for submission
698	>	* queues is almost identical. On each steal, the worker completes
699	>	* not only the task, but also all local tasks that this task may
700	>	* have generated. On detecting staleness or contention when
701	>	* trying to take a task, this method returns without finishing
702	>	* sweep, which allows global state rechecks before retry.
703		*
704	<	* @return new worker or null if creation failed
704	>	* @param w the worker
705	>	* @param a the number of active workers
706	>	* @return true if swept all queues without finding a task
707		*/
708	<	private ForkJoinWorkerThread addWorker() {
709	<	ForkJoinWorkerThread w = null;
710	<	try {
711	<	w = factory.newThread(this);
712	<	} finally { // Adjust on either null or exceptional factory return
713	<	if (w == null) {
714	<	onWorkerCreationFailure();
715	<	return null;
708	>	private boolean scan(ForkJoinWorkerThread w, int a) {
709	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
710	>	int m = parallelism == 1 - a? 0 : g & SMASK;
711	>	ForkJoinWorkerThread[] ws = workers;
712	>	if (ws == null || ws.length <= m)         // staleness check
713	>	return false;
714	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
715	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
716	>	ForkJoinWorkerThread v = ws[k & m];
717	>	if (v != null && (b = v.queueBase) != v.queueTop &&
718	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
719	>	long u = (i << ASHIFT) + ABASE;
720	>	if ((t = q[i]) != null && v.queueBase == b &&
721	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
722	>	int d = (v.queueBase = b + 1) - v.queueTop;
723	>	v.stealHint = w.poolIndex;
724	>	if (d != 0)
725	>	signalWork();             // propagate if nonempty
726	>	w.execTask(t);
727	>	}
728	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
729	>	return false;                     // store next seed
730	>	}
731	>	else if (j < 0) {                     // xorshift
732	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
733		}
734	+	else
735	+	++k;
736	+	}
737	+	if (scanGuard != g)                       // staleness check
738	+	return false;
739	+	else {                                    // try to take submission
740	+	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
741	+	if ((b = queueBase) != queueTop &&
742	+	(q = submissionQueue) != null &&
743	+	(i = (q.length - 1) & b) >= 0) {
744	+	long u = (i << ASHIFT) + ABASE;
745	+	if ((t = q[i]) != null && queueBase == b &&
746	+	UNSAFE.compareAndSwapObject(q, u, t, null)) {
747	+	queueBase = b + 1;
748	+	w.execTask(t);
749	+	}
750	+	return false;
751	+	}
752	+	return true;                         // all queues empty
753		}
628	–	w.start(recordWorker(w), ueh);
629	–	return w;
754		}
755
756		/**
757	<	* Adjusts counts upon failure to create worker
757	>	* Tries to enqueue worker in wait queue and await change in
758	>	* worker's eventCount.  Before blocking, rescans queues to avoid
759	>	* missed signals.  If the pool is quiescent, possibly terminates
760	>	* worker upon exit.
761	>	*
762	>	* @param w the calling worker
763	>	* @param c the ctl value on entry
764	>	* @return true if waited or another thread was released upon enq
765		*/
766	<	private void onWorkerCreationFailure() {
767	<	for (;;) {
768	<	int wc = workerCounts;
769	<	if ((wc >>> TOTAL_COUNT_SHIFT) > 0 &&
770	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
771	<	wc, wc - (ONE_RUNNING|ONE_TOTAL)))
772	<	break;
766	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
767	>	int v = w.eventCount;
768	>	w.nextWait = (int)c;                       // w's successor record
769	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
770	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
771	>	long d = ctl; // return true if lost to a deq, to force rescan
772	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
773	>	}
774	>	boolean rescanned = false;
775	>	for (int sc;;) {
776	>	if (w.eventCount != v)
777	>	return true;
778	>	if ((sc = w.stealCount) != 0) {
779	>	long s = stealCount;               // accumulate stealCount
780	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s+sc))
781	>	w.stealCount = 0;
782	>	}
783	>	else if (!rescanned) {
784	>	int g = scanGuard, m = g & SMASK;
785	>	ForkJoinWorkerThread[] ws = workers;
786	>	if (ws != null && m < ws.length) {
787	>	rescanned = true;
788	>	for (int i = 0; i <= m; ++i) {
789	>	ForkJoinWorkerThread u = ws[i];
790	>	if (u != null) {
791	>	if (u.queueBase != u.queueTop &&
792	>	!tryReleaseWaiter())
793	>	rescanned = false; // contended
794	>	if (w.eventCount != v)
795	>	return true;
796	>	}
797	>	}
798	>	}
799	>	if (scanGuard != g ||              // stale
800	>	(queueBase != queueTop && !tryReleaseWaiter()))
801	>	rescanned = false;
802	>	if (!rescanned)
803	>	Thread.yield();                // reduce contention
804	>	else
805	>	Thread.interrupted();          // clear before park
806	>	}
807	>	else if (parallelism + (int)(ctl >> AC_SHIFT) == 0 &&
808	>	blockedCount == 0 && quiescerCount == 0)
809	>	idleAwaitWork(w, v);               // quiescent -- maybe shrink
810	>	else {
811	>	w.parked = true;                   // must recheck
812	>	if (w.eventCount != v) {
813	>	w.parked = false;
814	>	return true;
815	>	}
816	>	LockSupport.park(this);
817	>	rescanned = w.parked = false;
818	>	}
819		}
643	–	tryTerminate(false); // in case of failure during shutdown
820		}
821
822		/**
823	<	* Create enough total workers to establish target parallelism,
824	<	* giving up if terminating or addWorker fails
825	<	*/
826	<	private void ensureEnoughTotalWorkers() {
827	<	int wc;
828	<	while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism &&
829	<	runState < TERMINATING) {
830	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
831	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
832	<	addWorker() == null))
833	<	break;
823	>	* If pool is quiescent, checks for termination, and waits for
824	>	* event signal for up to SHRINK_RATE nanosecs. On timeout, if ctl
825	>	* has not changed, terminates the worker. Upon its termination
826	>	* (see deregisterWorker), it may wake up another worker to
827	>	* possibly repeat this process.
828	>	*
829	>	* @param w the calling worker
830	>	* @param v the eventCount w must wait until changed
831	>	*/
832	>	private void idleAwaitWork(ForkJoinWorkerThread w, int v) {
833	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
834	>	if (shutdown)
835	>	tryTerminate(false);
836	>	long c = ctl;
837	>	long nc = (((c & (AC_MASK|TC_MASK)) + AC_UNIT) |
838	>	(long)(w.nextWait & E_MASK)); // ctl value to release w
839	>	if (w.eventCount == v &&
840	>	parallelism + (int)(c >> AC_SHIFT) == 0 &&
841	>	blockedCount == 0 && quiescerCount == 0) {
842	>	long startTime = System.nanoTime();
843	>	Thread.interrupted();
844	>	if (w.eventCount == v) {
845	>	w.parked = true;
846	>	if (w.eventCount == v)
847	>	LockSupport.parkNanos(this, SHRINK_RATE);
848	>	w.parked = false;
849	>	if (w.eventCount == v && ctl == c &&
850	>	System.nanoTime() - startTime >= SHRINK_RATE &&
851	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
852	>	w.terminate = true;
853	>	w.eventCount = ((int)c + EC_UNIT) & E_MASK;
854	>	}
855	>	}
856		}
857		}
858
859	+	// Submissions
860	+
861		/**
862	<	* Final callback from terminating worker.  Removes record of
863	<	* worker from array, and adjusts counts. If pool is shutting
664	<	* down, tries to complete terminatation, else possibly replaces
665	<	* the worker.
