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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/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import static java.util.concurrent.TimeUnit.MILLISECONDS; |
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import static java.util.concurrent.TimeUnit.NANOSECONDS; |
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|
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import java.util.AbstractQueue; |
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import java.util.Arrays; |
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import java.util.Collection; |
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import java.util.Iterator; |
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import java.util.List; |
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import java.util.NoSuchElementException; |
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import java.util.concurrent.atomic.AtomicLong; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReentrantLock; |
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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 periodically. |
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* This class is preferable to {@link java.util.Timer} when multiple |
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* worker threads are needed, or when the additional flexibility or |
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* capabilities of {@link ThreadPoolExecutor} (which this class |
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* 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 elapses. |
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* While this enables further inspection and monitoring, it may also |
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* cause unbounded retention of cancelled tasks. To avoid this, use |
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* {@link #setRemoveOnCancelPolicy} to cause tasks to be immediately |
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* removed from the work queue at time of cancellation. |
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* |
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* <p>Successive executions of a periodic task scheduled via |
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* {@link #scheduleAtFixedRate scheduleAtFixedRate} or |
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* {@link #scheduleWithFixedDelay scheduleWithFixedDelay} |
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* do not overlap. While different executions may be performed by |
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* different threads, the effects of prior executions |
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* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
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* those of subsequent ones. |
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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(Runnable) 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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volatile boolean removeOnCancel; |
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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(); |
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|
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/** |
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* Returns current nanosecond time. |
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*/ |
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static 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 volatile long time; |
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|
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/** |
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* Period in nanoseconds for repeating tasks. |
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* A positive value indicates fixed-rate execution. |
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* A negative value indicates fixed-delay execution. |
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* A value of 0 indicates a non-repeating (one-shot) 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 triggerTime, |
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long sequenceNumber) { |
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super(r, result); |
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this.time = triggerTime; |
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this.period = 0; |
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this.sequenceNumber = sequenceNumber; |
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} |
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|
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/** |
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* Creates a periodic action with given nanoTime-based initial |
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* trigger time and period. |
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*/ |
