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package jsr166y; |
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import java.util.concurrent.*; |
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import java.util.ArrayList; |
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import java.util.Arrays; |
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import java.util.Collection; |
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import java.util.Collections; |
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import java.util.List; |
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import java.util.concurrent.AbstractExecutorService; |
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import java.util.concurrent.Callable; |
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import java.util.concurrent.CountDownLatch; |
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import java.util.concurrent.ExecutorService; |
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import java.util.concurrent.Future; |
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import java.util.concurrent.RejectedExecutionException; |
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import java.util.concurrent.RunnableFuture; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.TimeoutException; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.locks.LockSupport; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.CountDownLatch; |
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
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* links to try to find such a task. |
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* |
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* Compensating: Unless there are already enough live threads, |
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* method helpMaintainParallelism() may create or or |
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* method helpMaintainParallelism() may create or |
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* re-activate a spare thread to compensate for blocked |
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* joiners until they unblock. |
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* |
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* about the same time as another is needlessly being created. We |
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* counteract this and related slop in part by requiring resumed |
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* spares to immediately recheck (in preStep) to see whether they |
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* they should re-suspend. |
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* should re-suspend. |
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* |
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* 6. Killing off unneeded workers. A timeout mechanism is used to |
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* shed unused workers: The oldest (first) event queue waiter uses |
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* exactly #parallelism threads running, which is an impossible |
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* task. We always need to create one when the number of running |
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* threads would become zero and all workers are busy. Beyond |
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* this, we must rely on heuristics that work well in the the |
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* presence of transients phenomena such as GC stalls, dynamic |
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* this, we must rely on heuristics that work well in the |
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* presence of transient phenomena such as GC stalls, dynamic |
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* compilation, and wake-up lags. These transients are extremely |
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* common -- we are normally trying to fully saturate the CPUs on |
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* a machine, so almost any activity other than running tasks |
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* "while ((local = field) != 0)") which are usually the simplest |
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* way to ensure the required read orderings (which are sometimes |
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* critical). Also several occurrences of the unusual "do {} |
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* while(!cas...)" which is the simplest way to force an update of |
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* while (!cas...)" which is the simplest way to force an update of |
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* a CAS'ed variable. There are also other coding oddities that |
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* help some methods perform reasonably even when interpreted (not |
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* compiled), at the expense of some messy constructions that |
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/** |
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* The wakeup interval (in nanoseconds) for the oldest worker |
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* worker waiting for an event invokes tryShutdownUnusedWorker to shrink |
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* the number of workers. The exact value does not matter too |
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* much, but should be long enough to slowly release resources |
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* during long periods without use without disrupting normal use. |
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* waiting for an event to invoke tryShutdownUnusedWorker to |
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* shrink the number of workers. The exact value does not matter |
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* too much. It must be short enough to release resources during |
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* sustained periods of idleness, but not so short that threads |
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* are continually re-created. |
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*/ |
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private static final long SHRINK_RATE_NANOS = |
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30L * 1000L * 1000L * 1000L; // 2 per minute |
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* Lifecycle control. The low word contains the number of workers |
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* that are (probably) executing tasks. This value is atomically |
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* incremented before a worker gets a task to run, and decremented |
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* when worker has no tasks and cannot find any. Bits 16-18 |
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* when a worker has no tasks and cannot find any. Bits 16-18 |
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* contain runLevel value. When all are zero, the pool is |
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* running. Level transitions are monotonic (running -> shutdown |
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* -> terminating -> terminated) so each transition adds a bit. |
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* (rarely) necessary when other count updates lag. |
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* |
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* @param dr -- either zero or ONE_RUNNING |
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* @param dt == either zero or ONE_TOTAL |
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* @param dt -- either zero or ONE_TOTAL |
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*/ |
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private void decrementWorkerCounts(int dr, int dt) { |
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for (;;) { |
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} |
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/** |
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* Nulls out record of worker in workers array |
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* Nulls out record of worker in workers array. |
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*/ |
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private void forgetWorker(ForkJoinWorkerThread w) { |
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int idx = w.poolIndex; |
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// Maintaining parallelism |
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/** |
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* Pushes worker onto the spare stack |
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* Pushes worker onto the spare stack. |
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*/ |
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final void pushSpare(ForkJoinWorkerThread w) { |
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int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1); |
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UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
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sw, w.nextSpare)) { |
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int c; // increment running count before resume |
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do {} while(!UNSAFE.compareAndSwapInt |
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(this, workerCountsOffset, |
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c = workerCounts, c + ONE_RUNNING)); |
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do {} while (!UNSAFE.compareAndSwapInt |
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(this, workerCountsOffset, |
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c = workerCounts, c + ONE_RUNNING)); |
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if (w.tryUnsuspend()) |
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LockSupport.unpark(w); |
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else // back out if w was shutdown |
