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) {
            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.
     *
     * @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);
    }

    /**
     * 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 {
            execute(next);
        }
        catch(RejectedExecutionException ex) {
            // lost race to detect shutdown; ignore
        }
    }
}


Revision:	1.13
Committed:	Fri Aug 8 17:48:44 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.12:	+32 -12 lines
Log Message:	Semi-lazily prestart core threads in SE
#	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			DelayedTask x = (DelayedTask)other;
102			long diff = time - x.time;
103			if (diff < 0)
104			return -1;
105			else if (diff > 0)
106			return 1;
107			else if (sequenceNumber < x.sequenceNumber)
108			return -1;
109			else
110			return 1;
111			}
112
113			/**
114			* Return true if this is a periodic (not a one-shot) action.
115	dl	1.9	* @return true if periodic
116	dl	1.4	*/
117			public boolean isPeriodic() {
118			return period > 0;
119			}
120
121			/**
122	tim	1.11	* Returns the period, or zero if non-periodic.
123			*
124	dl	1.9	* @return the period
125	dl	1.4	*/
126			public long getPeriod(TimeUnit unit) {
127			return unit.convert(period, TimeUnit.NANOSECONDS);
128			}
129
130			/**
131			* Return a new DelayedTask that will trigger in the period
132			* subsequent to current task, or null if non-periodic
133			* or canceled.
134			*/
135	dl	1.5	DelayedTask nextTask() {
136	dl	1.4	if (period <= 0 \|\| isCancelled())
137			return null;
138	dl	1.10	long nextTime = period + (rateBased ? time : System.nanoTime());
139	dl	1.7	return new DelayedTask(getRunnable(), nextTime, period, rateBased);
140	dl	1.4	}
141	dl	1.2
142	dl	1.4	}
143	dl	1.2
144	dl	1.4	/**
145			* A delayed result-bearing action.
146			*/
147	dl	1.8	public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
148	dl	1.4	/**
149			* Creates a Future that may trigger after the given delay.
150			*/
151			DelayedFutureTask(Callable<V> callable, long delay, TimeUnit unit) {
152			// must set after super ctor call to use inner class
153	dl	1.10	super(null, System.nanoTime() + unit.toNanos(delay));
154	dl	1.4	setRunnable(new InnerCancellableFuture<V>(callable));
155	dl	1.2	}
156
157	dl	1.4	/**
158			* Creates a one-shot action that may trigger after the given date.
159			*/
160			DelayedFutureTask(Callable<V> callable, Date date) {
161			super(null,
162			TimeUnit.MILLISECONDS.toNanos(date.getTime() -
163			System.currentTimeMillis()));
164			setRunnable(new InnerCancellableFuture<V>(callable));
165			}
166
167			public V get() throws InterruptedException, ExecutionException {
168			return ((InnerCancellableFuture<V>)getRunnable()).get();
169	dl	1.2	}
170
171	dl	1.4	public V get(long timeout, TimeUnit unit)
172			throws InterruptedException, ExecutionException, TimeoutException {
173			return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
174	dl	1.2	}
175	tim	1.1
176	dl	1.4	protected void set(V v) {
177			((InnerCancellableFuture<V>)getRunnable()).set(v);
178	dl	1.2	}
179	tim	1.1
180	dl	1.4	protected void setException(Throwable t) {
181			((InnerCancellableFuture<V>)getRunnable()).setException(t);
182			}
183			}
184
185
186			/**
187			* An annoying wrapper class to convince generics compiler to
188	dl	1.7	* use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
189	dl	1.4	*/
190	dl	1.12	private static class DelayedWorkQueue extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> {
191	dl	1.4	private final DelayQueue<DelayedTask> dq = new DelayQueue<DelayedTask>();
192			public Runnable poll() { return dq.poll(); }
193			public Runnable peek() { return dq.peek(); }
194			public Runnable take() throws InterruptedException { return dq.take(); }
195			public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
196			return dq.poll(timeout, unit);
197	dl	1.2	}
198	dl	1.12
