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Diffstat (limited to 'external/jsr166/java/util/concurrent/ThreadPoolExecutor.java')
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diff --git a/external/jsr166/java/util/concurrent/ThreadPoolExecutor.java b/external/jsr166/java/util/concurrent/ThreadPoolExecutor.java new file mode 100644 index 000000000..ea89a2c08 --- /dev/null +++ b/external/jsr166/java/util/concurrent/ThreadPoolExecutor.java @@ -0,0 +1,1605 @@ +/* + * 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.locks.*; +import java.util.*; + +/** + * An {@link ExecutorService} that executes each submitted task using + * one of possibly several pooled threads, normally configured + * using {@link Executors} factory methods. + * + * <p>Thread pools address two different problems: they usually + * provide improved performance when executing large numbers of + * asynchronous tasks, due to reduced per-task invocation overhead, + * and they provide a means of bounding and managing the resources, + * including threads, consumed when executing a collection of tasks. + * Each <tt>ThreadPoolExecutor</tt> also maintains some basic + * statistics, such as the number of completed tasks. + * + * <p>To be useful across a wide range of contexts, this class + * provides many adjustable parameters and extensibility + * hooks. However, programmers are urged to use the more convenient + * {@link Executors} factory methods {@link + * Executors#newCachedThreadPool} (unbounded thread pool, with + * automatic thread reclamation), {@link Executors#newFixedThreadPool} + * (fixed size thread pool) and {@link + * Executors#newSingleThreadExecutor} (single background thread), that + * preconfigure settings for the most common usage + * scenarios. Otherwise, use the following guide when manually + * configuring and tuning this class: + * + * <dl> + * + * <dt>Core and maximum pool sizes</dt> + * + * <dd>A <tt>ThreadPoolExecutor</tt> will automatically adjust the + * pool size + * (see {@link ThreadPoolExecutor#getPoolSize}) + * according to the bounds set by corePoolSize + * (see {@link ThreadPoolExecutor#getCorePoolSize}) + * and + * maximumPoolSize + * (see {@link ThreadPoolExecutor#getMaximumPoolSize}). + * When a new task is submitted in method {@link + * ThreadPoolExecutor#execute}, and fewer than corePoolSize threads + * are running, a new thread is created to handle the request, even if + * other worker threads are idle. If there are more than + * corePoolSize but less than maximumPoolSize threads running, a new + * thread will be created only if the queue is full. By setting + * corePoolSize and maximumPoolSize the same, you create a fixed-size + * thread pool. By setting maximumPoolSize to an essentially unbounded + * value such as <tt>Integer.MAX_VALUE</tt>, you allow the pool to + * accommodate an arbitrary number of concurrent tasks. Most typically, + * core and maximum pool sizes are set only upon construction, but they + * may also be changed dynamically using {@link + * ThreadPoolExecutor#setCorePoolSize} and {@link + * ThreadPoolExecutor#setMaximumPoolSize}. <dd> + * + * <dt> On-demand construction + * + * <dd> By default, even core threads are initially created and + * started only when new tasks arrive, but this can be overridden + * dynamically using method {@link + * ThreadPoolExecutor#prestartCoreThread} or + * {@link ThreadPoolExecutor#prestartAllCoreThreads}. + * You probably want to prestart threads if you construct the + * pool with a non-empty queue. </dd> + * + * <dt>Creating new threads</dt> + * + * <dd>New threads are created using a {@link + * java.util.concurrent.ThreadFactory}. If not otherwise specified, a + * {@link Executors#defaultThreadFactory} is used, that creates threads to all + * be in the same {@link ThreadGroup} and with the same + * <tt>NORM_PRIORITY</tt> priority and non-daemon status. By supplying + * a different ThreadFactory, you can alter the thread's name, thread + * group, priority, daemon status, etc. If a <tt>ThreadFactory</tt> fails to create + * a thread when asked by returning null from <tt>newThread</tt>, + * the executor will continue, but might + * not be able to execute any tasks. </dd> + * + * <dt>Keep-alive times</dt> + * + * <dd>If the pool currently has more than corePoolSize threads, + * excess threads will be terminated if they have been idle for more + * than the keepAliveTime (see {@link + * ThreadPoolExecutor#getKeepAliveTime}). This provides