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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.59 by dl, Fri Jul 23 14:09:17 2010 UTC vs.
Revision 1.100 by dl, Fri Apr 1 20:20:37 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.TimeoutException;
23	+	import java.util.concurrent.atomic.AtomicInteger;
24		import java.util.concurrent.locks.LockSupport;
25		import java.util.concurrent.locks.ReentrantLock;
26	<	import java.util.concurrent.atomic.AtomicInteger;
19	<	import java.util.concurrent.CountDownLatch;
26	>	import java.util.concurrent.locks.Condition;
27
28		/**
29		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
#	Line 52 | Line 59 | import java.util.concurrent.CountDownLat
59		* convenient form for informal monitoring.
60		*
61		* <p> As is the case with other ExecutorServices, there are three
62	<	* main task execution methods summarized in the follwoing
62	>	* main task execution methods summarized in the following
63		* table. These are designed to be used by clients not already engaged
64		* in fork/join computations in the current pool.  The main forms of
65		* these methods accept instances of {@code ForkJoinTask}, but
#	Line 69 | Line 76 | import java.util.concurrent.CountDownLat
76		*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
77		*  </tr>
78		*  <tr>
79	<	*    <td> <b>Arange async execution</td>
79	>	*    <td> <b>Arrange async execution</td>
80		*    <td> {@link #execute(ForkJoinTask)}</td>
81		*    <td> {@link ForkJoinTask#fork}</td>
82		*  </tr>
#	Line 110 | Line 117 | import java.util.concurrent.CountDownLat
117		*
118		* <p>This implementation rejects submitted tasks (that is, by throwing
119		* {@link RejectedExecutionException}) only when the pool is shut down
120	<	* or internal resources have been exhuasted.
120	>	* or internal resources have been exhausted.
121		*
122		* @since 1.7
123		* @author Doug Lea
#	Line 124 | Line 131 | public class ForkJoinPool extends Abstra
131		* set of worker threads: Submissions from non-FJ threads enter
132		* into a submission queue. Workers take these tasks and typically
133		* split them into subtasks that may be stolen by other workers.
134	<	* The main work-stealing mechanics implemented in class
135	<	* ForkJoinWorkerThread give first priority to processing tasks
136	<	* from their own queues (LIFO or FIFO, depending on mode), then
137	<	* to randomized FIFO steals of tasks in other worker queues, and
131	<	* lastly to new submissions. These mechanics do not consider
132	<	* affinities, loads, cache localities, etc, so rarely provide the
133	<	* best possible performance on a given machine, but portably
134	<	* provide good throughput by averaging over these factors.
135	<	* (Further, even if we did try to use such information, we do not
136	<	* usually have a basis for exploiting it. For example, some sets
137	<	* of tasks profit from cache affinities, but others are harmed by
138	<	* cache pollution effects.)
139	<	*
140	<	* Beyond work-stealing support and essential bookkeeping, the
141	<	* main responsibility of this framework is to arrange tactics for
142	<	* when one worker is waiting to join a task stolen (or always
143	<	* held by) another.  Becauae we are multiplexing many tasks on to
144	<	* a pool of workers, we can't just let them block (as in
145	<	* Thread.join).  We also cannot just reassign the joiner's
146	<	* run-time stack with another and replace it later, which would
147	<	* be a form of "continuation", that even if possible is not
148	<	* necessarily a good idea. Given that the creation costs of most
149	<	* threads on most systems mainly surrounds setting up runtime
150	<	* stacks, thread creation and switching is usually not much more
151	<	* expensive than stack creation and switching, and is more
152	<	* flexible). Instead we combine two tactics:
153	<	*
154	<	*   1. Arranging for the joiner to execute some task that it
155	<	*      would be running if the steal had not occurred.  Method
156	<	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	<	*      links to try to find such a task.
158	<	*
159	<	*   2. Unless there are already enough live threads, creating or
160	<	*      or re-activating a spare thread to compensate for the
161	<	*      (blocked) joiner until it unblocks.  Spares then suspend
162	<	*      at their next opportunity or eventually die if unused for
163	<	*      too long.  See below and the internal documentation
164	<	*      for tryAwaitJoin for more details about compensation
165	<	*      rules.
166	<	*
167	<	* Because the determining existence of conservatively safe
168	<	* helping targets, the availability of already-created spares,
169	<	* and the apparent need to create new spares are all racy and
170	<	* require heuristic guidance, joins (in
171	<	* ForkJoinWorkerThread.joinTask) interleave these options until
172	<	* successful.  Creating a new spare always succeeds, but also
173	<	* increases application footprint, so we try to avoid it, within
174	<	* reason.
175	<	*
176	<	* The ManagedBlocker extension API can't use option (1) so uses a
177	<	* special version of (2) in method awaitBlocker.
134	>	* Preference rules give first priority to processing tasks from
135	>	* their own queues (LIFO or FIFO, depending on mode), then to
136	>	* randomized FIFO steals of tasks in other worker queues, and
137	>	* lastly to new submissions.
138		*
139		* The main throughput advantages of work-stealing stem from
140	<	* decentralized control -- workers mostly steal tasks from each
141	<	* other. We do not want to negate this by creating bottlenecks
142	<	* implementing other management responsibilities. So we use a
143	<	* collection of techniques that avoid, reduce, or cope well with
144	<	* contention. These entail several instances of bit-packing into
145	<	* CASable fields to maintain only the minimally required
146	<	* atomicity. To enable such packing, we restrict maximum
147	<	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
148	<	* unbalanced increments and decrements) to fit into a 16 bit
149	<	* field, which is far in excess of normal operating range.  Even
150	<	* though updates to some of these bookkeeping fields do sometimes
151	<	* contend with each other, they don't normally cache-contend with
152	<	* updates to others enough to warrant memory padding or
153	<	* isolation. So they are all held as fields of ForkJoinPool
154	<	* objects.  The main capabilities are as follows:
155	<	*
156	<	* 1. Creating and removing workers. Workers are recorded in the
157	<	* "workers" array. This is an array as opposed to some other data
140	>	* decentralized control -- workers mostly take tasks from
141	>	* themselves or each other. We cannot negate this in the
142	>	* implementation of other management responsibilities. The main
143	>	* tactic for avoiding bottlenecks is packing nearly all
144	>	* essentially atomic control state into a single 64bit volatile
145	>	* variable ("ctl"). This variable is read on the order of 10-100
146	>	* times as often as it is modified (always via CAS). (There is
147	>	* some additional control state, for example variable "shutdown"
148	>	* for which we can cope with uncoordinated updates.)  This
149	>	* streamlines synchronization and control at the expense of messy
150	>	* constructions needed to repack status bits upon updates.
151	>	* Updates tend not to contend with each other except during
152	>	* bursts while submitted tasks begin or end.  In some cases when
153	>	* they do contend, threads can instead do something else
154	>	* (usually, scan for tasks) until contention subsides.
155	>	*
156	>	* To enable packing, we restrict maximum parallelism to (1<<15)-1
157	>	* (which is far in excess of normal operating range) to allow
158	>	* ids, counts, and their negations (used for thresholding) to fit
159	>	* into 16bit fields.
160	>	*
161	>	* Recording Workers.  Workers are recorded in the "workers" array
162	>	* that is created upon pool construction and expanded if (rarely)
163	>	* necessary.  This is an array as opposed to some other data
164		* structure to support index-based random steals by workers.
165		* Updates to the array recording new workers and unrecording
166	<	* terminated ones are protected from each other by a lock
167	<	* (workerLock) but the array is otherwise concurrently readable,
166	>	* terminated ones are protected from each other by a seqLock
167	>	* (scanGuard) but the array is otherwise concurrently readable,
168		* and accessed directly by workers. To simplify index-based
169		* operations, the array size is always a power of two, and all
170	<	* readers must tolerate null slots. Currently, all worker thread
171	<	* creation is on-demand, triggered by task submissions,
172	<	* replacement of terminated workers, and/or compensation for
173	<	* blocked workers. However, all other support code is set up to
174	<	* work with other policies.
175	<	*
176	<	* 2. Bookkeeping for dynamically adding and removing workers. We
177	<	* aim to approximately maintain the given level of parallelism.
178	<	* When some workers are known to be blocked (on joins or via
179	<	* ManagedBlocker), we may create or resume others to take their
180	<	* place until they unblock (see below). Implementing this
181	<	* requires counts of the number of "running" threads (i.e., those
182	<	* that are neither blocked nor artifically suspended) as well as
183	<	* the total number.  These two values are packed into one field,
184	<	* "workerCounts" because we need accurate snapshots when deciding
185	<	* to create, resume or suspend.  Note however that the
186	<	* correspondance of these counts to reality is not guaranteed. In
187	<	* particular updates for unblocked threads may lag until they
188	<	* actually wake up.
189	<	*
190	<	* 3. Maintaining global run state. The run state of the pool
191	<	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
192	<	* those in other Executor implementations, as well as a count of
193	<	* "active" workers -- those that are, or soon will be, or
194	<	* recently were executing tasks. The runLevel and active count
195	<	* are packed together in order to correctly trigger shutdown and
196	<	* termination. Without care, active counts can be subject to very
197	<	* high contention.  We substantially reduce this contention by
198	<	* relaxing update rules.  A worker must claim active status
199	<	* prospectively, by activating if it sees that a submitted or
200	<	* stealable task exists (it may find after activating that the
201	<	* task no longer exists). It stays active while processing this
202	<	* task (if it exists) and any other local subtasks it produces,
203	<	* until it cannot find any other tasks. It then tries
204	<	* inactivating (see method preStep), but upon update contention
205	<	* instead scans for more tasks, later retrying inactivation if it
206	<	* doesn't find any.
207	<	*
208	<	* 4. Managing idle workers waiting for tasks. We cannot let
209	<	* workers spin indefinitely scanning for tasks when none are
210	<	* available. On the other hand, we must quickly prod them into
211	<	* action when new tasks are submitted or generated.  We
212	<	* park/unpark these idle workers using an event-count scheme.
213	<	* Field eventCount is incremented upon events that may enable
214	<	* workers that previously could not find a task to now find one:
215	<	* Submission of a new task to the pool, or another worker pushing
216	<	* a task onto a previously empty queue.  (We also use this
217	<	* mechanism for termination and reconfiguration actions that
218	<	* require wakeups of idle workers).  Each worker maintains its
219	<	* last known event count, and blocks when a scan for work did not
220	<	* find a task AND its lastEventCount matches the current
221	<	* eventCount. Waiting idle workers are recorded in a variant of
222	<	* Treiber stack headed by field eventWaiters which, when nonzero,
223	<	* encodes the thread index and count awaited for by the worker
224	<	* thread most recently calling eventSync. This thread in turn has
225	<	* a record (field nextEventWaiter) for the next waiting worker.
226	<	* In addition to allowing simpler decisions about need for
227	<	* wakeup, the event count bits in eventWaiters serve the role of
228	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
229	<	* in task diffusion, workers not otherwise occupied may invoke
230	<	* method releaseWaiters, that removes and signals (unparks)
231	<	* workers not waiting on current count. To minimize task
232	<	* production stalls associate with signalling, any worker pushing
233	<	* a task on an empty queue invokes the weaker method signalWork,
234	<	* that only releases idle workers until it detects interference
235	<	* by other threads trying to release, and lets them take
236	<	* over. The net effect is a tree-like diffusion of signals, where
237	<	* released threads (and possibly others) help with unparks.  To
238	<	* further reduce contention effects a bit, failed CASes to
239	<	* increment field eventCount are tolerated without retries.
240	<	* Conceptually they are merged into the same event, which is OK
241	<	* when their only purpose is to enable workers to scan for work.
242	<	*
243	<	* 5. Managing suspension of extra workers. When a worker is about
244	<	* to block waiting for a join (or via ManagedBlockers), we may
245	<	* create a new thread to maintain parallelism level, or at least
246	<	* avoid starvation. Usually, extra threads are needed for only
247	<	* very short periods, yet join dependencies are such that we
248	<	* sometimes need them in bursts. Rather than create new threads
249	<	* each time this happens, we suspend no-longer-needed extra ones
250	<	* as "spares". For most purposes, we don't distinguish "extra"
251	<	* spare threads from normal "core" threads: On each call to
252	<	* preStep (the only point at which we can do this) a worker
253	<	* checks to see if there are now too many running workers, and if
254	<	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
255	<	* look for suspended threads to resume before considering
256	<	* creating a new replacement. We don't need a special data
257	<	* structure to maintain spares; simply scanning the workers array
258	<	* looking for worker.isSuspended() is fine because the calling
259	<	* thread is otherwise not doing anything useful anyway; we are at
260	<	* least as happy if after locating a spare, the caller doesn't
261	<	* actually block because the join is ready before we try to
262	<	* adjust and compensate.  Note that this is intrinsically racy.
263	<	* One thread may become a spare at about the same time as another
264	<	* is needlessly being created. We counteract this and related
265	<	* slop in part by requiring resumed spares to immediately recheck
266	<	* (in preStep) to see whether they they should re-suspend. The
267	<	* only effective difference between "extra" and "core" threads is
268	<	* that we allow the "extra" ones to time out and die if they are
269	<	* not resumed within a keep-alive interval of a few seconds. This
270	<	* is implemented mainly within ForkJoinWorkerThread, but requires
271	<	* some coordination (isTrimmed() -- meaning killed while
272	<	* suspended) to correctly maintain pool counts.
