util/concurrent/ScheduledExecutor.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.concurrent.atomic.*;
import java.util.*;

/**
 * An <tt>Executor</tt> that can schedule command to run after a given
 * delay, or to execute periodically. This class is preferable to
 * <tt>java.util.Timer</tt> when multiple worker threads are needed,
 * or when the additional flexibility or capabilities of
 * <tt>ThreadPoolExecutor</tt> (which this class extends) are
 * required.
 *
 * <p> The <tt>schedule</tt> methods create tasks with various delays
 * and return a task object that can be used to cancel or check
 * execution. The <tt>scheduleAtFixedRate</tt> and
 * <tt>scheduleWithFixedDelay</tt> methods create and execute tasks
 * that run periodically until cancelled.  Commands submitted using
 * the <tt>execute</tt> method are scheduled with a requested delay of
 * zero.
 *
 * <p> Delayed tasks execute no sooner than they are enabled, but
 * without any real-time guarantees about when, after they are enabled
 * they will commence. Tasks tied for the same execution time are
 * enabled in first-in-first-out (FIFO) order of submission. An
 * internal {@link DelayQueue} used for scheduling relies on relative
 * delays, which may drift from absolute times (as returned by
 * <tt>System.currentTimeMillis</tt>) over sufficiently long periods.
 *
 * <p>While this class inherits from {@link ThreadPoolExecutor}, a few
 * of the inherited tuning methods are not especially useful for
 * it. In particular, because a <tt>ScheduledExecutor</tt> always acts
 * as a fixed-sized pool using <tt>corePoolSize</tt> threads and an
 * unbounded queue, adjustments to <tt>maximumPoolSize</tt> have no
 * useful effect.
 *
 * @since 1.5
 * @see Executors
 *
 * @spec JSR-166
 * @author Doug Lea
 */
public class ScheduledExecutor extends ThreadPoolExecutor {

    /**
     * Sequence number to break scheduling ties, and in turn to
     * guarantee FIFO order among tied entries.
     */
    private static final AtomicLong sequencer = new AtomicLong(0);

    /**
     * A delayed or periodic action.
     */
    public static class DelayedTask extends CancellableTask implements Delayed {
        /** Sequence number to break ties FIFO */
        private final long sequenceNumber;
        /** The time the task is enabled to execute in nanoTime units */
        private final long time;
        /** The delay forllowing next time, or <= 0 if non-periodic */
        private final long period;
        /** true if at fixed rate; false if fixed delay */
        private final boolean rateBased; 

        /**
         * Creates a one-shot action with given nanoTime-based trigger time
         */
        DelayedTask(Runnable r, long ns) {
            super(r);
            this.time = ns;
            this.period = 0;
            rateBased = false;
            this.sequenceNumber = sequencer.getAndIncrement();
        }

        /**
         * Creates a periodic action with given nano time and period
         */
        DelayedTask(Runnable r, long ns,  long period, boolean rateBased) {
            super(r);
            if (period <= 0)
                throw new IllegalArgumentException();
            this.time = ns;
            this.period = period;
            this.rateBased = rateBased;
            this.sequenceNumber = sequencer.getAndIncrement();
        }


        public long getDelay(TimeUnit unit) {
            long d =  unit.convert(time - System.nanoTime(), 
                                TimeUnit.NANOSECONDS);
            return d;
        }

        public int compareTo(Object other) {
            if (other == this)
                return 0;
            DelayedTask x = (DelayedTask)other;
            long diff = time - x.time;
            if (diff < 0)
                return -1;
            else if (diff > 0)
                return 1;
            else if (sequenceNumber < x.sequenceNumber)
                return -1;
            else
                return 1;
        }

        /**
         * Return true if this is a periodic (not a one-shot) action.
         * @return true if periodic
         */
        public boolean isPeriodic() {
            return period > 0;
        }

        /**
         * Returns the period, or zero if non-periodic.
         *
         * @return the period
         */
        public long getPeriod(TimeUnit unit) {
            return unit.convert(period, TimeUnit.NANOSECONDS);
        }

        /**
         * Return a new DelayedTask that will trigger in the period
         * subsequent to current task, or null if non-periodic
         * or canceled.
         */
        DelayedTask nextTask() {
            if (period <= 0 || isCancelled())
                return null;
            long nextTime = period + (rateBased ? time : System.nanoTime());
            return new DelayedTask(getRunnable(), nextTime, period, rateBased);
        }

    }

    /**
     * A delayed result-bearing action.
     */
    public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
        /**
         * Creates a Future that may trigger after the given delay.
         */
        DelayedFutureTask(Callable<V> callable, long delay,  TimeUnit unit) {
            // must set after super ctor call to use inner class
            super(null, System.nanoTime() + unit.toNanos(delay));
            setRunnable(new InnerCancellableFuture<V>(callable));
        }