a means of + * reducing resource consumption when the pool is not being actively + * used. If the pool becomes more active later, new threads will be + * constructed. This parameter can also be changed dynamically using + * method {@link ThreadPoolExecutor#setKeepAliveTime}. Using a value + * of <tt>Long.MAX_VALUE</tt> {@link TimeUnit#NANOSECONDS} effectively + * disables idle threads from ever terminating prior to shut down. By + * default, the keep-alive policy applies only when there are more + * than corePoolSizeThreads. But method {@link + * ThreadPoolExecutor#allowCoreThreadTimeOut} can be used to apply + * this time-out policy to core threads as well, so long as + * the keepAliveTime value is non-zero. </dd> + * + * <dt>Queuing</dt> + * + * <dd>Any {@link BlockingQueue} may be used to transfer and hold + * submitted tasks. The use of this queue interacts with pool sizing: + * + * <ul> + * + * <li> If fewer than corePoolSize threads are running, the Executor + * always prefers adding a new thread + * rather than queuing.</li> + * + * <li> If corePoolSize or more threads are running, the Executor + * always prefers queuing a request rather than adding a new + * thread.</li> + * + * <li> If a request cannot be queued, a new thread is created unless + * this would exceed maximumPoolSize, in which case, the task will be + * rejected.</li> + * + * </ul> + * + * There are three general strategies for queuing: + * <ol> + * + * <li> <em> Direct handoffs.</em> A good default choice for a work + * queue is a {@link SynchronousQueue} that hands off tasks to threads + * without otherwise holding them. Here, an attempt to queue a task + * will fail if no threads are immediately available to run it, so a + * new thread will be constructed. This policy avoids lockups when + * handling sets of requests that might have internal dependencies. + * Direct handoffs generally require unbounded maximumPoolSizes to + * avoid rejection of new submitted tasks. This in turn admits the + * possibility of unbounded thread growth when commands continue to + * arrive on average faster than they can be processed. </li> + * + * <li><em> Unbounded queues.</em> Using an unbounded queue (for + * example a {@link LinkedBlockingQueue} without a predefined + * capacity) will cause new tasks to wait in the queue when all + * corePoolSize threads are busy. Thus, no more than corePoolSize + * threads will ever be created. (And the value of the maximumPoolSize + * therefore doesn't have any effect.) This may be appropriate when + * each task is completely independent of others, so tasks cannot + * affect each others execution; for example, in a web page server. + * While this style of queuing can be useful in smoothing out + * transient bursts of requests, it admits the possibility of + * unbounded work queue growth when commands continue to arrive on + * average faster than they can be processed. </li> + * + * <li><em>Bounded queues.</em> A bounded queue (for example, an + * {@link ArrayBlockingQueue}) helps prevent resource exhaustion when + * used with finite maximumPoolSizes, but can be more difficult to + * tune and control. Queue sizes and maximum pool sizes may be traded + * off for each other: Using large queues and small pools minimizes + * CPU usage, OS resources, and context-switching overhead, but can + * lead to artificially low throughput. If tasks frequently block (for + * example if they are I/O bound), a system may be able to schedule + * time for more threads than you otherwise allow. Use of small queues + * generally requires larger pool sizes, which keeps CPUs busier but + * may encounter unacceptable scheduling overhead, which also + * decreases throughput. </li> + * + * </ol> + * + * </dd> + * + * <dt>Rejected tasks</dt> + * + * <dd> New tasks submitted in method {@link + * ThreadPoolExecutor#execute} will be <em>rejected</em> when the + * Executor has been shut down, and also when the Executor uses finite + * bounds for both maximum threads and work queue capacity, and is + * saturated. In either case, the <tt>execute</tt> method invokes the + * {@link RejectedExecutionHandler#rejectedExecution} method of its + * {@link RejectedExecutionHandler}. Four predefined handler policies + * are provided: + * + * <ol> + * + * <li> In the + * default {@link ThreadPoolExecutor.AbortPolicy}, the handler throws a + * runtime {@link RejectedExecutionException} upon rejection. </li> + * + * <li> In {@link + * ThreadPoolExecutor.CallerRunsPolicy}, the