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:	1.14
Committed:	Fri Aug 8 20:05:07 2003 UTC (20 years, 9 months ago) by tim
Branch:	MAIN
Changes since 1.13:	+1 -2 lines
Log Message:	Scrunched catch, finally, else clauses.
#	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	* <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	* @since 1.5
43	* @see Executors
44	*
45	* @spec JSR-166
46	* @author Doug Lea
47	*/
48	public class ScheduledExecutor extends ThreadPoolExecutor {
49
50	/**
51	* 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	* A delayed or periodic action.
58	*/
59	public static class DelayedTask extends CancellableTask implements Delayed {
60	/** Sequence number to break ties FIFO */
61	private final long sequenceNumber;
62	/** The time the task is enabled to execute in nanoTime units */
63	private final long time;
64	/** The delay forllowing next time, or <= 0 if non-periodic */
65	private final long period;
66	/** true if at fixed rate; false if fixed delay */
67	private final boolean rateBased;
68
69	/**
70	* Creates a one-shot action with given nanoTime-based trigger time
71	*/
72	DelayedTask(Runnable r, long ns) {
73	super(r);
74	this.time = ns;
75	this.period = 0;
76	rateBased = false;
77	this.sequenceNumber = sequencer.getAndIncrement();
78	}
79
80	/**
81	* Creates a periodic action with given nano time and period
82	*/
83	DelayedTask(Runnable r, long ns, long period, boolean rateBased) {
84	super(r);
85	if (period <= 0)
86	throw new IllegalArgumentException();
87	this.time = ns;
88	this.period = period;
89	this.rateBased = rateBased;
90	this.sequenceNumber = sequencer.getAndIncrement();
91	}
92
93
94	public long getDelay(TimeUnit unit) {
95	long d = unit.convert(time - System.nanoTime(),
96	TimeUnit.NANOSECONDS);
97	return d;
98	}
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	* @return true if periodic
116	*/
117	public boolean isPeriodic() {
118	return period > 0;
119	}
120
121	/**
122	* Returns the period, or zero if non-periodic.
123	*
124	* @return the period
125	*/
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	DelayedTask nextTask() {
136	if (period <= 0 \|\| isCancelled())
137	return null;
138	long nextTime = period + (rateBased ? time : System.nanoTime());
139	return new DelayedTask(getRunnable(), nextTime, period, rateBased);
140	}
141
142	}
143
144	/**
145	* A delayed result-bearing action.
146	*/
147	public static class DelayedFutureTask<V> extends DelayedTask implements Future<V> {
148	/**
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	super(null, System.nanoTime() + unit.toNanos(delay));
154	setRunnable(new InnerCancellableFuture<V>(callable));
155	}
156
157	/**
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	}
170
171	public V get(long timeout, TimeUnit unit)
172	throws InterruptedException, ExecutionException, TimeoutException {
173	return ((InnerCancellableFuture<V>)getRunnable()).get(timeout, unit);
174	}
175
176	protected void set(V v) {
177	((InnerCancellableFuture<V>)getRunnable()).set(v);
178	}
179
180	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	* use a DelayQueue<DelayedTask> as a BlockingQueue<Runnable>
189	*/
190	private static class DelayedWorkQueue extends AbstractCollection<Runnable> implements BlockingQueue<Runnable> {
191	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	}
198
199	public boolean add(Runnable x) { return dq.add((DelayedTask)x); }
200	public boolean offer(Runnable x) { return dq.offer((DelayedTask)x); }
201	public void put(Runnable x) throws InterruptedException {
202	dq.put((DelayedTask)x);
203	}
204	public boolean offer(Runnable x, long timeout, TimeUnit unit) throws InterruptedException {
205	return dq.offer((DelayedTask)x, timeout, unit);
206	}
207
208	public Runnable remove() { return dq.remove(); }
209	public Runnable element() { return dq.element(); }
210	public void clear() { dq.clear(); }
211
212	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	public boolean isEmpty() { return dq.isEmpty(); }
217	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	}
225	}
226
227	/**
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
238	/**
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	}
251
252	/**
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
266	/**
267	* 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	* @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	*/
276	public ScheduledExecutor(int corePoolSize,
277	ThreadFactory threadFactory,
278	RejectedExecutionHandler handler) {
279	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
280	new DelayedWorkQueue(), threadFactory, handler);
281	}
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	}
299
300	/**
301	* Creates and executes a one-shot action that becomes enabled after
302	* the given delay.
303	* @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	*/
308
309	public DelayedTask schedule(Runnable command, long delay, TimeUnit unit) {
310	DelayedTask t = new DelayedTask(command, System.nanoTime() + unit.toNanos(delay));
311	delayedExecute(t);
312	return t;
313	}
314
315	/**
316	* Creates and executes a one-shot action that becomes enabled
317	* after the given date.
318	* @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	*/
324	public DelayedTask schedule(Runnable command, Date date) {
325	DelayedTask t = new DelayedTask
326	(command,
327	TimeUnit.MILLISECONDS.toNanos(date.getTime() -
328	System.currentTimeMillis()));
329	delayedExecute(t);
330	return t;
331	}
332
333	/**
334	* Creates and executes a periodic action that becomes enabled first
335	* after the given initial delay, and subsequently with the given
336	* 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	* @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	*/
347	public DelayedTask scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
348	DelayedTask t = new DelayedTask
349	(command, System.nanoTime() + unit.toNanos(initialDelay),
350	unit.toNanos(period), true);
351	delayedExecute(t);
352	return t;
353	}
354
355	/**
356	* 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	* @param command the task to execute.
362	* @param initialDate the time to delay first execution.
363	* @param period the period between commencement of successive
364	* executions.
365	* @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	*/
370	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	delayedExecute(t);
377	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	(command, System.nanoTime() + unit.toNanos(initialDelay),
397	unit.toNanos(delay), false);
398	delayedExecute(t);
399	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	DelayedTask t = new DelayedTask
418	(command,
419	TimeUnit.MILLISECONDS.toNanos(initialDate.getTime() -
420	System.currentTimeMillis()),
421	unit.toNanos(delay), false);
422	delayedExecute(t);
423	return t;
424	}
425
426
427	/**
428	* Creates and executes a Future that becomes enabled after the
429	* given delay.
430	* @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	*/
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	delayedExecute(t);
441	return t;
442	}
443
444	/**
445	* Creates and executes a one-shot action that becomes enabled after
446	* the given date.
447	* @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	*/
453	public <V> DelayedFutureTask<V> schedule(Callable<V> callable, Date date) {
454	DelayedFutureTask<V> t = new DelayedFutureTask<V>
455	(callable, date);
456	delayedExecute(t);
457	return t;
458	}
459
460	/**
461	* Execute command with zero required delay.
462	*
463	* @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	*/
468	public void execute(Runnable command) {
469	schedule(command, 0, TimeUnit.NANOSECONDS);
470	}
471
472	/**
473	* If executed task was periodic, cause the task for the next
474	* period to execute.
475	* @param r the task (assumed to be a DelayedTask)
476	* @param t the exception
477	*/
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	if (next == null)
485	return;
486	try {
487	execute(next);
488	} catch(RejectedExecutionException ex) {
489	// lost race to detect shutdown; ignore
490	}
491	}
492	}
493
494