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ScheduledFutureTask(Runnable r, V result, long triggerTime, |
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long period, long sequenceNumber) { |
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super(r, result); |
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this.time = triggerTime; |
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this.period = period; |
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this.sequenceNumber = sequenceNumber; |
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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 time. |
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*/ |
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ScheduledFutureTask(Callable<V> callable, long triggerTime, |
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long sequenceNumber) { |
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super(callable); |
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this.time = triggerTime; |
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this.period = 0; |
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this.sequenceNumber = sequenceNumber; |
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} |
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|
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public long getDelay(TimeUnit unit) { |
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return unit.convert(time - now(), NANOSECONDS); |
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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 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 diff = getDelay(NANOSECONDS) - other.getDelay(NANOSECONDS); |
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return (diff < 0) ? -1 : (diff > 0) ? 1 : 0; |
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} |
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|
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/** |
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* Returns {@code true} if this is a periodic (not a one-shot) action. |
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* |
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* @return {@code 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 = triggerTime(-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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super.run(); |
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else if (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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ensurePrestart(); |
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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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ensurePrestart(); |
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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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for (Object e : q.toArray()) |
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if (e instanceof RunnableScheduledFuture<?>) |
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((RunnableScheduledFuture<?>) e).cancel(false); |
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q.clear(); |
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} |
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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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* @param <V> the type of the task's result |
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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. |
391 |
* |
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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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* @param <V> the type of the task's result |
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* @return a task that can execute the callable |
396 |
* @since 1.6 |
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*/ |
398 |
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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* The default keep-alive time for pool threads. |
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* |
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* Normally, this value is unused because all pool threads will be |
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* core threads, but if a user creates a pool with a corePoolSize |
408 |
* of zero (against our advice), we keep a thread alive as long as |
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* there are queued tasks. If the keep alive time is zero (the |
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* historic value), we end up hot-spinning in getTask, wasting a |
411 |
* CPU. But on the other hand, if we set the value too high, and |
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* users create a one-shot pool which they don't cleanly shutdown, |
413 |
* the pool's non-daemon threads will prevent JVM termination. A |
414 |
* small but non-zero value (relative to a JVM's lifetime) seems |
