util/concurrent/ScheduledThreadPoolExecutor.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

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

/**
 * A {@link ThreadPoolExecutor} that can additionally schedule
 * commands to run after a given delay, or to execute
 * periodically. This class is preferable to {@link java.util.Timer}
 * when multiple worker threads are needed, or when the additional
 * flexibility or capabilities of {@link ThreadPoolExecutor} (which
 * this class extends) are required.
 *
 * <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. 
 *
 * <p>While this class inherits from {@link ThreadPoolExecutor}, a few
 * of the inherited tuning methods are not useful for it. In
 * particular, because it 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
 * @author Doug Lea
 */
public class ScheduledThreadPoolExecutor 
        extends ThreadPoolExecutor 
        implements ScheduledExecutorService {

    /**
     * False if should cancel/suppress periodic tasks on shutdown.
     */
    private volatile boolean continueExistingPeriodicTasksAfterShutdown;

    /**
     * False if should cancel non-periodic tasks on shutdown.
     */
    private volatile boolean executeExistingDelayedTasksAfterShutdown = true;


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

    /** Base of nanosecond timings, to avoid wrapping */
    private static final long NANO_ORIGIN = System.nanoTime();

    /**
     * Return nanosecond time offset by origin
     */
    private long now() {
        return System.nanoTime() - NANO_ORIGIN;
    }

    private class ScheduledFutureTask<V> 
            extends FutureTask<V> implements ScheduledFuture<V> {
        
        /** Sequence number to break ties FIFO */
        private final long sequenceNumber;
        /** The time the task is enabled to execute in nanoTime units */
        private long time;
        /** The delay following 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
         */
        ScheduledFutureTask(Runnable r, V result, long ns) {
            super(r, result);
            this.time = ns;
            this.period = 0;
            rateBased = false;
            this.sequenceNumber = sequencer.getAndIncrement();
        }

        /**
         * Creates a periodic action with given nano time and period
         */
        ScheduledFutureTask(Runnable r, V result, long ns,  long period, boolean rateBased) {
            super(r, result);
            this.time = ns;
            this.period = period;
            this.rateBased = rateBased;
            this.sequenceNumber = sequencer.getAndIncrement();
        }

        /**
         * Creates a one-shot action with given nanoTime-based trigger
         */
        ScheduledFutureTask(Callable<V> callable, long ns) {
            super(callable);
            this.time = ns;
            this.period = 0;
            rateBased = false;
            this.sequenceNumber = sequencer.getAndIncrement();
        }

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

        public int compareTo(Object other) {
            if (other == this) // compare zero ONLY if same object
                return 0;
            ScheduledFutureTask<?> x = (ScheduledFutureTask<?>)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
         */
        boolean isPeriodic() {
            return period > 0;
        }

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

        /**
         * Run a periodic task
         */
        private void runPeriodic() {
            boolean ok = ScheduledFutureTask.super.runAndReset();
            boolean down = isShutdown();
            // Reschedule if not cancelled and not shutdown or policy allows
            if (ok && (!down ||
                       (getContinueExistingPeriodicTasksAfterShutdownPolicy() && 
                        !isTerminating()))) {
                time = period + (rateBased ? time : now());
                ScheduledThreadPoolExecutor.super.getQueue().add(this);
            }
            // This might have been the final executed delayed
            // task.  Wake up threads to check.
            else if (down) 
                interruptIdleWorkers();
        }

        /**
         * Overrides FutureTask version so as to reset/requeue if periodic.
         */ 
        public void run() {
            if (isPeriodic())
                runPeriodic();
            else 
                ScheduledFutureTask.super.run();
        }
    }