        /**
         * Creates a one-shot action that may trigger after the given date.
         */
        DelayedFutureTask(Callable<V> callable, Date date) {
            super(null, 
                  TimeUnit.MILLISECONDS.toNanos(date.getTime() - 
                                                System.currentTimeMillis()));
            setRunnable(new InnerCancellableFuture<V>(callable));
        }
    
        public V get() throws InterruptedException, ExecutionException {
            return ((InnerCancellableFuture<V>)getRunnable()).get();
        }

        public V get(long timeout, TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
            return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
        }

        protected void set(V v) {
            ((InnerCancellableFuture<V>)getRunnable()).set(v);
        }

        protected void setException(Throwable t) {
            ((InnerCancellableFuture<V>)getRunnable()).setException(t);
        }
    }


    /**
     * An annoying wrapper class to convince generics compiler to
     * use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
     */ 
    private static class DelayedWorkQueue extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> {
        private final DelayQueue<DelayedTask> dq = new DelayQueue<DelayedTask>();
        public Runnable poll() { return dq.poll(); }
        public Runnable peek() { return dq.peek(); }
        public Runnable take() throws InterruptedException { return dq.take(); }
        public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
            return dq.poll(timeout, unit);
        }

        public boolean add(Runnable x) { return dq.add((DelayedTask)x); }
        public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
        public void put(Runnable x) throws InterruptedException {
            dq.put((DelayedTask)x); 
        }
        public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
            return dq.offer((DelayedTask)x, timeout, unit);
        }

        public Runnable remove() { return dq.remove(); }
        public Runnable element() { return dq.element(); }
        public void clear() { dq.clear(); }

        public int remainingCapacity() { return dq.remainingCapacity(); }
        public boolean remove(Object x) { return dq.remove(x); }
        public boolean contains(Object x) { return dq.contains(x); }
        public int size() { return dq.size(); }
        public boolean isEmpty() { return dq.isEmpty(); }
        public Iterator<Runnable> iterator() { 
            return new Iterator<Runnable>() {
                private Iterator<DelayedTask> it = dq.iterator();
                public boolean hasNext() { return it.hasNext(); }
                public Runnable next() { return it.next(); }
                public void remove() {  it.remove(); }
            };
        }
    }

    /**
     * Creates a new ScheduledExecutor with the given initial parameters.
     * 
     * @param corePoolSize the number of threads to keep in the pool,
     * even if they are idle.
     */
    public ScheduledExecutor(int corePoolSize) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue());
    }

    /**
     * Creates a new ScheduledExecutor with the given initial parameters.
     * 
     * @param corePoolSize the number of threads to keep in the pool,
     * even if they are idle.
     * @param threadFactory the factory to use when the executor
     * creates a new thread. 
     */
    public ScheduledExecutor(int corePoolSize,
                             ThreadFactory threadFactory) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), threadFactory);
    }

    /**
     * Creates a new ScheduledExecutor with the given initial parameters.
     * 
     * @param corePoolSize the number of threads to keep in the pool,
     * even if they are idle.
     * @param handler the handler to use when execution is blocked
     * because the thread bounds and queue capacities are reached.
     */
    public ScheduledExecutor(int corePoolSize,
                              RejectedExecutionHandler handler) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), handler);
    }

    /**
     * Creates a new ScheduledExecutor with the given initial parameters.
     * 
     * @param corePoolSize the number of threads to keep in the pool,
     * even if they are idle.
     * @param threadFactory the factory to use when the executor
     * creates a new thread. 
     * @param handler the handler to use when execution is blocked
     * because the thread bounds and queue capacities are reached.
     */
    public ScheduledExecutor(int corePoolSize,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), threadFactory, handler);
    }

    /**
     * Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
     */
    void delayedExecute(Runnable command) {
        if (isShutdown()) {
            reject(command);
            return;
        }
        // Prestart thread if necessary. We cannot prestart it running
        // the task because the task (probably) shouldn't be run yet,
        // so thread will just idle until delay elapses.
        if (getPoolSize() < getCorePoolSize())
            addIfUnderCorePoolSize(null);
            
        getQueue().offer(command);
    }

    /**
     * Creates and executes a one-shot action that becomes enabled after
     * the given delay.
     * @param command the task to execute.
     * @param delay the time from now to delay execution.
     * @param unit the time unit of the delay parameter.
     * @return a handle that can be used to cancel the task.
     */

    public DelayedTask schedule(Runnable command, long delay,  TimeUnit unit) {
        DelayedTask t = new DelayedTask(command, System.nanoTime() + unit.toNanos(delay));
        delayedExecute(t);
        return t;
    }