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* best. |
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*/ |
417 |
private static final long DEFAULT_KEEPALIVE_MILLIS = 10L; |
418 |
|
419 |
/** |
420 |
* Creates a new {@code ScheduledThreadPoolExecutor} with the |
421 |
* given core pool size. |
422 |
* |
423 |
* @param corePoolSize the number of threads to keep in the pool, even |
424 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
425 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
426 |
*/ |
427 |
public ScheduledThreadPoolExecutor(int corePoolSize) { |
428 |
super(corePoolSize, Integer.MAX_VALUE, |
429 |
DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS, |
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new DelayedWorkQueue()); |
431 |
} |
432 |
|
433 |
/** |
434 |
* Creates a new {@code ScheduledThreadPoolExecutor} with the |
435 |
* given initial parameters. |
436 |
* |
437 |
* @param corePoolSize the number of threads to keep in the pool, even |
438 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
439 |
* @param threadFactory the factory to use when the executor |
440 |
* creates a new thread |
441 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
442 |
* @throws NullPointerException if {@code threadFactory} is null |
443 |
*/ |
444 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
445 |
ThreadFactory threadFactory) { |
446 |
super(corePoolSize, Integer.MAX_VALUE, |
447 |
DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS, |
448 |
new DelayedWorkQueue(), threadFactory); |
449 |
} |
450 |
|
451 |
/** |
452 |
* Creates a new {@code ScheduledThreadPoolExecutor} with the |
453 |
* given initial parameters. |
454 |
* |
455 |
* @param corePoolSize the number of threads to keep in the pool, even |
456 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
457 |
* @param handler the handler to use when execution is blocked |
458 |
* because the thread bounds and queue capacities are reached |
459 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
460 |
* @throws NullPointerException if {@code handler} is null |
461 |
*/ |
462 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
463 |
RejectedExecutionHandler handler) { |
464 |
super(corePoolSize, Integer.MAX_VALUE, |
465 |
DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS, |
466 |
new DelayedWorkQueue(), handler); |
467 |
} |
468 |
|
469 |
/** |
470 |
* Creates a new {@code ScheduledThreadPoolExecutor} with the |
471 |
* given initial parameters. |
472 |
* |
473 |
* @param corePoolSize the number of threads to keep in the pool, even |
474 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
475 |
* @param threadFactory the factory to use when the executor |
476 |
* creates a new thread |
477 |
* @param handler the handler to use when execution is blocked |
478 |
* because the thread bounds and queue capacities are reached |
479 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
480 |
* @throws NullPointerException if {@code threadFactory} or |
481 |
* {@code handler} is null |
482 |
*/ |
483 |
public ScheduledThreadPoolExecutor(int corePoolSize, |
484 |
ThreadFactory threadFactory, |
485 |
RejectedExecutionHandler handler) { |
486 |
super(corePoolSize, Integer.MAX_VALUE, |
487 |
DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS, |
488 |
new DelayedWorkQueue(), threadFactory, handler); |
489 |
} |
490 |
|
491 |
/** |
492 |
* Returns the nanoTime-based trigger time of a delayed action. |
493 |
*/ |
494 |
private long triggerTime(long delay, TimeUnit unit) { |
495 |
return triggerTime(unit.toNanos((delay < 0) ? 0 : delay)); |
496 |
} |
497 |
|
498 |
/** |
499 |
* Returns the nanoTime-based trigger time of a delayed action. |
500 |
*/ |
501 |
long triggerTime(long delay) { |
502 |
return now() + |
503 |
((delay < (Long.MAX_VALUE >> 1)) ? delay : overflowFree(delay)); |
504 |
} |
505 |
|
506 |
/** |
507 |
* Constrains the values of all delays in the queue to be within |
508 |
* Long.MAX_VALUE of each other, to avoid overflow in compareTo. |
509 |
* This may occur if a task is eligible to be dequeued, but has |
510 |
* not yet been, while some other task is added with a delay of |
511 |
* Long.MAX_VALUE. |
512 |
*/ |
513 |
private long overflowFree(long delay) { |
514 |
Delayed head = (Delayed) super.getQueue().peek(); |
515 |
if (head != null) { |
516 |
long headDelay = head.getDelay(NANOSECONDS); |
517 |
if (headDelay < 0 && (delay - headDelay < 0)) |
518 |
delay = Long.MAX_VALUE + headDelay; |
519 |
} |
520 |
return delay; |
521 |
} |
522 |
|
523 |
/** |
524 |
* @throws RejectedExecutionException {@inheritDoc} |
525 |
* @throws NullPointerException {@inheritDoc} |
526 |
*/ |
527 |
public ScheduledFuture<?> schedule(Runnable command, |
528 |
long delay, |
529 |
TimeUnit unit) { |
530 |
if (command == null || unit == null) |
531 |
throw new NullPointerException(); |
532 |
RunnableScheduledFuture<Void> t = decorateTask(command, |
533 |
new ScheduledFutureTask<Void>(command, null, |
534 |
triggerTime(delay, unit), |
535 |
sequencer.getAndIncrement())); |
536 |
delayedExecute(t); |
537 |
return t; |
538 |
} |
539 |
|
540 |
/** |
541 |
* @throws RejectedExecutionException {@inheritDoc} |
542 |
