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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. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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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.*; |
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|
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/** |
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* An {@link Executor} that can schedule commands to run after a given |
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* delay, or to execute periodically. This class is preferable to |
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* {@link java.util.Timer} when multiple worker threads are needed, |
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* or when the additional flexibility or capabilities of |
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* {@link ThreadPoolExecutor} (which this class extends) are |
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* required. |
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* |
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* <p> The <tt>schedule</tt> methods create tasks with various delays |
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* and return a task object that can be used to cancel or check |
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* execution. The <tt>scheduleAtFixedRate</tt> and |
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* <tt>scheduleWithFixedDelay</tt> methods create and execute tasks |
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* that run periodically until cancelled. Commands submitted using |
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* the <tt>execute</tt> method are scheduled with a requested delay of |
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* zero. |
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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 enabled, |
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* they will commence. Tasks tied for the same execution time are |
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* enabled in first-in-first-out (FIFO) order of submission. |
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* |
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* <p>All <t>schedule</tt> methods accept <em>relative</em> delays and |
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* periods as arguments, not absolute times or dates. It is a simple |
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* matter to transform an absolute time represented as a {@link |
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* java.util.Date} to the required form. For example, to schedule at |
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* a certain future <tt>date</tt>, you can use: <tt>schedule(task, |
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* date.getTime() - System.currentTimeMillis(), |
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* TimeUnit.MILLISECONDS)</tt>. Beware however that expiration of a |
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* relative delay need not coincide with the current <tt>Date</tt> at |
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* which the task is enabled due to network time synchronization |
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* protocols, clock drift, or other factors. Negative relative delays |
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* (but not periods) are allowed in <tt>schedule</tt> methods, and are |
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* treated as requests for immediate execution. |
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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 especially useful for |
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* it. In particular, because a <tt>ScheduledExecutor</tt> always acts |
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* as a fixed-sized pool using <tt>corePoolSize</tt> threads and an |
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* unbounded queue, adjustments to <tt>maximumPoolSize</tt> have no |
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* useful effect. |
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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 ScheduledExecutor extends ThreadPoolExecutor { |
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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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/** |
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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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private static class ScheduledCancellableTask |
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extends CancellableTask implements ScheduledCancellable { |
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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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/** The time the task is enabled to execute in nanoTime units */ |
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private long time; |
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/** The delay following next time, or <= 0 if non-periodic */ |
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private final long period; |
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/** true if at fixed rate; false if fixed delay */ |
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private final boolean rateBased; |
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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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ScheduledCancellableTask(Runnable r, long ns) { |
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super(r); |
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this.time = ns; |
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this.period = 0; |
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rateBased = false; |
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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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* time but does not establish the action. (This is needed for |
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* the Future-based subclass). |
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*/ |
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ScheduledCancellableTask(long ns) { |
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super(); |
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this.time = ns; |
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this.period = 0; |
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rateBased = false; |
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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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ScheduledCancellableTask(Runnable r, long ns, long period, boolean rateBased) { |
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super(r); |
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this.time = ns; |
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this.period = period; |
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this.rateBased = rateBased; |
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this.sequenceNumber = sequencer.getAndIncrement(); |
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} |
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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 - System.nanoTime(), |
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TimeUnit.NANOSECONDS); |
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return d; |
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} |
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|
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public int compareTo(Object other) { |
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if (other == this) // compare zero ONLY if same object |
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return 0; |
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ScheduledCancellableTask x = (ScheduledCancellableTask)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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|
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/** |
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* Return true if this is a periodic (not a one-shot) action. |
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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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* Returns the period, or zero if non-periodic. |
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* |
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* @return the period |
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*/ |
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public long getPeriod(TimeUnit unit) { |
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return unit.convert(period, TimeUnit.NANOSECONDS); |
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} |
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|
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/** |
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* Overrides CancellableTask version so as to not setDone if |
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* periodic. |
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*/ |
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public void run() { |
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if (setRunning()) { |
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try { |
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getRunnable().run(); |
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} finally { |
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if (!isPeriodic()) |
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setDone(); |
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} |
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} |
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} |
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|
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/** |
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* Return a ScheduledCancellable task (which may be this task) |
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* that will trigger in the period subsequent to current task, |
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* or null if non-periodic or cancelled. |
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*/ |
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ScheduledCancellableTask nextTask() { |
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if (period <= 0 || !reset()) |
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return null; |
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time = period + (rateBased ? time : System.nanoTime()); |
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return this; |
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} |
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} |
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|
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private static class ScheduledFutureTask<V> |
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extends ScheduledCancellableTask implements ScheduledFuture<V> { |
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|
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/** |
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* Creates a ScheduledFuture that may trigger after the given delay. |
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*/ |
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ScheduledFutureTask(Callable<V> callable, long triggerTime) { |
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// must set callable after super ctor call to use inner class |
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super(triggerTime); |
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setRunnable(new InnerCancellableFuture<V>(callable)); |
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} |
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|
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public V get() throws InterruptedException, ExecutionException { |
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return ((InnerCancellableFuture<V>)getRunnable()).get(); |
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} |
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|
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public V get(long timeout, TimeUnit unit) |
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throws InterruptedException, ExecutionException, TimeoutException { |
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return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit); |
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} |
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|
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protected void set(V v) { |
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((InnerCancellableFuture<V>)getRunnable()).set(v); |
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} |
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|
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protected void setException(Throwable t) { |
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((InnerCancellableFuture<V>)getRunnable()).setException(t); |
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} |
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} |
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|
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|
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/** |
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* An annoying wrapper class to convince generics compiler to |
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* use a DelayQueue<ScheduledCancellableTask> as a BlockingQueue<Runnable> |
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*/ |
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private static class DelayedWorkQueue |
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extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> { |
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|
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private final DelayQueue<ScheduledCancellableTask> dq = new DelayQueue<ScheduledCancellableTask>(); |
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public Runnable poll() { return dq.poll(); } |
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public Runnable peek() { return dq.peek(); } |
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public Runnable take() throws InterruptedException { return dq.take(); } |
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public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException { |
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return dq.poll(timeout, unit); |
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} |
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|
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public boolean add(Runnable x) { return dq.add((ScheduledCancellableTask)x); } |
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public boolean offer(Runnable x) { return dq.offer((ScheduledCancellableTask)x); } |
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public void put(Runnable x) { |
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dq.put((ScheduledCancellableTask)x); |
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} |
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public boolean offer(Runnable x, long timeout, TimeUnit unit) { |
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return dq.offer((ScheduledCancellableTask)x, timeout, unit); |
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} |
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|
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public Runnable remove() { return dq.remove(); } |
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public Runnable element() { return dq.element(); } |
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public void clear() { dq.clear(); } |
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public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); } |
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public int drainTo(Collection<? super Runnable> c, int maxElements) { |
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return dq.drainTo(c, maxElements); |
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} |
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|
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public int remainingCapacity() { return dq.remainingCapacity(); } |
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public boolean remove(Object x) { return dq.remove(x); } |
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public boolean contains(Object x) { return dq.contains(x); } |
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public int size() { return dq.size(); } |
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public boolean isEmpty() { return dq.isEmpty(); } |
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public Object[] toArray() { return dq.toArray(); } |
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public <T> T[] toArray(T[] array) { return dq.toArray(array); } |
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public Iterator<Runnable> iterator() { |
