| /* |
| * 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.concurrent.atomic.*; |
| 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 {@code ThreadPoolExecutor} 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 {@code ThreadPoolExecutor} will automatically adjust the |
| * pool size (see {@link #getPoolSize}) |
| * according to the bounds set by |
| * corePoolSize (see {@link #getCorePoolSize}) and |
| * maximumPoolSize (see {@link #getMaximumPoolSize}). |
| * |
| * When a new task is submitted in method {@link #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 {@code Integer.MAX_VALUE}, 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 #setCorePoolSize} and {@link #setMaximumPoolSize}. </dd> |
| * |
| * <dt>On-demand construction</dt> |
| * |
| * <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 #prestartCoreThread} or {@link |
| * #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 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 {@code NORM_PRIORITY} 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 {@code ThreadFactory} fails to create a thread when asked |
| * by returning null from {@code newThread}, the executor will |
| * continue, but might not be able to execute any tasks. Threads |
| * should possess the "modifyThread" {@code RuntimePermission}. If |
| * worker threads or other threads using the pool do not possess this |
| * permission, service may be degraded: configuration changes may not |
| * take effect in a timely manner, and a shutdown pool may remain in a |
| * state in which termination is possible but not completed.</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 #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 #setKeepAliveTime}. Using a value |
| * of {@code Long.MAX_VALUE} {@link TimeUnit#NANOSECONDS} effectively |
| * disables idle threads from ever terminating prior to shut down. The |
| * keep-alive policy applies only when there are more than |
| * corePoolSizeThreads.</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 #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 {@code |
| * execute} 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 {@code execute} 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 {@code protected} overridable {@link |
| * #beforeExecute} and {@link #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 #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 #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 #remove} and {@link #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 {@code shutdown} automatically. If |
| * you would like to ensure that unreferenced pools are reclaimed even |
| * if users forget to call {@link #shutdown}, then you must arrange |
| * that unused threads eventually die, by setting appropriate |
| * keep-alive times using a lower bound of zero core threads. </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> {@code |
| * 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 { |
| /** |
| * The main pool control state, ctl, is an atomic integer packing |
| * two conceptual fields |
| * workerCount, indicating the effective number of threads |
| * runState, indicating whether running, shutting down etc |
| * |
| * In order to pack them into one int, we limit workerCount to |
| * (2^29)-1 (about 500 million) threads rather than (2^31)-1 (2 |
| * billion) otherwise representable. If this is ever an issue in |
| * the future, the variable can be changed to be an AtomicLong, |
| * and the shift/mask constants below adjusted. But until the need |
| * arises, this code is a bit faster and simpler using an int. |
| * |
| * The workerCount is the number of workers that have been |
| * permitted to start and not permitted to stop. The value may be |
| * transiently different from the actual number of live threads, |
| * for example when a ThreadFactory fails to create a thread when |
| * asked, and when exiting threads are still performing |
| * bookkeeping before terminating. The user-visible pool size is |
| * reported as the current size of the workers set. |
| * |
| * The runState provides the main lifecyle control, taking on values: |
| * |
| * RUNNING: Accept new tasks and process queued tasks |
| * SHUTDOWN: Don't accept new tasks, but process queued tasks |
| * STOP: Don't accept new tasks, don't process queued tasks, |
| * and interrupt in-progress tasks |
| * TIDYING: All tasks have terminated, workerCount is zero, |
| * the thread transitioning to state TIDYING |
| * will run the terminated() hook method |
| * TERMINATED: terminated() has completed |
| * |
| * The numerical order among these values matters, to allow |
| * ordered comparisons. The runState monotonically increases over |
