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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.59 by dl, Fri Jul 23 14:09:17 2010 UTC vs.
Revision 1.94 by dl, Tue Mar 1 10:59:04 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 69 | 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 110 | Line 117 | import java.util.concurrent.CountDownLat
117		*
118		* <p>This implementation rejects submitted tasks (that is, by throwing
119		* {@link RejectedExecutionException}) only when the pool is shut down
120	<	* or internal resources have been exhuasted.
120	>	* or internal resources have been exhausted.
121		*
122		* @since 1.7
123		* @author Doug Lea
#	Line 124 | 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
131	<	* lastly to new submissions. These mechanics do not consider
132	<	* affinities, loads, cache localities, etc, so rarely provide the
133	<	* best possible performance on a given machine, but portably
134	<	* provide good throughput by averaging over these factors.
135	<	* (Further, even if we did try to use such information, we do not
136	<	* usually have a basis for exploiting it. For example, some sets
137	<	* of tasks profit from cache affinities, but others are harmed by
138	<	* cache pollution effects.)
139	<	*
140	<	* Beyond work-stealing support and essential bookkeeping, the
141	<	* main responsibility of this framework is to arrange tactics for
142	<	* when one worker is waiting to join a task stolen (or always
143	<	* held by) another.  Becauae we are multiplexing many tasks on to
144	<	* a pool of workers, we can't just let them block (as in
145	<	* Thread.join).  We also cannot just reassign the joiner's
146	<	* run-time stack with another and replace it later, which would
147	<	* be a form of "continuation", that even if possible is not
148	<	* necessarily a good idea. Given that the creation costs of most
149	<	* threads on most systems mainly surrounds setting up runtime
150	<	* stacks, thread creation and switching is usually not much more
151	<	* expensive than stack creation and switching, and is more
152	<	* flexible). Instead we combine two tactics:
153	<	*
154	<	*   1. Arranging for the joiner to execute some task that it
155	<	*      would be running if the steal had not occurred.  Method
156	<	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	<	*      links to try to find such a task.
158	<	*
159	<	*   2. Unless there are already enough live threads, creating or
160	<	*      or re-activating a spare thread to compensate for the
161	<	*      (blocked) joiner until it unblocks.  Spares then suspend
162	<	*      at their next opportunity or eventually die if unused for
163	<	*      too long.  See below and the internal documentation
164	<	*      for tryAwaitJoin for more details about compensation
165	<	*      rules.
166	<	*
167	<	* Because the determining existence of conservatively safe
168	<	* helping targets, the availability of already-created spares,
169	<	* and the apparent need to create new spares are all racy and
170	<	* require heuristic guidance, joins (in
171	<	* ForkJoinWorkerThread.joinTask) interleave these options until
172	<	* successful.  Creating a new spare always succeeds, but also
173	<	* increases application footprint, so we try to avoid it, within
174	<	* reason.
175	<	*
176	<	* The ManagedBlocker extension API can't use option (1) so uses a
177	<	* special version of (2) in method awaitBlocker.
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 other management responsibilities. So we use a
143	<	* collection of techniques that avoid, reduce, or cope well with
144	<	* contention. These entail several instances of bit-packing into
145	<	* CASable fields to maintain only the minimally required
146	<	* atomicity. To enable such packing, we restrict maximum
147	<	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
148	<	* unbalanced increments and decrements) to fit into a 16 bit
149	<	* field, which is far in excess of normal operating range.  Even
150	<	* though updates to some of these bookkeeping fields do sometimes
151	<	* contend with each other, they don't normally cache-contend with
152	<	* updates to others enough to warrant memory padding or
153	<	* isolation. So they are all held as fields of ForkJoinPool
154	<	* objects.  The main capabilities are as follows:
155	<	*
156	<	* 1. Creating and removing workers. Workers are recorded in the
157	<	* "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.  Note however that the
186	<	* correspondance of these counts to reality is not guaranteed. In
187	<	* particular updates for unblocked threads may lag until they
188	<	* actually wake up.
189	<	*
190	<	* 3. Maintaining global run state. The run state of the pool
191	<	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
192	<	* those in other Executor implementations, as well as a count of
193	<	* "active" workers -- those that are, or soon will be, or
194	<	* recently were executing tasks. The runLevel and active count
195	<	* are packed together in order to correctly trigger shutdown and
196	<	* termination. Without care, active counts can be subject to very
197	<	* high contention.  We substantially reduce this contention by
198	<	* relaxing update rules.  A worker must claim active status
199	<	* prospectively, by activating if it sees that a submitted or
200	<	* stealable task exists (it may find after activating that the
201	<	* task no longer exists). It stays active while processing this
202	<	* task (if it exists) and any other local subtasks it produces,
203	<	* until it cannot find any other tasks. It then tries
204	<	* inactivating (see method preStep), but upon update contention
205	<	* instead scans for more tasks, later retrying inactivation if it
206	<	* doesn't find any.
207	<	*
208	<	* 4. Managing idle workers waiting for tasks. We cannot let
209	<	* workers spin indefinitely scanning for tasks when none are
210	<	* available. On the other hand, we must quickly prod them into
211	<	* action when new tasks are submitted or generated.  We
212	<	* park/unpark these idle workers using an event-count scheme.
213	<	* Field eventCount is incremented upon events that may enable
214	<	* workers that previously could not find a task to now find one:
215	<	* Submission of a new task to the pool, or another worker pushing
216	<	* a task onto a previously empty queue.  (We also use this
217	<	* mechanism for termination and reconfiguration actions that
218	<	* require wakeups of idle workers).  Each worker maintains its
219	<	* last known event count, and blocks when a scan for work did not
220	<	* find a task AND its lastEventCount matches the current
221	<	* eventCount. Waiting idle workers are recorded in a variant of
222	<	* Treiber stack headed by field eventWaiters which, when nonzero,
223	<	* encodes the thread index and count awaited for by the worker
224	<	* thread most recently calling eventSync. This thread in turn has
225	<	* a record (field nextEventWaiter) for the next waiting worker.
226	<	* In addition to allowing simpler decisions about need for
227	<	* wakeup, the event count bits in eventWaiters serve the role of
228	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
229	<	* in task diffusion, workers not otherwise occupied may invoke
230	<	* method releaseWaiters, that removes and signals (unparks)
231	<	* workers not waiting on current count. To minimize task
232	<	* production stalls associate with signalling, any worker pushing
233	<	* a task on an empty queue invokes the weaker method signalWork,
234	<	* that only releases idle workers until it detects interference
235	<	* by other threads trying to release, and lets them take
236	<	* over. The net effect is a tree-like diffusion of signals, where
237	<	* released threads (and possibly others) help with unparks.  To
238	<	* further reduce contention effects a bit, failed CASes to
239	<	* increment field eventCount are tolerated without retries.
240	<	* Conceptually they are merged into the same event, which is OK
241	<	* when their only purpose is to enable workers to scan for work.
242	<	*
243	<	* 5. Managing suspension of extra workers. When a worker is about
244	<	* to block waiting for a join (or via ManagedBlockers), we may
245	<	* create a new thread to maintain parallelism level, or at least
246	<	* avoid starvation. Usually, extra threads are needed for only
247	<	* very short periods, yet join dependencies are such that we
248	<	* sometimes need them in bursts. Rather than create new threads
249	<	* each time this happens, we suspend no-longer-needed extra ones
250	<	* as "spares". For most purposes, we don't distinguish "extra"
251	<	* spare threads from normal "core" threads: On each call to
252	<	* preStep (the only point at which we can do this) a worker
253	<	* checks to see if there are now too many running workers, and if
254	<	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
255	<	* look for suspended threads to resume before considering
256	<	* creating a new replacement. We don't need a special data
257	<	* structure to maintain spares; simply scanning the workers array
258	<	* looking for worker.isSuspended() is fine because the calling
259	<	* thread is otherwise not doing anything useful anyway; we are at
260	<	* least as happy if after locating a spare, the caller doesn't
261	<	* actually block because the join is ready before we try to
262	<	* adjust and compensate.  Note that this is intrinsically racy.
263	<	* One thread may become a spare at about the same time as another
264	<	* is needlessly being created. We counteract this and related
265	<	* slop in part by requiring resumed spares to immediately recheck
266	<	* (in preStep) to see whether they they should re-suspend. The
267	<	* only effective difference between "extra" and "core" threads is
268	<	* that we allow the "extra" ones to time out and die if they are
269	<	* not resumed within a keep-alive interval of a few seconds. This
270	<	* is implemented mainly within ForkJoinWorkerThread, but requires
271	<	* some coordination (isTrimmed() -- meaning killed while
272	<	* suspended) to correctly maintain pool counts.
273	<	*
274	<	* 6. Deciding when to create new workers. The main dynamic
275	<	* control in this class is deciding when to create extra threads,
276	<	* in methods awaitJoin and awaitBlocker. We always need to create
277	<	* one when the number of running threads would become zero and
278	<	* all workers are busy. However, this is not easy to detect
279	<	* reliably in the presence of transients so we use retries and
280	<	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
281	<	* effectively reduce churn at the price of systematically
282	<	* undershooting target parallelism when many threads are blocked.
283	<	* However, biasing toward undeshooting partially compensates for
284	<	* the above mechanics to suspend extra threads, that normally
285	<	* lead to overshoot because we can only suspend workers
286	<	* in-between top-level actions. It also better copes with the
287	<	* fact that some of the methods in this class tend to never
288	<	* become compiled (but are interpreted), so some components of
289	<	* the entire set of controls might execute many times faster than
290	<	* others. And similarly for cases where the apparent lack of work
291	<	* is just due 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 other
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), at the expense of messiness.
321	>	* when interpreted (not compiled).
322		*
323	<	* The order of declarations in this file is: (1) statics (2)
324	<	* fields (along with constants used when unpacking some of them)
325	<	* (3) internal control methods (4) callbacks and other support
326	<	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
327	<	* methods (plus a few little helpers).
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 380 | Line 362 | public class ForkJoinPool extends Abstra
362		* overridden in ForkJoinPool constructors.
363		*/
364		public static final ForkJoinWorkerThreadFactory
365	<	defaultForkJoinWorkerThreadFactory =
384	<	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 =
391	<	new RuntimePermission("modifyThread");
371	>	private static final RuntimePermission modifyThreadPermission;
372
373		/**
374		* If there is a security manager, makes sure caller has
#	Line 403 | 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
419	<	* state to be randomly accessed without locking by workers
420	<	* performing work-stealing, as well as other traversal-based
421	<	* methods in this class. All readers must tolerate that some
422	<	* 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 444 | 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_ID_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;
507	<	private static final int ONE_RUNNING        = 1;
508	<	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.
