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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.concurrent.atomic.*; |
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import java.util.concurrent.locks.*; |
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import java.util.*; |
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|
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/** |
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* A {@link ThreadPoolExecutor} that can additionally schedule |
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* commands to run after a given delay, or to execute |
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* periodically. This class is preferable to {@link java.util.Timer} |
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* when multiple worker threads are needed, or when the additional |
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* flexibility or capabilities of {@link ThreadPoolExecutor} (which |
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* this class extends) are required. |
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* |
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* <p>Delayed tasks execute no sooner than they are enabled, but |
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* without any real-time guarantees about when, after they are |
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* enabled, they will commence. Tasks scheduled for exactly the same |
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* execution time are enabled in first-in-first-out (FIFO) order of |
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* submission. |
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* |
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* <p>When a submitted task is cancelled before it is run, execution |
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* is suppressed. By default, such a cancelled task is not |
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* automatically removed from the work queue until its delay |
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* elapses. While this enables further inspection and monitoring, it |
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* may also cause unbounded retention of cancelled tasks. To avoid |
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* this, set {@link #setRemoveOnCancelPolicy} to {@code true}, which |
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* causes tasks to be immediately removed from the work queue at |
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* time of cancellation. |
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* |
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* <p>While this class inherits from {@link ThreadPoolExecutor}, a few |
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* of the inherited tuning methods are not useful for it. In |
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* particular, because it acts as a fixed-sized pool using |
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* {@code corePoolSize} threads and an unbounded queue, adjustments |
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* to {@code maximumPoolSize} have no useful effect. Additionally, it |
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* is almost never a good idea to set {@code corePoolSize} to zero or |
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* use {@code allowCoreThreadTimeOut} because this may leave the pool |
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* without threads to handle tasks once they become eligible to run. |
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* |
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* <p><b>Extension notes:</b> This class overrides the |
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* {@link ThreadPoolExecutor#execute execute} and |
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* {@link AbstractExecutorService#submit(Runnable) submit} |
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* methods to generate internal {@link ScheduledFuture} objects to |
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* control per-task delays and scheduling. To preserve |
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* functionality, any further overrides of these methods in |
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* subclasses must invoke superclass versions, which effectively |
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* disables additional task customization. However, this class |
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* provides alternative protected extension method |
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* {@code decorateTask} (one version each for {@code Runnable} and |
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* {@code Callable}) that can be used to customize the concrete task |
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* types used to execute commands entered via {@code execute}, |
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* {@code submit}, {@code schedule}, {@code scheduleAtFixedRate}, |
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* and {@code scheduleWithFixedDelay}. By default, a |
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* {@code ScheduledThreadPoolExecutor} uses a task type extending |
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* {@link FutureTask}. However, this may be modified or replaced using |
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* subclasses of the form: |
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* |
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* <pre> {@code |
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* public class CustomScheduledExecutor extends ScheduledThreadPoolExecutor { |
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* |
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* static class CustomTask<V> implements RunnableScheduledFuture<V> { ... } |
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* |
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* protected <V> RunnableScheduledFuture<V> decorateTask( |
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* Runnable r, RunnableScheduledFuture<V> task) { |
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* return new CustomTask<V>(r, task); |
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* } |
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* |
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* protected <V> RunnableScheduledFuture<V> decorateTask( |
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* Callable<V> c, RunnableScheduledFuture<V> task) { |
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* return new CustomTask<V>(c, task); |
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* } |
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* // ... add constructors, etc. |
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* }}</pre> |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class ScheduledThreadPoolExecutor |
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extends ThreadPoolExecutor |
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implements ScheduledExecutorService { |
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|
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/* |
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* This class specializes ThreadPoolExecutor implementation by |
