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.
 *
 * @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) {
            return unit.convert(time - TimeUnit.nanoTime(), 
                                TimeUnit.NANOSECONDS);
        }

        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 : TimeUnit.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, TimeUnit.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 AbstractQueue<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 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 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);
    }

    /**
     * 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, TimeUnit.nanoTime() + unit.toNanos(delay));
        super.execute(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()));
        super.execute(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, TimeUnit.nanoTime() + unit.toNanos(initialDelay),
             unit.toNanos(period), true);
        super.execute(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);
        super.execute(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, TimeUnit.nanoTime() + unit.toNanos(initialDelay),
             unit.toNanos(delay), false);
        super.execute(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);
        super.execute(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);
        super.execute(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);
        super.execute(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 {
            super.execute(next);
        }
        catch(RejectedExecutionException ex) {
            // lost race to detect shutdown; ignore
        }
    }
}


Revision:	1.9
Committed:	Tue Jun 24 14:34:48 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
Changes since 1.8:	+13 -3 lines
Log Message:	Added missing javadoc tags; minor reformatting
#	Content
1	/*
2	* 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	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.atomic.*;
9	import java.util.*;
10
11	/**
12	* 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	* <tt>java.util.Timer</tt> when multiple worker threads are needed,
15	* or when the additional flexibility or capabilities of
16	* <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	*
35	* @since 1.5
36	* @see Executors
37	*
38	* @spec JSR-166
39	* @author Doug Lea
40	*/
41	public class ScheduledExecutor extends ThreadPoolExecutor {
42
43	/**
44	* Sequence number to break scheduling ties, and in turn to
45	* guarantee FIFO order among tied entries.
46	*/
47	private static final AtomicLong sequencer = new AtomicLong(0);
48
49	/**
50	* A delayed or periodic action.
51	*/
52	public static class DelayedTask extends CancellableTask implements Delayed {
53	/** Sequence number to break ties FIFO */
54	private final long sequenceNumber;
55	/** The time the task is enabled to execute in nanoTime units */
56	private final long time;
57	/** The delay forllowing next time, or <= 0 if non-periodic */
58	private final long period;
59	/** true if at fixed rate; false if fixed delay */
60	private final boolean rateBased;
61
62	/**
63	* Creates a one-shot action with given nanoTime-based trigger time
64	*/
65	DelayedTask(Runnable r, long ns) {
66	super(r);
67	this.time = ns;
68	this.period = 0;
69	rateBased = false;
70	this.sequenceNumber = sequencer.getAndIncrement();
71	}
72
73	/**
74	* Creates a periodic action with given nano time and period
75	*/
76	DelayedTask(Runnable r, long ns, long period, boolean rateBased) {
77	super(r);
78	if (period <= 0)
79	throw new IllegalArgumentException();
80	this.time = ns;
81	this.period = period;
82	this.rateBased = rateBased;
83	this.sequenceNumber = sequencer.getAndIncrement();
84	}
85
86
87	public long getDelay(TimeUnit unit) {
88	return unit.convert(time - TimeUnit.nanoTime(),
89	TimeUnit.NANOSECONDS);
90	}
91
92	public int compareTo(Object other) {
93	DelayedTask x = (DelayedTask)other;
94	long diff = time - x.time;
95	if (diff < 0)
96	return -1;
97	else if (diff > 0)
98	return 1;
99	else if (sequenceNumber < x.sequenceNumber)
100	return -1;
101	else
102	return 1;
103	}
104
105	/**
106	* Return true if this is a periodic (not a one-shot) action.
107	* @return true if periodic
108	*/
109	public boolean isPeriodic() {
110	return period > 0;
111	}
112
113	/**
114	* Returns the period, or zero if non-periodic
115	* @return the period
116	*/
117	public long getPeriod(TimeUnit unit) {
118	return unit.convert(period, TimeUnit.NANOSECONDS);
119	}
120
121	/**
122	* Return a new DelayedTask that will trigger in the period
123	* subsequent to current task, or null if non-periodic
124	* or canceled.