482	>	*/
483	>	volatile long ctl;
484	>
485	>	// bit positions/shifts for fields
486	>	private static final int  AC_SHIFT   = 48;
487	>	private static final int  TC_SHIFT   = 32;
488	>	private static final int  ST_SHIFT   = 31;
489	>	private static final int  EC_SHIFT   = 16;
490	>
491	>	// bounds
492	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
493	>	private static final int  SMASK      = 0xffff;  // mask short bits
494	>	private static final int  SHORT_SIGN = 1 << 15;
495	>	private static final int  INT_SIGN   = 1 << 31;
496	>
497	>	// masks
498	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
499	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
500	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
501	>
502	>	// units for incrementing and decrementing
503	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
504	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
505	>
506	>	// masks and units for dealing with u = (int)(ctl >>> 32)
507	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
508	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
509	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
510	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
511	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
512	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
513	>
514	>	// masks and units for dealing with e = (int)ctl
515	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
516	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
517
518		/**
519		* The target parallelism level.
512	–	* Accessed directly by ForkJoinWorkerThreads.
520		*/
521		final int parallelism;
522
523		/**
524	<	* True if use local fifo, not default lifo, for local polling
525	<	* Read by, and replicated by ForkJoinWorkerThreads
524	>	* Index (mod submission queue length) of next element to take
525	>	* from submission queue.
526		*/
527	<	final boolean locallyFifo;
527	>	volatile int queueBase;
528
529		/**
530	<	* The uncaught exception handler used when any worker abruptly
531	<	* terminates.
530	>	* Index (mod submission queue length) of next element to add
531	>	* in submission queue.
532		*/
533	<	private final Thread.UncaughtExceptionHandler ueh;
533	>	int queueTop;
534
535		/**
536	<	* Pool number, just for assigning useful names to worker threads
536	>	* True when shutdown() has been called.
537		*/
538	<	private final int poolNumber;
538	>	volatile boolean shutdown;
539
540	<	// Utilities for CASing fields. Note that several of these
541	<	// are manually inlined by callers
540	>	/**
541	>	* True if use local fifo, not default lifo, for local polling
542	>	* Read by, and replicated by ForkJoinWorkerThreads
543	>	*/
544	>	final boolean locallyFifo;
545
546		/**
547	<	* Increments running count.  Also used by ForkJoinTask.
547	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
548	>	* When non-zero, suppresses automatic shutdown when active
549	>	* counts become zero.
550		*/
551	<	final void incrementRunningCount() {
540	<	int c;
541	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
542	<	c = workerCounts,
543	<	c + ONE_RUNNING));
544	<	}
551	>	volatile int quiescerCount;
552
553		/**
554	<	* Tries to decrement running count unless already zero
554	>	* The number of threads blocked in join.
555		*/
556	<	final boolean tryDecrementRunningCount() {
550	<	int wc = workerCounts;
551	<	if ((wc & RUNNING_COUNT_MASK) == 0)
552	<	return false;
553	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
554	<	wc, wc - ONE_RUNNING);
555	<	}
556	>	volatile int blockedCount;
557
558		/**
559	<	* Tries to increment running count
559	>	* Counter for worker Thread names (unrelated to their poolIndex)
560		*/
561	<	final boolean tryIncrementRunningCount() {
561	<	int wc;
562	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
563	<	wc = workerCounts, wc + ONE_RUNNING);
564	<	}
561	>	private volatile int nextWorkerNumber;
562
563		/**
564	<	* Tries incrementing active count; fails on contention.
568	<	* Called by workers before executing tasks.
569	<	*
570	<	* @return true on success
564	>	* The index for the next created worker. Accessed under scanGuard.
565		*/
566	<	final boolean tryIncrementActiveCount() {
573	<	int c;
574	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
575	<	c = runState, c + ONE_ACTIVE);
576	<	}
566	>	private int nextWorkerIndex;
567
568		/**
569	<	* Tries decrementing active count; fails on contention.
570	<	* Called when workers cannot find tasks to run.
569	>	* SeqLock and index masking for for updates to workers array.
570	>	* Locked when SG_UNIT is set. Unlocking clears bit by adding
571	>	* SG_UNIT. Staleness of read-only operations can be checked by
572	>	* comparing scanGuard to value before the reads. The low 16 bits
573	>	* (i.e, anding with SMASK) hold (the smallest power of two
574	>	* covering all worker indices, minus one, and is used to avoid
575	>	* dealing with large numbers of null slots when the workers array
576	>	* is overallocated.
577		*/
578	<	final boolean tryDecrementActiveCount() {
579	<	int c;
580	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
585	<	c = runState, c - ONE_ACTIVE);
586	<	}
578	>	volatile int scanGuard;
579	>
580	>	private static final int SG_UNIT = 1 << 16;
581
582		/**
583	<	* Advances to at least the given level. Returns true if not
584	<	* already in at least the given level.
583	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
584	>	* task when the pool is quiescent to instead try to shrink the
585	>	* number of workers.  The exact value does not matter too
586	>	* much. It must be short enough to release resources during
587	>	* sustained periods of idleness, but not so short that threads
588	>	* are continually re-created.
589		*/
590	<	private boolean advanceRunLevel(int level) {
591	<	for (;;) {
592	<	int s = runState;
593	<	if ((s & level) != 0)
594	<	return false;
595	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
596	<	return true;
590	>	private static final long SHRINK_RATE =
591	>	4L * 1000L * 1000L * 1000L; // 4 seconds
592	>
593	>	/**
594	>	* Top-level loop for worker threads: On each step: if the
595	>	* previous step swept through all queues and found no tasks, or
596	>	* there are excess threads, then possibly blocks. Otherwise,
597	>	* scans for and, if found, executes a task. Returns when pool
598	>	* and/or worker terminate.
599	>	*
600	>	* @param w the worker
601	>	*/
602	>	final void work(ForkJoinWorkerThread w) {
603	>	boolean swept = false;                // true on empty scans
604	>	long c;
605	>	while (!w.terminate && (int)(c = ctl) >= 0) {
606	>	int a;                            // active count
607	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
608	>	swept = scan(w, a);
609	>	else if (tryAwaitWork(w, c))
610	>	swept = false;
611		}
612		}
613
614	<	// workers array maintenance
614	>	// Signalling
615
616		/**
617	<	* Records and returns a workers array index for new worker.
617	>	* Wakes up or creates a worker.
618		*/
619	<	private int recordWorker(ForkJoinWorkerThread w) {
620	<	// Try using slot totalCount-1. If not available, scan and/or resize
621	<	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
622	<	final ReentrantLock lock = this.workerLock;
623	<	lock.lock();
624	<	try {
625	<	ForkJoinWorkerThread[] ws = workers;
626	<	int nws = ws.length;
627	<	if (k < 0 || k >= nws || ws[k] != null) {
628	<	for (k = 0; k < nws && ws[k] != null; ++k)
629	<	;
630	<	if (k == nws)
631	<	ws = Arrays.copyOf(ws, nws << 1);
619	>	final void signalWork() {
620	>	/*
621	>	* The while condition is true if: (there is are too few total
622	>	* workers OR there is at least one waiter) AND (there are too
623	>	* few active workers OR the pool is terminating).  The value
624	>	* of e distinguishes the remaining cases: zero (no waiters)
625	>	* for create, negative if terminating (in which case do
626	>	* nothing), else release a waiter. The secondary checks for
627	>	* release (non-null array etc) can fail if the pool begins
628	>	* terminating after the test, and don't impose any added cost
629	>	* because JVMs must perform null and bounds checks anyway.
630	>	*/
631	>	long c; int e, u;
632	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
633	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
634	>	if (e > 0) {                         // release a waiting worker
635	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
636	>	if ((ws = workers) == null ||
637	>	(i = ~e & SMASK) >= ws.length ||
638	>	(w = ws[i]) == null)
639	>	break;
640	>	long nc = (((long)(w.nextWait & E_MASK)) |
641	>	((long)(u + UAC_UNIT) << 32));
642	>	if (w.eventCount == e &&
643	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
644	>	w.eventCount = (e + EC_UNIT) & E_MASK;
645	>	if (w.parked)
646	>	UNSAFE.unpark(w);
647	>	break;
648	>	}
649	>	}
650	>	else if (UNSAFE.compareAndSwapLong
651	>	(this, ctlOffset, c,
652	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
653	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
654	>	addWorker();
655	>	break;
656		}
621	–	ws[k] = w;
622	–	workers = ws; // volatile array write ensures slot visibility
623	–	} finally {
624	–	lock.unlock();
657		}
626	–	return k;
658		}
659
660		/**
661	<	* Nulls out record of worker in workers array
661	>	* Variant of signalWork to help release waiters on rescans.
662	>	* Tries once to release a waiter if active count < 0.
663	>	*
664	>	* @return false if failed due to contention, else true
665		*/
666	<	private void forgetWorker(ForkJoinWorkerThread w) {
667	<	int idx = w.poolIndex;
668	<	// Locking helps method recordWorker avoid unecessary expansion
669	<	final ReentrantLock lock = this.workerLock;
670	<	lock.lock();
671	<	try {
672	<	ForkJoinWorkerThread[] ws = workers;
673	<	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
674	<	ws[idx] = null;
675	<	} finally {
676	<	lock.unlock();
666	>	private boolean tryReleaseWaiter() {
667	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
668	>	if ((e = (int)(c = ctl)) > 0 &&
669	>	(int)(c >> AC_SHIFT) < 0 &&
670	>	(ws = workers) != null &&
671	>	(i = ~e & SMASK) < ws.length &&
672	>	(w = ws[i]) != null) {
673	>	long nc = ((long)(w.nextWait & E_MASK) |
674	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
675	>	if (w.eventCount != e ||
676	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
677	>	return false;
678	>	w.eventCount = (e + EC_UNIT) & E_MASK;
679	>	if (w.parked)
680	>	UNSAFE.unpark(w);
681		}
682	+	return true;
683		}
684
685	<	// adding and removing workers
685	>	// Scanning for tasks
686
687		/**
688	<	* Tries to create and add new worker. Assumes that worker counts
689	<	* are already updated to accommodate the worker, so adjusts on
690	<	* failure.
688	>	* Scans for and, if found, executes one task. Scans start at a
689	>	* random index of workers array, and randomly select the first
690	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
691	>	* circular sweeps, which is necessary to check quiescence. and
692	>	* taking a submission only if no stealable tasks were found.  The
693	>	* steal code inside the loop is a specialized form of
694	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
695	>	* helpJoinTask and signal propagation. The code for submission
696	>	* queues is almost identical. On each steal, the worker completes
697	>	* not only the task, but also all local tasks that this task may
698	>	* have generated. On detecting staleness or contention when
699	>	* trying to take a task, this method returns without finishing
700	>	* sweep, which allows global state rechecks before retry.
