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 |
5 |
*/ |
6 |
|
7 |
package jsr166y; |
8 |
|
9 |
import java.util.concurrent.*; |
10 |
|
11 |
import java.util.ArrayList; |
12 |
import java.util.Arrays; |
13 |
import java.util.Collection; |
14 |
import java.util.Collections; |
15 |
import java.util.List; |
16 |
import java.util.concurrent.locks.LockSupport; |
17 |
import java.util.concurrent.locks.ReentrantLock; |
18 |
import java.util.concurrent.atomic.AtomicInteger; |
19 |
import java.util.concurrent.CountDownLatch; |
20 |
|
21 |
/** |
22 |
* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
23 |
* A {@code ForkJoinPool} provides the entry point for submissions |
24 |
* from non-{@code ForkJoinTask} clients, as well as management and |
25 |
* monitoring operations. |
26 |
* |
27 |
* <p>A {@code ForkJoinPool} differs from other kinds of {@link |
28 |
* ExecutorService} mainly by virtue of employing |
29 |
* <em>work-stealing</em>: all threads in the pool attempt to find and |
30 |
* execute subtasks created by other active tasks (eventually blocking |
31 |
* waiting for work if none exist). This enables efficient processing |
32 |
* when most tasks spawn other subtasks (as do most {@code |
33 |
* ForkJoinTask}s). When setting <em>asyncMode</em> to true in |
34 |
* constructors, {@code ForkJoinPool}s may also be appropriate for use |
35 |
* with event-style tasks that are never joined. |
36 |
* |
37 |
* <p>A {@code ForkJoinPool} is constructed with a given target |
38 |
* parallelism level; by default, equal to the number of available |
39 |
* processors. The pool attempts to maintain enough active (or |
40 |
* available) threads by dynamically adding, suspending, or resuming |
41 |
* internal worker threads, even if some tasks are stalled waiting to |
42 |
* join others. However, no such adjustments are guaranteed in the |
43 |
* face of blocked IO or other unmanaged synchronization. The nested |
44 |
* {@link ManagedBlocker} interface enables extension of the kinds of |
45 |
* synchronization accommodated. |
46 |
* |
47 |
* <p>In addition to execution and lifecycle control methods, this |
48 |
* class provides status check methods (for example |
49 |
* {@link #getStealCount}) that are intended to aid in developing, |
50 |
* tuning, and monitoring fork/join applications. Also, method |
51 |
* {@link #toString} returns indications of pool state in a |
52 |
* convenient form for informal monitoring. |
53 |
* |
54 |
* <p> As is the case with other ExecutorServices, there are three |
55 |
* main task execution methods summarized in the follwoing |
56 |
* table. These are designed to be used by clients not already engaged |
57 |
* in fork/join computations in the current pool. The main forms of |
58 |
* these methods accept instances of {@code ForkJoinTask}, but |
59 |
* overloaded forms also allow mixed execution of plain {@code |
60 |
* Runnable}- or {@code Callable}- based activities as well. However, |
61 |
* tasks that are already executing in a pool should normally |
62 |
* <em>NOT</em> use these pool execution methods, but instead use the |
63 |
* within-computation forms listed in the table. |
64 |
* |
65 |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
66 |
* <tr> |
67 |
* <td></td> |
68 |
* <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
69 |
* <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
70 |
* </tr> |
71 |
* <tr> |
72 |
* <td> <b>Arange async execution</td> |
73 |
* <td> {@link #execute(ForkJoinTask)}</td> |
74 |
* <td> {@link ForkJoinTask#fork}</td> |
75 |
* </tr> |
76 |
* <tr> |
77 |
* <td> <b>Await and obtain result</td> |
78 |
* <td> {@link #invoke(ForkJoinTask)}</td> |
79 |
* <td> {@link ForkJoinTask#invoke}</td> |
80 |
* </tr> |
81 |
* <tr> |
82 |
* <td> <b>Arrange exec and obtain Future</td> |
83 |
* <td> {@link #submit(ForkJoinTask)}</td> |
84 |
* <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
85 |
* </tr> |
86 |
* </table> |
87 |
* |
88 |
* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is |
89 |
* used for all parallel task execution in a program or subsystem. |
90 |
* Otherwise, use would not usually outweigh the construction and |
91 |
* bookkeeping overhead of creating a large set of threads. For |
92 |
* example, a common pool could be used for the {@code SortTasks} |
93 |
* illustrated in {@link RecursiveAction}. Because {@code |
94 |
* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon |
95 |
* daemon} mode, there is typically no need to explicitly {@link |
96 |
* #shutdown} such a pool upon program exit. |
97 |
* |
98 |
* <pre> |
99 |
* static final ForkJoinPool mainPool = new ForkJoinPool(); |
100 |
* ... |
101 |
* public void sort(long[] array) { |
102 |
* mainPool.invoke(new SortTask(array, 0, array.length)); |
103 |
* } |
104 |
* </pre> |
105 |
* |
106 |
* <p><b>Implementation notes</b>: This implementation restricts the |
107 |
* maximum number of running threads to 32767. Attempts to create |
108 |
* pools with greater than the maximum number result in |
109 |
* {@code IllegalArgumentException}. |
110 |
* |
111 |
* <p>This implementation rejects submitted tasks (that is, by throwing |
112 |
* {@link RejectedExecutionException}) only when the pool is shut down |
113 |
* or internal resources have been exhuasted. |
114 |
* |
115 |
* @since 1.7 |
116 |
* @author Doug Lea |
117 |
*/ |
118 |
public class ForkJoinPool extends AbstractExecutorService { |
119 |
|
120 |
/* |
121 |
* Implementation Overview |
122 |
* |
123 |
* This class provides the central bookkeeping and control for a |
124 |
* set of worker threads: Submissions from non-FJ threads enter |
125 |
* into a submission queue. Workers take these tasks and typically |
126 |
* split them into subtasks that may be stolen by other workers. |
127 |
* The main work-stealing mechanics implemented in class |
128 |
* ForkJoinWorkerThread give first priority to processing tasks |
129 |
* from their own queues (LIFO or FIFO, depending on mode), then |
130 |
* 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. |
178 |
* |
179 |
* The main throughput advantages of work-stealing stem from |
180 |
* decentralized control -- workers mostly steal tasks from each |
181 |
* other. We do not want to negate this by creating bottlenecks |
182 |
* implementing other management responsibilities. So we use a |
183 |
* collection of techniques that avoid, reduce, or cope well with |
184 |
* contention. These entail several instances of bit-packing into |
185 |
* CASable fields to maintain only the minimally required |
186 |
* atomicity. To enable such packing, we restrict maximum |
187 |
* parallelism to (1<<15)-1 (enabling twice this (to accommodate |
188 |
* unbalanced increments and decrements) to fit into a 16 bit |
189 |
* field, which is far in excess of normal operating range. Even |
190 |
* though updates to some of these bookkeeping fields do sometimes |
191 |
* contend with each other, they don't normally cache-contend with |
192 |
* updates to others enough to warrant memory padding or |
193 |
* isolation. So they are all held as fields of ForkJoinPool |
194 |
* objects. The main capabilities are as follows: |
195 |
* |
196 |
* 1. Creating and removing workers. Workers are recorded in the |
197 |
* "workers" array. This is an array as opposed to some other data |
198 |
* structure to support index-based random steals by workers. |
199 |
* Updates to the array recording new workers and unrecording |
200 |
* terminated ones are protected from each other by a lock |
201 |
* (workerLock) but the array is otherwise concurrently readable, |
202 |
* and accessed directly by workers. To simplify index-based |
203 |
* operations, the array size is always a power of two, and all |
204 |
* readers must tolerate null slots. Currently, all worker thread |
205 |
* creation is on-demand, triggered by task submissions, |
206 |
* replacement of terminated workers, and/or compensation for |
207 |
* blocked workers. However, all other support code is set up to |
208 |
* work with other policies. |
209 |
* |
210 |
* 2. Bookkeeping for dynamically adding and removing workers. We |
211 |
* aim to approximately maintain the given level of parallelism. |
212 |
* When some workers are known to be blocked (on joins or via |
213 |
* ManagedBlocker), we may create or resume others to take their |
214 |
* place until they unblock (see below). Implementing this |
215 |
* requires counts of the number of "running" threads (i.e., those |
216 |
* that are neither blocked nor artifically suspended) as well as |
217 |
* the total number. These two values are packed into one field, |
218 |
* "workerCounts" because we need accurate snapshots when deciding |
219 |
* to create, resume or suspend. Note however that the |
220 |
* correspondance of these counts to reality is not guaranteed. In |
221 |
* particular updates for unblocked threads may lag until they |
222 |
* actually wake up. |
223 |
* |
224 |
* 3. Maintaining global run state. The run state of the pool |
225 |
* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to |
226 |
* those in other Executor implementations, as well as a count of |
227 |
* "active" workers -- those that are, or soon will be, or |
228 |
* recently were executing tasks. The runLevel and active count |
229 |
* are packed together in order to correctly trigger shutdown and |
