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);
    
    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 - System.nanoTime(), 
                                   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 : System.nanoTime());
                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 = System.nanoTime() + 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 = System.nanoTime() + 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 = System.nanoTime() + 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 = System.nanoTime() + 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:	1.13
Committed:	Sun Jan 11 23:19:55 2004 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.12:	+148 -122 lines
Log Message:	formatting; grammar
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.11	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.1	*/
6
7			package java.util.concurrent;
8			import java.util.concurrent.atomic.*;
9			import java.util.*;
10
11			/**
12	dl	1.7	* 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	dl	1.1	*
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	dl	1.8	* 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	dl	1.1	*
30			* @since 1.5
31			* @author Doug Lea
32			*/
33	tim	1.3	public class ScheduledThreadPoolExecutor
34			extends ThreadPoolExecutor
35			implements ScheduledExecutorService {
36	dl	1.1
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	dl	1.5	private class ScheduledFutureTask<V>
55	dl	1.1	extends FutureTask<V> implements ScheduledFuture<V> {
56
57			/** Sequence number to break ties FIFO */
58			private final long sequenceNumber;
59			/** The time the task is enabled to execute in nanoTime units */
60			private long time;
61			/** The delay following next time, or <= 0 if non-periodic */
62			private final long period;
63			/** true if at fixed rate; false if fixed delay */
64			private final boolean rateBased;
65
66			/**
67			* Creates a one-shot action with given nanoTime-based trigger time
68			*/
69			ScheduledFutureTask(Runnable r, V result, long ns) {
70			super(r, result);
71			this.time = ns;
72			this.period = 0;
73			rateBased = false;
74			this.sequenceNumber = sequencer.getAndIncrement();
75			}
76
77			/**
78			* Creates a periodic action with given nano time and period
79			*/
80			ScheduledFutureTask(Runnable r, V result, long ns, long period, boolean rateBased) {
81			super(r, result);
82			this.time = ns;
83			this.period = period;
84			this.rateBased = rateBased;
85			this.sequenceNumber = sequencer.getAndIncrement();
86			}
87
88			/**
89			* Creates a one-shot action with given nanoTime-based trigger
90			*/
91			ScheduledFutureTask(Callable<V> callable, long ns) {
92			super(callable);
93			this.time = ns;
94			this.period = 0;
95			rateBased = false;
96			this.sequenceNumber = sequencer.getAndIncrement();
97			}
98
99			public long getDelay(TimeUnit unit) {
100			long d = unit.convert(time - System.nanoTime(),
101			TimeUnit.NANOSECONDS);
102			return d;
103			}
104
105			public int compareTo(Object other) {
106			if (other == this) // compare zero ONLY if same object
107			return 0;
108			ScheduledFutureTask<?> x = (ScheduledFutureTask<?>)other;
109			long diff = time - x.time;
110			if (diff < 0)
111			return -1;
112			else if (diff > 0)
113			return 1;
114			else if (sequenceNumber < x.sequenceNumber)
115			return -1;
116			else
117			return 1;
118			}
119
120			/**
121			* Return true if this is a periodic (not a one-shot) action.
122			* @return true if periodic
123			*/
124	dl	1.10	boolean isPeriodic() {
125	dl	1.1	return period > 0;
126			}
127
128			/**
129			* Returns the period, or zero if non-periodic.
130			*
131			* @return the period
132			*/
133	dl	1.10	long getPeriod(TimeUnit unit) {
134	dl	1.1	return unit.convert(period, TimeUnit.NANOSECONDS);
135			}
136
137			/**
138	dl	1.13	* RUn a periodic task
139			*/
140			private void runPeriodic() {
141			boolean ok = ScheduledFutureTask.super.runAndReset();
142			boolean down = isShutdown();
143			// Reschedule if not cancelled and not shutdown or policy allows
144			if (ok && (!down \|\|
145			(getContinueExistingPeriodicTasksAfterShutdownPolicy() &&
146			!isTerminating()))) {
147			time = period + (rateBased ? time : System.nanoTime());
148			ScheduledThreadPoolExecutor.super.getQueue().add(this);
149			}
150			// This might have been the final executed delayed
151			// task. Wake up threads to check.
152			else if (down)
153			interruptIdleWorkers();
154			}
155
156			/**
157	dl	1.5	* Overrides FutureTask version so as to reset/requeue if periodic.
