ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.62 by dl, Wed Aug 11 20:28:22 2010 UTC vs.
Revision 1.106 by jsr166, Fri Jul 1 01:15:06 2011 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
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.atomic.AtomicInteger;
23		import java.util.concurrent.locks.LockSupport;
24		import java.util.concurrent.locks.ReentrantLock;
25	<	import java.util.concurrent.atomic.AtomicInteger;
19	<	import java.util.concurrent.CountDownLatch;
25	>	import java.util.concurrent.locks.Condition;
26
27		/**
28		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
#	Line 69 | Line 75 | import java.util.concurrent.CountDownLat
75		*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
76		*  </tr>
77		*  <tr>
78	<	*    <td> <b>Arange async execution</td>
78	>	*    <td> <b>Arrange async execution</td>
79		*    <td> {@link #execute(ForkJoinTask)}</td>
80		*    <td> {@link ForkJoinTask#fork}</td>
81		*  </tr>
#	Line 95 | Line 101 | import java.util.concurrent.CountDownLat
101		* daemon} mode, there is typically no need to explicitly {@link
102		* #shutdown} such a pool upon program exit.
103		*
104	<	* <pre>
104	>	*  <pre> {@code
105		* static final ForkJoinPool mainPool = new ForkJoinPool();
106		* ...
107		* public void sort(long[] array) {
108		*   mainPool.invoke(new SortTask(array, 0, array.length));
109	<	* }
104	<	* </pre>
109	>	* }}</pre>
110		*
111		* <p><b>Implementation notes</b>: This implementation restricts the
112		* maximum number of running threads to 32767. Attempts to create
#	Line 124 | Line 129 | public class ForkJoinPool extends Abstra
129		* set of worker threads: Submissions from non-FJ threads enter
130		* into a submission queue. Workers take these tasks and typically
131		* split them into subtasks that may be stolen by other workers.
132	<	* The main work-stealing mechanics implemented in class
133	<	* ForkJoinWorkerThread give first priority to processing tasks
134	<	* from their own queues (LIFO or FIFO, depending on mode), then
135	<	* to randomized FIFO steals of tasks in other worker queues, and
136	<	* lastly to new submissions. These mechanics do not consider
137	<	* affinities, loads, cache localities, etc, so rarely provide the
138	<	* best possible performance on a given machine, but portably
139	<	* provide good throughput by averaging over these factors.
140	<	* (Further, even if we did try to use such information, we do not
141	<	* usually have a basis for exploiting it. For example, some sets
142	<	* of tasks profit from cache affinities, but others are harmed by
143	<	* cache pollution effects.)
144	<	*
145	<	* Beyond work-stealing support and essential bookkeeping, the
146	<	* main responsibility of this framework is to take actions when
147	<	* one worker is waiting to join a task stolen (or always held by)
148	<	* another.  Becauae we are multiplexing many tasks on to a pool
149	<	* of workers, we can't just let them block (as in Thread.join).
150	<	* We also cannot just reassign the joiner's run-time stack with
151	<	* another and replace it later, which would be a form of
152	<	* "continuation", that even if possible is not necessarily a good
153	<	* idea. Given that the creation costs of most threads on most
154	<	* systems mainly surrounds setting up runtime stacks, thread
155	<	* creation and switching is usually not much more expensive than
156	<	* stack creation and switching, and is more flexible). Instead we
132	>	* Preference rules give first priority to processing tasks from
133	>	* their own queues (LIFO or FIFO, depending on mode), then to
134	>	* randomized FIFO steals of tasks in other worker queues, and
135	>	* lastly to new submissions.
136	>	*
137	>	* The main throughput advantages of work-stealing stem from
138	>	* decentralized control -- workers mostly take tasks from
139	>	* themselves or each other. We cannot negate this in the
140	>	* implementation of other management responsibilities. The main
141	>	* tactic for avoiding bottlenecks is packing nearly all
142	>	* essentially atomic control state into a single 64bit volatile
143	>	* variable ("ctl"). This variable is read on the order of 10-100
144	>	* times as often as it is modified (always via CAS). (There is
145	>	* some additional control state, for example variable "shutdown"
146	>	* for which we can cope with uncoordinated updates.)  This
147	>	* streamlines synchronization and control at the expense of messy
148	>	* constructions needed to repack status bits upon updates.
149	>	* Updates tend not to contend with each other except during
150	>	* bursts while submitted tasks begin or end.  In some cases when
151	>	* they do contend, threads can instead do something else
152	>	* (usually, scan for tasks) until contention subsides.
153	>	*
154	>	* To enable packing, we restrict maximum parallelism to (1<<15)-1
155	>	* (which is far in excess of normal operating range) to allow
156	>	* ids, counts, and their negations (used for thresholding) to fit
157	>	* into 16bit fields.
158	>	*
159	>	* Recording Workers.  Workers are recorded in the "workers" array
160	>	* that is created upon pool construction and expanded if (rarely)
161	>	* necessary.  This is an array as opposed to some other data
162	>	* structure to support index-based random steals by workers.
163	>	* Updates to the array recording new workers and unrecording
164	>	* terminated ones are protected from each other by a seqLock
165	>	* (scanGuard) but the array is otherwise concurrently readable,
166	>	* and accessed directly by workers. To simplify index-based
167	>	* operations, the array size is always a power of two, and all
168	>	* readers must tolerate null slots. To avoid flailing during
169	>	* start-up, the array is presized to hold twice #parallelism
170	>	* workers (which is unlikely to need further resizing during
171	>	* execution). But to avoid dealing with so many null slots,
172	>	* variable scanGuard includes a mask for the nearest power of two
173	>	* that contains all current workers.  All worker thread creation
174	>	* is on-demand, triggered by task submissions, replacement of
175	>	* terminated workers, and/or compensation for blocked
176	>	* workers. However, all other support code is set up to work with
177	>	* other policies.  To ensure that we do not hold on to worker
178	>	* references that would prevent GC, ALL accesses to workers are
179	>	* via indices into the workers array (which is one source of some
180	>	* of the messy code constructions here). In essence, the workers
181	>	* array serves as a weak reference mechanism. Thus for example
182	>	* the wait queue field of ctl stores worker indices, not worker
183	>	* references.  Access to the workers in associated methods (for
184	>	* example signalWork) must both index-check and null-check the
185	>	* IDs. All such accesses ignore bad IDs by returning out early
186	>	* from what they are doing, since this can only be associated
187	>	* with termination, in which case it is OK to give up.
188	>	*
189	>	* All uses of the workers array, as well as queue arrays, check
190	>	* that the array is non-null (even if previously non-null). This
191	>	* allows nulling during termination, which is currently not
192	>	* necessary, but remains an option for resource-revocation-based
193	>	* shutdown schemes.
194	>	*
195	>	* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
196	>	* let workers spin indefinitely scanning for tasks when none can
197	>	* be found immediately, and we cannot start/resume workers unless
198	>	* there appear to be tasks available.  On the other hand, we must
199	>	* quickly prod them into action when new tasks are submitted or
200	>	* generated.  We park/unpark workers after placing in an event
201	>	* wait queue when they cannot find work. This "queue" is actually
202	>	* a simple Treiber stack, headed by the "id" field of ctl, plus a
203	>	* 15bit counter value to both wake up waiters (by advancing their
204	>	* count) and avoid ABA effects. Successors are held in worker
205	>	* field "nextWait".  Queuing deals with several intrinsic races,
206	>	* mainly that a task-producing thread can miss seeing (and
207	>	* signalling) another thread that gave up looking for work but
208	>	* has not yet entered the wait queue. We solve this by requiring
209	>	* a full sweep of all workers both before (in scan()) and after
210	>	* (in tryAwaitWork()) a newly waiting worker is added to the wait
211	>	* queue. During a rescan, the worker might release some other
212	>	* queued worker rather than itself, which has the same net
213	>	* effect. Because enqueued workers may actually be rescanning
214	>	* rather than waiting, we set and clear the "parked" field of
215	>	* ForkJoinWorkerThread to reduce unnecessary calls to unpark.
216	>	* (Use of the parked field requires a secondary recheck to avoid
217	>	* missed signals.)
218	>	*
219	>	* Signalling.  We create or wake up workers only when there
220	>	* appears to be at least one task they might be able to find and
221	>	* execute.  When a submission is added or another worker adds a
222	>	* task to a queue that previously had two or fewer tasks, they
223	>	* signal waiting workers (or trigger creation of new ones if
224	>	* fewer than the given parallelism level -- see signalWork).
225	>	* These primary signals are buttressed by signals during rescans
226	>	* as well as those performed when a worker steals a task and
227	>	* notices that there are more tasks too; together these cover the
228	>	* signals needed in cases when more than two tasks are pushed
229	>	* but untaken.
230	>	*
231	>	* Trimming workers. To release resources after periods of lack of
232	>	* use, a worker starting to wait when the pool is quiescent will
233	>	* time out and terminate if the pool has remained quiescent for
234	>	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
235	>	* terminating all workers after long periods of non-use.
236	>	*
237	>	* Submissions. External submissions are maintained in an
238	>	* array-based queue that is structured identically to
239	>	* ForkJoinWorkerThread queues except for the use of
240	>	* submissionLock in method addSubmission. Unlike the case for
241	>	* worker queues, multiple external threads can add new
242	>	* submissions, so adding requires a lock.
243	>	*
244	>	* Compensation. Beyond work-stealing support and lifecycle
245	>	* control, the main responsibility of this framework is to take
246	>	* actions when one worker is waiting to join a task stolen (or
247	>	* always held by) another.  Because we are multiplexing many
248	>	* tasks on to a pool of workers, we can't just let them block (as
249	>	* in Thread.join).  We also cannot just reassign the joiner's
250	>	* run-time stack with another and replace it later, which would
251	>	* be a form of "continuation", that even if possible is not
252	>	* necessarily a good idea since we sometimes need both an
253	>	* unblocked task and its continuation to progress. Instead we
254		* combine two tactics:
255		*
256		*   Helping: Arranging for the joiner to execute some task that it
257		*      would be running if the steal had not occurred.  Method
258	<	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
258	>	*      ForkJoinWorkerThread.joinTask tracks joining->stealing
259		*      links to try to find such a task.
260		*
261		*   Compensating: Unless there are already enough live threads,
262	<	*      method helpMaintainParallelism() may create or or
263	<	*      re-activate a spare thread to compensate for blocked
264	<	*      joiners until they unblock.
163	<	*
164	<	* Because the determining existence of conservatively safe
165	<	* helping targets, the availability of already-created spares,
166	<	* and the apparent need to create new spares are all racy and
167	<	* require heuristic guidance, we rely on multiple retries of
168	<	* each. Further, because it is impossible to keep exactly the
169	<	* target (parallelism) number of threads running at any given
170	<	* time, we allow compensation during joins to fail, and enlist
171	<	* all other threads to help out whenever they are not otherwise
172	<	* occupied (i.e., mainly in method preStep).
262	>	*      method tryPreBlock() may create or re-activate a spare
263	>	*      thread to compensate for blocked joiners until they
264	>	*      unblock.
265		*
266		* The ManagedBlocker extension API can't use helping so relies
267		* only on compensation in method awaitBlocker.
268		*
269	<	* The main throughput advantages of work-stealing stem from
270	<	* decentralized control -- workers mostly steal tasks from each
271	<	* other. We do not want to negate this by creating bottlenecks
272	<	* implementing other management responsibilities. So we use a
273	<	* collection of techniques that avoid, reduce, or cope well with
274	<	* contention. These entail several instances of bit-packing into
275	<	* CASable fields to maintain only the minimally required
276	<	* atomicity. To enable such packing, we restrict maximum
277	<	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
278	<	* unbalanced increments and decrements) to fit into a 16 bit
279	<	* field, which is far in excess of normal operating range.  Even
280	<	* though updates to some of these bookkeeping fields do sometimes
281	<	* contend with each other, they don't normally cache-contend with
282	<	* updates to others enough to warrant memory padding or
283	<	* isolation. So they are all held as fields of ForkJoinPool
284	<	* objects.  The main capabilities are as follows:
269	>	* It is impossible to keep exactly the target parallelism number
270	>	* of threads running at any given time.  Determining the
271	>	* existence of conservatively safe helping targets, the
272	>	* availability of already-created spares, and the apparent need
273	>	* to create new spares are all racy and require heuristic
274	>	* guidance, so we rely on multiple retries of each.  Currently,
275	>	* in keeping with on-demand signalling policy, we compensate only
276	>	* if blocking would leave less than one active (non-waiting,
277	>	* non-blocked) worker. Additionally, to avoid some false alarms
278	>	* due to GC, lagging counters, system activity, etc, compensated
279	>	* blocking for joins is only attempted after rechecks stabilize
280	>	* (retries are interspersed with Thread.yield, for good
281	>	* citizenship).  The variable blockedCount, incremented before
282	>	* blocking and decremented after, is sometimes needed to
283	>	* distinguish cases of waiting for work vs blocking on joins or
284	>	* other managed sync. Both cases are equivalent for most pool
285	>	* control, so we can update non-atomically. (Additionally,
286	>	* contention on blockedCount alleviates some contention on ctl).
