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;
        /**
         * Period in nanoseconds for repeating tasks.  A positive
         * value indicates fixed-rate execution.  A negative value
         * indicates fixed-delay execution.  A value of 0 indicates a
         * non-repeating task.
         */
        private final long period;

        /**
         * 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;
            this.sequenceNumber = sequencer.getAndIncrement();
        }

        /**
         * Creates a periodic action with given nano time and period
         */
        ScheduledFutureTask(Runnable r, V result, long ns,  long period) {
            super(r, result);
            this.time = ns;
            this.period = period;
            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;
            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()))) {
                long p = period;
                if (p > 0)
                    time += p;
                else
                    time = now() - p;
                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();
        if (delay < 0) delay = 0;
        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();
        if (initialDelay < 0) initialDelay = 0;
        long triggerTime = now() + unit.toNanos(initialDelay);
        ScheduledFutureTask<?> t = 
            new ScheduledFutureTask<Object>(command, 
                                            null,
                                            triggerTime,
                                            unit.toNanos(period));
        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();
        if (initialDelay < 0) initialDelay = 0;
        long triggerTime = now() + unit.toNanos(initialDelay);
        ScheduledFutureTask<?> t = 
            new ScheduledFutureTask<Boolean>(command, 
                                             null,
                                             triggerTime,
                                             unit.toNanos(-delay));
        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.
     * @see #getExecuteExistingDelayedTasksAfterShutdownPolicy
     */
    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.
     * @see #setContinueExistingPeriodicTasksAfterShutdownPolicy
     */
    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.
     * @see #getExecuteExistingDelayedTasksAfterShutdownPolicy
     */
    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.
     * @see #setExecuteExistingDelayedTasksAfterShutdownPolicy
     */
    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:	1.16
Committed:	Wed Jan 21 01:47:00 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.15:	+22 -13 lines
Log Message:	Use j.u.Timer internal conventions
#	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	/**
72	* Period in nanoseconds for repeating tasks. A positive
73	* value indicates fixed-rate execution. A negative value
74	* indicates fixed-delay execution. A value of 0 indicates a
75	* non-repeating task.
76	*/
77	private final long period;
78
79	/**
80	* Creates a one-shot action with given nanoTime-based trigger time
81	*/
82	ScheduledFutureTask(Runnable r, V result, long ns) {
83	super(r, result);
84	this.time = ns;
85	this.period = 0;
86	this.sequenceNumber = sequencer.getAndIncrement();
87	}
88
89	/**
90	* Creates a periodic action with given nano time and period
91	*/
92	ScheduledFutureTask(Runnable r, V result, long ns, long period) {
93	super(r, result);
94	this.time = ns;
95	this.period = period;
96	this.sequenceNumber = sequencer.getAndIncrement();
97	}
98
99	/**
100	* Creates a one-shot action with given nanoTime-based trigger
101	*/
102	ScheduledFutureTask(Callable<V> callable, long ns) {
103	super(callable);
104	this.time = ns;
105	this.period = 0;
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	long p = period;
157	if (p > 0)
158	time += p;
159	else
160	time = now() - p;
161	ScheduledThreadPoolExecutor.super.getQueue().add(this);
162	}
163	// This might have been the final executed delayed
164	// task. Wake up threads to check.
165	else if (down)
166	interruptIdleWorkers();
167	}
168
169	/**
170	* Overrides FutureTask version so as to reset/requeue if periodic.
171	*/
172	public void run() {
173	if (isPeriodic())
174	runPeriodic();
175	else
176	ScheduledFutureTask.super.run();
177	}
178	}
179
180	/**
181	* Specialized variant of ThreadPoolExecutor.execute for delayed tasks.
182	*/
183	private void delayedExecute(Runnable command) {
184	if (isShutdown()) {
185	reject(command);
186	return;
187	}
188	// Prestart a thread if necessary. We cannot prestart it
189	// running the task because the task (probably) shouldn't be
190	// run yet, so thread will just idle until delay elapses.
191	if (getPoolSize() < getCorePoolSize())
192	prestartCoreThread();
193
194	super.getQueue().add(command);
195	}
196
197	/**
198	* Cancel and clear the queue of all tasks that should not be run
199	* due to shutdown policy.