    /**
     * Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
     */
    private void delayedExecute(Runnable command) {
        if (isShutdown()) {
            reject(command);
            return;
        }
        // Prestart a 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())
            prestartCoreThread();
            
        super.getQueue().add(command);
    }

    /**
     * Cancel and clear the queue of all tasks that should not be run
     * due to shutdown policy.
     */
    private void cancelUnwantedTasks() {
        boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy();
        boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy();
        if (!keepDelayed && !keepPeriodic) 
            super.getQueue().clear();
        else if (keepDelayed || keepPeriodic) {
            Object[] entries = super.getQueue().toArray();
            for (int i = 0; i < entries.length; ++i) {
                Object e = entries[i];
                if (e instanceof ScheduledFutureTask) {
                    ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)e;
                    if (t.isPeriodic()? !keepPeriodic : !keepDelayed)
                        t.cancel(false);
                }
            }
            entries = null;
            purge();
        }
    }

    /**
     * Creates a new ScheduledThreadPoolExecutor with the given core
     * pool size.
     * 
     * @param corePoolSize the number of threads to keep in the pool,
     * even if they are idle.
     * @throws IllegalArgumentException if corePoolSize less than or
     * equal to zero
     */
    public ScheduledThreadPoolExecutor(int corePoolSize) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue());
    }

    /**
     * Creates a new ScheduledThreadPoolExecutor 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. 
     * @throws NullPointerException if threadFactory is null
     */
    public ScheduledThreadPoolExecutor(int corePoolSize,
                             ThreadFactory threadFactory) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), threadFactory);
    }

    /**
     * Creates a new ScheduledThreadPoolExecutor 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.
     * @throws NullPointerException if handler is null
     */
    public ScheduledThreadPoolExecutor(int corePoolSize,
                              RejectedExecutionHandler handler) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), handler);
    }

    /**
     * Creates a new ScheduledThreadPoolExecutor 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.
     * @throws NullPointerException if threadFactory or handler is null
     */
    public ScheduledThreadPoolExecutor(int corePoolSize,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), threadFactory, handler);
    }

    public ScheduledFuture<?> schedule(Runnable command, 
                                       long delay, 
                                       TimeUnit unit) {
        if (command == null || unit == null)
            throw new NullPointerException();
        long triggerTime = now() + unit.toNanos(delay);
        ScheduledFutureTask<?> t = 
            new ScheduledFutureTask<Boolean>(command, null, triggerTime);
        delayedExecute(t);
        return t;
    }

    public <V> ScheduledFuture<V> schedule(Callable<V> callable, 
                                           long delay, 
                                           TimeUnit unit) {
        if (callable == null || unit == null)
            throw new NullPointerException();
        long triggerTime = now() + unit.toNanos(delay);
        ScheduledFutureTask<V> t = 
            new ScheduledFutureTask<V>(callable, triggerTime);
        delayedExecute(t);
        return t;
    }

    public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, 
                                                  long initialDelay,  
                                                  long period, 
                                                  TimeUnit unit) {
        if (command == null || unit == null)
            throw new NullPointerException();
        if (period <= 0)
            throw new IllegalArgumentException();
        long triggerTime = now() + unit.toNanos(initialDelay);
        ScheduledFutureTask<?> t = 
            new ScheduledFutureTask<Object>(command, 
                                            null,
                                            triggerTime,
                                            unit.toNanos(period), 
                                            true);
        delayedExecute(t);
        return t;
    }
    
    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, 
                                                     long initialDelay,  
                                                     long delay, 
                                                     TimeUnit unit) {
        if (command == null || unit == null)
            throw new NullPointerException();
        if (delay <= 0)
            throw new IllegalArgumentException();
        long triggerTime = now() + unit.toNanos(initialDelay);
        ScheduledFutureTask<?> t = 
            new ScheduledFutureTask<Boolean>(command, 
                                             null,
                                             triggerTime,
                                             unit.toNanos(delay), 
                                             false);
        delayedExecute(t);
        return t;
    }
    

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

    // Override AbstractExecutorService methods

    public Future<?> submit(Runnable task) {
        return schedule(task, 0, TimeUnit.NANOSECONDS);
    }

    public <T> Future<T> submit(Runnable task, T result) {
        return schedule(Executors.callable(task, result), 
                        0, TimeUnit.NANOSECONDS);
    }

    public <T> Future<T> submit(Callable<T> task) {
        return schedule(task, 0, TimeUnit.NANOSECONDS);
    }