230 |
* termination. Without care, active counts can be subject to very |
231 |
* high contention. We substantially reduce this contention by |
232 |
* relaxing update rules. A worker must claim active status |
233 |
* prospectively, by activating if it sees that a submitted or |
234 |
* stealable task exists (it may find after activating that the |
235 |
* task no longer exists). It stays active while processing this |
236 |
* task (if it exists) and any other local subtasks it produces, |
237 |
* until it cannot find any other tasks. It then tries |
238 |
* inactivating (see method preStep), but upon update contention |
239 |
* instead scans for more tasks, later retrying inactivation if it |
240 |
* doesn't find any. |
241 |
* |
242 |
* 4. Managing idle workers waiting for tasks. We cannot let |
243 |
* workers spin indefinitely scanning for tasks when none are |
244 |
* available. On the other hand, we must quickly prod them into |
245 |
* action when new tasks are submitted or generated. We |
246 |
* park/unpark these idle workers using an event-count scheme. |
247 |
* Field eventCount is incremented upon events that may enable |
248 |
* workers that previously could not find a task to now find one: |
249 |
* Submission of a new task to the pool, or another worker pushing |
250 |
* a task onto a previously empty queue. (We also use this |
251 |
* mechanism for termination and reconfiguration actions that |
252 |
* require wakeups of idle workers). Each worker maintains its |
253 |
* last known event count, and blocks when a scan for work did not |
254 |
* find a task AND its lastEventCount matches the current |
255 |
* eventCount. Waiting idle workers are recorded in a variant of |
256 |
* Treiber stack headed by field eventWaiters which, when nonzero, |
257 |
* encodes the thread index and count awaited for by the worker |
258 |
* thread most recently calling eventSync. This thread in turn has |
259 |
* a record (field nextEventWaiter) for the next waiting worker. |
260 |
* In addition to allowing simpler decisions about need for |
261 |
* wakeup, the event count bits in eventWaiters serve the role of |
262 |
* tags to avoid ABA errors in Treiber stacks. To reduce delays |
263 |
* in task diffusion, workers not otherwise occupied may invoke |
264 |
* method releaseWaiters, that removes and signals (unparks) |
265 |
* workers not waiting on current count. To minimize task |
266 |
* production stalls associate with signalling, any worker pushing |
267 |
* a task on an empty queue invokes the weaker method signalWork, |
268 |
* that only releases idle workers until it detects interference |
269 |
* by other threads trying to release, and lets them take |
270 |
* over. The net effect is a tree-like diffusion of signals, where |
271 |
* released threads (and possibly others) help with unparks. To |
272 |
* further reduce contention effects a bit, failed CASes to |
273 |
* increment field eventCount are tolerated without retries. |
274 |
* Conceptually they are merged into the same event, which is OK |
275 |
* when their only purpose is to enable workers to scan for work. |
276 |
* |
277 |
* 5. Managing suspension of extra workers. When a worker is about |
278 |
* to block waiting for a join (or via ManagedBlockers), we may |
279 |
* create a new thread to maintain parallelism level, or at least |
280 |
* avoid starvation. Usually, extra threads are needed for only |
281 |
* very short periods, yet join dependencies are such that we |
282 |
* sometimes need them in bursts. Rather than create new threads |
283 |
* each time this happens, we suspend no-longer-needed extra ones |
284 |
* as "spares". For most purposes, we don't distinguish "extra" |
285 |
* spare threads from normal "core" threads: On each call to |
286 |
* preStep (the only point at which we can do this) a worker |
287 |
* checks to see if there are now too many running workers, and if |
288 |
* so, suspends itself. Methods tryAwaitJoin and awaitBlocker |
289 |
* look for suspended threads to resume before considering |
290 |
* creating a new replacement. We don't need a special data |
291 |
* structure to maintain spares; simply scanning the workers array |
292 |
* looking for worker.isSuspended() is fine because the calling |
293 |
* thread is otherwise not doing anything useful anyway; we are at |
294 |
* least as happy if after locating a spare, the caller doesn't |
295 |
* actually block because the join is ready before we try to |
296 |
* adjust and compensate. Note that this is intrinsically racy. |
297 |
* One thread may become a spare at about the same time as another |
298 |
* is needlessly being created. We counteract this and related |
299 |
* slop in part by requiring resumed spares to immediately recheck |
300 |
* (in preStep) to see whether they they should re-suspend. The |
301 |
* only effective difference between "extra" and "core" threads is |
302 |
* that we allow the "extra" ones to time out and die if they are |
303 |
* not resumed within a keep-alive interval of a few seconds. This |
304 |
* is implemented mainly within ForkJoinWorkerThread, but requires |
305 |
* some coordination (isTrimmed() -- meaning killed while |
306 |
* suspended) to correctly maintain pool counts. |
307 |
* |
308 |
* 6. Deciding when to create new workers. The main dynamic |
309 |
* control in this class is deciding when to create extra threads, |
310 |
* in methods awaitJoin and awaitBlocker. We always need to create |
311 |
* one when the number of running threads would become zero and |
312 |
* all workers are busy. However, this is not easy to detect |
313 |
* reliably in the presence of transients so we use retries and |
314 |
* allow slack (in tryAwaitJoin) to reduce false alarms. These |
315 |
* effectively reduce churn at the price of systematically |
316 |
* undershooting target parallelism when many threads are blocked. |
317 |
* However, biasing toward undeshooting partially compensates for |
318 |
* the above mechanics to suspend extra threads, that normally |
319 |
* lead to overshoot because we can only suspend workers |
320 |
* in-between top-level actions. It also better copes with the |
321 |
* fact that some of the methods in this class tend to never |
322 |
* become compiled (but are interpreted), so some components of |
323 |
* the entire set of controls might execute many times faster than |
324 |
* others. And similarly for cases where the apparent lack of work |
325 |
* is just due to GC stalls and other transient system activity. |
326 |
* |
327 |
* Beware that there is a lot of representation-level coupling |
328 |
* among classes ForkJoinPool, ForkJoinWorkerThread, and |
329 |
* ForkJoinTask. For example, direct access to "workers" array by |
330 |
* workers, and direct access to ForkJoinTask.status by both |
331 |
* ForkJoinPool and ForkJoinWorkerThread. There is little point |
332 |
* trying to reduce this, since any associated future changes in |
333 |
* representations will need to be accompanied by algorithmic |
334 |
* changes anyway. |
335 |
* |
336 |
* Style notes: There are lots of inline assignments (of form |
337 |
* "while ((local = field) != 0)") which are usually the simplest |
338 |
* way to ensure read orderings. Also several occurrences of the |
339 |
* unusual "do {} while(!cas...)" which is the simplest way to |
340 |
* force an update of a CAS'ed variable. There are also other |
341 |
* coding oddities that help some methods perform reasonably even |
342 |
* when interpreted (not compiled), at the expense of messiness. |
343 |
* |
344 |
* The order of declarations in this file is: (1) statics (2) |
345 |
* fields (along with constants used when unpacking some of them) |
346 |
* (3) internal control methods (4) callbacks and other support |
347 |
* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported |
348 |
* methods (plus a few little helpers). |
349 |
*/ |
350 |
|
351 |
/** |
352 |
* Factory for creating new {@link ForkJoinWorkerThread}s. |
353 |
* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
354 |
* for {@code ForkJoinWorkerThread} subclasses that extend base |
355 |
* functionality or initialize threads with different contexts. |
356 |
*/ |
357 |
public static interface ForkJoinWorkerThreadFactory { |
358 |
/** |
359 |
* Returns a new worker thread operating in the given pool. |
360 |
* |
361 |
* @param pool the pool this thread works in |
362 |
* @throws NullPointerException if the pool is null |
363 |
*/ |
364 |
public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
365 |
} |
366 |
|
367 |
/** |
368 |
* Default ForkJoinWorkerThreadFactory implementation; creates a |
369 |
* new ForkJoinWorkerThread. |
370 |
*/ |
371 |
static class DefaultForkJoinWorkerThreadFactory |
372 |
implements ForkJoinWorkerThreadFactory { |
373 |
public ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
374 |
return new ForkJoinWorkerThread(pool); |
375 |
} |
376 |
} |
377 |
|
378 |
/** |
379 |
* Creates a new ForkJoinWorkerThread. This factory is used unless |
380 |
* overridden in ForkJoinPool constructors. |
381 |
*/ |
382 |
public static final ForkJoinWorkerThreadFactory |
383 |
defaultForkJoinWorkerThreadFactory = |
384 |
new DefaultForkJoinWorkerThreadFactory(); |
385 |
|
386 |
/** |
387 |
* Permission required for callers of methods that may start or |
388 |