* @throws NullPointerException {@inheritDoc} |
543 |
*/ |
544 |
public <V> ScheduledFuture<V> schedule(Callable<V> callable, |
545 |
long delay, |
546 |
TimeUnit unit) { |
547 |
if (callable == null || unit == null) |
548 |
throw new NullPointerException(); |
549 |
RunnableScheduledFuture<V> t = decorateTask(callable, |
550 |
new ScheduledFutureTask<V>(callable, |
551 |
triggerTime(delay, unit), |
552 |
sequencer.getAndIncrement())); |
553 |
delayedExecute(t); |
554 |
return t; |
555 |
} |
556 |
|
557 |
/** |
558 |
* @throws RejectedExecutionException {@inheritDoc} |
559 |
* @throws NullPointerException {@inheritDoc} |
560 |
* @throws IllegalArgumentException {@inheritDoc} |
561 |
*/ |
562 |
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, |
563 |
long initialDelay, |
564 |
long period, |
565 |
TimeUnit unit) { |
566 |
if (command == null || unit == null) |
567 |
throw new NullPointerException(); |
568 |
if (period <= 0) |
569 |
throw new IllegalArgumentException(); |
570 |
ScheduledFutureTask<Void> sft = |
571 |
new ScheduledFutureTask<Void>(command, |
572 |
null, |
573 |
triggerTime(initialDelay, unit), |
574 |
unit.toNanos(period), |
575 |
sequencer.getAndIncrement()); |
576 |
RunnableScheduledFuture<Void> t = decorateTask(command, sft); |
577 |
sft.outerTask = t; |
578 |
delayedExecute(t); |
579 |
return t; |
580 |
} |
581 |
|
582 |
/** |
583 |
* @throws RejectedExecutionException {@inheritDoc} |
584 |
* @throws NullPointerException {@inheritDoc} |
585 |
* @throws IllegalArgumentException {@inheritDoc} |
586 |
*/ |
587 |
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, |
588 |
long initialDelay, |
589 |
long delay, |
590 |
TimeUnit unit) { |
591 |
if (command == null || unit == null) |
592 |
throw new NullPointerException(); |
593 |
if (delay <= 0) |
594 |
throw new IllegalArgumentException(); |
595 |
ScheduledFutureTask<Void> sft = |
596 |
new ScheduledFutureTask<Void>(command, |
597 |
null, |
598 |
triggerTime(initialDelay, unit), |
599 |
unit.toNanos(-delay), |
600 |
sequencer.getAndIncrement()); |
601 |
RunnableScheduledFuture<Void> t = decorateTask(command, sft); |
602 |
sft.outerTask = t; |
603 |
delayedExecute(t); |
604 |
return t; |
605 |
} |
606 |
|
607 |
/** |
608 |
* Executes {@code command} with zero required delay. |
609 |
* This has effect equivalent to |
610 |
* {@link #schedule(Runnable,long,TimeUnit) schedule(command, 0, anyUnit)}. |
611 |
* Note that inspections of the queue and of the list returned by |
612 |
* {@code shutdownNow} will access the zero-delayed |
613 |
* {@link ScheduledFuture}, not the {@code command} itself. |
614 |
* |
615 |
* <p>A consequence of the use of {@code ScheduledFuture} objects is |
616 |
* that {@link ThreadPoolExecutor#afterExecute afterExecute} is always |
617 |
* called with a null second {@code Throwable} argument, even if the |
618 |
* {@code command} terminated abruptly. Instead, the {@code Throwable} |
619 |
* thrown by such a task can be obtained via {@link Future#get}. |
620 |
* |
621 |
* @throws RejectedExecutionException at discretion of |
622 |
* {@code RejectedExecutionHandler}, if the task |
623 |
* cannot be accepted for execution because the |
624 |
* executor has been shut down |
625 |
* @throws NullPointerException {@inheritDoc} |
626 |
*/ |
627 |
public void execute(Runnable command) { |
628 |
schedule(command, 0, NANOSECONDS); |
629 |
} |
630 |
|
631 |
// Override AbstractExecutorService methods |
632 |
|
633 |
/** |
634 |
* @throws RejectedExecutionException {@inheritDoc} |
635 |
* @throws NullPointerException {@inheritDoc} |
636 |
*/ |
637 |
public Future<?> submit(Runnable task) { |
638 |
return schedule(task, 0, NANOSECONDS); |
639 |
} |
640 |
|
641 |
/** |
642 |
* @throws RejectedExecutionException {@inheritDoc} |
643 |
* @throws NullPointerException {@inheritDoc} |
644 |
*/ |
645 |
public <T> Future<T> submit(Runnable task, T result) { |
646 |
return schedule(Executors.callable(task, result), 0, NANOSECONDS); |
647 |
} |
648 |
|
649 |
/** |
650 |
* @throws RejectedExecutionException {@inheritDoc} |
651 |
* @throws NullPointerException {@inheritDoc} |
652 |
*/ |
653 |
public <T> Future<T> submit(Callable<T> task) { |
654 |
return schedule(task, 0, NANOSECONDS); |
655 |
} |
656 |
|
657 |
/** |
658 |
* Sets the policy on whether to continue executing existing |
659 |
* periodic tasks even when this executor has been {@code shutdown}. |
660 |
* In this case, these tasks will only terminate upon |
661 |
* {@code shutdownNow} or after setting the policy to |
662 |
* {@code false} when already shutdown. |
663 |
* This value is by default {@code false}. |
664 |
* |
665 |
* @param value if {@code true}, continue after shutdown, else don't |
666 |
* @see #getContinueExistingPeriodicTasksAfterShutdownPolicy |
667 |
*/ |
668 |
public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) { |
669 |
continueExistingPeriodicTasksAfterShutdown = value; |
670 |
if (!value && isShutdown()) |
671 |
onShutdown(); |
672 |
} |
673 |
|
674 |
/** |
675 |
* Gets the policy on whether to continue executing existing |
676 |
* periodic tasks even when this executor has been {@code shutdown}. |
677 |
