File	Doc	Category	Size	Date	Package
ThreadPoolExecutor.java	API Doc	Java SE 5 API	55011	Fri Aug 26 14:57:26 BST 2005	java.util.concurrent

ThreadPoolExecutor

• java.lang.Object
  • java.util.concurrent.AbstractExecutorService

class PausableThreadPoolExecutor extends ThreadPoolExecutor {
private boolean isPaused;
private ReentrantLock pauseLock = new ReentrantLock();
private Condition unpaused = pauseLock.newCondition();

public PausableThreadPoolExecutor(...) { super(...); }

protected void beforeExecute(Thread t, Runnable r) {
super.beforeExecute(t, r);
pauseLock.lock();
try {
while (isPaused) unpaused.await();
} catch(InterruptedException ie) {
t.interrupt();
} finally {
pauseLock.unlock();
}
}

public void pause() {
pauseLock.lock();
try {
isPaused = true;
} finally {
pauseLock.unlock();
}
}

public void resume() {
pauseLock.lock();
try {
isPaused = false;
unpaused.signalAll();
} finally {
pauseLock.unlock();
}
}
}

Fields Summary
private static final Runnable[]	EMPTY_RUNNABLE_ARRAY Only used to force toArray() to produce a Runnable[].
private static final RuntimePermission	shutdownPerm Permission for checking shutdown
private final BlockingQueue	workQueue Queue used for holding tasks and handing off to worker threads.
private final ReentrantLock	mainLock Lock held on updates to poolSize, corePoolSize, maximumPoolSize, and workers set.
private final Condition	termination Wait condition to support awaitTermination
private final HashSet	workers Set containing all worker threads in pool.
private volatile long	keepAliveTime Timeout in nanoseconds for idle threads waiting for work. Threads use this timeout only when there are more than corePoolSize present. Otherwise they wait forever for new work.
private volatile int	corePoolSize Core pool size, updated only while holding mainLock, but volatile to allow concurrent readability even during updates.
private volatile int	maximumPoolSize Maximum pool size, updated only while holding mainLock but volatile to allow concurrent readability even during updates.
private volatile int	poolSize Current pool size, updated only while holding mainLock but volatile to allow concurrent readability even during updates.
volatile int	runState Lifecycle state
static final int	RUNNING Normal, not-shutdown mode
static final int	SHUTDOWN Controlled shutdown mode
static final int	STOP Immediate shutdown mode
static final int	TERMINATED Final state
private volatile RejectedExecutionHandler	handler Handler called when saturated or shutdown in execute.
private volatile ThreadFactory	threadFactory Factory for new threads.
private int	largestPoolSize Tracks largest attained pool size.
private long	completedTaskCount Counter for completed tasks. Updated only on termination of worker threads.
private static final RejectedExecutionHandler	defaultHandler The default rejected execution handler