158	dl	1.1	*/
159			public void run() {
160	dl	1.13	if (isPeriodic())
161			runPeriodic();
162			else
163	dl	1.5	ScheduledFutureTask.super.run();
164	dl	1.1	}
165			}
166
167			/**
168	dl	1.13	* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
169			*/
170			private void delayedExecute(Runnable command) {
171			if (isShutdown()) {
172			reject(command);
173			return;
174	dl	1.1	}
175	dl	1.13	// Prestart a thread if necessary. We cannot prestart it
176			// running the task because the task (probably) shouldn't be
177			// run yet, so thread will just idle until delay elapses.
178			if (getPoolSize() < getCorePoolSize())
179			prestartCoreThread();
180
181			super.getQueue().add(command);
182			}
183	dl	1.1
184	dl	1.13	/**
185			* Cancel and clear the queue of all tasks that should not be run
186			* due to shutdown policy.
187			*/
188			private void cancelUnwantedTasks() {
189			boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy();
190			boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy();
191			if (!keepDelayed && !keepPeriodic)
192			super.getQueue().clear();
193			else if (keepDelayed \|\| keepPeriodic) {
194			Object[] entries = super.getQueue().toArray();
195			for (int i = 0; i < entries.length; ++i) {
196			Object e = entries[i];
197			if (e instanceof ScheduledFutureTask) {
198			ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)e;
199			if (t.isPeriodic()? !keepPeriodic : !keepDelayed)
200			t.cancel(false);
201			}
202			}
203			entries = null;
204			purge();
205	dl	1.1	}
206			}
207
208			/**
209	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given core
210			* pool size.
211	dl	1.1	*
212			* @param corePoolSize the number of threads to keep in the pool,
213			* even if they are idle.
214			* @throws IllegalArgumentException if corePoolSize less than or
215			* equal to zero
216			*/
217			public ScheduledThreadPoolExecutor(int corePoolSize) {
218			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
219			new DelayedWorkQueue());
220			}
221
222			/**
223	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
224			* initial parameters.
225	dl	1.1	*
226			* @param corePoolSize the number of threads to keep in the pool,
227			* even if they are idle.
228			* @param threadFactory the factory to use when the executor
229			* creates a new thread.
230			* @throws NullPointerException if threadFactory is null
231			*/
232			public ScheduledThreadPoolExecutor(int corePoolSize,
233			ThreadFactory threadFactory) {
234			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
235			new DelayedWorkQueue(), threadFactory);
236			}
237
238			/**
239	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
240			* initial parameters.
241	dl	1.1	*
242			* @param corePoolSize the number of threads to keep in the pool,
243			* even if they are idle.
244			* @param handler the handler to use when execution is blocked
245			* because the thread bounds and queue capacities are reached.
246			* @throws NullPointerException if handler is null
247			*/
248			public ScheduledThreadPoolExecutor(int corePoolSize,
249			RejectedExecutionHandler handler) {
250			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
251			new DelayedWorkQueue(), handler);
252			}
253
254			/**
255	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
256			* initial parameters.
257	dl	1.1	*
258			* @param corePoolSize the number of threads to keep in the pool,
259			* even if they are idle.
260			* @param threadFactory the factory to use when the executor
261			* creates a new thread.
262			* @param handler the handler to use when execution is blocked
263			* because the thread bounds and queue capacities are reached.
