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:	1.15
Committed:	Mon Jan 19 15:49:02 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.14:	+1 -1 lines
Log Message:	Javadoc fixes
#	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	dl	1.14
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	dl	1.5	private class ScheduledFutureTask<V>
65	dl	1.1	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	dl	1.14	long d = unit.convert(time - now(), TimeUnit.NANOSECONDS);
111	dl	1.1	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	dl	1.10	boolean isPeriodic() {
134	dl	1.1	return period > 0;
135			}
136
137			/**
138			* Returns the period, or zero if non-periodic.
139			*
140			* @return the period
141			*/
142	dl	1.10	long getPeriod(TimeUnit unit) {
143	dl	1.1	return unit.convert(period, TimeUnit.NANOSECONDS);
144			}
145
146			/**
147	dl	1.14	* Run a periodic task
148	dl	1.13	*/
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	dl	1.14	time = period + (rateBased ? time : now());
157	dl	1.13	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	dl	1.5	* Overrides FutureTask version so as to reset/requeue if periodic.
167	dl	1.1	*/
168			public void run() {
169	dl	1.13	if (isPeriodic())
170			runPeriodic();
171			else
172	dl	1.5	ScheduledFutureTask.super.run();
173	dl	1.1	}
174			}
175
176			/**
177	dl	1.13	* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
178			*/
179			private void delayedExecute(Runnable command) {
180			if (isShutdown()) {
181			reject(command);
182			return;
183	dl	1.1	}
184	dl	1.13	// 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	dl	1.1
193	dl	1.13	/**
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	dl	1.1	}
215			}
216
217			/**
218	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given core
219			* pool size.
220	dl	1.1	*
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	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
233			* initial parameters.
234	dl	1.1	*
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	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
249			* initial parameters.
250	dl	1.1	*
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	dl	1.13	* Creates a new ScheduledThreadPoolExecutor with the given
265			* initial parameters.
266	dl	1.1	*
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	dl	1.13	public ScheduledFuture<?> schedule(Runnable command,
283			long delay,
284			TimeUnit unit) {
285	dl	1.9	if (command == null \|\| unit == null)
286	dl	1.1	throw new NullPointerException();
287	dl	1.14	long triggerTime = now() + unit.toNanos(delay);
288	dl	1.13	ScheduledFutureTask<?> t =
289			new ScheduledFutureTask<Boolean>(command, null, triggerTime);
290	dl	1.1	delayedExecute(t);
291			return t;
292			}
293
294	dl	1.13	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
295			long delay,
296			TimeUnit unit) {
297	dl	1.9	if (callable == null \|\| unit == null)
298	dl	1.1	throw new NullPointerException();
299	dl	1.14	long triggerTime = now() + unit.toNanos(delay);
300	dl	1.13	ScheduledFutureTask<V> t =
301			new ScheduledFutureTask<V>(callable, triggerTime);
302	dl	1.1	delayedExecute(t);
303			return t;
304			}
305
306	dl	1.13	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
307			long initialDelay,
308			long period,
309			TimeUnit unit) {
310	dl	1.9	if (command == null \|\| unit == null)
311	dl	1.1	throw new NullPointerException();
312			if (period <= 0)
313			throw new IllegalArgumentException();
314	dl	1.14	long triggerTime = now() + unit.toNanos(initialDelay);
315	dl	1.13	ScheduledFutureTask<?> t =
316			new ScheduledFutureTask<Object>(command,
317			null,
318			triggerTime,
319			unit.toNanos(period),
320			true);
321	dl	1.1	delayedExecute(t);
322			return t;
323			}
324
325	dl	1.13	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
326			long initialDelay,
327			long delay,
328			TimeUnit unit) {
329	dl	1.9	if (command == null \|\| unit == null)
330	dl	1.1	throw new NullPointerException();
331			if (delay <= 0)
332			throw new IllegalArgumentException();
333	dl	1.14	long triggerTime = now() + unit.toNanos(initialDelay);
334	dl	1.13	ScheduledFutureTask<?> t =
335			new ScheduledFutureTask<Boolean>(command,
336			null,
337			triggerTime,
338			unit.toNanos(delay),
339			false);
340	dl	1.1	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	dl	1.13	// Override AbstractExecutorService methods
365
366	dl	1.7	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	dl	1.13	return schedule(Executors.callable(task, result),
372			0, TimeUnit.NANOSECONDS);
373	dl	1.7	}
374
375			public <T> Future<T> submit(Callable<T> task) {
376			return schedule(task, 0, TimeUnit.NANOSECONDS);
377			}
378	dl	1.1
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	tim	1.4	public List<Runnable> shutdownNow() {
468	dl	1.1	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	dl	1.15	* <em>not</em> guaranteed to traverse tasks in the order in
478	dl	1.1	* which they will execute.
479			*
480			* @return the task queue
481			*/
482			public BlockingQueue<Runnable> getQueue() {
483			return super.getQueue();
484			}
485
486	dl	1.13	/**
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	dl	1.1	}