701		*
702	<	* @return new worker or null if creation failed
702	>	* @param w the worker
703	>	* @param a the number of active workers
704	>	* @return true if swept all queues without finding a task
705		*/
706	<	private ForkJoinWorkerThread addWorker() {
707	<	ForkJoinWorkerThread w = null;
708	<	try {
709	<	w = factory.newThread(this);
710	<	} finally { // Adjust on either null or exceptional factory return
711	<	if (w == null) {
712	<	onWorkerCreationFailure();
713	<	return null;
706	>	private boolean scan(ForkJoinWorkerThread w, int a) {
707	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
708	>	int m = parallelism == 1 - a? 0 : g & SMASK;
709	>	ForkJoinWorkerThread[] ws = workers;
710	>	if (ws == null || ws.length <= m)         // staleness check
711	>	return false;
712	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
713	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
714	>	ForkJoinWorkerThread v = ws[k & m];
715	>	if (v != null && (b = v.queueBase) != v.queueTop &&
716	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
717	>	long u = (i << ASHIFT) + ABASE;
718	>	if ((t = q[i]) != null && v.queueBase == b &&
719	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
720	>	int d = (v.queueBase = b + 1) - v.queueTop;
721	>	v.stealHint = w.poolIndex;
722	>	if (d != 0)
723	>	signalWork();             // propagate if nonempty
724	>	w.execTask(t);
725	>	}
726	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
727	>	return false;                     // store next seed
728	>	}
729	>	else if (j < 0) {                     // xorshift
730	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
731		}
732	+	else
733	+	++k;
734	+	}
735	+	if (scanGuard != g)                       // staleness check
736	+	return false;
737	+	else {                                    // try to take submission
738	+	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
739	+	if ((b = queueBase) != queueTop &&
740	+	(q = submissionQueue) != null &&
741	+	(i = (q.length - 1) & b) >= 0) {
742	+	long u = (i << ASHIFT) + ABASE;
743	+	if ((t = q[i]) != null && queueBase == b &&
744	+	UNSAFE.compareAndSwapObject(q, u, t, null)) {
745	+	queueBase = b + 1;
746	+	w.execTask(t);
747	+	}
748	+	return false;
749	+	}
750	+	return true;                         // all queues empty
751		}
665	–	w.start(recordWorker(w), ueh);
666	–	return w;
752		}
753
754		/**
755	<	* Adjusts counts upon failure to create worker
756	<	*/
757	<	private void onWorkerCreationFailure() {
758	<	for (;;) {
759	<	int wc = workerCounts;
760	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
761	<	Thread.yield(); // wait for other counts to settle
762	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
763	<	wc - (ONE_RUNNING|ONE_TOTAL)))
764	<	break;
755	>	* Tries to enqueue worker w in wait queue and await change in
756	>	* worker's eventCount.  If the pool is quiescent, possibly
757	>	* terminates worker upon exit.  Otherwise, before blocking,
758	>	* rescans queues to avoid missed signals.  Upon finding work,
759	>	* releases at least one worker (which may be the current
760	>	* worker). Rescans restart upon detected staleness or failure to
761	>	* release due to contention.
762	>	*
763	>	* @param w the calling worker
764	>	* @param c the ctl value on entry
765	>	* @return true if waited or another thread was released upon enq
766	>	*/
767	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
768	>	int v = w.eventCount;
769	>	w.nextWait = (int)c;                      // w's successor record
770	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
771	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
772	>	long d = ctl; // return true if lost to a deq, to force scan
773	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
774	>	}
775	>	for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
776	>	long s = stealCount;
777	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
778	>	sc = w.stealCount = 0;
779	>	else if (w.eventCount != v)
780	>	return true;                      // update next time
781	>	}
782	>	if (parallelism + (int)(nc >> AC_SHIFT) == 0 &&
783	>	blockedCount == 0 && quiescerCount == 0)
784	>	idleAwaitWork(w, nc, c, v);           // quiescent
785	>	for (boolean rescanned = false;;) {
786	>	if (w.eventCount != v)
787	>	return true;
788	>	if (!rescanned) {
789	>	int g = scanGuard, m = g & SMASK;
790	>	ForkJoinWorkerThread[] ws = workers;
791	>	if (ws != null && m < ws.length) {
792	>	rescanned = true;
793	>	for (int i = 0; i <= m; ++i) {
794	>	ForkJoinWorkerThread u = ws[i];
795	>	if (u != null) {
796	>	if (u.queueBase != u.queueTop &&
797	>	!tryReleaseWaiter())
798	>	rescanned = false; // contended
799	>	if (w.eventCount != v)
800	>	return true;
801	>	}
802	>	}
803	>	}
804	>	if (scanGuard != g ||              // stale
805	>	(queueBase != queueTop && !tryReleaseWaiter()))
806	>	rescanned = false;
807	>	if (!rescanned)
808	>	Thread.yield();                // reduce contention
809	>	else
810	>	Thread.interrupted();          // clear before park
811	>	}
812	>	else {
813	>	w.parked = true;                   // must recheck
814	>	if (w.eventCount != v) {
815	>	w.parked = false;
816	>	return true;
817	>	}
818	>	LockSupport.park(this);
819	>	rescanned = w.parked = false;
820	>	}
821		}
681	–	tryTerminate(false); // in case of failure during shutdown
822		}
823
824		/**
825	<	* Creates and/or resumes enough workers to establish target
826	<	* parallelism, giving up if terminating or addWorker fails
827	<	*
828	<	* TODO: recast this to support lazier creation and automated
829	<	* parallelism maintenance
830	<	*/
831	<	private void ensureEnoughWorkers() {
832	<	while ((runState & TERMINATING) == 0) {
833	<	int pc = parallelism;
834	<	int wc = workerCounts;
835	<	int rc = wc & RUNNING_COUNT_MASK;
836	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
837	<	if (tc < pc) {
838	<	if (UNSAFE.compareAndSwapInt
839	<	(this, workerCountsOffset,
840	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
841	<	addWorker() == null)
825	>	* If inactivating worker w has caused pool to become
826	>	* quiescent, check for pool termination, and wait for event
827	>	* for up to SHRINK_RATE nanosecs (rescans are unnecessary in
828	>	* this case because quiescence reflects consensus about lack
829	>	* of work). On timeout, if ctl has not changed, terminate the
830	>	* worker. Upon its termination (see deregisterWorker), it may
831	>	* wake up another worker to possibly repeat this process.
832	>	*
833	>	* @param w the calling worker
834	>	* @param currentCtl the ctl value after enqueuing w
835	>	* @param prevCtl the ctl value if w terminated
836	>	* @param v the eventCount w awaits change
837	>	*/
838	>	private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
839	>	long prevCtl, int v) {
840	>	if (w.eventCount == v) {
841	>	if (shutdown)
842	>	tryTerminate(false);
843	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
844	>	while (ctl == currentCtl) {
845	>	long startTime = System.nanoTime();
846	>	w.parked = true;
847	>	if (w.eventCount == v)             // must recheck
848	>	LockSupport.parkNanos(this, SHRINK_RATE);
849	>	w.parked = false;
850	>	if (w.eventCount != v)
851	>	break;
852	>	else if (System.nanoTime() - startTime < SHRINK_RATE)
853	>	Thread.interrupted();          // spurious wakeup
854	>	else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
855	>	currentCtl, prevCtl)) {
856	>	w.terminate = true;            // restore previous
857	>	w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
858		break;
703	–	}
704	–	else if (tc > pc && rc < pc &&
705	–	tc > (runState & ACTIVE_COUNT_MASK)) {
706	–	ForkJoinWorkerThread spare = null;
707	–	ForkJoinWorkerThread[] ws = workers;
708	–	int nws = ws.length;
709	–	for (int i = 0; i < nws; ++i) {
710	–	ForkJoinWorkerThread w = ws[i];
711	–	if (w != null && w.isSuspended()) {
712	–	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
713	–	return;
714	–	if (w.tryResumeSpare())
715	–	incrementRunningCount();
716	–	break;
717	–	}
859		}
860		}
720	–	else
721	–	break;
861		}
862		}
863
864	+	// Submissions
865	+
866		/**
867	<	* Final callback from terminating worker.  Removes record of
868	<	* worker from array, and adjusts counts. If pool is shutting
728	<	* down, tries to complete terminatation, else possibly replaces
729	<	* the worker.
867	>	* Enqueues the given task in the submissionQueue.  Same idea as
868	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
869		*
870	<	* @param w the worker
870	>	* @param t the task
871		*/
872	<	final void workerTerminated(ForkJoinWorkerThread w) {
873	<	if (w.active) { // force inactive
874	<	w.active = false;
875	<	do {} while (!tryDecrementActiveCount());
876	<	}
877	<	forgetWorker(w);
878	<
879	<	// Decrement total count, and if was running, running count
880	<	// Spin (waiting for other updates) if either would be negative
881	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
882	<	int unit = ONE_TOTAL + nr;
883	<	for (;;) {
884	<	int wc = workerCounts;
885	<	int rc = wc & RUNNING_COUNT_MASK;
747	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
748	<	Thread.yield(); // back off if waiting for other updates
749	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
750	<	wc, wc - unit))
751	<	break;
872	>	private void addSubmission(ForkJoinTask<?> t) {
873	>	final ReentrantLock lock = this.submissionLock;
874	>	lock.lock();
875	>	try {
876	>	ForkJoinTask<?>[] q; int s, m;
877	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
878	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
879	>	UNSAFE.putOrderedObject(q, u, t);
880	>	queueTop = s + 1;
881	>	if (s - queueBase == m)
882	>	growSubmissionQueue();
883	>	}
884	>	} finally {
885	>	lock.unlock();
886		}
887	<
754	<	accumulateStealCount(w); // collect final count
755	<	if (!tryTerminate(false))
756	<	ensureEnoughWorkers();
887	>	signalWork();
888		}
889
890	<	// Waiting for and signalling events
890	>	//  (pollSubmission is defined below with exported methods)
891
892		/**
893	<	* Releases workers blocked on a count not equal to current count.
894	<	* @return true if any released
893	>	* Creates or doubles submissionQueue array.