    /**
     * Creates and executes a one-shot action that becomes enabled
     * after the given date.
     * @param command the task to execute.
     * @param date the time to commence excution.
     * @return a handle that can be used to cancel the task.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public DelayedTask schedule(Runnable command, Date date) {
        DelayedTask t = new DelayedTask
            (command, 
             TimeUnit.MILLISECONDS.toNanos(date.getTime() - 
                                           System.currentTimeMillis()));
        delayedExecute(t);
        return t;
    }
    
    /**
     * Creates and executes a periodic action that becomes enabled first
     * after the given initial delay, and subsequently with the given
     * period; that is executions will commence after
     * <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
     * <tt>initialDelay + 2 * period</tt>, and so on.
     * @param command the task to execute.
     * @param initialDelay the time to delay first execution.
     * @param period the period between successive executions.
     * @param unit the time unit of the delay and period parameters
     * @return a handle that can be used to cancel the task.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay,  long period, TimeUnit unit) {
        DelayedTask t = new DelayedTask
            (command, System.nanoTime() + unit.toNanos(initialDelay),
             unit.toNanos(period), true);
        delayedExecute(t);
        return t;
    }
    
    /**
     * Creates a periodic action that becomes enabled first after the
     * given date, and subsequently with the given period
     * period; that is executions will commence after
     * <tt>initialDate</tt> then <tt>initialDate+period</tt>, then
     * <tt>initialDate + 2 * period</tt>, and so on.
     * @param command the task to execute.
     * @param initialDate the time to delay first execution.
     * @param period the period between commencement of successive
     * executions.
     * @param unit the time unit of the  period parameter.
     * @return a handle that can be used to cancel the task.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public DelayedTask scheduleAtFixedRate(Runnable command, Date initialDate, long period, TimeUnit unit) {
        DelayedTask t = new DelayedTask
            (command, 
             TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() - 
                                           System.currentTimeMillis()),
             unit.toNanos(period), true);
        delayedExecute(t);
        return t;
    }

    /**
     * Creates and executes a periodic action that becomes enabled first
     * after the given initial delay, and and subsequently with the
     * given delay between the termination of one execution and the
     * commencement of the next.
     * @param command the task to execute.
     * @param initialDelay the time to delay first execution.
     * @param delay the delay between the termination of one
     * execution and the commencement of the next.
     * @param unit the time unit of the delay and delay parameters
     * @return a handle that can be used to cancel the task.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public DelayedTask scheduleWithFixedDelay(Runnable command, long initialDelay,  long delay, TimeUnit unit) {
        DelayedTask t = new DelayedTask
            (command, System.nanoTime() + unit.toNanos(initialDelay),
             unit.toNanos(delay), false);
        delayedExecute(t);
        return t;
    }
    
    /**
     * Creates a periodic action that becomes enabled first after the
     * given date, and subsequently with the given delay between
     * the termination of one execution and the commencement of the
     * next.
     * @param command the task to execute.
     * @param initialDate the time to delay first execution.
     * @param delay the delay between the termination of one
     * execution and the commencement of the next.
     * @param unit the time unit of the  delay parameter.
     * @return a handle that can be used to cancel the task.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public DelayedTask scheduleWithFixedDelay(Runnable command, Date initialDate, long delay, TimeUnit unit) {
        DelayedTask t = new DelayedTask
            (command, 
             TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() - 
                                           System.currentTimeMillis()),
             unit.toNanos(delay), false);
        delayedExecute(t);
        return t;
    }


    /**
     * Creates and executes a Future that becomes enabled after the
     * given delay.
     * @param callable the function to execute.
     * @param delay the time from now to delay execution.
     * @param unit the time unit of the delay parameter.
     * @return a Future that can be used to extract result or cancel.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public <V> DelayedFutureTask<V> schedule(Callable<V> callable, long delay,  TimeUnit unit) {
        DelayedFutureTask<V> t = new DelayedFutureTask<V>
            (callable, delay, unit);
        delayedExecute(t);
        return t;
    }

    /**
     * Creates and executes a one-shot action that becomes enabled after
     * the given date.
     * @param callable the function to execute.
     * @param date the time to commence excution.
     * @return a Future that can be used to extract result or cancel.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution because the executor has been shut down.
     */
    public <V> DelayedFutureTask<V> schedule(Callable<V> callable, Date date) {
        DelayedFutureTask<V> t = new DelayedFutureTask<V>
            (callable, date);
        delayedExecute(t);
        return t;
    }