* kill threads. |
389 |
*/ |
390 |
private static final RuntimePermission modifyThreadPermission = |
391 |
new RuntimePermission("modifyThread"); |
392 |
|
393 |
/** |
394 |
* If there is a security manager, makes sure caller has |
395 |
* permission to modify threads. |
396 |
*/ |
397 |
private static void checkPermission() { |
398 |
SecurityManager security = System.getSecurityManager(); |
399 |
if (security != null) |
400 |
security.checkPermission(modifyThreadPermission); |
401 |
} |
402 |
|
403 |
/** |
404 |
* Generator for assigning sequence numbers as pool names. |
405 |
*/ |
406 |
private static final AtomicInteger poolNumberGenerator = |
407 |
new AtomicInteger(); |
408 |
|
409 |
/** |
410 |
* Absolute bound for parallelism level. Twice this number must |
411 |
* fit into a 16bit field to enable word-packing for some counts. |
412 |
*/ |
413 |
private static final int MAX_THREADS = 0x7fff; |
414 |
|
415 |
/** |
416 |
* Array holding all worker threads in the pool. Array size must |
417 |
* be a power of two. Updates and replacements are protected by |
418 |
* 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. |
423 |
*/ |
424 |
volatile ForkJoinWorkerThread[] workers; |
425 |
|
426 |
/** |
427 |
* Queue for external submissions. |
428 |
*/ |
429 |
private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
430 |
|
431 |
/** |
432 |
* Lock protecting updates to workers array. |
433 |
*/ |
434 |
private final ReentrantLock workerLock; |
435 |
|
436 |
/** |
437 |
* Latch released upon termination. |
438 |
*/ |
439 |
private final Phaser termination; |
440 |
|
441 |
/** |
442 |
* Creation factory for worker threads. |
443 |
*/ |
444 |
private final ForkJoinWorkerThreadFactory factory; |
445 |
|
446 |
/** |
447 |
* Sum of per-thread steal counts, updated only when threads are |
448 |
* idle or terminating. |
449 |
*/ |
450 |
private volatile long stealCount; |
451 |
|
452 |
/** |
453 |
* Encoded record of top of treiber stack of threads waiting for |
454 |
* events. The top 32 bits contain the count being waited for. The |
455 |
* bottom word contains one plus the pool index of waiting worker |
456 |
* thread. |
457 |
*/ |
458 |
private volatile long eventWaiters; |
459 |
|
460 |
private static final int EVENT_COUNT_SHIFT = 32; |
461 |
private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L; |
462 |
|
463 |
/** |
464 |
* A counter for events that may wake up worker threads: |
465 |
* - Submission of a new task to the pool |
466 |
* - A worker pushing a task on an empty queue |
467 |
* - termination and reconfiguration |
468 |
*/ |
469 |
private volatile int eventCount; |
470 |
|
471 |
/** |
472 |
* Lifecycle control. The low word contains the number of workers |
473 |
* that are (probably) executing tasks. This value is atomically |
474 |
* incremented before a worker gets a task to run, and decremented |
475 |
* when worker has no tasks and cannot find any. Bits 16-18 |
476 |
* contain runLevel value. When all are zero, the pool is |
477 |
* running. Level transitions are monotonic (running -> shutdown |
478 |
* -> terminating -> terminated) so each transition adds a bit. |
479 |
* These are bundled together to ensure consistent read for |
480 |
* termination checks (i.e., that runLevel is at least SHUTDOWN |
481 |
* and active threads is zero). |
482 |
*/ |
483 |
private volatile int runState; |
484 |
|
485 |
// Note: The order among run level values matters. |
486 |
private static final int RUNLEVEL_SHIFT = 16; |
487 |
private static final int SHUTDOWN = 1 << RUNLEVEL_SHIFT; |
488 |
private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1); |
489 |
private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2); |
490 |
private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1; |
491 |
private static final int ONE_ACTIVE = 1; // active update delta |
492 |
|
493 |
/** |
494 |
* Holds number of total (i.e., created and not yet terminated) |
495 |
* and running (i.e., not blocked on joins or other managed sync) |
496 |
* threads, packed together to ensure consistent snapshot when |
497 |
* making decisions about creating and suspending spare |
498 |
* threads. Updated only by CAS. Note that adding a new worker |
499 |
* requires incrementing both counts, since workers start off in |
500 |
* running state. This field is also used for memory-fencing |
501 |
* configuration parameters. |
502 |
*/ |
503 |
private volatile int workerCounts; |
504 |
|
505 |
private static final int TOTAL_COUNT_SHIFT = 16; |
506 |
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; |
509 |
|
510 |
/** |
511 |
* The target parallelism level. |
512 |
* Accessed directly by ForkJoinWorkerThreads. |
513 |
*/ |
514 |
final int parallelism; |
515 |
|
516 |
/** |
517 |
* True if use local fifo, not default lifo, for local polling |
518 |
* Read by, and replicated by ForkJoinWorkerThreads |
519 |
*/ |
520 |
final boolean locallyFifo; |
521 |
|
522 |
/** |
523 |
* The uncaught exception handler used when any worker abruptly |
524 |
* terminates. |
525 |
*/ |
526 |
private final Thread.UncaughtExceptionHandler ueh; |
527 |
|
528 |
/** |
529 |
* Pool number, just for assigning useful names to worker threads |
530 |
*/ |
531 |
private final int poolNumber; |
532 |
|
533 |
// Utilities for CASing fields. Note that several of these |
534 |
// are manually inlined by callers |
535 |
|
536 |
/** |
537 |
* Increments running count. Also used by ForkJoinTask. |
538 |
*/ |
539 |
final void incrementRunningCount() { |
540 |
int c; |
541 |
do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
542 |
c = workerCounts, |
543 |
c + ONE_RUNNING)); |
544 |
} |
545 |
|
546 |
/** |
547 |
* Tries to decrement running count unless already zero |
548 |
*/ |
549 |
final boolean tryDecrementRunningCount() { |
550 |
int wc = workerCounts; |
551 |
if ((wc & RUNNING_COUNT_MASK) == 0) |
552 |
return false; |
553 |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
554 |
wc, wc - ONE_RUNNING); |
555 |
} |
556 |
|
557 |
/** |
558 |
* Tries to increment running count |
559 |
*/ |
560 |
final boolean tryIncrementRunningCount() { |
561 |
int wc; |
562 |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
563 |
wc = workerCounts, wc + ONE_RUNNING); |
564 |
} |
565 |
|
566 |
/** |
567 |
* Tries incrementing active count; fails on contention. |
568 |
* Called by workers before executing tasks. |
569 |
* |
570 |
* @return true on success |
571 |
*/ |
572 |
final boolean tryIncrementActiveCount() { |
573 |
int c; |
574 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
575 |
c = runState, c + ONE_ACTIVE); |
576 |
} |
577 |
|
578 |
/** |
579 |
* Tries decrementing active count; fails on contention. |
580 |
* Called when workers cannot find tasks to run. |
581 |
*/ |
582 |
final boolean tryDecrementActiveCount() { |
583 |
int c; |
584 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
585 |
c = runState, c - ONE_ACTIVE); |
586 |
} |
587 |
|
588 |
/** |
589 |
* Advances to at least the given level. Returns true if not |
590 |
* already in at least the given level. |
591 |
*/ |
592 |
private boolean advanceRunLevel(int level) { |
593 |
for (;;) { |
594 |
int s = runState; |
595 |
if ((s & level) != 0) |
596 |
return false; |
597 |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level)) |
598 |
return true; |
599 |
} |
600 |
} |
601 |
|
602 |
// workers array maintenance |
603 |
|
604 |
/** |
605 |
* Records and returns a workers array index for new worker. |
606 |
*/ |
607 |
private int recordWorker(ForkJoinWorkerThread w) { |
608 |
// Try using slot totalCount-1. If not available, scan and/or resize |
609 |
int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1; |
610 |
final ReentrantLock lock = this.workerLock; |
611 |
lock.lock(); |
612 |
try { |
613 |
ForkJoinWorkerThread[] ws = workers; |
614 |
int nws = ws.length; |
615 |
if (k < 0 || k >= nws || ws[k] != null) { |
616 |
for (k = 0; k < nws && ws[k] != null; ++k) |
617 |
; |
618 |
if (k == nws) |
619 |
ws = Arrays.copyOf(ws, nws << 1); |
620 |
} |
621 |
ws[k] = w; |
622 |
workers = ws; // volatile array write ensures slot visibility |
623 |
} finally { |
624 |
lock.unlock(); |
625 |
} |
626 |
return k; |
627 |
} |
628 |
|
629 |
/** |
630 |
* Nulls out record of worker in workers array |
631 |
*/ |
632 |
private void forgetWorker(ForkJoinWorkerThread w) { |
633 |
int idx = w.poolIndex; |
634 |
// Locking helps method recordWorker avoid unecessary expansion |
635 |
final ReentrantLock lock = this.workerLock; |
636 |
lock.lock(); |
637 |
try { |
638 |
ForkJoinWorkerThread[] ws = workers; |
639 |
if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify |
640 |
ws[idx] = null; |
641 |
} finally { |
642 |
lock.unlock(); |
643 |
} |
644 |
} |
645 |
|
646 |
// adding and removing workers |
647 |
|
648 |
/** |
649 |
* Tries to create and add new worker. Assumes that worker counts |
650 |
* are already updated to accommodate the worker, so adjusts on |
651 |
* failure. |
652 |
* |
653 |
* @return new worker or null if creation failed |
654 |
*/ |
655 |
private ForkJoinWorkerThread addWorker() { |
656 |
ForkJoinWorkerThread w = null; |
657 |
try { |
658 |
w = factory.newThread(this); |
659 |
} finally { // Adjust on either null or exceptional factory return |
660 |
if (w == null) { |
661 |
onWorkerCreationFailure(); |
662 |
return null; |
663 |
} |
664 |
} |
665 |
w.start(recordWorker(w), ueh); |
666 |
return w; |
667 |
} |
668 |
|
669 |
/** |
670 |
* Adjusts counts upon failure to create worker |
671 |
*/ |
672 |
private void onWorkerCreationFailure() { |
673 |
for (;;) { |
674 |
int wc = workerCounts; |
675 |
if ((wc >>> TOTAL_COUNT_SHIFT) == 0) |
676 |
Thread.yield(); // wait for other counts to settle |
677 |
else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
678 |
wc - (ONE_RUNNING|ONE_TOTAL))) |
679 |
break; |
680 |
} |
681 |
tryTerminate(false); // in case of failure during shutdown |
682 |
} |
683 |
|
684 |
/** |
685 |
* Creates and/or resumes enough workers to establish target |
686 |
* parallelism, giving up if terminating or addWorker fails |
687 |
* |
688 |
* TODO: recast this to support lazier creation and automated |
689 |
* parallelism maintenance |
690 |
*/ |
691 |
private void ensureEnoughWorkers() { |
692 |
for (;;) { |
693 |
int pc = parallelism; |
694 |
int wc = workerCounts; |
695 |
int rc = wc & RUNNING_COUNT_MASK; |
696 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
697 |
if (tc < pc) { |
698 |
if (runState == TERMINATING || |
699 |
(UNSAFE.compareAndSwapInt |
700 |
(this, workerCountsOffset, |
701 |
wc, wc + (ONE_RUNNING|ONE_TOTAL)) && |
702 |
addWorker() == null)) |
703 |
break; |
704 |
} |
705 |
else if (tc > pc && rc < pc && |
706 |
tc > (runState & ACTIVE_COUNT_MASK)) { |
707 |
ForkJoinWorkerThread spare = null; |
708 |
ForkJoinWorkerThread[] ws = workers; |
709 |
int nws = ws.length; |
710 |
for (int i = 0; i < nws; ++i) { |
711 |
ForkJoinWorkerThread w = ws[i]; |
712 |
if (w != null && w.isSuspended()) { |
713 |
if ((workerCounts & RUNNING_COUNT_MASK) > pc || |
714 |
runState == TERMINATING) |
715 |
return; |
716 |
if (w.tryResumeSpare()) |
717 |
incrementRunningCount(); |
718 |
break; |
719 |
} |
720 |
} |
721 |
} |
722 |
else |
723 |
break; |
724 |
} |
725 |
} |
726 |
|
727 |
/** |
728 |
* Final callback from terminating worker. Removes record of |
729 |
* worker from array, and adjusts counts. If pool is shutting |
730 |
* down, tries to complete terminatation, else possibly replaces |
731 |
* the worker. |
732 |
* |
733 |
* @param w the worker |
734 |
*/ |
735 |
final void workerTerminated(ForkJoinWorkerThread w) { |
736 |
if (w.active) { // force inactive |
737 |
w.active = false; |
738 |
do {} while (!tryDecrementActiveCount()); |
739 |
} |
740 |
forgetWorker(w); |
741 |
|
742 |
// Decrement total count, and if was running, running count |
743 |
// Spin (waiting for other updates) if either would be negative |
744 |
int nr = w.isTrimmed() ? 0 : ONE_RUNNING; |
745 |
int unit = ONE_TOTAL + nr; |
746 |
for (;;) { |
747 |
int wc = workerCounts; |
748 |
int rc = wc & RUNNING_COUNT_MASK; |
749 |
if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0) |
750 |
Thread.yield(); // back off if waiting for other updates |
751 |
else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
752 |
wc, wc - unit)) |
753 |
break; |
754 |
} |
755 |
|
756 |
accumulateStealCount(w); // collect final count |
757 |
if (!tryTerminate(false)) |
758 |
ensureEnoughWorkers(); |
759 |
} |
760 |
|
761 |
// Waiting for and signalling events |
762 |
|
763 |
/** |
764 |
* Releases workers blocked on a count not equal to current count. |
765 |
* @return true if any released |
766 |
*/ |
767 |
private void releaseWaiters() { |
768 |
long top; |
769 |
while ((top = eventWaiters) != 0L) { |
770 |
ForkJoinWorkerThread[] ws = workers; |
771 |
int n = ws.length; |
772 |
for (;;) { |
773 |
int i = ((int)(top & WAITER_ID_MASK)) - 1; |
774 |
if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount) |
775 |
return; |
776 |
ForkJoinWorkerThread w; |
777 |
if (i < n && (w = ws[i]) != null && |
778 |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
779 |
top, w.nextWaiter)) { |
780 |
LockSupport.unpark(w); |
781 |
top = eventWaiters; |
782 |
} |
783 |
else |
784 |
break; // possibly stale; reread |
785 |
} |
786 |
} |
787 |
} |
788 |
|
789 |
/** |
790 |
* Ensures eventCount on exit is different (mod 2^32) than on |
791 |
* entry and wakes up all waiters |
792 |
*/ |
793 |
private void signalEvent() { |
794 |
int c; |
795 |
do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset, |
796 |
c = eventCount, c+1)); |
797 |
releaseWaiters(); |
798 |
} |
799 |
|
800 |
/** |
801 |
* Advances eventCount and releases waiters until interference by |
802 |
* other releasing threads is detected. |
803 |
*/ |
804 |
final void signalWork() { |
805 |
int c; |
806 |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1); |
807 |
long top; |
808 |
while ((top = eventWaiters) != 0L) { |
809 |
int ec = eventCount; |
810 |
ForkJoinWorkerThread[] ws = workers; |
811 |
int n = ws.length; |
812 |
for (;;) { |
813 |
int i = ((int)(top & WAITER_ID_MASK)) - 1; |
814 |
if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec) |
815 |
return; |
816 |
ForkJoinWorkerThread w; |
817 |
if (i < n && (w = ws[i]) != null && |
818 |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
819 |
top, top = w.nextWaiter)) { |
820 |
LockSupport.unpark(w); |
821 |
if (top != eventWaiters) // let someone else take over |
822 |
return; |
823 |
} |
824 |
else |
825 |
break; // possibly stale; reread |
826 |
} |
827 |
} |
828 |
} |
829 |
|
830 |
/** |
831 |
* If worker is inactive, blocks until terminating or event count |
832 |
* advances from last value held by worker; in any case helps |
833 |
* release others. |
834 |
* |
835 |
* @param w the calling worker thread |
836 |
* @param retries the number of scans by caller failing to find work |
837 |
* @return false if now too many threads running |
838 |
*/ |
839 |
private boolean eventSync(ForkJoinWorkerThread w, int retries) { |
840 |
int wec = w.lastEventCount; |
841 |
if (retries > 1) { // can only block after 2nd miss |
842 |
long nextTop = (((long)wec << EVENT_COUNT_SHIFT) | |
843 |
((long)(w.poolIndex + 1))); |
844 |
long top; |
845 |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
846 |
(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 || |
847 |
(int)(top >>> EVENT_COUNT_SHIFT) == wec) && |
848 |
eventCount == wec) { |
849 |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
850 |
w.nextWaiter = top, nextTop)) { |
851 |
accumulateStealCount(w); // transfer steals while idle |
852 |
Thread.interrupted(); // clear/ignore interrupt |
853 |
while (eventCount == wec) |
854 |
w.doPark(); |
855 |
break; |
856 |
} |
857 |
} |
858 |
wec = eventCount; |
859 |
} |
860 |
releaseWaiters(); |
861 |
int wc = workerCounts; |
862 |
if ((wc & RUNNING_COUNT_MASK) <= parallelism) { |
863 |
w.lastEventCount = wec; |
864 |
return true; |
865 |
} |
866 |
if (wec != w.lastEventCount) // back up if may re-wait |
867 |
w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT); |
868 |
return false; |
869 |
} |
870 |
|
871 |
/** |
872 |
* Callback from workers invoked upon each top-level action (i.e., |
873 |
* stealing a task or taking a submission and running |
874 |
* it). Performs one or both of the following: |
875 |
* |
876 |
* * If the worker cannot find work, updates its active status to |
877 |
* inactive and updates activeCount unless there is contention, in |
878 |
* which case it may try again (either in this or a subsequent |
879 |
* call). Additionally, awaits the next task event and/or helps |
880 |
* wake up other releasable waiters. |
881 |
* |
882 |
* * If there are too many running threads, suspends this worker |
883 |
* (first forcing inactivation if necessary). If it is not |
884 |
* resumed before a keepAlive elapses, the worker may be "trimmed" |
885 |
* -- killed while suspended within suspendAsSpare. Otherwise, |
886 |
* upon resume it rechecks to make sure that it is still needed. |
887 |
* |
888 |
* @param w the worker |
889 |
* @param retries the number of scans by caller failing to find work |
890 |
* find any (in which case it may block waiting for work). |
891 |
*/ |
892 |
final void preStep(ForkJoinWorkerThread w, int retries) { |
893 |
boolean active = w.active; |
894 |
boolean inactivate = active && retries != 0; |
895 |
for (;;) { |
896 |
int rs, wc; |
897 |
if (inactivate && |
898 |
UNSAFE.compareAndSwapInt(this, runStateOffset, |
899 |
rs = runState, rs - ONE_ACTIVE)) |
900 |
inactivate = active = w.active = false; |
901 |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) { |
902 |
if (active || eventSync(w, retries)) |
903 |
break; |
904 |
} |
905 |
else if (!(inactivate |= active) && // must inactivate to suspend |
906 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
907 |
wc, wc - ONE_RUNNING) && |
908 |
!w.suspendAsSpare()) // false if trimmed |
909 |
break; |
910 |
} |
911 |
} |
912 |
|
913 |
/** |
914 |
* Awaits join of the given task if enough threads, or can resume |
915 |
* or create a spare. Fails (in which case the given task might |
916 |
* not be done) upon contention or lack of decision about |
917 |
* blocking. Returns void because caller must check |
918 |
* task status on return anyway. |
919 |
* |
920 |
* We allow blocking if: |
921 |
* |
922 |
* 1. There would still be at least as many running threads as |
923 |
* parallelism level if this thread blocks. |
924 |
* |
925 |
* 2. A spare is resumed to replace this worker. We tolerate |
926 |
* slop in the decision to replace if a spare is found without |
927 |
* first decrementing run count. This may release too many, |
928 |
* but if so, the superfluous ones will re-suspend via |
929 |
* preStep(). |
930 |
* |
931 |
* 3. After #spares repeated checks, there are no fewer than #spare |
932 |
* threads not running. We allow this slack to avoid hysteresis |
933 |
* and as a hedge against lag/uncertainty of running count |
934 |
* estimates when signalling or unblocking stalls. |
935 |
* |
936 |
* 4. All existing workers are busy (as rechecked via repeated |
937 |
* retries by caller) and a new spare is created. |
938 |
* |
939 |
* If none of the above hold, we try to escape out by |
940 |
* re-incrementing count and returning to caller, which can retry |
941 |
* later. |
942 |
* |
943 |
* @param joinMe the task to join |
944 |
* @param retries if negative, then serve only as a precheck |
945 |
* that the thread can be replaced by a spare. Otherwise, |
946 |
* the number of repeated calls to this method returning busy |
947 |
* @return true if the call must be retried because there |
948 |
* none of the blocking checks hold |
949 |
*/ |
950 |
final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) { |
951 |
if (joinMe.status < 0) // precheck to prime loop |
952 |
return false; |
953 |
int pc = parallelism; |
954 |
boolean running = true; // false when running count decremented |
955 |
outer:for (;;) { |
956 |
int wc = workerCounts; |
957 |
int rc = wc & RUNNING_COUNT_MASK; |
958 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
959 |
if (running) { // replace with spare or decrement count |
960 |
if (rc <= pc && tc > pc && |
961 |
(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) { |
962 |
ForkJoinWorkerThread[] ws = workers; |
963 |
int nws = ws.length; |
964 |
for (int i = 0; i < nws; ++i) { // search for spare |
965 |
ForkJoinWorkerThread w = ws[i]; |
966 |
if (w != null) { |
967 |
if (joinMe.status < 0) |
968 |
return false; |
969 |
if (w.isSuspended()) { |
970 |
if ((workerCounts & RUNNING_COUNT_MASK)>=pc && |
971 |
w.tryResumeSpare()) { |
972 |
running = false; |
973 |
break outer; |
974 |
} |
975 |
continue outer; // rescan |
976 |
} |
977 |
} |
978 |
} |
979 |
} |
980 |
if (retries < 0 || // < 0 means replacement check only |
981 |
rc == 0 || joinMe.status < 0 || workerCounts != wc || |
982 |
!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
983 |
wc, wc - ONE_RUNNING)) |
984 |
return false; // done or inconsistent or contended |
985 |
running = false; |
986 |
if (rc > pc) |
987 |
break; |
988 |
} |
989 |
else { // allow blocking if enough threads |
990 |
if (rc >= pc || joinMe.status < 0) |
991 |
break; |
992 |
int sc = tc - pc + 1; // = spare threads, plus the one to add |
993 |
if (retries > sc) { |
994 |
if (rc > 0 && rc >= pc - sc) // allow slack |
995 |
break; |
996 |
if (tc < MAX_THREADS && |
997 |
tc == (runState & ACTIVE_COUNT_MASK) && |
998 |
workerCounts == wc && |
999 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
1000 |
wc+(ONE_RUNNING|ONE_TOTAL))) { |
1001 |
addWorker(); |
1002 |
break; |
1003 |
} |
1004 |
} |
1005 |
if (workerCounts == wc && // back out to allow rescan |
1006 |
UNSAFE.compareAndSwapInt (this, workerCountsOffset, |
1007 |
wc, wc + ONE_RUNNING)) { |
1008 |
releaseWaiters(); // help others progress |
1009 |
return true; // let caller retry |
1010 |
} |
1011 |
} |
1012 |
} |
1013 |
// arrive here if can block |
1014 |
joinMe.internalAwaitDone(); |
1015 |
int c; // to inline incrementRunningCount |
1016 |
do {} while (!UNSAFE.compareAndSwapInt |
1017 |
(this, workerCountsOffset, |
1018 |
c = workerCounts, c + ONE_RUNNING)); |
1019 |
return false; |
1020 |
} |
1021 |
|
1022 |
/** |
1023 |
* Same idea as (and shares many code snippets with) tryAwaitJoin, |
1024 |
* but self-contained because there are no caller retries. |
1025 |
* TODO: Rework to use simpler API. |
1026 |
*/ |
1027 |
final void awaitBlocker(ManagedBlocker blocker) |
1028 |
throws InterruptedException { |
1029 |
boolean done; |
1030 |
if (done = blocker.isReleasable()) |
1031 |
return; |
1032 |
int pc = parallelism; |
1033 |
int retries = 0; |
1034 |
boolean running = true; // false when running count decremented |
1035 |
outer:for (;;) { |
1036 |
int wc = workerCounts; |
1037 |
int rc = wc & RUNNING_COUNT_MASK; |
1038 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1039 |
if (running) { |
1040 |
if (rc <= pc && tc > pc && |
1041 |
(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) { |
1042 |
ForkJoinWorkerThread[] ws = workers; |
1043 |
int nws = ws.length; |
1044 |
for (int i = 0; i < nws; ++i) { |
1045 |
ForkJoinWorkerThread w = ws[i]; |
1046 |
if (w != null) { |
1047 |
if (done = blocker.isReleasable()) |
1048 |
return; |
1049 |
if (w.isSuspended()) { |
1050 |
if ((workerCounts & RUNNING_COUNT_MASK)>=pc && |
1051 |
w.tryResumeSpare()) { |
1052 |
running = false; |
1053 |
break outer; |
1054 |
} |
1055 |
continue outer; // rescan |
1056 |
} |
1057 |
} |
1058 |
} |
1059 |
} |
1060 |
if (done = blocker.isReleasable()) |
1061 |
return; |
1062 |
if (rc == 0 || workerCounts != wc || |
1063 |
!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1064 |
wc, wc - ONE_RUNNING)) |
1065 |
continue; |
1066 |
running = false; |
1067 |
if (rc > pc) |
1068 |
break; |
1069 |
} |
1070 |
else { |
1071 |
if (rc >= pc || (done = blocker.isReleasable())) |
1072 |
break; |
1073 |
int sc = tc - pc + 1; |
1074 |
if (retries++ > sc) { |
1075 |
if (rc > 0 && rc >= pc - sc) |
1076 |
break; |
1077 |
if (tc < MAX_THREADS && |
1078 |
tc == (runState & ACTIVE_COUNT_MASK) && |
1079 |
workerCounts == wc && |
1080 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
1081 |
wc+(ONE_RUNNING|ONE_TOTAL))) { |
1082 |
addWorker(); |
1083 |
break; |
1084 |
} |
1085 |
} |
1086 |
Thread.yield(); |
1087 |
} |
1088 |
} |
1089 |
|
1090 |
try { |
1091 |
if (!done) |
1092 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1093 |
} finally { |
1094 |
if (!running) { |
1095 |
int c; |
1096 |
do {} while (!UNSAFE.compareAndSwapInt |
1097 |
(this, workerCountsOffset, |
1098 |
c = workerCounts, c + ONE_RUNNING)); |
1099 |
} |
1100 |
} |
1101 |
} |
1102 |
|
1103 |
/** |
1104 |
* Possibly initiates and/or completes termination. |
1105 |
* |
1106 |
* @param now if true, unconditionally terminate, else only |
1107 |
* if shutdown and empty queue and no active workers |
1108 |
* @return true if now terminating or terminated |
1109 |
*/ |
1110 |
private boolean tryTerminate(boolean now) { |
1111 |
if (now) |
1112 |
advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN |
1113 |
else if (runState < SHUTDOWN || |
1114 |
!submissionQueue.isEmpty() || |
1115 |
(runState & ACTIVE_COUNT_MASK) != 0) |
1116 |
return false; |
1117 |
|
1118 |
if (advanceRunLevel(TERMINATING)) |
1119 |
startTerminating(); |
1120 |
|
1121 |
// Finish now if all threads terminated; else in some subsequent call |
1122 |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) { |
1123 |
advanceRunLevel(TERMINATED); |
1124 |
termination.arrive(); |
1125 |
} |
1126 |
return true; |
1127 |
} |
1128 |
|
1129 |
/** |
1130 |
* Actions on transition to TERMINATING |
1131 |
*/ |
1132 |
private void startTerminating() { |
1133 |
for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers |
1134 |
cancelSubmissions(); |
1135 |
shutdownWorkers(); |
1136 |
cancelWorkerTasks(); |
1137 |
signalEvent(); |
1138 |
interruptWorkers(); |
1139 |
} |
1140 |
} |
1141 |
|
1142 |
/** |
1143 |
* Clear out and cancel submissions, ignoring exceptions |
1144 |
*/ |
1145 |
private void cancelSubmissions() { |
1146 |
ForkJoinTask<?> task; |
1147 |
while ((task = submissionQueue.poll()) != null) { |
1148 |
try { |
1149 |
task.cancel(false); |
1150 |
} catch (Throwable ignore) { |
1151 |
} |
1152 |
} |
1153 |
} |
1154 |
|
1155 |
/** |
1156 |
* Sets all worker run states to at least shutdown, |
1157 |
* also resuming suspended workers |
1158 |
*/ |
1159 |
private void shutdownWorkers() { |
1160 |
ForkJoinWorkerThread[] ws = workers; |
1161 |
int nws = ws.length; |
1162 |
for (int i = 0; i < nws; ++i) { |
1163 |
ForkJoinWorkerThread w = ws[i]; |
1164 |
if (w != null) |
1165 |
w.shutdown(); |
1166 |
} |
1167 |
} |
1168 |
|
1169 |
/** |
1170 |
* Clears out and cancels all locally queued tasks |
1171 |
*/ |
1172 |
private void cancelWorkerTasks() { |
1173 |
ForkJoinWorkerThread[] ws = workers; |
1174 |
int nws = ws.length; |
1175 |
for (int i = 0; i < nws; ++i) { |
1176 |
ForkJoinWorkerThread w = ws[i]; |
1177 |
if (w != null) |
1178 |
w.cancelTasks(); |
1179 |
} |
1180 |
} |
1181 |
|
1182 |
/** |
1183 |
* Unsticks all workers blocked on joins etc |
1184 |
*/ |
1185 |
private void interruptWorkers() { |
1186 |
ForkJoinWorkerThread[] ws = workers; |
1187 |
int nws = ws.length; |
1188 |
for (int i = 0; i < nws; ++i) { |
1189 |
ForkJoinWorkerThread w = ws[i]; |
1190 |
if (w != null && !w.isTerminated()) { |
1191 |
try { |
1192 |
w.interrupt(); |
1193 |
} catch (SecurityException ignore) { |
1194 |
} |
1195 |
} |
1196 |
} |
1197 |
} |
1198 |
|
1199 |
// misc support for ForkJoinWorkerThread |
1200 |
|
1201 |
/** |
1202 |
* Returns pool number |
1203 |
*/ |
1204 |
final int getPoolNumber() { |
1205 |
return poolNumber; |
1206 |
} |
1207 |
|
1208 |
/** |
1209 |
* Accumulates steal count from a worker, clearing |
1210 |
* the worker's value |
1211 |
*/ |
1212 |
final void accumulateStealCount(ForkJoinWorkerThread w) { |
1213 |
int sc = w.stealCount; |
1214 |
if (sc != 0) { |
1215 |
long c; |
1216 |
w.stealCount = 0; |
1217 |