894	>	* Basically identical to ForkJoinWorkerThread version
895		*/
896	<	private void releaseWaiters() {
897	<	long top;
898	<	while ((top = eventWaiters) != 0L) {
899	<	ForkJoinWorkerThread[] ws = workers;
900	<	int n = ws.length;
901	<	for (;;) {
902	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
903	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
904	<	return;
905	<	ForkJoinWorkerThread w;
906	<	if (i < n && (w = ws[i]) != null &&
907	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
908	<	top, w.nextWaiter)) {
909	<	LockSupport.unpark(w);
910	<	top = eventWaiters;
911	<	}
912	<	else
913	<	break;      // possibly stale; reread
896	>	private void growSubmissionQueue() {
897	>	ForkJoinTask<?>[] oldQ = submissionQueue;
898	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
899	>	if (size > MAXIMUM_QUEUE_CAPACITY)
900	>	throw new RejectedExecutionException("Queue capacity exceeded");
901	>	if (size < INITIAL_QUEUE_CAPACITY)
902	>	size = INITIAL_QUEUE_CAPACITY;
903	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
904	>	int mask = size - 1;
905	>	int top = queueTop;
906	>	int oldMask;
907	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
908	>	for (int b = queueBase; b != top; ++b) {
909	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
910	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
911	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
912	>	UNSAFE.putObjectVolatile
913	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
914		}
915		}
916		}
917
918	+	// Blocking support
919	+
920		/**
921	<	* Ensures eventCount on exit is different (mod 2^32) than on
922	<	* entry and wakes up all waiters
921	>	* Tries to increment blockedCount, decrement active count
922	>	* (sometimes implicitly) and possibly release or create a
923	>	* compensating worker in preparation for blocking. Fails
924	>	* on contention or termination.
925	>	*
926	>	* @return true if the caller can block, else should recheck and retry
927		*/
928	<	private void signalEvent() {
929	<	int c;
930	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
931	<	c = eventCount, c+1));
932	<	releaseWaiters();
928	>	private boolean tryPreBlock() {
929	>	int b = blockedCount;
930	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
931	>	int pc = parallelism;
932	>	do {
933	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
934	>	int e, ac, tc, rc, i;
935	>	long c = ctl;
936	>	int u = (int)(c >>> 32);
937	>	if ((e = (int)c) < 0) {
938	>	// skip -- terminating
939	>	}
940	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
941	>	(ws = workers) != null &&
942	>	(i = ~e & SMASK) < ws.length &&
943	>	(w = ws[i]) != null) {
944	>	long nc = ((long)(w.nextWait & E_MASK) |
945	>	(c & (AC_MASK|TC_MASK)));
946	>	if (w.eventCount == e &&
947	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
948	>	w.eventCount = (e + EC_UNIT) & E_MASK;
949	>	if (w.parked)
950	>	UNSAFE.unpark(w);
951	>	return true;             // release an idle worker
952	>	}
953	>	}
954	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
955	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
956	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
957	>	return true;             // no compensation needed
958	>	}
959	>	else if (tc + pc < MAX_ID) {
960	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
961	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
962	>	addWorker();
963	>	return true;            // create a replacement
964	>	}
965	>	}
966	>	// try to back out on any failure and let caller retry
967	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
968	>	b = blockedCount, b - 1));
969	>	}
970	>	return false;
971		}
972
973		/**
974	<	* Advances eventCount and releases waiters until interference by
800	<	* other releasing threads is detected.
974	>	* Decrements blockedCount and increments active count
975		*/
976	<	final void signalWork() {
977	<	int c;
978	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
979	<	long top;
980	<	while ((top = eventWaiters) != 0L) {
981	<	int ec = eventCount;
982	<	ForkJoinWorkerThread[] ws = workers;
983	<	int n = ws.length;
984	<	for (;;) {
985	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
986	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
987	<	return;
988	<	ForkJoinWorkerThread w;
989	<	if (i < n && (w = ws[i]) != null &&
990	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
991	<	top, top = w.nextWaiter)) {
992	<	LockSupport.unpark(w);
993	<	if (top != eventWaiters) // let someone else take over
994	<	return;
995	<	}
996	<	else
997	<	break;      // possibly stale; reread
976	>	private void postBlock() {
977	>	long c;
978	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
979	>	c = ctl, c + AC_UNIT));
980	>	int b;
981	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
982	>	b = blockedCount, b - 1));
983	>	}
984	>
985	>	/**
986	>	* Possibly blocks waiting for the given task to complete, or
987	>	* cancels the task if terminating.  Fails to wait if contended.
988	>	*
989	>	* @param joinMe the task
990	>	*/
991	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
992	>	int s;
993	>	Thread.interrupted(); // clear interrupts before checking termination
994	>	if (joinMe.status >= 0) {
995	>	if (tryPreBlock()) {
996	>	joinMe.tryAwaitDone(0L);
997	>	postBlock();
998		}
999	+	if ((ctl & STOP_BIT) != 0L)
1000	+	joinMe.cancelIgnoringExceptions();
1001		}
1002		}
1003
1004		/**
1005	<	* If worker is inactive, blocks until terminating or event count
1006	<	* advances from last value held by worker; in any case helps
1007	<	* release others.
1008	<	*
1009	<	* @param w the calling worker thread
1010	<	* @param retries the number of scans by caller failing to find work
1011	<	* @return false if now too many threads running
1012	<	*/
1013	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
1014	<	int wec = w.lastEventCount;
1015	<	if (retries > 1) { // can only block after 2nd miss
1016	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
1017	<	((long)(w.poolIndex + 1)));
1018	<	long top;
1019	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
1020	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
1021	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
1022	<	eventCount == wec) {
1023	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1024	<	w.nextWaiter = top, nextTop)) {
1025	<	accumulateStealCount(w); // transfer steals while idle
1026	<	Thread.interrupted();    // clear/ignore interrupt
1027	<	while (eventCount == wec)
1028	<	w.doPark();
1029	<	break;
1005	>	* Possibly blocks the given worker waiting for joinMe to
1006	>	* complete or timeout
1007	>	*
1008	>	* @param joinMe the task
1009	>	* @param millis the wait time for underlying Object.wait
1010	>	*/
1011	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1012	>	while (joinMe.status >= 0) {
1013	>	Thread.interrupted();
1014	>	if ((ctl & STOP_BIT) != 0L) {
1015	>	joinMe.cancelIgnoringExceptions();
1016	>	break;
1017	>	}
1018	>	if (tryPreBlock()) {
1019	>	long last = System.nanoTime();
1020	>	while (joinMe.status >= 0) {
1021	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1022	>	if (millis <= 0)
1023	>	break;
1024	>	joinMe.tryAwaitDone(millis);
1025	>	if (joinMe.status < 0)
1026	>	break;
1027	>	if ((ctl & STOP_BIT) != 0L) {
1028	>	joinMe.cancelIgnoringExceptions();
1029	>	break;
1030	>	}
1031	>	long now = System.nanoTime();
1032	>	nanos -= now - last;
1033	>	last = now;
1034		}
1035	+	postBlock();
1036	+	break;
1037		}
856	–	wec = eventCount;
857	–	}
858	–	releaseWaiters();
859	–	int wc = workerCounts;
860	–	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
861	–	w.lastEventCount = wec;
862	–	return true;
1038		}
864	–	if (wec != w.lastEventCount) // back up if may re-wait
865	–	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	–	return false;
1039		}
1040
1041		/**
1042	<	* Callback from workers invoked upon each top-level action (i.e.,
871	<	* stealing a task or taking a submission and running
872	<	* it). Performs one or both of the following:
873	<	*
874	<	* * If the worker cannot find work, updates its active status to
875	<	* inactive and updates activeCount unless there is contention, in
876	<	* which case it may try again (either in this or a subsequent
877	<	* call).  Additionally, awaits the next task event and/or helps
878	<	* wake up other releasable waiters.
879	<	*
880	<	* * If there are too many running threads, suspends this worker
881	<	* (first forcing inactivation if necessary).  If it is not
882	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
883	<	* -- killed while suspended within suspendAsSpare. Otherwise,
884	<	* upon resume it rechecks to make sure that it is still needed.
885	<	*
886	<	* @param w the worker
887	<	* @param retries the number of scans by caller failing to find work
888	<	* find any (in which case it may block waiting for work).
1042	>	* If necessary, compensates for blocker, and blocks
1043		*/
1044	<	final void preStep(ForkJoinWorkerThread w, int retries) {
1045	<	boolean active = w.active;
1046	<	boolean inactivate = active && retries != 0;
1047	<	for (;;) {
1048	<	int rs, wc;
1049	<	if (inactivate &&
1050	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
1051	<	rs = runState, rs - ONE_ACTIVE))
1052	<	inactivate = active = w.active = false;
899	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
900	<	if (active || eventSync(w, retries))
901	<	break;
902	<	}
903	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
904	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
905	<	wc, wc - ONE_RUNNING) &&
906	<	!w.suspendAsSpare())             // false if trimmed
1044	>	private void awaitBlocker(ManagedBlocker blocker)
1045	>	throws InterruptedException {
1046	>	while (!blocker.isReleasable()) {
1047	>	if (tryPreBlock()) {
1048	>	try {
1049	>	do {} while (!blocker.isReleasable() && !blocker.block());
1050	>	} finally {
1051	>	postBlock();
1052	>	}
1053		break;
1054	+	}
1055		}
1056		}
1057
1058	+	// Creating, registering and deregistring workers
1059	+
1060		/**
1061	<	* Awaits join of the given task if enough threads, or can resume
1062	<	* or create a spare. Fails (in which case the given task might
914	<	* not be done) upon contention or lack of decision about
915	<	* blocking. Returns void because caller must check
916	<	* task status on return anyway.
917	<	*
918	<	* We allow blocking if:
919	<	*
920	<	* 1. There would still be at least as many running threads as
921	<	*    parallelism level if this thread blocks.
922	<	*
923	<	* 2. A spare is resumed to replace this worker. We tolerate
924	<	*    slop in the decision to replace if a spare is found without
925	<	*    first decrementing run count.  This may release too many,
926	<	*    but if so, the superfluous ones will re-suspend via
927	<	*    preStep().
928	<	*
929	<	* 3. After #spares repeated checks, there are no fewer than #spare
930	<	*    threads not running. We allow this slack to avoid hysteresis
931	<	*    and as a hedge against lag/uncertainty of running count
932	<	*    estimates when signalling or unblocking stalls.
933	<	*
934	<	* 4. All existing workers are busy (as rechecked via repeated
935	<	*    retries by caller) and a new spare is created.
936	<	*
937	<	* If none of the above hold, we try to escape out by
938	<	* re-incrementing count and returning to caller, which can retry
939	<	* later.
940	<	*
941	<	* @param joinMe the task to join
942	<	* @param retries if negative, then serve only as a precheck
943	<	*   that the thread can be replaced by a spare. Otherwise,
944	<	*   the number of repeated calls to this method returning busy
945	<	* @return true if the call must be retried because there
946	<	*   none of the blocking checks hold
1061	>	* Tries to create and start a worker; minimally rolls back counts
1062	>	* on failure.