287	>	*
288	>	* Shutdown and Termination. A call to shutdownNow atomically sets
289	>	* the ctl stop bit and then (non-atomically) sets each workers
290	>	* "terminate" status, cancels all unprocessed tasks, and wakes up
291	>	* all waiting workers.  Detecting whether termination should
292	>	* commence after a non-abrupt shutdown() call requires more work
293	>	* and bookkeeping. We need consensus about quiescence (i.e., that
294	>	* there is no more work) which is reflected in active counts so
295	>	* long as there are no current blockers, as well as possible
296	>	* re-evaluations during independent changes in blocking or
297	>	* quiescing workers.
298		*
299	<	* 1. Creating and removing workers. Workers are recorded in the
195	<	* "workers" array. This is an array as opposed to some other data
196	<	* structure to support index-based random steals by workers.
197	<	* Updates to the array recording new workers and unrecording
198	<	* terminated ones are protected from each other by a lock
199	<	* (workerLock) but the array is otherwise concurrently readable,
200	<	* and accessed directly by workers. To simplify index-based
201	<	* operations, the array size is always a power of two, and all
202	<	* readers must tolerate null slots. Currently, all worker thread
203	<	* creation is on-demand, triggered by task submissions,
204	<	* replacement of terminated workers, and/or compensation for
205	<	* blocked workers. However, all other support code is set up to
206	<	* work with other policies.
207	<	*
208	<	* To ensure that we do not hold on to worker references that
209	<	* would prevent GC, ALL accesses to workers are via indices into
210	<	* the workers array (which is one source of some of the unusual
211	<	* code constructions here). In essence, the workers array serves
212	<	* as a WeakReference mechanism. Thus for example the event queue
213	<	* stores worker indices, not worker references. Access to the
214	<	* workers in associated methods (for example releaseEventWaiters)
215	<	* must both index-check and null-check the IDs. All such accesses
216	<	* ignore bad IDs by returning out early from what they are doing,
217	<	* since this can only be associated with shutdown, in which case
218	<	* it is OK to give up. On termination, we just clobber these
219	<	* data structures without trying to use them.
220	<	*
221	<	* 2. Bookkeeping for dynamically adding and removing workers. We
222	<	* aim to approximately maintain the given level of parallelism.
223	<	* When some workers are known to be blocked (on joins or via
224	<	* ManagedBlocker), we may create or resume others to take their
225	<	* place until they unblock (see below). Implementing this
226	<	* requires counts of the number of "running" threads (i.e., those
227	<	* that are neither blocked nor artifically suspended) as well as
228	<	* the total number.  These two values are packed into one field,
229	<	* "workerCounts" because we need accurate snapshots when deciding
230	<	* to create, resume or suspend.  Note however that the
231	<	* correspondance of these counts to reality is not guaranteed. In
232	<	* particular updates for unblocked threads may lag until they
233	<	* actually wake up.
234	<	*
235	<	* 3. Maintaining global run state. The run state of the pool
236	<	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
237	<	* those in other Executor implementations, as well as a count of
238	<	* "active" workers -- those that are, or soon will be, or
239	<	* recently were executing tasks. The runLevel and active count
240	<	* are packed together in order to correctly trigger shutdown and
241	<	* termination. Without care, active counts can be subject to very
242	<	* high contention.  We substantially reduce this contention by
243	<	* relaxing update rules.  A worker must claim active status
244	<	* prospectively, by activating if it sees that a submitted or
245	<	* stealable task exists (it may find after activating that the
246	<	* task no longer exists). It stays active while processing this
247	<	* task (if it exists) and any other local subtasks it produces,
248	<	* until it cannot find any other tasks. It then tries
249	<	* inactivating (see method preStep), but upon update contention
250	<	* instead scans for more tasks, later retrying inactivation if it
251	<	* doesn't find any.
252	<	*
253	<	* 4. Managing idle workers waiting for tasks. We cannot let
254	<	* workers spin indefinitely scanning for tasks when none are
255	<	* available. On the other hand, we must quickly prod them into
256	<	* action when new tasks are submitted or generated.  We
257	<	* park/unpark these idle workers using an event-count scheme.
258	<	* Field eventCount is incremented upon events that may enable
259	<	* workers that previously could not find a task to now find one:
260	<	* Submission of a new task to the pool, or another worker pushing
261	<	* a task onto a previously empty queue.  (We also use this
262	<	* mechanism for termination actions that require wakeups of idle
263	<	* workers).  Each worker maintains its last known event count,
264	<	* and blocks when a scan for work did not find a task AND its
265	<	* lastEventCount matches the current eventCount. Waiting idle
266	<	* workers are recorded in a variant of Treiber stack headed by
267	<	* field eventWaiters which, when nonzero, encodes the thread
268	<	* index and count awaited for by the worker thread most recently
269	<	* calling eventSync. This thread in turn has a record (field
270	<	* nextEventWaiter) for the next waiting worker.  In addition to
271	<	* allowing simpler decisions about need for wakeup, the event
272	<	* count bits in eventWaiters serve the role of tags to avoid ABA
273	<	* errors in Treiber stacks.  To reduce delays in task diffusion,
274	<	* workers not otherwise occupied may invoke method
275	<	* releaseEventWaiters, that removes and signals (unparks) workers
276	<	* not waiting on current count. To reduce stalls, To minimize
277	<	* task production stalls associate with signalling, any worker
278	<	* pushing a task on an empty queue invokes the weaker method
279	<	* signalWork, that only releases idle workers until it detects
280	<	* interference by other threads trying to release, and lets them
281	<	* take over.  The net effect is a tree-like diffusion of signals,
282	<	* where released threads (and possibly others) help with unparks.
283	<	* To further reduce contention effects a bit, failed CASes to
284	<	* increment field eventCount are tolerated without retries.
285	<	* Conceptually they are merged into the same event, which is OK
286	<	* when their only purpose is to enable workers to scan for work.
287	<	*
288	<	* 5. Managing suspension of extra workers. When a worker is about
289	<	* to block waiting for a join (or via ManagedBlockers), we may
290	<	* create a new thread to maintain parallelism level, or at least
291	<	* avoid starvation. Usually, extra threads are needed for only
292	<	* very short periods, yet join dependencies are such that we
293	<	* sometimes need them in bursts. Rather than create new threads
294	<	* each time this happens, we suspend no-longer-needed extra ones
295	<	* as "spares". For most purposes, we don't distinguish "extra"
296	<	* spare threads from normal "core" threads: On each call to
297	<	* preStep (the only point at which we can do this) a worker
298	<	* checks to see if there are now too many running workers, and if
299	<	* so, suspends itself.  Method helpMaintainParallelism looks for
300	<	* suspended threads to resume before considering creating a new
301	<	* replacement. The spares themselves are encoded on another
302	<	* variant of a Treiber Stack, headed at field "spareWaiters".
303	<	* Note that the use of spares is intrinsically racy.  One thread
304	<	* may become a spare at about the same time as another is
305	<	* needlessly being created. We counteract this and related slop
306	<	* in part by requiring resumed spares to immediately recheck (in
307	<	* preStep) to see whether they they should re-suspend.  To avoid
308	<	* long-term build-up of spares, the oldest spare (see
309	<	* ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if
310	<	* not signalled and calls tryTrimSpare, which uses two different
311	<	* thresholds: Always killing if the number of spares is greater
312	<	* that 25% of total, and killing others only at a slower rate
313	<	* (UNUSED_SPARE_TRIM_RATE_NANOS).
314	<	*
315	<	* 6. Deciding when to create new workers. The main dynamic
316	<	* control in this class is deciding when to create extra threads
317	<	* in method helpMaintainParallelism. We would like to keep
318	<	* exactly #parallelism threads running, which is an impossble
319	<	* task. We always need to create one when the number of running
320	<	* threads would become zero and all workers are busy. Beyond
321	<	* this, we must rely on heuristics that work well in the the
322	<	* presence of transients phenomena such as GC stalls, dynamic
323	<	* compilation, and wake-up lags. These transients are extremely
324	<	* common -- we are normally trying to fully saturate the CPUs on
325	<	* a machine, so almost any activity other than running tasks
326	<	* impedes accuracy. Our main defense is to allow some slack in
327	<	* creation thresholds, using rules that reflect the fact that the
328	<	* more threads we have running, the more likely that we are
329	<	* underestimating the number running threads. The rules also
330	<	* better cope with the fact that some of the methods in this
331	<	* class tend to never become compiled (but are interpreted), so
332	<	* some components of the entire set of controls might execute 100
333	<	* times faster than others. And similarly for cases where the
334	<	* apparent lack of work is just due to GC stalls and other
335	<	* transient system activity.
336	<	*
337	<	* Beware that there is a lot of representation-level coupling
299	>	* Style notes: There is a lot of representation-level coupling
300		* among classes ForkJoinPool, ForkJoinWorkerThread, and
301	<	* ForkJoinTask.  For example, direct access to "workers" array by
301	>	* ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
302	>	* data structures managed by ForkJoinPool, so are directly
303	>	* accessed.  Conversely we allow access to "workers" array by
304		* workers, and direct access to ForkJoinTask.status by both
305		* ForkJoinPool and ForkJoinWorkerThread.  There is little point
306		* trying to reduce this, since any associated future changes in
307		* representations will need to be accompanied by algorithmic
308	<	* changes anyway.
309	<	*
310	<	* Style notes: There are lots of inline assignments (of form
311	<	* "while ((local = field) != 0)") which are usually the simplest
312	<	* way to ensure the required read orderings (which are sometimes
313	<	* critical). Also several occurrences of the unusual "do {}
314	<	* while(!cas...)" which is the simplest way to force an update of
315	<	* a CAS'ed variable. There are also other coding oddities that
316	<	* help some methods perform reasonably even when interpreted (not
317	<	* compiled), at the expense of some messy constructions that
318	<	* reduce byte code counts.
319	<	*
320	<	* The order of declarations in this file is: (1) statics (2)
321	<	* fields (along with constants used when unpacking some of them)
322	<	* (3) internal control methods (4) callbacks and other support
323	<	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
324	<	* methods (plus a few little helpers).
308	>	* changes anyway. All together, these low-level implementation
309	>	* choices produce as much as a factor of 4 performance
310	>	* improvement compared to naive implementations, and enable the
311	>	* processing of billions of tasks per second, at the expense of
312	>	* some ugliness.
313	>	*
314	>	* Methods signalWork() and scan() are the main bottlenecks so are
315	>	* especially heavily micro-optimized/mangled.  There are lots of
316	>	* inline assignments (of form "while ((local = field) != 0)")
317	>	* which are usually the simplest way to ensure the required read
318	>	* orderings (which are sometimes critical). This leads to a
319	>	* "C"-like style of listing declarations of these locals at the
320	>	* heads of methods or blocks.  There are several occurrences of
321	>	* the unusual "do {} while (!cas...)"  which is the simplest way
322	>	* to force an update of a CAS'ed variable. There are also other
323	>	* coding oddities that help some methods perform reasonably even
324	>	* when interpreted (not compiled).
325	>	*
326	>	* The order of declarations in this file is: (1) declarations of
327	>	* statics (2) fields (along with constants used when unpacking
328	>	* some of them), listed in an order that tends to reduce
329	>	* contention among them a bit under most JVMs.  (3) internal
330	>	* control methods (4) callbacks and other support for
331	>	* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
332	>	* methods (plus a few little helpers). (6) static block
333	>	* initializing all statics in a minimally dependent order.
334		*/
335
336		/**
#	Line 392 | Line 365 | public class ForkJoinPool extends Abstra
365		* overridden in ForkJoinPool constructors.
366		*/
367		public static final ForkJoinWorkerThreadFactory
368	<	defaultForkJoinWorkerThreadFactory =
396	<	new DefaultForkJoinWorkerThreadFactory();
368	>	defaultForkJoinWorkerThreadFactory;
369
370		/**
371		* Permission required for callers of methods that may start or
372		* kill threads.
373		*/
374	<	private static final RuntimePermission modifyThreadPermission =
403	<	new RuntimePermission("modifyThread");
374	>	private static final RuntimePermission modifyThreadPermission;
375
376		/**
377		* If there is a security manager, makes sure caller has
#	Line 415 | Line 386 | public class ForkJoinPool extends Abstra
386		/**
387		* Generator for assigning sequence numbers as pool names.
388		*/
389	<	private static final AtomicInteger poolNumberGenerator =
419	<	new AtomicInteger();
389	>	private static final AtomicInteger poolNumberGenerator;
390
391		/**
392	<	* Absolute bound for parallelism level. Twice this number plus
393	<	* one (i.e., 0xfff) must fit into a 16bit field to enable
394	<	* word-packing for some counts and indices.
392	>	* Generator for initial random seeds for worker victim
393	>	* selection. This is used only to create initial seeds. Random
394	>	* steals use a cheaper xorshift generator per steal attempt. We
395	>	* don't expect much contention on seedGenerator, so just use a
396	>	* plain Random.