    /**
     * Execute command with zero required delay. This has effect
     * equivalent to <tt>schedule(command, 0, anyUnit)</tt>.  Note
     * that inspections of the queue and of the list returned by
     * <tt>shutdownNow</tt> will access the zero-delayed
     * <tt>DelayedTask</tt>, not the <tt>command</tt> itself.
     *
     * @param command the task to execute
     * @throws RejectedExecutionException at discretion of
     * <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
     * for execution because the executor has been shut down.
     */
    public void execute(Runnable command) {
        schedule(command, 0, TimeUnit.NANOSECONDS);
    }

    /**
     * Removes this task from internal queue if it is present, thus
     * causing it not to be run if it has not already started.  This
     * method may be useful as one part of a cancellation scheme.
     *
     * @param task the task to remove
     * @return true if the task was removed
     */
    public boolean remove(Runnable task) {
        if (task instanceof DelayedTask && getQueue().remove(task))
            return true;

        // The task might actually have been wrapped as a DelayedTask
        // in execute(), in which case we need to maually traverse
        // looking for it.

        DelayedTask wrap = null;
        Object[] entries = getQueue().toArray();
        for (int i = 0; i < entries.length; ++i) {
            DelayedTask t = (DelayedTask)entries[i];
            Runnable r = t.getRunnable();
            if (task.equals(r)) {
                wrap = t;
                break;
            }
        }
        entries = null;
        return wrap != null && getQueue().remove(wrap);
    }

    /**
     * If executed task was periodic, cause the task for the next
     * period to execute.
     * @param r the task (assumed to be a DelayedTask)
     * @param t the exception
     */
    protected void afterExecute(Runnable r, Throwable t) { 
        if (isShutdown()) 
            return;
        super.afterExecute(r, t);
        DelayedTask d = (DelayedTask)r;
        DelayedTask next = d.nextTask();
        if (next == null) 
            return;
        try {
            delayedExecute(next);
        } catch(RejectedExecutionException ex) {
            // lost race to detect shutdown; ignore
        }
    }
}