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* |
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* 1. Using a custom task type, ScheduledFutureTask for |
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* tasks, even those that don't require scheduling (i.e., |
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* those submitted using ExecutorService execute, not |
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* ScheduledExecutorService methods) which are treated as |
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* delayed tasks with a delay of zero. |
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* |
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* 2. Using a custom queue (DelayedWorkQueue), a variant of |
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* unbounded DelayQueue. The lack of capacity constraint and |
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* the fact that corePoolSize and maximumPoolSize are |
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* effectively identical simplifies some execution mechanics |
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* (see delayedExecute) compared to ThreadPoolExecutor. |
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* |
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* 3. Supporting optional run-after-shutdown parameters, which |
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* leads to overrides of shutdown methods to remove and cancel |
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* tasks that should NOT be run after shutdown, as well as |
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* different recheck logic when task (re)submission overlaps |
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* with a shutdown. |
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* |
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* 4. Task decoration methods to allow interception and |
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* instrumentation, which are needed because subclasses cannot |
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* otherwise override submit methods to get this effect. These |
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* don't have any impact on pool control logic though. |
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*/ |
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|
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/** |
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* False if should cancel/suppress periodic tasks on shutdown. |
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*/ |
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private volatile boolean continueExistingPeriodicTasksAfterShutdown; |
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|
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/** |
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* False if should cancel non-periodic tasks on shutdown. |
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*/ |
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private volatile boolean executeExistingDelayedTasksAfterShutdown = true; |
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|
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/** |
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* True if ScheduledFutureTask.cancel should remove from queue |
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*/ |
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private volatile boolean removeOnCancel = false; |
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|
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/** |
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* Sequence number to break scheduling ties, and in turn to |
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* guarantee FIFO order among tied entries. |
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*/ |
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private static final AtomicLong sequencer = new AtomicLong(0); |
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|
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/** |
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* Returns current nanosecond time. |
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*/ |
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final long now() { |
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return System.nanoTime(); |
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} |
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|
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private class ScheduledFutureTask<V> |
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extends FutureTask<V> implements RunnableScheduledFuture<V> { |
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|
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/** Sequence number to break ties FIFO */ |
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private final long sequenceNumber; |
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|
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/** The time the task is enabled to execute in nanoTime units */ |
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private long time; |
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|
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/** |
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* Period in nanoseconds for repeating tasks. A positive |
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* value indicates fixed-rate execution. A negative value |
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* indicates fixed-delay execution. A value of 0 indicates a |
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* non-repeating task. |
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*/ |
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private final long period; |
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|
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/** The actual task to be re-enqueued by reExecutePeriodic */ |
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RunnableScheduledFuture<V> outerTask = this; |
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|
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/** |
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* Index into delay queue, to support faster cancellation. |
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*/ |
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int heapIndex; |
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|
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/** |
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* Creates a one-shot action with given nanoTime-based trigger time. |
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*/ |
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ScheduledFutureTask(Runnable r, V result, long ns) { |
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super(r, result); |
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this.time = ns; |
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this.period = 0; |
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this.sequenceNumber = sequencer.getAndIncrement(); |
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} |
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|
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/** |
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* Creates a periodic action with given nano time and period. |
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*/ |