397		*/
398	<	private static final int MAX_WORKERS   = 0x7fff;
398	>	static final Random workerSeedGenerator;
399
400		/**
401	<	* Array holding all worker threads in the pool.  Array size must
402	<	* be a power of two.  Updates and replacements are protected by
403	<	* workerLock, but the array is always kept in a consistent enough
404	<	* state to be randomly accessed without locking by workers
405	<	* performing work-stealing, as well as other traversal-based
406	<	* methods in this class. All readers must tolerate that some
407	<	* array slots may be null.
401	>	* Array holding all worker threads in the pool.  Initialized upon
402	>	* construction. Array size must be a power of two.  Updates and
403	>	* replacements are protected by scanGuard, but the array is
404	>	* always kept in a consistent enough state to be randomly
405	>	* accessed without locking by workers performing work-stealing,
406	>	* as well as other traversal-based methods in this class, so long
407	>	* as reads memory-acquire by first reading ctl. All readers must
408	>	* tolerate that some array slots may be null.
409		*/
410	<	volatile ForkJoinWorkerThread[] workers;
410	>	ForkJoinWorkerThread[] workers;
411
412		/**
413	<	* Queue for external submissions.
413	>	* Initial size for submission queue array. Must be a power of
414	>	* two.  In many applications, these always stay small so we use a
415	>	* small initial cap.
416		*/
417	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
417	>	private static final int INITIAL_QUEUE_CAPACITY = 8;
418
419		/**
420	<	* Lock protecting updates to workers array.
420	>	* Maximum size for submission queue array. Must be a power of two
421	>	* less than or equal to 1 << (31 - width of array entry) to
422	>	* ensure lack of index wraparound, but is capped at a lower
423	>	* value to help users trap runaway computations.
424		*/
425	<	private final ReentrantLock workerLock;
425	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
426
427		/**
428	<	* Latch released upon termination.
428	>	* Array serving as submission queue. Initialized upon construction.
429		*/
430	<	private final Phaser termination;
430	>	private ForkJoinTask<?>[] submissionQueue;
431
432		/**
433	<	* Creation factory for worker threads.
433	>	* Lock protecting submissions array for addSubmission
434		*/
435	<	private final ForkJoinWorkerThreadFactory factory;
435	>	private final ReentrantLock submissionLock;
436
437		/**
438	<	* Sum of per-thread steal counts, updated only when threads are
439	<	* idle or terminating.
438	>	* Condition for awaitTermination, using submissionLock for
439	>	* convenience.
440		*/
441	<	private volatile long stealCount;
441	>	private final Condition termination;
442
443		/**
444	<	* The last nanoTime that a spare thread was trimmed
444	>	* Creation factory for worker threads.
445		*/
446	<	private volatile long trimTime;
446	>	private final ForkJoinWorkerThreadFactory factory;
447
448		/**
449	<	* The rate at which to trim unused spares
449	>	* The uncaught exception handler used when any worker abruptly
450	>	* terminates.
451		*/
452	<	static final long UNUSED_SPARE_TRIM_RATE_NANOS =
474	<	1000L * 1000L * 1000L; // 1 sec
452	>	final Thread.UncaughtExceptionHandler ueh;
453
454		/**
455	<	* Encoded record of top of treiber stack of threads waiting for
478	<	* events. The top 32 bits contain the count being waited for. The
479	<	* bottom 16 bits contains one plus the pool index of waiting
480	<	* worker thread. (Bits 16-31 are unused.)
455	>	* Prefix for assigning names to worker threads
456		*/
457	<	private volatile long eventWaiters;
483	<
484	<	private static final int  EVENT_COUNT_SHIFT = 32;
485	<	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
457	>	private final String workerNamePrefix;
458
459		/**
460	<	* A counter for events that may wake up worker threads:
461	<	*   - Submission of a new task to the pool
490	<	*   - A worker pushing a task on an empty queue
491	<	*   - termination
460	>	* Sum of per-thread steal counts, updated only when threads are
461	>	* idle or terminating.
462		*/
463	<	private volatile int eventCount;
463	>	private volatile long stealCount;
464
465		/**
466	<	* Encoded record of top of treiber stack of spare threads waiting
467	<	* for resumption. The top 16 bits contain an arbitrary count to
468	<	* avoid ABA effects. The bottom 16bits contains one plus the pool
469	<	* index of waiting worker thread.
470	<	*/
471	<	private volatile int spareWaiters;
472	<
473	<	private static final int SPARE_COUNT_SHIFT = 16;
474	<	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
466	>	* Main pool control -- a long packed with:
467	>	* AC: Number of active running workers minus target parallelism (16 bits)
468	>	* TC: Number of total workers minus target parallelism (16 bits)
469	>	* ST: true if pool is terminating (1 bit)
470	>	* EC: the wait count of top waiting thread (15 bits)
471	>	* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
472	>	*
473	>	* When convenient, we can extract the upper 32 bits of counts and
474	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
475	>	* (int)ctl.  The ec field is never accessed alone, but always
476	>	* together with id and st. The offsets of counts by the target
477	>	* parallelism and the positionings of fields makes it possible to
478	>	* perform the most common checks via sign tests of fields: When
479	>	* ac is negative, there are not enough active workers, when tc is
480	>	* negative, there are not enough total workers, when id is
481	>	* negative, there is at least one waiting worker, and when e is
482	>	* negative, the pool is terminating.  To deal with these possibly
483	>	* negative fields, we use casts in and out of "short" and/or
484	>	* signed shifts to maintain signedness.
485	>	*/
486	>	volatile long ctl;
487	>
488	>	// bit positions/shifts for fields
489	>	private static final int  AC_SHIFT   = 48;
490	>	private static final int  TC_SHIFT   = 32;
491	>	private static final int  ST_SHIFT   = 31;
492	>	private static final int  EC_SHIFT   = 16;
493	>
494	>	// bounds
495	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
496	>	private static final int  SMASK      = 0xffff;  // mask short bits
497	>	private static final int  SHORT_SIGN = 1 << 15;
498	>	private static final int  INT_SIGN   = 1 << 31;
499	>
500	>	// masks
501	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
502	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
503	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
504	>
505	>	// units for incrementing and decrementing
506	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
507	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
508	>
509	>	// masks and units for dealing with u = (int)(ctl >>> 32)
510	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
511	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
512	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
513	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
514	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
515	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
516	>
517	>	// masks and units for dealing with e = (int)ctl
518	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
519	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
520
521		/**
522	<	* Lifecycle control. The low word contains the number of workers
508	<	* that are (probably) executing tasks. This value is atomically
509	<	* incremented before a worker gets a task to run, and decremented
510	<	* when worker has no tasks and cannot find any.  Bits 16-18
511	<	* contain runLevel value. When all are zero, the pool is
512	<	* running. Level transitions are monotonic (running -> shutdown
513	<	* -> terminating -> terminated) so each transition adds a bit.
514	<	* These are bundled together to ensure consistent read for
515	<	* termination checks (i.e., that runLevel is at least SHUTDOWN
516	<	* and active threads is zero).
522	>	* The target parallelism level.
523		*/
524	<	private volatile int runState;
519	<
520	<	// Note: The order among run level values matters.
521	<	private static final int RUNLEVEL_SHIFT     = 16;
522	<	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
523	<	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
524	<	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
525	<	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
526	<	private static final int ONE_ACTIVE         = 1; // active update delta
524	>	final int parallelism;
525
526		/**
527	<	* Holds number of total (i.e., created and not yet terminated)
528	<	* and running (i.e., not blocked on joins or other managed sync)
529	<	* threads, packed together to ensure consistent snapshot when
530	<	* making decisions about creating and suspending spare
533	<	* threads. Updated only by CAS. Note that adding a new worker
534	<	* requires incrementing both counts, since workers start off in
535	<	* running state.
527	>	* Index (mod submission queue length) of next element to take
528	>	* from submission queue. Usage is identical to that for
529	>	* per-worker queues -- see ForkJoinWorkerThread internal
530	>	* documentation.
531		*/
532	<	private volatile int workerCounts;
532	>	volatile int queueBase;
533
534	<	private static final int TOTAL_COUNT_SHIFT  = 16;
535	<	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
536	<	private static final int ONE_RUNNING        = 1;
537	<	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
534	>	/**
535	>	* Index (mod submission queue length) of next element to add
536	>	* in submission queue. Usage is identical to that for
537	>	* per-worker queues -- see ForkJoinWorkerThread internal
538	>	* documentation.
539	>	*/
540	>	int queueTop;
541
542		/**
543	<	* The target parallelism level.
546	<	* Accessed directly by ForkJoinWorkerThreads.
543	>	* True when shutdown() has been called.
544		*/
545	<	final int parallelism;
545	>	volatile boolean shutdown;
546
547		/**
548		* True if use local fifo, not default lifo, for local polling
#	Line 554 | Line 551 | public class ForkJoinPool extends Abstra
551		final boolean locallyFifo;
552
553		/**
554	<	* The uncaught exception handler used when any worker abruptly
555	<	* terminates.
554	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
555	>	* When non-zero, suppresses automatic shutdown when active
556	>	* counts become zero.
557		*/
558	<	private final Thread.UncaughtExceptionHandler ueh;
558	>	volatile int quiescerCount;
559
560		/**
561	<	* Pool number, just for assigning useful names to worker threads
561	>	* The number of threads blocked in join.
562		*/
563	<	private final int poolNumber;
563	>	volatile int blockedCount;
564
565	+	/**
566	+	* Counter for worker Thread names (unrelated to their poolIndex)
567	+	*/
568	+	private volatile int nextWorkerNumber;
569
570	<	// Utilities for CASing fields. Note that several of these
571	<	// are manually inlined by callers
570	>	/**
571	>	* The index for the next created worker. Accessed under scanGuard.
572	>	*/
573	>	private int nextWorkerIndex;
574
575		/**
576	<	* Increments running count part of workerCounts
576	>	* SeqLock and index masking for updates to workers array.  Locked
577	>	* when SG_UNIT is set. Unlocking clears bit by adding
578	>	* SG_UNIT. Staleness of read-only operations can be checked by
579	>	* comparing scanGuard to value before the reads. The low 16 bits
580	>	* (i.e, anding with SMASK) hold (the smallest power of two
581	>	* covering all worker indices, minus one, and is used to avoid
582	>	* dealing with large numbers of null slots when the workers array
583	>	* is overallocated.
584		*/
585	<	final void incrementRunningCount() {
586	<	int c;
587	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
577	<	c = workerCounts,
578	<	c + ONE_RUNNING));
579	<	}
585	>	volatile int scanGuard;
586	>
587	>	private static final int SG_UNIT = 1 << 16;
588
589		/**
590	<	* Tries to decrement running count unless already zero
590	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
591	>	* task when the pool is quiescent to instead try to shrink the
592	>	* number of workers.  The exact value does not matter too
593	>	* much. It must be short enough to release resources during
594	>	* sustained periods of idleness, but not so short that threads
595	>	* are continually re-created.
596		*/
597	<	final boolean tryDecrementRunningCount() {
598	<	int wc = workerCounts;
586	<	if ((wc & RUNNING_COUNT_MASK) == 0)
587	<	return false;
588	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
589	<	wc, wc - ONE_RUNNING);
590	<	}
597	>	private static final long SHRINK_RATE =
598	>	4L * 1000L * 1000L * 1000L; // 4 seconds
599
600		/**
601	<	* Forces decrement of encoded workerCounts, awaiting nonzero if
602	<	* (rarely) necessary when other count updates lag.
601	>	* Top-level loop for worker threads: On each step: if the
602	>	* previous step swept through all queues and found no tasks, or
603	>	* there are excess threads, then possibly blocks. Otherwise,
604	>	* scans for and, if found, executes a task. Returns when pool
605	>	* and/or worker terminate.
606		*
607	<	* @param dr -- either zero or ONE_RUNNING
597	<	* @param dt == either zero or ONE_TOTAL
607	>	* @param w the worker
608		*/
609	<	private void decrementWorkerCounts(int dr, int dt) {
610	<	for (;;) {
611	<	int wc = workerCounts;
612	<	if (wc == 0 && (runState & TERMINATED) != 0)
613	<	return; // lagging termination on a backout
614	<	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
615	<	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0)
616	<	Thread.yield();
617	<	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
608	<	wc, wc - (dr + dt)))
609	<	return;
609	>	final void work(ForkJoinWorkerThread w) {
610	>	boolean swept = false;                // true on empty scans
611	>	long c;
612	>	while (!w.terminate && (int)(c = ctl) >= 0) {
613	>	int a;                            // active count
614	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
615	>	swept = scan(w, a);
616	>	else if (tryAwaitWork(w, c))
617	>	swept = false;
618		}
619		}
620
621	+	// Signalling
622	+
623		/**
624	<	* Increments event count
624	>	* Wakes up or creates a worker.