    /**
     * Set policy on whether to continue executing existing periodic
     * tasks even when this executor has been <tt>shutdown</tt>. In
     * this case, these tasks will only terminate upon
     * <tt>shutdownNow</tt>, or after setting the policy to
     * <tt>false</tt> when already shutdown. This value is by default
     * false.
     * @param value if true, continue after shutdown, else don't.
     */
    public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) {
        continueExistingPeriodicTasksAfterShutdown = value;
        if (!value && isShutdown())
            cancelUnwantedTasks();
    }

    /**
     * Get the policy on whether to continue executing existing
     * periodic tasks even when this executor has been
     * <tt>shutdown</tt>. In this case, these tasks will only
     * terminate upon <tt>shutdownNow</tt> or after setting the policy
     * to <tt>false</tt> when already shutdown. This value is by
     * default false.
     * @return true if will continue after shutdown.
     */
    public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() {
        return continueExistingPeriodicTasksAfterShutdown;
    }

    /**
     * Set policy on whether to execute existing delayed
     * tasks even when this executor has been <tt>shutdown</tt>. In
     * this case, these tasks will only terminate upon
     * <tt>shutdownNow</tt>, or after setting the policy to
     * <tt>false</tt> when already shutdown. This value is by default
     * true.
     * @param value if true, execute after shutdown, else don't.
     */
    public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) {
        executeExistingDelayedTasksAfterShutdown = value;
        if (!value && isShutdown())
            cancelUnwantedTasks();
    }

    /**
     * Get policy on whether to execute existing delayed
     * tasks even when this executor has been <tt>shutdown</tt>. In
     * this case, these tasks will only terminate upon
     * <tt>shutdownNow</tt>, or after setting the policy to
     * <tt>false</tt> when already shutdown. This value is by default
     * true.
     * @return true if will execute after shutdown.
     */
    public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() {
        return executeExistingDelayedTasksAfterShutdown;
    }


    /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be accepted. If the
     * <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has
     * been set <tt>false</tt>, existing delayed tasks whose delays
     * have not yet elapsed are cancelled. And unless the
     * <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has
     * been set <tt>true</tt>, future executions of existing periodic
     * tasks will be cancelled.
     */
    public void shutdown() {
        cancelUnwantedTasks();
        super.shutdown();
    }

    /**
     * Attempts to stop all actively executing tasks, halts the
     * processing of waiting tasks, and returns a list of the tasks that were
     * awaiting execution. 
     *  
     * <p>There are no guarantees beyond best-effort attempts to stop
     * processing actively executing tasks.  This implementations
     * cancels via {@link Thread#interrupt}, so if any tasks mask or
     * fail to respond to interrupts, they may never terminate.
     *
     * @return list of tasks that never commenced execution.  Each
     * element of this list is a {@link ScheduledFuture},
     * including those tasks submitted using <tt>execute</tt> which
     * are for scheduling purposes used as the basis of a zero-delay
     * <tt>ScheduledFuture</tt>.
     */
    public List<Runnable> shutdownNow() {
        return super.shutdownNow();
    }

    /**
     * Returns the task queue used by this executor.  Each element of
     * this queue is a {@link ScheduledFuture}, including those
     * tasks submitted using <tt>execute</tt> which are for scheduling
     * purposes used as the basis of a zero-delay
     * <tt>ScheduledFuture</tt>. Iteration over this queue is
     * </em>not</em> guaranteed to traverse tasks in the order in
     * which they will execute.
     *
     * @return the task queue
     */
    public BlockingQueue<Runnable> getQueue() {
        return super.getQueue();
    }

