| 81 |
|
* by the ForkJoinPool). This allows use in message-passing |
| 82 |
|
* frameworks in which tasks are never joined. |
| 83 |
|
* |
| 84 |
< |
* Efficient implementation of this approach currently relies on |
| 84 |
> |
* When a worker would otherwise be blocked waiting to join a |
| 85 |
> |
* task, it first tries a form of linear helping: Each worker |
| 86 |
> |
* records (in field stolen) the most recent task it stole |
| 87 |
> |
* from some other worker. Plus, it records (in field joining) the |
| 88 |
> |
* task it is currently actively joining. Method joinTask uses |
| 89 |
> |
* these markers to try to find a worker to help (i.e., steal back |
| 90 |
> |
* a task from and execute it) that could hasten completion of the |
| 91 |
> |
* actively joined task. In essence, the joiner executes a task |
| 92 |
> |
* that would be on its own local deque had the to-be-joined task |
| 93 |
> |
* not been stolen. This may be seen as a conservative variant of |
| 94 |
> |
* the approach in Wagner & Calder "Leapfrogging: a portable |
| 95 |
> |
* technique for implementing efficient futures" SIGPLAN Notices, |
| 96 |
> |
* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs |
| 97 |
> |
* in that: (1) We only maintain dependency links across workers |
| 98 |
> |
* upon steals, rather than maintain per-task bookkeeping. This |
| 99 |
> |
* requires a linear scan of workers array to locate stealers, |
| 100 |
> |
* which isolates cost to when it is needed, rather than adding to |
| 101 |
> |
* per-task overhead. (2) It is "shallow", ignoring nesting and |
| 102 |
> |
* potentially cyclic mutual steals. (3) It is intentionally |
| 103 |
> |
* racy: field joining is updated only while actively joining, |
| 104 |
> |
* which means that we could miss links in the chain during |
| 105 |
> |
* long-lived tasks, GC stalls etc. (4) We fall back to |
| 106 |
> |
* suspending the worker and if necessary replacing it with a |
| 107 |
> |
* spare (see ForkJoinPool.tryAwaitJoin). |
| 108 |
> |
* |
| 109 |
> |
* Efficient implementation of these algorithms currently relies on |
| 110 |
|
* an uncomfortable amount of "Unsafe" mechanics. To maintain |
| 111 |
|
* correct orderings, reads and writes of variable base require |
| 112 |
|
* volatile ordering. Variable sp does not require volatile |
| 161 |
|
|
| 162 |
|
/** |
| 163 |
|
* Capacity of work-stealing queue array upon initialization. |
| 164 |
< |
* Must be a power of two. Initial size must be at least 2, but is |
| 164 |
> |
* Must be a power of two. Initial size must be at least 4, but is |
| 165 |
|
* padded to minimize cache effects. |
| 166 |
|
*/ |
| 167 |
|
private static final int INITIAL_QUEUE_CAPACITY = 1 << 13; |
| 180 |
|
final ForkJoinPool pool; |
| 181 |
|
|
| 182 |
|
/** |
| 183 |
+ |
* The task most recently stolen from another worker |
| 184 |
+ |
*/ |
| 185 |
+ |
private volatile ForkJoinTask<?> stolen; |
| 186 |
+ |
|
| 187 |
+ |
/** |
| 188 |
+ |
* The task currently being joined, set only when actively |
| 189 |
+ |
* trying to helpStealer. |
| 190 |
+ |
*/ |
| 191 |
+ |
private volatile ForkJoinTask<?> joining; |
| 192 |
+ |
|
| 193 |
+ |
/** |
| 194 |
|
* The work-stealing queue array. Size must be a power of two. |