862	>	* Enqueues the given task in the submissionQueue.  Same idea as
863	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
864		*
865	<	* @param w the worker
865	>	* @param t the task
866		*/
867	<	final void workerTerminated(ForkJoinWorkerThread w) {
868	<	if (w.active) { // force inactive
869	<	w.active = false;
870	<	do {} while (!tryDecrementActiveCount());
871	<	}
872	<	forgetWorker(w);
873	<
874	<	// Decrement total count, and if was running, running count
875	<	// Spin (waiting for other updates) if either would be negative
876	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
877	<	int unit = ONE_TOTAL + nr;
878	<	for (;;) {
879	<	int wc = workerCounts;
880	<	int rc = wc & RUNNING_COUNT_MASK;
683	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
684	<	Thread.yield(); // back off if waiting for other updates
685	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
686	<	wc, wc - unit))
687	<	break;
867	>	private void addSubmission(ForkJoinTask<?> t) {
868	>	final ReentrantLock lock = this.submissionLock;
869	>	lock.lock();
870	>	try {
871	>	ForkJoinTask<?>[] q; int s, m;
872	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
873	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
874	>	UNSAFE.putOrderedObject(q, u, t);
875	>	queueTop = s + 1;
876	>	if (s - queueBase == m)
877	>	growSubmissionQueue();
878	>	}
879	>	} finally {
880	>	lock.unlock();
881		}
882	<
690	<	accumulateStealCount(w); // collect final count
691	<	if (!tryTerminate(false))
692	<	ensureEnoughTotalWorkers();
882	>	signalWork();
883		}
884
885	<	// Waiting for and signalling events
885	>	//  (pollSubmission is defined below with exported methods)
886
887		/**
888	<	* Releases workers blocked on a count not equal to current count.
888	>	* Creates or doubles submissionQueue array.
889	>	* Basically identical to ForkJoinWorkerThread version
890		*/
891	<	private void releaseWaiters() {
892	<	long top;
893	<	int id;
894	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
895	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
896	<	ForkJoinWorkerThread[] ws = workers;
897	<	ForkJoinWorkerThread w;
898	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
899	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
900	<	top, w.nextWaiter))
901	<	LockSupport.unpark(w);
891	>	private void growSubmissionQueue() {
892	>	ForkJoinTask<?>[] oldQ = submissionQueue;
893	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
894	>	if (size > MAXIMUM_QUEUE_CAPACITY)
895	>	throw new RejectedExecutionException("Queue capacity exceeded");
896	>	if (size < INITIAL_QUEUE_CAPACITY)
897	>	size = INITIAL_QUEUE_CAPACITY;
898	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
899	>	int mask = size - 1;
900	>	int top = queueTop;
901	>	int oldMask;
902	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
903	>	for (int b = queueBase; b != top; ++b) {
904	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
905	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
906	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
907	>	UNSAFE.putObjectVolatile
908	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
909	>	}
910		}
911		}
912
913	<	/**
715	<	* Ensures eventCount on exit is different (mod 2^32) than on
716	<	* entry and wakes up all waiters
717	<	*/
718	<	private void signalEvent() {
719	<	int c;
720	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
721	<	c = eventCount, c+1));
722	<	releaseWaiters();
723	<	}
913	>	// Blocking support
914
915		/**
916	<	* Advances eventCount and releases waiters until interference by
917	<	* other releasing threads is detected.
916	>	* Tries to increment blockedCount, decrement active count
917	>	* (sometimes implicitly) and possibly release or create a
918	>	* compensating worker in preparation for blocking. Fails
919	>	* on contention or termination.
920	>	*
921	>	* @return true if the caller can block, else should recheck and retry
922		*/
923	<	final void signalWork() {
924	<	// EventCount CAS failures are OK -- any change in count suffices.
925	<	int ec;
926	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
927	<	outer:for (;;) {
734	<	long top = eventWaiters;
735	<	ec = eventCount;
736	<	for (;;) {
923	>	private boolean tryPreBlock() {
924	>	int b = blockedCount;
925	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
926	>	int pc = parallelism;
927	>	do {
928		ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
929	<	int id = (int)(top & WAITER_INDEX_MASK);
930	<	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
931	<	return;
932	<	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
933	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
934	<	top, top = w.nextWaiter))
935	<	continue outer;      // possibly stale; reread
936	<	LockSupport.unpark(w);
937	<	if (top != eventWaiters) // let someone else take over
938	<	return;
939	<	}
929	>	int e, ac, tc, rc, i;
930	>	long c = ctl;
931	>	int u = (int)(c >>> 32);
932	>	if ((e = (int)c) < 0) {
933	>	// skip -- terminating
934	>	}
935	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
936	>	(ws = workers) != null &&
937	>	(i = ~e & SMASK) < ws.length &&
938	>	(w = ws[i]) != null) {
939	>	long nc = ((long)(w.nextWait & E_MASK) |
940	>	(c & (AC_MASK|TC_MASK)));
941	>	if (w.eventCount == e &&
942	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
943	>	w.eventCount = (e + EC_UNIT) & E_MASK;
944	>	if (w.parked)
945	>	UNSAFE.unpark(w);
946	>	return true;             // release an idle worker
947	>	}
948	>	}
949	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
950	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
951	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
952	>	return true;             // no compensation needed
953	>	}
954	>	else if (tc + pc < MAX_ID) {
955	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
956	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
957	>	addWorker();
958	>	return true;            // create a replacement
959	>	}
960	>	}
961	>	// try to back out on any failure and let caller retry
962	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
963	>	b = blockedCount, b - 1));
964		}
965	+	return false;
966		}
967
968		/**
969	<	* If worker is inactive, blocks until terminating or event count
970	<	* advances from last value held by worker; in any case helps
971	<	* release others.
972	<	*
973	<	* @param w the calling worker thread
974	<	*/
975	<	private void eventSync(ForkJoinWorkerThread w) {
976	<	if (!w.active) {
977	<	int prev = w.lastEventCount;
762	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
763	<	((long)(w.poolIndex + 1)));
764	<	long top;
765	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
766	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
767	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
768	<	eventCount == prev) {
769	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
770	<	w.nextWaiter = top, nextTop)) {
771	<	accumulateStealCount(w); // transfer steals while idle
772	<	Thread.interrupted();    // clear/ignore interrupt
773	<	while (eventCount == prev)
774	<	w.doPark();
775	<	break;
776	<	}
777	<	}
778	<	w.lastEventCount = eventCount;
779	<	}
780	<	releaseWaiters();
969	>	* Decrements blockedCount and increments active count
970	>	*/
971	>	private void postBlock() {
972	>	long c;
973	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
974	>	c = ctl, c + AC_UNIT));
975	>	int b;
976	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
977	>	b = blockedCount, b - 1));
978		}
979
980		/**
981	<	* Callback from workers invoked upon each top-level action (i.e.,
982	<	* stealing a task or taking a submission and running
786	<	* it). Performs one or both of the following:
981	>	* Possibly blocks waiting for the given task to complete, or
982	>	* cancels the task if terminating.  Fails to wait if contended.
983		*
984	<	* * If the worker cannot find work, updates its active status to
789	<	* inactive and updates activeCount unless there is contention, in
790	<	* which case it may try again (either in this or a subsequent
791	<	* call).  Additionally, awaits the next task event and/or helps
792	<	* wake up other releasable waiters.
793	<	*
794	<	* * If there are too many running threads, suspends this worker
795	<	* (first forcing inactivation if necessary).  If it is not
796	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
797	<	* -- killed while suspended within suspendAsSpare. Otherwise,
798	<	* upon resume it rechecks to make sure that it is still needed.
799	<	*
800	<	* @param w the worker
801	<	* @param worked false if the worker scanned for work but didn't
802	<	* find any (in which case it may block waiting for work).