1063		*/
1064	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
1065	<	if (joinMe.status < 0) // precheck for cancellation
1066	<	return false;
1067	<	if ((runState & TERMINATING) != 0) { // shutting down
1068	<	joinMe.cancelIgnoringExceptions();
1069	<	return false;
1064	>	private void addWorker() {
1065	>	Throwable ex = null;
1066	>	ForkJoinWorkerThread t = null;
1067	>	try {
1068	>	t = factory.newThread(this);
1069	>	} catch (Throwable e) {
1070	>	ex = e;
1071	>	}
1072	>	if (t == null) {  // null or exceptional factory return
1073	>	long c;       // adjust counts
1074	>	do {} while (!UNSAFE.compareAndSwapLong
1075	>	(this, ctlOffset, c = ctl,
1076	>	(((c - AC_UNIT) & AC_MASK) |
1077	>	((c - TC_UNIT) & TC_MASK) |
1078	>	(c & ~(AC_MASK|TC_MASK)))));
1079	>	// Propagate exception if originating from an external caller
1080	>	if (!tryTerminate(false) && ex != null &&
1081	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1082	>	UNSAFE.throwException(ex);
1083		}
1084	+	else
1085	+	t.start();
1086	+	}
1087
1088	<	int pc = parallelism;
1089	<	boolean running = true; // false when running count decremented
1090	<	outer:for (;;) {
1091	<	int wc = workerCounts;
1092	<	int rc = wc & RUNNING_COUNT_MASK;
1093	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1094	<	if (running) { // replace with spare or decrement count
1095	<	if (rc <= pc && tc > pc &&
1096	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
965	<	ForkJoinWorkerThread[] ws = workers;
966	<	int nws = ws.length;
967	<	for (int i = 0; i < nws; ++i) { // search for spare
968	<	ForkJoinWorkerThread w = ws[i];
969	<	if (w != null) {
970	<	if (joinMe.status < 0)
971	<	return false;
972	<	if (w.isSuspended()) {
973	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
974	<	w.tryResumeSpare()) {
975	<	running = false;
976	<	break outer;
977	<	}
978	<	continue outer; // rescan
979	<	}
980	<	}
981	<	}
982	<	}
983	<	if (retries < 0 || // < 0 means replacement check only
984	<	rc == 0 || joinMe.status < 0 || workerCounts != wc ||
985	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
986	<	wc, wc - ONE_RUNNING))
987	<	return false; // done or inconsistent or contended
988	<	running = false;
989	<	if (rc > pc)
990	<	break;
991	<	}
992	<	else { // allow blocking if enough threads
993	<	if (rc >= pc || joinMe.status < 0)
994	<	break;
995	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
996	<	if (retries > sc) {
997	<	if (rc > 0 && rc >= pc - sc) // allow slack
998	<	break;
999	<	if (tc < MAX_THREADS &&
1000	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1001	<	workerCounts == wc &&
1002	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1003	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1004	<	addWorker();
1005	<	break;
1006	<	}
1007	<	}
1008	<	if (workerCounts == wc &&        // back out to allow rescan
1009	<	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1010	<	wc, wc + ONE_RUNNING)) {
1011	<	releaseWaiters();            // help others progress
1012	<	return true;                 // let caller retry
1013	<	}
1014	<	}
1088	>	/**
1089	>	* Callback from ForkJoinWorkerThread constructor to assign a
1090	>	* public name
1091	>	*/
1092	>	final String nextWorkerName() {
1093	>	for (int n;;) {
1094	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1095	>	n = nextWorkerNumber, ++n))
1096	>	return workerNamePrefix + n;
1097		}
1016	–	// arrive here if can block
1017	–	joinMe.internalAwaitDone();
1018	–	int c;                      // to inline incrementRunningCount
1019	–	do {} while (!UNSAFE.compareAndSwapInt
1020	–	(this, workerCountsOffset,
1021	–	c = workerCounts, c + ONE_RUNNING));
1022	–	return false;
1098		}
1099
1100		/**
1101	<	* Same idea as (and shares many code snippets with) tryAwaitJoin,
1102	<	* but self-contained because there are no caller retries.
1103	<	* TODO: Rework to use simpler API.
1101	>	* Callback from ForkJoinWorkerThread constructor to
1102	>	* determine its poolIndex and record in workers array.
1103	>	*
1104	>	* @param w the worker
1105	>	* @return the worker's pool index
1106		*/
1107	<	final void awaitBlocker(ManagedBlocker blocker)
1108	<	throws InterruptedException {
1109	<	boolean done;
1110	<	if (done = blocker.isReleasable())
1111	<	return;
1112	<	int pc = parallelism;
1113	<	int retries = 0;
1114	<	boolean running = true; // false when running count decremented
1115	<	outer:for (;;) {
1116	<	int wc = workerCounts;
1117	<	int rc = wc & RUNNING_COUNT_MASK;
1118	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1119	<	if (running) {
1120	<	if (rc <= pc && tc > pc &&
1121	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1122	<	ForkJoinWorkerThread[] ws = workers;
1123	<	int nws = ws.length;
1124	<	for (int i = 0; i < nws; ++i) {
1125	<	ForkJoinWorkerThread w = ws[i];
1126	<	if (w != null) {
1127	<	if (done = blocker.isReleasable())
1128	<	return;
1129	<	if (w.isSuspended()) {
1053	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1054	<	w.tryResumeSpare()) {
1055	<	running = false;
1056	<	break outer;
1057	<	}
1058	<	continue outer; // rescan
1059	<	}
1107	>	final int registerWorker(ForkJoinWorkerThread w) {
1108	>	/*
1109	>	* In the typical case, a new worker acquires the lock, uses
1110	>	* next available index and returns quickly.  Since we should
1111	>	* not block callers (ultimately from signalWork or
1112	>	* tryPreBlock) waiting for the lock needed to do this, we
1113	>	* instead help release other workers while waiting for the
1114	>	* lock.
1115	>	*/
1116	>	for (int g;;) {
1117	>	ForkJoinWorkerThread[] ws;
1118	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1119	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1120	>	g, g | SG_UNIT)) {
1121	>	int k = nextWorkerIndex;
1122	>	try {
1123	>	if ((ws = workers) != null) { // ignore on shutdown
1124	>	int n = ws.length;
1125	>	if (k < 0 || k >= n || ws[k] != null) {
1126	>	for (k = 0; k < n && ws[k] != null; ++k)
1127	>	;
1128	>	if (k == n)
1129	>	ws = workers = Arrays.copyOf(ws, n << 1);
1130		}
1131	+	ws[k] = w;
1132	+	nextWorkerIndex = k + 1;
1133	+	int m = g & SMASK;
1134	+	g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1135		}
1136	+	} finally {
1137	+	scanGuard = g;
1138		}
1139	<	if (done = blocker.isReleasable())
1064	<	return;
1065	<	if (rc == 0 || workerCounts != wc ||
1066	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1067	<	wc, wc - ONE_RUNNING))
1068	<	continue;
1069	<	running = false;
1070	<	if (rc > pc)
1071	<	break;
1139	>	return k;
1140		}
1141	<	else {
1142	<	if (rc >= pc || (done = blocker.isReleasable()))
1143	<	break;
1144	<	int sc = tc - pc + 1;
1145	<	if (retries++ > sc) {
1078	<	if (rc > 0 && rc >= pc - sc)
1079	<	break;
1080	<	if (tc < MAX_THREADS &&
1081	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1082	<	workerCounts == wc &&
1083	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1084	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1085	<	addWorker();
1086	<	break;
1141	>	else if ((ws = workers) != null) { // help release others
1142	>	for (ForkJoinWorkerThread u : ws) {
1143	>	if (u != null && u.queueBase != u.queueTop) {
1144	>	if (tryReleaseWaiter())
1145	>	break;
1146		}
1147		}
1089	–	Thread.yield();
1148		}
1149		}
1150	+	}
1151
1152	<	try {
1153	<	if (!done)
1154	<	do {} while (!blocker.isReleasable() && !blocker.block());
1155	<	} finally {
1156	<	if (!running) {
1157	<	int c;
1158	<	do {} while (!UNSAFE.compareAndSwapInt
1159	<	(this, workerCountsOffset,
1160	<	c = workerCounts, c + ONE_RUNNING));
1152	>	/**
1153	>	* Final callback from terminating worker.  Removes record of
1154	>	* worker from array, and adjusts counts. If pool is shutting
1155	>	* down, tries to complete termination.
1156	>	*
1157	>	* @param w the worker
1158	>	*/
1159	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1160	>	int idx = w.poolIndex;
1161	>	int sc = w.stealCount;
1162	>	int steps = 0;
1163	>	// Remove from array, adjust worker counts and collect steal count.
1164	>	// We can intermix failed removes or adjusts with steal updates
1165	>	do {
1166	>	long s, c;
1167	>	int g;
1168	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1169	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1170	>	g, g |= SG_UNIT)) {
1171	>	ForkJoinWorkerThread[] ws = workers;
1172	>	if (ws != null && idx >= 0 &&
1173	>	idx < ws.length && ws[idx] == w)
1174	>	ws[idx] = null;    // verify
1175	>	nextWorkerIndex = idx;
1176	>	scanGuard = g + SG_UNIT;
1177	>	steps = 1;
1178		}
1179	+	if (steps == 1 &&
1180	+	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1181	+	(((c - AC_UNIT) & AC_MASK) |
1182	+	((c - TC_UNIT) & TC_MASK) |
1183	+	(c & ~(AC_MASK|TC_MASK)))))
1184	+	steps = 2;
1185	+	if (sc != 0 &&
1186	+	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1187	+	s = stealCount, s + sc))
1188	+	sc = 0;
1189	+	} while (steps != 2 || sc != 0);
1190	+	if (!tryTerminate(false)) {
1191	+	if (ex != null)   // possibly replace if died abnormally
1192	+	signalWork();
1193	+	else
1194	+	tryReleaseWaiter();
1195		}
1196		}
1197
1198	+	// Shutdown and termination
1199	+
1200		/**
1201		* Possibly initiates and/or completes termination.