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ScheduledFutureTask(Runnable r, V result, long ns, long period) { |
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super(r, result); |
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this.time = ns; |
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this.period = period; |
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this.sequenceNumber = sequencer.getAndIncrement(); |
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} |
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|
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/** |
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* Creates a one-shot action with given nanoTime-based trigger. |
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*/ |
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ScheduledFutureTask(Callable<V> callable, long ns) { |
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super(callable); |
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this.time = ns; |
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this.period = 0; |
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this.sequenceNumber = sequencer.getAndIncrement(); |
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} |
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|
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public long getDelay(TimeUnit unit) { |
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long d = unit.convert(time - now(), TimeUnit.NANOSECONDS); |
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return d; |
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} |
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|
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public int compareTo(Delayed other) { |
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if (other == this) // compare zero ONLY if same object |
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return 0; |
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if (other instanceof ScheduledFutureTask) { |
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ScheduledFutureTask<?> x = (ScheduledFutureTask<?>)other; |
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long diff = time - x.time; |
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if (diff < 0) |
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return -1; |
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else if (diff > 0) |
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return 1; |
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else if (sequenceNumber < x.sequenceNumber) |
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return -1; |
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else |
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return 1; |
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} |
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long d = (getDelay(TimeUnit.NANOSECONDS) - |
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other.getDelay(TimeUnit.NANOSECONDS)); |
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return (d == 0) ? 0 : ((d < 0) ? -1 : 1); |
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} |
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|
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/** |
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* Returns true if this is a periodic (not a one-shot) action. |
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* |
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* @return true if periodic |
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*/ |
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public boolean isPeriodic() { |
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return period != 0; |
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} |
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|
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/** |
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* Sets the next time to run for a periodic task. |
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*/ |
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private void setNextRunTime() { |
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long p = period; |
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if (p > 0) |
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time += p; |
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else |
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time = now() - p; |
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} |
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|
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public boolean cancel(boolean mayInterruptIfRunning) { |
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boolean cancelled = super.cancel(mayInterruptIfRunning); |
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if (cancelled && removeOnCancel && heapIndex >= 0) |
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remove(this); |
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return cancelled; |
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} |
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|
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/** |
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* Overrides FutureTask version so as to reset/requeue if periodic. |
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*/ |
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public void run() { |
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boolean periodic = isPeriodic(); |
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if (!canRunInCurrentRunState(periodic)) |
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cancel(false); |
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else if (!periodic) |
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ScheduledFutureTask.super.run(); |
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else if (ScheduledFutureTask.super.runAndReset()) { |
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setNextRunTime(); |
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reExecutePeriodic(outerTask); |
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} |
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} |
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} |
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|
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/** |
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* Returns true if can run a task given current run state |
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* and run-after-shutdown parameters. |
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* |
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* @param periodic true if this task periodic, false if delayed |
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*/ |
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boolean canRunInCurrentRunState(boolean periodic) { |
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return isRunningOrShutdown(periodic ? |
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continueExistingPeriodicTasksAfterShutdown : |
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executeExistingDelayedTasksAfterShutdown); |
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} |
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|
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/** |