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return new Iterator<Runnable>() { |
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private Iterator<ScheduledCancellableTask> it = dq.iterator(); |
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public boolean hasNext() { return it.hasNext(); } |
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public Runnable next() { return it.next(); } |
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public void remove() { it.remove(); } |
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}; |
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} |
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} |
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|
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/** |
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* Creates a new ScheduledExecutor with the given core pool size. |
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* |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @throws IllegalArgumentException if corePoolSize less than or |
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* equal to zero |
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*/ |
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public ScheduledExecutor(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 ScheduledExecutor with the given initial parameters. |
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* |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @param threadFactory the factory to use when the executor |
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* creates a new thread. |
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* @throws NullPointerException if threadFactory is null |
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*/ |
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public ScheduledExecutor(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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} |
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|
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/** |
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* Creates a new ScheduledExecutor with the given initial parameters. |
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* |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @param handler the handler to use when execution is blocked |
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* because the thread bounds and queue capacities are reached. |
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* @throws NullPointerException if handler is null |
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*/ |
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public ScheduledExecutor(int corePoolSize, |
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RejectedExecutionHandler handler) { |
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super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
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new DelayedWorkQueue(), handler); |
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} |
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|
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/** |
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* Creates a new ScheduledExecutor with the given initial parameters. |
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* |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @param threadFactory the factory to use when the executor |
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* creates a new thread. |
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* @param handler the handler to use when execution is blocked |
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* because the thread bounds and queue capacities are reached. |
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* @throws NullPointerException if threadFactory or handler is null |
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*/ |
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public ScheduledExecutor(int corePoolSize, |
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ThreadFactory threadFactory, |
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RejectedExecutionHandler handler) { |
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super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, |
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new DelayedWorkQueue(), threadFactory, handler); |
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} |
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|
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/** |
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* Specialized variant of ThreadPoolExecutor.execute for delayed tasks. |
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*/ |
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private void delayedExecute(Runnable command) { |
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if (isShutdown()) { |
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reject(command); |
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return; |
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} |
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// Prestart a thread if necessary. We cannot prestart it |
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// running the task because the task (probably) shouldn't be |
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// run yet, so thread will just idle until delay elapses. |
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if (getPoolSize() < getCorePoolSize()) |
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prestartCoreThread(); |
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|
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super.getQueue().add(command); |
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} |
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|
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/** |
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* Creates and executes a one-shot action that becomes enabled after |
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* the given delay. |
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* @param command the task to execute. |
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* @param delay the time from now to delay execution. |
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* @param unit the time unit of the delay parameter. |
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* @return a handle that can be used to cancel the task. |
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* @throws RejectedExecutionException if task cannot be scheduled |
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* for execution because the executor has been shut down. |
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* @throws NullPointerException if command is null |
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*/ |
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|
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public ScheduledCancellable schedule(Runnable command, long delay, TimeUnit unit) { |
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if (command == null) |
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throw new NullPointerException(); |
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long triggerTime = System.nanoTime() + unit.toNanos(delay); |
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ScheduledCancellableTask t = new ScheduledCancellableTask(command, triggerTime); |
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delayedExecute(t); |
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return t; |
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} |
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|
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/** |
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* Creates and executes a ScheduledFuture that becomes enabled after the |
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* given delay. |
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* @param callable the function to execute. |
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* @param delay the time from now to delay execution. |
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* @param unit the time unit of the delay parameter. |
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* @return a ScheduledFuture that can be used to extract result or cancel. |
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* @throws RejectedExecutionException if task cannot be scheduled |
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* for execution because the executor has been shut down. |
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* @throws NullPointerException if callable is null |
