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 - System.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 : 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 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, System.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, System.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, System.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:	1.10
Committed:	Sat Jul 12 00:50:34 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRELIMINARY_TEST_RELEASE_2
Changes since 1.9:	+6 -6 lines
Log Message:	Added LockSupport; moved nanoTime
#	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			* @since 1.5
36			* @see Executors
37			*
38			* @spec JSR-166
39	dl	1.9	* @author Doug Lea
40	tim	1.1	*/
41			public class ScheduledExecutor extends ThreadPoolExecutor {
42
43	dl	1.4	/**
44	dl	1.5	* 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	dl	1.4	* A delayed or periodic action.
51			*/
52	dl	1.8	public static class DelayedTask extends CancellableTask implements Delayed {
53	dl	1.9	/** Sequence number to break ties FIFO */
54	dl	1.4	private final long sequenceNumber;
55	dl	1.9	/** The time the task is enabled to execute in nanoTime units */
56	dl	1.4	private final long time;
57	dl	1.9	/** The delay forllowing next time, or <= 0 if non-periodic */
58	dl	1.4	private final long period;
59	dl	1.9	/** true if at fixed rate; false if fixed delay */
60			private final boolean rateBased;
61
62	dl	1.4	/**
63	dl	1.5	* Creates a one-shot action with given nanoTime-based trigger time
64	dl	1.4	*/
65			DelayedTask(Runnable r, long ns) {
66			super(r);
67			this.time = ns;
68			this.period = 0;
69	dl	1.7	rateBased = false;
70	dl	1.4	this.sequenceNumber = sequencer.getAndIncrement();
71			}
72
73			/**
74	dl	1.5	* Creates a periodic action with given nano time and period
75	dl	1.4	*/
76	dl	1.7	DelayedTask(Runnable r, long ns, long period, boolean rateBased) {
77	dl	1.4	super(r);
78			if (period <= 0)
79			throw new IllegalArgumentException();
80			this.time = ns;
81			this.period = period;
82	dl	1.7	this.rateBased = rateBased;
83	dl	1.4	this.sequenceNumber = sequencer.getAndIncrement();
84			}
85
86
87			public long getDelay(TimeUnit unit) {
88	dl	1.10	return unit.convert(time - System.nanoTime(),
89	dl	1.7	TimeUnit.NANOSECONDS);
90	dl	1.4	}
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	dl	1.9	* @return true if periodic
108	dl	1.4	*/
109			public boolean isPeriodic() {
110			return period > 0;
111			}
112
113			/**
114			* Returns the period, or zero if non-periodic
115	dl	1.9	* @return the period
116	dl	1.4	*/
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	dl	1.5	DelayedTask nextTask() {
127	dl	1.4	if (period <= 0 \|\| isCancelled())
128			return null;
129	dl	1.10	long nextTime = period + (rateBased ? time : System.nanoTime());
130	dl	1.7	return new DelayedTask(getRunnable(), nextTime, period, rateBased);
131	dl	1.4	}
132	dl	1.2
133	dl	1.4	}
134	dl	1.2
135	dl	1.4	/**
136			* A delayed result-bearing action.
137			*/
138	dl	1.8	public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
139	dl	1.4	/**
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	dl	1.10	super(null, System.nanoTime() + unit.toNanos(delay));
145	dl	1.4	setRunnable(new InnerCancellableFuture<V>(callable));
146	dl	1.2	}
147
148	dl	1.4	/**
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	dl	1.2	}
161
162	dl	1.4	public V get(long timeout, TimeUnit unit)
163			throws InterruptedException, ExecutionException, TimeoutException {
164			return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
165	dl	1.2	}
166	tim	1.1
167	dl	1.4	protected void set(V v) {
168			((InnerCancellableFuture<V>)getRunnable()).set(v);
169	dl	1.2	}
170	tim	1.1
171	dl	1.4	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	dl	1.7	* use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
180	dl	1.4	*/
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	dl	1.2	}
189	dl	1.4	public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
190			public void put(Runnable x) throws InterruptedException {
191			dq.put((DelayedTask)x);
192	dl	1.2	}
193	dl	1.4	public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
194			return dq.offer((DelayedTask)x, timeout, unit);
195	dl	1.2	}
196	dl	1.4	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	tim	1.1	}
209	dl	1.4	}
210	tim	1.1
211	dl	1.4	/**
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	tim	1.1
222	dl	1.4	/**
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	tim	1.1	}
235
236	dl	1.4	/**
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	dl	1.2
250	tim	1.1	/**
251	dl	1.2	* 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	dl	1.4	* @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	tim	1.1	*/
260	dl	1.4	public ScheduledExecutor(int corePoolSize,
261			ThreadFactory threadFactory,
262			RejectedExecutionHandler handler) {
263	dl	1.2	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
264	dl	1.4	new DelayedWorkQueue(), threadFactory, handler);
265			}
266
267			/**
268	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
269	dl	1.4	* the given delay.