273	<	*
274	<	* 6. Deciding when to create new workers. The main dynamic
275	<	* control in this class is deciding when to create extra threads,
276	<	* in methods awaitJoin and awaitBlocker. We always need to create
277	<	* one when the number of running threads would become zero and
278	<	* all workers are busy. However, this is not easy to detect
279	<	* reliably in the presence of transients so we use retries and
280	<	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
281	<	* effectively reduce churn at the price of systematically
282	<	* undershooting target parallelism when many threads are blocked.
283	<	* However, biasing toward undeshooting partially compensates for
284	<	* the above mechanics to suspend extra threads, that normally
285	<	* lead to overshoot because we can only suspend workers
286	<	* in-between top-level actions. It also better copes with the
287	<	* fact that some of the methods in this class tend to never
288	<	* become compiled (but are interpreted), so some components of
289	<	* the entire set of controls might execute many times faster than
290	<	* others. And similarly for cases where the apparent lack of work
291	<	* is just due to GC stalls and other transient system activity.
170	>	* readers must tolerate null slots. To avoid flailing during
171	>	* start-up, the array is presized to hold twice #parallelism
172	>	* workers (which is unlikely to need further resizing during
173	>	* execution). But to avoid dealing with so many null slots,
174	>	* variable scanGuard includes a mask for the nearest power of two
175	>	* that contains all current workers.  All worker thread creation
176	>	* is on-demand, triggered by task submissions, replacement of
177	>	* terminated workers, and/or compensation for blocked
178	>	* workers. However, all other support code is set up to work with
179	>	* other policies.  To ensure that we do not hold on to worker
180	>	* references that would prevent GC, ALL accesses to workers are
181	>	* via indices into the workers array (which is one source of some
182	>	* of the messy code constructions here). In essence, the workers
183	>	* array serves as a weak reference mechanism. Thus for example
184	>	* the wait queue field of ctl stores worker indices, not worker
185	>	* references.  Access to the workers in associated methods (for
186	>	* example signalWork) must both index-check and null-check the
187	>	* IDs. All such accesses ignore bad IDs by returning out early
188	>	* from what they are doing, since this can only be associated
189	>	* with termination, in which case it is OK to give up.
190	>	*
191	>	* All uses of the workers array, as well as queue arrays, check
192	>	* that the array is non-null (even if previously non-null). This
193	>	* allows nulling during termination, which is currently not
194	>	* necessary, but remains an option for resource-revocation-based
195	>	* shutdown schemes.
196	>	*
197	>	* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
198	>	* let workers spin indefinitely scanning for tasks when none can
199	>	* be found immediately, and we cannot start/resume workers unless
200	>	* there appear to be tasks available.  On the other hand, we must
201	>	* quickly prod them into action when new tasks are submitted or
202	>	* generated.  We park/unpark workers after placing in an event
203	>	* wait queue when they cannot find work. This "queue" is actually
204	>	* a simple Treiber stack, headed by the "id" field of ctl, plus a
205	>	* 15bit counter value to both wake up waiters (by advancing their
206	>	* count) and avoid ABA effects. Successors are held in worker
207	>	* field "nextWait".  Queuing deals with several intrinsic races,
208	>	* mainly that a task-producing thread can miss seeing (and
209	>	* signalling) another thread that gave up looking for work but
210	>	* has not yet entered the wait queue. We solve this by requiring
211	>	* a full sweep of all workers both before (in scan()) and after
212	>	* (in tryAwaitWork()) a newly waiting worker is added to the wait
213	>	* queue. During a rescan, the worker might release some other
214	>	* queued worker rather than itself, which has the same net
215	>	* effect. Because enqueued workers may actually be rescanning
216	>	* rather than waiting, we set and clear the "parked" field of
217	>	* ForkJoinWorkerThread to reduce unnecessary calls to unpark.
218	>	* (Use of the parked field requires a secondary recheck to avoid
219	>	* missed signals.)
220	>	*
221	>	* Signalling.  We create or wake up workers only when there
222	>	* appears to be at least one task they might be able to find and
223	>	* execute.  When a submission is added or another worker adds a
224	>	* task to a queue that previously had two or fewer tasks, they
225	>	* signal waiting workers (or trigger creation of new ones if
226	>	* fewer than the given parallelism level -- see signalWork).
227	>	* These primary signals are buttressed by signals during rescans
228	>	* as well as those performed when a worker steals a task and
229	>	* notices that there are more tasks too; together these cover the
230	>	* signals needed in cases when more than two tasks are pushed
231	>	* but untaken.
232	>	*
233	>	* Trimming workers. To release resources after periods of lack of
234	>	* use, a worker starting to wait when the pool is quiescent will
235	>	* time out and terminate if the pool has remained quiescent for
236	>	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
237	>	* terminating all workers after long periods of non-use.
238	>	*
239	>	* Submissions. External submissions are maintained in an
240	>	* array-based queue that is structured identically to
241	>	* ForkJoinWorkerThread queues except for the use of
242	>	* submissionLock in method addSubmission. Unlike the case for
243	>	* worker queues, multiple external threads can add new
244	>	* submissions, so adding requires a lock.
245	>	*
246	>	* Compensation. Beyond work-stealing support and lifecycle
247	>	* control, the main responsibility of this framework is to take
248	>	* actions when one worker is waiting to join a task stolen (or
249	>	* always held by) another.  Because we are multiplexing many
250	>	* tasks on to a pool of workers, we can't just let them block (as
251	>	* in Thread.join).  We also cannot just reassign the joiner's
252	>	* run-time stack with another and replace it later, which would
253	>	* be a form of "continuation", that even if possible is not
254	>	* necessarily a good idea since we sometimes need both an
255	>	* unblocked task and its continuation to progress. Instead we
256	>	* combine two tactics:
257	>	*
258	>	*   Helping: Arranging for the joiner to execute some task that it
259	>	*      would be running if the steal had not occurred.  Method
260	>	*      ForkJoinWorkerThread.joinTask tracks joining->stealing
261	>	*      links to try to find such a task.
262	>	*
263	>	*   Compensating: Unless there are already enough live threads,
264	>	*      method tryPreBlock() may create or re-activate a spare
265	>	*      thread to compensate for blocked joiners until they
266	>	*      unblock.
267	>	*
268	>	* The ManagedBlocker extension API can't use helping so relies
269	>	* only on compensation in method awaitBlocker.
270	>	*
271	>	* It is impossible to keep exactly the target parallelism number
272	>	* of threads running at any given time.  Determining the
273	>	* existence of conservatively safe helping targets, the
274	>	* availability of already-created spares, and the apparent need
275	>	* to create new spares are all racy and require heuristic
276	>	* guidance, so we rely on multiple retries of each.  Currently,
277	>	* in keeping with on-demand signalling policy, we compensate only
278	>	* if blocking would leave less than one active (non-waiting,
279	>	* non-blocked) worker. Additionally, to avoid some false alarms
280	>	* due to GC, lagging counters, system activity, etc, compensated
281	>	* blocking for joins is only attempted after rechecks stabilize
282	>	* (retries are interspersed with Thread.yield, for good
283	>	* citizenship).  The variable blockedCount, incremented before
284	>	* blocking and decremented after, is sometimes needed to
285	>	* distinguish cases of waiting for work vs blocking on joins or
286	>	* other managed sync. Both cases are equivalent for most pool
287	>	* control, so we can update non-atomically. (Additionally,
288	>	* contention on blockedCount alleviates some contention on ctl).
289	>	*
290	>	* Shutdown and Termination. A call to shutdownNow atomically sets
291	>	* the ctl stop bit and then (non-atomically) sets each workers
292	>	* "terminate" status, cancels all unprocessed tasks, and wakes up
293	>	* all waiting workers.  Detecting whether termination should
294	>	* commence after a non-abrupt shutdown() call requires more work
295	>	* and bookkeeping. We need consensus about quiesence (i.e., that
296	>	* there is no more work) which is reflected in active counts so
297	>	* long as there are no current blockers, as well as possible
298	>	* re-evaluations during independent changes in blocking or
299	>	* quiescing workers.
300		*
301	<	* Beware that there is a lot of representation-level coupling
301	>	* Style notes: There is a lot of representation-level coupling
302		* among classes ForkJoinPool, ForkJoinWorkerThread, and
303	<	* ForkJoinTask.  For example, direct access to "workers" array by
303	>	* ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
304	>	* data structures managed by ForkJoinPool, so are directly
305	>	* accessed.  Conversely we allow access to "workers" array by
306		* workers, and direct access to ForkJoinTask.status by both
307		* ForkJoinPool and ForkJoinWorkerThread.  There is little point
308		* trying to reduce this, since any associated future changes in
309		* representations will need to be accompanied by algorithmic
310	<	* changes anyway.
311	<	*
312	<	* Style notes: There are lots of inline assignments (of form
313	<	* "while ((local = field) != 0)") which are usually the simplest
314	<	* way to ensure read orderings. Also several occurrences of the
315	<	* unusual "do {} while(!cas...)" which is the simplest way to
316	<	* force an update of a CAS'ed variable. There are also other
310	>	* changes anyway. All together, these low-level implementation
311	>	* choices produce as much as a factor of 4 performance
312	>	* improvement compared to naive implementations, and enable the
313	>	* processing of billions of tasks per second, at the expense of
314	>	* some ugliness.
315	>	*
316	>	* Methods signalWork() and scan() are the main bottlenecks so are
317	>	* especially heavily micro-optimized/mangled.  There are lots of
318	>	* inline assignments (of form "while ((local = field) != 0)")
319	>	* which are usually the simplest way to ensure the required read
320	>	* orderings (which are sometimes critical). This leads to a
321	>	* "C"-like style of listing declarations of these locals at the
322	>	* heads of methods or blocks.  There are several occurrences of
323	>	* the unusual "do {} while (!cas...)"  which is the simplest way
324	>	* to force an update of a CAS'ed variable. There are also other
325		* coding oddities that help some methods perform reasonably even
326	<	* when interpreted (not compiled), at the expense of messiness.
326	>	* when interpreted (not compiled).
327		*
328	<	* The order of declarations in this file is: (1) statics (2)
329	<	* fields (along with constants used when unpacking some of them)
330	<	* (3) internal control methods (4) callbacks and other support
331	<	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
332	<	* methods (plus a few little helpers).
328	>	* The order of declarations in this file is: (1) declarations of
329	>	* statics (2) fields (along with constants used when unpacking
330	>	* some of them), listed in an order that tends to reduce
331	>	* contention among them a bit under most JVMs.  (3) internal
332	>	* control methods (4) callbacks and other support for
333	>	* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
334	>	* methods (plus a few little helpers). (6) static block
335	>	* initializing all statics in a minimally dependent order.
336		*/
337
338		/**
#	Line 380 | Line 367 | public class ForkJoinPool extends Abstra
367		* overridden in ForkJoinPool constructors.
368		*/
369		public static final ForkJoinWorkerThreadFactory
370	<	defaultForkJoinWorkerThreadFactory =
384	<	new DefaultForkJoinWorkerThreadFactory();
370	>	defaultForkJoinWorkerThreadFactory;
371
372		/**
373		* Permission required for callers of methods that may start or
374		* kill threads.
375		*/
376	<	private static final RuntimePermission modifyThreadPermission =
391	<	new RuntimePermission("modifyThread");
376	>	private static final RuntimePermission modifyThreadPermission;
377
378		/**
379		* If there is a security manager, makes sure caller has
#	Line 403 | Line 388 | public class ForkJoinPool extends Abstra
388		/**
389		* Generator for assigning sequence numbers as pool names.
390		*/
391	<	private static final AtomicInteger poolNumberGenerator =
392	<	new AtomicInteger();
391	>	private static final AtomicInteger poolNumberGenerator;
392	>
393	>	/**
394	>	* Generator for initial random seeds for worker victim
395	>	* selection. This is used only to create initial seeds. Random
396	>	* steals use a cheaper xorshift generator per steal attempt. We
397	>	* don't expect much contention on seedGenerator, so just use a
398	>	* plain Random.
399	>	*/
400	>	static final Random workerSeedGenerator;
401
402		/**
403	<	* Absolute bound for parallelism level. Twice this number must
404	<	* fit into a 16bit field to enable word-packing for some counts.
403	>	* Array holding all worker threads in the pool.  Initialized upon
404	>	* construction. Array size must be a power of two.  Updates and
405	>	* replacements are protected by scanGuard, but the array is
406	>	* always kept in a consistent enough state to be randomly
407	>	* accessed without locking by workers performing work-stealing,
408	>	* as well as other traversal-based methods in this class, so long
409	>	* as reads memory-acquire by first reading ctl. All readers must
410	>	* tolerate that some array slots may be null.
411		*/
412	<	private static final int MAX_THREADS = 0x7fff;
412	>	ForkJoinWorkerThread[] workers;
413
414		/**
415	<	* Array holding all worker threads in the pool.  Array size must
416	<	* be a power of two.  Updates and replacements are protected by
417	<	* workerLock, but the array is always kept in a consistent enough
419	<	* state to be randomly accessed without locking by workers
420	<	* performing work-stealing, as well as other traversal-based
421	<	* methods in this class. All readers must tolerate that some
422	<	* array slots may be null.
415	>	* Initial size for submission queue array. Must be a power of
416	>	* two.  In many applications, these always stay small so we use a
417	>	* small initial cap.