625		*/
626	<	private void advanceEventCount() {
627	<	int c;
628	<	do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
629	<	c = eventCount, c+1));
626	>	final void signalWork() {
627	>	/*
628	>	* The while condition is true if: (there is are too few total
629	>	* workers OR there is at least one waiter) AND (there are too
630	>	* few active workers OR the pool is terminating).  The value
631	>	* of e distinguishes the remaining cases: zero (no waiters)
632	>	* for create, negative if terminating (in which case do
633	>	* nothing), else release a waiter. The secondary checks for
634	>	* release (non-null array etc) can fail if the pool begins
635	>	* terminating after the test, and don't impose any added cost
636	>	* because JVMs must perform null and bounds checks anyway.
637	>	*/
638	>	long c; int e, u;
639	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
640	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
641	>	if (e > 0) {                         // release a waiting worker
642	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
643	>	if ((ws = workers) == null ||
644	>	(i = ~e & SMASK) >= ws.length ||
645	>	(w = ws[i]) == null)
646	>	break;
647	>	long nc = (((long)(w.nextWait & E_MASK)) |
648	>	((long)(u + UAC_UNIT) << 32));
649	>	if (w.eventCount == e &&
650	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
651	>	w.eventCount = (e + EC_UNIT) & E_MASK;
652	>	if (w.parked)
653	>	UNSAFE.unpark(w);
654	>	break;
655	>	}
656	>	}
657	>	else if (UNSAFE.compareAndSwapLong
658	>	(this, ctlOffset, c,
659	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
660	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
661	>	addWorker();
662	>	break;
663	>	}
664	>	}
665		}
666
667		/**
668	<	* Tries incrementing active count; fails on contention.
669	<	* Called by workers before executing tasks.
668	>	* Variant of signalWork to help release waiters on rescans.
669	>	* Tries once to release a waiter if active count < 0.
670		*
671	<	* @return true on success
671	>	* @return false if failed due to contention, else true
672		*/
673	<	final boolean tryIncrementActiveCount() {
674	<	int c;
675	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
676	<	c = runState, c + ONE_ACTIVE);
673	>	private boolean tryReleaseWaiter() {
674	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
675	>	if ((e = (int)(c = ctl)) > 0 &&
676	>	(int)(c >> AC_SHIFT) < 0 &&
677	>	(ws = workers) != null &&
678	>	(i = ~e & SMASK) < ws.length &&
679	>	(w = ws[i]) != null) {
680	>	long nc = ((long)(w.nextWait & E_MASK) |
681	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
682	>	if (w.eventCount != e ||
683	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
684	>	return false;
685	>	w.eventCount = (e + EC_UNIT) & E_MASK;
686	>	if (w.parked)
687	>	UNSAFE.unpark(w);
688	>	}
689	>	return true;
690		}
691
692	+	// Scanning for tasks
693	+
694		/**
695	<	* Tries decrementing active count; fails on contention.
696	<	* Called when workers cannot find tasks to run.
695	>	* Scans for and, if found, executes one task. Scans start at a
696	>	* random index of workers array, and randomly select the first
697	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
698	>	* circular sweeps, which is necessary to check quiescence. and
699	>	* taking a submission only if no stealable tasks were found.  The
700	>	* steal code inside the loop is a specialized form of
701	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
702	>	* helpJoinTask and signal propagation. The code for submission
703	>	* queues is almost identical. On each steal, the worker completes
704	>	* not only the task, but also all local tasks that this task may
705	>	* have generated. On detecting staleness or contention when
706	>	* trying to take a task, this method returns without finishing
707	>	* sweep, which allows global state rechecks before retry.
708	>	*
709	>	* @param w the worker
710	>	* @param a the number of active workers
711	>	* @return true if swept all queues without finding a task
712		*/
713	<	final boolean tryDecrementActiveCount() {
714	<	int c;
715	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
716	<	c = runState, c - ONE_ACTIVE);
713	>	private boolean scan(ForkJoinWorkerThread w, int a) {
714	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
715	>	int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK;
716	>	ForkJoinWorkerThread[] ws = workers;
717	>	if (ws == null || ws.length <= m)         // staleness check
718	>	return false;
719	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
720	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
721	>	ForkJoinWorkerThread v = ws[k & m];
722	>	if (v != null && (b = v.queueBase) != v.queueTop &&
723	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
724	>	long u = (i << ASHIFT) + ABASE;
725	>	if ((t = q[i]) != null && v.queueBase == b &&
726	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
727	>	int d = (v.queueBase = b + 1) - v.queueTop;
728	>	v.stealHint = w.poolIndex;
729	>	if (d != 0)
730	>	signalWork();             // propagate if nonempty
731	>	w.execTask(t);
732	>	}
733	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
734	>	return false;                     // store next seed
735	>	}
736	>	else if (j < 0) {                     // xorshift
737	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
738	>	}
739	>	else
740	>	++k;
741	>	}
742	>	if (scanGuard != g)                       // staleness check
743	>	return false;
744	>	else {                                    // try to take submission
745	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
746	>	if ((b = queueBase) != queueTop &&
747	>	(q = submissionQueue) != null &&
748	>	(i = (q.length - 1) & b) >= 0) {
749	>	long u = (i << ASHIFT) + ABASE;
750	>	if ((t = q[i]) != null && queueBase == b &&
751	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
752	>	queueBase = b + 1;
753	>	w.execTask(t);
754	>	}
755	>	return false;
756	>	}
757	>	return true;                         // all queues empty
758	>	}
759		}
760
761		/**
762	<	* Advances to at least the given level. Returns true if not
763	<	* already in at least the given level.
764	<	*/
765	<	private boolean advanceRunLevel(int level) {
766	<	for (;;) {
767	<	int s = runState;
768	<	if ((s & level) != 0)
769	<	return false;
770	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
762	>	* Tries to enqueue worker w in wait queue and await change in
763	>	* worker's eventCount.  If the pool is quiescent and there is
764	>	* more than one worker, possibly terminates worker upon exit.
765	>	* Otherwise, before blocking, rescans queues to avoid missed
766	>	* signals.  Upon finding work, releases at least one worker
767	>	* (which may be the current worker). Rescans restart upon
768	>	* detected staleness or failure to release due to
769	>	* contention. Note the unusual conventions about Thread.interrupt
770	>	* here and elsewhere: Because interrupts are used solely to alert
771	>	* threads to check termination, which is checked here anyway, we
772	>	* clear status (using Thread.interrupted) before any call to
773	>	* park, so that park does not immediately return due to status
774	>	* being set via some other unrelated call to interrupt in user
775	>	* code.
776	>	*
777	>	* @param w the calling worker
778	>	* @param c the ctl value on entry
779	>	* @return true if waited or another thread was released upon enq
780	>	*/
781	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
782	>	int v = w.eventCount;
783	>	w.nextWait = (int)c;                      // w's successor record
784	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
785	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
786	>	long d = ctl; // return true if lost to a deq, to force scan
787	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
788	>	}
789	>	for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
790	>	long s = stealCount;
791	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
792	>	sc = w.stealCount = 0;
793	>	else if (w.eventCount != v)
794	>	return true;                      // update next time
795	>	}
796	>	if ((!shutdown || !tryTerminate(false)) &&
797	>	(int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 &&
798	>	blockedCount == 0 && quiescerCount == 0)
799	>	idleAwaitWork(w, nc, c, v);           // quiescent
800	>	for (boolean rescanned = false;;) {
801	>	if (w.eventCount != v)
802		return true;
803	+	if (!rescanned) {
804	+	int g = scanGuard, m = g & SMASK;
805	+	ForkJoinWorkerThread[] ws = workers;
806	+	if (ws != null && m < ws.length) {
807	+	rescanned = true;
808	+	for (int i = 0; i <= m; ++i) {
809	+	ForkJoinWorkerThread u = ws[i];
810	+	if (u != null) {
811	+	if (u.queueBase != u.queueTop &&
812	+	!tryReleaseWaiter())
813	+	rescanned = false; // contended
814	+	if (w.eventCount != v)
815	+	return true;
816	+	}
817	+	}
818	+	}
819	+	if (scanGuard != g ||              // stale
820	+	(queueBase != queueTop && !tryReleaseWaiter()))
821	+	rescanned = false;
822	+	if (!rescanned)
823	+	Thread.yield();                // reduce contention
824	+	else
825	+	Thread.interrupted();          // clear before park
826	+	}
827	+	else {
828	+	w.parked = true;                   // must recheck
829	+	if (w.eventCount != v) {
830	+	w.parked = false;
831	+	return true;
832	+	}
833	+	LockSupport.park(this);
834	+	rescanned = w.parked = false;
835	+	}
836		}
837		}
838
658	–	// workers array maintenance
659	–
839		/**
840	<	* Records and returns a workers array index for new worker.
841	<	*/
842	<	private int recordWorker(ForkJoinWorkerThread w) {
843	<	// Try using slot totalCount-1. If not available, scan and/or resize
844	<	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
845	<	final ReentrantLock lock = this.workerLock;
846	<	lock.lock();
847	<	try {
848	<	ForkJoinWorkerThread[] ws = workers;
849	<	int n = ws.length;
850	<	if (k < 0 || k >= n || ws[k] != null) {
851	<	for (k = 0; k < n && ws[k] != null; ++k)
852	<	;
853	<	if (k == n)
854	<	ws = Arrays.copyOf(ws, n << 1);
840	>	* If inactivating worker w has caused pool to become
841	>	* quiescent, check for pool termination, and wait for event
842	>	* for up to SHRINK_RATE nanosecs (rescans are unnecessary in
843	>	* this case because quiescence reflects consensus about lack
844	>	* of work). On timeout, if ctl has not changed, terminate the
845	>	* worker. Upon its termination (see deregisterWorker), it may
846	>	* wake up another worker to possibly repeat this process.
847	>	*
848	>	* @param w the calling worker
849	>	* @param currentCtl the ctl value after enqueuing w
850	>	* @param prevCtl the ctl value if w terminated
851	>	* @param v the eventCount w awaits change
852	>	*/
853	>	private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
854	>	long prevCtl, int v) {
855	>	if (w.eventCount == v) {
856	>	if (shutdown)
857	>	tryTerminate(false);
858	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
859	>	while (ctl == currentCtl) {
860	>	long startTime = System.nanoTime();
861	>	w.parked = true;
862	>	if (w.eventCount == v)             // must recheck
863	>	LockSupport.parkNanos(this, SHRINK_RATE);
864	>	w.parked = false;
865	>	if (w.eventCount != v)
866	>	break;
867	>	else if (System.nanoTime() - startTime <
868	>	SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop
869	>	Thread.interrupted();          // spurious wakeup
870	>	else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
871	>	currentCtl, prevCtl)) {
872	>	w.terminate = true;            // restore previous
873	>	w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
874	>	break;
875	>	}
876		}
677	–	ws[k] = w;
678	–	workers = ws; // volatile array write ensures slot visibility
679	–	} finally {
680	–	lock.unlock();
877		}
682	–	return k;
878		}
879
880	+	// Submissions
881	+
882		/**
883	<	* Nulls out record of worker in workers array
883	>	* Enqueues the given task in the submissionQueue.  Same idea as
884	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
885	>	*
886	>	* @param t the task
887		*/
888	<	private void forgetWorker(ForkJoinWorkerThread w) {
889	<	int idx = w.poolIndex;
690	<	// Locking helps method recordWorker avoid unecessary expansion
691	<	final ReentrantLock lock = this.workerLock;
888	>	private void addSubmission(ForkJoinTask<?> t) {
889	>	final ReentrantLock lock = this.submissionLock;
890		lock.lock();
891		try {
892	<	ForkJoinWorkerThread[] ws = workers;
893	<	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
894	<	ws[idx] = null;
892	>	ForkJoinTask<?>[] q; int s, m;
893	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
894	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
895	>	UNSAFE.putOrderedObject(q, u, t);
896	>	queueTop = s + 1;
897	>	if (s - queueBase == m)
898	>	growSubmissionQueue();
899	>	}
900		} finally {
901		lock.unlock();
902		}
903	+	signalWork();
904		}
905
906	<	// adding and removing workers
906	>	//  (pollSubmission is defined below with exported methods)
907
908		/**
909	<	* Tries to create and add new worker. Assumes that worker counts
910	<	* are already updated to accommodate the worker, so adjusts on
707	<	* failure.
909	>	* Creates or doubles submissionQueue array.
910	>	* Basically identical to ForkJoinWorkerThread version.