199			public boolean add(Runnable x) { return dq.add((DelayedTask)x); }
200	dl	1.4	public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
201			public void put(Runnable x) throws InterruptedException {
202			dq.put((DelayedTask)x);
203	dl	1.2	}
204	dl	1.4	public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
205			return dq.offer((DelayedTask)x, timeout, unit);
206	dl	1.2	}
207	dl	1.12
208			public Runnable remove() { return dq.remove(); }
209			public Runnable element() { return dq.element(); }
210			public void clear() { dq.clear(); }
211
212	dl	1.4	public int remainingCapacity() { return dq.remainingCapacity(); }
213			public boolean remove(Object x) { return dq.remove(x); }
214			public boolean contains(Object x) { return dq.contains(x); }
215			public int size() { return dq.size(); }
216	tim	1.11	public boolean isEmpty() { return dq.isEmpty(); }
217	dl	1.4	public Iterator<Runnable> iterator() {
218			return new Iterator<Runnable>() {
219			private Iterator<DelayedTask> it = dq.iterator();
220			public boolean hasNext() { return it.hasNext(); }
221			public Runnable next() { return it.next(); }
222			public void remove() { it.remove(); }
223			};
224	tim	1.1	}
225	dl	1.4	}
226	tim	1.1
227	dl	1.4	/**
228			* Creates a new ScheduledExecutor with the given initial parameters.
229			*
230			* @param corePoolSize the number of threads to keep in the pool,
231			* even if they are idle.
232			*/
233			public ScheduledExecutor(int corePoolSize) {
234			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
235			new DelayedWorkQueue());
236			}
237	tim	1.1
238	dl	1.4	/**
239			* Creates a new ScheduledExecutor with the given initial parameters.
240			*
241			* @param corePoolSize the number of threads to keep in the pool,
242			* even if they are idle.
243			* @param threadFactory the factory to use when the executor
244			* creates a new thread.
245			*/
246			public ScheduledExecutor(int corePoolSize,
247			ThreadFactory threadFactory) {
248			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
249			new DelayedWorkQueue(), threadFactory);
250	tim	1.1	}
251
252	dl	1.4	/**
253			* Creates a new ScheduledExecutor with the given initial parameters.
254			*
255			* @param corePoolSize the number of threads to keep in the pool,
256			* even if they are idle.
257			* @param handler the handler to use when execution is blocked
258			* because the thread bounds and queue capacities are reached.
259			*/
260			public ScheduledExecutor(int corePoolSize,
261			RejectedExecutionHandler handler) {
262			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
263			new DelayedWorkQueue(), handler);
264			}
265	dl	1.2
266	tim	1.1	/**
267	dl	1.2	* Creates a new ScheduledExecutor with the given initial parameters.
268			*
269			* @param corePoolSize the number of threads to keep in the pool,
270			* even if they are idle.
271	dl	1.4	* @param threadFactory the factory to use when the executor
272			* creates a new thread.
273			* @param handler the handler to use when execution is blocked
274			* because the thread bounds and queue capacities are reached.
275	tim	1.1	*/
276	dl	1.4	public ScheduledExecutor(int corePoolSize,
277			ThreadFactory threadFactory,
278			RejectedExecutionHandler handler) {
279	dl	1.2	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
280	dl	1.4	new DelayedWorkQueue(), threadFactory, handler);
281	dl	1.13	}
282
283			/**
284			* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
285			*/
286			void delayedExecute(Runnable command) {
287			if (isShutdown()) {
288			reject(command);
289			return;
290			}
291			// Prestart thread if necessary. We cannot prestart it running
292			// the task because the task (probably) shouldn't be run yet,
293			// so thread will just idle until delay elapses.
294			if (getPoolSize() < getCorePoolSize())
295			addIfUnderCorePoolSize(null);
296
297			getQueue().offer(command);
298	dl	1.4	}
299
300			/**
301	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
302	dl	1.4	* the given delay.
