| /* |
| * 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); |
| } |
| } |
| } |
| } |