Constructors Summary
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue, RejectedExecutionHandler handler) Creates a new ThreadPoolExecutor with the given initial parameters. param corePoolSize the number of threads to keep in the pool, even if they are idle. param maximumPoolSize the maximum number of threads to allow in the pool. param keepAliveTime when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating. param unit the time unit for the keepAliveTime argument. param workQueue the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method. param handler the handler to use when execution is blocked because the thread bounds and queue capacities are reached. throws IllegalArgumentException if corePoolSize, or keepAliveTime less than zero, or if maximumPoolSize less than or equal to zero, or if corePoolSize greater than maximumPoolSize. throws NullPointerException if workQueue or handler are null. this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, Executors.defaultThreadFactory(), handler);
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) Creates a new ThreadPoolExecutor with the given initial parameters. param corePoolSize the number of threads to keep in the pool, even if they are idle. param maximumPoolSize the maximum number of threads to allow in the pool. param keepAliveTime when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating. param unit the time unit for the keepAliveTime argument. param workQueue the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method. 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, or keepAliveTime less than zero, or if maximumPoolSize less than or equal to zero, or if corePoolSize greater than maximumPoolSize. throws NullPointerException if workQueue or threadFactory or handler are null. if (corePoolSize < 0 || maximumPoolSize <= 0 || maximumPoolSize < corePoolSize || keepAliveTime < 0) throw new IllegalArgumentException(); if (workQueue == null || threadFactory == null || handler == null) throw new NullPointerException(); this.corePoolSize = corePoolSize; this.maximumPoolSize = maximumPoolSize; this.workQueue = workQueue; this.keepAliveTime = unit.toNanos(keepAliveTime); this.threadFactory = threadFactory; this.handler = handler;
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue) Creates a new ThreadPoolExecutor with the given initial parameters and default thread factory and handler. It may be more convenient to use one of the {@link Executors} factory methods instead of this general purpose constructor. param corePoolSize the number of threads to keep in the pool, even if they are idle. param maximumPoolSize the maximum number of threads to allow in the pool. param keepAliveTime when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating. param unit the time unit for the keepAliveTime argument. param workQueue the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method. throws IllegalArgumentException if corePoolSize, or keepAliveTime less than zero, or if maximumPoolSize less than or equal to zero, or if corePoolSize greater than maximumPoolSize. throws NullPointerException if workQueue is null this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, Executors.defaultThreadFactory(), defaultHandler);
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue, ThreadFactory threadFactory) Creates a new ThreadPoolExecutor with the given initial parameters. param corePoolSize the number of threads to keep in the pool, even if they are idle. param maximumPoolSize the maximum number of threads to allow in the pool. param keepAliveTime when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating. param unit the time unit for the keepAliveTime argument. param workQueue the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method. param threadFactory the factory to use when the executor creates a new thread. throws IllegalArgumentException if corePoolSize, or keepAliveTime less than zero, or if maximumPoolSize less than or equal to zero, or if corePoolSize greater than maximumPoolSize. throws NullPointerException if workQueue or threadFactory are null. this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, defaultHandler);