    /**
     * An annoying wrapper class to convince generics compiler to
     * use a DelayQueue<ScheduledFutureTask> as a BlockingQueue<Runnable>
     */ 
    private static class DelayedWorkQueue 
        extends AbstractCollection<Runnable> 
        implements BlockingQueue<Runnable> {
        
        private final DelayQueue<ScheduledFutureTask> dq = new DelayQueue<ScheduledFutureTask>();
        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((ScheduledFutureTask)x); }
        public boolean offer(Runnable x) { return dq.offer((ScheduledFutureTask)x); }
        public void put(Runnable x)  {
            dq.put((ScheduledFutureTask)x); 
        }
        public boolean offer(Runnable x, long timeout, TimeUnit unit) {
            return dq.offer((ScheduledFutureTask)x, timeout, unit);
        }

        public Runnable remove() { return dq.remove(); }
        public Runnable element() { return dq.element(); }
        public void clear() { dq.clear(); }
        public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); }
        public int drainTo(Collection<? super Runnable> c, int maxElements) { 
            return dq.drainTo(c, maxElements); 
        }

        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 Object[] toArray() { return dq.toArray(); }
        public <T> T[] toArray(T[] array) { return dq.toArray(array); }
        public Iterator<Runnable> iterator() { 
            return new Iterator<Runnable>() {
                private Iterator<ScheduledFutureTask> it = dq.iterator();
                public boolean hasNext() { return it.hasNext(); }
                public Runnable next() { return it.next(); }
                public void remove() {  it.remove(); }
            };
        }
    }
}
Revision:	1.14
Committed:	Fri Jan 16 18:15:59 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.13:	+18 -9 lines
Log Message:	Avoid overflow
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
5	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.atomic.*;
9	import java.util.*;
10
11	/**
12	* A {@link ThreadPoolExecutor} that can additionally schedule
13	* commands to run after a given delay, or to execute
14	* periodically. This class is preferable to {@link java.util.Timer}
15	* when multiple worker threads are needed, or when the additional
16	* flexibility or capabilities of {@link ThreadPoolExecutor} (which
17	* this class extends) are required.
18	*
19	* <p> Delayed tasks execute no sooner than they are enabled, but
20	* without any real-time guarantees about when, after they are enabled,
21	* they will commence. Tasks tied for the same execution time are
22	* enabled in first-in-first-out (FIFO) order of submission.
23	*
24	* <p>While this class inherits from {@link ThreadPoolExecutor}, a few
25	* of the inherited tuning methods are not useful for it. In
26	* particular, because it acts as a fixed-sized pool using
27	* <tt>corePoolSize</tt> threads and an unbounded queue, adjustments
28	* to <tt>maximumPoolSize</tt> have no useful effect.
29	*
30	* @since 1.5
31	* @author Doug Lea
32	*/
33	public class ScheduledThreadPoolExecutor
34	extends ThreadPoolExecutor
35	implements ScheduledExecutorService {
36
37	/**
38	* False if should cancel/suppress periodic tasks on shutdown.
39	*/
40	private volatile boolean continueExistingPeriodicTasksAfterShutdown;
41
42	/**
43	* False if should cancel non-periodic tasks on shutdown.
44	*/
45	private volatile boolean executeExistingDelayedTasksAfterShutdown = true;
46
47
48	/**
49	* Sequence number to break scheduling ties, and in turn to
50	* guarantee FIFO order among tied entries.
51	*/
52	private static final AtomicLong sequencer = new AtomicLong(0);
53
54	/** Base of nanosecond timings, to avoid wrapping */
55	private static final long NANO_ORIGIN = System.nanoTime();
56
57	/**
58	* Return nanosecond time offset by origin
59	*/
60	private long now() {
61	return System.nanoTime() - NANO_ORIGIN;
62	}
63
64	private class ScheduledFutureTask<V>