911		*/
912	<	private void addWorker() {
913	<	ForkJoinWorkerThread w = null;
914	<	try {
915	<	w = factory.newThread(this);
916	<	} finally { // Adjust on either null or exceptional factory return
917	<	if (w == null) {
918	<	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
919	<	tryTerminate(false); // in case of failure during shutdown
912	>	private void growSubmissionQueue() {
913	>	ForkJoinTask<?>[] oldQ = submissionQueue;
914	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
915	>	if (size > MAXIMUM_QUEUE_CAPACITY)
916	>	throw new RejectedExecutionException("Queue capacity exceeded");
917	>	if (size < INITIAL_QUEUE_CAPACITY)
918	>	size = INITIAL_QUEUE_CAPACITY;
919	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
920	>	int mask = size - 1;
921	>	int top = queueTop;
922	>	int oldMask;
923	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
924	>	for (int b = queueBase; b != top; ++b) {
925	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
926	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
927	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
928	>	UNSAFE.putObjectVolatile
929	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
930		}
931		}
719	–	if (w != null)
720	–	w.start(recordWorker(w), ueh);
932		}
933
934	+	// Blocking support
935	+
936		/**
937	<	* Final callback from terminating worker.  Removes record of
938	<	* worker from array, and adjusts counts. If pool is shutting
939	<	* down, tries to complete terminatation.
940	<	*
941	<	* @param w the worker
942	<	*/
943	<	final void workerTerminated(ForkJoinWorkerThread w) {
944	<	forgetWorker(w);
945	<	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
946	<	while (w.stealCount != 0) // collect final count
947	<	tryAccumulateStealCount(w);
948	<	tryTerminate(false);
937	>	* Tries to increment blockedCount, decrement active count
938	>	* (sometimes implicitly) and possibly release or create a
939	>	* compensating worker in preparation for blocking. Fails
940	>	* on contention or termination.
941	>	*
942	>	* @return true if the caller can block, else should recheck and retry
943	>	*/
944	>	private boolean tryPreBlock() {
945	>	int b = blockedCount;
946	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
947	>	int pc = parallelism;
948	>	do {
949	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
950	>	int e, ac, tc, i;
951	>	long c = ctl;
952	>	int u = (int)(c >>> 32);
953	>	if ((e = (int)c) < 0) {
954	>	// skip -- terminating
955	>	}
956	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
957	>	(ws = workers) != null &&
958	>	(i = ~e & SMASK) < ws.length &&
959	>	(w = ws[i]) != null) {
960	>	long nc = ((long)(w.nextWait & E_MASK) |
961	>	(c & (AC_MASK|TC_MASK)));
962	>	if (w.eventCount == e &&
963	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
964	>	w.eventCount = (e + EC_UNIT) & E_MASK;
965	>	if (w.parked)
966	>	UNSAFE.unpark(w);
967	>	return true;             // release an idle worker
968	>	}
969	>	}
970	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
971	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
972	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
973	>	return true;             // no compensation needed
974	>	}
975	>	else if (tc + pc < MAX_ID) {
976	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
977	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
978	>	addWorker();
979	>	return true;            // create a replacement
980	>	}
981	>	}
982	>	// try to back out on any failure and let caller retry
983	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
984	>	b = blockedCount, b - 1));
985	>	}
986	>	return false;
987		}
988
738	–	// Waiting for and signalling events
739	–
989		/**
990	<	* Releases workers blocked on a count not equal to current count.
742	<	* Normally called after precheck that eventWaiters isn't zero to
743	<	* avoid wasted array checks.
744	<	*
745	<	* @param signalling true if caller is a signalling worker so can
746	<	* exit upon (conservatively) detected contention by other threads
747	<	* who will continue to release
990	>	* Decrements blockedCount and increments active count.
991		*/
992	<	private void releaseEventWaiters(boolean signalling) {
993	<	ForkJoinWorkerThread[] ws = workers;
994	<	int n = ws.length;
995	<	long h; // head of stack
996	<	ForkJoinWorkerThread w; int id, ec;
997	<	while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 &&
998	<	(int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) &&
756	<	id < n && (w = ws[id]) != null) {
757	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
758	<	h, h = w.nextWaiter))
759	<	LockSupport.unpark(w);
760	<	if (signalling && (eventCount != ec || eventWaiters != h))
761	<	break;
762	<	}
992	>	private void postBlock() {
993	>	long c;
994	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
995	>	c = ctl, c + AC_UNIT));
996	>	int b;
997	>	do {} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
998	>	b = blockedCount, b - 1));
999		}
1000
1001		/**
1002	<	* Tries to advance eventCount and releases waiters. Called only
1003	<	* from workers.
1002	>	* Possibly blocks waiting for the given task to complete, or
1003	>	* cancels the task if terminating.  Fails to wait if contended.
1004	>	*
1005	>	* @param joinMe the task
1006		*/
1007	<	final void signalWork() {
1008	<	int c; // try to increment event count -- CAS failure OK
1009	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1010	<	if (eventWaiters != 0L)
1011	<	releaseEventWaiters(true);
1007	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
1008	>	Thread.interrupted(); // clear interrupts before checking termination
1009	>	if (joinMe.status >= 0) {
1010	>	if (tryPreBlock()) {
1011	>	joinMe.tryAwaitDone(0L);
1012	>	postBlock();
1013	>	}
1014	>	else if ((ctl & STOP_BIT) != 0L)
1015	>	joinMe.cancelIgnoringExceptions();
1016	>	}
1017		}
1018
1019		/**
1020	<	* Blocks worker until terminating or event count
1021	<	* advances from last value held by worker
1022	<	*
1023	<	* @param w the calling worker thread
1024	<	*/
1025	<	private void eventSync(ForkJoinWorkerThread w) {
1026	<	int wec = w.lastEventCount;
1027	<	long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
1028	<	long h;
1029	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
1030	<	((h = eventWaiters) == 0L ||
1031	<	(int)(h >>> EVENT_COUNT_SHIFT) == wec) &&
1032	<	eventCount == wec) {
1033	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1034	<	w.nextWaiter = h, nh)) {
1035	<	while (runState < TERMINATING && eventCount == wec) {
1036	<	if (!tryAccumulateStealCount(w))  // transfer while idle
1037	<	continue;
1038	<	Thread.interrupted();             // clear/ignore interrupt
1039	<	if (eventCount != wec)
1020	>	* Possibly blocks the given worker waiting for joinMe to
1021	>	* complete or timeout.
1022	>	*
1023	>	* @param joinMe the task
1024	>	* @param millis the wait time for underlying Object.wait
1025	>	*/
1026	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1027	>	while (joinMe.status >= 0) {
1028	>	Thread.interrupted();
1029	>	if ((ctl & STOP_BIT) != 0L) {
1030	>	joinMe.cancelIgnoringExceptions();
1031	>	break;
1032	>	}
1033	>	if (tryPreBlock()) {
1034	>	long last = System.nanoTime();
1035	>	while (joinMe.status >= 0) {
1036	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1037	>	if (millis <= 0)
1038	>	break;
1039	>	joinMe.tryAwaitDone(millis);
1040	>	if (joinMe.status < 0)
1041		break;
1042	<	LockSupport.park(w);
1042	>	if ((ctl & STOP_BIT) != 0L) {
1043	>	joinMe.cancelIgnoringExceptions();
1044	>	break;
1045	>	}
1046	>	long now = System.nanoTime();
1047	>	nanos -= now - last;
1048	>	last = now;
1049		}
1050	+	postBlock();
1051		break;
1052		}
1053		}
803	–	w.lastEventCount = eventCount;
1054		}
1055
806	–	// Maintaining spares
807	–
1056		/**
1057	<	* Pushes worker onto the spare stack
1057	>	* If necessary, compensates for blocker, and blocks.
1058		*/
1059	<	final void pushSpare(ForkJoinWorkerThread w) {
1060	<	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1);
1061	<	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
1062	<	w.nextSpare = spareWaiters,ns));
1063	<	}
1064	<
1065	<	/**
1066	<	* Tries (once) to resume a spare if running count is less than
1067	<	* target parallelism. Fails on contention or stale workers.
1068	<	*/
821	<	private void tryResumeSpare() {
822	<	int sw, id;
823	<	ForkJoinWorkerThread w;
824	<	ForkJoinWorkerThread[] ws;
825	<	if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
826	<	id < (ws = workers).length && (w = ws[id]) != null &&
827	<	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
828	<	eventWaiters == 0L &&
829	<	spareWaiters == sw &&
830	<	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
831	<	sw, w.nextSpare) &&
832	<	w.tryUnsuspend()) {
833	<	int c; // try increment; if contended, finish after unpark
834	<	boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
835	<	c = workerCounts,
836	<	c + ONE_RUNNING);
837	<	LockSupport.unpark(w);
838	<	if (!inc) {
839	<	do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
840	<	c = workerCounts,
841	<	c + ONE_RUNNING));
1059	>	private void awaitBlocker(ManagedBlocker blocker)
1060	>	throws InterruptedException {
1061	>	while (!blocker.isReleasable()) {
1062	>	if (tryPreBlock()) {
1063	>	try {
1064	>	do {} while (!blocker.isReleasable() && !blocker.block());
1065	>	} finally {
1066	>	postBlock();
1067	>	}
1068	>	break;
1069		}
1070		}
1071		}
1072
1073	<	/**
847	<	* Callback from oldest spare occasionally waking up.  Tries
848	<	* (once) to shutdown a spare if more than 25% spare overage, or
849	<	* if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at
850	<	* least #parallelism running threads. Note that we don't need CAS
851	<	* or locks here because the method is called only from the oldest
852	<	* suspended spare occasionally waking (and even misfires are OK).
853	<	*
854	<	* @param now the wake up nanoTime of caller
855	<	*/
856	<	final void tryTrimSpare(long now) {
857	<	long lastTrim = trimTime;
858	<	trimTime = now;
859	<	helpMaintainParallelism(); // first, help wake up any needed spares
860	<	int sw, id;
861	<	ForkJoinWorkerThread w;
862	<	ForkJoinWorkerThread[] ws;
863	<	int pc = parallelism;
864	<	int wc = workerCounts;
865	<	if ((wc & RUNNING_COUNT_MASK) >= pc &&
866	<	(((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25%
867	<	now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) &&
868	<	(id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
869	<	id < (ws = workers).length && (w = ws[id]) != null &&
870	<	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
871	<	sw, w.nextSpare))
872	<	w.shutdown(false);
873	<	}
1073	>	// Creating, registering and deregistring workers
1074
1075		/**
1076	<	* Does at most one of:
1077	<	*
1078	<	* 1. Help wake up existing workers waiting for work via
1079	<	*    releaseEventWaiters. (If any exist, then it probably doesn't
1080	<	*    matter right now if under target parallelism level.)
1081	<	*
1082	<	* 2. If below parallelism level and a spare exists, try (once)
1083	<	*    to resume it via tryResumeSpare.
1084	<	*
1085	<	* 3. If neither of the above, tries (once) to add a new
1086	<	*    worker if either there are not enough total, or if all
1087	<	*    existing workers are busy, there are either no running
1088	<	*    workers or the deficit is at least twice the surplus.
1089	<	*/
1090	<	private void helpMaintainParallelism() {
1091	<	// uglified to work better when not compiled
1092	<	int pc, wc, rc, tc, rs; long h;
1093	<	if ((h = eventWaiters) != 0L) {
1094	<	if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1095	<	releaseEventWaiters(false); // avoid useless call
1096	<	}
1097	<	else if ((pc = parallelism) >
898	<	(rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) {
899	<	if (spareWaiters != 0)
900	<	tryResumeSpare();
901	<	else if ((rs = runState) < TERMINATING &&
902	<	((tc = wc >>> TOTAL_COUNT_SHIFT) < pc ||
903	<	(tc == (rs & ACTIVE_COUNT_MASK) && // all busy
904	<	(rc == 0 ||                       // must add
905	<	rc < pc - ((tc - pc) << 1)) &&   // within slack
906	<	tc < MAX_WORKERS && runState == rs)) && // recheck busy
907	<	workerCounts == wc &&
908	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
909	<	wc + (ONE_RUNNING|ONE_TOTAL)))
910	<	addWorker();
1076	>	* Tries to create and start a worker; minimally rolls back counts
1077	>	* on failure.
1078	>	*/
1079	>	private void addWorker() {
1080	>	Throwable ex = null;
1081	>	ForkJoinWorkerThread t = null;
1082	>	try {
1083	>	t = factory.newThread(this);
1084	>	} catch (Throwable e) {
1085	>	ex = e;
1086	>	}
1087	>	if (t == null) {  // null or exceptional factory return
1088	>	long c;       // adjust counts
1089	>	do {} while (!UNSAFE.compareAndSwapLong
1090	>	(this, ctlOffset, c = ctl,
1091	>	(((c - AC_UNIT) & AC_MASK) |
1092	>	((c - TC_UNIT) & TC_MASK) |
1093	>	(c & ~(AC_MASK|TC_MASK)))));
1094	>	// Propagate exception if originating from an external caller
1095	>	if (!tryTerminate(false) && ex != null &&
1096	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1097	>	UNSAFE.throwException(ex);
1098		}
1099	+	else
1100	+	t.start();
1101		}
1102
1103		/**
1104	<	* Callback from workers invoked upon each top-level action (i.e.,
1105	<	* stealing a task or taking a submission and running
917	<	* it). Performs one or more of the following:
918	<	*
919	<	* 1. If the worker cannot find work (misses > 0), updates its
920	<	*    active status to inactive and updates activeCount unless
921	<	*    this is the first miss and there is contention, in which
922	<	*    case it may try again (either in this or a subsequent
923	<	*    call).