| * time, but need not hit each state. The transitions are: |
| * |
| * RUNNING -> SHUTDOWN |
| * On invocation of shutdown(), perhaps implicitly in finalize() |
| * (RUNNING or SHUTDOWN) -> STOP |
| * On invocation of shutdownNow() |
| * SHUTDOWN -> TIDYING |
| * When both queue and pool are empty |
| * STOP -> TIDYING |
| * When pool is empty |
| * TIDYING -> TERMINATED |
| * When the terminated() hook method has completed |
| * |
| * Threads waiting in awaitTermination() will return when the |
| * state reaches TERMINATED. |
| * |
| * Detecting the transition from SHUTDOWN to TIDYING is less |
| * straightforward than you'd like because the queue may become |
| * empty after non-empty and vice versa during SHUTDOWN state, but |
| * we can only terminate if, after seeing that it is empty, we see |
| * that workerCount is 0 (which sometimes entails a recheck -- see |
| * below). |
| */ |
| private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0)); |
| private static final int COUNT_BITS = Integer.SIZE - 3; |
| private static final int CAPACITY = (1 << COUNT_BITS) - 1; |
| |
| // runState is stored in the high-order bits |
| private static final int RUNNING = -1 << COUNT_BITS; |
| private static final int SHUTDOWN = 0 << COUNT_BITS; |
| private static final int STOP = 1 << COUNT_BITS; |
| private static final int TIDYING = 2 << COUNT_BITS; |
| private static final int TERMINATED = 3 << COUNT_BITS; |
| |
| // Packing and unpacking ctl |
| private static int runStateOf(int c) { return c & ~CAPACITY; } |
| private static int workerCountOf(int c) { return c & CAPACITY; } |
| private static int ctlOf(int rs, int wc) { return rs | wc; } |
| |
| /* |
| * Bit field accessors that don't require unpacking ctl. |
| * These depend on the bit layout and on workerCount being never negative. |
| */ |
| |
| private static boolean runStateLessThan(int c, int s) { |
| return c < s; |
| } |
| |
| private static boolean runStateAtLeast(int c, int s) { |
| return c >= s; |
| } |
| |
| private static boolean isRunning(int c) { |
| return c < SHUTDOWN; |
| } |
| |
| /** |
| * Attempt to CAS-increment the workerCount field of ctl. |
| */ |
| private boolean compareAndIncrementWorkerCount(int expect) { |
| return ctl.compareAndSet(expect, expect + 1); |
| } |
| |
| /** |
| * Attempt to CAS-decrement the workerCount field of ctl. |
| */ |
| private boolean compareAndDecrementWorkerCount(int expect) { |
| return ctl.compareAndSet(expect, expect - 1); |
| } |
| |
| /** |
| * Decrements the workerCount field of ctl. This is called only on |
| * abrupt termination of a thread (see processWorkerExit). Other |
| * decrements are performed within getTask. |
| */ |
| private void decrementWorkerCount() { |
| do {} while (! compareAndDecrementWorkerCount(ctl.get())); |
| } |
| |
| /** |
| * The queue used for holding tasks and handing off to worker |
| * threads. We do not require that workQueue.poll() returning |
| * null necessarily means that workQueue.isEmpty(), so rely |
| * solely on isEmpty to see if the queue is empty (which we must |
| * do for example when deciding whether to transition from |
| * SHUTDOWN to TIDYING). This accommodates special-purpose |
| * queues such as DelayQueues for which poll() is allowed to |
| * return null even if it may later return non-null when delays |
| * expire. |
| */ |
| private final BlockingQueue<Runnable> workQueue; |
| |
| /** |
| * Lock held on access to workers set and related bookkeeping. |
| * While we could use a concurrent set of some sort, it turns out |
| * to be generally preferable to use a lock. Among the reasons is |
| * that this serializes interruptIdleWorkers, which avoids |
| * unnecessary interrupt storms, especially during shutdown. |
| * Otherwise exiting threads would concurrently interrupt those |
| * that have not yet interrupted. It also simplifies some of the |
| * associated statistics bookkeeping of largestPoolSize etc. We |
| * also hold mainLock on shutdown and shutdownNow, for the sake of |
| * ensuring workers set is stable while separately checking |
| * permission to interrupt and actually interrupting. |
| */ |
| private final ReentrantLock mainLock = new ReentrantLock(); |
| |
| /** |
| * Set containing all worker threads in pool. Accessed only when |
| * holding mainLock. |
| */ |
| private final HashSet<Worker> workers = new HashSet<Worker>(); |
| |
| /** |
| * Wait condition to support awaitTermination |
| */ |
| private final Condition termination = mainLock.newCondition(); |
| |
| /** |
| * Tracks largest attained pool size. Accessed only under |
| * mainLock. |
| */ |
| private int largestPoolSize; |
| |
| /** |