264			* @throws NullPointerException if threadFactory or handler is null
265			*/
266			public ScheduledThreadPoolExecutor(int corePoolSize,
267			ThreadFactory threadFactory,
268			RejectedExecutionHandler handler) {
269			super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
270			new DelayedWorkQueue(), threadFactory, handler);
271			}
272
273	dl	1.13	public ScheduledFuture<?> schedule(Runnable command,
274			long delay,
275			TimeUnit unit) {
276	dl	1.9	if (command == null \|\| unit == null)
277	dl	1.1	throw new NullPointerException();
278			long triggerTime = System.nanoTime() + unit.toNanos(delay);
279	dl	1.13	ScheduledFutureTask<?> t =
280			new ScheduledFutureTask<Boolean>(command, null, triggerTime);
281	dl	1.1	delayedExecute(t);
282			return t;
283			}
284
285	dl	1.13	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
286			long delay,
287			TimeUnit unit) {
288	dl	1.9	if (callable == null \|\| unit == null)
289	dl	1.1	throw new NullPointerException();
290			long triggerTime = System.nanoTime() + unit.toNanos(delay);
291	dl	1.13	ScheduledFutureTask<V> t =
292			new ScheduledFutureTask<V>(callable, triggerTime);
293	dl	1.1	delayedExecute(t);
294			return t;
295			}
296
297	dl	1.13	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
298			long initialDelay,
299			long period,
300			TimeUnit unit) {
301	dl	1.9	if (command == null \|\| unit == null)
302	dl	1.1	throw new NullPointerException();
303			if (period <= 0)
304			throw new IllegalArgumentException();
305			long triggerTime = System.nanoTime() + unit.toNanos(initialDelay);
306	dl	1.13	ScheduledFutureTask<?> t =
307			new ScheduledFutureTask<Object>(command,
308			null,
309			triggerTime,
310			unit.toNanos(period),
311			true);
312	dl	1.1	delayedExecute(t);
313			return t;
314			}
315
316	dl	1.13	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
317			long initialDelay,
318			long delay,
319			TimeUnit unit) {
320	dl	1.9	if (command == null \|\| unit == null)
321	dl	1.1	throw new NullPointerException();
322			if (delay <= 0)
323			throw new IllegalArgumentException();
324			long triggerTime = System.nanoTime() + unit.toNanos(initialDelay);
325	dl	1.13	ScheduledFutureTask<?> t =
326			new ScheduledFutureTask<Boolean>(command,
327			null,
328			triggerTime,
329			unit.toNanos(delay),
330			false);
331	dl	1.1	delayedExecute(t);
332			return t;
333			}
334
335
336			/**
337			* Execute command with zero required delay. This has effect
338			* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note
339			* that inspections of the queue and of the list returned by
340			* <tt>shutdownNow</tt> will access the zero-delayed
341			* {@link ScheduledFuture}, not the <tt>command</tt> itself.
342			*
343			* @param command the task to execute
344			* @throws RejectedExecutionException at discretion of
345			* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
346			* for execution because the executor has been shut down.
347			* @throws NullPointerException if command is null
348			*/
349			public void execute(Runnable command) {
350			if (command == null)
351			throw new NullPointerException();
352			schedule(command, 0, TimeUnit.NANOSECONDS);
353			}
354
355	dl	1.13	// Override AbstractExecutorService methods
356
357	dl	1.7	public Future<?> submit(Runnable task) {
358			return schedule(task, 0, TimeUnit.NANOSECONDS);
359			}
360
361			public <T> Future<T> submit(Runnable task, T result) {
362	dl	1.13	return schedule(Executors.callable(task, result),
363			0, TimeUnit.NANOSECONDS);
364	dl	1.7	}
365
366			public <T> Future<T> submit(Callable<T> task) {
367			return schedule(task, 0, TimeUnit.NANOSECONDS);
368			}
369	dl	1.1
370			/**
371			* Set policy on whether to continue executing existing periodic
372			* tasks even when this executor has been <tt>shutdown</tt>. In
373			* this case, these tasks will only terminate upon
374			* <tt>shutdownNow</tt>, or after setting the policy to
375			* <tt>false</tt> when already shutdown. This value is by default
376			* false.
377			* @param value if true, continue after shutdown, else don't.
378			*/
379			public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) {
380			continueExistingPeriodicTasksAfterShutdown = value;
381			if (!value && isShutdown())
382			cancelUnwantedTasks();
383			}
384
385			/**
386			* Get the policy on whether to continue executing existing
387			* periodic tasks even when this executor has been
388			* <tt>shutdown</tt>. In this case, these tasks will only
389			* terminate upon <tt>shutdownNow</tt> or after setting the policy
390			* to <tt>false</tt> when already shutdown. This value is by
391			* default false.
392			* @return true if will continue after shutdown.
393			*/
394			public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() {
395			return continueExistingPeriodicTasksAfterShutdown;
396			}
397
398			/**
399			* Set policy on whether to execute existing delayed
400			* tasks even when this executor has been <tt>shutdown</tt>. In
401			* this case, these tasks will only terminate upon
402			* <tt>shutdownNow</tt>, or after setting the policy to
403			* <tt>false</tt> when already shutdown. This value is by default
404			* true.
405			* @param value if true, execute after shutdown, else don't.
406			*/
407			public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) {
408			executeExistingDelayedTasksAfterShutdown = value;
409			if (!value && isShutdown())
410			cancelUnwantedTasks();
411			}
412
413			/**
414			* Get policy on whether to execute existing delayed
415			* tasks even when this executor has been <tt>shutdown</tt>. In
416			* this case, these tasks will only terminate upon
417			* <tt>shutdownNow</tt>, or after setting the policy to
418			* <tt>false</tt> when already shutdown. This value is by default
419			* true.