270	dl	1.6	* @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	dl	1.4	*/
275
276	dl	1.6	public DelayedTask schedule(Runnable command, long delay, TimeUnit unit) {
277	dl	1.10	DelayedTask t = new DelayedTask(command, System.nanoTime() + unit.toNanos(delay));
278	dl	1.4	super.execute(t);
279			return t;
280			}
281
282			/**
283	dl	1.9	* Creates and executes a one-shot action that becomes enabled
284			* after the given date.
285	dl	1.6	* @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	dl	1.4	*/
291	dl	1.6	public DelayedTask schedule(Runnable command, Date date) {
292	dl	1.4	DelayedTask t = new DelayedTask
293	dl	1.6	(command,
294	dl	1.4	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
295			System.currentTimeMillis()));
296			super.execute(t);
297			return t;
298			}
299
300			/**
301	dl	1.7	* Creates and executes a periodic action that becomes enabled first
302	dl	1.4	* after the given initial delay, and subsequently with the given
303	dl	1.7	* 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	dl	1.6	* @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	dl	1.4	*/
314	dl	1.7	public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
315	dl	1.4	DelayedTask t = new DelayedTask
316	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
317	dl	1.7	unit.toNanos(period), true);
318	dl	1.4	super.execute(t);
319			return t;
320			}
321
322			/**
323	dl	1.7	* 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	dl	1.6	* @param command the task to execute.
329			* @param initialDate the time to delay first execution.
330	dl	1.7	* @param period the period between commencement of successive
331			* executions.
332	dl	1.6	* @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	dl	1.4	*/
337	dl	1.7	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	dl	1.10	(command, System.nanoTime() + unit.toNanos(initialDelay),
364	dl	1.7	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	dl	1.4	DelayedTask t = new DelayedTask
385	dl	1.6	(command,
386			TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
387	dl	1.4	System.currentTimeMillis()),
388	dl	1.7	unit.toNanos(delay), false);
389	dl	1.4	super.execute(t);
390			return t;
391	tim	1.1	}
392
393
394	dl	1.4	/**
395	dl	1.7	* Creates and executes a Future that becomes enabled after the
396			* given delay.
397	dl	1.6	* @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	dl	1.4	*/
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	dl	1.7	* Creates and executes a one-shot action that becomes enabled after
413	dl	1.4	* the given date.
414	dl	1.6	* @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	dl	1.4	*/
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	tim	1.1	}
426
427	dl	1.4	/**
428			* Execute command with zero required delay
429	dl	1.6	* @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	dl	1.4	*/
434			public void execute(Runnable command) {
435			schedule(command, 0, TimeUnit.NANOSECONDS);
436	tim	1.1	}
437
438	dl	1.4	/**
439			* If executed task was periodic, cause the task for the next
440			* period to execute.
441	dl	1.9	* @param r the task (assumed to be a DelayedTask)
442			* @param t the exception
443	dl	1.4	*/
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	dl	1.6	if (next == null)
451			return;
452			try {
453	dl	1.4	super.execute(next);
454	dl	1.6	}
455			catch(RejectedExecutionException ex) {
456			// lost race to detect shutdown; ignore
457			}
458	dl	1.4	}
459	tim	1.1	}
460	dl	1.4
461