thread that invokes + * <tt>execute</tt> itself runs the task. This provides a simple + * feedback control mechanism that will slow down the rate that new + * tasks are submitted. </li> + * + * <li> In {@link ThreadPoolExecutor.DiscardPolicy}, + * a task that cannot be executed is simply dropped. </li> + * + * <li>In {@link + * ThreadPoolExecutor.DiscardOldestPolicy}, if the executor is not + * shut down, the task at the head of the work queue is dropped, and + * then execution is retried (which can fail again, causing this to be + * repeated.) </li> + * + * </ol> + * + * It is possible to define and use other kinds of {@link + * RejectedExecutionHandler} classes. Doing so requires some care + * especially when policies are designed to work only under particular + * capacity or queuing policies. </dd> + * + * <dt>Hook methods</dt> + * + * <dd>This class provides <tt>protected</tt> overridable {@link + * ThreadPoolExecutor#beforeExecute} and {@link + * ThreadPoolExecutor#afterExecute} methods that are called before and + * after execution of each task. These can be used to manipulate the + * execution environment; for example, reinitializing ThreadLocals, + * gathering statistics, or adding log entries. Additionally, method + * {@link ThreadPoolExecutor#terminated} can be overridden to perform + * any special processing that needs to be done once the Executor has + * fully terminated. + * + * <p>If hook or callback methods throw + * exceptions, internal worker threads may in turn fail and + * abruptly terminate.</dd> + * + * <dt>Queue maintenance</dt> + * + * <dd> Method {@link ThreadPoolExecutor#getQueue} allows access to + * the work queue for purposes of monitoring and debugging. Use of + * this method for any other purpose is strongly discouraged. Two + * supplied methods, {@link ThreadPoolExecutor#remove} and {@link + * ThreadPoolExecutor#purge} are available to assist in storage + * reclamation when large numbers of queued tasks become + * cancelled.</dd> + * + * <dt>Finalization</dt> + * + * <dd> A pool that is no longer referenced in a program <em>AND</em> + * has no remaining threads will be <tt>shutdown</tt> + * automatically. If you would like to ensure that unreferenced pools + * are reclaimed even if users forget to call {@link + * ThreadPoolExecutor#shutdown}, then you must arrange that unused + * threads eventually die, by setting appropriate keep-alive times, + * using a lower bound of zero core threads and/or setting {@link + * ThreadPoolExecutor#allowCoreThreadTimeOut}. </dd> </dl> + * + * <p> <b>Extension example</b>. Most extensions of this class + * override one or more of the protected hook methods. For example, + * here is a subclass that adds a simple pause/resume feature: + * + * <pre> + * 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(); + * } + * } + * } + * </pre> + * @since 1.5 + * @author Doug Lea + */ +public class ThreadPoolExecutor extends AbstractExecutorService { + /** + * Only used to force toArray() to produce a Runnable[]. + */ + private static final Runnable[] EMPTY_RUNNABLE_ARRAY = new Runnable[0]; + + /** + * Permission for checking shutdown + */ + private static final RuntimePermission shutdownPerm = + new RuntimePermission("modifyThread"); + + /** + * Queue used for holding tasks and handing off to worker threads. + */ + private final BlockingQueue<Runnable> workQueue; + + /** + * Lock held on updates to poolSize, corePoolSize, maximumPoolSize, and + * workers set. + */ + private final ReentrantLock mainLock = new ReentrantLock(); + + /** + * Wait condition to support awaitTermination + */ + private final Condition termination = mainLock.newCondition(); + + /** + * Set containing all worker threads in pool. + */ + private final HashSet<Worker> workers = new HashSet<Worker>(); + + /** + * 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 long keepAliveTime; + + /** + * If false (default) core threads stay alive even when idle. + * If true, core threads use keepAliveTime to time out waiting for work. + */ + private volatile boolean allowCoreThreadTimeOut; + + /** + * Core pool size, updated only while holding mainLock, + * but volatile to allow concurrent readability even + * during updates. + */ + private volatile int corePoolSize; + + /** + * Maximum pool size, updated only while holding mainLock + * but volatile to allow concurrent readability even + * during updates. + */ + private volatile int maximumPoolSize; + + /** + * Current