420			* @return true if will execute after shutdown.
421			*/
422			public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() {
423			return executeExistingDelayedTasksAfterShutdown;
424			}
425
426
427			/**
428			* Initiates an orderly shutdown in which previously submitted
429			* tasks are executed, but no new tasks will be accepted. If the
430			* <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has
431			* been set <tt>false</tt>, existing delayed tasks whose delays
432			* have not yet elapsed are cancelled. And unless the
433			* <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has
434			* been set <tt>true</tt>, future executions of existing periodic
435			* tasks will be cancelled.
436			*/
437			public void shutdown() {
438			cancelUnwantedTasks();
439			super.shutdown();
440			}
441
442			/**
443			* Attempts to stop all actively executing tasks, halts the
444			* processing of waiting tasks, and returns a list of the tasks that were
445			* awaiting execution.
446			*
447			* <p>There are no guarantees beyond best-effort attempts to stop
448			* processing actively executing tasks. This implementations
449			* cancels via {@link Thread#interrupt}, so if any tasks mask or
450			* fail to respond to interrupts, they may never terminate.
451			*
452			* @return list of tasks that never commenced execution. Each
453			* element of this list is a {@link ScheduledFuture},
454			* including those tasks submitted using <tt>execute</tt> which
455			* are for scheduling purposes used as the basis of a zero-delay
456			* <tt>ScheduledFuture</tt>.
457			*/
458	tim	1.4	public List<Runnable> shutdownNow() {
459	dl	1.1	return super.shutdownNow();
460			}
461
462			/**
463			* Returns the task queue used by this executor. Each element of
464			* this queue is a {@link ScheduledFuture}, including those
465			* tasks submitted using <tt>execute</tt> which are for scheduling
466			* purposes used as the basis of a zero-delay
467			* <tt>ScheduledFuture</tt>. Iteration over this queue is
468			* </em>not</em> guaranteed to traverse tasks in the order in
469			* which they will execute.
470			*
471			* @return the task queue
472			*/
473			public BlockingQueue<Runnable> getQueue() {
474			return super.getQueue();
475			}
476
477	dl	1.13	/**
478			* An annoying wrapper class to convince generics compiler to
479			* use a DelayQueue<ScheduledFutureTask> as a BlockingQueue<Runnable>
480			*/
481			private static class DelayedWorkQueue
482			extends AbstractCollection<Runnable>
483			implements BlockingQueue<Runnable> {
484
485			private final DelayQueue<ScheduledFutureTask> dq = new DelayQueue<ScheduledFutureTask>();
486			public Runnable poll() { return dq.poll(); }
487			public Runnable peek() { return dq.peek(); }
488			public Runnable take() throws InterruptedException { return dq.take(); }
489			public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
490			return dq.poll(timeout, unit);
491			}
492
493			public boolean add(Runnable x) { return dq.add((ScheduledFutureTask)x); }
494			public boolean offer(Runnable x) { return dq.offer((ScheduledFutureTask)x); }
495			public void put(Runnable x) {
496			dq.put((ScheduledFutureTask)x);
497			}
498			public boolean offer(Runnable x, long timeout, TimeUnit unit) {
499			return dq.offer((ScheduledFutureTask)x, timeout, unit);
500			}
501
502			public Runnable remove() { return dq.remove(); }
503			public Runnable element() { return dq.element(); }
504			public void clear() { dq.clear(); }
505			public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); }
506			public int drainTo(Collection<? super Runnable> c, int maxElements) {
507			return dq.drainTo(c, maxElements);
508			}
509
510			public int remainingCapacity() { return dq.remainingCapacity(); }
511			public boolean remove(Object x) { return dq.remove(x); }
512			public boolean contains(Object x) { return dq.contains(x); }
513			public int size() { return dq.size(); }
514			public boolean isEmpty() { return dq.isEmpty(); }
515			public Object[] toArray() { return dq.toArray(); }
516			public <T> T[] toArray(T[] array) { return dq.toArray(array); }
517			public Iterator<Runnable> iterator() {
518			return new Iterator<Runnable>() {
519			private Iterator<ScheduledFutureTask> it = dq.iterator();
520			public boolean hasNext() { return it.hasNext(); }
521			public Runnable next() { return it.next(); }
522			public void remove() { it.remove(); }
523			};
524			}
525			}
526	dl	1.1	}