200	*/
201	private void cancelUnwantedTasks() {
202	boolean keepDelayed = getExecuteExistingDelayedTasksAfterShutdownPolicy();
203	boolean keepPeriodic = getContinueExistingPeriodicTasksAfterShutdownPolicy();
204	if (!keepDelayed && !keepPeriodic)
205	super.getQueue().clear();
206	else if (keepDelayed \|\| keepPeriodic) {
207	Object[] entries = super.getQueue().toArray();
208	for (int i = 0; i < entries.length; ++i) {
209	Object e = entries[i];
210	if (e instanceof ScheduledFutureTask) {
211	ScheduledFutureTask<?> t = (ScheduledFutureTask<?>)e;
212	if (t.isPeriodic()? !keepPeriodic : !keepDelayed)
213	t.cancel(false);
214	}
215	}
216	entries = null;
217	purge();
218	}
219	}
220
221	/**
222	* Creates a new ScheduledThreadPoolExecutor with the given core
223	* pool size.
224	*
225	* @param corePoolSize the number of threads to keep in the pool,
226	* even if they are idle.
227	* @throws IllegalArgumentException if corePoolSize less than or
228	* equal to zero
229	*/
230	public ScheduledThreadPoolExecutor(int corePoolSize) {
231	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
232	new DelayedWorkQueue());
233	}
234
235	/**
236	* Creates a new ScheduledThreadPoolExecutor with the given
237	* initial parameters.
238	*
239	* @param corePoolSize the number of threads to keep in the pool,
240	* even if they are idle.
241	* @param threadFactory the factory to use when the executor
242	* creates a new thread.
243	* @throws NullPointerException if threadFactory is null
244	*/
245	public ScheduledThreadPoolExecutor(int corePoolSize,
246	ThreadFactory threadFactory) {
247	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
248	new DelayedWorkQueue(), threadFactory);
249	}
250
251	/**
252	* Creates a new ScheduledThreadPoolExecutor with the given
253	* initial parameters.
254	*
255	* @param corePoolSize the number of threads to keep in the pool,
256	* even if they are idle.
257	* @param handler the handler to use when execution is blocked
258	* because the thread bounds and queue capacities are reached.
259	* @throws NullPointerException if handler is null
260	*/
261	public ScheduledThreadPoolExecutor(int corePoolSize,
262	RejectedExecutionHandler handler) {
263	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
264	new DelayedWorkQueue(), handler);
265	}
266
267	/**
268	* Creates a new ScheduledThreadPoolExecutor with the given
269	* initial parameters.
270	*
271	* @param corePoolSize the number of threads to keep in the pool,
272	* even if they are idle.
273	* @param threadFactory the factory to use when the executor
274	* creates a new thread.
275	* @param handler the handler to use when execution is blocked
276	* because the thread bounds and queue capacities are reached.
277	* @throws NullPointerException if threadFactory or handler is null
278	*/
279	public ScheduledThreadPoolExecutor(int corePoolSize,
280	ThreadFactory threadFactory,
281	RejectedExecutionHandler handler) {
282	super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
283	new DelayedWorkQueue(), threadFactory, handler);
284	}
285
286	public ScheduledFuture<?> schedule(Runnable command,
287	long delay,
288	TimeUnit unit) {
289	if (command == null \|\| unit == null)
290	throw new NullPointerException();
291	long triggerTime = now() + unit.toNanos(delay);
292	ScheduledFutureTask<?> t =
293	new ScheduledFutureTask<Boolean>(command, null, triggerTime);
294	delayedExecute(t);
295	return t;
296	}
297
298	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
299	long delay,
300	TimeUnit unit) {
301	if (callable == null \|\| unit == null)
302	throw new NullPointerException();
303	if (delay < 0) delay = 0;
304	long triggerTime = now() + unit.toNanos(delay);
305	ScheduledFutureTask<V> t =
306	new ScheduledFutureTask<V>(callable, triggerTime);
307	delayedExecute(t);
308	return t;
309	}
310
311	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
312	long initialDelay,
313	long period,
314	TimeUnit unit) {
315	if (command == null \|\| unit == null)
316	throw new NullPointerException();
317	if (period <= 0)
318	throw new IllegalArgumentException();
319	if (initialDelay < 0) initialDelay = 0;
320	long triggerTime = now() + unit.toNanos(initialDelay);
321	ScheduledFutureTask<?> t =
322	new ScheduledFutureTask<Object>(command,
323	null,
324	triggerTime,
325	unit.toNanos(period));
326	delayedExecute(t);
327	return t;
328	}
329
330	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
331	long initialDelay,
332	long delay,
333	TimeUnit unit) {
334	if (command == null \|\| unit == null)
335	throw new NullPointerException();
336	if (delay <= 0)
337	throw new IllegalArgumentException();
338	if (initialDelay < 0) initialDelay = 0;
339	long triggerTime = now() + unit.toNanos(initialDelay);
340	ScheduledFutureTask<?> t =
341	new ScheduledFutureTask<Boolean>(command,
342	null,
343	triggerTime,
344	unit.toNanos(-delay));
345	delayedExecute(t);
346	return t;
347	}
348
349
350	/**
351	* Execute command with zero required delay. This has effect
352	* equivalent to <tt>schedule(command, 0, anyUnit)</tt>. Note
353	* that inspections of the queue and of the list returned by
354	* <tt>shutdownNow</tt> will access the zero-delayed
355	* {@link ScheduledFuture}, not the <tt>command</tt> itself.