924	<	*
925	<	* 2. If there are at least 2 misses, awaits the next task event
926	<	*    via eventSync
927	<	*
928	<	* 3. If there are too many running threads, suspends this worker
929	<	*    (first forcing inactivation if necessary).  If it is not
930	<	*    needed, it may be killed while suspended via
931	<	*    tryTrimSpare. Otherwise, upon resume it rechecks to make
932	<	*    sure that it is still needed.
933	<	*
934	<	* 4. Helps release and/or reactivate other workers via
935	<	*    helpMaintainParallelism
936	<	*
937	<	* @param w the worker
938	<	* @param misses the number of scans by caller failing to find work
939	<	* (saturating at 2 just to avoid wraparound)
1104	>	* Callback from ForkJoinWorkerThread constructor to assign a
1105	>	* public name
1106		*/
1107	<	final void preStep(ForkJoinWorkerThread w, int misses) {
1108	<	boolean active = w.active;
1109	<	int pc = parallelism;
1110	<	for (;;) {
1111	<	int wc = workerCounts;
946	<	int rc = wc & RUNNING_COUNT_MASK;
947	<	if (active && (misses > 0 || rc > pc)) {
948	<	int rs;                      // try inactivate
949	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
950	<	rs = runState, rs - ONE_ACTIVE))
951	<	active = w.active = false;
952	<	else if (misses > 1 || rc > pc ||
953	<	(rs & ACTIVE_COUNT_MASK) >= pc)
954	<	continue;                // force inactivate
955	<	}
956	<	if (misses > 1) {
957	<	misses = 0;                  // don't re-sync
958	<	eventSync(w);                // continue loop to recheck rc
959	<	}
960	<	else if (rc > pc) {
961	<	if (workerCounts == wc &&   // try to suspend as spare
962	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
963	<	wc, wc - ONE_RUNNING) &&
964	<	!w.suspendAsSpare())    // false if killed
965	<	break;
966	<	}
967	<	else {
968	<	if (rc < pc || eventWaiters != 0L)
969	<	helpMaintainParallelism();
970	<	break;
971	<	}
1107	>	final String nextWorkerName() {
1108	>	for (int n;;) {
1109	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1110	>	n = nextWorkerNumber, ++n))
1111	>	return workerNamePrefix + n;
1112		}
1113		}
1114
1115		/**
1116	<	* Helps and/or blocks awaiting join of the given task.
1117	<	* Alternates between helpJoinTask() and helpMaintainParallelism()
978	<	* as many times as there is a deficit in running count (or longer
979	<	* if running count would become zero), then blocks if task still
980	<	* not done.
1116	>	* Callback from ForkJoinWorkerThread constructor to
1117	>	* determine its poolIndex and record in workers array.
1118		*
1119	<	* @param joinMe the task to join
1119	>	* @param w the worker
1120	>	* @return the worker's pool index
1121		*/
1122	<	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1123	<	int threshold = parallelism;         // descend blocking thresholds
1124	<	while (joinMe.status >= 0) {
1125	<	boolean block; int wc;
1126	<	worker.helpJoinTask(joinMe);
1127	<	if (joinMe.status < 0)
1128	<	break;
1129	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
1130	<	if (threshold > 0)
1131	<	--threshold;
1132	<	else
1133	<	advanceEventCount(); // force release
1134	<	block = false;
1122	>	final int registerWorker(ForkJoinWorkerThread w) {
1123	>	/*
1124	>	* In the typical case, a new worker acquires the lock, uses
1125	>	* next available index and returns quickly.  Since we should
1126	>	* not block callers (ultimately from signalWork or
1127	>	* tryPreBlock) waiting for the lock needed to do this, we
1128	>	* instead help release other workers while waiting for the
1129	>	* lock.
1130	>	*/
1131	>	for (int g;;) {
1132	>	ForkJoinWorkerThread[] ws;
1133	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1134	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1135	>	g, g | SG_UNIT)) {
1136	>	int k = nextWorkerIndex;
1137	>	try {
1138	>	if ((ws = workers) != null) { // ignore on shutdown
1139	>	int n = ws.length;
1140	>	if (k < 0 || k >= n || ws[k] != null) {
1141	>	for (k = 0; k < n && ws[k] != null; ++k)
1142	>	;
1143	>	if (k == n)
1144	>	ws = workers = Arrays.copyOf(ws, n << 1);
1145	>	}
1146	>	ws[k] = w;
1147	>	nextWorkerIndex = k + 1;
1148	>	int m = g & SMASK;
1149	>	g = (k > m) ? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1150	>	}
1151	>	} finally {
1152	>	scanGuard = g;
1153	>	}
1154	>	return k;
1155		}
1156	<	else
1157	<	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1158	<	wc, wc - ONE_RUNNING);
1159	<	helpMaintainParallelism();
1160	<	if (block) {
1161	<	int c;
1162	<	joinMe.internalAwaitDone();
1005	<	do {} while (!UNSAFE.compareAndSwapInt
1006	<	(this, workerCountsOffset,
1007	<	c = workerCounts, c + ONE_RUNNING));
1008	<	break;
1156	>	else if ((ws = workers) != null) { // help release others
1157	>	for (ForkJoinWorkerThread u : ws) {
1158	>	if (u != null && u.queueBase != u.queueTop) {
1159	>	if (tryReleaseWaiter())
1160	>	break;
1161	>	}
1162	>	}
1163		}
1164		}
1165		}
1166
1167		/**
1168	<	* Same idea as awaitJoin, but no helping
1168	>	* Final callback from terminating worker.  Removes record of
1169	>	* worker from array, and adjusts counts. If pool is shutting
1170	>	* down, tries to complete termination.
1171	>	*
1172	>	* @param w the worker
1173		*/
1174	<	final void awaitBlocker(ManagedBlocker blocker)
1175	<	throws InterruptedException {
1176	<	int threshold = parallelism;
1177	<	while (!blocker.isReleasable()) {
1178	<	boolean block; int wc;
1179	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
1180	<	if (threshold > 0)
1181	<	--threshold;
1182	<	else
1183	<	advanceEventCount();
1184	<	block = false;
1174	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1175	>	int idx = w.poolIndex;
1176	>	int sc = w.stealCount;
1177	>	int steps = 0;
1178	>	// Remove from array, adjust worker counts and collect steal count.
1179	>	// We can intermix failed removes or adjusts with steal updates
1180	>	do {
1181	>	long s, c;
1182	>	int g;
1183	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1184	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1185	>	g, g |= SG_UNIT)) {
1186	>	ForkJoinWorkerThread[] ws = workers;
1187	>	if (ws != null && idx >= 0 &&
1188	>	idx < ws.length && ws[idx] == w)
1189	>	ws[idx] = null;    // verify
1190	>	nextWorkerIndex = idx;
1191	>	scanGuard = g + SG_UNIT;
1192	>	steps = 1;
1193		}
1194	+	if (steps == 1 &&
1195	+	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1196	+	(((c - AC_UNIT) & AC_MASK) |
1197	+	((c - TC_UNIT) & TC_MASK) |
1198	+	(c & ~(AC_MASK|TC_MASK)))))
1199	+	steps = 2;
1200	+	if (sc != 0 &&
1201	+	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1202	+	s = stealCount, s + sc))
1203	+	sc = 0;
1204	+	} while (steps != 2 || sc != 0);
1205	+	if (!tryTerminate(false)) {
1206	+	if (ex != null)   // possibly replace if died abnormally
1207	+	signalWork();
1208		else
1209	<	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1030	<	wc, wc - ONE_RUNNING);
1031	<	helpMaintainParallelism();
1032	<	if (block) {
1033	<	try {
1034	<	do {} while (!blocker.isReleasable() && !blocker.block());
1035	<	} finally {
1036	<	int c;
1037	<	do {} while (!UNSAFE.compareAndSwapInt
1038	<	(this, workerCountsOffset,
1039	<	c = workerCounts, c + ONE_RUNNING));
1040	<	}
1041	<	break;
1042	<	}
1209	>	tryReleaseWaiter();
1210		}
1211		}
1212
1213	+	// Shutdown and termination
1214	+
1215		/**
1216		* Possibly initiates and/or completes termination.
1217		*
#	Line 1051 | Line 1220 | public class ForkJoinPool extends Abstra
1220		* @return true if now terminating or terminated
1221		*/
1222		private boolean tryTerminate(boolean now) {
1223	<	if (now)
1224	<	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1225	<	else if (runState < SHUTDOWN ||
1226	<	!submissionQueue.isEmpty() ||
1227	<	(runState & ACTIVE_COUNT_MASK) != 0)
1228	<	return false;
1229	<
1230	<	if (advanceRunLevel(TERMINATING))
1231	<	startTerminating();
1232	<
1233	<	// Finish now if all threads terminated; else in some subsequent call
1234	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1235	<	advanceRunLevel(TERMINATED);
1236	<	termination.arrive();
1223	>	long c;
1224	>	while (((c = ctl) & STOP_BIT) == 0) {
1225	>	if (!now) {
1226	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1227	>	return false;
1228	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1229	>	queueBase != queueTop) {
1230	>	if (ctl == c) // staleness check
1231	>	return false;
1232	>	continue;
1233	>	}
1234	>	}
1235	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1236	>	startTerminating();
1237	>	}
1238	>	if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
1239	>	final ReentrantLock lock = this.submissionLock;
1240	>	lock.lock();
1241	>	try {
1242	>	termination.signalAll();
1243	>	} finally {
1244	>	lock.unlock();
1245	>	}
1246		}
1247		return true;
1248		}
1249
1250		/**
1251	<	* Actions on transition to TERMINATING
1252	<	*
1253	<	* Runs up to four passes through workers: (0) shutting down each
1254	<	* quietly (without waking up if parked) to quickly spread
1255	<	* notifications without unnecessary bouncing around event queues
1256	<	* etc (1) wake up and help cancel tasks (2) interrupt (3) mop up
1079	<	* races with interrupted workers
1251	>	* Runs up to three passes through workers: (0) Setting
1252	>	* termination status for each worker, followed by wakeups up to
1253	>	* queued workers; (1) helping cancel tasks; (2) interrupting
1254	>	* lagging threads (likely in external tasks, but possibly also
1255	>	* blocked in joins).  Each pass repeats previous steps because of
1256	>	* potential lagging thread creation.
1257		*/
1258		private void startTerminating() {
1259		cancelSubmissions();
1260	<	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1084	<	advanceEventCount();
1085	<	eventWaiters = 0L; // clobber lists
1086	<	spareWaiters = 0;
1260	>	for (int pass = 0; pass < 3; ++pass) {
1261		ForkJoinWorkerThread[] ws = workers;
1262	<	int n = ws.length;
1263	<	for (int i = 0; i < n; ++i) {
1264	<	ForkJoinWorkerThread w = ws[i];
1265	<	if (w != null) {
1266	<	w.shutdown(true);
1267	<	if (passes > 0 && !w.isTerminated()) {
1268	<	w.cancelTasks();
1269	<	LockSupport.unpark(w);
1270	<	if (passes > 1) {
1271	<	try {
1272	<	w.interrupt();
1099	<	} catch (SecurityException ignore) {
1262	>	if (ws != null) {
1263	>	for (ForkJoinWorkerThread w : ws) {
1264	>	if (w != null) {
1265	>	w.terminate = true;
1266	>	if (pass > 0) {
1267	>	w.cancelTasks();
1268	>	if (pass > 1 && !w.isInterrupted()) {
1269	>	try {
1270	>	w.interrupt();
1271	>	} catch (SecurityException ignore) {
1272	>	}
1273		}
1274		}
1275		}
1276		}
1277	+	terminateWaiters();
1278		}
1279		}
1280		}
1281
1282		/**
1283	<	* Clear out and cancel submissions, ignoring exceptions
1283	>	* Polls and cancels all submissions. Called only during termination.
1284		*/
1285		private void cancelSubmissions() {
1286	<	ForkJoinTask<?> task;
1287	<	while ((task = submissionQueue.poll()) != null) {
1288	<	try {
1289	<	task.cancel(false);
1290	<	} catch (Throwable ignore) {
1286	>	while (queueBase != queueTop) {
1287	>	ForkJoinTask<?> task = pollSubmission();
1288	>	if (task != null) {
1289	>	try {
1290	>	task.cancel(false);
1291	>	} catch (Throwable ignore) {
1292	>	}
1293		}
1294		}
1295		}
1296
1297	<	// misc support for ForkJoinWorkerThread
1297	>	/**
1298	>	* Tries to set the termination status of waiting workers, and
1299	>	* then wakes them up (after which they will terminate).