1202		*
#	Line 1111 | Line 1205 | public class ForkJoinPool extends Abstra
1205		* @return true if now terminating or terminated
1206		*/
1207		private boolean tryTerminate(boolean now) {
1208	<	if (now)
1209	<	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1210	<	else if (runState < SHUTDOWN ||
1211	<	!submissionQueue.isEmpty() ||
1212	<	(runState & ACTIVE_COUNT_MASK) != 0)
1213	<	return false;
1214	<
1215	<	if (advanceRunLevel(TERMINATING))
1216	<	startTerminating();
1217	<
1218	<	// Finish now if all threads terminated; else in some subsequent call
1219	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1220	<	advanceRunLevel(TERMINATED);
1221	<	termination.arrive();
1208	>	long c;
1209	>	while (((c = ctl) & STOP_BIT) == 0) {
1210	>	if (!now) {
1211	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1212	>	return false;
1213	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1214	>	queueTop - queueBase > 0) {
1215	>	if (ctl == c) // staleness check
1216	>	return false;
1217	>	continue;
1218	>	}
1219	>	}
1220	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1221	>	startTerminating();
1222	>	}
1223	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
1224	>	submissionLock.lock();
1225	>	termination.signalAll();
1226	>	submissionLock.unlock();
1227		}
1228		return true;
1229		}
1230
1231		/**
1232	<	* Actions on transition to TERMINATING
1232	>	* Runs up to three passes through workers: (0) Setting
1233	>	* termination status for each worker, followed by wakeups up
1234	>	* queued workers (1) helping cancel tasks (2) interrupting
1235	>	* lagging threads (likely in external tasks, but possibly also
1236	>	* blocked in joins).  Each pass repeats previous steps because of
1237	>	* potential lagging thread creation.
1238		*/
1239		private void startTerminating() {
1240	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1241	<	cancelSubmissions();
1242	<	shutdownWorkers();
1243	<	cancelWorkerTasks();
1244	<	signalEvent();
1245	<	interruptWorkers();
1240	>	cancelSubmissions();
1241	>	for (int pass = 0; pass < 3; ++pass) {
1242	>	ForkJoinWorkerThread[] ws = workers;
1243	>	if (ws != null) {
1244	>	for (ForkJoinWorkerThread w : ws) {
1245	>	if (w != null) {
1246	>	w.terminate = true;
1247	>	if (pass > 0) {
1248	>	w.cancelTasks();
1249	>	if (pass > 1 && !w.isInterrupted()) {
1250	>	try {
1251	>	w.interrupt();
1252	>	} catch (SecurityException ignore) {
1253	>	}
1254	>	}
1255	>	}
1256	>	}
1257	>	}
1258	>	terminateWaiters();
1259	>	}
1260		}
1261		}
1262
1263		/**
1264	<	* Clear out and cancel submissions, ignoring exceptions
1264	>	* Polls and cancels all submissions. Called only during termination.
1265		*/
1266		private void cancelSubmissions() {
1267	<	ForkJoinTask<?> task;
1268	<	while ((task = submissionQueue.poll()) != null) {
1269	<	try {
1270	<	task.cancel(false);
1271	<	} catch (Throwable ignore) {
1267	>	while (queueBase != queueTop) {
1268	>	ForkJoinTask<?> task = pollSubmission();
1269	>	if (task != null) {
1270	>	try {
1271	>	task.cancel(false);
1272	>	} catch (Throwable ignore) {
1273	>	}
1274		}
1275		}
1276		}
1277
1278		/**
1279	<	* Sets all worker run states to at least shutdown,
1280	<	* also resuming suspended workers
1161	<	*/
1162	<	private void shutdownWorkers() {
1163	<	ForkJoinWorkerThread[] ws = workers;
1164	<	int nws = ws.length;
1165	<	for (int i = 0; i < nws; ++i) {
1166	<	ForkJoinWorkerThread w = ws[i];
1167	<	if (w != null)
1168	<	w.shutdown();
1169	<	}
1170	<	}
1171	<
1172	<	/**
1173	<	* Clears out and cancels all locally queued tasks
1174	<	*/
1175	<	private void cancelWorkerTasks() {
1176	<	ForkJoinWorkerThread[] ws = workers;
1177	<	int nws = ws.length;
1178	<	for (int i = 0; i < nws; ++i) {
1179	<	ForkJoinWorkerThread w = ws[i];
1180	<	if (w != null)
1181	<	w.cancelTasks();
1182	<	}
1183	<	}
1184	<
1185	<	/**
1186	<	* Unsticks all workers blocked on joins etc
1279	>	* Tries to set the termination status of waiting workers, and
1280	>	* then wake them up (after which they will terminate).
1281		*/
1282	<	private void interruptWorkers() {
1282	>	private void terminateWaiters() {
1283		ForkJoinWorkerThread[] ws = workers;
1284	<	int nws = ws.length;
1285	<	for (int i = 0; i < nws; ++i) {
1286	<	ForkJoinWorkerThread w = ws[i];
1287	<	if (w != null && !w.isTerminated()) {
1288	<	try {
1289	<	w.interrupt();
1290	<	} catch (SecurityException ignore) {
1284	>	if (ws != null) {
1285	>	ForkJoinWorkerThread w; long c; int i, e;
1286	>	int n = ws.length;
1287	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1288	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1289	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1290	>	(long)(w.nextWait & E_MASK) |
1291	>	((c + AC_UNIT) & AC_MASK) |
1292	>	(c & (TC_MASK|STOP_BIT)))) {
1293	>	w.terminate = true;
1294	>	w.eventCount = e + EC_UNIT;
1295	>	if (w.parked)
1296	>	UNSAFE.unpark(w);
1297		}
1298		}
1299		}
1300		}
1301
1302	<	// misc support for ForkJoinWorkerThread
1302	>	// misc ForkJoinWorkerThread support
1303
1304		/**
1305	<	* Returns pool number
1305	>	* Increment or decrement quiescerCount. Needed only to prevent
1306	>	* triggering shutdown if a worker is transiently inactive while
1307	>	* checking quiescence.
1308	>	*
1309	>	* @param delta 1 for increment, -1 for decrement
1310		*/
1311	<	final int getPoolNumber() {
1312	<	return poolNumber;
1311	>	final void addQuiescerCount(int delta) {
1312	>	int c;
1313	>	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1314	>	c = quiescerCount, c + delta));
1315		}
1316
1317		/**
1318	<	* Accumulates steal count from a worker, clearing
1319	<	* the worker's value
1318	>	* Directly increment or decrement active count without
1319	>	* queuing. This method is used to transiently assert inactivation
1320	>	* while checking quiescence.
1321	>	*
1322	>	* @param delta 1 for increment, -1 for decrement
1323		*/
1324	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1325	<	int sc = w.stealCount;
1326	<	if (sc != 0) {
1327	<	long c;
1328	<	w.stealCount = 0;
1329	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1221	<	c = stealCount, c + sc));
1222	<	}
1324	>	final void addActiveCount(int delta) {
1325	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1326	>	long c;
1327	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1328	>	((c + d) & AC_MASK) |
1329	>	(c & ~AC_MASK)));
1330		}
1331
1332		/**
#	Line 1227 | Line 1334 | public class ForkJoinPool extends Abstra
1334		* active thread.
1335		*/
1336		final int idlePerActive() {
1337	<	int pc = parallelism; // use parallelism, not rc
1338	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1339	<	// Use exact results for small values, saturate past 4
1340	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1337	>	// Approximate at powers of two for small values, saturate past 4
1338	>	int p = parallelism;
1339	>	int a = p + (int)(ctl >> AC_SHIFT);
1340	>	return (a > (p >>>= 1) ? 0 :
1341	>	a > (p >>>= 1) ? 1 :
1342	>	a > (p >>>= 1) ? 2 :
1343	>	a > (p >>>= 1) ? 4 :
1344	>	8);
1345		}
1346
1347	<	// Public and protected methods
1347	>	// Exported methods
1348
1349		// Constructors
1350
#	Line 1280 | Line 1391 | public class ForkJoinPool extends Abstra
1391		* use {@link #defaultForkJoinWorkerThreadFactory}.
1392		* @param handler the handler for internal worker threads that
1393		* terminate due to unrecoverable errors encountered while executing
1394	<	* tasks. For default value, use <code>null</code>.
1394	>	* tasks. For default value, use {@code null}.
1395		* @param asyncMode if true,
1396		* establishes local first-in-first-out scheduling mode for forked
1397		* tasks that are never joined. This mode may be more appropriate
1398		* than default locally stack-based mode in applications in which
1399		* worker threads only process event-style asynchronous tasks.
1400	<	* For default value, use <code>false</code>.
1400	>	* For default value, use {@code false}.
1401		* @throws IllegalArgumentException if parallelism less than or
1402		*         equal to zero, or greater than implementation limit
1403		* @throws NullPointerException if the factory is null
#	Line 1302 | Line 1413 | public class ForkJoinPool extends Abstra
1413		checkPermission();
1414		if (factory == null)
1415		throw new NullPointerException();
1416	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1416	>	if (parallelism <= 0 || parallelism > MAX_ID)
1417		throw new IllegalArgumentException();
1418		this.parallelism = parallelism;
1419		this.factory = factory;
1420		this.ueh = handler;
1421		this.locallyFifo = asyncMode;
1422	<	int arraySize = initialArraySizeFor(parallelism);
1423	<	this.workers = new ForkJoinWorkerThread[arraySize];
1424	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1425	<	this.workerLock = new ReentrantLock();
1426	<	this.termination = new Phaser(1);
1427	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
1428	<	}
1429	<
1430	<	/**
1431	<	* Returns initial power of two size for workers array.
1432	<	* @param pc the initial parallelism level
1433	<	*/
1434	<	private static int initialArraySizeFor(int pc) {
1435	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1436	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1437	<	size |= size >>> 1;
1438	<	size |= size >>> 2;
1328	<	size |= size >>> 4;
1329	<	size |= size >>> 8;
1330	<	return size + 1;
1422	>	long np = (long)(-parallelism); // offset ctl counts
1423	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1424	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1425	>	// initialize workers array with room for 2*parallelism if possible
1426	>	int n = parallelism << 1;
1427	>	if (n >= MAX_ID)
1428	>	n = MAX_ID;
1429	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1430	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1431	>	}
1432	>	workers = new ForkJoinWorkerThread[n + 1];
1433	>	this.submissionLock = new ReentrantLock();
1434	>	this.termination = submissionLock.newCondition();
1435	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1436	>	sb.append(poolNumberGenerator.incrementAndGet());
1437	>	sb.append("-worker-");
1438	>	this.workerNamePrefix = sb.toString();
1439		}
1440
1441		// Execution methods
1442
1443		/**
1336	–	* Common code for execute, invoke and submit
1337	–	*/
1338	–	private <T> void doSubmit(ForkJoinTask<T> task) {
1339	–	if (task == null)
1340	–	throw new NullPointerException();
1341	–	if (runState >= SHUTDOWN)
1342	–	throw new RejectedExecutionException();
1343	–	submissionQueue.offer(task);
1344	–	signalEvent();
1345	–	ensureEnoughWorkers();
1346	–	}
1347	–
1348	–	/**
1444		* Performs the given task, returning its result upon completion.
1445	<	* If the caller is already engaged in a fork/join computation in
1446	<	* the current pool, this method is equivalent in effect to
1447	<	* {@link ForkJoinTask#invoke}.