356	*
357	* @param command the task to execute
358	* @throws RejectedExecutionException at discretion of
359	* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted
360	* for execution because the executor has been shut down.
361	* @throws NullPointerException if command is null
362	*/
363	public void execute(Runnable command) {
364	if (command == null)
365	throw new NullPointerException();
366	schedule(command, 0, TimeUnit.NANOSECONDS);
367	}
368
369	// Override AbstractExecutorService methods
370
371	public Future<?> submit(Runnable task) {
372	return schedule(task, 0, TimeUnit.NANOSECONDS);
373	}
374
375	public <T> Future<T> submit(Runnable task, T result) {
376	return schedule(Executors.callable(task, result),
377	0, TimeUnit.NANOSECONDS);
378	}
379
380	public <T> Future<T> submit(Callable<T> task) {
381	return schedule(task, 0, TimeUnit.NANOSECONDS);
382	}
383
384	/**
385	* Set policy on whether to continue executing existing periodic
386	* tasks even when this executor has been <tt>shutdown</tt>. In
387	* this case, these tasks will only terminate upon
388	* <tt>shutdownNow</tt>, or after setting the policy to
389	* <tt>false</tt> when already shutdown. This value is by default
390	* false.
391	* @param value if true, continue after shutdown, else don't.
392	* @see #getExecuteExistingDelayedTasksAfterShutdownPolicy
393	*/
394	public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) {
395	continueExistingPeriodicTasksAfterShutdown = value;
396	if (!value && isShutdown())
397	cancelUnwantedTasks();
398	}
399
400	/**
401	* Get the policy on whether to continue executing existing
402	* periodic tasks even when this executor has been
403	* <tt>shutdown</tt>. In this case, these tasks will only
404	* terminate upon <tt>shutdownNow</tt> or after setting the policy
405	* to <tt>false</tt> when already shutdown. This value is by
406	* default false.
407	* @return true if will continue after shutdown.
408	* @see #setContinueExistingPeriodicTasksAfterShutdownPolicy
409	*/
410	public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() {
411	return continueExistingPeriodicTasksAfterShutdown;
412	}
413
414	/**
415	* Set policy on whether to execute existing delayed
416	* tasks even when this executor has been <tt>shutdown</tt>. In
417	* this case, these tasks will only terminate upon
418	* <tt>shutdownNow</tt>, or after setting the policy to
419	* <tt>false</tt> when already shutdown. This value is by default
420	* true.
421	* @param value if true, execute after shutdown, else don't.
422	* @see #getExecuteExistingDelayedTasksAfterShutdownPolicy
423	*/
424	public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) {
425	executeExistingDelayedTasksAfterShutdown = value;
426	if (!value && isShutdown())
427	cancelUnwantedTasks();
428	}
429
430	/**
431	* Get policy on whether to execute existing delayed
432	* tasks even when this executor has been <tt>shutdown</tt>. In
433	* this case, these tasks will only terminate upon
434	* <tt>shutdownNow</tt>, or after setting the policy to
435	* <tt>false</tt> when already shutdown. This value is by default
436	* true.
437	* @return true if will execute after shutdown.