1300	>	*/
1301	>	private void terminateWaiters() {
1302	>	ForkJoinWorkerThread[] ws = workers;
1303	>	if (ws != null) {
1304	>	ForkJoinWorkerThread w; long c; int i, e;
1305	>	int n = ws.length;
1306	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1307	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1308	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1309	>	(long)(w.nextWait & E_MASK) |
1310	>	((c + AC_UNIT) & AC_MASK) |
1311	>	(c & (TC_MASK|STOP_BIT)))) {
1312	>	w.terminate = true;
1313	>	w.eventCount = e + EC_UNIT;
1314	>	if (w.parked)
1315	>	UNSAFE.unpark(w);
1316	>	}
1317	>	}
1318	>	}
1319	>	}
1320	>
1321	>	// misc ForkJoinWorkerThread support
1322
1323		/**
1324	<	* Returns pool number
1324	>	* Increment or decrement quiescerCount. Needed only to prevent
1325	>	* triggering shutdown if a worker is transiently inactive while
1326	>	* checking quiescence.
1327	>	*
1328	>	* @param delta 1 for increment, -1 for decrement
1329		*/
1330	<	final int getPoolNumber() {
1331	<	return poolNumber;
1330	>	final void addQuiescerCount(int delta) {
1331	>	int c;
1332	>	do {} while (!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1333	>	c = quiescerCount, c + delta));
1334		}
1335
1336		/**
1337	<	* Tries to accumulates steal count from a worker, clearing
1338	<	* the worker's value.
1337	>	* Directly increment or decrement active count without
1338	>	* queuing. This method is used to transiently assert inactivation
1339	>	* while checking quiescence.
1340		*
1341	<	* @return true if worker steal count now zero
1341	>	* @param delta 1 for increment, -1 for decrement
1342		*/
1343	<	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1344	<	int sc = w.stealCount;
1345	<	long c = stealCount;
1346	<	// CAS even if zero, for fence effects
1347	<	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1348	<	if (sc != 0)
1142	<	w.stealCount = 0;
1143	<	return true;
1144	<	}
1145	<	return sc == 0;
1343	>	final void addActiveCount(int delta) {
1344	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1345	>	long c;
1346	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1347	>	((c + d) & AC_MASK) |
1348	>	(c & ~AC_MASK)));
1349		}
1350
1351		/**
#	Line 1150 | Line 1353 | public class ForkJoinPool extends Abstra
1353		* active thread.
1354		*/
1355		final int idlePerActive() {
1356	<	int pc = parallelism; // use parallelism, not rc
1357	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1358	<	// Use exact results for small values, saturate past 4
1359	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1356	>	// Approximate at powers of two for small values, saturate past 4
1357	>	int p = parallelism;
1358	>	int a = p + (int)(ctl >> AC_SHIFT);
1359	>	return (a > (p >>>= 1) ? 0 :
1360	>	a > (p >>>= 1) ? 1 :
1361	>	a > (p >>>= 1) ? 2 :
1362	>	a > (p >>>= 1) ? 4 :
1363	>	8);
1364		}
1365
1366	<	// Public and protected methods
1366	>	// Exported methods
1367
1368		// Constructors
1369
#	Line 1203 | Line 1410 | public class ForkJoinPool extends Abstra
1410		* use {@link #defaultForkJoinWorkerThreadFactory}.
1411		* @param handler the handler for internal worker threads that
1412		* terminate due to unrecoverable errors encountered while executing
1413	<	* tasks. For default value, use <code>null</code>.
1413	>	* tasks. For default value, use {@code null}.
1414		* @param asyncMode if true,
1415		* establishes local first-in-first-out scheduling mode for forked
1416		* tasks that are never joined. This mode may be more appropriate
1417		* than default locally stack-based mode in applications in which
1418		* worker threads only process event-style asynchronous tasks.
1419	<	* For default value, use <code>false</code>.
1419	>	* For default value, use {@code false}.
1420		* @throws IllegalArgumentException if parallelism less than or
1421		*         equal to zero, or greater than implementation limit
1422		* @throws NullPointerException if the factory is null
#	Line 1225 | Line 1432 | public class ForkJoinPool extends Abstra
1432		checkPermission();
1433		if (factory == null)
1434		throw new NullPointerException();
1435	<	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1435	>	if (parallelism <= 0 || parallelism > MAX_ID)
1436		throw new IllegalArgumentException();
1437		this.parallelism = parallelism;
1438		this.factory = factory;
1439		this.ueh = handler;
1440		this.locallyFifo = asyncMode;
1441	<	int arraySize = initialArraySizeFor(parallelism);
1442	<	this.workers = new ForkJoinWorkerThread[arraySize];
1443	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1444	<	this.workerLock = new ReentrantLock();
1445	<	this.termination = new Phaser(1);
1446	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
1447	<	this.trimTime = System.nanoTime();
1448	<	}
1449	<
1450	<	/**
1451	<	* Returns initial power of two size for workers array.
1452	<	* @param pc the initial parallelism level
1453	<	*/
1454	<	private static int initialArraySizeFor(int pc) {
1455	<	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1456	<	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1457	<	size |= size >>> 1;
1251	<	size |= size >>> 2;
1252	<	size |= size >>> 4;
1253	<	size |= size >>> 8;
1254	<	return size + 1;
1441	>	long np = (long)(-parallelism); // offset ctl counts
1442	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1443	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1444	>	// initialize workers array with room for 2*parallelism if possible
1445	>	int n = parallelism << 1;
1446	>	if (n >= MAX_ID)
1447	>	n = MAX_ID;
1448	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1449	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1450	>	}
1451	>	workers = new ForkJoinWorkerThread[n + 1];
1452	>	this.submissionLock = new ReentrantLock();
1453	>	this.termination = submissionLock.newCondition();
1454	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1455	>	sb.append(poolNumberGenerator.incrementAndGet());
1456	>	sb.append("-worker-");
1457	>	this.workerNamePrefix = sb.toString();
1458		}
1459
1460		// Execution methods
1461
1462		/**
1260	–	* Common code for execute, invoke and submit
1261	–	*/
1262	–	private <T> void doSubmit(ForkJoinTask<T> task) {
1263	–	if (task == null)
1264	–	throw new NullPointerException();
1265	–	if (runState >= SHUTDOWN)
1266	–	throw new RejectedExecutionException();
1267	–	submissionQueue.offer(task);
1268	–	advanceEventCount();
1269	–	helpMaintainParallelism();         // start or wake up workers
1270	–	}
1271	–
1272	–	/**
1463		* Performs the given task, returning its result upon completion.
1464	<	* If the caller is already engaged in a fork/join computation in
1465	<	* the current pool, this method is equivalent in effect to
1466	<	* {@link ForkJoinTask#invoke}.
1464	>	* If the computation encounters an unchecked Exception or Error,
1465	>	* it is rethrown as the outcome of this invocation.  Rethrown
1466	>	* exceptions behave in the same way as regular exceptions, but,
1467	>	* when possible, contain stack traces (as displayed for example
1468	>	* using {@code ex.printStackTrace()}) of both the current thread
1469	>	* as well as the thread actually encountering the exception;
1470	>	* minimally only the latter.
1471		*
1472		* @param task the task
1473		* @return the task's result
#	Line 1282 | Line 1476 | public class ForkJoinPool extends Abstra
1476		*         scheduled for execution
1477		*/
1478		public <T> T invoke(ForkJoinTask<T> task) {
1479	<	doSubmit(task);
1480	<	return task.join();
1479	>	Thread t = Thread.currentThread();
1480	>	if (task == null)
1481	>	throw new NullPointerException();
1482	>	if (shutdown)
1483	>	throw new RejectedExecutionException();
1484	>	if ((t instanceof ForkJoinWorkerThread) &&
1485	>	((ForkJoinWorkerThread)t).pool == this)
1486	>	return task.invoke();  // bypass submit if in same pool
1487	>	else {
1488	>	addSubmission(task);
1489	>	return task.join();
1490	>	}
1491	>	}
1492	>
1493	>	/**
1494	>	* Unless terminating, forks task if within an ongoing FJ
1495	>	* computation in the current pool, else submits as external task.
1496	>	*/
1497	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1498	>	ForkJoinWorkerThread w;
1499	>	Thread t = Thread.currentThread();
1500	>	if (shutdown)
1501	>	throw new RejectedExecutionException();
1502	>	if ((t instanceof ForkJoinWorkerThread) &&
1503	>	(w = (ForkJoinWorkerThread)t).pool == this)
1504	>	w.pushTask(task);
1505	>	else
1506	>	addSubmission(task);
1507		}
1508
1509		/**
1510		* Arranges for (asynchronous) execution of the given task.
1291	–	* If the caller is already engaged in a fork/join computation in
1292	–	* the current pool, this method is equivalent in effect to
1293	–	* {@link ForkJoinTask#fork}.
1511		*
1512		* @param task the task
1513		* @throws NullPointerException if the task is null
#	Line 1298 | Line 1515 | public class ForkJoinPool extends Abstra
1515		*         scheduled for execution
1516		*/
1517		public void execute(ForkJoinTask<?> task) {
1518	<	doSubmit(task);
1518	>	if (task == null)
1519	>	throw new NullPointerException();
1520	>	forkOrSubmit(task);
1521		}
1522
1523		// AbstractExecutorService methods
#	Line 1309 | Line 1528 | public class ForkJoinPool extends Abstra
1528		*         scheduled for execution
1529		*/
1530		public void execute(Runnable task) {
1531	+	if (task == null)
1532	+	throw new NullPointerException();
1533		ForkJoinTask<?> job;
1534		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1535		job = (ForkJoinTask<?>) task;
1536		else
1537		job = ForkJoinTask.adapt(task, null);
1538	<	doSubmit(job);
1538	>	forkOrSubmit(job);
1539		}
1540
1541		/**
1542		* Submits a ForkJoinTask for execution.
1322	–	* If the caller is already engaged in a fork/join computation in
1323	–	* the current pool, this method is equivalent in effect to
1324	–	* {@link ForkJoinTask#fork}.
1543		*
1544		* @param task the task to submit
1545		* @return the task
#	Line 1330 | Line 1548 | public class ForkJoinPool extends Abstra
1548		*         scheduled for execution
1549		*/
1550		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1551	<	doSubmit(task);
1551	>	if (task == null)
1552	>	throw new NullPointerException();
1553	>	forkOrSubmit(task);
1554		return task;
1555		}
1556
#	Line 1340 | Line 1560 | public class ForkJoinPool extends Abstra
1560		*         scheduled for execution
1561		*/
1562		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1563	+	if (task == null)
1564	+	throw new NullPointerException();
1565		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1566	<	doSubmit(job);
1566	>	forkOrSubmit(job);
1567		return job;
1568		}
1569
#	Line 1351 | Line 1573 | public class ForkJoinPool extends Abstra
1573		*         scheduled for execution
1574		*/
1575		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1576	+	if (task == null)
1577	+	throw new NullPointerException();
1578		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1579	<	doSubmit(job);
1579	>	forkOrSubmit(job);
1580		return job;
1581		}
1582
#	Line 1362 | Line 1586 | public class ForkJoinPool extends Abstra
1586		*         scheduled for execution
1587		*/
1588		public ForkJoinTask<?> submit(Runnable task) {
1589	+	if (task == null)
1590	+	throw new NullPointerException();
1591		ForkJoinTask<?> job;
1592		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1593		job = (ForkJoinTask<?>) task;
1594		else
1595		job = ForkJoinTask.adapt(task, null);
1596	<	doSubmit(job);
1596	>	forkOrSubmit(job);
1597		return job;
1598		}
1599
#	Line 1427 | Line 1653 | public class ForkJoinPool extends Abstra
1653
1654		/**
1655		* Returns the number of worker threads that have started but not
1656	<	* yet terminated.  This result returned by this method may differ
1656	>	* yet terminated.  The result returned by this method may differ
1657		* from {@link #getParallelism} when threads are created to
1658		* maintain parallelism when others are cooperatively blocked.
1659		*
1660		* @return the number of worker threads
1661		*/
1662		public int getPoolSize() {
1663	<	return workerCounts >>> TOTAL_COUNT_SHIFT;
1663	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1664		}
1665
1666		/**
#	Line 1456 | Line 1682 | public class ForkJoinPool extends Abstra
1682		* @return the number of worker threads
1683		*/
1684		public int getRunningThreadCount() {
1685	<	return workerCounts & RUNNING_COUNT_MASK;
1685	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1686	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
1687		}
1688
1689		/**
#	Line 1467 | Line 1694 | public class ForkJoinPool extends Abstra
1694		* @return the number of active threads
1695		*/
1696		public int getActiveThreadCount() {
1697	<	return runState & ACTIVE_COUNT_MASK;
1697	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1698	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
1699		}
1700
1701		/**
#	Line 1482 | Line 1710 | public class ForkJoinPool extends Abstra
1710		* @return {@code true} if all threads are currently idle
1711		*/
1712		public boolean isQuiescent() {
1713	<	return (runState & ACTIVE_COUNT_MASK) == 0;
1713	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1714		}
1715
1716		/**
#	Line 1512 | Line 1740 | public class ForkJoinPool extends Abstra
1740		*/
1741		public long getQueuedTaskCount() {
1742		long count = 0;
1743	<	ForkJoinWorkerThread[] ws = workers;
1744	<	int n = ws.length;
1745	<	for (int i = 0; i < n; ++i) {
1746	<	ForkJoinWorkerThread w = ws[i];
1747	<	if (w != null)
1748	<	count += w.getQueueSize();
1743	>	ForkJoinWorkerThread[] ws;
1744	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1745	>	(ws = workers) != null) {
1746	>	for (ForkJoinWorkerThread w : ws)
1747	>	if (w != null)
1748	>	count -= w.queueBase - w.queueTop; // must read base first
1749		}
1750		return count;
1751		}
1752
1753		/**
1754		* Returns an estimate of the number of tasks submitted to this
1755	<	* pool that have not yet begun executing.  This method takes time
1756	<	* proportional to the number of submissions.