| 195 |
|
* Initialized in onStart, to improve memory locality. |
| 196 |
|
*/ |
| 230 |
|
* currently not exported but included because volatile write upon |
| 231 |
|
* park also provides a workaround for a JVM bug. |
| 232 |
|
*/ |
| 233 |
< |
private volatile int parkCount; |
| 233 |
> |
volatile int parkCount; |
| 234 |
|
|
| 235 |
|
/** |
| 236 |
|
* Number of steals, transferred and reset in pool callbacks pool |
| 255 |
|
* Shadows value from ForkJoinPool, which resets it if changed |
| 256 |
|
* pool-wide. |
| 257 |
|
*/ |
| 258 |
< |
private boolean locallyFifo; |
| 259 |
< |
|
| 258 |
> |
private final boolean locallyFifo; |
| 259 |
> |
|
| 260 |
|
/** |
| 261 |
|
* Index of this worker in pool array. Set once by pool before |
| 262 |
|
* running, and accessed directly by pool to locate this worker in |
| 283 |
|
* @throws NullPointerException if pool is null |
| 284 |
|
*/ |
| 285 |
|
protected ForkJoinWorkerThread(ForkJoinPool pool) { |
| 250 |
– |
if (pool == null) throw new NullPointerException(); |
| 286 |
|
this.pool = pool; |
| 287 |
+ |
this.locallyFifo = pool.locallyFifo; |
| 288 |
|
// To avoid exposing construction details to subclasses, |
| 289 |
|
// remaining initialization is in start() and onStart() |
| 290 |
|
} |
| 292 |
|
/** |
| 293 |
|
* Performs additional initialization and starts this thread |
| 294 |
|
*/ |
| 295 |
< |
final void start(int poolIndex, boolean locallyFifo, |
| 260 |
< |
UncaughtExceptionHandler ueh) { |
| 295 |
> |
final void start(int poolIndex, UncaughtExceptionHandler ueh) { |
| 296 |
|
this.poolIndex = poolIndex; |
| 262 |
– |
this.locallyFifo = locallyFifo; |
| 297 |
|
if (ueh != null) |
| 298 |
|
setUncaughtExceptionHandler(ueh); |
| 299 |
|
setDaemon(true); |
| 337 |
|
int rs = seedGenerator.nextInt(); |
| 338 |
|
seed = rs == 0? 1 : rs; // seed must be nonzero |
| 339 |
|
|
| 340 |
< |
// Allocate name string and queue array in this thread |
| 340 |
> |
// Allocate name string and arrays in this thread |
| 341 |
|
String pid = Integer.toString(pool.getPoolNumber()); |
| 342 |
|
String wid = Integer.toString(poolIndex); |
| 343 |
|
setName("ForkJoinPool-" + pid + "-worker-" + wid); |
| 355 |
|
*/ |
| 356 |
|
protected void onTermination(Throwable exception) { |
| 357 |
|
try { |
| 358 |
+ |
stolen = null; |
| 359 |
+ |
joining = null; |
| 360 |
|
cancelTasks(); |
| 361 |
|
setTerminated(); |
| 362 |
|
pool.workerTerminated(this); |
| 392 |
|
* Find and execute tasks and check status while running |
| 393 |
|
*/ |
| 394 |
|
private void mainLoop() { |
| 395 |
< |
boolean ran = false; // true if ran task on previous step |
| 395 |
> |
boolean ran = false; // true if ran task in last loop iter |
| 396 |
> |
boolean prevRan = false; // true if ran on last or previous step |
| 397 |
|
ForkJoinPool p = pool; |
| 398 |
|
for (;;) { |
| 399 |
< |
p.preStep(this, ran); |
| 399 |
> |
p.preStep(this, prevRan); |
| 400 |
|
if (runState != 0) |
| 401 |
|
return; |
| 402 |
|
ForkJoinTask<?> t; // try to get and run stolen or submitted task |
| 403 |
< |
if (ran = (t = scan()) != null || (t = pollSubmission()) != null) { |
| 403 |
> |
if ((t = scan()) != null || (t = pollSubmission()) != null) { |
| 404 |
|
t.tryExec(); |
| 405 |
|
if (base != sp) |
| 406 |
|
runLocalTasks(); |
| 407 |
+ |
stolen = null; |
| 408 |
+ |
prevRan = ran = true; |
| 409 |
+ |
} |
| 410 |
+ |
else { |
| 411 |
+ |
prevRan = ran; |
| 412 |
+ |
ran = false; |
| 413 |
|
} |
| 414 |
|
} |
| 415 |
|
} |
| 488 |
|
* @param t the task. Caller must ensure non-null. |
| 489 |
|
*/ |
| 490 |
|
final void pushTask(ForkJoinTask<?> t) { |
| 448 |
– |
int s; |
| 491 |
|
ForkJoinTask<?>[] q = queue; |
| 492 |
|
int mask = q.length - 1; // implicit assert q != null |
| 493 |
< |
UNSAFE.putOrderedObject(q, (((s = sp++) & mask) << qShift) + qBase, t); |
| 494 |
< |
if ((s -= base) <= 0) |
| 495 |
< |
pool.signalWork(); |
| 496 |
< |
else if (s + 1 >= mask) |
| 497 |
< |
growQueue(); |
| 493 |
> |
int s = sp++; // ok to increment sp before slot write |
| 494 |
> |
UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t); |
| 495 |
> |
if ((s -= base) == 0) |
| 496 |
> |
pool.signalWork(); // was empty |
| 497 |
> |
else if (s == mask) |
| 498 |
> |
growQueue(); // is full |
| 499 |
|
} |
| 500 |
|
|
| 501 |
|
/** |
| 502 |
|
* Tries to take a task from the base of the queue, failing if |
| 503 |
|
* empty or contended. Note: Specializations of this code appear |
| 504 |
< |
* in scan and scanWhileJoining. |
| 504 |
> |
* in locallyDeqTask and elsewhere. |
| 505 |
|
* |
| 506 |
|
* @return a task, or null if none or contended |
| 507 |
|
*/ |
| 511 |
|
int b, i; |
| 512 |
|
if ((b = base) != sp && |
| 513 |
|
(q = queue) != null && // must read q after b |
| 514 |
< |
(t = q[i = (q.length - 1) & b]) != null && |
| 514 |
> |
(t = q[i = (q.length - 1) & b]) != null && base == b && |
| 515 |
|
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) { |
| 516 |
|
base = b + 1; |
| 517 |
|
return t; |
| 531 |
|
ForkJoinTask<?> t; |
| 532 |
|
int b, i; |
| 533 |
|
while (sp != (b = base)) { |
| 534 |
< |
if ((t = q[i = (q.length - 1) & b]) != null && |
| 534 |
> |
if ((t = q[i = (q.length - 1) & b]) != null && base == b && |
| 535 |
|
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, |
| 536 |
|
t, null)) { |
| 537 |
|
base = b + 1; |
| 664 |
|
ForkJoinWorkerThread v = ws[k & mask]; |
| 665 |
|
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift |
| 666 |
|
if (v != null && v.base != v.sp) { |
| 667 |
< |
int b, i; // inline specialized deqTask |
| 668 |
< |
ForkJoinTask<?>[] q; |
| 669 |
< |
ForkJoinTask<?> t; |
| 670 |
< |
if ((canSteal || // ensure active status |
| 671 |
< |
(canSteal = active = p.tryIncrementActiveCount())) && |
| 672 |
< |
(q = v.queue) != null && |
| 673 |
< |
(t = q[i = (q.length - 1) & (b = v.base)]) != null && |
| 674 |
< |
UNSAFE.compareAndSwapObject |
| 675 |
< |
(q, (i << qShift) + qBase, t, null)) { |
| 676 |
< |
v.base = b + 1; |
| 677 |
< |
seed = r; |
| 678 |
< |
++stealCount; |
| 679 |
< |
return t; |
| 667 |
> |
if (canSteal || // ensure active status |
| 668 |
> |
(canSteal = active = p.tryIncrementActiveCount())) { |
| 669 |
> |
int b = v.base; // inline specialized deqTask |
| 670 |
> |
ForkJoinTask<?>[] q; |
| 671 |
> |
if (b != v.sp && (q = v.queue) != null) { |
| 672 |
> |
ForkJoinTask<?> t; |
| 673 |
> |
int i = (q.length - 1) & b; |