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*/ |
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public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) { |
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if (callable == null) |
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throw new NullPointerException(); |
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long triggerTime = System.nanoTime() + unit.toNanos(delay); |
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ScheduledFutureTask<V> t = new ScheduledFutureTask<V>(callable, triggerTime); |
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delayedExecute(t); |
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return t; |
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} |
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|
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/** |
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* Creates and executes a periodic action that becomes enabled first |
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* after the given initial delay, and subsequently with the given |
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* period; that is executions will commence after |
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* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then |
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* <tt>initialDelay + 2 * period</tt>, and so on. The |
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* task will only terminate via cancellation. |
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* @param command the task to execute. |
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* @param initialDelay the time to delay first execution. |
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* @param period the period between successive executions. |
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* @param unit the time unit of the delay and period parameters |
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* @return a handle that can be used to cancel the task. |
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* @throws RejectedExecutionException if task cannot be scheduled |
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* for execution because the executor has been shut down. |
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* @throws NullPointerException if command is null |
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* @throws IllegalArgumentException if period less than or equal to zero. |
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*/ |
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public ScheduledCancellable scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) { |
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if (command == null) |
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throw new NullPointerException(); |
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if (period <= 0) |
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throw new IllegalArgumentException(); |
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long triggerTime = System.nanoTime() + unit.toNanos(initialDelay); |
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ScheduledCancellableTask t = new ScheduledCancellableTask(command, |
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triggerTime, |
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unit.toNanos(period), |
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true); |
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delayedExecute(t); |
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return t; |
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} |
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|
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/** |
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* Creates and executes a periodic action that becomes enabled first |
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* after the given initial delay, and subsequently with the |
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* given delay between the termination of one execution and the |
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* commencement of the next. |
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* The task will only terminate via cancellation. |
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* @param command the task to execute. |
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* @param initialDelay the time to delay first execution. |
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* @param delay the delay between the termination of one |
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* execution and the commencement of the next. |
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* @param unit the time unit of the delay and delay parameters |
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* @return a handle that can be used to cancel the task. |
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* @throws RejectedExecutionException if task cannot be scheduled |
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* for execution because the executor has been shut down. |
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* @throws NullPointerException if command is null |
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* @throws IllegalArgumentException if delay less than or equal to zero. |
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*/ |
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public ScheduledCancellable scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) { |
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if (command == null) |
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throw new NullPointerException(); |
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if (delay <= 0) |
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throw new IllegalArgumentException(); |
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long triggerTime = System.nanoTime() + unit.toNanos(initialDelay); |
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ScheduledCancellableTask t = new ScheduledCancellableTask(command, |
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triggerTime, |
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unit.toNanos(delay), |
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false); |
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delayedExecute(t); |
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return t; |
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} |
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|
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|
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/** |
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* Execute command with zero required delay. This has effect |
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* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note |
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* that inspections of the queue and of the list returned by |
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* <tt>shutdownNow</tt> will access the zero-delayed |
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* {@link ScheduledCancellable}, not the <tt>command</tt> itself. |
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* |
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* @param command the task to execute |
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* @throws RejectedExecutionException at discretion of |
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* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
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* for execution because the executor has been shut down. |
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* @throws NullPointerException if command is null |
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*/ |
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public void execute(Runnable command) { |
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if (command == null) |
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throw new NullPointerException(); |
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schedule(command, 0, TimeUnit.NANOSECONDS); |
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} |
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|
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|
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/** |
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* Set policy on whether to continue executing existing periodic |
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* tasks even when this executor has been <tt>shutdown</tt>. In |