1755	>	* pool that have not yet begun executing.  This method may take
1756	>	* time proportional to the number of submissions.
1757		*
1758		* @return the number of queued submissions
1759		*/
1760		public int getQueuedSubmissionCount() {
1761	<	return submissionQueue.size();
1761	>	return -queueBase + queueTop;
1762		}
1763
1764		/**
#	Line 1540 | Line 1768 | public class ForkJoinPool extends Abstra
1768		* @return {@code true} if there are any queued submissions
1769		*/
1770		public boolean hasQueuedSubmissions() {
1771	<	return !submissionQueue.isEmpty();
1771	>	return queueBase != queueTop;
1772		}
1773
1774		/**
#	Line 1551 | Line 1779 | public class ForkJoinPool extends Abstra
1779		* @return the next submission, or {@code null} if none
1780		*/
1781		protected ForkJoinTask<?> pollSubmission() {
1782	<	return submissionQueue.poll();
1782	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1783	>	while ((b = queueBase) != queueTop &&
1784	>	(q = submissionQueue) != null &&
1785	>	(i = (q.length - 1) & b) >= 0) {
1786	>	long u = (i << ASHIFT) + ABASE;
1787	>	if ((t = q[i]) != null &&
1788	>	queueBase == b &&
1789	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1790	>	queueBase = b + 1;
1791	>	return t;
1792	>	}
1793	>	}
1794	>	return null;
1795		}
1796
1797		/**
#	Line 1572 | Line 1812 | public class ForkJoinPool extends Abstra
1812		* @return the number of elements transferred
1813		*/
1814		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1815	<	int count = submissionQueue.drainTo(c);
1816	<	ForkJoinWorkerThread[] ws = workers;
1817	<	int n = ws.length;
1818	<	for (int i = 0; i < n; ++i) {
1819	<	ForkJoinWorkerThread w = ws[i];
1820	<	if (w != null)
1821	<	count += w.drainTasksTo(c);
1815	>	int count = 0;
1816	>	while (queueBase != queueTop) {
1817	>	ForkJoinTask<?> t = pollSubmission();
1818	>	if (t != null) {
1819	>	c.add(t);
1820	>	++count;
1821	>	}
1822	>	}
1823	>	ForkJoinWorkerThread[] ws;
1824	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1825	>	(ws = workers) != null) {
1826	>	for (ForkJoinWorkerThread w : ws)
1827	>	if (w != null)
1828	>	count += w.drainTasksTo(c);
1829		}
1830		return count;
1831		}
#	Line 1594 | Line 1841 | public class ForkJoinPool extends Abstra
1841		long st = getStealCount();
1842		long qt = getQueuedTaskCount();
1843		long qs = getQueuedSubmissionCount();
1597	–	int wc = workerCounts;
1598	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
1599	–	int rc = wc & RUNNING_COUNT_MASK;
1844		int pc = parallelism;
1845	<	int rs = runState;
1846	<	int ac = rs & ACTIVE_COUNT_MASK;
1845	>	long c = ctl;
1846	>	int tc = pc + (short)(c >>> TC_SHIFT);
1847	>	int rc = pc + (int)(c >> AC_SHIFT);
1848	>	if (rc < 0) // ignore transient negative
1849	>	rc = 0;
1850	>	int ac = rc + blockedCount;
1851	>	String level;
1852	>	if ((c & STOP_BIT) != 0)
1853	>	level = (tc == 0) ? "Terminated" : "Terminating";
1854	>	else
1855	>	level = shutdown ? "Shutting down" : "Running";
1856		return super.toString() +
1857	<	"[" + runLevelToString(rs) +
1857	>	"[" + level +
1858		", parallelism = " + pc +
1859		", size = " + tc +
1860		", active = " + ac +
#	Line 1612 | Line 1865 | public class ForkJoinPool extends Abstra
1865		"]";
1866		}
1867
1615	–	private static String runLevelToString(int s) {
1616	–	return ((s & TERMINATED) != 0 ? "Terminated" :
1617	–	((s & TERMINATING) != 0 ? "Terminating" :
1618	–	((s & SHUTDOWN) != 0 ? "Shutting down" :
1619	–	"Running")));
1620	–	}
1621	–
1868		/**
1869		* Initiates an orderly shutdown in which previously submitted
1870		* tasks are executed, but no new tasks will be accepted.
#	Line 1633 | Line 1879 | public class ForkJoinPool extends Abstra
1879		*/
1880		public void shutdown() {
1881		checkPermission();
1882	<	advanceRunLevel(SHUTDOWN);
1882	>	shutdown = true;
1883		tryTerminate(false);
1884		}
1885
#	Line 1655 | Line 1901 | public class ForkJoinPool extends Abstra
1901		*/
1902		public List<Runnable> shutdownNow() {
1903		checkPermission();
1904	+	shutdown = true;
1905		tryTerminate(true);
1906		return Collections.emptyList();
1907		}
#	Line 1665 | Line 1912 | public class ForkJoinPool extends Abstra
1912		* @return {@code true} if all tasks have completed following shut down
1913		*/
1914		public boolean isTerminated() {
1915	<	return runState >= TERMINATED;
1915	>	long c = ctl;
1916	>	return ((c & STOP_BIT) != 0L &&
1917	>	(short)(c >>> TC_SHIFT) == -parallelism);
1918		}
1919
1920		/**
#	Line 1673 | Line 1922 | public class ForkJoinPool extends Abstra
1922		* commenced but not yet completed.  This method may be useful for
1923		* debugging. A return of {@code true} reported a sufficient
1924		* period after shutdown may indicate that submitted tasks have
1925	<	* ignored or suppressed interruption, causing this executor not
1926	<	* to properly terminate.
1925	>	* ignored or suppressed interruption, or are waiting for IO,
1926	>	* causing this executor not to properly terminate. (See the
1927	>	* advisory notes for class {@link ForkJoinTask} stating that
1928	>	* tasks should not normally entail blocking operations.  But if
1929	>	* they do, they must abort them on interrupt.)
1930		*
1931		* @return {@code true} if terminating but not yet terminated
1932		*/
1933		public boolean isTerminating() {
1934	<	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1934	>	long c = ctl;
1935	>	return ((c & STOP_BIT) != 0L &&
1936	>	(short)(c >>> TC_SHIFT) != -parallelism);
1937	>	}
1938	>
1939	>	/**
1940	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1941	>	*/
1942	>	final boolean isAtLeastTerminating() {
1943	>	return (ctl & STOP_BIT) != 0L;
1944		}
1945
1946		/**
#	Line 1688 | Line 1949 | public class ForkJoinPool extends Abstra
1949		* @return {@code true} if this pool has been shut down
1950		*/
1951		public boolean isShutdown() {
1952	<	return runState >= SHUTDOWN;
1952	>	return shutdown;
1953		}
1954
1955		/**
#	Line 1704 | Line 1965 | public class ForkJoinPool extends Abstra
1965		*/
1966		public boolean awaitTermination(long timeout, TimeUnit unit)
1967		throws InterruptedException {
1968	+	long nanos = unit.toNanos(timeout);
1969	+	final ReentrantLock lock = this.submissionLock;
1970	+	lock.lock();
1971		try {
1972	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1973	<	} catch(TimeoutException ex) {
1974	<	return false;
1972	>	for (;;) {
1973	>	if (isTerminated())
1974	>	return true;
1975	>	if (nanos <= 0)
1976	>	return false;
1977	>	nanos = termination.awaitNanos(nanos);
1978	>	}
1979	>	} finally {
1980	>	lock.unlock();
1981		}
1982		}
1983
#	Line 1719 | Line 1989 | public class ForkJoinPool extends Abstra
1989		* {@code isReleasable} must return {@code true} if blocking is
1990		* not necessary. Method {@code block} blocks the current thread
1991		* if necessary (perhaps internally invoking {@code isReleasable}
1992	<	* before actually blocking). The unusual methods in this API
1993	<	* accommodate synchronizers that may, but don't usually, block
1994	<	* for long periods. Similarly, they allow more efficient internal
1995	<	* handling of cases in which additional workers may be, but
1996	<	* usually are not, needed to ensure sufficient parallelism.
1997	<	* Toward this end, implementations of method {@code isReleasable}
1998	<	* must be amenable to repeated invocation.
1992	>	* before actually blocking). These actions are performed by any
1993	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
1994	>	* unusual methods in this API accommodate synchronizers that may,
1995	>	* but don't usually, block for long periods. Similarly, they
1996	>	* allow more efficient internal handling of cases in which
1997	>	* additional workers may be, but usually are not, needed to
1998	>	* ensure sufficient parallelism.  Toward this end,
1999	>	* implementations of method {@code isReleasable} must be amenable
2000	>	* to repeated invocation.
2001		*
2002		* <p>For example, here is a ManagedBlocker based on a
2003		* ReentrantLock:
#	Line 1753 | Line 2025 | public class ForkJoinPool extends Abstra
2025		*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2026		*   public boolean block() throws InterruptedException {
2027		*     if (item == null)
2028	<	*       item = queue.take
2028	>	*       item = queue.take();
2029		*     return true;
2030		*   }
2031		*   public boolean isReleasable() {
2032	<	*     return item != null || (item = queue.poll) != null;
2032	>	*     return item != null || (item = queue.poll()) != null;
2033		*   }
2034		*   public E getItem() { // call after pool.managedBlock completes
2035		*     return item;
#	Line 1827 | Line 2099 | public class ForkJoinPool extends Abstra
2099		}
2100
2101		// Unsafe mechanics
2102	<
2103	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2104	<	private static final long workerCountsOffset =
2105	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2106	<	private static final long runStateOffset =
2107	<	objectFieldOffset("runState", ForkJoinPool.class);
2108	<	private static final long eventCountOffset =
2109	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2110	<	private static final long eventWaitersOffset =
2111	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
2112	<	private static final long stealCountOffset =
2113	<	objectFieldOffset("stealCount",ForkJoinPool.class);
2114	<	private static final long spareWaitersOffset =
2115	<	objectFieldOffset("spareWaiters",ForkJoinPool.class);
2116	<
2117	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2102	>	private static final sun.misc.Unsafe UNSAFE;
2103	>	private static final long ctlOffset;
2104	>	private static final long stealCountOffset;
2105	>	private static final long blockedCountOffset;
2106	>	private static final long quiescerCountOffset;
2107	>	private static final long scanGuardOffset;
2108	>	private static final long nextWorkerNumberOffset;
2109	>	private static final long ABASE;
2110	>	private static final int ASHIFT;
2111	>
2112	>	static {
2113	>	poolNumberGenerator = new AtomicInteger();
2114	>	workerSeedGenerator = new Random();
2115	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2116	>	defaultForkJoinWorkerThreadFactory =
2117	>	new DefaultForkJoinWorkerThreadFactory();
2118		try {
2119	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2120	<	} catch (NoSuchFieldException e) {
2121	<	// Convert Exception to corresponding Error
2122	<	NoSuchFieldError error = new NoSuchFieldError(field);
2123	<	error.initCause(e);
2124	<	throw error;
2125	<	}
2119	>	UNSAFE = getUnsafe();
2120	>	Class<?> k = ForkJoinPool.class;
2121	>	ctlOffset = UNSAFE.objectFieldOffset
2122	>	(k.getDeclaredField("ctl"));
2123	>	stealCountOffset = UNSAFE.objectFieldOffset
2124	>	(k.getDeclaredField("stealCount"));
2125	>	blockedCountOffset = UNSAFE.objectFieldOffset
2126	>	(k.getDeclaredField("blockedCount"));
2127	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2128	>	(k.getDeclaredField("quiescerCount"));
2129	>	scanGuardOffset = UNSAFE.objectFieldOffset
2130	>	(k.getDeclaredField("scanGuard"));
2131	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2132	>	(k.getDeclaredField("nextWorkerNumber"));
2133	>	} catch (Exception e) {
2134	>	throw new Error(e);
2135	>	}
2136	>	Class<?> a = ForkJoinTask[].class;
2137	>	ABASE = UNSAFE.arrayBaseOffset(a);
2138	>	int s = UNSAFE.arrayIndexScale(a);
2139	>	if ((s & (s-1)) != 0)
2140	>	throw new Error("data type scale not a power of two");
2141	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2142		}
2143
2144		/**

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines