/* * 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. * *

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 scheduled for exactly the same * execution time are enabled in first-in-first-out (FIFO) order of * submission. * *

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 * corePoolSize threads and an unbounded queue, adjustments * to maximumPoolSize have no useful effect. * *

Extension notes: This class overrides {@link * AbstractExecutorService} submit methods to generate * internal objects to control per-task delays and scheduling. To * preserve functionality, any further overrides of these methods in * subclasses must invoke superclass versions, which effectively * disables additional task customization. However, this class * provides alternative protected extension method * decorateTask (one version each for Runnable and * Callable) that can be used to customize the concrete task * types used to execute commands entered via execute, * submit, schedule, scheduleAtFixedRate, * and scheduleWithFixedDelay. By default, a * ScheduledThreadPoolExecutor uses a task type extending * {@link FutureTask}. However, this may be modified or replaced using * subclasses of the form: * *

 * public class CustomScheduledExecutor extends ScheduledThreadPoolExecutor {
 *
 *   static class CustomTask<V> implements RunnableScheduledFuture<V> { ... }
 *
 *   protected <V> RunnableScheduledFuture<V> decorateTask(
 *                Runnable r, RunnableScheduledFuture<V> task) {
 *       return new CustomTask<V>(r, task);
 *   }
 *
 *   protected <V> RunnableScheduledFuture<V> decorateTask(
 *                Callable<V> c, RunnableScheduledFuture<V> task) {
 *       return new CustomTask<V>(c, task);
 *   }
 *   // ... add constructors, etc.
 * }
 * 
* @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(); /** * Returns nanosecond time offset by origin */ final long now() { return System.nanoTime() - NANO_ORIGIN; } private class ScheduledFutureTask extends FutureTask implements RunnableScheduledFuture { /** 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 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(Delayed other) { if (other == this) // compare zero ONLY if same object return 0; if (other instanceof ScheduledFutureTask) { 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; } long d = (getDelay(TimeUnit.NANOSECONDS) - other.getDelay(TimeUnit.NANOSECONDS)); return (d == 0)? 0 : ((d < 0)? -1 : 1); } /** * Returns true if this is a periodic (not a one-shot) action. * * @return true if periodic */ public boolean isPeriodic() { return period != 0; } /** * Runs 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; // Classpath local: ecj from eclipse 3.1 does not // compile this. // ScheduledThreadPoolExecutor.super.getQueue().add(this); ScheduledThreadPoolExecutor.super.getQueue().add((Runnable) 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); } /** * Cancels and clears 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 RunnableScheduledFuture) { RunnableScheduledFuture t = (RunnableScheduledFuture)e; if (t.isPeriodic()? !keepPeriodic : !keepDelayed) t.cancel(false); } } entries = null; purge(); } } public boolean remove(Runnable task) { if (!(task instanceof RunnableScheduledFuture)) return false; return getQueue().remove(task); } /** * Modifies or replaces the task used to execute a runnable. * This method can be used to override the concrete * class used for managing internal tasks. * The default implementation simply returns the given task. * * @param runnable the submitted Runnable * @param task the task created to execute the runnable * @return a task that can execute the runnable * @since 1.6 */ protected RunnableScheduledFuture decorateTask( Runnable runnable, RunnableScheduledFuture task) { return task; } /** * Modifies or replaces the task used to execute a callable. * This method can be used to override the concrete * class used for managing internal tasks. * The default implementation simply returns the given task. * * @param callable the submitted Callable * @param task the task created to execute the callable * @return a task that can execute the callable * @since 1.6 */ protected RunnableScheduledFuture decorateTask( Callable callable, RunnableScheduledFuture task) { return task; } /** * 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 < 0 */ 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 IllegalArgumentException if corePoolSize < 0 * @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 IllegalArgumentException if corePoolSize < 0 * @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 IllegalArgumentException if corePoolSize < 0 * @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); RunnableScheduledFuture t = decorateTask(command, new ScheduledFutureTask(command, null, triggerTime)); delayedExecute(t); return t; } public ScheduledFuture schedule(Callable callable, long delay, TimeUnit unit) { if (callable == null || unit == null) throw new NullPointerException(); if (delay < 0) delay = 0; long triggerTime = now() + unit.toNanos(delay); RunnableScheduledFuture t = decorateTask(callable, new ScheduledFutureTask(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); RunnableScheduledFuture t = decorateTask(command, new ScheduledFutureTask(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); RunnableScheduledFuture t = decorateTask(command, new ScheduledFutureTask(command, null, triggerTime, unit.toNanos(-delay))); delayedExecute(t); return t; } /** * Executes command with zero required delay. This has effect * equivalent to schedule(command, 0, anyUnit). Note * that inspections of the queue and of the list returned by * shutdownNow will access the zero-delayed * {@link ScheduledFuture}, not the command itself. * * @param command the task to execute * @throws RejectedExecutionException at discretion of * RejectedExecutionHandler, 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 Future submit(Runnable task, T result) { return schedule(Executors.callable(task, result), 0, TimeUnit.NANOSECONDS); } public Future submit(Callable task) { return schedule(task, 0, TimeUnit.NANOSECONDS); } /** * Sets the policy on whether to continue executing existing periodic * tasks even when this executor has been shutdown. In * this case, these tasks will only terminate upon * shutdownNow, or after setting the policy to * false when already shutdown. This value is by default * false. * * @param value if true, continue after shutdown, else don't. * @see #getContinueExistingPeriodicTasksAfterShutdownPolicy */ public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) { continueExistingPeriodicTasksAfterShutdown = value; if (!value && isShutdown()) cancelUnwantedTasks(); } /** * Gets the policy on whether to continue executing existing * periodic tasks even when this executor has been * shutdown. In this case, these tasks will only * terminate upon shutdownNow or after setting the policy * to false when already shutdown. This value is by * default false. * * @return true if will continue after shutdown * @see #setContinueExistingPeriodicTasksAfterShutdownPolicy */ public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() { return continueExistingPeriodicTasksAfterShutdown; } /** * Sets the policy on whether to execute existing delayed * tasks even when this executor has been shutdown. In * this case, these tasks will only terminate upon * shutdownNow, or after setting the policy to * false 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(); } /** * Gets the policy on whether to execute existing delayed * tasks even when this executor has been shutdown. In * this case, these tasks will only terminate upon * shutdownNow, or after setting the policy to * false 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 * ExecuteExistingDelayedTasksAfterShutdownPolicy has * been set false, existing delayed tasks whose delays * have not yet elapsed are cancelled. And unless the * ContinueExistingPeriodicTasksAfterShutdownPolicy has * been set true, 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. * *