125	*/
126	DelayedTask nextTask() {
127	if (period <= 0 \|\| isCancelled())
128	return null;
129	long nextTime = period + (rateBased ? time : TimeUnit.nanoTime());
130	return new DelayedTask(getRunnable(), nextTime, period, rateBased);
131	}
132
133	}
134
135	/**
136	* A delayed result-bearing action.
137	*/
138	public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
139	/**
140	* Creates a Future that may trigger after the given delay.
141	*/
142	DelayedFutureTask(Callable<V> callable, long delay, TimeUnit unit) {
143	// must set after super ctor call to use inner class
144	super(null, TimeUnit.nanoTime() + unit.toNanos(delay));
145	setRunnable(new InnerCancellableFuture<V>(callable));
146	}
147
148	/**
149	* Creates a one-shot action that may trigger after the given date.
150	*/
151	DelayedFutureTask(Callable<V> callable, Date date) {
152	super(null,
153	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
154	System.currentTimeMillis()));
155	setRunnable(new InnerCancellableFuture<V>(callable));
156	}
157
158	public V get() throws InterruptedException, ExecutionException {
159	return ((InnerCancellableFuture<V>)getRunnable()).get();
160	}
161
162	public V get(long timeout, TimeUnit unit)
163	throws InterruptedException, ExecutionException, TimeoutException {
164	return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
165	}
166
167	protected void set(V v) {
168	((InnerCancellableFuture<V>)getRunnable()).set(v);
169	}
170
171	protected void setException(Throwable t) {
172	((InnerCancellableFuture<V>)getRunnable()).setException(t);
173	}
174	}
175
176
177	/**
178	* An annoying wrapper class to convince generics compiler to
179	* use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
180	*/
181	private static class DelayedWorkQueue extends AbstractQueue<Runnable> implements BlockingQueue<Runnable> {
182	private final DelayQueue<DelayedTask> dq = new DelayQueue<DelayedTask>();
183	public Runnable poll() { return dq.poll(); }
184	public Runnable peek() { return dq.peek(); }
185	public Runnable take() throws InterruptedException { return dq.take(); }
186	public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
187	return dq.poll(timeout, unit);
188	}
189	public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
190	public void put(Runnable x) throws InterruptedException {
191	dq.put((DelayedTask)x);
192	}
193	public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
194	return dq.offer((DelayedTask)x, timeout, unit);
195	}
196	public int remainingCapacity() { return dq.remainingCapacity(); }
197	public boolean remove(Object x) { return dq.remove(x); }
198	public boolean contains(Object x) { return dq.contains(x); }
199	public int size() { return dq.size(); }
200	public boolean isEmpty() { return dq.isEmpty(); }
201	public Iterator<Runnable> iterator() {
202	return new Iterator<Runnable>() {
203	private Iterator<DelayedTask> it = dq.iterator();
204	public boolean hasNext() { return it.hasNext(); }
205	public Runnable next() { return it.next(); }
206	public void remove() { it.remove(); }
207	};
208	}
209	}
210
211	/**
212	* Creates a new ScheduledExecutor with the given initial parameters.
213	*
214	* @param corePoolSize the number of threads to keep in the pool,
215	* even if they are idle.
216	*/
217	public ScheduledExecutor(int corePoolSize) {
218	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
219	new DelayedWorkQueue());
220	}
221
222	/**
223	* Creates a new ScheduledExecutor with the given initial parameters.
224	*
225	* @param corePoolSize the number of threads to keep in the pool,
226	* even if they are idle.
227	* @param threadFactory the factory to use when the executor
228	* creates a new thread.
229	*/
230	public ScheduledExecutor(int corePoolSize,
231	ThreadFactory threadFactory) {
232	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
233	new DelayedWorkQueue(), threadFactory);
234	}
235
236	/**
237	* Creates a new ScheduledExecutor with the given initial parameters.