| 674 |
> |
long u = (i << qShift) + qBase; // raw offset |
| 675 |
> |
if ((t = q[i]) != null && v.base == b && |
| 676 |
> |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 677 |
> |
stolen = t; |
| 678 |
> |
v.base = b + 1; |
| 679 |
> |
seed = r; |
| 680 |
> |
++stealCount; |
| 681 |
> |
return t; |
| 682 |
> |
} |
| 683 |
> |
} |
| 684 |
|
} |
| 685 |
|
j = -n; |
| 686 |
|
k = r; // restart on contention |
| 735 |
|
} |
| 736 |
|
|
| 737 |
|
/** |
| 738 |
< |
* Instrumented version of park. Also used by ForkJoinPool.awaitEvent |
| 738 |
> |
* Instrumented version of park used by ForkJoinPool.awaitEvent |
| 739 |
|
*/ |
| 740 |
|
final void doPark() { |
| 741 |
|
++parkCount; |
| 749 |
|
* @return true if successful |
| 750 |
|
*/ |
| 751 |
|
final boolean tryUnsuspend() { |
| 752 |
< |
int s; |
| 753 |
< |
return (((s = runState) & SUSPENDED) != 0 && |
| 754 |
< |
UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
| 755 |
< |
s & ~SUSPENDED)); |
| 752 |
> |
int s = runState; |
| 753 |
> |
if ((s & SUSPENDED) != 0) |
| 754 |
> |
return UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
| 755 |
> |
s & ~SUSPENDED); |
| 756 |
> |
return false; |
| 757 |
|
} |
| 758 |
|
|
| 759 |
|
/** |
| 774 |
|
s | SUSPENDED)) |
| 775 |
|
break; |
| 776 |
|
} |
| 777 |
+ |
boolean timed; |
| 778 |
+ |
long nanos; |
| 779 |
+ |
long startTime; |
| 780 |
+ |
if (poolIndex < pool.parallelism) { |
| 781 |
+ |
timed = false; |
| 782 |
+ |
nanos = 0L; |
| 783 |
+ |
startTime = 0L; |
| 784 |
+ |
} |
| 785 |
+ |
else { |
| 786 |
+ |
timed = true; |
| 787 |
+ |
nanos = SPARE_KEEPALIVE_NANOS; |
| 788 |
+ |
startTime = System.nanoTime(); |
| 789 |
+ |
} |
| 790 |
+ |
pool.accumulateStealCount(this); |
| 791 |
|
lastEventCount = 0; // reset upon resume |
| 730 |
– |
ForkJoinPool p = pool; |
| 731 |
– |
p.releaseWaiters(); // help others progress |
| 732 |
– |
p.accumulateStealCount(this); |
| 792 |
|
interrupted(); // clear/ignore interrupts |
| 734 |
– |
if (poolIndex < p.getParallelism()) { // untimed wait |
| 735 |
– |
while ((runState & SUSPENDED) != 0) |
| 736 |
– |
doPark(); |
| 737 |
– |
return true; |
| 738 |
– |
} |
| 739 |
– |
return timedSuspend(); // timed wait if apparently non-core |
| 740 |
– |
} |
| 741 |
– |
|
| 742 |
– |
/** |
| 743 |
– |
* Blocks as spare until resumed or timed out |
| 744 |
– |
* @return false if trimmed |
| 745 |
– |
*/ |
| 746 |
– |
private boolean timedSuspend() { |
| 747 |
– |
long nanos = SPARE_KEEPALIVE_NANOS; |
| 748 |
– |
long startTime = System.nanoTime(); |
| 793 |
|
while ((runState & SUSPENDED) != 0) { |
| 794 |
|
++parkCount; |
| 795 |
< |
if ((nanos -= (System.nanoTime() - startTime)) > 0) |
| 795 |
> |
if (!timed) |
| 796 |
> |
LockSupport.park(this); |
| 797 |
> |
else if ((nanos -= (System.nanoTime() - startTime)) > 0) |
| 798 |
|
LockSupport.parkNanos(this, nanos); |
| 799 |
|
else { // try to trim on timeout |
| 800 |
|
int s = runState; |
| 818 |
|
} |
| 819 |
|
|
| 820 |
|
/** |
| 775 |
– |
* Set locallyFifo mode. Called only by ForkJoinPool |
| 776 |
– |
*/ |
| 777 |
– |
final void setAsyncMode(boolean async) { |
| 778 |
– |
locallyFifo = async; |
| 779 |
– |
} |
| 780 |
– |
|
| 781 |
– |
/** |
| 821 |
|