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* Main execution method for delayed or periodic tasks. If pool |
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* is shut down, rejects the task. Otherwise adds task to queue |
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* and starts a thread, if necessary, to run it. (We cannot |
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* prestart the thread to run the task because the task (probably) |
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* shouldn't be run yet,) If the pool is shut down while the task |
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* is being added, cancel and remove it if required by state and |
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* run-after-shutdown parameters. |
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* |
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* @param task the task |
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*/ |
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private void delayedExecute(RunnableScheduledFuture<?> task) { |
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if (isShutdown()) |
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reject(task); |
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else { |
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super.getQueue().add(task); |
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if (isShutdown() && |
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!canRunInCurrentRunState(task.isPeriodic()) && |
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remove(task)) |
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task.cancel(false); |
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else |
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prestartCoreThread(); |
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} |
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} |
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|
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/** |
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* Requeues a periodic task unless current run state precludes it. |
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* Same idea as delayedExecute except drops task rather than rejecting. |
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* |
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* @param task the task |
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*/ |
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void reExecutePeriodic(RunnableScheduledFuture<?> task) { |
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if (canRunInCurrentRunState(true)) { |
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super.getQueue().add(task); |
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if (!canRunInCurrentRunState(true) && remove(task)) |
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task.cancel(false); |
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else |
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prestartCoreThread(); |
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} |
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} |
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|
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/** |
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* Cancels and clears the queue of all tasks that should not be run |
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* due to shutdown policy. Invoked within super.shutdown. |
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*/ |
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@Override void onShutdown() { |
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BlockingQueue<Runnable> q = super.getQueue(); |
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boolean keepDelayed = |
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getExecuteExistingDelayedTasksAfterShutdownPolicy(); |
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boolean keepPeriodic = |
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getContinueExistingPeriodicTasksAfterShutdownPolicy(); |
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if (!keepDelayed && !keepPeriodic) |
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q.clear(); |
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else { |
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// Traverse snapshot to avoid iterator exceptions |
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for (Object e : q.toArray()) { |
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if (e instanceof RunnableScheduledFuture) { |
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RunnableScheduledFuture<?> t = |
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(RunnableScheduledFuture<?>)e; |
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if ((t.isPeriodic() ? !keepPeriodic : !keepDelayed) || |
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t.isCancelled()) { // also remove if already cancelled |
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if (q.remove(t)) |
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t.cancel(false); |
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} |
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} |
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} |
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} |
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tryTerminate(); |
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} |
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|
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/** |
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* Modifies or replaces the task used to execute a runnable. |
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* This method can be used to override the concrete |
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* class used for managing internal tasks. |
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* The default implementation simply returns the given task. |
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* |
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* @param runnable the submitted Runnable |
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* @param task the task created to execute the runnable |
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* @return a task that can execute the runnable |
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* @since 1.6 |
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*/ |
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protected <V> RunnableScheduledFuture<V> decorateTask( |
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Runnable runnable, RunnableScheduledFuture<V> task) { |
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return task; |
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} |
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|
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/** |
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* Modifies or replaces the task used to execute a callable. |
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* This method can be used to override the concrete |
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* class used for managing internal tasks. |
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* The default implementation simply returns the given task. |
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* |
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* @param callable the submitted Callable |