984	>	* @param joinMe the task
985		*/
986	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
987	<	boolean active = w.active;
988	<	boolean inactivate = !worked & active;
989	<	for (;;) {
990	<	if (inactivate) {
991	<	int rs = runState;
992	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
993	<	rs, rs - ONE_ACTIVE))
994	<	inactivate = active = w.active = false;
995	<	}
814	<	int wc = workerCounts;
815	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
816	<	if (!worked)
817	<	eventSync(w);
818	<	return;
819	<	}
820	<	if (!(inactivate |= active) &&  // must inactivate to suspend
821	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
822	<	wc, wc - ONE_RUNNING) &&
823	<	!w.suspendAsSpare())        // false if trimmed
824	<	return;
986	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
987	>	int s;
988	>	Thread.interrupted(); // clear interrupts before checking termination
989	>	if (joinMe.status >= 0) {
990	>	if (tryPreBlock()) {
991	>	joinMe.tryAwaitDone(0L);
992	>	postBlock();
993	>	}
994	>	if ((ctl & STOP_BIT) != 0L)
995	>	joinMe.cancelIgnoringExceptions();
996		}
997		}
998
999		/**
1000	<	* Tries to decrement running count, and if so, possibly creates
1001	<	* or resumes compensating threads before blocking on task joinMe.
1002	<	* This code is sprawled out with manual inlining to evade some
1003	<	* JIT oddities.
1004	<	*
1005	<	* @param joinMe the task to join
1006	<	* @return task status on exit
1007	<	*/
1008	<	final int tryAwaitJoin(ForkJoinTask<?> joinMe) {
1009	<	int cw = workerCounts; // read now to spoil CAS if counts change as ...
1010	<	releaseWaiters();      // ... a byproduct of releaseWaiters
1011	<	int stat = joinMe.status;
1012	<	if (stat >= 0 && // inline variant of tryDecrementRunningCount
1013	<	(cw & RUNNING_COUNT_MASK) > 0 &&
1014	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1015	<	cw, cw - ONE_RUNNING)) {
1016	<	int pc = parallelism;
1017	<	int scans = 0;  // to require confirming passes to add threads
847	<	outer: while ((workerCounts & RUNNING_COUNT_MASK) < pc) {
848	<	if ((stat = joinMe.status) < 0)
849	<	break;
850	<	ForkJoinWorkerThread spare = null;
851	<	ForkJoinWorkerThread[] ws = workers;
852	<	int nws = ws.length;
853	<	for (int i = 0; i < nws; ++i) {
854	<	ForkJoinWorkerThread w = ws[i];
855	<	if (w != null && w.isSuspended()) {
856	<	spare = w;
1000	>	* Possibly blocks the given worker waiting for joinMe to
1001	>	* complete or timeout
1002	>	*
1003	>	* @param joinMe the task
1004	>	* @param millis the wait time for underlying Object.wait
1005	>	*/
1006	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1007	>	while (joinMe.status >= 0) {
1008	>	Thread.interrupted();
1009	>	if ((ctl & STOP_BIT) != 0L) {
1010	>	joinMe.cancelIgnoringExceptions();
1011	>	break;
1012	>	}
1013	>	if (tryPreBlock()) {
1014	>	long last = System.nanoTime();
1015	>	while (joinMe.status >= 0) {
1016	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1017	>	if (millis <= 0)
1018		break;
1019	<	}
1020	<	}
1021	<	if ((stat = joinMe.status) < 0) // recheck to narrow race
1022	<	break;
1023	<	int wc = workerCounts;
863	<	int rc = wc & RUNNING_COUNT_MASK;
864	<	if (rc >= pc)
865	<	break;
866	<	if (spare != null) {
867	<	if (spare.tryUnsuspend()) {
868	<	int c; // inline incrementRunningCount
869	<	do {} while (!UNSAFE.compareAndSwapInt
870	<	(this, workerCountsOffset,
871	<	c = workerCounts, c + ONE_RUNNING));
872	<	LockSupport.unpark(spare);
1019	>	joinMe.tryAwaitDone(millis);
1020	>	if (joinMe.status < 0)
1021	>	break;
1022	>	if ((ctl & STOP_BIT) != 0L) {
1023	>	joinMe.cancelIgnoringExceptions();
1024		break;
1025		}
1026	<	continue;
1027	<	}
1028	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
878	<	int sc = tc - pc;
879	<	if (rc > 0) {
880	<	int p = pc;
881	<	int s = sc;
882	<	while (s-- >= 0) { // try keeping 3/4 live
883	<	if (rc > (p -= (p >>> 2) + 1))
884	<	break outer;
885	<	}
886	<	}
887	<	if (scans++ > sc && tc < MAX_THREADS &&
888	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
889	<	wc + (ONE_RUNNING|ONE_TOTAL))) {
890	<	addWorker();
891	<	break;
1026	>	long now = System.nanoTime();
1027	>	nanos -= now - last;
1028	>	last = now;
1029		}
1030	+	postBlock();
1031	+	break;
1032		}
894	–	if (stat >= 0)
895	–	stat = joinMe.internalAwaitDone();
896	–	int c; // inline incrementRunningCount
897	–	do {} while (!UNSAFE.compareAndSwapInt
898	–	(this, workerCountsOffset,
899	–	c = workerCounts, c + ONE_RUNNING));
1033		}
901	–	return stat;
1034		}
1035
1036		/**
1037	<	* Same idea as (and mostly pasted from) tryAwaitJoin, but
906	<	* self-contained
1037	>	* If necessary, compensates for blocker, and blocks
1038		*/
1039	<	final void awaitBlocker(ManagedBlocker blocker)
1039	>	private void awaitBlocker(ManagedBlocker blocker)
1040		throws InterruptedException {
1041	<	for (;;) {
1042	<	if (blocker.isReleasable())
1043	<	return;
1044	<	int cw = workerCounts;
1045	<	releaseWaiters();
1046	<	if ((cw & RUNNING_COUNT_MASK) > 0 &&
916	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
917	<	cw, cw - ONE_RUNNING))
918	<	break;
919	<	}
920	<	boolean done = false;
921	<	int pc = parallelism;
922	<	int scans = 0;
923	<	outer: while ((workerCounts & RUNNING_COUNT_MASK) < pc) {
924	<	if (done = blocker.isReleasable())
925	<	break;
926	<	ForkJoinWorkerThread spare = null;
927	<	ForkJoinWorkerThread[] ws = workers;
928	<	int nws = ws.length;
929	<	for (int i = 0; i < nws; ++i) {
930	<	ForkJoinWorkerThread w = ws[i];
931	<	if (w != null && w.isSuspended()) {
932	<	spare = w;
933	<	break;
934	<	}
935	<	}
936	<	if (done = blocker.isReleasable())
937	<	break;
938	<	int wc = workerCounts;
939	<	int rc = wc & RUNNING_COUNT_MASK;
940	<	if (rc >= pc)
941	<	break;
942	<	if (spare != null) {
943	<	if (spare.tryUnsuspend()) {
944	<	int c;
945	<	do {} while (!UNSAFE.compareAndSwapInt
946	<	(this, workerCountsOffset,
947	<	c = workerCounts, c + ONE_RUNNING));
948	<	LockSupport.unpark(spare);
949	<	break;
950	<	}
951	<	continue;
952	<	}
953	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
954	<	int sc = tc - pc;
955	<	if (rc > 0) {
956	<	int p = pc;
957	<	int s = sc;
958	<	while (s-- >= 0) {
959	<	if (rc > (p -= (p >>> 2) + 1))
960	<	break outer;
1041	>	while (!blocker.isReleasable()) {
1042	>	if (tryPreBlock()) {
1043	>	try {
1044	>	do {} while (!blocker.isReleasable() && !blocker.block());
1045	>	} finally {
1046	>	postBlock();
1047		}
962	–	}
963	–	if (scans++ > sc && tc < MAX_THREADS &&
964	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
965	–	wc + (ONE_RUNNING|ONE_TOTAL))) {
966	–	addWorker();
1048		break;
1049		}
1050		}
1051	+	}
1052	+
1053	+	// Creating, registering and deregistring workers
1054	+
1055	+	/**
1056	+	* Tries to create and start a worker; minimally rolls back counts
1057	+	* on failure.