| * Counter for completed tasks. Updated only on termination of |
| * worker threads. Accessed only under mainLock. |
| */ |
| private long completedTaskCount; |
| |
| /* |
| * All user control parameters are declared as volatiles so that |
| * ongoing actions are based on freshest values, but without need |
| * for locking, since no internal invariants depend on them |
| * changing synchronously with respect to other actions. |
| */ |
| |
| /** |
| * Factory for new threads. All threads are created using this |
| * factory (via method addWorker). All callers must be prepared |
| * for addWorker to fail, which may reflect a system or user's |
| * policy limiting the number of threads. Even though it is not |
| * treated as an error, failure to create threads may result in |
| * new tasks being rejected or existing ones remaining stuck in |
| * the queue. On the other hand, no special precautions exist to |
| * handle OutOfMemoryErrors that might be thrown while trying to |
| * create threads, since there is generally no recourse from |
| * within this class. |
| */ |
| private volatile ThreadFactory threadFactory; |
| |
| /** |
| * Handler called when saturated or shutdown in execute. |
| */ |
| private volatile RejectedExecutionHandler handler; |
| |
| /** |
| * Timeout in nanoseconds for idle threads waiting for work. |
| * Threads use this timeout when there are more than corePoolSize |
| * present. Otherwise they wait forever for new work. |
| */ |
| private volatile long keepAliveTime; |
| |
| /** |
| * Core pool size is the minimum number of workers to keep alive |
| * (and not allow to time out etc). |
| */ |
| private volatile int corePoolSize; |
| |
| /** |
| * Maximum pool size. Note that the actual maximum is internally |
| * bounded by CAPACITY. |
| */ |
| private volatile int maximumPoolSize; |
| |
| /** |
| * The default rejected execution handler |
| */ |
| private static final RejectedExecutionHandler defaultHandler = |
| new AbortPolicy(); |
| |
| /** |
| * Permission required for callers of shutdown and shutdownNow. |
| * We additionally require (see checkShutdownAccess) that callers |
| * have permission to actually interrupt threads in the worker set |
| * (as governed by Thread.interrupt, which relies on |
| * ThreadGroup.checkAccess, which in turn relies on |
| * SecurityManager.checkAccess). Shutdowns are attempted only if |
| * these checks pass. |
| * |
| * All actual invocations of Thread.interrupt (see |
| * interruptIdleWorkers and interruptWorkers) ignore |
| * SecurityExceptions, meaning that the attempted interrupts |
| * silently fail. In the case of shutdown, they should not fail |
| * unless the SecurityManager has inconsistent policies, sometimes |
| * allowing access to a thread and sometimes not. In such cases, |
| * failure to actually interrupt threads may disable or delay full |
| * termination. Other uses of interruptIdleWorkers are advisory, |
| * and failure to actually interrupt will merely delay response to |
| * configuration changes so is not handled exceptionally. |
| */ |
| private static final RuntimePermission shutdownPerm = |
| new RuntimePermission("modifyThread"); |
| |
| /** |
| * Class Worker mainly maintains interrupt control state for |
| * threads running tasks, along with other minor bookkeeping. |
| * This class opportunistically extends AbstractQueuedSynchronizer |
| * to simplify acquiring and releasing a lock surrounding each |
| * task execution. This protects against interrupts that are |
| * intended to wake up a worker thread waiting for a task from |
| * instead interrupting a task being run. We implement a simple |
| * non-reentrant mutual exclusion lock rather than use ReentrantLock |
| * because we do not want worker tasks to be able to reacquire the |
| * lock when they invoke pool control methods like setCorePoolSize. |
| */ |
| private final class Worker |
| extends AbstractQueuedSynchronizer |
| implements Runnable |
| { |
| /** |
| * This class will never be serialized, but we provide a |
| * serialVersionUID to suppress a javac warning. |
| */ |
| private static final long serialVersionUID = 6138294804551838833L; |
| |
| /** Thread this worker is running in. Null if factory fails. */ |
| final Thread thread; |
| /** Initial task to run. Possibly null. */ |
| Runnable firstTask; |
| /** Per-thread task counter */ |
| volatile long completedTasks; |
| |
| /** |
| * Creates with given first task and thread from ThreadFactory. |
| * @param firstTask the first task (null if none) |
| */ |
| Worker(Runnable firstTask) { |
| this.firstTask = firstTask; |
| this.thread = getThreadFactory().newThread(this); |
| } |
| |
| /** Delegates main run loop to outer runWorker */ |