1445	>	* If the computation encounters an unchecked Exception or Error,
1446	>	* it is rethrown as the outcome of this invocation.  Rethrown
1447	>	* exceptions behave in the same way as regular exceptions, but,
1448	>	* when possible, contain stack traces (as displayed for example
1449	>	* using {@code ex.printStackTrace()}) of both the current thread
1450	>	* as well as the thread actually encountering the exception;
1451	>	* minimally only the latter.
1452		*
1453		* @param task the task
1454		* @return the task's result
#	Line 1358 | Line 1457 | public class ForkJoinPool extends Abstra
1457		*         scheduled for execution
1458		*/
1459		public <T> T invoke(ForkJoinTask<T> task) {
1460	<	doSubmit(task);
1461	<	return task.join();
1460	>	Thread t = Thread.currentThread();
1461	>	if (task == null)
1462	>	throw new NullPointerException();
1463	>	if (shutdown)
1464	>	throw new RejectedExecutionException();
1465	>	if ((t instanceof ForkJoinWorkerThread) &&
1466	>	((ForkJoinWorkerThread)t).pool == this)
1467	>	return task.invoke();  // bypass submit if in same pool
1468	>	else {
1469	>	addSubmission(task);
1470	>	return task.join();
1471	>	}
1472	>	}
1473	>
1474	>	/**
1475	>	* Unless terminating, forks task if within an ongoing FJ
1476	>	* computation in the current pool, else submits as external task.
1477	>	*/
1478	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1479	>	ForkJoinWorkerThread w;
1480	>	Thread t = Thread.currentThread();
1481	>	if (shutdown)
1482	>	throw new RejectedExecutionException();
1483	>	if ((t instanceof ForkJoinWorkerThread) &&
1484	>	(w = (ForkJoinWorkerThread)t).pool == this)
1485	>	w.pushTask(task);
1486	>	else
1487	>	addSubmission(task);
1488		}
1489
1490		/**
1491		* Arranges for (asynchronous) execution of the given task.
1367	–	* If the caller is already engaged in a fork/join computation in
1368	–	* the current pool, this method is equivalent in effect to
1369	–	* {@link ForkJoinTask#fork}.
1492		*
1493		* @param task the task
1494		* @throws NullPointerException if the task is null
#	Line 1374 | Line 1496 | public class ForkJoinPool extends Abstra
1496		*         scheduled for execution
1497		*/
1498		public void execute(ForkJoinTask<?> task) {
1499	<	doSubmit(task);
1499	>	if (task == null)
1500	>	throw new NullPointerException();
1501	>	forkOrSubmit(task);
1502		}
1503
1504		// AbstractExecutorService methods
#	Line 1385 | Line 1509 | public class ForkJoinPool extends Abstra
1509		*         scheduled for execution
1510		*/
1511		public void execute(Runnable task) {
1512	+	if (task == null)
1513	+	throw new NullPointerException();
1514		ForkJoinTask<?> job;
1515		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1516		job = (ForkJoinTask<?>) task;
1517		else
1518		job = ForkJoinTask.adapt(task, null);
1519	<	doSubmit(job);
1519	>	forkOrSubmit(job);
1520		}
1521
1522		/**
1523		* Submits a ForkJoinTask for execution.
1398	–	* If the caller is already engaged in a fork/join computation in
1399	–	* the current pool, this method is equivalent in effect to
1400	–	* {@link ForkJoinTask#fork}.
1524		*
1525		* @param task the task to submit
1526		* @return the task
#	Line 1406 | Line 1529 | public class ForkJoinPool extends Abstra
1529		*         scheduled for execution
1530		*/
1531		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1532	<	doSubmit(task);
1532	>	if (task == null)
1533	>	throw new NullPointerException();
1534	>	forkOrSubmit(task);
1535		return task;
1536		}
1537
#	Line 1416 | Line 1541 | public class ForkJoinPool extends Abstra
1541		*         scheduled for execution
1542		*/
1543		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1544	+	if (task == null)
1545	+	throw new NullPointerException();
1546		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1547	<	doSubmit(job);
1547	>	forkOrSubmit(job);
1548		return job;
1549		}
1550
#	Line 1427 | Line 1554 | public class ForkJoinPool extends Abstra
1554		*         scheduled for execution
1555		*/
1556		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1557	+	if (task == null)
1558	+	throw new NullPointerException();
1559		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1560	<	doSubmit(job);
1560	>	forkOrSubmit(job);
1561		return job;
1562		}
1563
#	Line 1438 | Line 1567 | public class ForkJoinPool extends Abstra
1567		*         scheduled for execution
1568		*/
1569		public ForkJoinTask<?> submit(Runnable task) {
1570	+	if (task == null)
1571	+	throw new NullPointerException();
1572		ForkJoinTask<?> job;
1573		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1574		job = (ForkJoinTask<?>) task;
1575		else
1576		job = ForkJoinTask.adapt(task, null);
1577	<	doSubmit(job);
1577	>	forkOrSubmit(job);
1578		return job;
1579		}
1580
#	Line 1503 | Line 1634 | public class ForkJoinPool extends Abstra
1634
1635		/**
1636		* Returns the number of worker threads that have started but not
1637	<	* yet terminated.  This result returned by this method may differ
1637	>	* yet terminated.  The result returned by this method may differ
1638		* from {@link #getParallelism} when threads are created to
1639		* maintain parallelism when others are cooperatively blocked.
1640		*
1641		* @return the number of worker threads
1642		*/
1643		public int getPoolSize() {
1644	<	return workerCounts >>> TOTAL_COUNT_SHIFT;
1644	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1645		}
1646
1647		/**
#	Line 1532 | Line 1663 | public class ForkJoinPool extends Abstra
1663		* @return the number of worker threads
1664		*/
1665		public int getRunningThreadCount() {
1666	<	return workerCounts & RUNNING_COUNT_MASK;
1666	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1667	>	return r <= 0? 0 : r; // suppress momentarily negative values
1668		}
1669
1670		/**
#	Line 1543 | Line 1675 | public class ForkJoinPool extends Abstra
1675		* @return the number of active threads
1676		*/
1677		public int getActiveThreadCount() {
1678	<	return runState & ACTIVE_COUNT_MASK;
1678	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1679	>	return r <= 0? 0 : r; // suppress momentarily negative values
1680		}
1681
1682		/**
#	Line 1558 | Line 1691 | public class ForkJoinPool extends Abstra
1691		* @return {@code true} if all threads are currently idle
1692		*/
1693		public boolean isQuiescent() {
1694	<	return (runState & ACTIVE_COUNT_MASK) == 0;
1694	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1695		}
1696
1697		/**
#	Line 1588 | Line 1721 | public class ForkJoinPool extends Abstra
1721		*/
1722		public long getQueuedTaskCount() {
1723		long count = 0;
1724	<	ForkJoinWorkerThread[] ws = workers;
1725	<	int nws = ws.length;
1726	<	for (int i = 0; i < nws; ++i) {
1727	<	ForkJoinWorkerThread w = ws[i];
1728	<	if (w != null)
1729	<	count += w.getQueueSize();
1724	>	ForkJoinWorkerThread[] ws;
1725	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1726	>	(ws = workers) != null) {
1727	>	for (ForkJoinWorkerThread w : ws)
1728	>	if (w != null)
1729	>	count -= w.queueBase - w.queueTop; // must read base first
1730		}
1731		return count;
1732		}
1733
1734		/**
1735		* Returns an estimate of the number of tasks submitted to this
1736	<	* pool that have not yet begun executing.  This method takes time
1737	<	* proportional to the number of submissions.
1736	>	* pool that have not yet begun executing.  This method may take
1737	>	* time proportional to the number of submissions.
1738		*
1739		* @return the number of queued submissions
1740		*/
1741		public int getQueuedSubmissionCount() {
1742	<	return submissionQueue.size();
1742	>	return -queueBase + queueTop;
1743		}
1744
1745		/**
#	Line 1616 | Line 1749 | public class ForkJoinPool extends Abstra
1749		* @return {@code true} if there are any queued submissions
1750		*/
1751		public boolean hasQueuedSubmissions() {
1752	<	return !submissionQueue.isEmpty();
1752	>	return queueBase != queueTop;
1753		}
1754
1755		/**
#	Line 1627 | Line 1760 | public class ForkJoinPool extends Abstra
1760		* @return the next submission, or {@code null} if none
1761		*/
1762		protected ForkJoinTask<?> pollSubmission() {
1763	<	return submissionQueue.poll();
1763	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1764	>	while ((b = queueBase) != queueTop &&
1765	>	(q = submissionQueue) != null &&
1766	>	(i = (q.length - 1) & b) >= 0) {
1767	>	long u = (i << ASHIFT) + ABASE;
1768	>	if ((t = q[i]) != null &&
1769	>	queueBase == b &&
1770	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1771	>	queueBase = b + 1;
1772	>	return t;
1773	>	}
1774	>	}
1775	>	return null;
1776		}
1777
1778		/**
#	Line 1648 | Line 1793 | public class ForkJoinPool extends Abstra
1793		* @return the number of elements transferred
1794		*/
1795		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1651	–	int n = submissionQueue.drainTo(c);
1652	–	ForkJoinWorkerThread[] ws = workers;
1653	–	int nws = ws.length;
1654	–	for (int i = 0; i < nws; ++i) {
1655	–	ForkJoinWorkerThread w = ws[i];
1656	–	if (w != null)
1657	–	n += w.drainTasksTo(c);
1658	–	}
1659	–	return n;
1660	–	}
1661	–
1662	–	/**
1663	–	* Returns count of total parks by existing workers.
1664	–	* Used during development only since not meaningful to users.