1058	+	*/
1059	+	private void addWorker() {
1060	+	Throwable ex = null;
1061	+	ForkJoinWorkerThread t = null;
1062		try {
1063	<	if (!done)
1064	<	do {} while (!blocker.isReleasable() &&
1065	<	!blocker.block());
1066	<	} finally {
1067	<	int c;
1068	<	do {} while (!UNSAFE.compareAndSwapInt
1069	<	(this, workerCountsOffset,
1070	<	c = workerCounts, c + ONE_RUNNING));
1063	>	t = factory.newThread(this);
1064	>	} catch (Throwable e) {
1065	>	ex = e;
1066	>	}
1067	>	if (t == null) {  // null or exceptional factory return
1068	>	long c;       // adjust counts
1069	>	do {} while (!UNSAFE.compareAndSwapLong
1070	>	(this, ctlOffset, c = ctl,
1071	>	(((c - AC_UNIT) & AC_MASK) |
1072	>	((c - TC_UNIT) & TC_MASK) |
1073	>	(c & ~(AC_MASK|TC_MASK)))));
1074	>	// Propagate exception if originating from an external caller
1075	>	if (!tryTerminate(false) && ex != null &&
1076	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1077	>	UNSAFE.throwException(ex);
1078		}
1079	<	}
1079	>	else
1080	>	t.start();
1081	>	}
1082
1083		/**
1084	<	* Possibly initiates and/or completes termination.
1085	<	*
985	<	* @param now if true, unconditionally terminate, else only
986	<	* if shutdown and empty queue and no active workers
987	<	* @return true if now terminating or terminated
1084	>	* Callback from ForkJoinWorkerThread constructor to assign a
1085	>	* public name
1086		*/
1087	<	private boolean tryTerminate(boolean now) {
1088	<	if (now)
1089	<	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1090	<	else if (runState < SHUTDOWN ||
1091	<	!submissionQueue.isEmpty() ||
1092	<	(runState & ACTIVE_COUNT_MASK) != 0)
1093	<	return false;
996	<
997	<	if (advanceRunLevel(TERMINATING))
998	<	startTerminating();
1087	>	final String nextWorkerName() {
1088	>	for (int n;;) {
1089	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1090	>	n = nextWorkerNumber, ++n))
1091	>	return workerNamePrefix + n;
1092	>	}
1093	>	}
1094
1095	<	// Finish now if all threads terminated; else in some subsequent call
1096	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1097	<	advanceRunLevel(TERMINATED);
1098	<	termination.arrive();
1095	>	/**
1096	>	* Callback from ForkJoinWorkerThread constructor to
1097	>	* determine its poolIndex and record in workers array.
1098	>	*
1099	>	* @param w the worker
1100	>	* @return the worker's pool index
1101	>	*/
1102	>	final int registerWorker(ForkJoinWorkerThread w) {
1103	>	/*
1104	>	* In the typical case, a new worker acquires the lock, uses
1105	>	* next available index and returns quickly.  Since we should
1106	>	* not block callers (ultimately from signalWork or
1107	>	* tryPreBlock) waiting for the lock needed to do this, we
1108	>	* instead help release other workers while waiting for the
1109	>	* lock.
1110	>	*/
1111	>	for (int g;;) {
1112	>	ForkJoinWorkerThread[] ws;
1113	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1114	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1115	>	g, g | SG_UNIT)) {
1116	>	int k = nextWorkerIndex;
1117	>	try {
1118	>	if ((ws = workers) != null) { // ignore on shutdown
1119	>	int n = ws.length;
1120	>	if (k < 0 || k >= n || ws[k] != null) {
1121	>	for (k = 0; k < n && ws[k] != null; ++k)
1122	>	;
1123	>	if (k == n)
1124	>	ws = workers = Arrays.copyOf(ws, n << 1);
1125	>	}
1126	>	ws[k] = w;
1127	>	nextWorkerIndex = k + 1;
1128	>	int m = g & SMASK;
1129	>	g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1130	>	}
1131	>	} finally {
1132	>	scanGuard = g;
1133	>	}
1134	>	return k;
1135	>	}
1136	>	else if ((ws = workers) != null) { // help release others
1137	>	for (ForkJoinWorkerThread u : ws) {
1138	>	if (u != null && u.queueBase != u.queueTop) {
1139	>	if (tryReleaseWaiter())
1140	>	break;
1141	>	}
1142	>	}
1143	>	}
1144		}
1005	–	return true;
1145		}
1146
1147		/**
1148	<	* Actions on transition to TERMINATING
1148	>	* Final callback from terminating worker.  Removes record of
1149	>	* worker from array, and adjusts counts. If pool is shutting
1150	>	* down, tries to complete termination.
1151	>	*
1152	>	* @param w the worker
1153		*/
1154	<	private void startTerminating() {
1155	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1156	<	cancelSubmissions();
1157	<	shutdownWorkers();
1158	<	cancelWorkerTasks();
1159	<	signalEvent();
1160	<	interruptWorkers();
1154	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1155	>	int idx = w.poolIndex;
1156	>	int sc = w.stealCount;
1157	>	int steps = 0;
1158	>	// Remove from array, adjust worker counts and collect steal count.
1159	>	// We can intermix failed removes or adjusts with steal updates
1160	>	do {
1161	>	long s, c;
1162	>	int g;
1163	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1164	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1165	>	g, g |= SG_UNIT)) {
1166	>	ForkJoinWorkerThread[] ws = workers;
1167	>	if (ws != null && idx >= 0 &&
1168	>	idx < ws.length && ws[idx] == w)
1169	>	ws[idx] = null;    // verify
1170	>	nextWorkerIndex = idx;
1171	>	scanGuard = g + SG_UNIT;
1172	>	steps = 1;
1173	>	}
1174	>	if (steps == 1 &&
1175	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1176	>	(((c - AC_UNIT) & AC_MASK) |
1177	>	((c - TC_UNIT) & TC_MASK) |
1178	>	(c & ~(AC_MASK|TC_MASK)))))
1179	>	steps = 2;
1180	>	if (sc != 0 &&
1181	>	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1182	>	s = stealCount, s + sc))
1183	>	sc = 0;
1184	>	} while (steps != 2 || sc != 0);
1185	>	if (!tryTerminate(false)) {
1186	>	if (ex != null)   // possibly replace if died abnormally
1187	>	signalWork();
1188	>	else
1189	>	tryReleaseWaiter();
1190		}
1191		}
1192
1193	+	// Shutdown and termination
1194	+
1195		/**
1196	<	* Clear out and cancel submissions, ignoring exceptions
1196	>	* Possibly initiates and/or completes termination.
1197	>	*
1198	>	* @param now if true, unconditionally terminate, else only
1199	>	* if shutdown and empty queue and no active workers
1200	>	* @return true if now terminating or terminated
1201		*/
1202	<	private void cancelSubmissions() {
1203	<	ForkJoinTask<?> task;
1204	<	while ((task = submissionQueue.poll()) != null) {
1205	<	try {
1206	<	task.cancel(false);
1207	<	} catch (Throwable ignore) {
1202	>	private boolean tryTerminate(boolean now) {
1203	>	long c;
1204	>	while (((c = ctl) & STOP_BIT) == 0) {
1205	>	if (!now) {
1206	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1207	>	return false;
1208	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1209	>	queueTop - queueBase > 0) {
1210	>	if (ctl == c) // staleness check
1211	>	return false;
1212	>	continue;
1213	>	}
1214		}
1215	+	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1216	+	startTerminating();
1217	+	}
1218	+	if ((short)(c >>> TC_SHIFT) == -parallelism) {
1219	+	submissionLock.lock();
1220	+	termination.signalAll();
1221	+	submissionLock.unlock();
1222		}
1223	+	return true;
1224		}
1225
1226		/**
1227	<	* Sets all worker run states to at least shutdown,
1228	<	* also resuming suspended workers
1227	>	* Runs up to three passes through workers: (0) Setting
1228	>	* termination status for each worker, followed by wakeups up
1229	>	* queued workers (1) helping cancel tasks (2) interrupting
1230	>	* lagging threads (likely in external tasks, but possibly also
1231	>	* blocked in joins).  Each pass repeats previous steps because of
1232	>	* potential lagging thread creation.