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* @param task the task created to execute the callable |
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* @return a task that can execute the callable |
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* @since 1.6 |
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*/ |
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protected <V> RunnableScheduledFuture<V> decorateTask( |
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Callable<V> callable, RunnableScheduledFuture<V> task) { |
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return task; |
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} |
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|
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/** |
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* Creates a new {@code ScheduledThreadPoolExecutor} with the |
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* given core pool size. |
381 |
* |
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* @param corePoolSize the number of threads to keep in the pool, even |
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* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
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* @throws IllegalArgumentException if {@code corePoolSize < 0} |
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*/ |
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public ScheduledThreadPoolExecutor(int corePoolSize) { |
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super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
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new DelayedWorkQueue()); |
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} |
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|
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/** |
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* Creates a new {@code ScheduledThreadPoolExecutor} with the |
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* given initial parameters. |
394 |
* |
395 |
* @param corePoolSize the number of threads to keep in the pool, even |
396 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
397 |
* @param threadFactory the factory to use when the executor |
398 |
* creates a new thread |
399 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
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* @throws NullPointerException if {@code threadFactory} is null |
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*/ |
402 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
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ThreadFactory threadFactory) { |
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super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
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new DelayedWorkQueue(), threadFactory); |
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} |
407 |
|
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/** |
409 |
* Creates a new ScheduledThreadPoolExecutor with the given |
410 |
* initial parameters. |
411 |
* |
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* @param corePoolSize the number of threads to keep in the pool, even |
413 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
414 |
* @param handler the handler to use when execution is blocked |
415 |
* because the thread bounds and queue capacities are reached |
416 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
417 |
* @throws NullPointerException if {@code handler} is null |
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*/ |
419 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
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RejectedExecutionHandler handler) { |
421 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
422 |
new DelayedWorkQueue(), handler); |
423 |
} |
424 |
|
425 |
/** |
426 |
* Creates a new ScheduledThreadPoolExecutor with the given |
427 |
* initial parameters. |
428 |
* |
429 |
* @param corePoolSize the number of threads to keep in the pool, even |
430 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
431 |
* @param threadFactory the factory to use when the executor |
432 |
* creates a new thread |
433 |
* @param handler the handler to use when execution is blocked |
434 |
* because the thread bounds and queue capacities are reached |
435 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
436 |
* @throws NullPointerException if {@code threadFactory} or |
437 |
* {@code handler} is null |
438 |
*/ |
439 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
440 |
ThreadFactory threadFactory, |
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RejectedExecutionHandler handler) { |
442 |
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
443 |
new DelayedWorkQueue(), threadFactory, handler); |
444 |
} |
445 |
|
446 |
/** |
447 |
* @throws RejectedExecutionException {@inheritDoc} |
448 |
* @throws NullPointerException {@inheritDoc} |
449 |
*/ |
450 |
public ScheduledFuture<?> schedule(Runnable command, |
451 |
long delay, |
452 |
TimeUnit unit) { |
453 |
if (command == null || unit == null) |
454 |
throw new NullPointerException(); |
455 |
if (delay < 0) delay = 0; |
456 |
long triggerTime = now() + unit.toNanos(delay); |
457 |
RunnableScheduledFuture<?> t = decorateTask(command, |
458 |
new ScheduledFutureTask<Void>(command, null, triggerTime)); |
459 |
delayedExecute(t); |
460 |
return t; |
461 |
} |
462 |
|
463 |
/** |
464 |
* @throws RejectedExecutionException {@inheritDoc} |
465 |
* @throws NullPointerException {@inheritDoc} |
466 |
*/ |
467 |
public <V> ScheduledFuture<V> schedule(Callable<V> callable, |
468 |
long delay, |
469 |
TimeUnit unit) { |
470 |
if (callable == null || unit == null) |
471 |
throw new NullPointerException(); |
472 |
if (delay < 0) delay = 0; |
473 |
long triggerTime = now() + unit.toNanos(delay); |
474 |
RunnableScheduledFuture<V> t = decorateTask(callable, |
475 |
new ScheduledFutureTask<V>(callable, triggerTime)); |
476 |
delayedExecute(t); |
477 |
return t; |
478 |
} |
479 |
|
480 |
/** |
481 |
* @throws RejectedExecutionException {@inheritDoc} |
482 |
* @throws NullPointerException {@inheritDoc} |
483 |
* @throws IllegalArgumentException {@inheritDoc} |
484 |
*/ |
485 |
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, |
486 |
long initialDelay, |
487 |
long period, |
488 |
TimeUnit unit) { |
489 |
if (command == null || unit == null) |
490 |
throw new NullPointerException(); |
491 |
if (period <= 0) |
492 |
throw new IllegalArgumentException(); |
493 |
if (initialDelay < 0) initialDelay = 0; |
494 |
long triggerTime = now() + unit.toNanos(initialDelay); |
495 |
ScheduledFutureTask<Void> sft = |
496 |
new ScheduledFutureTask<Void>(command, |
497 |
null, |
498 |
triggerTime, |
499 |
unit.toNanos(period)); |
500 |
RunnableScheduledFuture<Void> t = decorateTask(command, sft); |
501 |
sft.outerTask = t; |
502 |
delayedExecute(t); |
503 |
return t; |
504 |
} |
505 |
|
506 |
/** |
507 |
* @throws RejectedExecutionException {@inheritDoc} |
508 |
* @throws NullPointerException {@inheritDoc} |
509 |
* @throws IllegalArgumentException {@inheritDoc} |
510 |
*/ |
511 |
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, |
512 |
long initialDelay, |
513 |
long delay, |
514 |
TimeUnit unit) { |
515 |
if (command == null || unit == null) |
516 |
throw new NullPointerException(); |
517 |
if (delay <= 0) |
518 |
throw new IllegalArgumentException(); |
519 |
if (initialDelay < 0) initialDelay = 0; |
520 |
long triggerTime = now() + unit.toNanos(initialDelay); |
521 |