pool size, updated only while holding mainLock + * but volatile to allow concurrent readability even + * during updates. + */ + private volatile int poolSize; + + /** + * Lifecycle state + */ + volatile int runState; + + // Special values for runState + /** Normal, not-shutdown mode */ + static final int RUNNING = 0; + /** Controlled shutdown mode */ + static final int SHUTDOWN = 1; + /** Immediate shutdown mode */ + static final int STOP = 2; + /** Final state */ + static final int TERMINATED = 3; + + /** + * Handler called when saturated or shutdown in execute. + */ + private volatile RejectedExecutionHandler handler; + + /** + * Factory for new threads. + */ + private volatile ThreadFactory threadFactory; + + /** + * Tracks largest attained pool size. + */ + private int largestPoolSize; + + /** + * Counter for completed tasks. Updated only on termination of + * worker threads. + */ + private long completedTaskCount; + + /** + * The default rejected execution handler + */ + private static final RejectedExecutionHandler defaultHandler = + new AbortPolicy(); + + /** + * Invokes the rejected execution handler for the given command. + */ + void reject(Runnable command) { + handler.rejectedExecution(command, this); + } + + /** + * Creates and returns 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 + */ + private Thread addThread(Runnable firstTask) { + if (runState == TERMINATED) // Don't create thread if terminated + return null; + 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; + } + + /** + * Creates and starts 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. + */ + private boolean addIfUnderCorePoolSize(Runnable firstTask) { + 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; + } + + /** + * Creates and starts 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 0 if a new thread cannot be created, a positive number + * if firstTask will be run in a new thread, or a negative number + * if a new thread was created but is running some other task, in + * which case the caller must try some other way to run firstTask + * (perhaps by calling this method again). + */ + private int addIfUnderMaximumPoolSize(Runnable firstTask) { + Thread t = null; + int status = 0; + final ReentrantLock mainLock = this.mainLock; + mainLock.lock(); + try { + if (poolSize < maximumPoolSize) { + Runnable next = workQueue.poll(); + if (next == null) { + next = firstTask; + status = 1; + } else + status = -1; + t = addThread(next); + } + } finally { + mainLock.unlock(); + } + if (t == null) + return 0; + t.start(); + return status; + } + + + /** + * Gets the next task for a worker thread to run. + * @return the task + */ + Runnable getTask() { + for (;;) { + try { + switch (runState) { + case RUNNING: { + // untimed wait if core and not allowing core timeout + if (poolSize <= corePoolSize && !allowCoreThreadTimeOut) + 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 || allowCoreThreadTimeOut) + return null; // timed out + // Else, after timeout, the pool shrank. 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; + } + + // Else there could still be delayed tasks in queue. + return workQueue.take(); + } + + case STOP: + return null; + default: + assert false; + } + } catch (InterruptedException ie) { + // On interruption, re-check runstate + } + } + } + + /** + * Wakes up all threads that might be waiting for tasks. + */ + void interruptIdleWorkers() { + final ReentrantLock mainLock = this.mainLock; + mainLock.lock(); + try { + for (Worker w : workers) + w.interruptIfIdle(); + } finally { + mainLock.unlock(); + } + } + + /** + * Performs bookkeeping for a terminated worker thread. + * @param w the worker + */ + void workerDone(Worker w) { + 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(); + } + + /** + * Worker threads + */ + private class Worker implements Runnable { + + /** + * The runLock is acquired and released surrounding each task + * execution. It mainly protects against interrupts that are + * intended to cancel the worker thread from instead + * interrupting the task being run. + */ + private final ReentrantLock runLock = new ReentrantLock(); + + /** + * Initial task to run before entering run loop + */ + private Runnable firstTask; + + /** + * Per thread completed task counter; accumulated + * into completedTaskCount upon termination. + */ + volatile long completedTasks; + + /** + * Thread this worker is running in. Acts as a final field, + * but cannot be set until thread is