238	*
239	* @param corePoolSize the number of threads to keep in the pool,
240	* even if they are idle.
241	* @param handler the handler to use when execution is blocked
242	* because the thread bounds and queue capacities are reached.
243	*/
244	public ScheduledExecutor(int corePoolSize,
245	RejectedExecutionHandler handler) {
246	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
247	new DelayedWorkQueue(), handler);
248	}
249
250	/**
251	* Creates a new ScheduledExecutor with the given initial parameters.
252	*
253	* @param corePoolSize the number of threads to keep in the pool,
254	* even if they are idle.
255	* @param threadFactory the factory to use when the executor
256	* creates a new thread.
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	ThreadFactory threadFactory,
262	RejectedExecutionHandler handler) {
263	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
264	new DelayedWorkQueue(), threadFactory, handler);
265	}
266
267	/**
268	* Creates and executes a one-shot action that becomes enabled after
269	* the given delay.
270	* @param command the task to execute.
271	* @param delay the time from now to delay execution.
272	* @param unit the time unit of the delay parameter.
273	* @return a handle that can be used to cancel the task.
274	*/
275
276	public DelayedTask schedule(Runnable command, long delay, TimeUnit unit) {
277	DelayedTask t = new DelayedTask(command, TimeUnit.nanoTime() + unit.toNanos(delay));
278	super.execute(t);
279	return t;
280	}
281
282	/**
283	* Creates and executes a one-shot action that becomes enabled
284	* after the given date.
285	* @param command the task to execute.
286	* @param date the time to commence excution.
287	* @return a handle that can be used to cancel the task.
288	* @throws RejectedExecutionException if task cannot be scheduled
289	* for execution because the executor has been shut down.
290	*/
291	public DelayedTask schedule(Runnable command, Date date) {
292	DelayedTask t = new DelayedTask
293	(command,
294	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
295	System.currentTimeMillis()));
296	super.execute(t);
297	return t;
298	}
299
300	/**
301	* Creates and executes a periodic action that becomes enabled first
302	* after the given initial delay, and subsequently with the given
303	* period; that is executions will commence after
304	* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
305	* <tt>initialDelay + 2 * period</tt>, and so on.
306	* @param command the task to execute.
307	* @param initialDelay the time to delay first execution.
308	* @param period the period between successive executions.
309	* @param unit the time unit of the delay and period parameters
310	* @return a handle that can be used to cancel the task.
311	* @throws RejectedExecutionException if task cannot be scheduled
312	* for execution because the executor has been shut down.
313	*/
314	public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
315	DelayedTask t = new DelayedTask
316	(command, TimeUnit.nanoTime() + unit.toNanos(initialDelay),
317	unit.toNanos(period), true);
318	super.execute(t);
319	return t;
320	}
321
322	/**
323	* Creates a periodic action that becomes enabled first after the
324	* given date, and subsequently with the given period
325	* period; that is executions will commence after
326	* <tt>initialDate</tt> then <tt>initialDate+period</tt>, then
327	* <tt>initialDate + 2 * period</tt>, and so on.
328	* @param command the task to execute.
329	* @param initialDate the time to delay first execution.
330	* @param period the period between commencement of successive
331	* executions.
332	* @param unit the time unit of the period parameter.
333	* @return a handle that can be used to cancel the task.
334	* @throws RejectedExecutionException if task cannot be scheduled
335	* for execution because the executor has been shut down.
336	*/
337	public DelayedTask scheduleAtFixedRate(Runnable command, Date initialDate, long period, TimeUnit unit) {
338	DelayedTask t = new DelayedTask
339	(command,
340	TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
341	System.currentTimeMillis()),
342	unit.toNanos(period), true);
343	super.execute(t);
344	return t;
345	}
346
347	/**
348	* Creates and executes a periodic action that becomes enabled first
349	* after the given initial delay, and and subsequently with the
350	* given delay between the termination of one execution and the
351	* commencement of the next.