Methods Summary
private boolean	addIfUnderCorePoolSize(java.lang.Runnable firstTask) Create and start a new thread running firstTask as its first task, only if fewer than corePoolSize threads are running. param firstTask the task the new thread should run first (or null if none) return true if successful. Thread t = null; final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { if (poolSize < corePoolSize) t = addThread(firstTask); } finally { mainLock.unlock(); } if (t == null) return false; t.start(); return true;
private java.lang.Runnable	addIfUnderMaximumPoolSize(java.lang.Runnable firstTask) Create and start a new thread only if fewer than maximumPoolSize threads are running. The new thread runs as its first task the next task in queue, or if there is none, the given task. param firstTask the task the new thread should run first (or null if none) return null on failure, else the first task to be run by new thread. Thread t = null; Runnable next = null; final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { if (poolSize < maximumPoolSize) { next = workQueue.poll(); if (next == null) next = firstTask; t = addThread(next); } } finally { mainLock.unlock(); } if (t == null) return null; t.start(); return next;
private java.lang.Thread	addThread(java.lang.Runnable firstTask) Create and return a new thread running firstTask as its first task. Call only while holding mainLock param firstTask the task the new thread should run first (or null if none) return the new thread, or null if threadFactory fails to create thread Worker w = new Worker(firstTask); Thread t = threadFactory.newThread(w); if (t != null) { w.thread = t; workers.add(w); int nt = ++poolSize; if (nt > largestPoolSize) largestPoolSize = nt; } return t;
protected void	afterExecute(java.lang.Runnable r, java.lang.Throwable t) Method invoked upon completion of execution of the given Runnable. This method is invoked by the thread that executed the task. If non-null, the Throwable is the uncaught exception that caused execution to terminate abruptly. Note: To properly nest multiple overridings, subclasses should generally invoke super.afterExecute at the beginning of this method. param r the runnable that has completed. param t the exception that caused termination, or null if execution completed normally.
public boolean	awaitTermination(long timeout, java.util.concurrent.TimeUnit unit) long nanos = unit.toNanos(timeout); final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { for (;;) { if (runState == TERMINATED) return true; if (nanos <= 0) return false; nanos = termination.awaitNanos(nanos); } } finally { mainLock.unlock(); }
protected void	beforeExecute(java.lang.Thread t, java.lang.Runnable r) Method invoked prior to executing the given Runnable in the given thread. This method is invoked by thread t that will execute task r, and may be used to re-initialize ThreadLocals, or to perform logging. Note: To properly nest multiple overridings, subclasses should generally invoke super.beforeExecute at the end of this method. param t the thread that will run task r. param r the task that will be executed.
public void	execute(java.lang.Runnable command) Executes the given task sometime in the future. The task may execute in a new thread or in an existing pooled thread. If the task cannot be submitted for execution, either because this executor has been shutdown or because its capacity has been reached, the task is handled by the current RejectedExecutionHandler. param command the task to execute throws RejectedExecutionException at discretion of RejectedExecutionHandler, if task cannot be accepted for execution throws NullPointerException if command is null if (command == null) throw new NullPointerException(); for (;;) { if (runState != RUNNING) { reject(command); return; } if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) return; if (workQueue.offer(command)) return; Runnable r = addIfUnderMaximumPoolSize(command); if (r == command) return; if (r == null) { reject(command); return; } // else retry }
protected void	finalize() Invokes shutdown when this executor is no longer referenced. shutdown();
public int	getActiveCount() Returns the approximate number of threads that are actively executing tasks. return the number of threads final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { int n = 0; for (Worker w : workers) { if (w.isActive()) ++n; } return n; } finally { mainLock.unlock(); }
public long	getCompletedTaskCount() Returns the approximate total number of tasks that have completed execution. Because the states of tasks and threads may change dynamically during computation, the returned value is only an approximation, but one that does not ever decrease across successive calls. return the number of tasks final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { long n = completedTaskCount; for (Worker w : workers) n += w.completedTasks; return n; } finally { mainLock.unlock(); }
public int	getCorePoolSize() Returns the core number of threads. return the core number of threads see #setCorePoolSize return corePoolSize;
public long	getKeepAliveTime(java.util.concurrent.TimeUnit unit) Returns the thread keep-alive time, which is the amount of time which threads in excess of the core pool size may remain idle before being terminated. param unit the desired time unit of the result return the time limit see #setKeepAliveTime return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS);
public int	getLargestPoolSize() Returns the largest number of threads that have ever simultaneously been in the pool. return the number of threads final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { return largestPoolSize; } finally { mainLock.unlock(); }
public int	getMaximumPoolSize() Returns the maximum allowed number of threads. return the maximum allowed number of threads see #setMaximumPoolSize return maximumPoolSize;
public int	getPoolSize() Returns the current number of threads in the pool. return the number of threads return poolSize;
public java.util.concurrent.BlockingQueue	getQueue() Returns the task queue used by this executor. Access to the task queue is intended primarily for debugging and monitoring. This queue may be in active use. Retrieving the task queue does not prevent queued tasks from executing. return the task queue return workQueue;
