| 69 |
|
* <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
| 70 |
|
* </tr> |
| 71 |
|
* <tr> |
| 72 |
< |
* <td> <b>Arange async execution</td> |
| 72 |
> |
* <td> <b>Arrange async execution</td> |
| 73 |
|
* <td> {@link #execute(ForkJoinTask)}</td> |
| 74 |
|
* <td> {@link ForkJoinTask#fork}</td> |
| 75 |
|
* </tr> |
| 140 |
|
* Beyond work-stealing support and essential bookkeeping, the |
| 141 |
|
* main responsibility of this framework is to take actions when |
| 142 |
|
* one worker is waiting to join a task stolen (or always held by) |
| 143 |
< |
* another. Becauae we are multiplexing many tasks on to a pool |
| 143 |
> |
* another. Because we are multiplexing many tasks on to a pool |
| 144 |
|
* of workers, we can't just let them block (as in Thread.join). |
| 145 |
|
* We also cannot just reassign the joiner's run-time stack with |
| 146 |
|
* another and replace it later, which would be a form of |
| 157 |
|
* links to try to find such a task. |
| 158 |
|
* |
| 159 |
|
* Compensating: Unless there are already enough live threads, |
| 160 |
< |
* method helpMaintainParallelism() may create or or |
| 160 |
> |
* method helpMaintainParallelism() may create or |
| 161 |
|
* re-activate a spare thread to compensate for blocked |
| 162 |
|
* joiners until they unblock. |
| 163 |
|
* |
| 226 |
|
* ManagedBlocker), we may create or resume others to take their |
| 227 |
|
* place until they unblock (see below). Implementing this |
| 228 |
|
* requires counts of the number of "running" threads (i.e., those |
| 229 |
< |
* that are neither blocked nor artifically suspended) as well as |
| 229 |
> |
* that are neither blocked nor artificially suspended) as well as |
| 230 |
|
* the total number. These two values are packed into one field, |
| 231 |
|
* "workerCounts" because we need accurate snapshots when deciding |
| 232 |
|
* to create, resume or suspend. Note however that the |
| 233 |
< |
* correspondance of these counts to reality is not guaranteed. In |
| 233 |
> |
* correspondence of these counts to reality is not guaranteed. In |
| 234 |
|
* particular updates for unblocked threads may lag until they |
| 235 |
|
* actually wake up. |
| 236 |
|
* |
| 315 |
|
* 7. Deciding when to create new workers. The main dynamic |
| 316 |
|
* control in this class is deciding when to create extra threads |
| 317 |
|
* in method helpMaintainParallelism. We would like to keep |
| 318 |
< |
* exactly #parallelism threads running, which is an impossble |
| 318 |
> |
* exactly #parallelism threads running, which is an impossible |
| 319 |
|
* task. We always need to create one when the number of running |
| 320 |
|
* threads would become zero and all workers are busy. Beyond |
| 321 |
< |
* this, we must rely on heuristics that work well in the the |
| 322 |
< |
* presence of transients phenomena such as GC stalls, dynamic |
| 321 |
> |
* this, we must rely on heuristics that work well in the |
| 322 |
> |
* presence of transient phenomena such as GC stalls, dynamic |
| 323 |
|
* compilation, and wake-up lags. These transients are extremely |
| 324 |
|
* common -- we are normally trying to fully saturate the CPUs on |
| 325 |
|
* a machine, so almost any activity other than running tasks |
| 346 |
|
* "while ((local = field) != 0)") which are usually the simplest |
| 347 |
|
* way to ensure the required read orderings (which are sometimes |
| 348 |
|
* critical). Also several occurrences of the unusual "do {} |
| 349 |
< |
* while(!cas...)" which is the simplest way to force an update of |
| 349 |
> |
* while (!cas...)" which is the simplest way to force an update of |
| 350 |
|
* a CAS'ed variable. There are also other coding oddities that |
| 351 |
|
* help some methods perform reasonably even when interpreted (not |
| 352 |
|
* compiled), at the expense of some messy constructions that |
| 420 |
|
/** |
| 421 |
|
* The time to block in a join (see awaitJoin) before checking if |
| 422 |
|
* a new worker should be (re)started to maintain parallelism |