65	extends FutureTask<V> implements ScheduledFuture<V> {
66
67	/** Sequence number to break ties FIFO */
68	private final long sequenceNumber;
69	/** The time the task is enabled to execute in nanoTime units */
70	private long time;
71	/** The delay following next time, or <= 0 if non-periodic */
72	private final long period;
73	/** true if at fixed rate; false if fixed delay */
74	private final boolean rateBased;
75
76	/**
77	* Creates a one-shot action with given nanoTime-based trigger time
78	*/
79	ScheduledFutureTask(Runnable r, V result, long ns) {
80	super(r, result);
81	this.time = ns;
82	this.period = 0;
83	rateBased = false;
84	this.sequenceNumber = sequencer.getAndIncrement();
85	}
86
87	/**
88	* Creates a periodic action with given nano time and period
89	*/
90	ScheduledFutureTask(Runnable r, V result, long ns, long period, boolean rateBased) {
91	super(r, result);
92	this.time = ns;
93	this.period = period;
94	this.rateBased = rateBased;
95	this.sequenceNumber = sequencer.getAndIncrement();
96	}
97
98	/**
99	* Creates a one-shot action with given nanoTime-based trigger
100	*/
101	ScheduledFutureTask(Callable<V> callable, long ns) {
102	super(callable);
103	this.time = ns;
104	this.period = 0;
105	rateBased = false;
106	this.sequenceNumber = sequencer.getAndIncrement();
107	}
108
109	public long getDelay(TimeUnit unit) {
110	long d = unit.convert(time - now(), TimeUnit.NANOSECONDS);
111	return d;
112	}
113
114	public int compareTo(Object other) {
115	if (other == this) // compare zero ONLY if same object
116	return 0;
117	ScheduledFutureTask<?> x = (ScheduledFutureTask<?>)other;
118	long diff = time - x.time;
119	if (diff < 0)
120	return -1;
121	else if (diff > 0)
122	return 1;
123	else if (sequenceNumber < x.sequenceNumber)
124	return -1;
125	else
126	return 1;
127	}
128
129	/**
130	* Return true if this is a periodic (not a one-shot) action.
131	* @return true if periodic
132	*/
133	boolean isPeriodic() {
134	return period > 0;
135	}
136
137	/**
138	* Returns the period, or zero if non-periodic.
139	*
140	* @return the period
141	*/
142	long getPeriod(TimeUnit unit) {
143	return unit.convert(period, TimeUnit.NANOSECONDS);
144	}
145
146	/**
147	* Run a periodic task
148	*/
149	private void runPeriodic() {
150	boolean ok = ScheduledFutureTask.super.runAndReset();
151	boolean down = isShutdown();
152	// Reschedule if not cancelled and not shutdown or policy allows
153	if (ok && (!down \|\|
154	(getContinueExistingPeriodicTasksAfterShutdownPolicy() &&
155	!isTerminating()))) {
156	time = period + (rateBased ? time : now());
157	ScheduledThreadPoolExecutor.super.getQueue().add(this);
158	}
159	// This might have been the final executed delayed
160	// task. Wake up threads to check.
161	else if (down)
162	interruptIdleWorkers();
163	}
164
165	/**
166	* Overrides FutureTask version so as to reset/requeue if periodic.
167	*/
168	public void run() {
169	if (isPeriodic())
170	runPeriodic();
171	else
172	ScheduledFutureTask.super.run();
173	}
174	}
175
176	/**
177	* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
178	*/
179	private void delayedExecute(Runnable command) {
180	if (isShutdown()) {
181	reject(command);
182	return;
183	}
184	// Prestart a thread if necessary. We cannot prestart it
185	// running the task because the task (probably) shouldn't be
186	// run yet, so thread will just idle until delay elapses.
187	if (getPoolSize() < getCorePoolSize())
188	prestartCoreThread();
189
190	super.getQueue().add(command);
191	}
192
193	/**
194	* Cancel and clear the queue of all tasks that should not be run
195	* due to shutdown policy.
196	*/
197	private void cancelUnwantedTasks() {
198	boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy();
199	boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy();
200	if (!keepDelayed && !keepPeriodic)
201	super.getQueue().clear();
202	else if (keepDelayed \|\| keepPeriodic) {
203	Object[] entries = super.getQueue().toArray();