| public void run() { |
| runWorker(this); |
| } |
| |
| // Lock methods |
| // |
| // The value 0 represents the unlocked state. |
| // The value 1 represents the locked state. |
| |
| protected boolean isHeldExclusively() { |
| return getState() == 1; |
| } |
| |
| protected boolean tryAcquire(int unused) { |
| if (compareAndSetState(0, 1)) { |
| setExclusiveOwnerThread(Thread.currentThread()); |
| return true; |
| } |
| return false; |
| } |
| |
| protected boolean tryRelease(int unused) { |
| setExclusiveOwnerThread(null); |
| setState(0); |
| return true; |
| } |
| |
| public void lock() { acquire(1); } |
| public boolean tryLock() { return tryAcquire(1); } |
| public void unlock() { release(1); } |
| public boolean isLocked() { return isHeldExclusively(); } |
| } |
| |
| /* |
| * Methods for setting control state |
| */ |
| |
| /** |
| * Transitions runState to given target, or leaves it alone if |
| * already at least the given target. |
| * |
| * @param targetState the desired state, either SHUTDOWN or STOP |
| * (but not TIDYING or TERMINATED -- use tryTerminate for that) |
| */ |
| private void advanceRunState(int targetState) { |
| for (;;) { |
| int c = ctl.get(); |
| if (runStateAtLeast(c, targetState) || |
| ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c)))) |
| break; |
| } |
| } |
| |
| /** |
| * Transitions to TERMINATED state if either (SHUTDOWN and pool |
| * and queue empty) or (STOP and pool empty). If otherwise |
| * eligible to terminate but workerCount is nonzero, interrupts an |
| * idle worker to ensure that shutdown signals propagate. This |
| * method must be called following any action that might make |
| * termination possible -- reducing worker count or removing tasks |
| * from the queue during shutdown. The method is non-private to |
| * allow access from ScheduledThreadPoolExecutor. |
| */ |
| final void tryTerminate() { |
| for (;;) { |
| int c = ctl.get(); |
| if (isRunning(c) || |
| runStateAtLeast(c, TIDYING) || |
| (runStateOf(c) == SHUTDOWN && ! workQueue.isEmpty())) |
| return; |
| if (workerCountOf(c) != 0) { // Eligible to terminate |
| interruptIdleWorkers(ONLY_ONE); |
| return; |
| } |
| |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) { |
| try { |
| terminated(); |
| } finally { |
| ctl.set(ctlOf(TERMINATED, 0)); |
| termination.signalAll(); |
| } |
| return; |
| } |
| } finally { |
| mainLock.unlock(); |
| } |
| // else retry on failed CAS |
| } |
| } |
| |
| /* |
| * Methods for controlling interrupts to worker threads. |
| */ |
| |
| /** |
| * If there is a security manager, makes sure caller has |
| * permission to shut down threads in general (see shutdownPerm). |
| * If this passes, additionally makes sure the caller is allowed |
| * to interrupt each worker thread. This might not be true even if |
| * first check passed, if the SecurityManager treats some threads |
| * specially. |
| */ |
| private void checkShutdownAccess() { |
| SecurityManager security = System.getSecurityManager(); |
| if (security != null) { |
| security.checkPermission(shutdownPerm); |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| for (Worker w : workers) |
| security.checkAccess(w.thread); |
| } finally { |
| mainLock.unlock(); |
| } |
| } |
| } |
| |
| /** |
| * Interrupts all threads, even if active. Ignores SecurityExceptions |
| * (in which case some threads may remain uninterrupted). |
| */ |
| private void interruptWorkers() { |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| for (Worker w : workers) { |
| try { |
| w.thread.interrupt(); |
| } catch (SecurityException ignore) { |
| } |
| } |
| } finally { |
| mainLock.unlock(); |
| } |
| } |
| |
| /** |
| * Interrupts threads that might be waiting for tasks (as |
| * indicated by not being locked) so they can check for |
| * termination or configuration changes. Ignores |
| * SecurityExceptions (in which case some threads may remain |
| * uninterrupted). |
| * |
| * @param onlyOne If true, interrupt at most one worker. This is |
| * called only from tryTerminate when termination is otherwise |
| * enabled but there are still other workers. In this case, at |
| * most one waiting worker is interrupted to propagate shutdown |
| * signals in case all threads are currently waiting. |
| * Interrupting any arbitrary thread ensures that newly arriving |
| * workers since shutdown began will also eventually exit. |
| * To guarantee eventual termination, it suffices to always |
| * interrupt only one idle worker, but shutdown() interrupts all |
| * idle workers so that redundant workers exit promptly, not |
| * waiting for a straggler task to finish. |
| */ |