* Removes and cancels all tasks in queue. Can be called from any |
| 822 |
|
* thread. |
| 823 |
|
*/ |
| 849 |
|
// Support methods for ForkJoinTask |
| 850 |
|
|
| 851 |
|
/** |
| 852 |
+ |
* Possibly runs some tasks and/or blocks, until task is done. |
| 853 |
+ |
* |
| 854 |
+ |
* @param joinMe the task to join |
| 855 |
+ |
*/ |
| 856 |
+ |
final void joinTask(ForkJoinTask<?> joinMe) { |
| 857 |
+ |
ForkJoinTask<?> prevJoining = joining; |
| 858 |
+ |
joining = joinMe; |
| 859 |
+ |
while (joinMe.status >= 0) { |
| 860 |
+ |
int s = sp; |
| 861 |
+ |
if (s == base) { |
| 862 |
+ |
nonlocalJoinTask(joinMe); |
| 863 |
+ |
break; |
| 864 |
+ |
} |
| 865 |
+ |
// process local task |
| 866 |
+ |
ForkJoinTask<?> t; |
| 867 |
+ |
ForkJoinTask<?>[] q = queue; |
| 868 |
+ |
int i = (q.length - 1) & --s; |
| 869 |
+ |
long u = (i << qShift) + qBase; // raw offset |
| 870 |
+ |
if ((t = q[i]) != null && |
| 871 |
+ |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 872 |
+ |
/* |
| 873 |
+ |
* This recheck (and similarly in nonlocalJoinTask) |
| 874 |
+ |
* handles cases where joinMe is independently |
| 875 |
+ |
* cancelled or forced even though there is other work |
| 876 |
+ |
* available. Back out of the pop by putting t back |
| 877 |
+ |
* into slot before we commit by setting sp. |
| 878 |
+ |
*/ |
| 879 |
+ |
if (joinMe.status < 0) { |
| 880 |
+ |
UNSAFE.putObjectVolatile(q, u, t); |
| 881 |
+ |
break; |
| 882 |
+ |
} |
| 883 |
+ |
sp = s; |
| 884 |
+ |
t.tryExec(); |
| 885 |
+ |
} |
| 886 |
+ |
} |
| 887 |
+ |
joining = prevJoining; |
| 888 |
+ |
} |
| 889 |
+ |
|
| 890 |
+ |
/** |
| 891 |
+ |
* Tries to locate and help perform tasks for a stealer of the |
| 892 |
+ |
* given task (or in turn one of its stealers), blocking (via |
| 893 |
+ |
* pool.tryAwaitJoin) upon failure to find work. Traces |
| 894 |
+ |
* stolen->joining links looking for a thread working on |
| 895 |
+ |
* a descendant of the given task and with a non-empty queue to |
| 896 |
+ |
* steal back and execute tasks from. Inhibits mutual steal chains |
| 897 |
+ |
* and scans on outer joins upon nesting to avoid unbounded |
| 898 |
+ |
* growth. Restarts search upon encountering inconsistencies. |
| 899 |
+ |
* Tries to block if two passes agree that there are no remaining |
| 900 |
+ |
* targets. |
| 901 |
+ |
* |
| 902 |
+ |
* @param joinMe the task to join |
| 903 |
+ |
*/ |
| 904 |
+ |
private void nonlocalJoinTask(ForkJoinTask<?> joinMe) { |
| 905 |
+ |
ForkJoinPool p = pool; |
| 906 |
+ |
int scans = p.parallelism; // give up if too many retries |
| 907 |
+ |
ForkJoinTask<?> bottom = null; // target seen when can't descend |
| 908 |
+ |
restart: while (joinMe.status >= 0) { |
| 909 |
+ |
ForkJoinTask<?> target = null; |
| 910 |
+ |
ForkJoinTask<?> next = joinMe; |
| 911 |
+ |
while (scans >= 0 && next != null) { |
| 912 |
+ |
--scans; |
| 913 |
+ |
target = next; |
| 914 |
+ |
next = null; |
| 915 |
+ |
ForkJoinWorkerThread v = null; |
| 916 |
+ |
ForkJoinWorkerThread[] ws = p.workers; |
| 917 |
+ |
int n = ws.length; |
| 918 |
+ |
for (int j = 0; j < n; ++j) { |
| 919 |
+ |
ForkJoinWorkerThread w = ws[j]; |
| 920 |
+ |
if (w != null && w.stolen == target) { |
| 921 |
+ |