1233		*/
1234	<	private void shutdownWorkers() {
1235	<	ForkJoinWorkerThread[] ws = workers;
1236	<	int nws = ws.length;
1237	<	for (int i = 0; i < nws; ++i) {
1238	<	ForkJoinWorkerThread w = ws[i];
1239	<	if (w != null)
1240	<	w.shutdown();
1234	>	private void startTerminating() {
1235	>	cancelSubmissions();
1236	>	for (int pass = 0; pass < 3; ++pass) {
1237	>	ForkJoinWorkerThread[] ws = workers;
1238	>	if (ws != null) {
1239	>	for (ForkJoinWorkerThread w : ws) {
1240	>	if (w != null) {
1241	>	w.terminate = true;
1242	>	if (pass > 0) {
1243	>	w.cancelTasks();
1244	>	if (pass > 1 && !w.isInterrupted()) {
1245	>	try {
1246	>	w.interrupt();
1247	>	} catch (SecurityException ignore) {
1248	>	}
1249	>	}
1250	>	}
1251	>	}
1252	>	}
1253	>	terminateWaiters();
1254	>	}
1255		}
1256		}
1257
1258		/**
1259	<	* Clears out and cancels all locally queued tasks
1259	>	* Polls and cancels all submissions. Called only during termination.
1260		*/
1261	<	private void cancelWorkerTasks() {
1262	<	ForkJoinWorkerThread[] ws = workers;
1263	<	int nws = ws.length;
1264	<	for (int i = 0; i < nws; ++i) {
1265	<	ForkJoinWorkerThread w = ws[i];
1266	<	if (w != null)
1267	<	w.cancelTasks();
1261	>	private void cancelSubmissions() {
1262	>	while (queueBase != queueTop) {
1263	>	ForkJoinTask<?> task = pollSubmission();
1264	>	if (task != null) {
1265	>	try {
1266	>	task.cancel(false);
1267	>	} catch (Throwable ignore) {
1268	>	}
1269	>	}
1270		}
1271		}
1272
1273		/**
1274	<	* Unsticks all workers blocked on joins etc
1274	>	* Tries to set the termination status of waiting workers, and
1275	>	* then wake them up (after which they will terminate).
1276		*/
1277	<	private void interruptWorkers() {
1277	>	private void terminateWaiters() {
1278		ForkJoinWorkerThread[] ws = workers;
1279	<	int nws = ws.length;
1280	<	for (int i = 0; i < nws; ++i) {
1281	<	ForkJoinWorkerThread w = ws[i];
1282	<	if (w != null && !w.isTerminated()) {
1283	<	try {
1284	<	w.interrupt();
1285	<	} catch (SecurityException ignore) {
1279	>	if (ws != null) {
1280	>	ForkJoinWorkerThread w; long c; int i, e;
1281	>	int n = ws.length;
1282	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1283	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1284	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1285	>	(long)(w.nextWait & E_MASK) |
1286	>	((c + AC_UNIT) & AC_MASK) |
1287	>	(c & (TC_MASK|STOP_BIT)))) {
1288	>	w.terminate = true;
1289	>	w.eventCount = e + EC_UNIT;
1290	>	if (w.parked)
1291	>	UNSAFE.unpark(w);
1292		}
1293		}
1294		}
1295		}
1296
1297	<	// misc support for ForkJoinWorkerThread
1297	>	// misc ForkJoinWorkerThread support
1298
1299		/**
1300	<	* Returns pool number
1300	>	* Increment or decrement quiescerCount. Needed only to prevent
1301	>	* triggering shutdown if a worker is transiently inactive while
1302	>	* checking quiescence.
1303	>	*
1304	>	* @param delta 1 for increment, -1 for decrement
1305		*/
1306	<	final int getPoolNumber() {
1307	<	return poolNumber;
1306	>	final void addQuiescerCount(int delta) {
1307	>	int c;
1308	>	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1309	>	c = quiescerCount, c + delta));
1310		}
1311
1312		/**
1313	<	* Accumulates steal count from a worker, clearing
1314	<	* the worker's value
1313	>	* Directly increment or decrement active count without
1314	>	* queuing. This method is used to transiently assert inactivation
1315	>	* while checking quiescence.
1316	>	*
1317	>	* @param delta 1 for increment, -1 for decrement
1318		*/
1319	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1320	<	int sc = w.stealCount;
1321	<	if (sc != 0) {
1322	<	long c;
1323	<	w.stealCount = 0;
1324	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1097	<	c = stealCount, c + sc));
1098	<	}
1319	>	final void addActiveCount(int delta) {
1320	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1321	>	long c;
1322	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1323	>	((c + d) & AC_MASK) |
1324	>	(c & ~AC_MASK)));
1325		}
1326
1327		/**
#	Line 1103 | Line 1329 | public class ForkJoinPool extends Abstra
1329		* active thread.
1330		*/
1331		final int idlePerActive() {
1332	<	int pc = parallelism; // use targeted parallelism, not rc
1333	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1334	<	// Use exact results for small values, saturate past 4
1335	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1332	>	// Approximate at powers of two for small values, saturate past 4
1333	>	int p = parallelism;
1334	>	int a = p + (int)(ctl >> AC_SHIFT);
1335	>	return (a > (p >>>= 1) ? 0 :
1336	>	a > (p >>>= 1) ? 1 :
1337	>	a > (p >>>= 1) ? 2 :
1338	>	a > (p >>>= 1) ? 4 :
1339	>	8);
1340		}
1341
1342	<	// Public and protected methods
1342	>	// Exported methods
1343
1344		// Constructors
1345
#	Line 1154 | Line 1384 | public class ForkJoinPool extends Abstra
1384		* use {@link java.lang.Runtime#availableProcessors}.
1385		* @param factory the factory for creating new threads. For default value,
1386		* use {@link #defaultForkJoinWorkerThreadFactory}.
1387	<	* @param handler the handler for internal worker threads that
1388	<	* terminate due to unrecoverable errors encountered while executing
1389	<	* tasks. For default value, use <code>null</code>.
1390	<	* @param asyncMode if true,
1387	>	* @param handler the handler for internal worker threads that
1388	>	* terminate due to unrecoverable errors encountered while executing
1389	>	* tasks. For default value, use {@code null}.
1390	>	* @param asyncMode if true,
1391		* establishes local first-in-first-out scheduling mode for forked
1392		* tasks that are never joined. This mode may be more appropriate
1393		* than default locally stack-based mode in applications in which
1394		* worker threads only process event-style asynchronous tasks.
1395	<	* For default value, use <code>false</code>.
1395	>	* For default value, use {@code false}.
1396		* @throws IllegalArgumentException if parallelism less than or
1397		*         equal to zero, or greater than implementation limit
1398		* @throws NullPointerException if the factory is null
#	Line 1171 | Line 1401 | public class ForkJoinPool extends Abstra
1401		*         because it does not hold {@link
1402		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1403		*/
1404	<	public ForkJoinPool(int parallelism,
1404	>	public ForkJoinPool(int parallelism,
1405		ForkJoinWorkerThreadFactory factory,
1406		Thread.UncaughtExceptionHandler handler,
1407		boolean asyncMode) {
1408		checkPermission();
1409		if (factory == null)
1410		throw new NullPointerException();
1411	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1411	>	if (parallelism <= 0 || parallelism > MAX_ID)
1412		throw new IllegalArgumentException();
1413		this.parallelism = parallelism;
1414		this.factory = factory;
1415		this.ueh = handler;
1416		this.locallyFifo = asyncMode;
1417	<	int arraySize = initialArraySizeFor(parallelism);
1418	<	this.workers = new ForkJoinWorkerThread[arraySize];
1419	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1420	<	this.workerLock = new ReentrantLock();
1421	<	this.termination = new Phaser(1);
1422	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
1423	<	}
1424	<
1425	<	/**
1426	<	* Returns initial power of two size for workers array.