created. + */ + Thread thread; + + Worker(Runnable firstTask) { + this.firstTask = firstTask; + } + + boolean isActive() { + return runLock.isLocked(); + } + + /** + * Interrupts thread if not running a task. + */ + void interruptIfIdle() { + final ReentrantLock runLock = this.runLock; + if (runLock.tryLock()) { + try { + thread.interrupt(); + } finally { + runLock.unlock(); + } + } + } + + /** + * Interrupts thread even if running a task. + */ + void interruptNow() { + thread.interrupt(); + } + + /** + * Runs a single task between before/after methods. + */ + private void runTask(Runnable task) { + final ReentrantLock runLock = this.runLock; + runLock.lock(); + try { + // If not shutting down then clear an outstanding interrupt. + if (runState != STOP && + Thread.interrupted() && + runState == STOP) // Re-interrupt if stopped after clearing + thread.interrupt(); + boolean ran = false; + beforeExecute(thread, task); + try { + task.run(); + ran = true; + afterExecute(task, null); + ++completedTasks; + } catch (RuntimeException ex) { + if (!ran) + afterExecute(task, ex); + // Else the exception occurred within + // afterExecute itself in which case we don't + // want to call it again. + throw ex; + } + } finally { + runLock.unlock(); + } + } + + /** + * Main run loop + */ + public void run() { + try { + Runnable task = firstTask; + firstTask = null; + while (task != null || (task = getTask()) != null) { + runTask(task); + task = null; // unnecessary but can help GC + } + } finally { + workerDone(this); + } + } + } + + // Public methods + + /** + * Creates a new <tt>ThreadPoolExecutor</tt> with the given initial + * parameters and default thread factory and rejected execution 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 <tt>Runnable</tt> + * tasks submitted by the <tt>execute</tt> 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 <tt>workQueue</tt> is null + */ + public ThreadPoolExecutor(int corePoolSize, + int maximumPoolSize, + long keepAliveTime, + TimeUnit unit, + BlockingQueue<Runnable> workQueue) { + this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, + Executors.defaultThreadFactory(), defaultHandler); + } + + /** + * Creates a new <tt>ThreadPoolExecutor</tt> with the given initial + * parameters and default rejected execution handler. + * + * @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 <tt>Runnable</tt> + * tasks submitted by the <tt>execute</tt> 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 <tt>workQueue</tt> + * or <tt>threadFactory</tt> are null. + */ + public ThreadPoolExecutor(int corePoolSize, + int maximumPoolSize, + long keepAliveTime, + TimeUnit unit, + BlockingQueue<Runnable> workQueue, + ThreadFactory threadFactory) { + this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, + threadFactory, defaultHandler); + } + + /** + * Creates a new <tt>ThreadPoolExecutor</tt> with the given initial + * parameters and default thread factory. + * + * @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 <tt>Runnable</tt> + * tasks submitted by the <tt>execute</tt> 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 <tt>workQueue</tt> + * or <tt>handler</tt> are null. + */ + public ThreadPoolExecutor(int corePoolSize, + int maximumPoolSize, + long keepAliveTime, + TimeUnit unit, + BlockingQueue<Runnable> workQueue, + RejectedExecutionHandler handler) { + this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, + Executors.defaultThreadFactory(), handler); + } + + /** + * Creates a new <tt>ThreadPoolExecutor</tt> 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 <tt>Runnable</tt> + * tasks submitted by the <tt>execute</tt> 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 <tt>workQueue</tt> + * or <tt>threadFactory</tt> or <tt>handler</tt> are null. + */ + public ThreadPoolExecutor(int corePoolSize, + int maximumPoolSize, + long keepAliveTime, + TimeUnit unit, + BlockingQueue<Runnable> workQueue, + ThreadFactory threadFactory, + RejectedExecutionHandler handler) { + 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; + } + + + /** + * 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 <tt>RejectedExecutionHandler</tt>. + * + * @param command the task to execute + * @throws RejectedExecutionException at discretion of + * <tt>RejectedExecutionHandler</tt>, if task cannot be accepted + * for execution + * @throws NullPointerException if command is null + */ + public void execute(Runnable command) { + if (command == null) + throw new NullPointerException(); + for (;;) { + if (runState != RUNNING) { + reject(command); + return; + } + if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) + return; + if (workQueue.offer(command)) + return; + int status = addIfUnderMaximumPoolSize(command); + if (status > 0) // created new thread + return; + if (status == 0) { // failed to create thread + reject(command); + return; + } + // Retry if created a new thread but it is busy with another task + } + } + + /** + * 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}<tt>("modifyThread")</tt>, + * or the security manager's <tt>checkAccess</tt> method denies access. + */ + public void shutdown() { + // Fail if caller doesn't have modifyThread permission. + SecurityManager security = System.getSecurityManager(); + if (security != null) + security.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(); + } + + + /** + * 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 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 + * @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}<tt>("modifyThread")</tt>, + * or the security manager's <tt>checkAccess</tt> method denies access. + */ + public List<Runnable> shutdownNow() { + // Almost the same code as shutdown() + SecurityManager security = System.getSecurityManager(); + if (security != null) + security.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)); + } + + public boolean isShutdown() { + return runState != RUNNING; + } + + /** + * Returns true if this executor is in the process of terminating + * after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not + * completely terminated. This method may be useful for + * debugging. A return of <tt>true</tt> 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. + */ + public boolean isTerminating() { + return runState == STOP; + } + + public boolean isTerminated() { + return runState == TERMINATED; + } + + public boolean awaitTermination(long timeout, TimeUnit unit) + throws InterruptedException { + 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(); + } + } + + /** + * Invokes <tt>shutdown</tt> when this executor is no longer + * referenced. + */ + protected void finalize() { + shutdown(); + } + + /** + * Sets the thread factory used to create new threads. + * + * @param threadFactory the new thread factory + * @throws NullPointerException if threadFactory is null + * @see #getThreadFactory + */ + public void setThreadFactory(ThreadFactory threadFactory) { + if (threadFactory == null) + throw new NullPointerException(); + this.threadFactory = threadFactory; + } + + /** + * Returns the thread factory used to create new threads. + * + * @return the current thread factory + * @see #setThreadFactory + */ + public ThreadFactory getThreadFactory() { + return threadFactory; + } + + /** + * Sets a new handler for unexecutable tasks. + * + * @param handler the new handler + * @throws NullPointerException if handler is null + * @see #getRejectedExecutionHandler + */ + public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { + if (handler == null) + throw new NullPointerException(); + this.handler = handler; + } + + /** + * Returns the current handler for unexecutable tasks. + * + * @return the current handler + * @see #setRejectedExecutionHandler + */ + public RejectedExecutionHandler getRejectedExecutionHandler() { + return handler; + } + + /** + * 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 + */ + public BlockingQueue<Runnable> getQueue() { + return workQueue; + } + + /** + * 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. + * + * <p> 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 <tt>submit</tt> might be + * converted into a form that maintains <tt>Future</tt> 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 + */ + public boolean remove(Runnable task) { + return getQueue().remove(task); + } + + + /** + * 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. + */ + public void purge() { + // 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; + } + } + + /** + * 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 <tt>corePoolSize</tt> + * less than zero + * @see #getCorePoolSize + */ + public void setCorePoolSize(int corePoolSize) { + 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(); + } + } + + /** + * Returns the core number of threads. + * + * @return the core number of threads + * @see #setCorePoolSize + */ + public int getCorePoolSize() { + return corePoolSize; + } + + /** + * 