204	for (int i = 0; i < entries.length; ++i) {
205	Object e = entries[i];
206	if (e instanceof ScheduledFutureTask) {
207	ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)e;
208	if (t.isPeriodic()? !keepPeriodic : !keepDelayed)
209	t.cancel(false);
210	}
211	}
212	entries = null;
213	purge();
214	}
215	}
216
217	/**
218	* Creates a new ScheduledThreadPoolExecutor with the given core
219	* pool size.
220	*
221	* @param corePoolSize the number of threads to keep in the pool,
222	* even if they are idle.
223	* @throws IllegalArgumentException if corePoolSize less than or
224	* equal to zero
225	*/
226	public ScheduledThreadPoolExecutor(int corePoolSize) {
227	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
228	new DelayedWorkQueue());
229	}
230
231	/**
232	* Creates a new ScheduledThreadPoolExecutor with the given
233	* initial parameters.
234	*
235	* @param corePoolSize the number of threads to keep in the pool,
236	* even if they are idle.
237	* @param threadFactory the factory to use when the executor
238	* creates a new thread.
239	* @throws NullPointerException if threadFactory is null
240	*/
241	public ScheduledThreadPoolExecutor(int corePoolSize,
242	ThreadFactory threadFactory) {
243	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
244	new DelayedWorkQueue(), threadFactory);
245	}
246
247	/**
248	* Creates a new ScheduledThreadPoolExecutor with the given
249	* initial parameters.
250	*
251	* @param corePoolSize the number of threads to keep in the pool,
252	* even if they are idle.
253	* @param handler the handler to use when execution is blocked
254	* because the thread bounds and queue capacities are reached.
255	* @throws NullPointerException if handler is null
256	*/
257	public ScheduledThreadPoolExecutor(int corePoolSize,
258	RejectedExecutionHandler handler) {
259	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
260	new DelayedWorkQueue(), handler);
261	}
262
263	/**
264	* Creates a new ScheduledThreadPoolExecutor with the given
265	* initial parameters.
266	*
267	* @param corePoolSize the number of threads to keep in the pool,
268	* even if they are idle.
269	* @param threadFactory the factory to use when the executor
270	* creates a new thread.
271	* @param handler the handler to use when execution is blocked
272	* because the thread bounds and queue capacities are reached.
273	* @throws NullPointerException if threadFactory or handler is null
274	*/
275	public ScheduledThreadPoolExecutor(int corePoolSize,
276	ThreadFactory threadFactory,
277	RejectedExecutionHandler handler) {
278	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
279	new DelayedWorkQueue(), threadFactory, handler);
280	}
281
282	public ScheduledFuture<?> schedule(Runnable command,
283	long delay,
284	TimeUnit unit) {
285	if (command == null \|\| unit == null)
286	throw new NullPointerException();
287	long triggerTime = now() + unit.toNanos(delay);
288	ScheduledFutureTask<?> t =
289	new ScheduledFutureTask<Boolean>(command, null, triggerTime);
290	delayedExecute(t);
291	return t;
292	}
293
294	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
295	long delay,
296	TimeUnit unit) {
297	if (callable == null \|\| unit == null)
298	throw new NullPointerException();
299	long triggerTime = now() + unit.toNanos(delay);
300	ScheduledFutureTask<V> t =
301	new ScheduledFutureTask<V>(callable, triggerTime);
302	delayedExecute(t);
303	return t;
304	}
305
306	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
307	long initialDelay,
308	long period,
309	TimeUnit unit) {
310	if (command == null \|\| unit == null)
311	throw new NullPointerException();
312	if (period <= 0)
313	throw new IllegalArgumentException();
314	long triggerTime = now() + unit.toNanos(initialDelay);
315	ScheduledFutureTask<?> t =
316	new ScheduledFutureTask<Object>(command,
317	null,
318	triggerTime,
319	unit.toNanos(period),
320	true);
321	delayedExecute(t);
322	return t;
323	}
324
325	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