| 423 |
< |
* level. The value should be short enough to maintain gloabal |
| 423 |
> |
* level. The value should be short enough to maintain global |
| 424 |
|
* responsiveness and progress but long enough to avoid |
| 425 |
|
* counterproductive firings during GC stalls or unrelated system |
| 426 |
|
* activity, and to not bog down systems with continual re-firings |
| 483 |
|
private volatile long stealCount; |
| 484 |
|
|
| 485 |
|
/** |
| 486 |
< |
* Encoded record of top of treiber stack of threads waiting for |
| 486 |
> |
* Encoded record of top of Treiber stack of threads waiting for |
| 487 |
|
* events. The top 32 bits contain the count being waited for. The |
| 488 |
|
* bottom 16 bits contains one plus the pool index of waiting |
| 489 |
|
* worker thread. (Bits 16-31 are unused.) |
| 502 |
|
private volatile int eventCount; |
| 503 |
|
|
| 504 |
|
/** |
| 505 |
< |
* Encoded record of top of treiber stack of spare threads waiting |
| 505 |
> |
* Encoded record of top of Treiber stack of spare threads waiting |
| 506 |
|
* for resumption. The top 16 bits contain an arbitrary count to |
| 507 |
|
* avoid ABA effects. The bottom 16bits contains one plus the pool |
| 508 |
|
* index of waiting worker thread. |
| 678 |
|
*/ |
| 679 |
|
private void forgetWorker(ForkJoinWorkerThread w) { |
| 680 |
|
int idx = w.poolIndex; |
| 681 |
< |
// Locking helps method recordWorker avoid unecessary expansion |
| 681 |
> |
// Locking helps method recordWorker avoid unnecessary expansion |
| 682 |
|
final ReentrantLock lock = this.workerLock; |
| 683 |
|
lock.lock(); |
| 684 |
|
try { |
| 693 |
|
/** |
| 694 |
|
* Final callback from terminating worker. Removes record of |
| 695 |
|
* worker from array, and adjusts counts. If pool is shutting |
| 696 |
< |
* down, tries to complete terminatation. |
| 696 |
> |
* down, tries to complete termination. |
| 697 |
|
* |
| 698 |
|
* @param w the worker |
| 699 |
|
*/ |
| 832 |
|
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
| 833 |
|
sw, w.nextSpare)) { |
| 834 |
|
int c; // increment running count before resume |
| 835 |
< |
do {} while(!UNSAFE.compareAndSwapInt |
| 836 |
< |
(this, workerCountsOffset, |
| 837 |
< |
c = workerCounts, c + ONE_RUNNING)); |
| 835 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
| 836 |
> |
(this, workerCountsOffset, |
| 837 |
> |
c = workerCounts, c + ONE_RUNNING)); |
| 838 |
|
if (w.tryUnsuspend()) |
| 839 |
|
LockSupport.unpark(w); |
| 840 |
|
else // back out if w was shutdown |
| 846 |
|
* Tries to increase the number of running workers if below target |
| 847 |
|
* parallelism: If a spare exists tries to resume it via |
| 848 |
|
* tryResumeSpare. Otherwise, if not enough total workers or all |
| 849 |
< |
* existing workers are busy, adds a new worker. In all casses also |
| 849 |
> |
* existing workers are busy, adds a new worker. In all cases also |
| 850 |
|
* helps wake up releasable workers waiting for work. |
| 851 |
|
*/ |
| 852 |
|
private void helpMaintainParallelism() { |
| 985 |
|
w.lastEventCount = ec; // no need to wait |
| 986 |
|
break; |
| 987 |
|
} |
| 988 |
< |
else if (!(inactivate |= active)) |
| 988 |
> |
else if (!(inactivate |= active)) |
| 989 |
|
eventSync(w, wec); // must inactivate before sync |
| 990 |
|
} |
| 991 |
|
else |
| 1174 |
|
*/ |
| 1175 |
|
final int idlePerActive() { |
| 1176 |
|
int pc = parallelism; // use parallelism, not rc |
| 1177 |
< |
int ac = runState; // no mask -- artifically boosts during shutdown |
| 1177 |
> |
int ac = runState; // no mask -- artificially boosts during shutdown |
| 1178 |
|
// Use exact results for small values, saturate past 4 |
| 1179 |
|
return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3; |
| 1180 |
|
} |
| 1721 |
|
throws InterruptedException { |
| 1722 |
|
try { |
| 1723 |
|
return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
| 1724 |
< |
} catch(TimeoutException ex) { |
| 1724 |
> |
} catch (TimeoutException ex) { |
| 1725 |
|
return false; |
| 1726 |
|
} |
| 1727 |
|
} |