do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset, |
1218 |
c = stealCount, c + sc)); |
1219 |
} |
1220 |
} |
1221 |
|
1222 |
/** |
1223 |
* Returns the approximate (non-atomic) number of idle threads per |
1224 |
* active thread. |
1225 |
*/ |
1226 |
final int idlePerActive() { |
1227 |
int pc = parallelism; // use parallelism, not rc |
1228 |
int ac = runState; // no mask -- artifically boosts during shutdown |
1229 |
// Use exact results for small values, saturate past 4 |
1230 |
return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3; |
1231 |
} |
1232 |
|
1233 |
// Public and protected methods |
1234 |
|
1235 |
// Constructors |
1236 |
|
1237 |
/** |
1238 |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
1239 |
* java.lang.Runtime#availableProcessors}, using the {@linkplain |
1240 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1241 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1242 |
* |
1243 |
* @throws SecurityException if a security manager exists and |
1244 |
* the caller is not permitted to modify threads |
1245 |
* because it does not hold {@link |
1246 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1247 |
*/ |
1248 |
public ForkJoinPool() { |
1249 |
this(Runtime.getRuntime().availableProcessors(), |
1250 |
defaultForkJoinWorkerThreadFactory, null, false); |
1251 |
} |
1252 |
|
1253 |
/** |
1254 |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
1255 |
* level, the {@linkplain |
1256 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1257 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1258 |
* |
1259 |
* @param parallelism the parallelism level |
1260 |
* @throws IllegalArgumentException if parallelism less than or |
1261 |
* equal to zero, or greater than implementation limit |
1262 |
* @throws SecurityException if a security manager exists and |
1263 |
* the caller is not permitted to modify threads |
1264 |
* because it does not hold {@link |
1265 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1266 |
*/ |
1267 |
public ForkJoinPool(int parallelism) { |
1268 |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
1269 |
} |
1270 |
|
1271 |
/** |
1272 |
* Creates a {@code ForkJoinPool} with the given parameters. |
1273 |
* |
1274 |
* @param parallelism the parallelism level. For default value, |
1275 |
* use {@link java.lang.Runtime#availableProcessors}. |
1276 |
* @param factory the factory for creating new threads. For default value, |
1277 |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
1278 |
* @param handler the handler for internal worker threads that |
1279 |
* terminate due to unrecoverable errors encountered while executing |
1280 |
* tasks. For default value, use <code>null</code>. |
1281 |
* @param asyncMode if true, |
1282 |
* establishes local first-in-first-out scheduling mode for forked |
1283 |
* tasks that are never joined. This mode may be more appropriate |
1284 |
* than default locally stack-based mode in applications in which |
1285 |
* worker threads only process event-style asynchronous tasks. |
1286 |
* For default value, use <code>false</code>. |
1287 |
* @throws IllegalArgumentException if parallelism less than or |
1288 |
* equal to zero, or greater than implementation limit |
1289 |
* @throws NullPointerException if the factory is null |
1290 |
* @throws SecurityException if a security manager exists and |
1291 |
* the caller is not permitted to modify threads |
1292 |
* because it does not hold {@link |
1293 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1294 |
*/ |
1295 |
public ForkJoinPool(int parallelism, |
1296 |
ForkJoinWorkerThreadFactory factory, |
1297 |
Thread.UncaughtExceptionHandler handler, |
1298 |
boolean asyncMode) { |
1299 |
checkPermission(); |
1300 |
if (factory == null) |
1301 |
throw new NullPointerException(); |
1302 |
if (parallelism <= 0 || parallelism > MAX_THREADS) |
1303 |
throw new IllegalArgumentException(); |
1304 |
this.parallelism = parallelism; |
1305 |
this.factory = factory; |
1306 |
this.ueh = handler; |
1307 |
this.locallyFifo = asyncMode; |
1308 |
int arraySize = initialArraySizeFor(parallelism); |
1309 |
this.workers = new ForkJoinWorkerThread[arraySize]; |
1310 |
this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
1311 |
this.workerLock = new ReentrantLock(); |
1312 |
this.termination = new Phaser(1); |
1313 |
this.poolNumber = poolNumberGenerator.incrementAndGet(); |
1314 |
} |
1315 |
|
1316 |
/** |
1317 |
* Returns initial power of two size for workers array. |
1318 |
* @param pc the initial parallelism level |
1319 |
*/ |
1320 |
private static int initialArraySizeFor(int pc) { |
1321 |
// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16) |
1322 |
int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS; |
1323 |
size |= size >>> 1; |
1324 |
size |= size >>> 2; |
1325 |
size |= size >>> 4; |
1326 |
size |= size >>> 8; |
1327 |
return size + 1; |
1328 |
} |
1329 |
|
1330 |
// Execution methods |
1331 |
|
1332 |
/** |
1333 |
* Common code for execute, invoke and submit |
1334 |
*/ |
1335 |
private <T> void doSubmit(ForkJoinTask<T> task) { |
1336 |
if (task == null) |
1337 |
throw new NullPointerException(); |
1338 |
if (runState >= SHUTDOWN) |
1339 |
throw new RejectedExecutionException(); |
1340 |
submissionQueue.offer(task); |
1341 |
signalEvent(); |
1342 |
ensureEnoughWorkers(); |
1343 |
} |
1344 |
|
1345 |
/** |
1346 |
* Performs the given task, returning its result upon completion. |
1347 |
* If the caller is already engaged in a fork/join computation in |
1348 |
* the current pool, this method is equivalent in effect to |
1349 |
* {@link ForkJoinTask#invoke}. |
1350 |
* |
1351 |
* @param task the task |
1352 |
* @return the task's result |
1353 |
* @throws NullPointerException if the task is null |
1354 |
* @throws RejectedExecutionException if the task cannot be |
1355 |
* scheduled for execution |
1356 |
*/ |
1357 |
public <T> T invoke(ForkJoinTask<T> task) { |
1358 |
doSubmit(task); |
1359 |
return task.join(); |
1360 |
} |
1361 |
|
1362 |
/** |
1363 |
* Arranges for (asynchronous) execution of the given task. |
1364 |
* If the caller is already engaged in a fork/join computation in |
1365 |
* the current pool, this method is equivalent in effect to |
1366 |
* {@link ForkJoinTask#fork}. |
1367 |
* |
1368 |
* @param task the task |
1369 |
* @throws NullPointerException if the task is null |
1370 |
* @throws RejectedExecutionException if the task cannot be |
1371 |
* scheduled for execution |
1372 |
*/ |
1373 |
public void execute(ForkJoinTask<?> task) { |
1374 |
doSubmit(task); |
1375 |
} |
1376 |
|
1377 |
// AbstractExecutorService methods |
1378 |
|
1379 |
/** |
1380 |
* @throws NullPointerException if the task is null |
1381 |
* @throws RejectedExecutionException if the task cannot be |
1382 |
* scheduled for execution |
1383 |
*/ |
1384 |
public void execute(Runnable task) { |
1385 |
ForkJoinTask<?> job; |
1386 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1387 |
job = (ForkJoinTask<?>) task; |
1388 |
else |
1389 |
job = ForkJoinTask.adapt(task, null); |
1390 |
doSubmit(job); |
1391 |
} |
1392 |
|
1393 |
/** |
1394 |
* Submits a ForkJoinTask for execution. |
1395 |
* If the caller is already engaged in a fork/join computation in |
1396 |
* the current pool, this method is equivalent in effect to |
1397 |
* {@link ForkJoinTask#fork}. |
1398 |
* |
1399 |
* @param task the task to submit |
1400 |
* @return the task |
1401 |
* @throws NullPointerException if the task is null |
1402 |
* @throws RejectedExecutionException if the task cannot be |
1403 |
* scheduled for execution |
1404 |
*/ |
1405 |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
1406 |
doSubmit(task); |
1407 |
return task; |
1408 |
} |
1409 |
|
1410 |
/** |
1411 |
* @throws NullPointerException if the task is null |
1412 |
* @throws RejectedExecutionException if the task cannot be |
1413 |
* scheduled for execution |
1414 |
*/ |
1415 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
1416 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task); |
1417 |
doSubmit(job); |
1418 |
return job; |
1419 |
} |
1420 |
|
1421 |
/** |
1422 |
* @throws NullPointerException if the task is null |
1423 |
* @throws RejectedExecutionException if the task cannot be |
1424 |
* scheduled for execution |
1425 |
*/ |
1426 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
1427 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); |
1428 |
doSubmit(job); |
1429 |
return job; |
1430 |
} |
1431 |
|
1432 |
/** |
1433 |
* @throws NullPointerException if the task is null |
1434 |
* @throws RejectedExecutionException if the task cannot be |
1435 |
* scheduled for execution |
1436 |
*/ |
1437 |
public ForkJoinTask<?> submit(Runnable task) { |
1438 |
ForkJoinTask<?> job; |
1439 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1440 |
job = (ForkJoinTask<?>) task; |
1441 |
else |
1442 |
job = ForkJoinTask.adapt(task, null); |
1443 |
doSubmit(job); |
1444 |
return job; |
1445 |
} |
1446 |
|
1447 |
/** |
1448 |
* @throws NullPointerException {@inheritDoc} |
1449 |
* @throws RejectedExecutionException {@inheritDoc} |
1450 |
*/ |
1451 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
1452 |
ArrayList<ForkJoinTask<T>> forkJoinTasks = |
1453 |
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
1454 |
for (Callable<T> task : tasks) |
1455 |