* In this case, these tasks will only terminate upon |
678 |
* {@code shutdownNow} or after setting the policy to |
679 |
* {@code false} when already shutdown. |
680 |
* This value is by default {@code false}. |
681 |
* |
682 |
* @return {@code true} if will continue after shutdown |
683 |
* @see #setContinueExistingPeriodicTasksAfterShutdownPolicy |
684 |
*/ |
685 |
public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() { |
686 |
return continueExistingPeriodicTasksAfterShutdown; |
687 |
} |
688 |
|
689 |
/** |
690 |
* Sets the policy on whether to execute existing delayed |
691 |
* tasks even when this executor has been {@code shutdown}. |
692 |
* In this case, these tasks will only terminate upon |
693 |
* {@code shutdownNow}, or after setting the policy to |
694 |
* {@code false} when already shutdown. |
695 |
* This value is by default {@code true}. |
696 |
* |
697 |
* @param value if {@code true}, execute after shutdown, else don't |
698 |
* @see #getExecuteExistingDelayedTasksAfterShutdownPolicy |
699 |
*/ |
700 |
public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) { |
701 |
executeExistingDelayedTasksAfterShutdown = value; |
702 |
if (!value && isShutdown()) |
703 |
onShutdown(); |
704 |
} |
705 |
|
706 |
/** |
707 |
* Gets the policy on whether to execute existing delayed |
708 |
* tasks even when this executor has been {@code shutdown}. |
709 |
* In this case, these tasks will only terminate upon |
710 |
* {@code shutdownNow}, or after setting the policy to |
711 |
* {@code false} when already shutdown. |
712 |
* This value is by default {@code true}. |
713 |
* |
714 |
* @return {@code true} if will execute after shutdown |
715 |
* @see #setExecuteExistingDelayedTasksAfterShutdownPolicy |
716 |
*/ |
717 |
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() { |
718 |
return executeExistingDelayedTasksAfterShutdown; |
719 |
} |
720 |
|
721 |
/** |
722 |
* Sets the policy on whether cancelled tasks should be immediately |
723 |
* removed from the work queue at time of cancellation. This value is |
724 |
* by default {@code false}. |
725 |
* |
726 |
* @param value if {@code true}, remove on cancellation, else don't |
727 |
* @see #getRemoveOnCancelPolicy |
728 |
* @since 1.7 |
729 |
*/ |
730 |
public void setRemoveOnCancelPolicy(boolean value) { |
731 |
removeOnCancel = value; |
732 |
} |
733 |
|
734 |
/** |
735 |
* Gets the policy on whether cancelled tasks should be immediately |
736 |
* removed from the work queue at time of cancellation. This value is |
737 |
* by default {@code false}. |
738 |
* |
739 |
* @return {@code true} if cancelled tasks are immediately removed |
740 |
* from the queue |
741 |
* @see #setRemoveOnCancelPolicy |
742 |
* @since 1.7 |
743 |
*/ |
744 |
public boolean getRemoveOnCancelPolicy() { |
745 |
return removeOnCancel; |
746 |
} |
747 |
|
748 |
/** |
749 |
* Initiates an orderly shutdown in which previously submitted |
750 |
* tasks are executed, but no new tasks will be accepted. |
751 |
* Invocation has no additional effect if already shut down. |
752 |
* |
753 |
* <p>This method does not wait for previously submitted tasks to |
754 |
* complete execution. Use {@link #awaitTermination awaitTermination} |
755 |
* to do that. |
756 |
* |
757 |
* <p>If the {@code ExecuteExistingDelayedTasksAfterShutdownPolicy} |
758 |
* has been set {@code false}, existing delayed tasks whose delays |
759 |
* have not yet elapsed are cancelled. And unless the {@code |
760 |
* ContinueExistingPeriodicTasksAfterShutdownPolicy} has been set |
761 |
* {@code true}, future executions of existing periodic tasks will |
762 |
* be cancelled. |
763 |
* |
764 |
* @throws SecurityException {@inheritDoc} |
765 |
*/ |
766 |
public void shutdown() { |
767 |
super.shutdown(); |
768 |
} |
769 |
|
770 |
/** |
771 |
* Attempts to stop all actively executing tasks, halts the |
772 |
* processing of waiting tasks, and returns a list of the tasks |
773 |
* that were awaiting execution. |
774 |
* |
775 |
* <p>This method does not wait for actively executing tasks to |
776 |
* terminate. Use {@link #awaitTermination awaitTermination} to |
777 |
* do that. |
778 |
* |
779 |
* <p>There are no guarantees beyond best-effort attempts to stop |
780 |
* processing actively executing tasks. This implementation |
781 |
* cancels tasks via {@link Thread#interrupt}, so any task that |
782 |
* fails to respond to interrupts may never terminate. |
783 |
* |
784 |
* @return list of tasks that never commenced execution. |
785 |
* Each element of this list is a {@link ScheduledFuture}. |
786 |
* For tasks submitted via one of the {@code schedule} |
787 |
* methods, the element will be identical to the returned |
788 |
* {@code ScheduledFuture}. For tasks submitted using |
789 |
* {@link #execute execute}, the element will be a |
790 |
* zero-delay {@code ScheduledFuture}. |
791 |
* @throws SecurityException {@inheritDoc} |
792 |
*/ |
793 |
public List<Runnable> shutdownNow() { |
794 |
return super.shutdownNow(); |
795 |
} |
796 |
|
797 |
/** |
798 |
* Returns the task queue used by this executor. |
799 |
* Each element of this list is a {@link ScheduledFuture}. |
800 |