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w.lastEventCount = ec; // no need to wait |
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break; |
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} |
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else if (!(inactivate |= active)) |
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else if (!(inactivate |= active)) |
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eventSync(w, wec); // must inactivate before sync |
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} |
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else |
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c = eventCount, c+1); |
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eventWaiters = 0L; // clobber lists |
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spareWaiters = 0; |
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ForkJoinWorkerThread[] ws = workers; |
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int n = ws.length; |
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for (int i = 0; i < n; ++i) { |
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ForkJoinWorkerThread w = ws[i]; |
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for (ForkJoinWorkerThread w : workers) { |
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if (w != null) { |
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w.shutdown(); |
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if (passes > 0 && !w.isTerminated()) { |
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} |
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/** |
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* Clear out and cancel submissions, ignoring exceptions |
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* Clears out and cancels submissions, ignoring exceptions. |
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*/ |
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private void cancelSubmissions() { |
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ForkJoinTask<?> task; |
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// misc support for ForkJoinWorkerThread |
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/** |
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* Returns pool number |
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* Returns pool number. |
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*/ |
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final int getPoolNumber() { |
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return poolNumber; |
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} |
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/** |
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* Tries to accumulates steal count from a worker, clearing |
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* the worker's value. |
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* Tries to accumulate steal count from a worker, clearing |
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* the worker's value if successful. |
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* |
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* @return true if worker steal count now zero |
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*/ |
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int pc = parallelism; // use parallelism, not rc |
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int ac = runState; // no mask -- artificially boosts during shutdown |
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// Use exact results for small values, saturate past 4 |
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return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3; |
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return ((pc <= ac) ? 0 : |
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(pc >>> 1 <= ac) ? 1 : |
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(pc >>> 2 <= ac) ? 3 : |
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pc >>> 3); |
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} |
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// Public and protected methods |
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* use {@link #defaultForkJoinWorkerThreadFactory}. |
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* @param handler the handler for internal worker threads that |
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* terminate due to unrecoverable errors encountered while executing |
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* tasks. For default value, use <code>null</code>. |
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* tasks. For default value, use {@code null}. |
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* @param asyncMode if true, |
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* establishes local first-in-first-out scheduling mode for forked |
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* tasks that are never joined. This mode may be more appropriate |
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* than default locally stack-based mode in applications in which |
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* worker threads only process event-style asynchronous tasks. |
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* For default value, use <code>false</code>. |
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* For default value, use {@code false}. |
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* @throws IllegalArgumentException if parallelism less than or |
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* equal to zero, or greater than implementation limit |
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* @throws NullPointerException if the factory is null |
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/** |
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* Returns the number of worker threads that have started but not |
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* yet terminated. This result returned by this method may differ |
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* yet terminated. The result returned by this method may differ |
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* from {@link #getParallelism} when threads are created to |
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* maintain parallelism when others are cooperatively blocked. |
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* |
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*/ |
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public long getQueuedTaskCount() { |
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long count = 0; |
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ForkJoinWorkerThread[] ws = workers; |
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int n = ws.length; |
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for (int i = 0; i < n; ++i) { |
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ForkJoinWorkerThread w = ws[i]; |
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for (ForkJoinWorkerThread w : workers) |
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if (w != null) |
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count += w.getQueueSize(); |
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} |
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return count; |
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} |
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*/ |
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protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
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int count = submissionQueue.drainTo(c); |
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ForkJoinWorkerThread[] ws = workers; |
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int n = ws.length; |
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for (int i = 0; i < n; ++i) { |
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ForkJoinWorkerThread w = ws[i]; |
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for (ForkJoinWorkerThread w : workers) |
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if (w != null) |
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count += w.drainTasksTo(c); |
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} |
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return count; |
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} |
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throws InterruptedException { |
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try { |
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return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
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} catch(TimeoutException ex) { |
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} catch (TimeoutException ex) { |
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return false; |
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} |
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} |
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private static final long eventCountOffset = |
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objectFieldOffset("eventCount", ForkJoinPool.class); |
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private static final long eventWaitersOffset = |
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objectFieldOffset("eventWaiters",ForkJoinPool.class); |
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objectFieldOffset("eventWaiters", ForkJoinPool.class); |
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private static final long stealCountOffset = |
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objectFieldOffset("stealCount",ForkJoinPool.class); |
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objectFieldOffset("stealCount", ForkJoinPool.class); |
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private static final long spareWaitersOffset = |
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objectFieldOffset("spareWaiters",ForkJoinPool.class); |
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objectFieldOffset("spareWaiters", ForkJoinPool.class); |
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private static long objectFieldOffset(String field, Class<?> klazz) { |
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try { |