418		*/
419	<	volatile ForkJoinWorkerThread[] workers;
419	>	private static final int INITIAL_QUEUE_CAPACITY = 8;
420
421		/**
422	<	* Queue for external submissions.
422	>	* Maximum size for submission queue array. Must be a power of two
423	>	* less than or equal to 1 << (31 - width of array entry) to
424	>	* ensure lack of index wraparound, but is capped at a lower
425	>	* value to help users trap runaway computations.
426		*/
427	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
427	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
428
429		/**
430	<	* Lock protecting updates to workers array.
430	>	* Array serving as submission queue. Initialized upon construction.
431		*/
432	<	private final ReentrantLock workerLock;
432	>	private ForkJoinTask<?>[] submissionQueue;
433
434		/**
435	<	* Latch released upon termination.
435	>	* Lock protecting submissions array for addSubmission
436		*/
437	<	private final Phaser termination;
437	>	private final ReentrantLock submissionLock;
438	>
439	>	/**
440	>	* Condition for awaitTermination, using submissionLock for
441	>	* convenience.
442	>	*/
443	>	private final Condition termination;
444
445		/**
446		* Creation factory for worker threads.
#	Line 444 | Line 448 | public class ForkJoinPool extends Abstra
448		private final ForkJoinWorkerThreadFactory factory;
449
450		/**
451	+	* The uncaught exception handler used when any worker abruptly
452	+	* terminates.
453	+	*/
454	+	final Thread.UncaughtExceptionHandler ueh;
455	+
456	+	/**
457	+	* Prefix for assigning names to worker threads
458	+	*/
459	+	private final String workerNamePrefix;
460	+
461	+	/**
462		* Sum of per-thread steal counts, updated only when threads are
463		* idle or terminating.
464		*/
465		private volatile long stealCount;
466
467		/**
468	<	* Encoded record of top of treiber stack of threads waiting for
469	<	* events. The top 32 bits contain the count being waited for. The
470	<	* bottom word contains one plus the pool index of waiting worker
471	<	* thread.
472	<	*/
473	<	private volatile long eventWaiters;
474	<
475	<	private static final int  EVENT_COUNT_SHIFT = 32;
476	<	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
477	<
478	<	/**
479	<	* A counter for events that may wake up worker threads:
480	<	*   - Submission of a new task to the pool
481	<	*   - A worker pushing a task on an empty queue
482	<	*   - termination and reconfiguration
483	<	*/
484	<	private volatile int eventCount;
485	<
486	<	/**
487	<	* Lifecycle control. The low word contains the number of workers
488	<	* that are (probably) executing tasks. This value is atomically
489	<	* incremented before a worker gets a task to run, and decremented
490	<	* when worker has no tasks and cannot find any.  Bits 16-18
491	<	* contain runLevel value. When all are zero, the pool is
492	<	* running. Level transitions are monotonic (running -> shutdown
493	<	* -> terminating -> terminated) so each transition adds a bit.
494	<	* These are bundled together to ensure consistent read for
495	<	* termination checks (i.e., that runLevel is at least SHUTDOWN
496	<	* and active threads is zero).
497	<	*/
498	<	private volatile int runState;
499	<
500	<	// Note: The order among run level values matters.
501	<	private static final int RUNLEVEL_SHIFT     = 16;
502	<	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
503	<	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
504	<	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
505	<	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
506	<	private static final int ONE_ACTIVE         = 1; // active update delta
507	<
508	<	/**
509	<	* Holds number of total (i.e., created and not yet terminated)
510	<	* and running (i.e., not blocked on joins or other managed sync)
511	<	* threads, packed together to ensure consistent snapshot when
512	<	* making decisions about creating and suspending spare
513	<	* threads. Updated only by CAS. Note that adding a new worker
514	<	* requires incrementing both counts, since workers start off in
515	<	* running state.  This field is also used for memory-fencing
516	<	* configuration parameters.
517	<	*/
518	<	private volatile int workerCounts;
519	<
520	<	private static final int TOTAL_COUNT_SHIFT  = 16;
521	<	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
507	<	private static final int ONE_RUNNING        = 1;
508	<	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
468	>	* Main pool control -- a long packed with:
469	>	* AC: Number of active running workers minus target parallelism (16 bits)
470	>	* TC: Number of total workers minus target parallelism (16bits)
471	>	* ST: true if pool is terminating (1 bit)
472	>	* EC: the wait count of top waiting thread (15 bits)
473	>	* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
474	>	*
475	>	* When convenient, we can extract the upper 32 bits of counts and
476	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
477	>	* (int)ctl.  The ec field is never accessed alone, but always
478	>	* together with id and st. The offsets of counts by the target
479	>	* parallelism and the positionings of fields makes it possible to
480	>	* perform the most common checks via sign tests of fields: When
481	>	* ac is negative, there are not enough active workers, when tc is
482	>	* negative, there are not enough total workers, when id is
483	>	* negative, there is at least one waiting worker, and when e is
484	>	* negative, the pool is terminating.  To deal with these possibly
485	>	* negative fields, we use casts in and out of "short" and/or
486	>	* signed shifts to maintain signedness.
487	>	*/
488	>	volatile long ctl;
489	>
490	>	// bit positions/shifts for fields
491	>	private static final int  AC_SHIFT   = 48;
492	>	private static final int  TC_SHIFT   = 32;
493	>	private static final int  ST_SHIFT   = 31;
494	>	private static final int  EC_SHIFT   = 16;
495	>
496	>	// bounds
497	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
498	>	private static final int  SMASK      = 0xffff;  // mask short bits
499	>	private static final int  SHORT_SIGN = 1 << 15;
500	>	private static final int  INT_SIGN   = 1 << 31;
501	>
502	>	// masks
503	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
504	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
505	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
506	>
507	>	// units for incrementing and decrementing
508	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
509	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
510	>
511	>	// masks and units for dealing with u = (int)(ctl >>> 32)
512	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
513	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
514	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
515	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
516	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
517	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
518	>
519	>	// masks and units for dealing with e = (int)ctl
520	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
521	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
522
523		/**
524		* The target parallelism level.
512	–	* Accessed directly by ForkJoinWorkerThreads.
525		*/
526		final int parallelism;
527
528		/**
529	<	* True if use local fifo, not default lifo, for local polling
530	<	* Read by, and replicated by ForkJoinWorkerThreads
529	>	* Index (mod submission queue length) of next element to take
530	>	* from submission queue. Usage is identical to that for
531	>	* per-worker queues -- see ForkJoinWorkerThread internal
532	>	* documentation.
533		*/
534	<	final boolean locallyFifo;
534	>	volatile int queueBase;
535
536		/**
537	<	* The uncaught exception handler used when any worker abruptly
538	<	* terminates.
537	>	* Index (mod submission queue length) of next element to add
538	>	* in submission queue. Usage is identical to that for
539	>	* per-worker queues -- see ForkJoinWorkerThread internal
540	>	* documentation.
541		*/
542	<	private final Thread.UncaughtExceptionHandler ueh;
542	>	int queueTop;
543
544		/**
545	<	* Pool number, just for assigning useful names to worker threads
545	>	* True when shutdown() has been called.
546		*/
547	<	private final int poolNumber;
547	>	volatile boolean shutdown;
548
549	<	// Utilities for CASing fields. Note that several of these
550	<	// are manually inlined by callers
549	>	/**
550	>	* True if use local fifo, not default lifo, for local polling
551	>	* Read by, and replicated by ForkJoinWorkerThreads
552	>	*/
553	>	final boolean locallyFifo;
554
555		/**
556	<	* Increments running count.  Also used by ForkJoinTask.
556	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
557	>	* When non-zero, suppresses automatic shutdown when active
558	>	* counts become zero.
559		*/
560	<	final void incrementRunningCount() {
540	<	int c;
541	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
542	<	c = workerCounts,
543	<	c + ONE_RUNNING));
544	<	}
560	>	volatile int quiescerCount;
561
562		/**
563	<	* Tries to decrement running count unless already zero
563	>	* The number of threads blocked in join.
564		*/
565	<	final boolean tryDecrementRunningCount() {
550	<	int wc = workerCounts;
551	<	if ((wc & RUNNING_COUNT_MASK) == 0)
552	<	return false;
553	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
554	<	wc, wc - ONE_RUNNING);
555	<	}
565	>	volatile int blockedCount;
566
567		/**
568	<	* Tries to increment running count
568	>	* Counter for worker Thread names (unrelated to their poolIndex)
569		*/
570	<	final boolean tryIncrementRunningCount() {
561	<	int wc;
562	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
563	<	wc = workerCounts, wc + ONE_RUNNING);
564	<	}
570	>	private volatile int nextWorkerNumber;
571
572		/**
573	<	* Tries incrementing active count; fails on contention.
568	<	* Called by workers before executing tasks.
569	<	*
570	<	* @return true on success
573	>	* The index for the next created worker. Accessed under scanGuard.
574		*/
575	<	final boolean tryIncrementActiveCount() {
573	<	int c;
574	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
575	<	c = runState, c + ONE_ACTIVE);
576	<	}
575	>	private int nextWorkerIndex;
576
577		/**
578	<	* Tries decrementing active count; fails on contention.
579	<	* Called when workers cannot find tasks to run.
578	>	* SeqLock and index masking for updates to workers array.  Locked
579	>	* when SG_UNIT is set. Unlocking clears bit by adding
580	>	* SG_UNIT. Staleness of read-only operations can be checked by
581	>	* comparing scanGuard to value before the reads. The low 16 bits
582	>	* (i.e, anding with SMASK) hold (the smallest power of two
583	>	* covering all worker indices, minus one, and is used to avoid
584	>	* dealing with large numbers of null slots when the workers array
585	>	* is overallocated.
586		*/
587	<	final boolean tryDecrementActiveCount() {
588	<	int c;
589	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
585	<	c = runState, c - ONE_ACTIVE);
586	<	}
587	>	volatile int scanGuard;
588	>
589	>	private static final int SG_UNIT = 1 << 16;
590
591		/**
592	<	* Advances to at least the given level. Returns true if not
593	<	* already in at least the given level.
592	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
593	>	* task when the pool is quiescent to instead try to shrink the
594	>	* number of workers.  The exact value does not matter too
595	>	* much. It must be short enough to release resources during
596	>	* sustained periods of idleness, but not so short that threads
597	>	* are continually re-created.
598		*/
599	<	private boolean advanceRunLevel(int level) {
600	<	for (;;) {
601	<	int s = runState;
602	<	if ((s & level) != 0)
603	<	return false;
604	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
605	<	return true;
599	>	private static final long SHRINK_RATE =
600	>	4L * 1000L * 1000L * 1000L; // 4 seconds
601	>
602	>	/**
603	>	* Top-level loop for worker threads: On each step: if the
604	>	* previous step swept through all queues and found no tasks, or
605	>	* there are excess threads, then possibly blocks. Otherwise,
606	>	* scans for and, if found, executes a task. Returns when pool
607	>	* and/or worker terminate.
608	>	*
609	>	* @param w the worker
610	>	*/
611	>	final void work(ForkJoinWorkerThread w) {
612	>	boolean swept = false;                // true on empty scans
613	>	long c;
614	>	while (!w.terminate && (int)(c = ctl) >= 0) {
615	>	int a;                            // active count
616	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
617	>	swept = scan(w, a);
618	>	else if (tryAwaitWork(w, c))
619	>	swept = false;
620		}
621		}
622
623	<	// workers array maintenance
623	>	// Signalling
624
625		/**
626	<	* Records and returns a workers array index for new worker.
626	>	* Wakes up or creates a worker.
627		*/
628	<	private int recordWorker(ForkJoinWorkerThread w) {
629	<	// Try using slot totalCount-1. If not available, scan and/or resize
630	<	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
631	<	final ReentrantLock lock = this.workerLock;
632	<	lock.lock();
633	<	try {
634	<	ForkJoinWorkerThread[] ws = workers;
635	<	int nws = ws.length;
636	<	if (k < 0 || k >= nws || ws[k] != null) {
637	<	for (k = 0; k < nws && ws[k] != null; ++k)
638	<	;
639	<	if (k == nws)
640	<	ws = Arrays.copyOf(ws, nws << 1);
628	>	final void signalWork() {
629	>	/*
630	>	* The while condition is true if: (there is are too few total
631	>	* workers OR there is at least one waiter) AND (there are too
632	>	* few active workers OR the pool is terminating).  The value
633	>	* of e distinguishes the remaining cases: zero (no waiters)
634	>	* for create, negative if terminating (in which case do
635	>	* nothing), else release a waiter. The secondary checks for
636	>	* release (non-null array etc) can fail if the pool begins
637	>	* terminating after the test, and don't impose any added cost
638	>	* because JVMs must perform null and bounds checks anyway.
639	>	*/
640	>	long c; int e, u;
641	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
642	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
643	>	if (e > 0) {                         // release a waiting worker
644	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
645	>	if ((ws = workers) == null ||
646	>	(i = ~e & SMASK) >= ws.length ||
647	>	(w = ws[i]) == null)
648	>	break;
649	>	long nc = (((long)(w.nextWait & E_MASK)) |
650	>	((long)(u + UAC_UNIT) << 32));
651	>	if (w.eventCount == e &&
652	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
653	>	w.eventCount = (e + EC_UNIT) & E_MASK;
654	>	if (w.parked)
655	>	UNSAFE.unpark(w);
656	>	break;
657	>	}
658	>	}
659	>	else if (UNSAFE.compareAndSwapLong
660	>	(this, ctlOffset, c,
661	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
662	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
663	>	addWorker();
664	>	break;
665		}
621	–	ws[k] = w;
622	–	workers = ws; // volatile array write ensures slot visibility
623	–	} finally {
624	–	lock.unlock();
666		}
626	–	return k;
667		}
668
669		/**
670	<	* Nulls out record of worker in workers array
670	>	* Variant of signalWork to help release waiters on rescans.