Revision:	1.16
Committed:	Mon Aug 11 19:41:03 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.15:	+5 -1 lines
Log Message:	Clarified execute javadoc
#	User	Rev	Content
1	tim	1.1	/*
2	dl	1.4	* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5	tim	1.1	*/
6
7			package java.util.concurrent;
8	dl	1.4	import java.util.concurrent.atomic.*;
9	dl	1.2	import java.util.*;
10	tim	1.1
11			/**
12	dl	1.7	* An <tt>Executor</tt> that can schedule command to run after a given
13			* delay, or to execute periodically. This class is preferable to
14	tim	1.1	* <tt>java.util.Timer</tt> when multiple worker threads are needed,
15			* or when the additional flexibility or capabilities of
16	dl	1.7	* <tt>ThreadPoolExecutor</tt> (which this class extends) are
17			* required.
18			*
19			* <p> The <tt>schedule</tt> methods create tasks with various delays
20			* and return a task object that can be used to cancel or check
21			* execution. The <tt>scheduleAtFixedRate</tt> and
22			* <tt>scheduleWithFixedDelay</tt> methods create and execute tasks
23			* that run periodically until cancelled. Commands submitted using
24			* the <tt>execute</tt> method are scheduled with a requested delay of
25			* zero.
26			*
27			* <p> Delayed tasks execute no sooner than they are enabled, but
28			* without any real-time guarantees about when, after they are enabled
29			* they will commence. Tasks tied for the same execution time are
30			* enabled in first-in-first-out (FIFO) order of submission. An
31			* internal {@link DelayQueue} used for scheduling relies on relative
32			* delays, which may drift from absolute times (as returned by
33			* <tt>System.currentTimeMillis</tt>) over sufficiently long periods.
34	tim	1.1	*
35	dl	1.13	* <p>While this class inherits from {@link ThreadPoolExecutor}, a few
36			* of the inherited tuning methods are not especially useful for
37			* it. In particular, because a <tt>ScheduledExecutor</tt> always acts
38			* as a fixed-sized pool using <tt>corePoolSize</tt> threads and an
39			* unbounded queue, adjustments to <tt>maximumPoolSize</tt> have no
40			* useful effect.
41			*
42	tim	1.1	* @since 1.5
43			* @see Executors
44			*
45			* @spec JSR-166
46	dl	1.9	* @author Doug Lea
47	tim	1.1	*/
48			public class ScheduledExecutor extends ThreadPoolExecutor {
49
50	dl	1.4	/**
51	dl	1.5	* Sequence number to break scheduling ties, and in turn to
52			* guarantee FIFO order among tied entries.
53			*/
54			private static final AtomicLong sequencer = new AtomicLong(0);
55
56			/**
57	dl	1.4	* A delayed or periodic action.
58			*/
59	dl	1.8	public static class DelayedTask extends CancellableTask implements Delayed {
60	dl	1.9	/** Sequence number to break ties FIFO */
61	dl	1.4	private final long sequenceNumber;
62	dl	1.9	/** The time the task is enabled to execute in nanoTime units */
63	dl	1.4	private final long time;
64	dl	1.9	/** The delay forllowing next time, or <= 0 if non-periodic */
65	dl	1.4	private final long period;
66	dl	1.9	/** true if at fixed rate; false if fixed delay */
67			private final boolean rateBased;
68
69	dl	1.4	/**
70	dl	1.5	* Creates a one-shot action with given nanoTime-based trigger time
71	dl	1.4	*/
72			DelayedTask(Runnable r, long ns) {
73			super(r);
74			this.time = ns;
75			this.period = 0;
76	dl	1.7	rateBased = false;
77	dl	1.4	this.sequenceNumber = sequencer.getAndIncrement();
78			}
79
80			/**
81	dl	1.5	* Creates a periodic action with given nano time and period
82	dl	1.4	*/
83	dl	1.7	DelayedTask(Runnable r, long ns, long period, boolean rateBased) {
84	dl	1.4	super(r);
85			if (period <= 0)
86			throw new IllegalArgumentException();
87			this.time = ns;
88			this.period = period;
89	dl	1.7	this.rateBased = rateBased;
90	dl	1.4	this.sequenceNumber = sequencer.getAndIncrement();
91			}
92
93
94			public long getDelay(TimeUnit unit) {
95	dl	1.12	long d = unit.convert(time - System.nanoTime(),
96	dl	1.7	TimeUnit.NANOSECONDS);
97	dl	1.12	return d;
98	dl	1.4	}
99
100			public int compareTo(Object other) {
101	dl	1.15	if (other == this)
102			return 0;
103	dl	1.4	DelayedTask x = (DelayedTask)other;
104			long diff = time - x.time;
105			if (diff < 0)
106			return -1;
107			else if (diff > 0)
108			return 1;
109			else if (sequenceNumber < x.sequenceNumber)
110			return -1;
111			else
112			return 1;
113			}
114
115			/**
116			* Return true if this is a periodic (not a one-shot) action.
117	dl	1.9	* @return true if periodic
118	dl	1.4	*/
119			public boolean isPeriodic() {
120			return period > 0;
121			}
122
123			/**
124	tim	1.11	* Returns the period, or zero if non-periodic.
125			*
126	dl	1.9	* @return the period
127	dl	1.4	*/
128			public long getPeriod(TimeUnit unit) {
129			return unit.convert(period, TimeUnit.NANOSECONDS);
130			}
131
132			/**
133			* Return a new DelayedTask that will trigger in the period
134			* subsequent to current task, or null if non-periodic
135			* or canceled.
136			*/
137	dl	1.5	DelayedTask nextTask() {
138	dl	1.4	if (period <= 0 \|\| isCancelled())
139			return null;
140	dl	1.10	long nextTime = period + (rateBased ? time : System.nanoTime());
141	dl	1.7	return new DelayedTask(getRunnable(), nextTime, period, rateBased);