* For tasks submitted via one of the {@code schedule} methods, the |
801 |
* element will be identical to the returned {@code ScheduledFuture}. |
802 |
* For tasks submitted using {@link #execute execute}, the element |
803 |
* will be a zero-delay {@code ScheduledFuture}. |
804 |
* |
805 |
* <p>Iteration over this queue is <em>not</em> guaranteed to traverse |
806 |
* tasks in the order in which they will execute. |
807 |
* |
808 |
* @return the task queue |
809 |
*/ |
810 |
public BlockingQueue<Runnable> getQueue() { |
811 |
return super.getQueue(); |
812 |
} |
813 |
|
814 |
/** |
815 |
* Specialized delay queue. To mesh with TPE declarations, this |
816 |
* class must be declared as a BlockingQueue<Runnable> even though |
817 |
* it can only hold RunnableScheduledFutures. |
818 |
*/ |
819 |
static class DelayedWorkQueue extends AbstractQueue<Runnable> |
820 |
implements BlockingQueue<Runnable> { |
821 |
|
822 |
/* |
823 |
* A DelayedWorkQueue is based on a heap-based data structure |
824 |
* like those in DelayQueue and PriorityQueue, except that |
825 |
* every ScheduledFutureTask also records its index into the |
826 |
* heap array. This eliminates the need to find a task upon |
827 |
* cancellation, greatly speeding up removal (down from O(n) |
828 |
* to O(log n)), and reducing garbage retention that would |
829 |
* otherwise occur by waiting for the element to rise to top |
830 |
* before clearing. But because the queue may also hold |
831 |
* RunnableScheduledFutures that are not ScheduledFutureTasks, |
832 |
* we are not guaranteed to have such indices available, in |
833 |
* which case we fall back to linear search. (We expect that |
834 |
* most tasks will not be decorated, and that the faster cases |
835 |
* will be much more common.) |
836 |
* |
837 |
* All heap operations must record index changes -- mainly |
838 |
* within siftUp and siftDown. Upon removal, a task's |
839 |
* heapIndex is set to -1. Note that ScheduledFutureTasks can |
840 |
* appear at most once in the queue (this need not be true for |
841 |
* other kinds of tasks or work queues), so are uniquely |
842 |
* identified by heapIndex. |
843 |
*/ |
844 |
|
845 |
private static final int INITIAL_CAPACITY = 16; |
846 |
private RunnableScheduledFuture<?>[] queue = |
847 |
new RunnableScheduledFuture<?>[INITIAL_CAPACITY]; |
848 |
private final ReentrantLock lock = new ReentrantLock(); |
849 |
private int size; |
850 |
|
851 |
/** |
852 |
* Thread designated to wait for the task at the head of the |
853 |
* queue. This variant of the Leader-Follower pattern |
854 |
* (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to |
855 |
* minimize unnecessary timed waiting. When a thread becomes |
856 |
* the leader, it waits only for the next delay to elapse, but |
857 |
* other threads await indefinitely. The leader thread must |
858 |
* signal some other thread before returning from take() or |
859 |
* poll(...), unless some other thread becomes leader in the |
860 |
* interim. Whenever the head of the queue is replaced with a |
861 |
* task with an earlier expiration time, the leader field is |
862 |
* invalidated by being reset to null, and some waiting |
863 |
* thread, but not necessarily the current leader, is |
864 |
* signalled. So waiting threads must be prepared to acquire |
865 |
* and lose leadership while waiting. |
866 |
*/ |
867 |
private Thread leader; |
868 |
|
869 |
/** |
870 |
* Condition signalled when a newer task becomes available at the |
871 |
* head of the queue or a new thread may need to become leader. |
872 |
*/ |
873 |
private final Condition available = lock.newCondition(); |
874 |
|
875 |
/** |
876 |
* Sets f's heapIndex if it is a ScheduledFutureTask. |
877 |
*/ |
878 |
private void setIndex(RunnableScheduledFuture<?> f, int idx) { |
879 |
if (f instanceof ScheduledFutureTask) |
880 |
((ScheduledFutureTask)f).heapIndex = idx; |
881 |
} |
882 |
|
883 |
/** |
884 |
* Sifts element added at bottom up to its heap-ordered spot. |
885 |
* Call only when holding lock. |
886 |
*/ |
887 |
private void siftUp(int k, RunnableScheduledFuture<?> key) { |
888 |
while (k > 0) { |
889 |
int parent = (k - 1) >>> 1; |
890 |
RunnableScheduledFuture<?> e = queue[parent]; |
891 |
if (key.compareTo(e) >= 0) |
892 |
break; |
893 |
queue[k] = e; |
894 |
setIndex(e, k); |
895 |
k = parent; |
896 |
} |
897 |
queue[k] = key; |
898 |
setIndex(key, k); |
899 |
} |
900 |
|
901 |
/** |
902 |
* Sifts element added at top down to its heap-ordered spot. |
903 |
* Call only when holding lock. |
904 |
*/ |
905 |
private void siftDown(int k, RunnableScheduledFuture<?> key) { |
906 |
int half = size >>> 1; |
907 |
while (k < half) { |
908 |
int child = (k << 1) + 1; |
909 |
RunnableScheduledFuture<?> c = queue[child]; |
910 |
int right = child + 1; |
911 |
if (right < size && c.compareTo(queue[right]) > 0) |
912 |
c = queue[child = right]; |
913 |
if (key.compareTo(c) <= 0) |
914 |
break; |
915 |
queue[k] = c; |
916 |
setIndex(c, k); |
917 |
k = child; |
918 |
} |
919 |
queue[k] = key; |
920 |
setIndex(key, k); |
921 |
} |
922 |
|
923 |
/** |
924 |
* Resizes the heap array. Call only when holding lock. |
925 |
*/ |
926 |