There are no guarantees beyond best-effort attempts to stop * processing actively executing tasks. This implementation * cancels tasks via {@link Thread#interrupt}, so any task that * fails to respond to interrupts 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 execute, which * are for scheduling purposes used as the basis of a zero-delay * ScheduledFuture. * @throws SecurityException {@inheritDoc} */ public List 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 execute which are for scheduling * purposes used as the basis of a zero-delay * ScheduledFuture. Iteration over this queue is * not guaranteed to traverse tasks in the order in * which they will execute. * * @return the task queue */ public BlockingQueue getQueue() { return super.getQueue(); } /** * An annoying wrapper class to convince javac to use a * DelayQueue as a BlockingQueue */ private static class DelayedWorkQueue extends AbstractCollection implements BlockingQueue { private final DelayQueue dq = new DelayQueue(); 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((RunnableScheduledFuture)x); } public boolean offer(Runnable x) { return dq.offer((RunnableScheduledFuture)x); } public void put(Runnable x) { dq.put((RunnableScheduledFuture)x); } public boolean offer(Runnable x, long timeout, TimeUnit unit) { return dq.offer((RunnableScheduledFuture)x, timeout, unit); } public Runnable remove() { return dq.remove(); } public Runnable element() { return dq.element(); } public void clear() { dq.clear(); } public int drainTo(Collection c) { return dq.drainTo(c); } public int drainTo(Collection 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[] toArray(T[] array) { return dq.toArray(array); } public Iterator iterator() { return new Iterator() { private Iterator it = dq.iterator(); public boolean hasNext() { return it.hasNext(); } public Runnable next() { return it.next(); } public void remove() { it.remove(); } }; } } }