326	long initialDelay,
327	long delay,
328	TimeUnit unit) {
329	if (command == null \|\| unit == null)
330	throw new NullPointerException();
331	if (delay <= 0)
332	throw new IllegalArgumentException();
333	long triggerTime = now() + unit.toNanos(initialDelay);
334	ScheduledFutureTask<?> t =
335	new ScheduledFutureTask<Boolean>(command,
336	null,
337	triggerTime,
338	unit.toNanos(delay),
339	false);
340	delayedExecute(t);
341	return t;
342	}
343
344
345	/**
346	* Execute command with zero required delay. This has effect
347	* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note
348	* that inspections of the queue and of the list returned by
349	* <tt>shutdownNow</tt> will access the zero-delayed
350	* {@link ScheduledFuture}, not the <tt>command</tt> itself.
351	*
352	* @param command the task to execute
353	* @throws RejectedExecutionException at discretion of
354	* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
355	* for execution because the executor has been shut down.
356	* @throws NullPointerException if command is null
357	*/
358	public void execute(Runnable command) {
359	if (command == null)
360	throw new NullPointerException();
361	schedule(command, 0, TimeUnit.NANOSECONDS);
362	}
363
364	// Override AbstractExecutorService methods
365
366	public Future<?> submit(Runnable task) {
367	return schedule(task, 0, TimeUnit.NANOSECONDS);
368	}
369
370	public <T> Future<T> submit(Runnable task, T result) {
371	return schedule(Executors.callable(task, result),
372	0, TimeUnit.NANOSECONDS);
373	}
374
375	public <T> Future<T> submit(Callable<T> task) {
376	return schedule(task, 0, TimeUnit.NANOSECONDS);
377	}
378
379	/**
380	* Set policy on whether to continue executing existing periodic
381	* tasks even when this executor has been <tt>shutdown</tt>. In
382	* this case, these tasks will only terminate upon
383	* <tt>shutdownNow</tt>, or after setting the policy to
384	* <tt>false</tt> when already shutdown. This value is by default
385	* false.
386	* @param value if true, continue after shutdown, else don't.
387	*/
388	public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) {
389	continueExistingPeriodicTasksAfterShutdown = value;
390	if (!value && isShutdown())
391	cancelUnwantedTasks();
392	}
393
394	/**
395	* Get the policy on whether to continue executing existing
396	* periodic tasks even when this executor has been
397	* <tt>shutdown</tt>. In this case, these tasks will only
398	* terminate upon <tt>shutdownNow</tt> or after setting the policy
399	* to <tt>false</tt> when already shutdown. This value is by
400	* default false.
401	* @return true if will continue after shutdown.
402	*/
403	public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() {
404	return continueExistingPeriodicTasksAfterShutdown;
405	}
406
407	/**
408	* Set policy on whether to execute existing delayed
409	* tasks even when this executor has been <tt>shutdown</tt>. In
410	* this case, these tasks will only terminate upon
411	* <tt>shutdownNow</tt>, or after setting the policy to
412	* <tt>false</tt> when already shutdown. This value is by default
413	* true.
414	* @param value if true, execute after shutdown, else don't.
415	*/
416	public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) {
417	executeExistingDelayedTasksAfterShutdown = value;
418	if (!value && isShutdown())
419	cancelUnwantedTasks();
420	}
421
422	/**
423	* Get policy on whether to execute existing delayed
424	* tasks even when this executor has been <tt>shutdown</tt>. In
425	* this case, these tasks will only terminate upon
426	* <tt>shutdownNow</tt>, or after setting the policy to
427	* <tt>false</tt> when already shutdown. This value is by default
428	* true.
429	* @return true if will execute after shutdown.
430	*/
431	public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() {
432	return executeExistingDelayedTasksAfterShutdown;
433	}
434
435
436	/**
437	* Initiates an orderly shutdown in which previously submitted