352	* @param command the task to execute.
353	* @param initialDelay the time to delay first execution.
354	* @param delay the delay between the termination of one
355	* execution and the commencement of the next.
356	* @param unit the time unit of the delay and delay parameters
357	* @return a handle that can be used to cancel the task.
358	* @throws RejectedExecutionException if task cannot be scheduled
359	* for execution because the executor has been shut down.
360	*/
361	public DelayedTask scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
362	DelayedTask t = new DelayedTask
363	(command, TimeUnit.nanoTime() + unit.toNanos(initialDelay),
364	unit.toNanos(delay), false);
365	super.execute(t);
366	return t;
367	}
368
369	/**
370	* Creates a periodic action that becomes enabled first after the
371	* given date, and subsequently with the given delay between
372	* the termination of one execution and the commencement of the
373	* next.
374	* @param command the task to execute.
375	* @param initialDate the time to delay first execution.
376	* @param delay the delay between the termination of one
377	* execution and the commencement of the next.
378	* @param unit the time unit of the delay parameter.
379	* @return a handle that can be used to cancel the task.
380	* @throws RejectedExecutionException if task cannot be scheduled
381	* for execution because the executor has been shut down.
382	*/
383	public DelayedTask scheduleWithFixedDelay(Runnable command, Date initialDate, long delay, TimeUnit unit) {
384	DelayedTask t = new DelayedTask
385	(command,
386	TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
387	System.currentTimeMillis()),
388	unit.toNanos(delay), false);
389	super.execute(t);
390	return t;
391	}
392
393
394	/**
395	* Creates and executes a Future that becomes enabled after the
396	* given delay.
397	* @param callable the function to execute.
398	* @param delay the time from now to delay execution.
399	* @param unit the time unit of the delay parameter.
400	* @return a Future that can be used to extract result or cancel.
401	* @throws RejectedExecutionException if task cannot be scheduled
402	* for execution because the executor has been shut down.
403	*/
404	public <V> DelayedFutureTask<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
405	DelayedFutureTask<V> t = new DelayedFutureTask<V>
406	(callable, delay, unit);
407	super.execute(t);
408	return t;
409	}
410
411	/**
412	* Creates and executes a one-shot action that becomes enabled after
413	* the given date.
414	* @param callable the function to execute.
415	* @param date the time to commence excution.
416	* @return a Future that can be used to extract result or cancel.
417	* @throws RejectedExecutionException if task cannot be scheduled
418	* for execution because the executor has been shut down.
419	*/
420	public <V> DelayedFutureTask<V> schedule(Callable<V> callable, Date date) {
421	DelayedFutureTask<V> t = new DelayedFutureTask<V>
422	(callable, date);
423	super.execute(t);
424	return t;
425	}
426
427	/**
428	* Execute command with zero required delay
429	* @param command the task to execute
430	* @throws RejectedExecutionException at discretion of
431	* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
432	* for execution because the executor has been shut down.
433	*/
434	public void execute(Runnable command) {
435	schedule(command, 0, TimeUnit.NANOSECONDS);
436	}
437
438	/**
439	* If executed task was periodic, cause the task for the next
440	* period to execute.
441	* @param r the task (assumed to be a DelayedTask)
442	* @param t the exception
443	*/
444	protected void afterExecute(Runnable r, Throwable t) {
445	if (isShutdown())
446	return;
447	super.afterExecute(r, t);
448	DelayedTask d = (DelayedTask)r;
449	DelayedTask next = d.nextTask();
450	if (next == null)
451	return;
452	try {
453	super.execute(next);
454	}
455	catch(RejectedExecutionException ex) {
456	// lost race to detect shutdown; ignore
457	}
458	}
459	}
460
461