142	dl	1.4	}
143	dl	1.2
144	dl	1.4	}
145	dl	1.2
146	dl	1.4	/**
147			* A delayed result-bearing action.
148			*/
149	dl	1.8	public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
150	dl	1.4	/**
151			* Creates a Future that may trigger after the given delay.
152			*/
153			DelayedFutureTask(Callable<V> callable, long delay, TimeUnit unit) {
154			// must set after super ctor call to use inner class
155	dl	1.10	super(null, System.nanoTime() + unit.toNanos(delay));
156	dl	1.4	setRunnable(new InnerCancellableFuture<V>(callable));
157	dl	1.2	}
158
159	dl	1.4	/**
160			* Creates a one-shot action that may trigger after the given date.
161			*/
162			DelayedFutureTask(Callable<V> callable, Date date) {
163			super(null,
164			TimeUnit.MILLISECONDS.toNanos(date.getTime() -
165			System.currentTimeMillis()));
166			setRunnable(new InnerCancellableFuture<V>(callable));
167			}
168
169			public V get() throws InterruptedException, ExecutionException {
170			return ((InnerCancellableFuture<V>)getRunnable()).get();
171	dl	1.2	}
172
173	dl	1.4	public V get(long timeout, TimeUnit unit)
174			throws InterruptedException, ExecutionException, TimeoutException {
175			return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
176	dl	1.2	}
177	tim	1.1
178	dl	1.4	protected void set(V v) {
179			((InnerCancellableFuture<V>)getRunnable()).set(v);
180	dl	1.2	}
181	tim	1.1
182	dl	1.4	protected void setException(Throwable t) {
183			((InnerCancellableFuture<V>)getRunnable()).setException(t);
184			}
185			}
186
187
188			/**
189			* An annoying wrapper class to convince generics compiler to
190	dl	1.7	* use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
191	dl	1.4	*/
192	dl	1.12	private static class DelayedWorkQueue extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> {
193	dl	1.4	private final DelayQueue<DelayedTask> dq = new DelayQueue<DelayedTask>();
194			public Runnable poll() { return dq.poll(); }
195			public Runnable peek() { return dq.peek(); }
196			public Runnable take() throws InterruptedException { return dq.take(); }
197			public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
198			return dq.poll(timeout, unit);
199	dl	1.2	}
200	dl	1.12
201			public boolean add(Runnable x) { return dq.add((DelayedTask)x); }
202	dl	1.4	public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
203			public void put(Runnable x) throws InterruptedException {
204			dq.put((DelayedTask)x);
205	dl	1.2	}
206	dl	1.4	public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
207			return dq.offer((DelayedTask)x, timeout, unit);
208	dl	1.2	}
209	dl	1.12
210			public Runnable remove() { return dq.remove(); }
211			public Runnable element() { return dq.element(); }
212			public void clear() { dq.clear(); }
213
214	dl	1.4	public int remainingCapacity() { return dq.remainingCapacity(); }
215			public boolean remove(Object x) { return dq.remove(x); }
216			public boolean contains(Object x) { return dq.contains(x); }
217			public int size() { return dq.size(); }
218	tim	1.11	public boolean isEmpty() { return dq.isEmpty(); }
219	dl	1.4	public Iterator<Runnable> iterator() {
220			return new Iterator<Runnable>() {
221			private Iterator<DelayedTask> it = dq.iterator();
222			public boolean hasNext() { return it.hasNext(); }
223			public Runnable next() { return it.next(); }
224			public void remove() { it.remove(); }
225			};
226	tim	1.1	}
227	dl	1.4	}
228	tim	1.1
229	dl	1.4	/**
230			* Creates a new ScheduledExecutor with the given initial parameters.
231			*
232			* @param corePoolSize the number of threads to keep in the pool,
233			* even if they are idle.
234			*/
235			public ScheduledExecutor(int corePoolSize) {
236			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
237			new DelayedWorkQueue());
238			}
239	tim	1.1
240	dl	1.4	/**
241			* Creates a new ScheduledExecutor with the given initial parameters.
242			*
243			* @param corePoolSize the number of threads to keep in the pool,
244			* even if they are idle.
245			* @param threadFactory the factory to use when the executor
246			* creates a new thread.
247			*/
248			public ScheduledExecutor(int corePoolSize,
249			ThreadFactory threadFactory) {
250			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
251			new DelayedWorkQueue(), threadFactory);
252	tim	1.1	}
253
254	dl	1.4	/**
255			* Creates a new ScheduledExecutor with the given initial parameters.
256			*
257			* @param corePoolSize the number of threads to keep in the pool,
258			* even if they are idle.
259			* @param handler the handler to use when execution is blocked
260			* because the thread bounds and queue capacities are reached.
261			*/
262			public ScheduledExecutor(int corePoolSize,
263			RejectedExecutionHandler handler) {
264			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
265			new DelayedWorkQueue(), handler);
266			}
267	dl	1.2
268	tim	1.1	/**
269	dl	1.2	* Creates a new ScheduledExecutor with the given initial parameters.
270			*
271			* @param corePoolSize the number of threads to keep in the pool,
272			* even if they are idle.
273	dl	1.4	* @param threadFactory the factory to use when the executor
274			* creates a new thread.