ScheduledFutureTask<Void> sft = |
522 |
new ScheduledFutureTask<Void>(command, |
523 |
null, |
524 |
triggerTime, |
525 |
unit.toNanos(-delay)); |
526 |
RunnableScheduledFuture<Void> t = decorateTask(command, sft); |
527 |
sft.outerTask = t; |
528 |
delayedExecute(t); |
529 |
return t; |
530 |
} |
531 |
|
532 |
/** |
533 |
* Executes {@code command} with zero required delay. |
534 |
* This has effect equivalent to |
535 |
* {@link #schedule(Runnable,long,TimeUnit) schedule(command, 0, anyUnit)}. |
536 |
* Note that inspections of the queue and of the list returned by |
537 |
* {@code shutdownNow} will access the zero-delayed |
538 |
* {@link ScheduledFuture}, not the {@code command} itself. |
539 |
* |
540 |
* <p>A consequence of the use of {@code ScheduledFuture} objects is |
541 |
* that {@link ThreadPoolExecutor#afterExecute afterExecute} is always |
542 |
* called with a null second {@code Throwable} argument, even if the |
543 |
* {@code command} terminated abruptly. Instead, the {@code Throwable} |
544 |
* thrown by such a task can be obtained via {@link Future#get}. |
545 |
* |
546 |
* @throws RejectedExecutionException at discretion of |
547 |
* {@code RejectedExecutionHandler}, if the task |
548 |
* cannot be accepted for execution because the |
549 |
* executor has been shut down |
550 |
* @throws NullPointerException {@inheritDoc} |
551 |
*/ |
552 |
public void execute(Runnable command) { |
553 |
schedule(command, 0, TimeUnit.NANOSECONDS); |
554 |
} |
555 |
|
556 |
// Override AbstractExecutorService methods |
557 |
|
558 |
/** |
559 |
* @throws RejectedExecutionException {@inheritDoc} |
560 |
* @throws NullPointerException {@inheritDoc} |
561 |
*/ |
562 |
public Future<?> submit(Runnable task) { |
563 |
return schedule(task, 0, TimeUnit.NANOSECONDS); |
564 |
} |
565 |
|
566 |
/** |
567 |
* @throws RejectedExecutionException {@inheritDoc} |
568 |
* @throws NullPointerException {@inheritDoc} |
569 |
*/ |
570 |
public <T> Future<T> submit(Runnable task, T result) { |
571 |
return schedule(Executors.callable(task, result), |
572 |
0, TimeUnit.NANOSECONDS); |
573 |
} |
574 |
|
575 |
/** |
576 |
* @throws RejectedExecutionException {@inheritDoc} |
577 |
* @throws NullPointerException {@inheritDoc} |
578 |
*/ |
579 |
public <T> Future<T> submit(Callable<T> task) { |
580 |
return schedule(task, 0, TimeUnit.NANOSECONDS); |
581 |
} |
582 |
|
583 |
/** |
584 |
* Sets the policy on whether to continue executing existing |
585 |
* periodic tasks even when this executor has been {@code shutdown}. |
586 |
* In this case, these tasks will only terminate upon |
587 |
* {@code shutdownNow} or after setting the policy to |
588 |
* {@code false} when already shutdown. |
589 |
* This value is by default {@code false}. |
590 |
* |
591 |
* @param value if {@code true}, continue after shutdown, else don't. |
592 |
* @see #getContinueExistingPeriodicTasksAfterShutdownPolicy |
593 |
*/ |
594 |
public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) { |
595 |
continueExistingPeriodicTasksAfterShutdown = value; |
596 |
if (!value && isShutdown()) |
597 |
onShutdown(); |
598 |
} |
599 |
|
600 |
/** |
601 |
* Gets the policy on whether to continue executing existing |
602 |
* periodic tasks even when this executor has been {@code shutdown}. |
603 |
* In this case, these tasks will only terminate upon |
604 |
* {@code shutdownNow} or after setting the policy to |
605 |
* {@code false} when already shutdown. |
606 |
* This value is by default {@code false}. |
607 |
* |
608 |
* @return {@code true} if will continue after shutdown |
609 |
* @see #setContinueExistingPeriodicTasksAfterShutdownPolicy |
610 |
*/ |
611 |
public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() { |
612 |
return continueExistingPeriodicTasksAfterShutdown; |
613 |
} |
614 |
|
615 |
/** |
616 |
* Sets the policy on whether to execute existing delayed |
617 |
* tasks even when this executor has been {@code shutdown}. |
618 |
* In this case, these tasks will only terminate upon |
619 |
* {@code shutdownNow}, or after setting the policy to |
620 |
* {@code false} when already shutdown. |
621 |
* This value is by default {@code true}. |
622 |
* |
623 |
* @param value if {@code true}, execute after shutdown, else don't. |
624 |
* @see #getExecuteExistingDelayedTasksAfterShutdownPolicy |
625 |
*/ |
626 |
public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) { |
627 |
executeExistingDelayedTasksAfterShutdown = value; |
628 |
if (!value && isShutdown()) |
629 |
onShutdown(); |
630 |
} |
631 |
|
632 |
/** |
633 |
* Gets the policy on whether to execute existing delayed |
634 |
* tasks even when this executor has been {@code shutdown}. |
635 |
* In this case, these tasks will only terminate upon |
636 |
* {@code shutdownNow}, or after setting the policy to |
637 |
* {@code false} when already shutdown. |
638 |
* This value is by default {@code true}. |
639 |
* |
640 |
* @return {@code true} if will execute after shutdown |
641 |
* @see #setExecuteExistingDelayedTasksAfterShutdownPolicy |
642 |
*/ |
643 |
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() { |
644 |
return executeExistingDelayedTasksAfterShutdown; |
645 |
} |
646 |
|
647 |
/** |
648 |
* Sets the policy on whether cancelled tasks should be immediately |
649 |
* removed from the work queue at time of cancellation. This value is |
650 |
* by default {@code false}. |
651 |
* |
652 |
* @param value if {@code true}, remove on cancellation, else don't |
653 |
* @see #getRemoveOnCancelPolicy |
654 |
* @since 1.7 |
655 |
*/ |
656 |
public void setRemoveOnCancelPolicy(boolean value) { |
657 |
removeOnCancel = value; |
658 |
} |
659 |
|
660 |
/** |
661 |
* Gets the policy on whether cancelled tasks should be immediately |
662 |
* removed from the work queue at time of cancellation. This value is |
663 |
* by default {@code false}. |
664 |
* |
665 |
* @return {@code true} if cancelled tasks are immediately removed |
666 |
* from the queue |
667 |
* @see #setRemoveOnCancelPolicy |
668 |
* @since 1.7 |
669 |
*/ |
670 |
public boolean getRemoveOnCancelPolicy() { |
671 |
return removeOnCancel; |
672 |
} |
673 |
|
674 |
/** |
675 |
* Initiates an orderly shutdown in which previously submitted |
676 |
* tasks are executed, but no new tasks will be accepted. If the |
677 |
* {@code ExecuteExistingDelayedTasksAfterShutdownPolicy} has |
678 |
* been set {@code false}, existing delayed tasks whose delays |
679 |
* have not yet elapsed are cancelled. And unless the |
680 |
* {@code ContinueExistingPeriodicTasksAfterShutdownPolicy} has |
681 |
* been set {@code true}, future executions of existing periodic |
682 |
* tasks will be cancelled. |
683 |
* |
684 |
* @throws SecurityException {@inheritDoc} |
685 |
*/ |
686 |
public void shutdown() { |
687 |
super.shutdown(); |
688 |
} |
689 |
|
690 |
/** |
691 |
* Attempts to stop all actively executing tasks, halts the |
692 |
* processing of waiting tasks, and returns a list of the tasks |
693 |
* that were awaiting execution. |
694 |
* |
695 |
* <p>There are no guarantees beyond best-effort attempts to stop |
696 |
* processing actively executing tasks. This implementation |
697 |
* cancels tasks via {@link Thread#interrupt}, so any task that |
698 |
* fails to respond to interrupts may never terminate. |
699 |
* |
700 |
* @return list of tasks that never commenced execution. |
701 |
* Each element of this list is a {@link ScheduledFuture}, |
702 |
* including those tasks submitted using {@code execute}, |
703 |
* which are for scheduling purposes used as the basis of a |
704 |
* zero-delay {@code ScheduledFuture}. |
705 |
* @throws SecurityException {@inheritDoc} |