forkJoinTasks.add(ForkJoinTask.adapt(task)); |
1456 |
invoke(new InvokeAll<T>(forkJoinTasks)); |
1457 |
|
1458 |
@SuppressWarnings({"unchecked", "rawtypes"}) |
1459 |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1460 |
return futures; |
1461 |
} |
1462 |
|
1463 |
static final class InvokeAll<T> extends RecursiveAction { |
1464 |
final ArrayList<ForkJoinTask<T>> tasks; |
1465 |
InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } |
1466 |
public void compute() { |
1467 |
try { invokeAll(tasks); } |
1468 |
catch (Exception ignore) {} |
1469 |
} |
1470 |
private static final long serialVersionUID = -7914297376763021607L; |
1471 |
} |
1472 |
|
1473 |
/** |
1474 |
* Returns the factory used for constructing new workers. |
1475 |
* |
1476 |
* @return the factory used for constructing new workers |
1477 |
*/ |
1478 |
public ForkJoinWorkerThreadFactory getFactory() { |
1479 |
return factory; |
1480 |
} |
1481 |
|
1482 |
/** |
1483 |
* Returns the handler for internal worker threads that terminate |
1484 |
* due to unrecoverable errors encountered while executing tasks. |
1485 |
* |
1486 |
* @return the handler, or {@code null} if none |
1487 |
*/ |
1488 |
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
1489 |
return ueh; |
1490 |
} |
1491 |
|
1492 |
/** |
1493 |
* Returns the targeted parallelism level of this pool. |
1494 |
* |
1495 |
* @return the targeted parallelism level of this pool |
1496 |
*/ |
1497 |
public int getParallelism() { |
1498 |
return parallelism; |
1499 |
} |
1500 |
|
1501 |
/** |
1502 |
* Returns the number of worker threads that have started but not |
1503 |
* yet terminated. This result returned by this method may differ |
1504 |
* from {@link #getParallelism} when threads are created to |
1505 |
* maintain parallelism when others are cooperatively blocked. |
1506 |
* |
1507 |
* @return the number of worker threads |
1508 |
*/ |
1509 |
public int getPoolSize() { |
1510 |
return workerCounts >>> TOTAL_COUNT_SHIFT; |
1511 |
} |
1512 |
|
1513 |
/** |
1514 |
* Returns {@code true} if this pool uses local first-in-first-out |
1515 |
* scheduling mode for forked tasks that are never joined. |
1516 |
* |
1517 |
* @return {@code true} if this pool uses async mode |
1518 |
*/ |
1519 |
public boolean getAsyncMode() { |
1520 |
return locallyFifo; |
1521 |
} |
1522 |
|
1523 |
/** |
1524 |
* Returns an estimate of the number of worker threads that are |
1525 |
* not blocked waiting to join tasks or for other managed |
1526 |
* synchronization. This method may overestimate the |
1527 |
* number of running threads. |
1528 |
* |
1529 |
* @return the number of worker threads |
1530 |
*/ |
1531 |
public int getRunningThreadCount() { |
1532 |
return workerCounts & RUNNING_COUNT_MASK; |
1533 |
} |
1534 |
|
1535 |
/** |
1536 |
* Returns an estimate of the number of threads that are currently |
1537 |
* stealing or executing tasks. This method may overestimate the |
1538 |
* number of active threads. |
1539 |
* |
1540 |
* @return the number of active threads |
1541 |
*/ |
1542 |
public int getActiveThreadCount() { |
1543 |
return runState & ACTIVE_COUNT_MASK; |
1544 |
} |
1545 |
|
1546 |
/** |
1547 |
* Returns {@code true} if all worker threads are currently idle. |
1548 |
* An idle worker is one that cannot obtain a task to execute |
1549 |
* because none are available to steal from other threads, and |
1550 |
* there are no pending submissions to the pool. This method is |
1551 |
* conservative; it might not return {@code true} immediately upon |
1552 |
* idleness of all threads, but will eventually become true if |
1553 |
* threads remain inactive. |
1554 |
* |
1555 |
* @return {@code true} if all threads are currently idle |
1556 |
*/ |
1557 |
public boolean isQuiescent() { |
1558 |
return (runState & ACTIVE_COUNT_MASK) == 0; |
1559 |
} |
1560 |
|
1561 |
/** |
1562 |
* Returns an estimate of the total number of tasks stolen from |
1563 |
* one thread's work queue by another. The reported value |
1564 |
* underestimates the actual total number of steals when the pool |
1565 |
* is not quiescent. This value may be useful for monitoring and |
1566 |
* tuning fork/join programs: in general, steal counts should be |
1567 |
* high enough to keep threads busy, but low enough to avoid |
1568 |
* overhead and contention across threads. |
1569 |
* |
1570 |
* @return the number of steals |
1571 |
*/ |
1572 |
public long getStealCount() { |
1573 |
return stealCount; |
1574 |
} |
1575 |
|
1576 |
/** |
1577 |
* Returns an estimate of the total number of tasks currently held |
1578 |
* in queues by worker threads (but not including tasks submitted |
1579 |
* to the pool that have not begun executing). This value is only |
1580 |
* an approximation, obtained by iterating across all threads in |
1581 |
* the pool. This method may be useful for tuning task |
1582 |
* granularities. |
1583 |
* |
1584 |
* @return the number of queued tasks |
1585 |
*/ |
1586 |
public long getQueuedTaskCount() { |
1587 |
long count = 0; |
1588 |
ForkJoinWorkerThread[] ws = workers; |
1589 |
int nws = ws.length; |
1590 |
for (int i = 0; i < nws; ++i) { |
1591 |
ForkJoinWorkerThread w = ws[i]; |
1592 |
if (w != null) |
1593 |
count += w.getQueueSize(); |
1594 |
} |
1595 |
return count; |
1596 |
} |
1597 |
|
1598 |
/** |
1599 |
* Returns an estimate of the number of tasks submitted to this |
1600 |
* pool that have not yet begun executing. This method takes time |
1601 |
* proportional to the number of submissions. |
1602 |
* |
1603 |
* @return the number of queued submissions |
1604 |
*/ |
1605 |
public int getQueuedSubmissionCount() { |
1606 |
return submissionQueue.size(); |
1607 |
} |
1608 |
|
1609 |
/** |
1610 |
* Returns {@code true} if there are any tasks submitted to this |
1611 |
* pool that have not yet begun executing. |
1612 |
* |
1613 |
* @return {@code true} if there are any queued submissions |
1614 |
*/ |
1615 |
public boolean hasQueuedSubmissions() { |
1616 |
return !submissionQueue.isEmpty(); |
1617 |
} |
1618 |
|
1619 |
/** |
1620 |
* Removes and returns the next unexecuted submission if one is |
1621 |
* available. This method may be useful in extensions to this |
1622 |
* class that re-assign work in systems with multiple pools. |
1623 |
* |
1624 |
* @return the next submission, or {@code null} if none |
1625 |
*/ |
1626 |
protected ForkJoinTask<?> pollSubmission() { |
1627 |
return submissionQueue.poll(); |
1628 |
} |
1629 |
|
1630 |
/** |
1631 |
* Removes all available unexecuted submitted and forked tasks |
1632 |
* from scheduling queues and adds them to the given collection, |
1633 |
* without altering their execution status. These may include |
1634 |
* artificially generated or wrapped tasks. This method is |
1635 |
* designed to be invoked only when the pool is known to be |
1636 |
* quiescent. Invocations at other times may not remove all |
1637 |
* tasks. A failure encountered while attempting to add elements |
1638 |
* to collection {@code c} may result in elements being in |
1639 |
* neither, either or both collections when the associated |
1640 |
* exception is thrown. The behavior of this operation is |
1641 |
* undefined if the specified collection is modified while the |
1642 |
* operation is in progress. |
1643 |
* |
1644 |
* @param c the collection to transfer elements into |
1645 |
* @return the number of elements transferred |
1646 |
*/ |
1647 |
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1648 |
int n = submissionQueue.drainTo(c); |
1649 |
ForkJoinWorkerThread[] ws = workers; |
1650 |
int nws = ws.length; |
1651 |
for (int i = 0; i < nws; ++i) { |
1652 |
ForkJoinWorkerThread w = ws[i]; |
1653 |
if (w != null) |
1654 |
n += w.drainTasksTo(c); |
1655 |
} |
1656 |
return n; |
1657 |
} |
1658 |
|
1659 |
/** |
1660 |
* Returns count of total parks by existing workers. |
1661 |
* Used during development only since not meaningful to users. |
1662 |
*/ |
1663 |
private int collectParkCount() { |
1664 |
int count = 0; |
1665 |
ForkJoinWorkerThread[] ws = workers; |
1666 |
int nws = ws.length; |
1667 |
for (int i = 0; i < nws; ++i) { |
1668 |
ForkJoinWorkerThread w = ws[i]; |
1669 |
if (w != null) |
1670 |
count += w.parkCount; |
1671 |
} |
1672 |
return count; |
1673 |
} |
1674 |
|
1675 |
/** |
1676 |
* Returns a string identifying this pool, as well as its state, |
1677 |
* including indications of run state, parallelism level, and |
1678 |
* worker and task counts. |
1679 |
* |
1680 |
* @return a string identifying this pool, as well as its state |
1681 |
*/ |
1682 |
public String toString() { |
1683 |
long st = getStealCount(); |
1684 |
long qt = getQueuedTaskCount(); |
1685 |
long qs = getQueuedSubmissionCount(); |
1686 |
int wc = workerCounts; |
1687 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1688 |
int rc = wc & RUNNING_COUNT_MASK; |
1689 |
int pc = parallelism; |
1690 |
int rs = runState; |
1691 |
int ac = rs & ACTIVE_COUNT_MASK; |
1692 |
// int pk = collectParkCount(); |
1693 |
return super.toString() + |
1694 |
"[" + runLevelToString(rs) + |
1695 |
", parallelism = " + pc + |
1696 |
", size = " + tc + |
1697 |
", active = " + ac + |
1698 |
", running = " + rc + |
1699 |
", steals = " + st + |
1700 |
", tasks = " + qt + |
1701 |
", submissions = " + qs + |
1702 |
// ", parks = " + pk + |
1703 |
"]"; |
1704 |
} |
1705 |
|
1706 |
private static String runLevelToString(int s) { |