1427	<	* @param pc the initial parallelism level
1428	<	*/
1429	<	private static int initialArraySizeFor(int pc) {
1430	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1431	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1432	<	size |= size >>> 1;
1433	<	size |= size >>> 2;
1204	<	size |= size >>> 4;
1205	<	size |= size >>> 8;
1206	<	return size + 1;
1417	>	long np = (long)(-parallelism); // offset ctl counts
1418	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1419	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1420	>	// initialize workers array with room for 2*parallelism if possible
1421	>	int n = parallelism << 1;
1422	>	if (n >= MAX_ID)
1423	>	n = MAX_ID;
1424	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1425	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1426	>	}
1427	>	workers = new ForkJoinWorkerThread[n + 1];
1428	>	this.submissionLock = new ReentrantLock();
1429	>	this.termination = submissionLock.newCondition();
1430	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1431	>	sb.append(poolNumberGenerator.incrementAndGet());
1432	>	sb.append("-worker-");
1433	>	this.workerNamePrefix = sb.toString();
1434		}
1435
1436		// Execution methods
1437
1438		/**
1439	<	* Common code for execute, invoke and submit
1439	>	* Performs the given task, returning its result upon completion.
1440	>	* If the computation encounters an unchecked Exception or Error,
1441	>	* it is rethrown as the outcome of this invocation.  Rethrown
1442	>	* exceptions behave in the same way as regular exceptions, but,
1443	>	* when possible, contain stack traces (as displayed for example
1444	>	* using {@code ex.printStackTrace()}) of both the current thread
1445	>	* as well as the thread actually encountering the exception;
1446	>	* minimally only the latter.
1447	>	*
1448	>	* @param task the task
1449	>	* @return the task's result
1450	>	* @throws NullPointerException if the task is null
1451	>	* @throws RejectedExecutionException if the task cannot be
1452	>	*         scheduled for execution
1453		*/
1454	<	private <T> void doSubmit(ForkJoinTask<T> task) {
1454	>	public <T> T invoke(ForkJoinTask<T> task) {
1455	>	Thread t = Thread.currentThread();
1456		if (task == null)
1457		throw new NullPointerException();
1458	<	if (runState >= SHUTDOWN)
1458	>	if (shutdown)
1459		throw new RejectedExecutionException();
1219	–	// Convert submissions to current pool into forks
1220	–	Thread t = Thread.currentThread();
1221	–	ForkJoinWorkerThread w;
1460		if ((t instanceof ForkJoinWorkerThread) &&
1461	<	(w = (ForkJoinWorkerThread) t).pool == this)
1462	<	w.pushTask(task);
1461	>	((ForkJoinWorkerThread)t).pool == this)
1462	>	return task.invoke();  // bypass submit if in same pool
1463		else {
1464	<	submissionQueue.offer(task);
1465	<	signalEvent();
1228	<	ensureEnoughTotalWorkers();
1464	>	addSubmission(task);
1465	>	return task.join();
1466		}
1467		}
1468
1469		/**
1470	<	* Performs the given task, returning its result upon completion.
1471	<	* If the caller is already engaged in a fork/join computation in
1235	<	* the current pool, this method is equivalent in effect to
1236	<	* {@link ForkJoinTask#invoke}.
1237	<	*
1238	<	* @param task the task
1239	<	* @return the task's result
1240	<	* @throws NullPointerException if the task is null
1241	<	* @throws RejectedExecutionException if the task cannot be
1242	<	*         scheduled for execution
1470	>	* Unless terminating, forks task if within an ongoing FJ
1471	>	* computation in the current pool, else submits as external task.
1472		*/
1473	<	public <T> T invoke(ForkJoinTask<T> task) {
1474	<	doSubmit(task);
1475	<	return task.join();
1473	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1474	>	ForkJoinWorkerThread w;
1475	>	Thread t = Thread.currentThread();
1476	>	if (shutdown)
1477	>	throw new RejectedExecutionException();
1478	>	if ((t instanceof ForkJoinWorkerThread) &&
1479	>	(w = (ForkJoinWorkerThread)t).pool == this)
1480	>	w.pushTask(task);
1481	>	else
1482	>	addSubmission(task);
1483		}
1484
1485		/**
1486		* Arranges for (asynchronous) execution of the given task.
1251	–	* If the caller is already engaged in a fork/join computation in
1252	–	* the current pool, this method is equivalent in effect to
1253	–	* {@link ForkJoinTask#fork}.
1487		*
1488		* @param task the task
1489		* @throws NullPointerException if the task is null
#	Line 1258 | Line 1491 | public class ForkJoinPool extends Abstra
1491		*         scheduled for execution
1492		*/
1493		public void execute(ForkJoinTask<?> task) {
1494	<	doSubmit(task);
1494	>	if (task == null)
1495	>	throw new NullPointerException();
1496	>	forkOrSubmit(task);
1497		}
1498
1499		// AbstractExecutorService methods
#	Line 1269 | Line 1504 | public class ForkJoinPool extends Abstra
1504		*         scheduled for execution
1505		*/
1506		public void execute(Runnable task) {
1507	+	if (task == null)
1508	+	throw new NullPointerException();
1509		ForkJoinTask<?> job;
1510		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1511		job = (ForkJoinTask<?>) task;
1512		else
1513		job = ForkJoinTask.adapt(task, null);
1514	<	doSubmit(job);
1514	>	forkOrSubmit(job);
1515		}
1516
1517		/**
1518		* Submits a ForkJoinTask for execution.
1282	–	* If the caller is already engaged in a fork/join computation in
1283	–	* the current pool, this method is equivalent in effect to
1284	–	* {@link ForkJoinTask#fork}.
1519		*
1520		* @param task the task to submit
1521		* @return the task
#	Line 1290 | Line 1524 | public class ForkJoinPool extends Abstra
1524		*         scheduled for execution
1525		*/
1526		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1527	<	doSubmit(task);
1527	>	if (task == null)
1528	>	throw new NullPointerException();
1529	>	forkOrSubmit(task);
1530		return task;
1531		}
1532
#	Line 1300 | Line 1536 | public class ForkJoinPool extends Abstra
1536		*         scheduled for execution
1537		*/
1538		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1539	+	if (task == null)
1540	+	throw new NullPointerException();
1541		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1542	<	doSubmit(job);
1542	>	forkOrSubmit(job);
1543		return job;
1544		}
1545
#	Line 1311 | Line 1549 | public class ForkJoinPool extends Abstra
1549		*         scheduled for execution
1550		*/
1551		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1552	+	if (task == null)
1553	+	throw new NullPointerException();
1554		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1555	<	doSubmit(job);
1555	>	forkOrSubmit(job);
1556		return job;
1557		}
1558
#	Line 1322 | Line 1562 | public class ForkJoinPool extends Abstra
1562		*         scheduled for execution
1563		*/
1564		public ForkJoinTask<?> submit(Runnable task) {
1565	+	if (task == null)
1566	+	throw new NullPointerException();
1567		ForkJoinTask<?> job;
1568		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1569		job = (ForkJoinTask<?>) task;
1570		else
1571		job = ForkJoinTask.adapt(task, null);
1572	<	doSubmit(job);
1572	>	forkOrSubmit(job);
1573		return job;
1574		}
1575
#	Line 1387 | Line 1629 | public class ForkJoinPool extends Abstra
1629
1630		/**
1631		* Returns the number of worker threads that have started but not
1632	<	* yet terminated.  This result returned by this method may differ
1632	>	* yet terminated.  The result returned by this method may differ
1633		* from {@link #getParallelism} when threads are created to
1634		* maintain parallelism when others are cooperatively blocked.