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 <tt>false</tt> + * if all core threads have already been started. + * @return true if a thread was started + */ + public boolean prestartCoreThread() { + return addIfUnderCorePoolSize(null); + } + + /** + * 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. + */ + public int prestartAllCoreThreads() { + int n = 0; + while (addIfUnderCorePoolSize(null)) + ++n; + return n; + } + + /** + * Returns true if this pool allows core threads to time out and + * terminate if no tasks arrive within the keepAlive time, being + * replaced if needed when new tasks arrive. When true, the same + * keep-alive policy applying to non-core threads applies also to + * core threads. When false (the default), core threads are never + * terminated due to lack of incoming tasks. + * @return <tt>true</tt> if core threads are allowed to time out, + * else <tt>false</tt> + * + * @since 1.6 + */ + public boolean allowsCoreThreadTimeOut() { + return allowCoreThreadTimeOut; + } + + /** + * Sets the policy governing whether core threads may time out and + * terminate if no tasks arrive within the keep-alive time, being + * replaced if needed when new tasks arrive. When false, core + * threads are never terminated due to lack of incoming + * tasks. When true, the same keep-alive policy applying to + * non-core threads applies also to core threads. To avoid + * continual thread replacement, the keep-alive time must be + * greater than zero when setting <tt>true</tt>. This method + * should in general be called before the pool is actively used. + * @param value <tt>true</tt> if should time out, else <tt>false</tt> + * @throws IllegalArgumentException if value is <tt>true</tt> + * and the current keep-alive time is not greater than zero. + * + * @since 1.6 + */ + public void allowCoreThreadTimeOut(boolean value) { + if (value && keepAliveTime <= 0) + throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); + + allowCoreThreadTimeOut = value; + } + + /** + * 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 the new maximum is + * less than or equal to zero, or + * less than the {@linkplain #getCorePoolSize core pool size} + * @see #getMaximumPoolSize + */ + public void setMaximumPoolSize(int maximumPoolSize) { + 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(); + } + } + + /** + * Returns the maximum allowed number of threads. + * + * @return the maximum allowed number of threads + * @see #setMaximumPoolSize + */ + public int getMaximumPoolSize() { + return maximumPoolSize; + } + + /** + * 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 or + * if time is zero and allowsCoreThreadTimeOut + * @see #getKeepAliveTime + */ + public void setKeepAliveTime(long time, TimeUnit unit) { + if (time < 0) + throw new IllegalArgumentException(); + if (time == 0 && allowsCoreThreadTimeOut()) + throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); + this.keepAliveTime = unit.toNanos(time); + } + + /** + * 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 + */ + public long getKeepAliveTime(TimeUnit unit) { + return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); + } + + /* Statistics */ + + /** + * Returns the current number of threads in the pool. + * + * @return the number of threads + */ + public int getPoolSize() { + return poolSize; + } + + /** + * Returns the approximate number of threads that are actively + * executing tasks. + * + * @return the number of threads + */ + public int getActiveCount() { + final ReentrantLock mainLock = this.mainLock; + mainLock.lock(); + try { + int n = 0; + for (Worker w : workers) { + if (w.isActive()) + ++n; + } + return n; + } finally { + mainLock.unlock(); + } + } + + /** + * Returns the largest number of threads that have ever + * simultaneously been in the pool. + * + * @return the number of threads + */ + public int getLargestPoolSize() { + final ReentrantLock mainLock = this.mainLock; + mainLock.lock(); + try { + return largestPoolSize; + } finally { + mainLock.unlock(); + } + } + + /** + * 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 + */ + public long getTaskCount() { + 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(); + } + } + + /** + * 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 + */ + public long getCompletedTaskCount() { + final ReentrantLock mainLock = this.mainLock; + mainLock.lock(); + try { + long n = completedTaskCount; + for (Worker w : workers) + n += w.completedTasks; + return n; + } finally { + mainLock.unlock(); + } + } + + /** + * Method invoked prior to executing the given Runnable in the + * given thread. This method is invoked by thread <tt>t</tt> that + * will execute task <tt>r</tt>, and may be used to re-initialize + * ThreadLocals, or to perform logging. + * + * <p>This implementation does nothing, but may be customized in + * subclasses. Note: To properly nest multiple overridings, subclasses + * should generally invoke <tt>super.beforeExecute</tt> at the end of + * this method. + * + * @param t the thread that will run task r. + * @param r the task that will be executed. + */ + protected void beforeExecute(Thread t, Runnable r) { } + + /** + * 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 <tt>RuntimeException</tt> + * or <tt>Error</tt> that caused execution to terminate abruptly. + * + * <p><b>Note:</b> When actions are enclosed in tasks (such as + * {@link FutureTask}) either explicitly or via methods such as + * <tt>submit</tt>, these task objects catch and maintain + * computational exceptions, and so they do not cause abrupt + * termination, and the internal exceptions are <em>not</em> + * passed to this method. + * + * <p>This implementation does nothing, but may be customized in + * subclasses. Note: To properly nest multiple overridings, subclasses + * should generally invoke <tt>super.afterExecute</tt> 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. + */ + protected void afterExecute(Runnable r, Throwable t) { } + + /** + * Method invoked when the Executor has terminated. Default + * implementation does nothing. Note: To properly nest multiple + * overridings, subclasses should generally invoke + * <tt>super.terminated</tt> within this method. + */ + protected void terminated() { } + + /** + * A handler for rejected tasks that runs the rejected task + * directly in the calling thread of the <tt>execute</tt> method, + * unless the executor has been shut down, in which case the task + * is discarded. + */ + public static class CallerRunsPolicy implements RejectedExecutionHandler { + /** + * Creates a <tt>CallerRunsPolicy</tt>. + */ + public CallerRunsPolicy() { } + + /** + * Executes task r in the caller's thread, unless the executor + * has been shut down, in which case the task is discarded. + * @param r the runnable task requested to be executed + * @param e the executor attempting to execute this task + */ + public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { + if (!e.isShutdown()) { + r.run(); + } + } + } + + /** + * A handler for rejected tasks that throws a + * <tt>RejectedExecutionException</tt>. + */ + public static class AbortPolicy implements RejectedExecutionHandler { + /** + * Creates an <tt>AbortPolicy</tt>. + */ + public AbortPolicy() { } + + /** + * Always throws RejectedExecutionException. + * @param r the runnable task requested to be executed + * @param e the executor attempting to execute this task + * @throws RejectedExecutionException always. + */ + public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { + throw new RejectedExecutionException(); + } + } + + /** + * A handler for rejected tasks that silently discards the + * rejected task. + */ + public static class DiscardPolicy implements RejectedExecutionHandler { + /** + * Creates a <tt>DiscardPolicy</tt>. + */ + public DiscardPolicy() { } + + /** + * Does nothing, which has the effect of discarding task r. + * @param r the runnable task requested to be executed + * @param e the executor attempting to execute this task + */ + public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { + } + } + + /** + * A handler for rejected tasks that discards the oldest unhandled + * request and then retries <tt>execute</tt>, unless the executor + * is shut down, in which case the task is discarded. + */ + public static class DiscardOldestPolicy implements RejectedExecutionHandler { + /** + * Creates a <tt>DiscardOldestPolicy</tt> for the given executor. + */ + public DiscardOldestPolicy() { } + + /** + * Obtains and ignores the next task that the executor + * would otherwise execute, if one is immediately available, + * and then retries execution of task r, unless the executor + * is shut down, in which case task r is instead discarded. + * @param r the runnable task requested to be executed + * @param e the executor attempting to execute this task + */ + public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { + if (!e.isShutdown()) { + e.getQueue().poll(); + e.execute(r); + } + } + } +} |