private void grow() { |
927 |
int oldCapacity = queue.length; |
928 |
int newCapacity = oldCapacity + (oldCapacity >> 1); // grow 50% |
929 |
if (newCapacity < 0) // overflow |
930 |
newCapacity = Integer.MAX_VALUE; |
931 |
queue = Arrays.copyOf(queue, newCapacity); |
932 |
} |
933 |
|
934 |
/** |
935 |
* Finds index of given object, or -1 if absent. |
936 |
*/ |
937 |
private int indexOf(Object x) { |
938 |
if (x != null) { |
939 |
if (x instanceof ScheduledFutureTask) { |
940 |
int i = ((ScheduledFutureTask) x).heapIndex; |
941 |
// Sanity check; x could conceivably be a |
942 |
// ScheduledFutureTask from some other pool. |
943 |
if (i >= 0 && i < size && queue[i] == x) |
944 |
return i; |
945 |
} else { |
946 |
for (int i = 0; i < size; i++) |
947 |
if (x.equals(queue[i])) |
948 |
return i; |
949 |
} |
950 |
} |
951 |
return -1; |
952 |
} |
953 |
|
954 |
public boolean contains(Object x) { |
955 |
final ReentrantLock lock = this.lock; |
956 |
lock.lock(); |
957 |
try { |
958 |
return indexOf(x) != -1; |
959 |
} finally { |
960 |
lock.unlock(); |
961 |
} |
962 |
} |
963 |
|
964 |
public boolean remove(Object x) { |
965 |
final ReentrantLock lock = this.lock; |
966 |
lock.lock(); |
967 |
try { |
968 |
int i = indexOf(x); |
969 |
if (i < 0) |
970 |
return false; |
971 |
|
972 |
setIndex(queue[i], -1); |
973 |
int s = --size; |
974 |
RunnableScheduledFuture<?> replacement = queue[s]; |
975 |
queue[s] = null; |
976 |
if (s != i) { |
977 |
siftDown(i, replacement); |
978 |
if (queue[i] == replacement) |
979 |
siftUp(i, replacement); |
980 |
} |
981 |
return true; |
982 |
} finally { |
983 |
lock.unlock(); |
984 |
} |
985 |
} |
986 |
|
987 |
public int size() { |
988 |
final ReentrantLock lock = this.lock; |
989 |
lock.lock(); |
990 |
try { |
991 |
return size; |
992 |
} finally { |
993 |
lock.unlock(); |
994 |
} |
995 |
} |
996 |
|
997 |
public boolean isEmpty() { |
998 |
return size() == 0; |
999 |
} |
1000 |
|
1001 |
public int remainingCapacity() { |
1002 |
return Integer.MAX_VALUE; |
1003 |
} |
1004 |
|
1005 |
public RunnableScheduledFuture<?> peek() { |
1006 |
final ReentrantLock lock = this.lock; |
1007 |
lock.lock(); |
1008 |
try { |
1009 |
return queue[0]; |
1010 |
} finally { |
1011 |
lock.unlock(); |
1012 |
} |
1013 |
} |
1014 |
|
1015 |
public boolean offer(Runnable x) { |
1016 |
if (x == null) |
1017 |
throw new NullPointerException(); |
1018 |
RunnableScheduledFuture<?> e = (RunnableScheduledFuture<?>)x; |
1019 |
final ReentrantLock lock = this.lock; |
1020 |
lock.lock(); |
1021 |
try { |
1022 |
int i = size; |
1023 |
if (i >= queue.length) |
1024 |
grow(); |
1025 |
size = i + 1; |
1026 |
if (i == 0) { |
1027 |
queue[0] = e; |
1028 |
setIndex(e, 0); |
1029 |
} else { |
1030 |
siftUp(i, e); |
1031 |
} |
1032 |
if (queue[0] == e) { |
1033 |
leader = null; |
1034 |
available.signal(); |
1035 |
} |
1036 |
} finally { |
1037 |
lock.unlock(); |
1038 |
} |
1039 |
return true; |
1040 |
} |
1041 |
|
1042 |
public void put(Runnable e) { |
1043 |
offer(e); |
1044 |
} |
1045 |
|
1046 |
public boolean add(Runnable e) { |
1047 |
return offer(e); |
1048 |
} |
1049 |
|
1050 |
public boolean offer(Runnable e, long timeout, TimeUnit unit) { |
1051 |
return offer(e); |
1052 |
} |
1053 |
|
1054 |
/** |
1055 |
* Performs common bookkeeping for poll and take: Replaces |
1056 |
* first element with last and sifts it down. Call only when |
1057 |
* holding lock. |
1058 |
* @param f the task to remove and return |
1059 |
*/ |
1060 |
private RunnableScheduledFuture<?> finishPoll(RunnableScheduledFuture<?> f) { |
1061 |
int s = --size; |
1062 |
RunnableScheduledFuture<?> x = queue[s]; |
1063 |
queue[s] = null; |
1064 |
if (s != 0) |
1065 |
siftDown(0, x); |
1066 |
setIndex(f, -1); |
1067 |
return f; |
1068 |
} |
1069 |
|
1070 |
public RunnableScheduledFuture<?> poll() { |
1071 |
final ReentrantLock lock = this.lock; |
1072 |
lock.lock(); |
1073 |
try { |
1074 |
RunnableScheduledFuture<?> first = queue[0]; |
1075 |
return (first == null || first.getDelay(NANOSECONDS) > 0) |
1076 |
? null |
1077 |
: finishPoll(first); |
1078 |
} finally { |
1079 |
lock.unlock(); |
1080 |
} |
1081 |
} |
1082 |
|
1083 |
public RunnableScheduledFuture<?> take() throws InterruptedException { |
1084 |
final ReentrantLock lock = this.lock; |
1085 |
lock.lockInterruptibly(); |
1086 |
try { |
1087 |
for (;;) { |
1088 |
RunnableScheduledFuture<?> first = queue[0]; |
1089 |
if (first == null) |
1090 |
available.await(); |
1091 |
else { |
1092 |
long delay = first.getDelay(NANOSECONDS); |
1093 |
if (delay <= 0) |
1094 |
return finishPoll(first); |
1095 |
first = null; // don't retain ref while waiting |
1096 |
if (leader != null) |
1097 |
available.await(); |
1098 |
else { |
1099 |
Thread thisThread = Thread.currentThread(); |
1100 |
leader = thisThread; |
1101 |
try { |
1102 |
available.awaitNanos(delay); |
1103 |
} finally { |
1104 |
if (leader == thisThread) |
1105 |
leader = null; |
1106 |
} |
1107 |
} |
1108 |
} |
1109 |
} |
1110 |
} finally { |
1111 |
if (leader == null && queue[0] != null) |
1112 |
available.signal(); |
1113 |
lock.unlock(); |
1114 |
} |
1115 |
} |
1116 |
|
1117 |