v = w; |
| 922 |
+ |
break; |
| 923 |
+ |
} |
| 924 |
+ |
} |
| 925 |
+ |
if (v != null && v != this) { |
| 926 |
+ |
ForkJoinTask<?> prevStolen = stolen; |
| 927 |
+ |
int b; |
| 928 |
+ |
ForkJoinTask<?>[] q; |
| 929 |
+ |
while ((b = v.base) != v.sp && (q = v.queue) != null) { |
| 930 |
+ |
int i = (q.length - 1) & b; |
| 931 |
+ |
long u = (i << qShift) + qBase; |
| 932 |
+ |
ForkJoinTask<?> t = q[i]; |
| 933 |
+ |
if (target.status < 0) |
| 934 |
+ |
continue restart; |
| 935 |
+ |
if (t != null && v.base == b && |
| 936 |
+ |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 937 |
+ |
if (joinMe.status < 0) { |
| 938 |
+ |
UNSAFE.putObjectVolatile(q, u, t); |
| 939 |
+ |
return; // back out |
| 940 |
+ |
} |
| 941 |
+ |
stolen = t; |
| 942 |
+ |
v.base = b + 1; |
| 943 |
+ |
t.tryExec(); |
| 944 |
+ |
stolen = prevStolen; |
| 945 |
+ |
} |
| 946 |
+ |
if (joinMe.status < 0) |
| 947 |
+ |
return; |
| 948 |
+ |
} |
| 949 |
+ |
next = v.joining; |
| 950 |
+ |
} |
| 951 |
+ |
if (target.status < 0) |
| 952 |
+ |
continue restart; // inconsistent |
| 953 |
+ |
if (joinMe.status < 0) |
| 954 |
+ |
return; |
| 955 |
+ |
} |
| 956 |
+ |
|
| 957 |
+ |
if (bottom != target) |
| 958 |
+ |
bottom = target; // recheck landing spot |
| 959 |
+ |
else if (p.tryAwaitJoin(joinMe) < 0) |
| 960 |
+ |
return; // successfully blocked |
| 961 |
+ |
Thread.yield(); // tame spin in case too many active |
| 962 |
+ |
} |
| 963 |
+ |
} |
| 964 |
+ |
|
| 965 |
+ |
/** |
| 966 |
|
* Returns an estimate of the number of tasks, offset by a |
| 967 |
|
* function of number of idle workers. |
| 968 |
|
* |
| 1019 |
|
* @return a task, if available |
| 1020 |
|
*/ |
| 1021 |
|
final ForkJoinTask<?> pollLocalTask() { |
| 1022 |
< |
while (base != sp) { |
| 1022 |
> |
while (sp != base) { |
| 1023 |
|
if (active || (active = pool.tryIncrementActiveCount())) |
| 1024 |
|
return locallyFifo? locallyDeqTask() : popTask(); |
| 1025 |
|
} |
| 1037 |
|
} |
| 1038 |
|
|
| 1039 |
|
/** |
| 887 |
– |
* Executes or processes other tasks awaiting the given task |
| 888 |
– |
* @return task completion status |
| 889 |
– |
*/ |
| 890 |
– |
final int execWhileJoining(ForkJoinTask<?> joinMe) { |
| 891 |
– |
int s; |
| 892 |
– |
while ((s = joinMe.status) >= 0) { |
| 893 |
– |
ForkJoinTask<?> t = base != sp? |
| 894 |
– |
popWhileJoining(joinMe) : |
| 895 |
– |
scanWhileJoining(joinMe); |
| 896 |
– |
if (t != null) |
| 897 |
– |
t.tryExec(); |
| 898 |
– |
} |
| 899 |
– |
return s; |
| 900 |
– |
} |
| 901 |
– |
|
| 902 |
– |
/** |
| 903 |
– |
* Returns or stolen task, if available, unless joinMe is done |
| 904 |
– |
* |
| 905 |
– |
* This method is intrinsically nonmodular. To maintain the |
| 906 |
– |
* property that tasks are never stolen if the awaited task is |
| 907 |
– |
* ready, we must interleave mechanics of scan with status |
| 908 |
– |
* checks. We rely here on the commit points of deq that allow us |
| 909 |
– |
* to cancel a steal even after CASing slot to null, but before |
| 910 |
– |
* adjusting base index: If, after the CAS, we see that joinMe is |
| 911 |
– |
* ready, we can back out by placing the task back into the slot, |
| 912 |
– |
* without adjusting index. The loop is otherwise a variant of the |