671	>	* Tries once to release a waiter if active count < 0.
672	>	*
673	>	* @return false if failed due to contention, else true
674		*/
675	<	private void forgetWorker(ForkJoinWorkerThread w) {
676	<	int idx = w.poolIndex;
677	<	// Locking helps method recordWorker avoid unecessary expansion
678	<	final ReentrantLock lock = this.workerLock;
679	<	lock.lock();
680	<	try {
681	<	ForkJoinWorkerThread[] ws = workers;
682	<	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
683	<	ws[idx] = null;
684	<	} finally {
685	<	lock.unlock();
675	>	private boolean tryReleaseWaiter() {
676	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
677	>	if ((e = (int)(c = ctl)) > 0 &&
678	>	(int)(c >> AC_SHIFT) < 0 &&
679	>	(ws = workers) != null &&
680	>	(i = ~e & SMASK) < ws.length &&
681	>	(w = ws[i]) != null) {
682	>	long nc = ((long)(w.nextWait & E_MASK) |
683	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
684	>	if (w.eventCount != e ||
685	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
686	>	return false;
687	>	w.eventCount = (e + EC_UNIT) & E_MASK;
688	>	if (w.parked)
689	>	UNSAFE.unpark(w);
690		}
691	+	return true;
692		}
693
694	<	// adding and removing workers
694	>	// Scanning for tasks
695
696		/**
697	<	* Tries to create and add new worker. Assumes that worker counts
698	<	* are already updated to accommodate the worker, so adjusts on
699	<	* failure.
697	>	* Scans for and, if found, executes one task. Scans start at a
698	>	* random index of workers array, and randomly select the first
699	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
700	>	* circular sweeps, which is necessary to check quiescence. and
701	>	* taking a submission only if no stealable tasks were found.  The
702	>	* steal code inside the loop is a specialized form of
703	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
704	>	* helpJoinTask and signal propagation. The code for submission
705	>	* queues is almost identical. On each steal, the worker completes
706	>	* not only the task, but also all local tasks that this task may
707	>	* have generated. On detecting staleness or contention when
708	>	* trying to take a task, this method returns without finishing
709	>	* sweep, which allows global state rechecks before retry.
710		*
711	<	* @return new worker or null if creation failed
711	>	* @param w the worker
712	>	* @param a the number of active workers
713	>	* @return true if swept all queues without finding a task
714		*/
715	<	private ForkJoinWorkerThread addWorker() {
716	<	ForkJoinWorkerThread w = null;
717	<	try {
718	<	w = factory.newThread(this);
719	<	} finally { // Adjust on either null or exceptional factory return
720	<	if (w == null) {
721	<	onWorkerCreationFailure();
722	<	return null;
715	>	private boolean scan(ForkJoinWorkerThread w, int a) {
716	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
717	>	int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK;
718	>	ForkJoinWorkerThread[] ws = workers;
719	>	if (ws == null || ws.length <= m)         // staleness check
720	>	return false;
721	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
722	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
723	>	ForkJoinWorkerThread v = ws[k & m];
724	>	if (v != null && (b = v.queueBase) != v.queueTop &&
725	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
726	>	long u = (i << ASHIFT) + ABASE;
727	>	if ((t = q[i]) != null && v.queueBase == b &&
728	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
729	>	int d = (v.queueBase = b + 1) - v.queueTop;
730	>	v.stealHint = w.poolIndex;
731	>	if (d != 0)
732	>	signalWork();             // propagate if nonempty
733	>	w.execTask(t);
734	>	}
735	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
736	>	return false;                     // store next seed
737	>	}
738	>	else if (j < 0) {                     // xorshift
739	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
740		}
741	+	else
742	+	++k;
743	+	}
744	+	if (scanGuard != g)                       // staleness check
745	+	return false;
746	+	else {                                    // try to take submission
747	+	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
748	+	if ((b = queueBase) != queueTop &&
749	+	(q = submissionQueue) != null &&
750	+	(i = (q.length - 1) & b) >= 0) {
751	+	long u = (i << ASHIFT) + ABASE;
752	+	if ((t = q[i]) != null && queueBase == b &&
753	+	UNSAFE.compareAndSwapObject(q, u, t, null)) {
754	+	queueBase = b + 1;
755	+	w.execTask(t);
756	+	}
757	+	return false;
758	+	}
759	+	return true;                         // all queues empty
760		}
665	–	w.start(recordWorker(w), ueh);
666	–	return w;
761		}
762
763		/**
764	<	* Adjusts counts upon failure to create worker
765	<	*/
766	<	private void onWorkerCreationFailure() {
767	<	for (;;) {
768	<	int wc = workerCounts;
769	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
770	<	Thread.yield(); // wait for other counts to settle
771	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
772	<	wc - (ONE_RUNNING|ONE_TOTAL)))
773	<	break;
764	>	* Tries to enqueue worker w in wait queue and await change in
765	>	* worker's eventCount.  If the pool is quiescent and there is
766	>	* more than one worker, possibly terminates worker upon exit.
767	>	* Otherwise, before blocking, rescans queues to avoid missed
768	>	* signals.  Upon finding work, releases at least one worker
769	>	* (which may be the current worker). Rescans restart upon
770	>	* detected staleness or failure to release due to
771	>	* contention. Note the unusual conventions about Thread.interrupt
772	>	* here and elsewhere: Because interrupts are used solely to alert
773	>	* threads to check termination, which is checked here anyway, we
774	>	* clear status (using Thread.interrupted) before any call to
775	>	* park, so that park does not immediately return due to status
776	>	* being set via some other unrelated call to interrupt in user
777	>	* code.
778	>	*
779	>	* @param w the calling worker
780	>	* @param c the ctl value on entry
781	>	* @return true if waited or another thread was released upon enq
782	>	*/
783	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
784	>	int v = w.eventCount;
785	>	w.nextWait = (int)c;                      // w's successor record
786	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
787	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
788	>	long d = ctl; // return true if lost to a deq, to force scan
789	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
790	>	}
791	>	for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
792	>	long s = stealCount;
793	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
794	>	sc = w.stealCount = 0;
795	>	else if (w.eventCount != v)
796	>	return true;                      // update next time
797	>	}
798	>	if ((int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 &&
799	>	blockedCount == 0 && quiescerCount == 0)
800	>	idleAwaitWork(w, nc, c, v);           // quiescent
801	>	for (boolean rescanned = false;;) {
802	>	if (w.eventCount != v)
803	>	return true;
804	>	if (!rescanned) {
805	>	int g = scanGuard, m = g & SMASK;
806	>	ForkJoinWorkerThread[] ws = workers;
807	>	if (ws != null && m < ws.length) {
808	>	rescanned = true;
809	>	for (int i = 0; i <= m; ++i) {
810	>	ForkJoinWorkerThread u = ws[i];
811	>	if (u != null) {
812	>	if (u.queueBase != u.queueTop &&
813	>	!tryReleaseWaiter())
814	>	rescanned = false; // contended
815	>	if (w.eventCount != v)
816	>	return true;
817	>	}
818	>	}
819	>	}
820	>	if (scanGuard != g ||              // stale
821	>	(queueBase != queueTop && !tryReleaseWaiter()))
822	>	rescanned = false;
823	>	if (!rescanned)
824	>	Thread.yield();                // reduce contention
825	>	else
826	>	Thread.interrupted();          // clear before park
827	>	}
828	>	else {
829	>	w.parked = true;                   // must recheck
830	>	if (w.eventCount != v) {
831	>	w.parked = false;
832	>	return true;
833	>	}
834	>	LockSupport.park(this);
835	>	rescanned = w.parked = false;
836	>	}
837		}
681	–	tryTerminate(false); // in case of failure during shutdown
838		}
839
840		/**
841	<	* Creates and/or resumes enough workers to establish target
842	<	* parallelism, giving up if terminating or addWorker fails
843	<	*
844	<	* TODO: recast this to support lazier creation and automated
845	<	* parallelism maintenance
846	<	*/
847	<	private void ensureEnoughWorkers() {
848	<	while ((runState & TERMINATING) == 0) {
849	<	int pc = parallelism;
850	<	int wc = workerCounts;
851	<	int rc = wc & RUNNING_COUNT_MASK;
852	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
853	<	if (tc < pc) {
854	<	if (UNSAFE.compareAndSwapInt
855	<	(this, workerCountsOffset,
856	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
857	<	addWorker() == null)
841	>	* If inactivating worker w has caused pool to become
842	>	* quiescent, check for pool termination, and wait for event
843	>	* for up to SHRINK_RATE nanosecs (rescans are unnecessary in
844	>	* this case because quiescence reflects consensus about lack
845	>	* of work). On timeout, if ctl has not changed, terminate the
846	>	* worker. Upon its termination (see deregisterWorker), it may
847	>	* wake up another worker to possibly repeat this process.
848	>	*
849	>	* @param w the calling worker
850	>	* @param currentCtl the ctl value after enqueuing w
851	>	* @param prevCtl the ctl value if w terminated
852	>	* @param v the eventCount w awaits change
853	>	*/
854	>	private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
855	>	long prevCtl, int v) {
856	>	if (w.eventCount == v) {
857	>	if (shutdown)
858	>	tryTerminate(false);
859	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
860	>	while (ctl == currentCtl) {
861	>	long startTime = System.nanoTime();
862	>	w.parked = true;
863	>	if (w.eventCount == v)             // must recheck
864	>	LockSupport.parkNanos(this, SHRINK_RATE);
865	>	w.parked = false;
866	>	if (w.eventCount != v)
867	>	break;
868	>	else if (System.nanoTime() - startTime <
869	>	SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop
870	>	Thread.interrupted();          // spurious wakeup
871	>	else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
872	>	currentCtl, prevCtl)) {
873	>	w.terminate = true;            // restore previous
874	>	w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
875		break;
703	–	}
704	–	else if (tc > pc && rc < pc &&
705	–	tc > (runState & ACTIVE_COUNT_MASK)) {
706	–	ForkJoinWorkerThread spare = null;
707	–	ForkJoinWorkerThread[] ws = workers;
708	–	int nws = ws.length;
709	–	for (int i = 0; i < nws; ++i) {
710	–	ForkJoinWorkerThread w = ws[i];
711	–	if (w != null && w.isSuspended()) {
712	–	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
713	–	return;
714	–	if (w.tryResumeSpare())
715	–	incrementRunningCount();
716	–	break;
717	–	}
876		}
877		}
720	–	else
721	–	break;
878		}
879		}
880
881	+	// Submissions
882	+
883		/**
884	<	* Final callback from terminating worker.  Removes record of
885	<	* worker from array, and adjusts counts. If pool is shutting
728	<	* down, tries to complete terminatation, else possibly replaces
729	<	* the worker.
884	>	* Enqueues the given task in the submissionQueue.  Same idea as
885	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
886		*
887	<	* @param w the worker
887	>	* @param t the task
888		*/
889	<	final void workerTerminated(ForkJoinWorkerThread w) {
890	<	if (w.active) { // force inactive
891	<	w.active = false;
892	<	do {} while (!tryDecrementActiveCount());
893	<	}
894	<	forgetWorker(w);
895	<
896	<	// Decrement total count, and if was running, running count
897	<	// Spin (waiting for other updates) if either would be negative
898	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
899	<	int unit = ONE_TOTAL + nr;
900	<	for (;;) {
901	<	int wc = workerCounts;
902	<	int rc = wc & RUNNING_COUNT_MASK;
747	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
748	<	Thread.yield(); // back off if waiting for other updates
749	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
750	<	wc, wc - unit))
751	<	break;
889	>	private void addSubmission(ForkJoinTask<?> t) {
890	>	final ReentrantLock lock = this.submissionLock;
891	>	lock.lock();
892	>	try {
893	>	ForkJoinTask<?>[] q; int s, m;
894	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
895	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
896	>	UNSAFE.putOrderedObject(q, u, t);
897	>	queueTop = s + 1;
898	>	if (s - queueBase == m)
899	>	growSubmissionQueue();
900	>	}
901	>	} finally {
902	>	lock.unlock();
903		}
904	<
754	<	accumulateStealCount(w); // collect final count
755	<	if (!tryTerminate(false))
756	<	ensureEnoughWorkers();
904	>	signalWork();
905		}
906
907	<	// Waiting for and signalling events
907	>	//  (pollSubmission is defined below with exported methods)
908
909		/**
910	<	* Releases workers blocked on a count not equal to current count.
911	<	* @return true if any released
910	>	* Creates or doubles submissionQueue array.
911	>	* Basically identical to ForkJoinWorkerThread version.