public RunnableScheduledFuture<?> poll(long timeout, TimeUnit unit) |
1118 |
throws InterruptedException { |
1119 |
long nanos = unit.toNanos(timeout); |
1120 |
final ReentrantLock lock = this.lock; |
1121 |
lock.lockInterruptibly(); |
1122 |
try { |
1123 |
for (;;) { |
1124 |
RunnableScheduledFuture<?> first = queue[0]; |
1125 |
if (first == null) { |
1126 |
if (nanos <= 0) |
1127 |
return null; |
1128 |
else |
1129 |
nanos = available.awaitNanos(nanos); |
1130 |
} else { |
1131 |
long delay = first.getDelay(NANOSECONDS); |
1132 |
if (delay <= 0) |
1133 |
return finishPoll(first); |
1134 |
if (nanos <= 0) |
1135 |
return null; |
1136 |
first = null; // don't retain ref while waiting |
1137 |
if (nanos < delay || leader != null) |
1138 |
nanos = available.awaitNanos(nanos); |
1139 |
else { |
1140 |
Thread thisThread = Thread.currentThread(); |
1141 |
leader = thisThread; |
1142 |
try { |
1143 |
long timeLeft = available.awaitNanos(delay); |
1144 |
nanos -= delay - timeLeft; |
1145 |
} finally { |
1146 |
if (leader == thisThread) |
1147 |
leader = null; |
1148 |
} |
1149 |
} |
1150 |
} |
1151 |
} |
1152 |
} finally { |
1153 |
if (leader == null && queue[0] != null) |
1154 |
available.signal(); |
1155 |
lock.unlock(); |
1156 |
} |
1157 |
} |
1158 |
|
1159 |
public void clear() { |
1160 |
final ReentrantLock lock = this.lock; |
1161 |
lock.lock(); |
1162 |
try { |
1163 |
for (int i = 0; i < size; i++) { |
1164 |
RunnableScheduledFuture<?> t = queue[i]; |
1165 |
if (t != null) { |
1166 |
queue[i] = null; |
1167 |
setIndex(t, -1); |
1168 |
} |
1169 |
} |
1170 |
size = 0; |
1171 |
} finally { |
1172 |
lock.unlock(); |
1173 |
} |
1174 |
} |
1175 |
|
1176 |
/** |
1177 |
* Returns first element only if it is expired. |
1178 |
* Used only by drainTo. Call only when holding lock. |
1179 |
*/ |
1180 |
private RunnableScheduledFuture<?> peekExpired() { |
1181 |
// assert lock.isHeldByCurrentThread(); |
1182 |
RunnableScheduledFuture<?> first = queue[0]; |
1183 |
return (first == null || first.getDelay(NANOSECONDS) > 0) ? |
1184 |
null : first; |
1185 |
} |
1186 |
|
1187 |
public int drainTo(Collection<? super Runnable> c) { |
1188 |
if (c == null) |
1189 |
throw new NullPointerException(); |
1190 |
if (c == this) |
1191 |
throw new IllegalArgumentException(); |
1192 |
final ReentrantLock lock = this.lock; |
1193 |
lock.lock(); |
1194 |
try { |
1195 |
RunnableScheduledFuture<?> first; |
1196 |
int n = 0; |
1197 |
while ((first = peekExpired()) != null) { |
1198 |
c.add(first); // In this order, in case add() throws. |
1199 |
finishPoll(first); |
1200 |
++n; |
1201 |
} |
1202 |
return n; |
1203 |
} finally { |
1204 |
lock.unlock(); |
1205 |
} |
1206 |
} |
1207 |
|
1208 |
public int drainTo(Collection<? super Runnable> c, int maxElements) { |
1209 |
if (c == null) |
1210 |
throw new NullPointerException(); |
1211 |
if (c == this) |
1212 |
throw new IllegalArgumentException(); |
1213 |
if (maxElements <= 0) |
1214 |
return 0; |
1215 |
final ReentrantLock lock = this.lock; |
1216 |
lock.lock(); |
1217 |
try { |
1218 |
RunnableScheduledFuture<?> first; |
1219 |
int n = 0; |
1220 |
while (n < maxElements && (first = peekExpired()) != null) { |
1221 |
c.add(first); // In this order, in case add() throws. |
1222 |
finishPoll(first); |
1223 |
++n; |
1224 |
} |
1225 |
return n; |
1226 |
} finally { |
1227 |
lock.unlock(); |
1228 |
} |
1229 |
} |
1230 |
|
1231 |
public Object[] toArray() { |
1232 |
final ReentrantLock lock = this.lock; |
1233 |
lock.lock(); |
1234 |
try { |
1235 |
return Arrays.copyOf(queue, size, Object[].class); |
1236 |
} finally { |
1237 |
lock.unlock(); |
1238 |
} |
1239 |
} |
1240 |
|
1241 |
@SuppressWarnings("unchecked") |
1242 |
public <T> T[] toArray(T[] a) { |
1243 |
final ReentrantLock lock = this.lock; |
1244 |
lock.lock(); |
1245 |
try { |
1246 |
if (a.length < size) |
1247 |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
1248 |
System.arraycopy(queue, 0, a, 0, size); |
1249 |
if (a.length > size) |
1250 |
a[size] = null; |
1251 |
return a; |
1252 |
} finally { |
1253 |
lock.unlock(); |
1254 |
} |
1255 |
} |
1256 |
|
1257 |
public Iterator<Runnable> iterator() { |
1258 |
return new Itr(Arrays.copyOf(queue, size)); |
1259 |
} |
1260 |
|
1261 |
/** |
1262 |
* Snapshot iterator that works off copy of underlying q array. |
1263 |
*/ |
1264 |
private class Itr implements Iterator<Runnable> { |
1265 |
final RunnableScheduledFuture<?>[] array; |
1266 |
int cursor; // index of next element to return; initially 0 |
1267 |
int lastRet = -1; // index of last element returned; -1 if no such |
1268 |
|
1269 |
Itr(RunnableScheduledFuture<?>[] array) { |
1270 |
this.array = array; |
1271 |
} |
1272 |
|
1273 |
public boolean hasNext() { |
1274 |
return cursor < array.length; |
1275 |
} |
1276 |
|
1277 |
public Runnable next() { |
1278 |
if (cursor >= array.length) |
1279 |
throw new NoSuchElementException(); |
1280 |
lastRet = cursor; |
1281 |
return array[cursor++]; |
1282 |
} |
1283 |
|
1284 |
public void remove() { |
1285 |
if (lastRet < 0) |
1286 |
throw new IllegalStateException(); |
1287 |
DelayedWorkQueue.this.remove(array[lastRet]); |
1288 |
lastRet = -1; |
1289 |
} |
1290 |
} |
1291 |
} |
1292 |
} |