public java.util.concurrent.RejectedExecutionHandler	getRejectedExecutionHandler() Returns the current handler for unexecutable tasks. return the current handler see #setRejectedExecutionHandler return handler;
java.lang.Runnable	getTask() Get the next task for a worker thread to run. return the task throws InterruptedException if interrupted while waiting for task for (;;) { switch(runState) { case RUNNING: { if (poolSize <= corePoolSize) // untimed wait if core return workQueue.take(); long timeout = keepAliveTime; if (timeout <= 0) // die immediately for 0 timeout return null; Runnable r = workQueue.poll(timeout, TimeUnit.NANOSECONDS); if (r != null) return r; if (poolSize > corePoolSize) // timed out return null; // else, after timeout, pool shrank so shouldn't die, so retry break; } case SHUTDOWN: { // Help drain queue Runnable r = workQueue.poll(); if (r != null) return r; // Check if can terminate if (workQueue.isEmpty()) { interruptIdleWorkers(); return null; } // There could still be delayed tasks in queue. // Wait for one, re-checking state upon interruption try { return workQueue.take(); } catch(InterruptedException ignore) {} break; } case STOP: return null; default: assert false; } }
public long	getTaskCount() Returns the approximate total number of tasks that have been scheduled for execution. Because the states of tasks and threads may change dynamically during computation, the returned value is only an approximation, but one that does not ever decrease across successive calls. return the number of tasks final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { long n = completedTaskCount; for (Worker w : workers) { n += w.completedTasks; if (w.isActive()) ++n; } return n + workQueue.size(); } finally { mainLock.unlock(); }
public java.util.concurrent.ThreadFactory	getThreadFactory() Returns the thread factory used to create new threads. return the current thread factory see #setThreadFactory return threadFactory;
void	interruptIdleWorkers() Wake up all threads that might be waiting for tasks. final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { for (Worker w : workers) w.interruptIfIdle(); } finally { mainLock.unlock(); }
public boolean	isShutdown() return runState != RUNNING;
public boolean	isTerminated() return runState == TERMINATED;
public boolean	isTerminating() Returns true if this executor is in the process of terminating after shutdown or shutdownNow but has not completely terminated. This method may be useful for debugging. A return of true reported a sufficient period after shutdown may indicate that submitted tasks have ignored or suppressed interruption, causing this executor not to properly terminate. return true if terminating but not yet terminated. return runState == STOP;
public int	prestartAllCoreThreads() Starts all core threads, causing them to idly wait for work. This overrides the default policy of starting core threads only when new tasks are executed. return the number of threads started. int n = 0; while (addIfUnderCorePoolSize(null)) ++n; return n;
public boolean	prestartCoreThread() Starts a core thread, causing it to idly wait for work. This overrides the default policy of starting core threads only when new tasks are executed. This method will return false if all core threads have already been started. return true if a thread was started return addIfUnderCorePoolSize(null);
public void	purge() Tries to remove from the work queue all {@link Future} tasks that have been cancelled. This method can be useful as a storage reclamation operation, that has no other impact on functionality. Cancelled tasks are never executed, but may accumulate in work queues until worker threads can actively remove them. Invoking this method instead tries to remove them now. However, this method may fail to remove tasks in the presence of interference by other threads. // Fail if we encounter interference during traversal try { Iterator<Runnable> it = getQueue().iterator(); while (it.hasNext()) { Runnable r = it.next(); if (r instanceof Future<?>) { Future<?> c = (Future<?>)r; if (c.isCancelled()) it.remove(); } } } catch(ConcurrentModificationException ex) { return; }
void	reject(java.lang.Runnable command) Invoke the rejected execution handler for the given command. handler.rejectedExecution(command, this);
public boolean	remove(java.lang.Runnable task) Removes this task from the executor's internal queue if it is present, thus causing it not to be run if it has not already started. This method may be useful as one part of a cancellation scheme. It may fail to remove tasks that have been converted into other forms before being placed on the internal queue. For example, a task entered using submit might be converted into a form that maintains Future status. However, in such cases, method {@link ThreadPoolExecutor#purge} may be used to remove those Futures that have been cancelled. param task the task to remove return true if the task was removed return getQueue().remove(task);
public void	setCorePoolSize(int corePoolSize) Sets the core number of threads. This overrides any value set in the constructor. If the new value is smaller than the current value, excess existing threads will be terminated when they next become idle. If larger, new threads will, if needed, be started to execute any queued tasks. param corePoolSize the new core size throws IllegalArgumentException if corePoolSize less than zero see #getCorePoolSize if (corePoolSize < 0) throw new IllegalArgumentException(); final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { int extra = this.corePoolSize - corePoolSize; this.corePoolSize = corePoolSize; if (extra < 0) { int n = workQueue.size(); // We have to create initially-idle threads here // because we otherwise have no recourse about // what to do with a dequeued task if addThread fails. while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize ) { Thread t = addThread(null); if (t != null) t.start(); else break; } } else if (extra > 0 && poolSize > corePoolSize) { Iterator<Worker> it = workers.iterator(); while (it.hasNext() && extra-- > 0 && poolSize > corePoolSize && workQueue.remainingCapacity() == 0) it.next().interruptIfIdle(); } } finally { mainLock.unlock(); }