912		*/
913	<	private void releaseWaiters() {
914	<	long top;
915	<	while ((top = eventWaiters) != 0L) {
916	<	ForkJoinWorkerThread[] ws = workers;
917	<	int n = ws.length;
918	<	for (;;) {
919	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
920	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
921	<	return;
922	<	ForkJoinWorkerThread w;
923	<	if (i < n && (w = ws[i]) != null &&
924	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
925	<	top, w.nextWaiter)) {
926	<	LockSupport.unpark(w);
927	<	top = eventWaiters;
928	<	}
929	<	else
930	<	break;      // possibly stale; reread
913	>	private void growSubmissionQueue() {
914	>	ForkJoinTask<?>[] oldQ = submissionQueue;
915	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
916	>	if (size > MAXIMUM_QUEUE_CAPACITY)
917	>	throw new RejectedExecutionException("Queue capacity exceeded");
918	>	if (size < INITIAL_QUEUE_CAPACITY)
919	>	size = INITIAL_QUEUE_CAPACITY;
920	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
921	>	int mask = size - 1;
922	>	int top = queueTop;
923	>	int oldMask;
924	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
925	>	for (int b = queueBase; b != top; ++b) {
926	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
927	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
928	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
929	>	UNSAFE.putObjectVolatile
930	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
931		}
932		}
933		}
934
935	+	// Blocking support
936	+
937		/**
938	<	* Ensures eventCount on exit is different (mod 2^32) than on
939	<	* entry and wakes up all waiters
938	>	* Tries to increment blockedCount, decrement active count
939	>	* (sometimes implicitly) and possibly release or create a
940	>	* compensating worker in preparation for blocking. Fails
941	>	* on contention or termination.
942	>	*
943	>	* @return true if the caller can block, else should recheck and retry
944		*/
945	<	private void signalEvent() {
946	<	int c;
947	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
948	<	c = eventCount, c+1));
949	<	releaseWaiters();
945	>	private boolean tryPreBlock() {
946	>	int b = blockedCount;
947	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
948	>	int pc = parallelism;
949	>	do {
950	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
951	>	int e, ac, tc, rc, i;
952	>	long c = ctl;
953	>	int u = (int)(c >>> 32);
954	>	if ((e = (int)c) < 0) {
955	>	// skip -- terminating
956	>	}
957	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
958	>	(ws = workers) != null &&
959	>	(i = ~e & SMASK) < ws.length &&
960	>	(w = ws[i]) != null) {
961	>	long nc = ((long)(w.nextWait & E_MASK) |
962	>	(c & (AC_MASK|TC_MASK)));
963	>	if (w.eventCount == e &&
964	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
965	>	w.eventCount = (e + EC_UNIT) & E_MASK;
966	>	if (w.parked)
967	>	UNSAFE.unpark(w);
968	>	return true;             // release an idle worker
969	>	}
970	>	}
971	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
972	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
973	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
974	>	return true;             // no compensation needed
975	>	}
976	>	else if (tc + pc < MAX_ID) {
977	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
978	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
979	>	addWorker();
980	>	return true;            // create a replacement
981	>	}
982	>	}
983	>	// try to back out on any failure and let caller retry
984	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
985	>	b = blockedCount, b - 1));
986	>	}
987	>	return false;
988		}
989
990		/**
991	<	* Advances eventCount and releases waiters until interference by
800	<	* other releasing threads is detected.
991	>	* Decrements blockedCount and increments active count
992		*/
993	<	final void signalWork() {
994	<	int c;
995	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
996	<	long top;
997	<	while ((top = eventWaiters) != 0L) {
998	<	int ec = eventCount;
999	<	ForkJoinWorkerThread[] ws = workers;
1000	<	int n = ws.length;
1001	<	for (;;) {
1002	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
1003	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
1004	<	return;
1005	<	ForkJoinWorkerThread w;
1006	<	if (i < n && (w = ws[i]) != null &&
1007	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1008	<	top, top = w.nextWaiter)) {
1009	<	LockSupport.unpark(w);
1010	<	if (top != eventWaiters) // let someone else take over
1011	<	return;
1012	<	}
1013	<	else
1014	<	break;      // possibly stale; reread
993	>	private void postBlock() {
994	>	long c;
995	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
996	>	c = ctl, c + AC_UNIT));
997	>	int b;
998	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
999	>	b = blockedCount, b - 1));
1000	>	}
1001	>
1002	>	/**
1003	>	* Possibly blocks waiting for the given task to complete, or
1004	>	* cancels the task if terminating.  Fails to wait if contended.
1005	>	*
1006	>	* @param joinMe the task
1007	>	*/
1008	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
1009	>	int s;
1010	>	Thread.interrupted(); // clear interrupts before checking termination
1011	>	if (joinMe.status >= 0) {
1012	>	if (tryPreBlock()) {
1013	>	joinMe.tryAwaitDone(0L);
1014	>	postBlock();
1015		}
1016	+	else if ((ctl & STOP_BIT) != 0L)
1017	+	joinMe.cancelIgnoringExceptions();
1018		}
1019		}
1020
1021		/**
1022	<	* If worker is inactive, blocks until terminating or event count
1023	<	* advances from last value held by worker; in any case helps
1024	<	* release others.
1025	<	*
1026	<	* @param w the calling worker thread
1027	<	* @param retries the number of scans by caller failing to find work
1028	<	* @return false if now too many threads running
1029	<	*/
1030	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
1031	<	int wec = w.lastEventCount;
1032	<	if (retries > 1) { // can only block after 2nd miss
1033	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
1034	<	((long)(w.poolIndex + 1)));
1035	<	long top;
1036	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
1037	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
1038	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
1039	<	eventCount == wec) {
1040	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1041	<	w.nextWaiter = top, nextTop)) {
1042	<	accumulateStealCount(w); // transfer steals while idle
1043	<	Thread.interrupted();    // clear/ignore interrupt
1044	<	while (eventCount == wec)
1045	<	w.doPark();
1046	<	break;
1022	>	* Possibly blocks the given worker waiting for joinMe to
1023	>	* complete or timeout
1024	>	*
1025	>	* @param joinMe the task
1026	>	* @param millis the wait time for underlying Object.wait
1027	>	*/
1028	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1029	>	while (joinMe.status >= 0) {
1030	>	Thread.interrupted();
1031	>	if ((ctl & STOP_BIT) != 0L) {
1032	>	joinMe.cancelIgnoringExceptions();
1033	>	break;
1034	>	}
1035	>	if (tryPreBlock()) {
1036	>	long last = System.nanoTime();
1037	>	while (joinMe.status >= 0) {
1038	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1039	>	if (millis <= 0)
1040	>	break;
1041	>	joinMe.tryAwaitDone(millis);
1042	>	if (joinMe.status < 0)
1043	>	break;
1044	>	if ((ctl & STOP_BIT) != 0L) {
1045	>	joinMe.cancelIgnoringExceptions();
1046	>	break;
1047	>	}
1048	>	long now = System.nanoTime();
1049	>	nanos -= now - last;
1050	>	last = now;
1051		}
1052	+	postBlock();
1053	+	break;
1054		}
856	–	wec = eventCount;
1055		}
858	–	releaseWaiters();
859	–	int wc = workerCounts;
860	–	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
861	–	w.lastEventCount = wec;
862	–	return true;
863	–	}
864	–	if (wec != w.lastEventCount) // back up if may re-wait
865	–	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	–	return false;
1056		}
1057
1058		/**
1059	<	* Callback from workers invoked upon each top-level action (i.e.,
871	<	* stealing a task or taking a submission and running
872	<	* it). Performs one or both of the following:
873	<	*
874	<	* * If the worker cannot find work, updates its active status to
875	<	* inactive and updates activeCount unless there is contention, in
876	<	* which case it may try again (either in this or a subsequent
877	<	* call).  Additionally, awaits the next task event and/or helps
878	<	* wake up other releasable waiters.
879	<	*
880	<	* * If there are too many running threads, suspends this worker
881	<	* (first forcing inactivation if necessary).  If it is not
882	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
883	<	* -- killed while suspended within suspendAsSpare. Otherwise,
884	<	* upon resume it rechecks to make sure that it is still needed.
885	<	*
886	<	* @param w the worker
887	<	* @param retries the number of scans by caller failing to find work
888	<	* find any (in which case it may block waiting for work).
1059	>	* If necessary, compensates for blocker, and blocks
1060		*/
1061	<	final void preStep(ForkJoinWorkerThread w, int retries) {
1062	<	boolean active = w.active;
1063	<	boolean inactivate = active && retries != 0;
1064	<	for (;;) {
1065	<	int rs, wc;
1066	<	if (inactivate &&
1067	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
1068	<	rs = runState, rs - ONE_ACTIVE))
1069	<	inactivate = active = w.active = false;
899	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
900	<	if (active || eventSync(w, retries))
901	<	break;
902	<	}
903	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
904	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
905	<	wc, wc - ONE_RUNNING) &&
906	<	!w.suspendAsSpare())             // false if trimmed
1061	>	private void awaitBlocker(ManagedBlocker blocker)
1062	>	throws InterruptedException {
1063	>	while (!blocker.isReleasable()) {
1064	>	if (tryPreBlock()) {
1065	>	try {
1066	>	do {} while (!blocker.isReleasable() && !blocker.block());
1067	>	} finally {
1068	>	postBlock();
1069	>	}
1070		break;
1071	+	}
1072		}
1073		}
1074
1075	+	// Creating, registering and deregistring workers
1076	+
1077		/**
1078	<	* Awaits join of the given task if enough threads, or can resume
1079	<	* or create a spare. Fails (in which case the given task might
914	<	* not be done) upon contention or lack of decision about
915	<	* blocking. Returns void because caller must check
916	<	* task status on return anyway.
917	<	*
918	<	* We allow blocking if:
919	<	*
920	<	* 1. There would still be at least as many running threads as
921	<	*    parallelism level if this thread blocks.
922	<	*
923	<	* 2. A spare is resumed to replace this worker. We tolerate
924	<	*    slop in the decision to replace if a spare is found without
925	<	*    first decrementing run count.  This may release too many,
926	<	*    but if so, the superfluous ones will re-suspend via
927	<	*    preStep().
928	<	*
929	<	* 3. After #spares repeated checks, there are no fewer than #spare
930	<	*    threads not running. We allow this slack to avoid hysteresis
931	<	*    and as a hedge against lag/uncertainty of running count
932	<	*    estimates when signalling or unblocking stalls.
933	<	*
934	<	* 4. All existing workers are busy (as rechecked via repeated
935	<	*    retries by caller) and a new spare is created.
936	<	*
937	<	* If none of the above hold, we try to escape out by
938	<	* re-incrementing count and returning to caller, which can retry
939	<	* later.
940	<	*
941	<	* @param joinMe the task to join
942	<	* @param retries if negative, then serve only as a precheck
943	<	*   that the thread can be replaced by a spare. Otherwise,
944	<	*   the number of repeated calls to this method returning busy
945	<	* @return true if the call must be retried because there
946	<	*   none of the blocking checks hold
1078	>	* Tries to create and start a worker; minimally rolls back counts
1079	>	* on failure.
1080		*/
1081	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
1082	<	if (joinMe.status < 0) // precheck for cancellation
1083	<	return false;
1084	<	if ((runState & TERMINATING) != 0) { // shutting down
1085	<	joinMe.cancelIgnoringExceptions();
1086	<	return false;
1081	>	private void addWorker() {
1082	>	Throwable ex = null;
1083	>	ForkJoinWorkerThread t = null;
1084	>	try {
1085	>	t = factory.newThread(this);
1086	>	} catch (Throwable e) {
1087	>	ex = e;
1088	>	}
1089	>	if (t == null) {  // null or exceptional factory return
1090	>	long c;       // adjust counts
1091	>	do {} while (!UNSAFE.compareAndSwapLong
1092	>	(this, ctlOffset, c = ctl,
1093	>	(((c - AC_UNIT) & AC_MASK) |
1094	>	((c - TC_UNIT) & TC_MASK) |
1095	>	(c & ~(AC_MASK|TC_MASK)))));
1096	>	// Propagate exception if originating from an external caller
1097	>	if (!tryTerminate(false) && ex != null &&
1098	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1099	>	UNSAFE.throwException(ex);
1100		}
1101	+	else
1102	+	t.start();
1103	+	}
1104
1105	<	int pc = parallelism;
1106	<	boolean running = true; // false when running count decremented
1107	<	outer:for (;;) {
1108	<	int wc = workerCounts;
1109	<	int rc = wc & RUNNING_COUNT_MASK;
1110	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1111	<	if (running) { // replace with spare or decrement count
1112	<	if (rc <= pc && tc > pc &&
1113	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
965	<	ForkJoinWorkerThread[] ws = workers;
966	<	int nws = ws.length;
967	<	for (int i = 0; i < nws; ++i) { // search for spare
968	<	ForkJoinWorkerThread w = ws[i];
969	<	if (w != null) {
970	<	if (joinMe.status < 0)
971	<	return false;
972	<	if (w.isSuspended()) {
973	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
974	<	w.tryResumeSpare()) {
975	<	running = false;
976	<	break outer;
977	<	}
978	<	continue outer; // rescan
979	<	}
980	<	}
981	<	}
982	<	}
983	<	if (retries < 0 || // < 0 means replacement check only
984	<	rc == 0 || joinMe.status < 0 || workerCounts != wc ||
985	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
986	<	wc, wc - ONE_RUNNING))
987	<	return false; // done or inconsistent or contended
988	<	running = false;
989	<	if (rc > pc)
990	<	break;
991	<	}
992	<	else { // allow blocking if enough threads
993	<	if (rc >= pc || joinMe.status < 0)
994	<	break;
995	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
996	<	if (retries > sc) {
997	<	if (rc > 0 && rc >= pc - sc) // allow slack
998	<	break;
999	<	if (tc < MAX_THREADS &&
1000	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1001	<	workerCounts == wc &&
1002	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1003	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1004	<	addWorker();
1005	<	break;
1006	<	}
1007	<	}
1008	<	if (workerCounts == wc &&        // back out to allow rescan
1009	<	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1010	<	wc, wc + ONE_RUNNING)) {
1011	<	releaseWaiters();            // help others progress
1012	<	return true;                 // let caller retry
1013	<	}
1014	<	}
1105	>	/**
1106	>	* Callback from ForkJoinWorkerThread constructor to assign a
1107	>	* public name
1108	>	*/
1109	>	final String nextWorkerName() {
1110	>	for (int n;;) {
1111	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1112	>	n = nextWorkerNumber, ++n))
1113	>	return workerNamePrefix + n;
1114		}
1016	–	// arrive here if can block
1017	–	joinMe.internalAwaitDone();
1018	–	int c;                      // to inline incrementRunningCount
1019	–	do {} while (!UNSAFE.compareAndSwapInt
1020	–	(this, workerCountsOffset,
1021	–	c = workerCounts, c + ONE_RUNNING));
1022	–	return false;
1115		}
1116
1117		/**
1118	<	* Same idea as (and shares many code snippets with) tryAwaitJoin,
1119	<	* but self-contained because there are no caller retries.