275			* @param handler the handler to use when execution is blocked
276			* because the thread bounds and queue capacities are reached.
277	tim	1.1	*/
278	dl	1.4	public ScheduledExecutor(int corePoolSize,
279			ThreadFactory threadFactory,
280			RejectedExecutionHandler handler) {
281	dl	1.2	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
282	dl	1.4	new DelayedWorkQueue(), threadFactory, handler);
283	dl	1.13	}
284
285			/**
286			* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
287			*/
288			void delayedExecute(Runnable command) {
289			if (isShutdown()) {
290			reject(command);
291			return;
292			}
293			// Prestart thread if necessary. We cannot prestart it running
294			// the task because the task (probably) shouldn't be run yet,
295			// so thread will just idle until delay elapses.
296			if (getPoolSize() < getCorePoolSize())
297			addIfUnderCorePoolSize(null);
298
299			getQueue().offer(command);
300	dl	1.4	}
301
302			/**
303	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
304	dl	1.4	* the given delay.
305	dl	1.6	* @param command the task to execute.
306			* @param delay the time from now to delay execution.
307			* @param unit the time unit of the delay parameter.
308			* @return a handle that can be used to cancel the task.
309	dl	1.4	*/
310
311	dl	1.6	public DelayedTask schedule(Runnable command, long delay, TimeUnit unit) {
312	dl	1.10	DelayedTask t = new DelayedTask(command, System.nanoTime() + unit.toNanos(delay));
313	dl	1.13	delayedExecute(t);
314	dl	1.4	return t;
315			}
316
317			/**
318	dl	1.9	* Creates and executes a one-shot action that becomes enabled
319			* after the given date.
320	dl	1.6	* @param command the task to execute.
321			* @param date the time to commence excution.
322			* @return a handle that can be used to cancel the task.
323			* @throws RejectedExecutionException if task cannot be scheduled
324			* for execution because the executor has been shut down.
325	dl	1.4	*/
326	dl	1.6	public DelayedTask schedule(Runnable command, Date date) {
327	dl	1.4	DelayedTask t = new DelayedTask
328	dl	1.6	(command,
329	dl	1.4	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
330			System.currentTimeMillis()));
331	dl	1.13	delayedExecute(t);
332	dl	1.4	return t;
333			}
334
335			/**
336	dl	1.7	* Creates and executes a periodic action that becomes enabled first
337	dl	1.4	* after the given initial delay, and subsequently with the given
338	dl	1.7	* period; that is executions will commence after
339			* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
340			* <tt>initialDelay + 2 * period</tt>, and so on.
341	dl	1.6	* @param command the task to execute.
342			* @param initialDelay the time to delay first execution.
343			* @param period the period between successive executions.
344			* @param unit the time unit of the delay and period parameters
345			* @return a handle that can be used to cancel the task.
346			* @throws RejectedExecutionException if task cannot be scheduled
347			* for execution because the executor has been shut down.
348	dl	1.4	*/
349	dl	1.7	public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
350	dl	1.4	DelayedTask t = new DelayedTask
351	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
352	dl	1.7	unit.toNanos(period), true);
353	dl	1.13	delayedExecute(t);
354	dl	1.4	return t;
355			}
356
357			/**
358	dl	1.7	* Creates a periodic action that becomes enabled first after the
359			* given date, and subsequently with the given period
360			* period; that is executions will commence after
361			* <tt>initialDate</tt> then <tt>initialDate+period</tt>, then
362			* <tt>initialDate + 2 * period</tt>, and so on.
363	dl	1.6	* @param command the task to execute.
364			* @param initialDate the time to delay first execution.
365	dl	1.7	* @param period the period between commencement of successive
366			* executions.
367	dl	1.6	* @param unit the time unit of the period parameter.
368			* @return a handle that can be used to cancel the task.
369			* @throws RejectedExecutionException if task cannot be scheduled
370			* for execution because the executor has been shut down.
371	dl	1.4	*/
372	dl	1.7	public DelayedTask scheduleAtFixedRate(Runnable command, Date initialDate, long period, TimeUnit unit) {
373			DelayedTask t = new DelayedTask
374			(command,
375			TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
376			System.currentTimeMillis()),
377			unit.toNanos(period), true);
378	dl	1.13	delayedExecute(t);
379	dl	1.7	return t;
380			}
381
382			/**
383			* Creates and executes a periodic action that becomes enabled first
384			* after the given initial delay, and and subsequently with the
385			* given delay between the termination of one execution and the
386			* commencement of the next.
387			* @param command the task to execute.
388			* @param initialDelay the time to delay first execution.
389			* @param delay the delay between the termination of one
390			* execution and the commencement of the next.
391			* @param unit the time unit of the delay and delay parameters
392			* @return a handle that can be used to cancel the task.
393			* @throws RejectedExecutionException if task cannot be scheduled
394			* for execution because the executor has been shut down.