706 |
*/ |
707 |
public List<Runnable> shutdownNow() { |
708 |
return super.shutdownNow(); |
709 |
} |
710 |
|
711 |
/** |
712 |
* Returns the task queue used by this executor. Each element of |
713 |
* this queue is a {@link ScheduledFuture}, including those |
714 |
* tasks submitted using {@code execute} which are for scheduling |
715 |
* purposes used as the basis of a zero-delay |
716 |
* {@code ScheduledFuture}. Iteration over this queue is |
717 |
* <em>not</em> guaranteed to traverse tasks in the order in |
718 |
* which they will execute. |
719 |
* |
720 |
* @return the task queue |
721 |
*/ |
722 |
public BlockingQueue<Runnable> getQueue() { |
723 |
return super.getQueue(); |
724 |
} |
725 |
|
726 |
/** |
727 |
* Specialized delay queue. To mesh with TPE declarations, this |
728 |
* class must be declared as a BlockingQueue<Runnable> even though |
729 |
* it can only hold RunnableScheduledFutures. |
730 |
*/ |
731 |
static class DelayedWorkQueue extends AbstractQueue<Runnable> |
732 |
implements BlockingQueue<Runnable> { |
733 |
|
734 |
/* |
735 |
* A DelayedWorkQueue is based on a heap-based data structure |
736 |
* like those in DelayQueue and PriorityQueue, except that |
737 |
* every ScheduledFutureTask also records its index into the |
738 |
* heap array. This eliminates the need to find a task upon |
739 |
* cancellation, greatly speeding up removal (down from O(n) |
740 |
* to O(log n)), and reducing garbage retention that would |
741 |
* otherwise occur by waiting for the element to rise to top |
742 |
* before clearing. But because the queue may also hold |
743 |
* RunnableScheduledFutures that are not ScheduledFutureTasks, |
744 |
* we are not guaranteed to have such indices available, in |
745 |
* which case we fall back to linear search. (We expect that |
746 |
* most tasks will not be decorated, and that the faster cases |
747 |
* will be much more common.) |
748 |
* |
749 |
* All heap operations must record index changes -- mainly |
750 |
* within siftUp and siftDown. Upon removal, a task's |
751 |
* heapIndex is set to -1. Note that ScheduledFutureTasks can |
752 |
* appear at most once in the queue (this need not be true for |
753 |
* other kinds of tasks or work queues), so are uniquely |
754 |
* identified by heapIndex. |
755 |
*/ |
756 |
|
757 |
private static final int INITIAL_CAPACITY = 16; |
758 |
private RunnableScheduledFuture[] queue = |
759 |
new RunnableScheduledFuture[INITIAL_CAPACITY]; |
760 |
private final ReentrantLock lock = new ReentrantLock(); |
761 |
private int size = 0; |
762 |
|
763 |
/** |
764 |
* Thread designated to wait for the task at the head of the |
765 |
* queue. This variant of the Leader-Follower pattern |
766 |
* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to |
767 |
* minimize unnecessary timed waiting. When a thread becomes |
768 |
* the leader, it waits only for the next delay to elapse, but |
769 |
* other threads await indefinitely. The leader thread must |
770 |
* signal some other thread before returning from take() or |
771 |
* poll(...), unless some other thread becomes leader in the |
772 |
* interim. Whenever the head of the queue is replaced with a |
773 |
* task with an earlier expiration time, the leader field is |
774 |
* invalidated by being reset to null, and some waiting |
775 |
* thread, but not necessarily the current leader, is |
776 |
* signalled. So waiting threads must be prepared to acquire |
777 |
* and lose leadership while waiting. |
778 |
*/ |
779 |
private Thread leader = null; |
780 |
|
781 |
/** |
782 |
* Condition signalled when a newer task becomes available at the |
783 |
* head of the queue or a new thread may need to become leader. |
784 |
*/ |
785 |
private final Condition available = lock.newCondition(); |
786 |
|
787 |
/** |
788 |
* Set f's heapIndex if it is a ScheduledFutureTask. |
789 |
*/ |
790 |
private void setIndex(RunnableScheduledFuture f, int idx) { |
791 |
if (f instanceof ScheduledFutureTask) |
792 |
((ScheduledFutureTask)f).heapIndex = idx; |
793 |
} |
794 |
|
795 |
/** |
796 |
* Sift element added at bottom up to its heap-ordered spot. |
797 |
* Call only when holding lock. |
798 |
*/ |
799 |
private void siftUp(int k, RunnableScheduledFuture key) { |
800 |
while (k > 0) { |
801 |
int parent = (k - 1) >>> 1; |
802 |
RunnableScheduledFuture e = queue[parent]; |
803 |
if (key.compareTo(e) >= 0) |
804 |
break; |
805 |
queue[k] = e; |
806 |
setIndex(e, k); |
807 |
k = parent; |
808 |
} |
809 |
queue[k] = key; |
810 |
setIndex(key, k); |
811 |
} |
812 |
|
813 |
/** |
814 |
* Sift element added at top down to its heap-ordered spot. |
815 |
* Call only when holding lock. |
816 |
*/ |
817 |
private void siftDown(int k, RunnableScheduledFuture key) { |
818 |
int half = size >>> 1; |
819 |
while (k < half) { |
820 |
int child = (k << 1) + 1; |
821 |
RunnableScheduledFuture c = queue[child]; |
822 |
int right = child + 1; |
823 |
if (right < size && c.compareTo(queue[right]) > 0) |
824 |
c = queue[child = right]; |
825 |
if (key.compareTo(c) <= 0) |
826 |
break; |
827 |
queue[k] = c; |
828 |
setIndex(c, k); |
829 |
k = child; |
830 |
} |
831 |
queue[k] = key; |
832 |
setIndex(key, k); |
833 |
} |
834 |
|
835 |
/** |
836 |
* Resize the heap array. Call only when holding lock. |
837 |
*/ |
838 |
private void grow() { |
839 |
int oldCapacity = queue.length; |
840 |
int newCapacity = oldCapacity + (oldCapacity >> 1); // grow 50% |
841 |
if (newCapacity < 0) // overflow |
842 |
newCapacity = Integer.MAX_VALUE; |
843 |
queue = Arrays.copyOf(queue, newCapacity); |
844 |
} |
845 |
|
846 |
/** |
847 |
* Find index of given object, or -1 if absent |
848 |
*/ |
849 |
private int indexOf(Object x) { |
850 |
if (x != null) { |
851 |
if (x instanceof ScheduledFutureTask) { |
852 |
int i = ((ScheduledFutureTask) x).heapIndex; |
853 |
// Sanity check; x could conceivably be a |
854 |
// ScheduledFutureTask from some other pool. |
855 |
if (i >= 0 && i < size && queue[i] == x) |
856 |
return i; |
857 |
} else { |
858 |
for (int i = 0; i < size; i++) |
859 |
if (x.equals(queue[i])) |
860 |
return i; |
861 |
} |
862 |
} |
863 |
return -1; |
864 |
} |
865 |
|
866 |
public boolean contains(Object x) { |
867 |
final ReentrantLock lock = this.lock; |
868 |
lock.lock(); |
869 |
try { |
870 |
return indexOf(x) != -1; |
871 |
} finally { |
872 |
lock.unlock(); |
873 |
} |
874 |
} |
875 |
|
876 |
public boolean remove(Object x) { |
877 |
final ReentrantLock lock = this.lock; |
878 |
lock.lock(); |
879 |
try { |
880 |
int i = indexOf(x); |
881 |
if (i < 0) |
882 |
return false; |
883 |
|
884 |
setIndex(queue[i], -1); |
885 |
int s = --size; |
886 |
RunnableScheduledFuture replacement = queue[s]; |
887 |
queue[s] = null; |
888 |
if (s != i) { |
889 |
siftDown(i, replacement); |
890 |
if (queue[i] == replacement) |
891 |
siftUp(i, replacement); |
892 |
} |
893 |
return true; |
894 |
} finally { |
895 |
lock.unlock(); |
896 |
} |
897 |
} |
898 |
|
899 |
public int size() { |
900 |
final ReentrantLock lock = this.lock; |
901 |
lock.lock(); |
902 |
try { |
903 |
return size; |
904 |
} finally { |
905 |
lock.unlock(); |
906 |
} |
907 |
} |
908 |
|
909 |
public boolean isEmpty() { |
910 |
return size() == 0; |
911 |
} |
912 |
|
913 |
public int remainingCapacity() { |
914 |
return Integer.MAX_VALUE; |
915 |
} |
916 |
|
917 |
public RunnableScheduledFuture peek() { |
918 |
final ReentrantLock lock = this.lock; |
919 |
lock.lock(); |
920 |
try { |
921 |
return queue[0]; |
922 |
} finally { |
923 |
lock.unlock(); |
924 |
} |
925 |
} |
926 |
|
927 |
public boolean offer(Runnable x) { |
928 |
if (x == null) |