1120	<	* TODO: Rework to use simpler API.
1118	>	* Callback from ForkJoinWorkerThread constructor to
1119	>	* determine its poolIndex and record in workers array.
1120	>	*
1121	>	* @param w the worker
1122	>	* @return the worker's pool index
1123		*/
1124	<	final void awaitBlocker(ManagedBlocker blocker)
1125	<	throws InterruptedException {
1126	<	boolean done;
1127	<	if (done = blocker.isReleasable())
1128	<	return;
1129	<	int pc = parallelism;
1130	<	int retries = 0;
1131	<	boolean running = true; // false when running count decremented
1132	<	outer:for (;;) {
1133	<	int wc = workerCounts;
1134	<	int rc = wc & RUNNING_COUNT_MASK;
1135	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1136	<	if (running) {
1137	<	if (rc <= pc && tc > pc &&
1138	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1139	<	ForkJoinWorkerThread[] ws = workers;
1140	<	int nws = ws.length;
1141	<	for (int i = 0; i < nws; ++i) {
1142	<	ForkJoinWorkerThread w = ws[i];
1143	<	if (w != null) {
1144	<	if (done = blocker.isReleasable())
1145	<	return;
1146	<	if (w.isSuspended()) {
1053	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1054	<	w.tryResumeSpare()) {
1055	<	running = false;
1056	<	break outer;
1057	<	}
1058	<	continue outer; // rescan
1059	<	}
1124	>	final int registerWorker(ForkJoinWorkerThread w) {
1125	>	/*
1126	>	* In the typical case, a new worker acquires the lock, uses
1127	>	* next available index and returns quickly.  Since we should
1128	>	* not block callers (ultimately from signalWork or
1129	>	* tryPreBlock) waiting for the lock needed to do this, we
1130	>	* instead help release other workers while waiting for the
1131	>	* lock.
1132	>	*/
1133	>	for (int g;;) {
1134	>	ForkJoinWorkerThread[] ws;
1135	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1136	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1137	>	g, g | SG_UNIT)) {
1138	>	int k = nextWorkerIndex;
1139	>	try {
1140	>	if ((ws = workers) != null) { // ignore on shutdown
1141	>	int n = ws.length;
1142	>	if (k < 0 || k >= n || ws[k] != null) {
1143	>	for (k = 0; k < n && ws[k] != null; ++k)
1144	>	;
1145	>	if (k == n)
1146	>	ws = workers = Arrays.copyOf(ws, n << 1);
1147		}
1148	+	ws[k] = w;
1149	+	nextWorkerIndex = k + 1;
1150	+	int m = g & SMASK;
1151	+	g = k > m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1152		}
1153	+	} finally {
1154	+	scanGuard = g;
1155		}
1156	<	if (done = blocker.isReleasable())
1064	<	return;
1065	<	if (rc == 0 || workerCounts != wc ||
1066	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1067	<	wc, wc - ONE_RUNNING))
1068	<	continue;
1069	<	running = false;
1070	<	if (rc > pc)
1071	<	break;
1156	>	return k;
1157		}
1158	<	else {
1159	<	if (rc >= pc || (done = blocker.isReleasable()))
1160	<	break;
1161	<	int sc = tc - pc + 1;
1162	<	if (retries++ > sc) {
1078	<	if (rc > 0 && rc >= pc - sc)
1079	<	break;
1080	<	if (tc < MAX_THREADS &&
1081	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1082	<	workerCounts == wc &&
1083	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1084	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1085	<	addWorker();
1086	<	break;
1158	>	else if ((ws = workers) != null) { // help release others
1159	>	for (ForkJoinWorkerThread u : ws) {
1160	>	if (u != null && u.queueBase != u.queueTop) {
1161	>	if (tryReleaseWaiter())
1162	>	break;
1163		}
1164		}
1089	–	Thread.yield();
1165		}
1166		}
1167	+	}
1168
1169	<	try {
1170	<	if (!done)
1171	<	do {} while (!blocker.isReleasable() && !blocker.block());
1172	<	} finally {
1173	<	if (!running) {
1174	<	int c;
1175	<	do {} while (!UNSAFE.compareAndSwapInt
1176	<	(this, workerCountsOffset,
1177	<	c = workerCounts, c + ONE_RUNNING));
1169	>	/**
1170	>	* Final callback from terminating worker.  Removes record of
1171	>	* worker from array, and adjusts counts. If pool is shutting
1172	>	* down, tries to complete termination.
1173	>	*
1174	>	* @param w the worker
1175	>	*/
1176	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1177	>	int idx = w.poolIndex;
1178	>	int sc = w.stealCount;
1179	>	int steps = 0;
1180	>	// Remove from array, adjust worker counts and collect steal count.
1181	>	// We can intermix failed removes or adjusts with steal updates
1182	>	do {
1183	>	long s, c;
1184	>	int g;
1185	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1186	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1187	>	g, g |= SG_UNIT)) {
1188	>	ForkJoinWorkerThread[] ws = workers;
1189	>	if (ws != null && idx >= 0 &&
1190	>	idx < ws.length && ws[idx] == w)
1191	>	ws[idx] = null;    // verify
1192	>	nextWorkerIndex = idx;
1193	>	scanGuard = g + SG_UNIT;
1194	>	steps = 1;
1195		}
1196	+	if (steps == 1 &&
1197	+	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1198	+	(((c - AC_UNIT) & AC_MASK) |
1199	+	((c - TC_UNIT) & TC_MASK) |
1200	+	(c & ~(AC_MASK|TC_MASK)))))
1201	+	steps = 2;
1202	+	if (sc != 0 &&
1203	+	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1204	+	s = stealCount, s + sc))
1205	+	sc = 0;
1206	+	} while (steps != 2 || sc != 0);
1207	+	if (!tryTerminate(false)) {
1208	+	if (ex != null)   // possibly replace if died abnormally
1209	+	signalWork();
1210	+	else
1211	+	tryReleaseWaiter();
1212		}
1213		}
1214
1215	+	// Shutdown and termination
1216	+
1217		/**
1218		* Possibly initiates and/or completes termination.
1219		*
#	Line 1111 | Line 1222 | public class ForkJoinPool extends Abstra
1222		* @return true if now terminating or terminated
1223		*/
1224		private boolean tryTerminate(boolean now) {
1225	<	if (now)
1226	<	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1227	<	else if (runState < SHUTDOWN ||
1228	<	!submissionQueue.isEmpty() ||
1229	<	(runState & ACTIVE_COUNT_MASK) != 0)
1230	<	return false;
1231	<
1232	<	if (advanceRunLevel(TERMINATING))
1233	<	startTerminating();
1234	<
1235	<	// Finish now if all threads terminated; else in some subsequent call
1236	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1237	<	advanceRunLevel(TERMINATED);
1238	<	termination.arrive();
1225	>	long c;
1226	>	while (((c = ctl) & STOP_BIT) == 0) {
1227	>	if (!now) {
1228	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1229	>	return false;
1230	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1231	>	queueBase != queueTop) {
1232	>	if (ctl == c) // staleness check
1233	>	return false;
1234	>	continue;
1235	>	}
1236	>	}
1237	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1238	>	startTerminating();
1239	>	}
1240	>	if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
1241	>	final ReentrantLock lock = this.submissionLock;
1242	>	lock.lock();
1243	>	try {
1244	>	termination.signalAll();
1245	>	} finally {
1246	>	lock.unlock();
1247	>	}
1248		}
1249		return true;
1250		}
1251
1252		/**
1253	<	* Actions on transition to TERMINATING
1253	>	* Runs up to three passes through workers: (0) Setting
1254	>	* termination status for each worker, followed by wakeups up to
1255	>	* queued workers; (1) helping cancel tasks; (2) interrupting
1256	>	* lagging threads (likely in external tasks, but possibly also
1257	>	* blocked in joins).  Each pass repeats previous steps because of
1258	>	* potential lagging thread creation.
1259		*/
1260		private void startTerminating() {
1261	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1262	<	cancelSubmissions();
1263	<	shutdownWorkers();
1264	<	cancelWorkerTasks();
1265	<	signalEvent();
1266	<	interruptWorkers();
1261	>	cancelSubmissions();
1262	>	for (int pass = 0; pass < 3; ++pass) {
1263	>	ForkJoinWorkerThread[] ws = workers;
1264	>	if (ws != null) {
1265	>	for (ForkJoinWorkerThread w : ws) {
1266	>	if (w != null) {
1267	>	w.terminate = true;
1268	>	if (pass > 0) {
1269	>	w.cancelTasks();
1270	>	if (pass > 1 && !w.isInterrupted()) {
1271	>	try {
1272	>	w.interrupt();
1273	>	} catch (SecurityException ignore) {
1274	>	}
1275	>	}
1276	>	}
1277	>	}
1278	>	}
1279	>	terminateWaiters();
1280	>	}
1281		}
1282		}
1283
1284		/**
1285	<	* Clear out and cancel submissions, ignoring exceptions
1285	>	* Polls and cancels all submissions. Called only during termination.
1286		*/
1287		private void cancelSubmissions() {
1288	<	ForkJoinTask<?> task;
1289	<	while ((task = submissionQueue.poll()) != null) {
1290	<	try {
1291	<	task.cancel(false);
1292	<	} catch (Throwable ignore) {
1288	>	while (queueBase != queueTop) {
1289	>	ForkJoinTask<?> task = pollSubmission();
1290	>	if (task != null) {
1291	>	try {
1292	>	task.cancel(false);
1293	>	} catch (Throwable ignore) {
1294	>	}
1295		}
1296		}
1297		}
1298
1299		/**
1300	<	* Sets all worker run states to at least shutdown,
1301	<	* also resuming suspended workers
1161	<	*/
1162	<	private void shutdownWorkers() {
1163	<	ForkJoinWorkerThread[] ws = workers;
1164	<	int nws = ws.length;
1165	<	for (int i = 0; i < nws; ++i) {
1166	<	ForkJoinWorkerThread w = ws[i];
1167	<	if (w != null)
1168	<	w.shutdown();
1169	<	}
1170	<	}
1171	<
1172	<	/**
1173	<	* Clears out and cancels all locally queued tasks
1174	<	*/
1175	<	private void cancelWorkerTasks() {
1176	<	ForkJoinWorkerThread[] ws = workers;
1177	<	int nws = ws.length;
1178	<	for (int i = 0; i < nws; ++i) {
1179	<	ForkJoinWorkerThread w = ws[i];
1180	<	if (w != null)
1181	<	w.cancelTasks();
1182	<	}
1183	<	}
1184	<
1185	<	/**
1186	<	* Unsticks all workers blocked on joins etc
1300	>	* Tries to set the termination status of waiting workers, and
1301	>	* then wakes them up (after which they will terminate).
1302		*/
1303	<	private void interruptWorkers() {
1303	>	private void terminateWaiters() {
1304		ForkJoinWorkerThread[] ws = workers;
1305	<	int nws = ws.length;
1306	<	for (int i = 0; i < nws; ++i) {
1307	<	ForkJoinWorkerThread w = ws[i];
1308	<	if (w != null && !w.isTerminated()) {
1309	<	try {
1310	<	w.interrupt();
1311	<	} catch (SecurityException ignore) {
1305	>	if (ws != null) {
1306	>	ForkJoinWorkerThread w; long c; int i, e;
1307	>	int n = ws.length;
1308	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1309	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1310	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1311	>	(long)(w.nextWait & E_MASK) |
1312	>	((c + AC_UNIT) & AC_MASK) |
1313	>	(c & (TC_MASK|STOP_BIT)))) {
1314	>	w.terminate = true;
1315	>	w.eventCount = e + EC_UNIT;
1316	>	if (w.parked)
1317	>	UNSAFE.unpark(w);
1318		}
1319		}
1320		}
1321		}
1322
1323	<	// misc support for ForkJoinWorkerThread
1323	>	// misc ForkJoinWorkerThread support
1324
1325		/**
1326	<	* Returns pool number
1326	>	* Increment or decrement quiescerCount. Needed only to prevent
1327	>	* triggering shutdown if a worker is transiently inactive while
1328	>	* checking quiescence.