438	* @see #setExecuteExistingDelayedTasksAfterShutdownPolicy
439	*/
440	public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy() {
441	return executeExistingDelayedTasksAfterShutdown;
442	}
443
444
445	/**
446	* Initiates an orderly shutdown in which previously submitted
447	* tasks are executed, but no new tasks will be accepted. If the
448	* <tt>ExecuteExistingDelayedTasksAfterShutdownPolicy</tt> has
449	* been set <tt>false</tt>, existing delayed tasks whose delays
450	* have not yet elapsed are cancelled. And unless the
451	* <tt>ContinueExistingPeriodicTasksAfterShutdownPolicy</tt> has
452	* been set <tt>true</tt>, future executions of existing periodic
453	* tasks will be cancelled.
454	*/
455	public void shutdown() {
456	cancelUnwantedTasks();
457	super.shutdown();
458	}
459
460	/**
461	* Attempts to stop all actively executing tasks, halts the
462	* processing of waiting tasks, and returns a list of the tasks that were
463	* awaiting execution.
464	*
465	* <p>There are no guarantees beyond best-effort attempts to stop
466	* processing actively executing tasks. This implementations
467	* cancels via {@link Thread#interrupt}, so if any tasks mask or
468	* fail to respond to interrupts, they may never terminate.
469	*
470	* @return list of tasks that never commenced execution. Each
471	* element of this list is a {@link ScheduledFuture},
472	* including those tasks submitted using <tt>execute</tt> which
473	* are for scheduling purposes used as the basis of a zero-delay
474	* <tt>ScheduledFuture</tt>.
475	*/
476	public List<Runnable> shutdownNow() {
477	return super.shutdownNow();
478	}
479
480	/**
481	* Returns the task queue used by this executor. Each element of
482	* this queue is a {@link ScheduledFuture}, including those
483	* tasks submitted using <tt>execute</tt> which are for scheduling
484	* purposes used as the basis of a zero-delay
485	* <tt>ScheduledFuture</tt>. Iteration over this queue is
486	* <em>not</em> guaranteed to traverse tasks in the order in
487	* which they will execute.
488	*
489	* @return the task queue
490	*/
491	public BlockingQueue<Runnable> getQueue() {
492	return super.getQueue();
493	}
494
495	/**
496	* An annoying wrapper class to convince generics compiler to
497	* use a DelayQueue<ScheduledFutureTask> as a BlockingQueue<Runnable>
498	*/
499	private static class DelayedWorkQueue
500	extends AbstractCollection<Runnable>
501	implements BlockingQueue<Runnable> {
502
503	private final DelayQueue<ScheduledFutureTask> dq = new DelayQueue<ScheduledFutureTask>();
504	public Runnable poll() { return dq.poll(); }
505	public Runnable peek() { return dq.peek(); }
506	public Runnable take() throws InterruptedException { return dq.take(); }
507	public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
508	return dq.poll(timeout, unit);
509	}
510
511	public boolean add(Runnable x) { return dq.add((ScheduledFutureTask)x); }
512	public boolean offer(Runnable x) { return dq.offer((ScheduledFutureTask)x); }
513	public void put(Runnable x) {
514	dq.put((ScheduledFutureTask)x);
515	}
516	public boolean offer(Runnable x, long timeout, TimeUnit unit) {
517	return dq.offer((ScheduledFutureTask)x, timeout, unit);
518	}
519
520	public Runnable remove() { return dq.remove(); }
521	public Runnable element() { return dq.element(); }
522	public void clear() { dq.clear(); }
523	public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); }
524	public int drainTo(Collection<? super Runnable> c, int maxElements) {
525	return dq.drainTo(c, maxElements);
526	}
527
528	public int remainingCapacity() { return dq.remainingCapacity(); }
529	public boolean remove(Object x) { return dq.remove(x); }
530	public boolean contains(Object x) { return dq.contains(x); }
531	public int size() { return dq.size(); }
532	public boolean isEmpty() { return dq.isEmpty(); }
533	public Object[] toArray() { return dq.toArray(); }
534	public <T> T[] toArray(T[] array) { return dq.toArray(array); }
535	public Iterator<Runnable> iterator() {
536	return new Iterator<Runnable>() {
537	private Iterator<ScheduledFutureTask> it = dq.iterator();
538	public boolean hasNext() { return it.hasNext(); }
539	public Runnable next() { return it.next(); }
540	public void remove() { it.remove(); }
541	};
542	}
543	}
544	}