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* this case, these tasks will only terminate upon |
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* <tt>shutdownNow</tt>, or after setting the policy to |
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* <tt>false</tt> when already shutdown. This value is by default |
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* false. |
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* @param value if true, continue after shutdown, else don't. |
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*/ |
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public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) { |
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continueExistingPeriodicTasksAfterShutdown = value; |
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if (!value && isShutdown()) |
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cancelUnwantedTasks(); |
483 |
} |
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|
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/** |
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* Get the policy on whether to continue executing existing |
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* periodic tasks even when this executor has been |
488 |
* <tt>shutdown</tt>. In this case, these tasks will only |
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* terminate upon <tt>shutdownNow</tt> or after setting the policy |
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* to <tt>false</tt> when already shutdown. This value is by |
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* default false. |
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* @return true if will continue after shutdown. |
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*/ |
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public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() { |
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return continueExistingPeriodicTasksAfterShutdown; |
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} |
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|
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/** |
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* Set policy on whether to execute existing delayed |
500 |
* tasks even when this executor has been <tt>shutdown</tt>. In |
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* this case, these tasks will only terminate upon |
502 |
* <tt>shutdownNow</tt>, or after setting the policy to |
503 |
* <tt>false</tt> when already shutdown. This value is by default |
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* true. |
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* @param value if true, execute after shutdown, else don't. |
506 |
*/ |
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public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) { |
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executeExistingDelayedTasksAfterShutdown = value; |
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if (!value && isShutdown()) |
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cancelUnwantedTasks(); |
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} |
512 |
|
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/** |
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* Get policy on whether to execute existing delayed |
515 |
* tasks even when this executor has been <tt>shutdown</tt>. In |
516 |
* this case, these tasks will only terminate upon |
517 |
* <tt>shutdownNow</tt>, or after setting the policy to |
518 |
* <tt>false</tt> when already shutdown. This value is by default |
519 |
* true. |
520 |
* @return true if will execute after shutdown. |
521 |
*/ |
522 |
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() { |
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return executeExistingDelayedTasksAfterShutdown; |
524 |
} |
525 |
|
526 |
/** |
527 |
* Cancel and clear the queue of all tasks that should not be run |
528 |
* due to shutdown policy. |
529 |
*/ |
530 |
private void cancelUnwantedTasks() { |
531 |
boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy(); |
532 |
boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy(); |
533 |
if (!keepDelayed && !keepPeriodic) |
534 |
super.getQueue().clear(); |
535 |
else if (keepDelayed || keepPeriodic) { |
536 |
Object[] entries = super.getQueue().toArray(); |
537 |
for (int i = 0; i < entries.length; ++i) { |
538 |
ScheduledCancellableTask t = (ScheduledCancellableTask)entries[i]; |
539 |
if (t.isPeriodic()? !keepPeriodic : !keepDelayed) |
540 |
t.cancel(false); |
541 |
} |
542 |
entries = null; |
543 |
purge(); |
544 |
} |
545 |
} |
546 |
|
547 |
/** |
548 |
* Initiates an orderly shutdown in which previously submitted |
549 |
* tasks are executed, but no new tasks will be accepted. If the |
550 |
* <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has |
551 |
* been set <tt>false</tt>, existing delayed tasks whose delays |
552 |
* have not yet elapsed are cancelled. And unless the |
553 |
* <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has |
554 |
* been set <tt>true</tt>, future executions of existing periodic |
555 |
* tasks will be cancelled. |
556 |
*/ |
557 |
public void shutdown() { |
558 |
cancelUnwantedTasks(); |
559 |
super.shutdown(); |
560 |
} |
561 |
|
562 |
/** |
563 |
* Attempts to stop all actively executing tasks, halts the |
564 |
* processing of waiting tasks, and returns a list of the tasks that were |
565 |
* awaiting execution. |
566 |
* |
567 |
* <p>There are no guarantees beyond best-effort attempts to stop |
568 |
* processing actively executing tasks. This implementations |
569 |
* cancels via {@link Thread#interrupt}, so if any tasks mask or |
570 |
* fail to respond to interrupts, they may never terminate. |
571 |
* |
572 |
* @return list of tasks that never commenced execution. Each |
573 |
* element of this list is a {@link ScheduledCancellable}, |
574 |
* including those tasks submitted using <tt>execute</tt> which |
575 |
* are for scheduling purposes used as the basis of a zero-delay |
576 |
* <tt>ScheduledCancellable</tt>. |
577 |
*/ |
578 |
public List shutdownNow() { |
579 |
return super.shutdownNow(); |
580 |
} |
581 |
|
582 |
/** |
583 |
* Removes this task from internal queue if it is present, thus |
584 |
* causing it not to be run if it has not already started. This |
585 |
* method may be useful as one part of a cancellation scheme. |
586 |
* |
587 |
* @param task the task to remove |
588 |
* @return true if the task was removed |
589 |
*/ |
590 |
public boolean remove(Runnable task) { |
591 |
if (task instanceof ScheduledCancellable) |
592 |
return super.remove(task); |
593 |
|
594 |
// The task might actually have been wrapped as a ScheduledCancellable |
595 |
// in execute(), in which case we need to manually traverse |
596 |
// looking for it. |
597 |
|
598 |
ScheduledCancellable wrap = null; |
599 |
Object[] entries = super.getQueue().toArray(); |
600 |
for (int i = 0; i < entries.length; ++i) { |
601 |
ScheduledCancellableTask t = (ScheduledCancellableTask)entries[i]; |
602 |
Runnable r = t.getRunnable(); |
603 |
if (task.equals(r)) { |
604 |
wrap = t; |
605 |
break; |
606 |
} |
607 |
} |
608 |
entries = null; |
609 |
return wrap != null && super.getQueue().remove(wrap); |
610 |
} |
611 |
|
612 |
|
613 |
/** |
614 |
* Returns the task queue used by this executor. Each element of |
615 |
* this queue is a {@link ScheduledCancellable}, including those |
616 |
* tasks submitted using <tt>execute</tt> which are for scheduling |
617 |
* purposes used as the basis of a zero-delay |
618 |
* <tt>ScheduledCancellable</tt>. Iteration over this queue is |
619 |
* </em>not</em> guaranteed to traverse tasks in the order in |
620 |
* which they will execute. |
621 |
* |
622 |
* @return the task queue |
623 |
*/ |
624 |
public BlockingQueue<Runnable> getQueue() { |
625 |
return super.getQueue(); |
626 |
} |
627 |
|
628 |
/** |
629 |
* Override of <tt>Executor</tt> hook method to support periodic |
630 |
* tasks. If the executed task was periodic, causes the task for |
631 |
* the next period to execute. |
632 |
* @param r the task (assumed to be a ScheduledCancellable) |
633 |
* @param t the exception |
634 |
*/ |
635 |
protected void afterExecute(Runnable r, Throwable t) { |
636 |
super.afterExecute(r, t); |
637 |
ScheduledCancellableTask next = ((ScheduledCancellableTask)r).nextTask(); |
638 |
if (next != null && |
639 |
(!isShutdown() || |
640 |
(getContinueExistingPeriodicTasksAfterShutdownPolicy() && |
641 |
!isTerminating()))) |
642 |
super.getQueue().add(next); |
643 |
|
644 |
// This might have been the final executed delayed task. Wake |
645 |
// up threads to check. |
646 |
else if (isShutdown()) |
647 |
interruptIdleWorkers(); |
648 |
} |
649 |
} |