1329	>	*
1330	>	* @param delta 1 for increment, -1 for decrement
1331		*/
1332	<	final int getPoolNumber() {
1333	<	return poolNumber;
1332	>	final void addQuiescerCount(int delta) {
1333	>	int c;
1334	>	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1335	>	c = quiescerCount, c + delta));
1336		}
1337
1338		/**
1339	<	* Accumulates steal count from a worker, clearing
1340	<	* the worker's value
1339	>	* Directly increment or decrement active count without
1340	>	* queuing. This method is used to transiently assert inactivation
1341	>	* while checking quiescence.
1342	>	*
1343	>	* @param delta 1 for increment, -1 for decrement
1344		*/
1345	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1346	<	int sc = w.stealCount;
1347	<	if (sc != 0) {
1348	<	long c;
1349	<	w.stealCount = 0;
1350	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1221	<	c = stealCount, c + sc));
1222	<	}
1345	>	final void addActiveCount(int delta) {
1346	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1347	>	long c;
1348	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1349	>	((c + d) & AC_MASK) |
1350	>	(c & ~AC_MASK)));
1351		}
1352
1353		/**
#	Line 1227 | Line 1355 | public class ForkJoinPool extends Abstra
1355		* active thread.
1356		*/
1357		final int idlePerActive() {
1358	<	int pc = parallelism; // use parallelism, not rc
1359	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1360	<	// Use exact results for small values, saturate past 4
1361	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1358	>	// Approximate at powers of two for small values, saturate past 4
1359	>	int p = parallelism;
1360	>	int a = p + (int)(ctl >> AC_SHIFT);
1361	>	return (a > (p >>>= 1) ? 0 :
1362	>	a > (p >>>= 1) ? 1 :
1363	>	a > (p >>>= 1) ? 2 :
1364	>	a > (p >>>= 1) ? 4 :
1365	>	8);
1366		}
1367
1368	<	// Public and protected methods
1368	>	// Exported methods
1369
1370		// Constructors
1371
#	Line 1280 | Line 1412 | public class ForkJoinPool extends Abstra
1412		* use {@link #defaultForkJoinWorkerThreadFactory}.
1413		* @param handler the handler for internal worker threads that
1414		* terminate due to unrecoverable errors encountered while executing
1415	<	* tasks. For default value, use <code>null</code>.
1415	>	* tasks. For default value, use {@code null}.
1416		* @param asyncMode if true,
1417		* establishes local first-in-first-out scheduling mode for forked
1418		* tasks that are never joined. This mode may be more appropriate
1419		* than default locally stack-based mode in applications in which
1420		* worker threads only process event-style asynchronous tasks.
1421	<	* For default value, use <code>false</code>.
1421	>	* For default value, use {@code false}.
1422		* @throws IllegalArgumentException if parallelism less than or
1423		*         equal to zero, or greater than implementation limit
1424		* @throws NullPointerException if the factory is null
#	Line 1302 | Line 1434 | public class ForkJoinPool extends Abstra
1434		checkPermission();
1435		if (factory == null)
1436		throw new NullPointerException();
1437	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1437	>	if (parallelism <= 0 || parallelism > MAX_ID)
1438		throw new IllegalArgumentException();
1439		this.parallelism = parallelism;
1440		this.factory = factory;
1441		this.ueh = handler;
1442		this.locallyFifo = asyncMode;
1443	<	int arraySize = initialArraySizeFor(parallelism);
1444	<	this.workers = new ForkJoinWorkerThread[arraySize];
1445	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1446	<	this.workerLock = new ReentrantLock();
1447	<	this.termination = new Phaser(1);
1448	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
1449	<	}
1450	<
1451	<	/**
1452	<	* Returns initial power of two size for workers array.
1453	<	* @param pc the initial parallelism level
1454	<	*/
1455	<	private static int initialArraySizeFor(int pc) {
1456	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1457	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1458	<	size |= size >>> 1;
1459	<	size |= size >>> 2;
1328	<	size |= size >>> 4;
1329	<	size |= size >>> 8;
1330	<	return size + 1;
1443	>	long np = (long)(-parallelism); // offset ctl counts
1444	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1445	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1446	>	// initialize workers array with room for 2*parallelism if possible
1447	>	int n = parallelism << 1;
1448	>	if (n >= MAX_ID)
1449	>	n = MAX_ID;
1450	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1451	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1452	>	}
1453	>	workers = new ForkJoinWorkerThread[n + 1];
1454	>	this.submissionLock = new ReentrantLock();
1455	>	this.termination = submissionLock.newCondition();
1456	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1457	>	sb.append(poolNumberGenerator.incrementAndGet());
1458	>	sb.append("-worker-");
1459	>	this.workerNamePrefix = sb.toString();
1460		}
1461
1462		// Execution methods
1463
1464		/**
1336	–	* Common code for execute, invoke and submit
1337	–	*/
1338	–	private <T> void doSubmit(ForkJoinTask<T> task) {
1339	–	if (task == null)
1340	–	throw new NullPointerException();
1341	–	if (runState >= SHUTDOWN)
1342	–	throw new RejectedExecutionException();
1343	–	submissionQueue.offer(task);
1344	–	signalEvent();
1345	–	ensureEnoughWorkers();
1346	–	}
1347	–
1348	–	/**
1465		* Performs the given task, returning its result upon completion.
1466	<	* If the caller is already engaged in a fork/join computation in
1467	<	* the current pool, this method is equivalent in effect to
1468	<	* {@link ForkJoinTask#invoke}.
1466	>	* If the computation encounters an unchecked Exception or Error,
1467	>	* it is rethrown as the outcome of this invocation.  Rethrown
1468	>	* exceptions behave in the same way as regular exceptions, but,
1469	>	* when possible, contain stack traces (as displayed for example
1470	>	* using {@code ex.printStackTrace()}) of both the current thread
1471	>	* as well as the thread actually encountering the exception;
1472	>	* minimally only the latter.
1473		*
1474		* @param task the task
1475		* @return the task's result
#	Line 1358 | Line 1478 | public class ForkJoinPool extends Abstra
1478		*         scheduled for execution
1479		*/
1480		public <T> T invoke(ForkJoinTask<T> task) {
1481	<	doSubmit(task);
1482	<	return task.join();
1481	>	Thread t = Thread.currentThread();
1482	>	if (task == null)
1483	>	throw new NullPointerException();
1484	>	if (shutdown)
1485	>	throw new RejectedExecutionException();
1486	>	if ((t instanceof ForkJoinWorkerThread) &&
1487	>	((ForkJoinWorkerThread)t).pool == this)
1488	>	return task.invoke();  // bypass submit if in same pool
1489	>	else {
1490	>	addSubmission(task);
1491	>	return task.join();
1492	>	}
1493	>	}
1494	>
1495	>	/**
1496	>	* Unless terminating, forks task if within an ongoing FJ
1497	>	* computation in the current pool, else submits as external task.
1498	>	*/
1499	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1500	>	ForkJoinWorkerThread w;
1501	>	Thread t = Thread.currentThread();
1502	>	if (shutdown)
1503	>	throw new RejectedExecutionException();
1504	>	if ((t instanceof ForkJoinWorkerThread) &&
1505	>	(w = (ForkJoinWorkerThread)t).pool == this)
1506	>	w.pushTask(task);
1507	>	else
1508	>	addSubmission(task);
1509		}
1510
1511		/**
1512		* Arranges for (asynchronous) execution of the given task.
1367	–	* If the caller is already engaged in a fork/join computation in
1368	–	* the current pool, this method is equivalent in effect to
1369	–	* {@link ForkJoinTask#fork}.
1513		*
1514		* @param task the task
1515		* @throws NullPointerException if the task is null
#	Line 1374 | Line 1517 | public class ForkJoinPool extends Abstra
1517		*         scheduled for execution
1518		*/
1519		public void execute(ForkJoinTask<?> task) {
1520	<	doSubmit(task);
1520	>	if (task == null)
1521	>	throw new NullPointerException();
1522	>	forkOrSubmit(task);
1523		}
1524
1525		// AbstractExecutorService methods
#	Line 1385 | Line 1530 | public class ForkJoinPool extends Abstra
1530		*         scheduled for execution
1531		*/
1532		public void execute(Runnable task) {
1533	+	if (task == null)
1534	+	throw new NullPointerException();
1535		ForkJoinTask<?> job;
1536		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1537		job = (ForkJoinTask<?>) task;
1538		else
1539		job = ForkJoinTask.adapt(task, null);
1540	<	doSubmit(job);
1540	>	forkOrSubmit(job);
1541		}
1542
1543		/**
1544		* Submits a ForkJoinTask for execution.
1398	–	* If the caller is already engaged in a fork/join computation in
1399	–	* the current pool, this method is equivalent in effect to
1400	–	* {@link ForkJoinTask#fork}.
1545		*
1546		* @param task the task to submit
1547		* @return the task
#	Line 1406 | Line 1550 | public class ForkJoinPool extends Abstra
1550		*         scheduled for execution
1551		*/
1552		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1553	<	doSubmit(task);
1553	>	if (task == null)
1554	>	throw new NullPointerException();
1555	>	forkOrSubmit(task);
1556		return task;
1557		}
1558
#	Line 1416 | Line 1562 | public class ForkJoinPool extends Abstra
1562		*         scheduled for execution
1563		*/
1564		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1565	+	if (task == null)
1566	+	throw new NullPointerException();
1567		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1568	<	doSubmit(job);
1568	>	forkOrSubmit(job);
1569		return job;
1570		}
1571
#	Line 1427 | Line 1575 | public class ForkJoinPool extends Abstra
1575		*         scheduled for execution
1576		*/
1577		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1578	+	if (task == null)
1579	+	throw new NullPointerException();
1580		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1581	<	doSubmit(job);
1581	>	forkOrSubmit(job);
1582		return job;
1583		}
1584
#	Line 1438 | Line 1588 | public class ForkJoinPool extends Abstra
1588		*         scheduled for execution
1589		*/
1590		public ForkJoinTask<?> submit(Runnable task) {
1591	+	if (task == null)
1592	+	throw new NullPointerException();
1593		ForkJoinTask<?> job;
1594		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1595		job = (ForkJoinTask<?>) task;
1596		else
1597		job = ForkJoinTask.adapt(task, null);
1598	<	doSubmit(job);
1598	>	forkOrSubmit(job);
1599		return job;
1600		}
1601
#	Line 1503 | Line 1655 | public class ForkJoinPool extends Abstra
1655
1656		/**
1657		* Returns the number of worker threads that have started but not
1658	<	* yet terminated.  This result returned by this method may differ
1658	>	* yet terminated.  The result returned by this method may differ
1659		* from {@link #getParallelism} when threads are created to
1660		* maintain parallelism when others are cooperatively blocked.
1661		*
1662		* @return the number of worker threads
1663		*/
1664		public int getPoolSize() {
1665	<	return workerCounts >>> TOTAL_COUNT_SHIFT;
1665	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1666		}
1667
1668		/**
#	Line 1532 | Line 1684 | public class ForkJoinPool extends Abstra
1684		* @return the number of worker threads
1685		*/
1686		public int getRunningThreadCount() {
1687	<	return workerCounts & RUNNING_COUNT_MASK;
1687	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1688	>	return r <= 0? 0 : r; // suppress momentarily negative values
1689		}
1690
1691		/**
#	Line 1543 | Line 1696 | public class ForkJoinPool extends Abstra
1696		* @return the number of active threads
1697		*/
1698		public int getActiveThreadCount() {
1699	<	return runState & ACTIVE_COUNT_MASK;
1699	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1700	>	return r <= 0? 0 : r; // suppress momentarily negative values
1701		}
1702
1703		/**
#	Line 1558 | Line 1712 | public class ForkJoinPool extends Abstra
1712		* @return {@code true} if all threads are currently idle
1713		*/
1714		public boolean isQuiescent() {
1715	<	return (runState & ACTIVE_COUNT_MASK) == 0;
1715	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1716		}
1717
1718		/**
#	Line 1588 | Line 1742 | public class ForkJoinPool extends Abstra
1742		*/
1743		public long getQueuedTaskCount() {
1744		long count = 0;
1745	<	ForkJoinWorkerThread[] ws = workers;
1746	<	int nws = ws.length;
1747	<	for (int i = 0; i < nws; ++i) {
1748	<	ForkJoinWorkerThread w = ws[i];
1749	<	if (w != null)
1750	<	count += w.getQueueSize();
1745	>	ForkJoinWorkerThread[] ws;
1746	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1747	>	(ws = workers) != null) {
1748	>	for (ForkJoinWorkerThread w : ws)
1749	>	if (w != null)
1750	>	count -= w.queueBase - w.queueTop; // must read base first
1751		}
1752		return count;
1753		}
1754
1755		/**
1756		* Returns an estimate of the number of tasks submitted to this
1757	<	* pool that have not yet begun executing.  This method takes time
1758	<	* proportional to the number of submissions.
1757	>	* pool that have not yet begun executing.  This method may take
1758	>	* time proportional to the number of submissions.