1665	–	*/
1666	–	private int collectParkCount() {
1796		int count = 0;
1797	<	ForkJoinWorkerThread[] ws = workers;
1798	<	int nws = ws.length;
1799	<	for (int i = 0; i < nws; ++i) {
1800	<	ForkJoinWorkerThread w = ws[i];
1801	<	if (w != null)
1802	<	count += w.parkCount;
1797	>	while (queueBase != queueTop) {
1798	>	ForkJoinTask<?> t = pollSubmission();
1799	>	if (t != null) {
1800	>	c.add(t);
1801	>	++count;
1802	>	}
1803	>	}
1804	>	ForkJoinWorkerThread[] ws;
1805	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1806	>	(ws = workers) != null) {
1807	>	for (ForkJoinWorkerThread w : ws)
1808	>	if (w != null)
1809	>	count += w.drainTasksTo(c);
1810		}
1811		return count;
1812		}
#	Line 1686 | Line 1822 | public class ForkJoinPool extends Abstra
1822		long st = getStealCount();
1823		long qt = getQueuedTaskCount();
1824		long qs = getQueuedSubmissionCount();
1689	–	int wc = workerCounts;
1690	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
1691	–	int rc = wc & RUNNING_COUNT_MASK;
1825		int pc = parallelism;
1826	<	int rs = runState;
1827	<	int ac = rs & ACTIVE_COUNT_MASK;
1828	<	//        int pk = collectParkCount();
1826	>	long c = ctl;
1827	>	int tc = pc + (short)(c >>> TC_SHIFT);
1828	>	int rc = pc + (int)(c >> AC_SHIFT);
1829	>	if (rc < 0) // ignore transient negative
1830	>	rc = 0;
1831	>	int ac = rc + blockedCount;
1832	>	String level;
1833	>	if ((c & STOP_BIT) != 0)
1834	>	level = (tc == 0)? "Terminated" : "Terminating";
1835	>	else
1836	>	level = shutdown? "Shutting down" : "Running";
1837		return super.toString() +
1838	<	"[" + runLevelToString(rs) +
1838	>	"[" + level +
1839		", parallelism = " + pc +
1840		", size = " + tc +
1841		", active = " + ac +
#	Line 1702 | Line 1843 | public class ForkJoinPool extends Abstra
1843		", steals = " + st +
1844		", tasks = " + qt +
1845		", submissions = " + qs +
1705	–	//            ", parks = " + pk +
1846		"]";
1847		}
1848
1709	–	private static String runLevelToString(int s) {
1710	–	return ((s & TERMINATED) != 0 ? "Terminated" :
1711	–	((s & TERMINATING) != 0 ? "Terminating" :
1712	–	((s & SHUTDOWN) != 0 ? "Shutting down" :
1713	–	"Running")));
1714	–	}
1715	–
1849		/**
1850		* Initiates an orderly shutdown in which previously submitted
1851		* tasks are executed, but no new tasks will be accepted.
#	Line 1727 | Line 1860 | public class ForkJoinPool extends Abstra
1860		*/
1861		public void shutdown() {
1862		checkPermission();
1863	<	advanceRunLevel(SHUTDOWN);
1863	>	shutdown = true;
1864		tryTerminate(false);
1865		}
1866
#	Line 1749 | Line 1882 | public class ForkJoinPool extends Abstra
1882		*/
1883		public List<Runnable> shutdownNow() {
1884		checkPermission();
1885	+	shutdown = true;
1886		tryTerminate(true);
1887		return Collections.emptyList();
1888		}
#	Line 1759 | Line 1893 | public class ForkJoinPool extends Abstra
1893		* @return {@code true} if all tasks have completed following shut down
1894		*/
1895		public boolean isTerminated() {
1896	<	return runState >= TERMINATED;
1896	>	long c = ctl;
1897	>	return ((c & STOP_BIT) != 0L &&
1898	>	(short)(c >>> TC_SHIFT) == -parallelism);
1899		}
1900
1901		/**
#	Line 1767 | Line 1903 | public class ForkJoinPool extends Abstra
1903		* commenced but not yet completed.  This method may be useful for
1904		* debugging. A return of {@code true} reported a sufficient
1905		* period after shutdown may indicate that submitted tasks have
1906	<	* ignored or suppressed interruption, causing this executor not
1907	<	* to properly terminate.
1906	>	* ignored or suppressed interruption, or are waiting for IO,
1907	>	* causing this executor not to properly terminate. (See the
1908	>	* advisory notes for class {@link ForkJoinTask} stating that
1909	>	* tasks should not normally entail blocking operations.  But if
1910	>	* they do, they must abort them on interrupt.)
1911		*
1912		* @return {@code true} if terminating but not yet terminated
1913		*/
1914		public boolean isTerminating() {
1915	<	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1915	>	long c = ctl;
1916	>	return ((c & STOP_BIT) != 0L &&
1917	>	(short)(c >>> TC_SHIFT) != -parallelism);
1918	>	}
1919	>
1920	>	/**
1921	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1922	>	*/
1923	>	final boolean isAtLeastTerminating() {
1924	>	return (ctl & STOP_BIT) != 0L;
1925		}
1926
1927		/**
#	Line 1782 | Line 1930 | public class ForkJoinPool extends Abstra
1930		* @return {@code true} if this pool has been shut down
1931		*/
1932		public boolean isShutdown() {
1933	<	return runState >= SHUTDOWN;
1933	>	return shutdown;
1934		}
1935
1936		/**
#	Line 1798 | Line 1946 | public class ForkJoinPool extends Abstra
1946		*/
1947		public boolean awaitTermination(long timeout, TimeUnit unit)
1948		throws InterruptedException {
1949	+	long nanos = unit.toNanos(timeout);
1950	+	final ReentrantLock lock = this.submissionLock;
1951	+	lock.lock();
1952		try {
1953	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1954	<	} catch(TimeoutException ex) {
1955	<	return false;
1953	>	for (;;) {
1954	>	if (isTerminated())
1955	>	return true;
1956	>	if (nanos <= 0)
1957	>	return false;
1958	>	nanos = termination.awaitNanos(nanos);
1959	>	}
1960	>	} finally {
1961	>	lock.unlock();
1962		}
1963		}
1964
#	Line 1809 | Line 1966 | public class ForkJoinPool extends Abstra
1966		* Interface for extending managed parallelism for tasks running
1967		* in {@link ForkJoinPool}s.
1968		*
1969	<	* <p>A {@code ManagedBlocker} provides two methods.
1970	<	* Method {@code isReleasable} must return {@code true} if
1971	<	* blocking is not necessary. Method {@code block} blocks the
1972	<	* current thread if necessary (perhaps internally invoking
1973	<	* {@code isReleasable} before actually blocking).
1969	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1970	>	* {@code isReleasable} must return {@code true} if blocking is
1971	>	* not necessary. Method {@code block} blocks the current thread
1972	>	* if necessary (perhaps internally invoking {@code isReleasable}
1973	>	* before actually blocking). These actions are performed by any
1974	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
1975	>	* unusual methods in this API accommodate synchronizers that may,
1976	>	* but don't usually, block for long periods. Similarly, they
1977	>	* allow more efficient internal handling of cases in which
1978	>	* additional workers may be, but usually are not, needed to
1979	>	* ensure sufficient parallelism.  Toward this end,
1980	>	* implementations of method {@code isReleasable} must be amenable
1981	>	* to repeated invocation.
1982		*
1983		* <p>For example, here is a ManagedBlocker based on a
1984		* ReentrantLock:
#	Line 1831 | Line 1996 | public class ForkJoinPool extends Abstra
1996		*     return hasLock || (hasLock = lock.tryLock());
1997		*   }
1998		* }}</pre>
1999	+	*
2000	+	* <p>Here is a class that possibly blocks waiting for an
2001	+	* item on a given queue:
2002	+	*  <pre> {@code
2003	+	* class QueueTaker<E> implements ManagedBlocker {
2004	+	*   final BlockingQueue<E> queue;
2005	+	*   volatile E item = null;
2006	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2007	+	*   public boolean block() throws InterruptedException {
2008	+	*     if (item == null)
2009	+	*       item = queue.take();
2010	+	*     return true;
2011	+	*   }
2012	+	*   public boolean isReleasable() {
2013	+	*     return item != null || (item = queue.poll()) != null;
2014	+	*   }
2015	+	*   public E getItem() { // call after pool.managedBlock completes
2016	+	*     return item;
2017	+	*   }
2018	+	* }}</pre>
2019		*/
2020		public static interface ManagedBlocker {
2021		/**
#	Line 1873 | Line 2058 | public class ForkJoinPool extends Abstra
2058		public static void managedBlock(ManagedBlocker blocker)
2059		throws InterruptedException {
2060		Thread t = Thread.currentThread();
2061	<	if (t instanceof ForkJoinWorkerThread)
2062	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
2061	>	if (t instanceof ForkJoinWorkerThread) {
2062	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2063	>	w.pool.awaitBlocker(blocker);
2064	>	}
2065		else {
2066		do {} while (!blocker.isReleasable() && !blocker.block());
2067		}
#	Line 1893 | Line 2080 | public class ForkJoinPool extends Abstra
2080		}
2081
2082		// Unsafe mechanics
2083	<
2084	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2085	<	private static final long workerCountsOffset =
2086	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2087	<	private static final long runStateOffset =
2088	<	objectFieldOffset("runState", ForkJoinPool.class);
2089	<	private static final long eventCountOffset =
2090	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2091	<	private static final long eventWaitersOffset =
2092	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
2093	<	private static final long stealCountOffset =
2094	<	objectFieldOffset("stealCount",ForkJoinPool.class);
2095	<
2096	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2083	>	private static final sun.misc.Unsafe UNSAFE;
2084	>	private static final long ctlOffset;
2085	>	private static final long stealCountOffset;
2086	>	private static final long blockedCountOffset;
2087	>	private static final long quiescerCountOffset;
2088	>	private static final long scanGuardOffset;
2089	>	private static final long nextWorkerNumberOffset;
2090	>	private static final long ABASE;
2091	>	private static final int ASHIFT;
2092	>
2093	>	static {
2094	>	poolNumberGenerator = new AtomicInteger();
2095	>	workerSeedGenerator = new Random();
2096	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2097	>	defaultForkJoinWorkerThreadFactory =
2098	>	new DefaultForkJoinWorkerThreadFactory();
2099	>	int s;
2100		try {
2101	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2102	<	} catch (NoSuchFieldException e) {
2103	<	// Convert Exception to corresponding Error
2104	<	NoSuchFieldError error = new NoSuchFieldError(field);
2105	<	error.initCause(e);
2106	<	throw error;
2107	<	}
2101	>	UNSAFE = getUnsafe();
2102	>	Class k = ForkJoinPool.class;
2103	>	ctlOffset = UNSAFE.objectFieldOffset
2104	>	(k.getDeclaredField("ctl"));
2105	>	stealCountOffset = UNSAFE.objectFieldOffset
2106	>	(k.getDeclaredField("stealCount"));
2107	>	blockedCountOffset = UNSAFE.objectFieldOffset
2108	>	(k.getDeclaredField("blockedCount"));
2109	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2110	>	(k.getDeclaredField("quiescerCount"));
2111	>	scanGuardOffset = UNSAFE.objectFieldOffset
2112	>	(k.getDeclaredField("scanGuard"));
2113	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2114	>	(k.getDeclaredField("nextWorkerNumber"));
2115	>	Class a = ForkJoinTask[].class;
2116	>	ABASE = UNSAFE.arrayBaseOffset(a);
2117	>	s = UNSAFE.arrayIndexScale(a);
2118	>	} catch (Exception e) {
2119	>	throw new Error(e);
2120	>	}
2121	>	if ((s & (s-1)) != 0)
2122	>	throw new Error("data type scale not a power of two");
2123	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2124		}
2125
2126		/**

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