395			*/
396			public DelayedTask scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
397			DelayedTask t = new DelayedTask
398	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
399	dl	1.7	unit.toNanos(delay), false);
400	dl	1.13	delayedExecute(t);
401	dl	1.7	return t;
402			}
403
404			/**
405			* Creates a periodic action that becomes enabled first after the
406			* given date, and subsequently with the given delay between
407			* the termination of one execution and the commencement of the
408			* next.
409			* @param command the task to execute.
410			* @param initialDate the time to delay first execution.
411			* @param delay the delay between the termination of one
412			* execution and the commencement of the next.
413			* @param unit the time unit of the delay parameter.
414			* @return a handle that can be used to cancel the task.
415			* @throws RejectedExecutionException if task cannot be scheduled
416			* for execution because the executor has been shut down.
417			*/
418			public DelayedTask scheduleWithFixedDelay(Runnable command, Date initialDate, long delay, TimeUnit unit) {
419	dl	1.4	DelayedTask t = new DelayedTask
420	dl	1.6	(command,
421			TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
422	dl	1.4	System.currentTimeMillis()),
423	dl	1.7	unit.toNanos(delay), false);
424	dl	1.13	delayedExecute(t);
425	dl	1.4	return t;
426	tim	1.1	}
427
428
429	dl	1.4	/**
430	dl	1.7	* Creates and executes a Future that becomes enabled after the
431			* given delay.
432	dl	1.6	* @param callable the function to execute.
433			* @param delay the time from now to delay execution.
434			* @param unit the time unit of the delay parameter.
435			* @return a Future that can be used to extract result or cancel.
436			* @throws RejectedExecutionException if task cannot be scheduled
437			* for execution because the executor has been shut down.
438	dl	1.4	*/
439			public <V> DelayedFutureTask<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
440			DelayedFutureTask<V> t = new DelayedFutureTask<V>
441			(callable, delay, unit);
442	dl	1.13	delayedExecute(t);
443	dl	1.4	return t;
444			}
445
446			/**
447	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
448	dl	1.4	* the given date.
449	dl	1.6	* @param callable the function to execute.
450			* @param date the time to commence excution.
451			* @return a Future that can be used to extract result or cancel.
452			* @throws RejectedExecutionException if task cannot be scheduled
453			* for execution because the executor has been shut down.
454	dl	1.4	*/
455			public <V> DelayedFutureTask<V> schedule(Callable<V> callable, Date date) {
456			DelayedFutureTask<V> t = new DelayedFutureTask<V>
457			(callable, date);
458	dl	1.13	delayedExecute(t);
459	dl	1.4	return t;
460	tim	1.1	}
461
462	dl	1.4	/**
463	dl	1.16	* Execute command with zero required delay. This has effect
464			* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note
465			* that inspections of the queue and of the list returned by
466			* <tt>shutdownNow</tt> will access the zero-delayed
467			* <tt>DelayedTask</tt>, not the <tt>command</tt> itself.
468	tim	1.11	*
469	dl	1.6	* @param command the task to execute
470			* @throws RejectedExecutionException at discretion of
471			* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
472			* for execution because the executor has been shut down.
473	dl	1.4	*/
474			public void execute(Runnable command) {
475			schedule(command, 0, TimeUnit.NANOSECONDS);
476	tim	1.1	}
477
478	dl	1.4	/**
479	dl	1.15	* Removes this task from internal queue if it is present, thus
480			* causing it not to be run if it has not already started. This
481			* method may be useful as one part of a cancellation scheme.
482			*
483			* @param task the task to remove
484			* @return true if the task was removed
485			*/
486			public boolean remove(Runnable task) {
487			if (task instanceof DelayedTask && getQueue().remove(task))
488			return true;
489
490			// The task might actually have been wrapped as a DelayedTask
491			// in execute(), in which case we need to maually traverse
492			// looking for it.
493
494			DelayedTask wrap = null;
495			Object[] entries = getQueue().toArray();
496			for (int i = 0; i < entries.length; ++i) {
497			DelayedTask t = (DelayedTask)entries[i];
498			Runnable r = t.getRunnable();
499			if (task.equals(r)) {
500			wrap = t;
501			break;
502			}
503			}
504			entries = null;
505			return wrap != null && getQueue().remove(wrap);
506			}
507
508			/**
509	dl	1.4	* If executed task was periodic, cause the task for the next
510			* period to execute.
511	dl	1.9	* @param r the task (assumed to be a DelayedTask)
512			* @param t the exception
513	dl	1.4	*/
514			protected void afterExecute(Runnable r, Throwable t) {
515			if (isShutdown())
516			return;
517			super.afterExecute(r, t);
518			DelayedTask d = (DelayedTask)r;
519			DelayedTask next = d.nextTask();
520	dl	1.6	if (next == null)
521			return;
522			try {
523	dl	1.15	delayedExecute(next);
524	tim	1.14	} catch(RejectedExecutionException ex) {
525	dl	1.6	// lost race to detect shutdown; ignore
526			}
527	dl	1.4	}
528	tim	1.1	}
529	dl	1.4
530