303	dl	1.6	* @param command the task to execute.
304			* @param delay the time from now to delay execution.
305			* @param unit the time unit of the delay parameter.
306			* @return a handle that can be used to cancel the task.
307	dl	1.4	*/
308
309	dl	1.6	public DelayedTask schedule(Runnable command, long delay, TimeUnit unit) {
310	dl	1.10	DelayedTask t = new DelayedTask(command, System.nanoTime() + unit.toNanos(delay));
311	dl	1.13	delayedExecute(t);
312	dl	1.4	return t;
313			}
314
315			/**
316	dl	1.9	* Creates and executes a one-shot action that becomes enabled
317			* after the given date.
318	dl	1.6	* @param command the task to execute.
319			* @param date the time to commence excution.
320			* @return a handle that can be used to cancel the task.
321			* @throws RejectedExecutionException if task cannot be scheduled
322			* for execution because the executor has been shut down.
323	dl	1.4	*/
324	dl	1.6	public DelayedTask schedule(Runnable command, Date date) {
325	dl	1.4	DelayedTask t = new DelayedTask
326	dl	1.6	(command,
327	dl	1.4	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
328			System.currentTimeMillis()));
329	dl	1.13	delayedExecute(t);
330	dl	1.4	return t;
331			}
332
333			/**
334	dl	1.7	* Creates and executes a periodic action that becomes enabled first
335	dl	1.4	* after the given initial delay, and subsequently with the given
336	dl	1.7	* period; that is executions will commence after
337			* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
338			* <tt>initialDelay + 2 * period</tt>, and so on.
339	dl	1.6	* @param command the task to execute.
340			* @param initialDelay the time to delay first execution.
341			* @param period the period between successive executions.
342			* @param unit the time unit of the delay and period parameters
343			* @return a handle that can be used to cancel the task.
344			* @throws RejectedExecutionException if task cannot be scheduled
345			* for execution because the executor has been shut down.
346	dl	1.4	*/
347	dl	1.7	public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
348	dl	1.4	DelayedTask t = new DelayedTask
349	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
350	dl	1.7	unit.toNanos(period), true);
351	dl	1.13	delayedExecute(t);
352	dl	1.4	return t;
353			}
354
355			/**
356	dl	1.7	* Creates a periodic action that becomes enabled first after the
357			* given date, and subsequently with the given period
358			* period; that is executions will commence after
359			* <tt>initialDate</tt> then <tt>initialDate+period</tt>, then
360			* <tt>initialDate + 2 * period</tt>, and so on.
361	dl	1.6	* @param command the task to execute.
362			* @param initialDate the time to delay first execution.
363	dl	1.7	* @param period the period between commencement of successive
364			* executions.
365	dl	1.6	* @param unit the time unit of the period parameter.
366			* @return a handle that can be used to cancel the task.
367			* @throws RejectedExecutionException if task cannot be scheduled
368			* for execution because the executor has been shut down.
369	dl	1.4	*/
370	dl	1.7	public DelayedTask scheduleAtFixedRate(Runnable command, Date initialDate, long period, TimeUnit unit) {
371			DelayedTask t = new DelayedTask
372			(command,
373			TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
374			System.currentTimeMillis()),
375			unit.toNanos(period), true);
376	dl	1.13	delayedExecute(t);
377	dl	1.7	return t;
378			}
379
380			/**
381			* Creates and executes a periodic action that becomes enabled first
382			* after the given initial delay, and and subsequently with the
383			* given delay between the termination of one execution and the
384			* commencement of the next.
385			* @param command the task to execute.
386			* @param initialDelay the time to delay first execution.
387			* @param delay the delay between the termination of one
388			* execution and the commencement of the next.
389			* @param unit the time unit of the delay and delay parameters
390			* @return a handle that can be used to cancel the task.