438	* tasks are executed, but no new tasks will be accepted. If the
439	* <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has
440	* been set <tt>false</tt>, existing delayed tasks whose delays
441	* have not yet elapsed are cancelled. And unless the
442	* <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has
443	* been set <tt>true</tt>, future executions of existing periodic
444	* tasks will be cancelled.
445	*/
446	public void shutdown() {
447	cancelUnwantedTasks();
448	super.shutdown();
449	}
450
451	/**
452	* Attempts to stop all actively executing tasks, halts the
453	* processing of waiting tasks, and returns a list of the tasks that were
454	* awaiting execution.
455	*
456	* <p>There are no guarantees beyond best-effort attempts to stop
457	* processing actively executing tasks. This implementations
458	* cancels via {@link Thread#interrupt}, so if any tasks mask or
459	* fail to respond to interrupts, they may never terminate.
460	*
461	* @return list of tasks that never commenced execution. Each
462	* element of this list is a {@link ScheduledFuture},
463	* including those tasks submitted using <tt>execute</tt> which
464	* are for scheduling purposes used as the basis of a zero-delay
465	* <tt>ScheduledFuture</tt>.
466	*/
467	public List<Runnable> shutdownNow() {
468	return super.shutdownNow();
469	}
470
471	/**
472	* Returns the task queue used by this executor. Each element of
473	* this queue is a {@link ScheduledFuture}, including those
474	* tasks submitted using <tt>execute</tt> which are for scheduling
475	* purposes used as the basis of a zero-delay
476	* <tt>ScheduledFuture</tt>. Iteration over this queue is
477	* </em>not</em> guaranteed to traverse tasks in the order in
478	* which they will execute.
479	*
480	* @return the task queue
481	*/
482	public BlockingQueue<Runnable> getQueue() {
483	return super.getQueue();
484	}
485
486	/**
487	* An annoying wrapper class to convince generics compiler to
488	* use a DelayQueue<ScheduledFutureTask> as a BlockingQueue<Runnable>
489	*/
490	private static class DelayedWorkQueue
491	extends AbstractCollection<Runnable>
492	implements BlockingQueue<Runnable> {
493
494	private final DelayQueue<ScheduledFutureTask> dq = new DelayQueue<ScheduledFutureTask>();
495	public Runnable poll() { return dq.poll(); }
496	public Runnable peek() { return dq.peek(); }
497	public Runnable take() throws InterruptedException { return dq.take(); }
498	public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
499	return dq.poll(timeout, unit);
500	}
501
502	public boolean add(Runnable x) { return dq.add((ScheduledFutureTask)x); }
503	public boolean offer(Runnable x) { return dq.offer((ScheduledFutureTask)x); }
504	public void put(Runnable x) {
505	dq.put((ScheduledFutureTask)x);
506	}
507	public boolean offer(Runnable x, long timeout, TimeUnit unit) {
508	return dq.offer((ScheduledFutureTask)x, timeout, unit);
509	}
510
511	public Runnable remove() { return dq.remove(); }
512	public Runnable element() { return dq.element(); }
513	public void clear() { dq.clear(); }
514	public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); }
515	public int drainTo(Collection<? super Runnable> c, int maxElements) {
516	return dq.drainTo(c, maxElements);
517	}
518
519	public int remainingCapacity() { return dq.remainingCapacity(); }
520	public boolean remove(Object x) { return dq.remove(x); }
521	public boolean contains(Object x) { return dq.contains(x); }
522	public int size() { return dq.size(); }
523	public boolean isEmpty() { return dq.isEmpty(); }
524	public Object[] toArray() { return dq.toArray(); }
525	public <T> T[] toArray(T[] array) { return dq.toArray(array); }
526	public Iterator<Runnable> iterator() {
527	return new Iterator<Runnable>() {
528	private Iterator<ScheduledFutureTask> it = dq.iterator();
529	public boolean hasNext() { return it.hasNext(); }
530	public Runnable next() { return it.next(); }
531	public void remove() { it.remove(); }
532	};
533	}
534	}
535	}