1635		*
1636		* @return the number of worker threads
1637		*/
1638		public int getPoolSize() {
1639	<	return workerCounts >>> TOTAL_COUNT_SHIFT;
1639	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1640		}
1641
1642		/**
#	Line 1416 | Line 1658 | public class ForkJoinPool extends Abstra
1658		* @return the number of worker threads
1659		*/
1660		public int getRunningThreadCount() {
1661	<	return workerCounts & RUNNING_COUNT_MASK;
1661	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1662	>	return r <= 0? 0 : r; // suppress momentarily negative values
1663		}
1664
1665		/**
#	Line 1427 | Line 1670 | public class ForkJoinPool extends Abstra
1670		* @return the number of active threads
1671		*/
1672		public int getActiveThreadCount() {
1673	<	return runState & ACTIVE_COUNT_MASK;
1673	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1674	>	return r <= 0? 0 : r; // suppress momentarily negative values
1675		}
1676
1677		/**
#	Line 1442 | Line 1686 | public class ForkJoinPool extends Abstra
1686		* @return {@code true} if all threads are currently idle
1687		*/
1688		public boolean isQuiescent() {
1689	<	return (runState & ACTIVE_COUNT_MASK) == 0;
1689	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1690		}
1691
1692		/**
#	Line 1472 | Line 1716 | public class ForkJoinPool extends Abstra
1716		*/
1717		public long getQueuedTaskCount() {
1718		long count = 0;
1719	<	ForkJoinWorkerThread[] ws = workers;
1720	<	int nws = ws.length;
1721	<	for (int i = 0; i < nws; ++i) {
1722	<	ForkJoinWorkerThread w = ws[i];
1723	<	if (w != null)
1724	<	count += w.getQueueSize();
1719	>	ForkJoinWorkerThread[] ws;
1720	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1721	>	(ws = workers) != null) {
1722	>	for (ForkJoinWorkerThread w : ws)
1723	>	if (w != null)
1724	>	count -= w.queueBase - w.queueTop; // must read base first
1725		}
1726		return count;
1727		}
1728
1729		/**
1730		* Returns an estimate of the number of tasks submitted to this
1731	<	* pool that have not yet begun executing.  This method takes time
1732	<	* proportional to the number of submissions.
1731	>	* pool that have not yet begun executing.  This meThod may take
1732	>	* time proportional to the number of submissions.
1733		*
1734		* @return the number of queued submissions
1735		*/
1736		public int getQueuedSubmissionCount() {
1737	<	return submissionQueue.size();
1737	>	return -queueBase + queueTop;
1738		}
1739
1740		/**
#	Line 1500 | Line 1744 | public class ForkJoinPool extends Abstra
1744		* @return {@code true} if there are any queued submissions
1745		*/
1746		public boolean hasQueuedSubmissions() {
1747	<	return !submissionQueue.isEmpty();
1747	>	return queueBase != queueTop;
1748		}
1749
1750		/**
#	Line 1511 | Line 1755 | public class ForkJoinPool extends Abstra
1755		* @return the next submission, or {@code null} if none
1756		*/
1757		protected ForkJoinTask<?> pollSubmission() {
1758	<	return submissionQueue.poll();
1758	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1759	>	while ((b = queueBase) != queueTop &&
1760	>	(q = submissionQueue) != null &&
1761	>	(i = (q.length - 1) & b) >= 0) {
1762	>	long u = (i << ASHIFT) + ABASE;
1763	>	if ((t = q[i]) != null &&
1764	>	queueBase == b &&
1765	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1766	>	queueBase = b + 1;
1767	>	return t;
1768	>	}
1769	>	}
1770	>	return null;
1771		}
1772
1773		/**
#	Line 1532 | Line 1788 | public class ForkJoinPool extends Abstra
1788		* @return the number of elements transferred
1789		*/
1790		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1535	–	int n = submissionQueue.drainTo(c);
1536	–	ForkJoinWorkerThread[] ws = workers;
1537	–	int nws = ws.length;
1538	–	for (int i = 0; i < nws; ++i) {
1539	–	ForkJoinWorkerThread w = ws[i];
1540	–	if (w != null)
1541	–	n += w.drainTasksTo(c);
1542	–	}
1543	–	return n;
1544	–	}
1545	–
1546	–	/**
1547	–	* Returns count of total parks by existing workers.
1548	–	* Used during development only since not meaningful to users.
1549	–	*/
1550	–	private int collectParkCount() {
1791		int count = 0;
1792	<	ForkJoinWorkerThread[] ws = workers;
1793	<	int nws = ws.length;
1794	<	for (int i = 0; i < nws; ++i) {
1795	<	ForkJoinWorkerThread w = ws[i];
1796	<	if (w != null)
1797	<	count += w.parkCount;
1792	>	while (queueBase != queueTop) {
1793	>	ForkJoinTask<?> t = pollSubmission();
1794	>	if (t != null) {
1795	>	c.add(t);
1796	>	++count;
1797	>	}
1798	>	}
1799	>	ForkJoinWorkerThread[] ws;
1800	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1801	>	(ws = workers) != null) {
1802	>	for (ForkJoinWorkerThread w : ws)
1803	>	if (w != null)
1804	>	count += w.drainTasksTo(c);
1805		}
1806		return count;
1807		}
#	Line 1570 | Line 1817 | public class ForkJoinPool extends Abstra
1817		long st = getStealCount();
1818		long qt = getQueuedTaskCount();
1819		long qs = getQueuedSubmissionCount();
1573	–	int wc = workerCounts;
1574	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
1575	–	int rc = wc & RUNNING_COUNT_MASK;
1820		int pc = parallelism;
1821	<	int rs = runState;
1822	<	int ac = rs & ACTIVE_COUNT_MASK;
1823	<	//        int pk = collectParkCount();
1821	>	long c = ctl;
1822	>	int tc = pc + (short)(c >>> TC_SHIFT);
1823	>	int rc = pc + (int)(c >> AC_SHIFT);
1824	>	if (rc < 0) // ignore transient negative
1825	>	rc = 0;
1826	>	int ac = rc + blockedCount;
1827	>	String level;
1828	>	if ((c & STOP_BIT) != 0)
1829	>	level = (tc == 0)? "Terminated" : "Terminating";
1830	>	else
1831	>	level = shutdown? "Shutting down" : "Running";
1832		return super.toString() +
1833	<	"[" + runLevelToString(rs) +
1833	>	"[" + level +
1834		", parallelism = " + pc +
1835		", size = " + tc +
1836		", active = " + ac +
#	Line 1586 | Line 1838 | public class ForkJoinPool extends Abstra
1838		", steals = " + st +
1839		", tasks = " + qt +
1840		", submissions = " + qs +
1589	–	//            ", parks = " + pk +
1841		"]";
1842		}
1843
1593	–	private static String runLevelToString(int s) {
1594	–	return ((s & TERMINATED) != 0 ? "Terminated" :
1595	–	((s & TERMINATING) != 0 ? "Terminating" :
1596	–	((s & SHUTDOWN) != 0 ? "Shutting down" :
1597	–	"Running")));
1598	–	}
1599	–
1844		/**
1845		* Initiates an orderly shutdown in which previously submitted
1846		* tasks are executed, but no new tasks will be accepted.
#	Line 1611 | Line 1855 | public class ForkJoinPool extends Abstra
1855		*/
1856		public void shutdown() {
1857		checkPermission();
1858	<	advanceRunLevel(SHUTDOWN);
1858	>	shutdown = true;
1859		tryTerminate(false);
1860		}
1861
#	Line 1633 | Line 1877 | public class ForkJoinPool extends Abstra
1877		*/
1878		public List<Runnable> shutdownNow() {
1879		checkPermission();
1880	+	shutdown = true;
1881		tryTerminate(true);
1882		return Collections.emptyList();
1883		}
#	Line 1643 | Line 1888 | public class ForkJoinPool extends Abstra
1888		* @return {@code true} if all tasks have completed following shut down
1889		*/
1890		public boolean isTerminated() {
1891	<	return runState >= TERMINATED;
1891	>	long c = ctl;
1892	>	return ((c & STOP_BIT) != 0L &&
1893	>	(short)(c >>> TC_SHIFT) == -parallelism);
1894		}
1895
1896		/**
#	Line 1651 | Line 1898 | public class ForkJoinPool extends Abstra
1898		* commenced but not yet completed.  This method may be useful for
1899		* debugging. A return of {@code true} reported a sufficient
1900		* period after shutdown may indicate that submitted tasks have
1901	<	* ignored or suppressed interruption, causing this executor not
1902	<	* to properly terminate.