391			* @throws RejectedExecutionException if task cannot be scheduled
392			* for execution because the executor has been shut down.
393			*/
394			public DelayedTask scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
395			DelayedTask t = new DelayedTask
396	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
397	dl	1.7	unit.toNanos(delay), false);
398	dl	1.13	delayedExecute(t);
399	dl	1.7	return t;
400			}
401
402			/**
403			* Creates a periodic action that becomes enabled first after the
404			* given date, and subsequently with the given delay between
405			* the termination of one execution and the commencement of the
406			* next.
407			* @param command the task to execute.
408			* @param initialDate the time to delay first execution.
409			* @param delay the delay between the termination of one
410			* execution and the commencement of the next.
411			* @param unit the time unit of the delay parameter.
412			* @return a handle that can be used to cancel the task.
413			* @throws RejectedExecutionException if task cannot be scheduled
414			* for execution because the executor has been shut down.
415			*/
416			public DelayedTask scheduleWithFixedDelay(Runnable command, Date initialDate, long delay, TimeUnit unit) {
417	dl	1.4	DelayedTask t = new DelayedTask
418	dl	1.6	(command,
419			TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
420	dl	1.4	System.currentTimeMillis()),
421	dl	1.7	unit.toNanos(delay), false);
422	dl	1.13	delayedExecute(t);
423	dl	1.4	return t;
424	tim	1.1	}
425
426
427	dl	1.4	/**
428	dl	1.7	* Creates and executes a Future that becomes enabled after the
429			* given delay.
430	dl	1.6	* @param callable the function to execute.
431			* @param delay the time from now to delay execution.
432			* @param unit the time unit of the delay parameter.
433			* @return a Future that can be used to extract result or cancel.
434			* @throws RejectedExecutionException if task cannot be scheduled
435			* for execution because the executor has been shut down.
436	dl	1.4	*/
437			public <V> DelayedFutureTask<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
438			DelayedFutureTask<V> t = new DelayedFutureTask<V>
439			(callable, delay, unit);
440	dl	1.13	delayedExecute(t);
441	dl	1.4	return t;
442			}
443
444			/**
445	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
446	dl	1.4	* the given date.
447	dl	1.6	* @param callable the function to execute.
448			* @param date the time to commence excution.
449			* @return a Future that can be used to extract result or cancel.
450			* @throws RejectedExecutionException if task cannot be scheduled
451			* for execution because the executor has been shut down.
452	dl	1.4	*/
453			public <V> DelayedFutureTask<V> schedule(Callable<V> callable, Date date) {
454			DelayedFutureTask<V> t = new DelayedFutureTask<V>
455			(callable, date);
456	dl	1.13	delayedExecute(t);
457	dl	1.4	return t;
458	tim	1.1	}
459
460	dl	1.4	/**
461	tim	1.11	* Execute command with zero required delay.
462			*
463	dl	1.6	* @param command the task to execute
464			* @throws RejectedExecutionException at discretion of
465			* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
466			* for execution because the executor has been shut down.
467	dl	1.4	*/
468			public void execute(Runnable command) {
469			schedule(command, 0, TimeUnit.NANOSECONDS);
470	tim	1.1	}
471
472	dl	1.4	/**
473			* If executed task was periodic, cause the task for the next
474			* period to execute.
475	dl	1.9	* @param r the task (assumed to be a DelayedTask)
476			* @param t the exception
477	dl	1.4	*/
478			protected void afterExecute(Runnable r, Throwable t) {
479			if (isShutdown())
480			return;
481			super.afterExecute(r, t);
482			DelayedTask d = (DelayedTask)r;
483			DelayedTask next = d.nextTask();
484	dl	1.6	if (next == null)
485			return;
486			try {
487	dl	1.12	execute(next);
488	dl	1.6	}
489			catch(RejectedExecutionException ex) {
490			// lost race to detect shutdown; ignore
491			}
492	dl	1.4	}
493	tim	1.1	}
494	dl	1.4
495