public void	setKeepAliveTime(long time, java.util.concurrent.TimeUnit unit) Sets the time limit for which threads may remain idle before being terminated. If there are more than the core number of threads currently in the pool, after waiting this amount of time without processing a task, excess threads will be terminated. This overrides any value set in the constructor. param time the time to wait. A time value of zero will cause excess threads to terminate immediately after executing tasks. param unit the time unit of the time argument throws IllegalArgumentException if time less than zero see #getKeepAliveTime if (time < 0) throw new IllegalArgumentException(); this.keepAliveTime = unit.toNanos(time);
public void	setMaximumPoolSize(int maximumPoolSize) Sets the maximum allowed number of threads. This overrides any value set in the constructor. If the new value is smaller than the current value, excess existing threads will be terminated when they next become idle. param maximumPoolSize the new maximum throws IllegalArgumentException if maximumPoolSize less than zero or the {@link #getCorePoolSize core pool size} see #getMaximumPoolSize if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) throw new IllegalArgumentException(); final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { int extra = this.maximumPoolSize - maximumPoolSize; this.maximumPoolSize = maximumPoolSize; if (extra > 0 && poolSize > maximumPoolSize) { Iterator<Worker> it = workers.iterator(); while (it.hasNext() && extra > 0 && poolSize > maximumPoolSize) { it.next().interruptIfIdle(); --extra; } } } finally { mainLock.unlock(); }
public void	setRejectedExecutionHandler(java.util.concurrent.RejectedExecutionHandler handler) Sets a new handler for unexecutable tasks. param handler the new handler throws NullPointerException if handler is null see #getRejectedExecutionHandler if (handler == null) throw new NullPointerException(); this.handler = handler;
public void	setThreadFactory(java.util.concurrent.ThreadFactory threadFactory) Sets the thread factory used to create new threads. param threadFactory the new thread factory throws NullPointerException if threadFactory is null see #getThreadFactory if (threadFactory == null) throw new NullPointerException(); this.threadFactory = threadFactory;
public void	shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down. throws SecurityException if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold {@link java.lang.RuntimePermission}("modifyThread"), or the security manager's checkAccess method denies access. // Fail if caller doesn't have modifyThread permission. We // explicitly check permissions directly because we can't trust // implementations of SecurityManager to correctly override // the "check access" methods such that our documented // security policy is implemented. SecurityManager security = System.getSecurityManager(); if (security != null) java.security.AccessController.checkPermission(shutdownPerm); boolean fullyTerminated = false; final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { if (workers.size() > 0) { // Check if caller can modify worker threads. This // might not be true even if passed above check, if // the SecurityManager treats some threads specially. if (security != null) { for (Worker w: workers) security.checkAccess(w.thread); } int state = runState; if (state == RUNNING) // don't override shutdownNow runState = SHUTDOWN; try { for (Worker w: workers) w.interruptIfIdle(); } catch(SecurityException se) { // If SecurityManager allows above checks, but // then unexpectedly throws exception when // interrupting threads (which it ought not do), // back out as cleanly as we can. Some threads may // have been killed but we remain in non-shutdown // state. runState = state; throw se; } } else { // If no workers, trigger full termination now fullyTerminated = true; runState = TERMINATED; termination.signalAll(); } } finally { mainLock.unlock(); } if (fullyTerminated) terminated();
public java.util.List	shutdownNow() Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. This implementation cancels tasks 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 throws SecurityException if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold {@link java.lang.RuntimePermission}("modifyThread"), or the security manager's checkAccess method denies access. // Almost the same code as shutdown() SecurityManager security = System.getSecurityManager(); if (security != null) java.security.AccessController.checkPermission(shutdownPerm); boolean fullyTerminated = false; final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { if (workers.size() > 0) { if (security != null) { for (Worker w: workers) security.checkAccess(w.thread); } int state = runState; if (state != TERMINATED) runState = STOP; try { for (Worker w : workers) w.interruptNow(); } catch(SecurityException se) { runState = state; // back out; throw se; } } else { // If no workers, trigger full termination now fullyTerminated = true; runState = TERMINATED; termination.signalAll(); } } finally { mainLock.unlock(); } if (fullyTerminated) terminated(); return Arrays.asList(workQueue.toArray(EMPTY_RUNNABLE_ARRAY));
protected void	terminated() Method invoked when the Executor has terminated. Default implementation does nothing. Note: To properly nest multiple overridings, subclasses should generally invoke super.terminated within this method.
void	workerDone(java.util.concurrent.ThreadPoolExecutor$Worker w) Perform bookkeeping for a terminated worker thread. param w the worker final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { completedTaskCount += w.completedTasks; workers.remove(w); if (--poolSize > 0) return; // Else, this is the last thread. Deal with potential shutdown. int state = runState; assert state != TERMINATED; if (state != STOP) { // If there are queued tasks but no threads, create // replacement thread. We must create it initially // idle to avoid orphaned tasks in case addThread // fails. This also handles case of delayed tasks // that will sometime later become runnable. if (!workQueue.isEmpty()) { Thread t = addThread(null); if (t != null) t.start(); return; } // Otherwise, we can exit without replacement if (state == RUNNING) return; } // Either state is STOP, or state is SHUTDOWN and there is // no work to do. So we can terminate. termination.signalAll(); runState = TERMINATED; // fall through to call terminate() outside of lock. } finally { mainLock.unlock(); } assert runState == TERMINATED; terminated();