1707 |
return ((s & TERMINATED) != 0 ? "Terminated" : |
1708 |
((s & TERMINATING) != 0 ? "Terminating" : |
1709 |
((s & SHUTDOWN) != 0 ? "Shutting down" : |
1710 |
"Running"))); |
1711 |
} |
1712 |
|
1713 |
/** |
1714 |
* Initiates an orderly shutdown in which previously submitted |
1715 |
* tasks are executed, but no new tasks will be accepted. |
1716 |
* Invocation has no additional effect if already shut down. |
1717 |
* Tasks that are in the process of being submitted concurrently |
1718 |
* during the course of this method may or may not be rejected. |
1719 |
* |
1720 |
* @throws SecurityException if a security manager exists and |
1721 |
* the caller is not permitted to modify threads |
1722 |
* because it does not hold {@link |
1723 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1724 |
*/ |
1725 |
public void shutdown() { |
1726 |
checkPermission(); |
1727 |
advanceRunLevel(SHUTDOWN); |
1728 |
tryTerminate(false); |
1729 |
} |
1730 |
|
1731 |
/** |
1732 |
* Attempts to cancel and/or stop all tasks, and reject all |
1733 |
* subsequently submitted tasks. Tasks that are in the process of |
1734 |
* being submitted or executed concurrently during the course of |
1735 |
* this method may or may not be rejected. This method cancels |
1736 |
* both existing and unexecuted tasks, in order to permit |
1737 |
* termination in the presence of task dependencies. So the method |
1738 |
* always returns an empty list (unlike the case for some other |
1739 |
* Executors). |
1740 |
* |
1741 |
* @return an empty list |
1742 |
* @throws SecurityException if a security manager exists and |
1743 |
* the caller is not permitted to modify threads |
1744 |
* because it does not hold {@link |
1745 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1746 |
*/ |
1747 |
public List<Runnable> shutdownNow() { |
1748 |
checkPermission(); |
1749 |
tryTerminate(true); |
1750 |
return Collections.emptyList(); |
1751 |
} |
1752 |
|
1753 |
/** |
1754 |
* Returns {@code true} if all tasks have completed following shut down. |
1755 |
* |
1756 |
* @return {@code true} if all tasks have completed following shut down |
1757 |
*/ |
1758 |
public boolean isTerminated() { |
1759 |
return runState >= TERMINATED; |
1760 |
} |
1761 |
|
1762 |
/** |
1763 |
* Returns {@code true} if the process of termination has |
1764 |
* commenced but not yet completed. This method may be useful for |
1765 |
* debugging. A return of {@code true} reported a sufficient |
1766 |
* period after shutdown may indicate that submitted tasks have |
1767 |
* ignored or suppressed interruption, causing this executor not |
1768 |
* to properly terminate. |
1769 |
* |
1770 |
* @return {@code true} if terminating but not yet terminated |
1771 |
*/ |
1772 |
public boolean isTerminating() { |
1773 |
return (runState & (TERMINATING|TERMINATED)) == TERMINATING; |
1774 |
} |
1775 |
|
1776 |
/** |
1777 |
* Returns {@code true} if this pool has been shut down. |
1778 |
* |
1779 |
* @return {@code true} if this pool has been shut down |
1780 |
*/ |
1781 |
public boolean isShutdown() { |
1782 |
return runState >= SHUTDOWN; |
1783 |
} |
1784 |
|
1785 |
/** |
1786 |
* Blocks until all tasks have completed execution after a shutdown |
1787 |
* request, or the timeout occurs, or the current thread is |
1788 |
* interrupted, whichever happens first. |
1789 |
* |
1790 |
* @param timeout the maximum time to wait |
1791 |
* @param unit the time unit of the timeout argument |
1792 |
* @return {@code true} if this executor terminated and |
1793 |
* {@code false} if the timeout elapsed before termination |
1794 |
* @throws InterruptedException if interrupted while waiting |
1795 |
*/ |
1796 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1797 |
throws InterruptedException { |
1798 |
try { |
1799 |
return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
1800 |
} catch(TimeoutException ex) { |
1801 |
return false; |
1802 |
} |
1803 |
} |
1804 |
|
1805 |
/** |
1806 |
* Interface for extending managed parallelism for tasks running |
1807 |
* in {@link ForkJoinPool}s. |
1808 |
* |
1809 |
* <p>A {@code ManagedBlocker} provides two methods. |
1810 |
* Method {@code isReleasable} must return {@code true} if |
1811 |
* blocking is not necessary. Method {@code block} blocks the |
1812 |
* current thread if necessary (perhaps internally invoking |
1813 |
* {@code isReleasable} before actually blocking). |
1814 |
* |
1815 |
* <p>For example, here is a ManagedBlocker based on a |
1816 |
* ReentrantLock: |
1817 |
* <pre> {@code |
1818 |
* class ManagedLocker implements ManagedBlocker { |
1819 |
* final ReentrantLock lock; |
1820 |
* boolean hasLock = false; |
1821 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
1822 |
* public boolean block() { |
1823 |
* if (!hasLock) |
1824 |
* lock.lock(); |
1825 |
* return true; |
1826 |
* } |
1827 |
* public boolean isReleasable() { |
1828 |
* return hasLock || (hasLock = lock.tryLock()); |
1829 |
* } |
1830 |
* }}</pre> |
1831 |
*/ |
1832 |
public static interface ManagedBlocker { |
1833 |
/** |
1834 |
* Possibly blocks the current thread, for example waiting for |
1835 |
* a lock or condition. |
1836 |
* |
1837 |
* @return {@code true} if no additional blocking is necessary |
1838 |
* (i.e., if isReleasable would return true) |
1839 |
* @throws InterruptedException if interrupted while waiting |
1840 |
* (the method is not required to do so, but is allowed to) |
1841 |
*/ |
1842 |
boolean block() throws InterruptedException; |
1843 |
|
1844 |
/** |
1845 |
* Returns {@code true} if blocking is unnecessary. |
1846 |
*/ |
1847 |
boolean isReleasable(); |
1848 |
} |
1849 |
|
1850 |
/** |
1851 |
* Blocks in accord with the given blocker. If the current thread |
1852 |
* is a {@link ForkJoinWorkerThread}, this method possibly |
1853 |
* arranges for a spare thread to be activated if necessary to |
1854 |
* ensure sufficient parallelism while the current thread is blocked. |
1855 |
* |
1856 |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
1857 |
* behaviorally equivalent to |
1858 |
* <pre> {@code |
1859 |
* while (!blocker.isReleasable()) |
1860 |
* if (blocker.block()) |
1861 |
* return; |
1862 |
* }</pre> |
1863 |
* |
1864 |
* If the caller is a {@code ForkJoinTask}, then the pool may |
1865 |
* first be expanded to ensure parallelism, and later adjusted. |
1866 |
* |
1867 |
* @param blocker the blocker |
1868 |
* @throws InterruptedException if blocker.block did so |
1869 |
*/ |
1870 |
public static void managedBlock(ManagedBlocker blocker) |
1871 |
throws InterruptedException { |
1872 |
Thread t = Thread.currentThread(); |
1873 |
if (t instanceof ForkJoinWorkerThread) |
1874 |
((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker); |
1875 |
else { |
1876 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1877 |
} |
1878 |
} |
1879 |
|
1880 |
// AbstractExecutorService overrides. These rely on undocumented |
1881 |
// fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
1882 |
// implement RunnableFuture. |
1883 |
|
1884 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
1885 |
return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); |
1886 |
} |
1887 |
|
1888 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
1889 |
return (RunnableFuture<T>) ForkJoinTask.adapt(callable); |
1890 |
} |
1891 |
|
1892 |
// Unsafe mechanics |
1893 |
|
1894 |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1895 |
private static final long workerCountsOffset = |
1896 |
objectFieldOffset("workerCounts", ForkJoinPool.class); |
1897 |
private static final long runStateOffset = |
1898 |
objectFieldOffset("runState", ForkJoinPool.class); |
1899 |
private static final long eventCountOffset = |
1900 |
objectFieldOffset("eventCount", ForkJoinPool.class); |
1901 |
private static final long eventWaitersOffset = |
1902 |
objectFieldOffset("eventWaiters",ForkJoinPool.class); |
1903 |
private static final long stealCountOffset = |
1904 |
objectFieldOffset("stealCount",ForkJoinPool.class); |
1905 |
|
1906 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
1907 |
try { |
1908 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1909 |
} catch (NoSuchFieldException e) { |
1910 |
// Convert Exception to corresponding Error |
1911 |
NoSuchFieldError error = new NoSuchFieldError(field); |
1912 |
error.initCause(e); |
1913 |
throw error; |
1914 |
} |
1915 |
} |
1916 |
|
1917 |
/** |
1918 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1919 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1920 |
* into a jdk. |
1921 |
* |
1922 |
* @return a sun.misc.Unsafe |
1923 |
*/ |
1924 |
private static sun.misc.Unsafe getUnsafe() { |
1925 |
try { |
1926 |
return sun.misc.Unsafe.getUnsafe(); |
1927 |
} catch (SecurityException se) { |
1928 |
try { |
1929 |
return java.security.AccessController.doPrivileged |
1930 |
(new java.security |
1931 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1932 |
public sun.misc.Unsafe run() throws Exception { |
1933 |
java.lang.reflect.Field f = sun.misc |
1934 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1935 |
f.setAccessible(true); |
1936 |
return (sun.misc.Unsafe) f.get(null); |
1937 |
}}); |
1938 |
} catch (java.security.PrivilegedActionException e) { |
1939 |
throw new RuntimeException("Could not initialize intrinsics", |
1940 |
e.getCause()); |
1941 |
} |
1942 |
} |
1943 |
} |
1944 |
} |