1759		*
1760		* @return the number of queued submissions
1761		*/
1762		public int getQueuedSubmissionCount() {
1763	<	return submissionQueue.size();
1763	>	return -queueBase + queueTop;
1764		}
1765
1766		/**
#	Line 1616 | Line 1770 | public class ForkJoinPool extends Abstra
1770		* @return {@code true} if there are any queued submissions
1771		*/
1772		public boolean hasQueuedSubmissions() {
1773	<	return !submissionQueue.isEmpty();
1773	>	return queueBase != queueTop;
1774		}
1775
1776		/**
#	Line 1627 | Line 1781 | public class ForkJoinPool extends Abstra
1781		* @return the next submission, or {@code null} if none
1782		*/
1783		protected ForkJoinTask<?> pollSubmission() {
1784	<	return submissionQueue.poll();
1784	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1785	>	while ((b = queueBase) != queueTop &&
1786	>	(q = submissionQueue) != null &&
1787	>	(i = (q.length - 1) & b) >= 0) {
1788	>	long u = (i << ASHIFT) + ABASE;
1789	>	if ((t = q[i]) != null &&
1790	>	queueBase == b &&
1791	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1792	>	queueBase = b + 1;
1793	>	return t;
1794	>	}
1795	>	}
1796	>	return null;
1797		}
1798
1799		/**
#	Line 1648 | Line 1814 | public class ForkJoinPool extends Abstra
1814		* @return the number of elements transferred
1815		*/
1816		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1651	–	int n = submissionQueue.drainTo(c);
1652	–	ForkJoinWorkerThread[] ws = workers;
1653	–	int nws = ws.length;
1654	–	for (int i = 0; i < nws; ++i) {
1655	–	ForkJoinWorkerThread w = ws[i];
1656	–	if (w != null)
1657	–	n += w.drainTasksTo(c);
1658	–	}
1659	–	return n;
1660	–	}
1661	–
1662	–	/**
1663	–	* Returns count of total parks by existing workers.
1664	–	* Used during development only since not meaningful to users.
1665	–	*/
1666	–	private int collectParkCount() {
1817		int count = 0;
1818	<	ForkJoinWorkerThread[] ws = workers;
1819	<	int nws = ws.length;
1820	<	for (int i = 0; i < nws; ++i) {
1821	<	ForkJoinWorkerThread w = ws[i];
1822	<	if (w != null)
1823	<	count += w.parkCount;
1818	>	while (queueBase != queueTop) {
1819	>	ForkJoinTask<?> t = pollSubmission();
1820	>	if (t != null) {
1821	>	c.add(t);
1822	>	++count;
1823	>	}
1824	>	}
1825	>	ForkJoinWorkerThread[] ws;
1826	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1827	>	(ws = workers) != null) {
1828	>	for (ForkJoinWorkerThread w : ws)
1829	>	if (w != null)
1830	>	count += w.drainTasksTo(c);
1831		}
1832		return count;
1833		}
#	Line 1686 | Line 1843 | public class ForkJoinPool extends Abstra
1843		long st = getStealCount();
1844		long qt = getQueuedTaskCount();
1845		long qs = getQueuedSubmissionCount();
1689	–	int wc = workerCounts;
1690	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
1691	–	int rc = wc & RUNNING_COUNT_MASK;
1846		int pc = parallelism;
1847	<	int rs = runState;
1848	<	int ac = rs & ACTIVE_COUNT_MASK;
1849	<	//        int pk = collectParkCount();
1847	>	long c = ctl;
1848	>	int tc = pc + (short)(c >>> TC_SHIFT);
1849	>	int rc = pc + (int)(c >> AC_SHIFT);
1850	>	if (rc < 0) // ignore transient negative
1851	>	rc = 0;
1852	>	int ac = rc + blockedCount;
1853	>	String level;
1854	>	if ((c & STOP_BIT) != 0)
1855	>	level = (tc == 0)? "Terminated" : "Terminating";
1856	>	else
1857	>	level = shutdown? "Shutting down" : "Running";
1858		return super.toString() +
1859	<	"[" + runLevelToString(rs) +
1859	>	"[" + level +
1860		", parallelism = " + pc +
1861		", size = " + tc +
1862		", active = " + ac +
#	Line 1702 | Line 1864 | public class ForkJoinPool extends Abstra
1864		", steals = " + st +
1865		", tasks = " + qt +
1866		", submissions = " + qs +
1705	–	//            ", parks = " + pk +
1867		"]";
1868		}
1869
1709	–	private static String runLevelToString(int s) {
1710	–	return ((s & TERMINATED) != 0 ? "Terminated" :
1711	–	((s & TERMINATING) != 0 ? "Terminating" :
1712	–	((s & SHUTDOWN) != 0 ? "Shutting down" :
1713	–	"Running")));
1714	–	}
1715	–
1870		/**
1871		* Initiates an orderly shutdown in which previously submitted
1872		* tasks are executed, but no new tasks will be accepted.
#	Line 1727 | Line 1881 | public class ForkJoinPool extends Abstra
1881		*/
1882		public void shutdown() {
1883		checkPermission();
1884	<	advanceRunLevel(SHUTDOWN);
1884	>	shutdown = true;
1885		tryTerminate(false);
1886		}
1887
#	Line 1749 | Line 1903 | public class ForkJoinPool extends Abstra
1903		*/
1904		public List<Runnable> shutdownNow() {
1905		checkPermission();
1906	+	shutdown = true;
1907		tryTerminate(true);
1908		return Collections.emptyList();
1909		}
#	Line 1759 | Line 1914 | public class ForkJoinPool extends Abstra
1914		* @return {@code true} if all tasks have completed following shut down
1915		*/
1916		public boolean isTerminated() {
1917	<	return runState >= TERMINATED;
1917	>	long c = ctl;
1918	>	return ((c & STOP_BIT) != 0L &&
1919	>	(short)(c >>> TC_SHIFT) == -parallelism);
1920		}
1921
1922		/**
#	Line 1767 | Line 1924 | public class ForkJoinPool extends Abstra
1924		* commenced but not yet completed.  This method may be useful for
1925		* debugging. A return of {@code true} reported a sufficient
1926		* period after shutdown may indicate that submitted tasks have
1927	<	* ignored or suppressed interruption, causing this executor not
1928	<	* to properly terminate.
1927	>	* ignored or suppressed interruption, or are waiting for IO,
1928	>	* causing this executor not to properly terminate. (See the
1929	>	* advisory notes for class {@link ForkJoinTask} stating that
1930	>	* tasks should not normally entail blocking operations.  But if
1931	>	* they do, they must abort them on interrupt.)
1932		*
1933		* @return {@code true} if terminating but not yet terminated
1934		*/
1935		public boolean isTerminating() {
1936	<	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1936	>	long c = ctl;
1937	>	return ((c & STOP_BIT) != 0L &&
1938	>	(short)(c >>> TC_SHIFT) != -parallelism);
1939	>	}
1940	>
1941	>	/**
1942	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1943	>	*/
1944	>	final boolean isAtLeastTerminating() {
1945	>	return (ctl & STOP_BIT) != 0L;
1946		}
1947
1948		/**
#	Line 1782 | Line 1951 | public class ForkJoinPool extends Abstra
1951		* @return {@code true} if this pool has been shut down
1952		*/
1953		public boolean isShutdown() {
1954	<	return runState >= SHUTDOWN;
1954	>	return shutdown;
1955		}
1956
1957		/**
#	Line 1798 | Line 1967 | public class ForkJoinPool extends Abstra
1967		*/
1968		public boolean awaitTermination(long timeout, TimeUnit unit)
1969		throws InterruptedException {
1970	+	long nanos = unit.toNanos(timeout);
1971	+	final ReentrantLock lock = this.submissionLock;
1972	+	lock.lock();
1973		try {
1974	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1975	<	} catch(TimeoutException ex) {
1976	<	return false;
1974	>	for (;;) {
1975	>	if (isTerminated())
1976	>	return true;
1977	>	if (nanos <= 0)
1978	>	return false;
1979	>	nanos = termination.awaitNanos(nanos);
1980	>	}
1981	>	} finally {
1982	>	lock.unlock();
1983		}
1984		}
1985
#	Line 1809 | Line 1987 | public class ForkJoinPool extends Abstra
1987		* Interface for extending managed parallelism for tasks running
1988		* in {@link ForkJoinPool}s.
1989		*
1990	<	* <p>A {@code ManagedBlocker} provides two methods.
1991	<	* Method {@code isReleasable} must return {@code true} if
1992	<	* blocking is not necessary. Method {@code block} blocks the
1993	<	* current thread if necessary (perhaps internally invoking
1994	<	* {@code isReleasable} before actually blocking).
1990	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1991	>	* {@code isReleasable} must return {@code true} if blocking is
1992	>	* not necessary. Method {@code block} blocks the current thread
1993	>	* if necessary (perhaps internally invoking {@code isReleasable}
1994	>	* before actually blocking). These actions are performed by any
1995	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
1996	>	* unusual methods in this API accommodate synchronizers that may,
1997	>	* but don't usually, block for long periods. Similarly, they
1998	>	* allow more efficient internal handling of cases in which
1999	>	* additional workers may be, but usually are not, needed to
2000	>	* ensure sufficient parallelism.  Toward this end,
2001	>	* implementations of method {@code isReleasable} must be amenable
2002	>	* to repeated invocation.
2003		*
2004		* <p>For example, here is a ManagedBlocker based on a
2005		* ReentrantLock:
#	Line 1831 | Line 2017 | public class ForkJoinPool extends Abstra
2017		*     return hasLock || (hasLock = lock.tryLock());
2018		*   }
2019		* }}</pre>
2020	+	*
2021	+	* <p>Here is a class that possibly blocks waiting for an
2022	+	* item on a given queue:
2023	+	*  <pre> {@code
2024	+	* class QueueTaker<E> implements ManagedBlocker {
2025	+	*   final BlockingQueue<E> queue;
2026	+	*   volatile E item = null;
2027	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2028	+	*   public boolean block() throws InterruptedException {
2029	+	*     if (item == null)
2030	+	*       item = queue.take();
2031	+	*     return true;
2032	+	*   }
2033	+	*   public boolean isReleasable() {
2034	+	*     return item != null || (item = queue.poll()) != null;
2035	+	*   }
2036	+	*   public E getItem() { // call after pool.managedBlock completes
2037	+	*     return item;
2038	+	*   }
2039	+	* }}</pre>
2040		*/
2041		public static interface ManagedBlocker {
2042		/**
#	Line 1873 | Line 2079 | public class ForkJoinPool extends Abstra
2079		public static void managedBlock(ManagedBlocker blocker)
2080		throws InterruptedException {
2081		Thread t = Thread.currentThread();
2082	<	if (t instanceof ForkJoinWorkerThread)
2083	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
2082	>	if (t instanceof ForkJoinWorkerThread) {
2083	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2084	>	w.pool.awaitBlocker(blocker);
2085	>	}
2086		else {
2087		do {} while (!blocker.isReleasable() && !blocker.block());
2088		}
#	Line 1893 | Line 2101 | public class ForkJoinPool extends Abstra
2101		}
2102
2103		// Unsafe mechanics
2104	<
2105	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2106	<	private static final long workerCountsOffset =
2107	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2108	<	private static final long runStateOffset =
2109	<	objectFieldOffset("runState", ForkJoinPool.class);
2110	<	private static final long eventCountOffset =
2111	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2112	<	private static final long eventWaitersOffset =
2113	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
2114	<	private static final long stealCountOffset =
2115	<	objectFieldOffset("stealCount",ForkJoinPool.class);
2116	<
2117	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2104	>	private static final sun.misc.Unsafe UNSAFE;
2105	>	private static final long ctlOffset;
2106	>	private static final long stealCountOffset;
2107	>	private static final long blockedCountOffset;
2108	>	private static final long quiescerCountOffset;
2109	>	private static final long scanGuardOffset;
2110	>	private static final long nextWorkerNumberOffset;
2111	>	private static final long ABASE;
2112	>	private static final int ASHIFT;
2113	>
2114	>	static {
2115	>	poolNumberGenerator = new AtomicInteger();
2116	>	workerSeedGenerator = new Random();
2117	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2118	>	defaultForkJoinWorkerThreadFactory =
2119	>	new DefaultForkJoinWorkerThreadFactory();
2120	>	int s;
2121		try {
2122	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2123	<	} catch (NoSuchFieldException e) {
2124	<	// Convert Exception to corresponding Error
2125	<	NoSuchFieldError error = new NoSuchFieldError(field);
2126	<	error.initCause(e);
2127	<	throw error;
2128	<	}
2122	>	UNSAFE = getUnsafe();
2123	>	Class k = ForkJoinPool.class;
2124	>	ctlOffset = UNSAFE.objectFieldOffset
2125	>	(k.getDeclaredField("ctl"));
2126	>	stealCountOffset = UNSAFE.objectFieldOffset
2127	>	(k.getDeclaredField("stealCount"));
2128	>	blockedCountOffset = UNSAFE.objectFieldOffset
2129	>	(k.getDeclaredField("blockedCount"));
2130	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2131	>	(k.getDeclaredField("quiescerCount"));
2132	>	scanGuardOffset = UNSAFE.objectFieldOffset
2133	>	(k.getDeclaredField("scanGuard"));
2134	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2135	>	(k.getDeclaredField("nextWorkerNumber"));
2136	>	Class a = ForkJoinTask[].class;
2137	>	ABASE = UNSAFE.arrayBaseOffset(a);
2138	>	s = UNSAFE.arrayIndexScale(a);
2139	>	} catch (Exception e) {
2140	>	throw new Error(e);
2141	>	}
2142	>	if ((s & (s-1)) != 0)
2143	>	throw new Error("data type scale not a power of two");
2144	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2145		}
2146
2147		/**

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