| 913 |
– |
* one in scan(). |
| 914 |
– |
* |
| 915 |
– |
*/ |
| 916 |
– |
private ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) { |
| 917 |
– |
int r = seed; |
| 918 |
– |
ForkJoinPool p = pool; |
| 919 |
– |
ForkJoinWorkerThread[] ws; |
| 920 |
– |
int n; |
| 921 |
– |
outer:while ((ws = p.workers) != null && (n = ws.length) > 1) { |
| 922 |
– |
int mask = n - 1; |
| 923 |
– |
int k = r; |
| 924 |
– |
boolean contended = false; // to retry loop if deq contends |
| 925 |
– |
for (int j = -n; j <= n; ++j) { |
| 926 |
– |
if (joinMe.status < 0) |
| 927 |
– |
break outer; |
| 928 |
– |
int b; |
| 929 |
– |
ForkJoinTask<?>[] q; |
| 930 |
– |
ForkJoinWorkerThread v = ws[k & mask]; |
| 931 |
– |
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift |
| 932 |
– |
if (v != null && (b=v.base) != v.sp && (q=v.queue) != null) { |
| 933 |
– |
int i = (q.length - 1) & b; |
| 934 |
– |
ForkJoinTask<?> t = q[i]; |
| 935 |
– |
if (t != null && UNSAFE.compareAndSwapObject |
| 936 |
– |
(q, (i << qShift) + qBase, t, null)) { |
| 937 |
– |
if (joinMe.status >= 0) { |
| 938 |
– |
v.base = b + 1; |
| 939 |
– |
seed = r; |
| 940 |
– |
++stealCount; |
| 941 |
– |
return t; |
| 942 |
– |
} |
| 943 |
– |
UNSAFE.putObjectVolatile(q, (i<<qShift)+qBase, t); |
| 944 |
– |
break outer; // back out |
| 945 |
– |
} |
| 946 |
– |
contended = true; |
| 947 |
– |
} |
| 948 |
– |
k = j < 0 ? r : (k + ((n >>> 1) | 1)); |
| 949 |
– |
} |
| 950 |
– |
if (!contended && p.tryAwaitBusyJoin(joinMe)) |
| 951 |
– |
break; |
| 952 |
– |
} |
| 953 |
– |
return null; |
| 954 |
– |
} |
| 955 |
– |
|
| 956 |
– |
/** |
| 957 |
– |
* Version of popTask with join checks surrounding extraction. |
| 958 |
– |
* Uses the same backout strategy as helpJoinTask. Note that |
| 959 |
– |
* we ignore locallyFifo flag for local tasks here since helping |
| 960 |
– |
* joins only make sense in LIFO mode. |
| 961 |
– |
* |
| 962 |
– |
* @return a popped task, if available, unless joinMe is done |
| 963 |
– |
*/ |
| 964 |
– |
private ForkJoinTask<?> popWhileJoining(ForkJoinTask<?> joinMe) { |
| 965 |
– |
int s; |
| 966 |
– |
ForkJoinTask<?>[] q; |
| 967 |
– |
while ((s = sp) != base && (q = queue) != null && joinMe.status >= 0) { |
| 968 |
– |
int i = (q.length - 1) & --s; |
| 969 |
– |
ForkJoinTask<?> t = q[i]; |
| 970 |
– |
if (t != null && UNSAFE.compareAndSwapObject |
| 971 |
– |
(q, (i << qShift) + qBase, t, null)) { |
| 972 |
– |
if (joinMe.status >= 0) { |
| 973 |
– |
sp = s; |
| 974 |
– |
return t; |
| 975 |
– |
} |
| 976 |
– |
UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t); |
| 977 |
– |
break; // back out |
| 978 |
– |
} |
| 979 |
– |
} |
| 980 |
– |
return null; |
| 981 |
– |
} |
| 982 |
– |
|
| 983 |
– |
/** |
| 1040 |
|
* Runs tasks until {@code pool.isQuiescent()}. |
| 1041 |
|
*/ |
| 1042 |
|
final void helpQuiescePool() { |
| 1043 |
|
for (;;) { |
| 1044 |
|
ForkJoinTask<?> t = pollLocalTask(); |
| 1045 |
< |
if (t != null || (t = scan()) != null) |
| 1045 |
> |
if (t != null || (t = scan()) != null) { |
| 1046 |
|
t.tryExec(); |
| 1047 |
+ |
stolen = null; |
| 1048 |
+ |
} |
| 1049 |
|
else { |
| 1050 |
|
ForkJoinPool p = pool; |
| 1051 |
|
if (active) { |