929 |
throw new NullPointerException(); |
930 |
RunnableScheduledFuture e = (RunnableScheduledFuture)x; |
931 |
final ReentrantLock lock = this.lock; |
932 |
lock.lock(); |
933 |
try { |
934 |
int i = size; |
935 |
if (i >= queue.length) |
936 |
grow(); |
937 |
size = i + 1; |
938 |
if (i == 0) { |
939 |
queue[0] = e; |
940 |
setIndex(e, 0); |
941 |
} else { |
942 |
siftUp(i, e); |
943 |
} |
944 |
if (queue[0] == e) { |
945 |
leader = null; |
946 |
available.signal(); |
947 |
} |
948 |
} finally { |
949 |
lock.unlock(); |
950 |
} |
951 |
return true; |
952 |
} |
953 |
|
954 |
public void put(Runnable e) { |
955 |
offer(e); |
956 |
} |
957 |
|
958 |
public boolean add(Runnable e) { |
959 |
return offer(e); |
960 |
} |
961 |
|
962 |
public boolean offer(Runnable e, long timeout, TimeUnit unit) { |
963 |
return offer(e); |
964 |
} |
965 |
|
966 |
/** |
967 |
* Performs common bookkeeping for poll and take: Replaces |
968 |
* first element with last and sifts it down. Call only when |
969 |
* holding lock. |
970 |
* @param f the task to remove and return |
971 |
*/ |
972 |
private RunnableScheduledFuture finishPoll(RunnableScheduledFuture f) { |
973 |
int s = --size; |
974 |
RunnableScheduledFuture x = queue[s]; |
975 |
queue[s] = null; |
976 |
if (s != 0) |
977 |
siftDown(0, x); |
978 |
setIndex(f, -1); |
979 |
return f; |
980 |
} |
981 |
|
982 |
public RunnableScheduledFuture poll() { |
983 |
final ReentrantLock lock = this.lock; |
984 |
lock.lock(); |
985 |
try { |
986 |
RunnableScheduledFuture first = queue[0]; |
987 |
if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) |
988 |
return null; |
989 |
else |
990 |
return finishPoll(first); |
991 |
} finally { |
992 |
lock.unlock(); |
993 |
} |
994 |
} |
995 |
|
996 |
public RunnableScheduledFuture take() throws InterruptedException { |
997 |
final ReentrantLock lock = this.lock; |
998 |
lock.lockInterruptibly(); |
999 |
try { |
1000 |
for (;;) { |
1001 |
RunnableScheduledFuture first = queue[0]; |
1002 |
if (first == null) |
1003 |
available.await(); |
1004 |
else { |
1005 |
long delay = first.getDelay(TimeUnit.NANOSECONDS); |
1006 |
if (delay <= 0) |
1007 |
return finishPoll(first); |
1008 |
else if (leader != null) |
1009 |
available.await(); |
1010 |
else { |
1011 |
Thread thisThread = Thread.currentThread(); |
1012 |
leader = thisThread; |
1013 |
try { |
1014 |
available.awaitNanos(delay); |
1015 |
} finally { |
1016 |
if (leader == thisThread) |
1017 |
leader = null; |
1018 |
} |
1019 |
} |
1020 |
} |
1021 |
} |
1022 |
} finally { |
1023 |
if (leader == null && queue[0] != null) |
1024 |
available.signal(); |
1025 |
lock.unlock(); |
1026 |
} |
1027 |
} |
1028 |
|
1029 |
public RunnableScheduledFuture poll(long timeout, TimeUnit unit) |
1030 |
throws InterruptedException { |
1031 |
long nanos = unit.toNanos(timeout); |
1032 |
final ReentrantLock lock = this.lock; |
1033 |
lock.lockInterruptibly(); |
1034 |
try { |
1035 |
for (;;) { |
1036 |
RunnableScheduledFuture first = queue[0]; |
1037 |
if (first == null) { |
1038 |
if (nanos <= 0) |
1039 |
return null; |
1040 |
else |
1041 |
nanos = available.awaitNanos(nanos); |
1042 |
} else { |
1043 |
long delay = first.getDelay(TimeUnit.NANOSECONDS); |
1044 |
if (delay <= 0) |
1045 |
return finishPoll(first); |
1046 |
if (nanos <= 0) |
1047 |
return null; |
1048 |
if (nanos < delay || leader != null) |
1049 |
nanos = available.awaitNanos(nanos); |
1050 |
else { |
1051 |
Thread thisThread = Thread.currentThread(); |
1052 |
leader = thisThread; |
1053 |
try { |
1054 |
long timeLeft = available.awaitNanos(delay); |
1055 |
nanos -= delay - timeLeft; |
1056 |
} finally { |
1057 |
if (leader == thisThread) |
1058 |
leader = null; |
1059 |
} |
1060 |
} |
1061 |
} |
1062 |
} |
1063 |
} finally { |
1064 |
if (leader == null && queue[0] != null) |
1065 |
available.signal(); |
1066 |
lock.unlock(); |
1067 |
} |
1068 |
} |
1069 |
|
1070 |
public void clear() { |
1071 |
final ReentrantLock lock = this.lock; |
1072 |
lock.lock(); |
1073 |
try { |
1074 |
for (int i = 0; i < size; i++) { |
1075 |
RunnableScheduledFuture t = queue[i]; |
1076 |
if (t != null) { |
1077 |
queue[i] = null; |
1078 |
setIndex(t, -1); |
1079 |
} |
1080 |
} |
1081 |
size = 0; |
1082 |
} finally { |
1083 |
lock.unlock(); |
1084 |
} |
1085 |
} |
1086 |
|
1087 |
/** |
1088 |
* Return and remove first element only if it is expired. |
1089 |
* Used only by drainTo. Call only when holding lock. |
1090 |
*/ |
1091 |
private RunnableScheduledFuture pollExpired() { |
1092 |
RunnableScheduledFuture first = queue[0]; |
1093 |
if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) |
1094 |
return null; |
1095 |
return finishPoll(first); |
1096 |
} |
1097 |
|
1098 |
public int drainTo(Collection<? super Runnable> c) { |
1099 |
if (c == null) |
1100 |
throw new NullPointerException(); |
1101 |
if (c == this) |
1102 |
throw new IllegalArgumentException(); |
1103 |
final ReentrantLock lock = this.lock; |
1104 |
lock.lock(); |
1105 |
try { |
1106 |
RunnableScheduledFuture first; |
1107 |
int n = 0; |
1108 |
while ((first = pollExpired()) != null) { |
1109 |
c.add(first); |
1110 |
++n; |
1111 |
} |
1112 |
return n; |
1113 |
} finally { |
1114 |
lock.unlock(); |
1115 |
} |
1116 |
} |
1117 |
|
1118 |
public int drainTo(Collection<? super Runnable> c, int maxElements) { |
1119 |
if (c == null) |
1120 |
throw new NullPointerException(); |
1121 |
if (c == this) |
1122 |
throw new IllegalArgumentException(); |
1123 |
if (maxElements <= 0) |
1124 |
return 0; |
1125 |
final ReentrantLock lock = this.lock; |
1126 |
lock.lock(); |
1127 |
try { |
1128 |
RunnableScheduledFuture first; |
1129 |
int n = 0; |
1130 |
while (n < maxElements && (first = pollExpired()) != null) { |
1131 |
c.add(first); |
1132 |
++n; |
1133 |
} |
1134 |
return n; |
1135 |
} finally { |
1136 |
lock.unlock(); |
1137 |
} |
1138 |
} |
1139 |
|
1140 |
public Object[] toArray() { |
1141 |
final ReentrantLock lock = this.lock; |
1142 |
lock.lock(); |
1143 |
try { |
1144 |
return Arrays.copyOf(queue, size, Object[].class); |
1145 |
} finally { |
1146 |
lock.unlock(); |
1147 |
} |
1148 |
} |
1149 |
|
1150 |
@SuppressWarnings("unchecked") |
1151 |
public <T> T[] toArray(T[] a) { |
1152 |
final ReentrantLock lock = this.lock; |
1153 |
lock.lock(); |
1154 |
try { |
1155 |
if (a.length < size) |
1156 |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
1157 |
System.arraycopy(queue, 0, a, 0, size); |
1158 |
if (a.length > size) |
1159 |
a[size] = null; |
1160 |
return a; |
1161 |
} finally { |
1162 |
lock.unlock(); |
1163 |
} |
1164 |
} |
1165 |
|
1166 |
public Iterator<Runnable> iterator() { |
1167 |
return new Itr(Arrays.copyOf(queue, size)); |
1168 |
} |
1169 |
|
1170 |
/** |
1171 |
* Snapshot iterator that works off copy of underlying q array. |
1172 |
*/ |
1173 |
private class Itr implements Iterator<Runnable> { |
1174 |
final RunnableScheduledFuture[] array; |
1175 |
int cursor = 0; // index of next element to return |
1176 |
int lastRet = -1; // index of last element, or -1 if no such |
1177 |
|
1178 |
Itr(RunnableScheduledFuture[] array) { |
1179 |
this.array = array; |
1180 |
} |
1181 |
|
1182 |
public boolean hasNext() { |
1183 |
return cursor < array.length; |
1184 |
} |
1185 |
|
1186 |
public Runnable next() { |
1187 |
if (cursor >= array.length) |
1188 |
throw new NoSuchElementException(); |
1189 |
lastRet = cursor; |
1190 |
return array[cursor++]; |
1191 |
} |
1192 |
|
1193 |
public void remove() { |
1194 |
if (lastRet < 0) |
1195 |
throw new IllegalStateException(); |
1196 |
DelayedWorkQueue.this.remove(array[lastRet]); |
1197 |
lastRet = -1; |
1198 |
} |
1199 |
} |
1200 |
} |
1201 |
} |