1901	>	* ignored or suppressed interruption, or are waiting for IO,
1902	>	* causing this executor not to properly terminate. (See the
1903	>	* advisory notes for class {@link ForkJoinTask} stating that
1904	>	* tasks should not normally entail blocking operations.  But if
1905	>	* they do, they must abort them on interrupt.)
1906		*
1907		* @return {@code true} if terminating but not yet terminated
1908		*/
1909		public boolean isTerminating() {
1910	<	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1910	>	long c = ctl;
1911	>	return ((c & STOP_BIT) != 0L &&
1912	>	(short)(c >>> TC_SHIFT) != -parallelism);
1913	>	}
1914	>
1915	>	/**
1916	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1917	>	*/
1918	>	final boolean isAtLeastTerminating() {
1919	>	return (ctl & STOP_BIT) != 0L;
1920		}
1921
1922		/**
#	Line 1666 | Line 1925 | public class ForkJoinPool extends Abstra
1925		* @return {@code true} if this pool has been shut down
1926		*/
1927		public boolean isShutdown() {
1928	<	return runState >= SHUTDOWN;
1928	>	return shutdown;
1929		}
1930
1931		/**
#	Line 1682 | Line 1941 | public class ForkJoinPool extends Abstra
1941		*/
1942		public boolean awaitTermination(long timeout, TimeUnit unit)
1943		throws InterruptedException {
1944	+	long nanos = unit.toNanos(timeout);
1945	+	final ReentrantLock lock = this.submissionLock;
1946	+	lock.lock();
1947		try {
1948	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1949	<	} catch(TimeoutException ex) {
1950	<	return false;
1948	>	for (;;) {
1949	>	if (isTerminated())
1950	>	return true;
1951	>	if (nanos <= 0)
1952	>	return false;
1953	>	nanos = termination.awaitNanos(nanos);
1954	>	}
1955	>	} finally {
1956	>	lock.unlock();
1957		}
1958		}
1959
#	Line 1693 | Line 1961 | public class ForkJoinPool extends Abstra
1961		* Interface for extending managed parallelism for tasks running
1962		* in {@link ForkJoinPool}s.
1963		*
1964	<	* <p>A {@code ManagedBlocker} provides two methods.
1965	<	* Method {@code isReleasable} must return {@code true} if
1966	<	* blocking is not necessary. Method {@code block} blocks the
1967	<	* current thread if necessary (perhaps internally invoking
1968	<	* {@code isReleasable} before actually blocking).
1964	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1965	>	* {@code isReleasable} must return {@code true} if blocking is
1966	>	* not necessary. Method {@code block} blocks the current thread
1967	>	* if necessary (perhaps internally invoking {@code isReleasable}
1968	>	* before actually blocking). The unusual methods in this API
1969	>	* accommodate synchronizers that may, but don't usually, block
1970	>	* for long periods. Similarly, they allow more efficient internal
1971	>	* handling of cases in which additional workers may be, but
1972	>	* usually are not, needed to ensure sufficient parallelism.
1973	>	* Toward this end, implementations of method {@code isReleasable}
1974	>	* must be amenable to repeated invocation.
1975		*
1976		* <p>For example, here is a ManagedBlocker based on a
1977		* ReentrantLock:
#	Line 1715 | Line 1989 | public class ForkJoinPool extends Abstra
1989		*     return hasLock || (hasLock = lock.tryLock());
1990		*   }
1991		* }}</pre>
1992	+	*
1993	+	* <p>Here is a class that possibly blocks waiting for an
1994	+	* item on a given queue:
1995	+	*  <pre> {@code
1996	+	* class QueueTaker<E> implements ManagedBlocker {
1997	+	*   final BlockingQueue<E> queue;
1998	+	*   volatile E item = null;
1999	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2000	+	*   public boolean block() throws InterruptedException {
2001	+	*     if (item == null)
2002	+	*       item = queue.take();
2003	+	*     return true;
2004	+	*   }
2005	+	*   public boolean isReleasable() {
2006	+	*     return item != null || (item = queue.poll()) != null;
2007	+	*   }
2008	+	*   public E getItem() { // call after pool.managedBlock completes
2009	+	*     return item;
2010	+	*   }
2011	+	* }}</pre>
2012		*/
2013		public static interface ManagedBlocker {
2014		/**
#	Line 1757 | Line 2051 | public class ForkJoinPool extends Abstra
2051		public static void managedBlock(ManagedBlocker blocker)
2052		throws InterruptedException {
2053		Thread t = Thread.currentThread();
2054	<	if (t instanceof ForkJoinWorkerThread)
2055	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
2054	>	if (t instanceof ForkJoinWorkerThread) {
2055	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2056	>	w.pool.awaitBlocker(blocker);
2057	>	}
2058		else {
2059		do {} while (!blocker.isReleasable() && !blocker.block());
2060		}
#	Line 1777 | Line 2073 | public class ForkJoinPool extends Abstra
2073		}
2074
2075		// Unsafe mechanics
2076	<
2077	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2078	<	private static final long workerCountsOffset =
2079	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2080	<	private static final long runStateOffset =
2081	<	objectFieldOffset("runState", ForkJoinPool.class);
2082	<	private static final long eventCountOffset =
2083	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2084	<	private static final long eventWaitersOffset =
2085	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
2086	<	private static final long stealCountOffset =
2087	<	objectFieldOffset("stealCount",ForkJoinPool.class);
2088	<
2089	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2076	>	private static final sun.misc.Unsafe UNSAFE;
2077	>	private static final long ctlOffset;
2078	>	private static final long stealCountOffset;
2079	>	private static final long blockedCountOffset;
2080	>	private static final long quiescerCountOffset;
2081	>	private static final long scanGuardOffset;
2082	>	private static final long nextWorkerNumberOffset;
2083	>	private static final long ABASE;
2084	>	private static final int ASHIFT;
2085	>
2086	>	static {
2087	>	poolNumberGenerator = new AtomicInteger();
2088	>	workerSeedGenerator = new Random();
2089	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2090	>	defaultForkJoinWorkerThreadFactory =
2091	>	new DefaultForkJoinWorkerThreadFactory();
2092	>	int s;
2093		try {
2094	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2095	<	} catch (NoSuchFieldException e) {
2096	<	// Convert Exception to corresponding Error
2097	<	NoSuchFieldError error = new NoSuchFieldError(field);
2098	<	error.initCause(e);
2099	<	throw error;
2100	<	}
2094	>	UNSAFE = getUnsafe();
2095	>	Class k = ForkJoinPool.class;
2096	>	ctlOffset = UNSAFE.objectFieldOffset
2097	>	(k.getDeclaredField("ctl"));
2098	>	stealCountOffset = UNSAFE.objectFieldOffset
2099	>	(k.getDeclaredField("stealCount"));
2100	>	blockedCountOffset = UNSAFE.objectFieldOffset
2101	>	(k.getDeclaredField("blockedCount"));
2102	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2103	>	(k.getDeclaredField("quiescerCount"));
2104	>	scanGuardOffset = UNSAFE.objectFieldOffset
2105	>	(k.getDeclaredField("scanGuard"));
2106	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2107	>	(k.getDeclaredField("nextWorkerNumber"));
2108	>	Class a = ForkJoinTask[].class;
2109	>	ABASE = UNSAFE.arrayBaseOffset(a);
2110	>	s = UNSAFE.arrayIndexScale(a);
2111	>	} catch (Exception e) {
2112	>	throw new Error(e);
2113	>	}
2114	>	if ((s & (s-1)) != 0)
2115	>	throw new Error("data type scale not a power of two");
2116	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2117		}
2118
2119		/**

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