| private void interruptIdleWorkers(boolean onlyOne) { |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| for (Worker w : workers) { |
| Thread t = w.thread; |
| if (!t.isInterrupted() && w.tryLock()) { |
| try { |
| t.interrupt(); |
| } catch (SecurityException ignore) { |
| } finally { |
| w.unlock(); |
| } |
| } |
| if (onlyOne) |
| break; |
| } |
| } finally { |
| mainLock.unlock(); |
| } |
| } |
| |
| /** |
| * Common form of interruptIdleWorkers, to avoid having to |
| * remember what the boolean argument means. |
| */ |
| private void interruptIdleWorkers() { |
| interruptIdleWorkers(false); |
| } |
| |
| private static final boolean ONLY_ONE = true; |
| |
| /** |
| * Ensures that unless the pool is stopping, the current thread |
| * does not have its interrupt set. This requires a double-check |
| * of state in case the interrupt was cleared concurrently with a |
| * shutdownNow -- if so, the interrupt is re-enabled. |
| */ |
| private void clearInterruptsForTaskRun() { |
| if (runStateLessThan(ctl.get(), STOP) && |
| Thread.interrupted() && |
| runStateAtLeast(ctl.get(), STOP)) |
| Thread.currentThread().interrupt(); |
| } |
| |
| /* |
| * Misc utilities, most of which are also exported to |
| * ScheduledThreadPoolExecutor |
| */ |
| |
| /** |
| * Invokes the rejected execution handler for the given command. |
| * Package-protected for use by ScheduledThreadPoolExecutor. |
| */ |
| final void reject(Runnable command) { |
| handler.rejectedExecution(command, this); |
| } |
| |
| /** |
| * Performs any further cleanup following run state transition on |
| * invocation of shutdown. A no-op here, but used by |
| * ScheduledThreadPoolExecutor to cancel delayed tasks. |
| */ |
| void onShutdown() { |
| } |
| |
| /** |
| * State check needed by ScheduledThreadPoolExecutor to |
| * enable running tasks during shutdown. |
| * |
| * @param shutdownOK true if should return true if SHUTDOWN |
| */ |
| final boolean isRunningOrShutdown(boolean shutdownOK) { |
| int rs = runStateOf(ctl.get()); |
| return rs == RUNNING || (rs == SHUTDOWN && shutdownOK); |
| } |
| |
| /** |
| * Drains the task queue into a new list, normally using |
| * drainTo. But if the queue is a DelayQueue or any other kind of |
| * queue for which poll or drainTo may fail to remove some |
| * elements, it deletes them one by one. |
| */ |
| private List<Runnable> drainQueue() { |
| BlockingQueue<Runnable> q = workQueue; |
| List<Runnable> taskList = new ArrayList<Runnable>(); |
| q.drainTo(taskList); |
| if (!q.isEmpty()) { |
| for (Runnable r : q.toArray(new Runnable[0])) { |
| if (q.remove(r)) |
| taskList.add(r); |
| } |
| } |
| return taskList; |
| } |
| |
| /* |
| * Methods for creating, running and cleaning up after workers |
| */ |
| |
| /** |
| * Checks if a new worker can be added with respect to current |
| * pool state and the given bound (either core or maximum). If so, |
| * the worker count is adjusted accordingly, and, if possible, a |
| * new worker is created and started running firstTask as its |
| * first task. This method returns false if the pool is stopped or |
| * eligible to shut down. It also returns false if the thread |
| * factory fails to create a thread when asked, which requires a |
| * backout of workerCount, and a recheck for termination, in case |
| * the existence of this worker was holding up termination. |
| * |
| * @param firstTask the task the new thread should run first (or |
| * null if none). Workers are created with an initial first task |
| * (in method execute()) to bypass queuing when there are fewer |
| * than corePoolSize threads (in which case we always start one), |
| * or when the queue is full (in which case we must bypass queue). |
| * Initially idle threads are usually created via |
| * prestartCoreThread or to replace other dying workers. |
| * |
| * @param core if true use corePoolSize as bound, else |
| * maximumPoolSize. (A boolean indicator is used here rather than a |
| * value to ensure reads of fresh values after checking other pool |
| * state). |
| * @return true if successful |
| */ |
| private boolean addWorker(Runnable firstTask, boolean core) { |
| retry: |
| for (;;) { |
| int c = ctl.get(); |
| int rs = runStateOf(c); |
| |
| // Check if queue empty only if necessary. |
| if (rs >= SHUTDOWN && |
| ! (rs == SHUTDOWN && |
| firstTask == null && |
| ! workQueue.isEmpty())) |
| return false; |
| |
| for (;;) { |
| int wc = workerCountOf(c); |
| if (wc >= CAPACITY || |
| wc >= (core ? corePoolSize : maximumPoolSize)) |
| return false; |
| if (compareAndIncrementWorkerCount(c)) |
| break retry; |
| c = ctl.get(); // Re-read ctl |
| if (runStateOf(c) != rs) |
| continue retry; |
| // else CAS failed due to workerCount change; retry inner loop |
| } |
| } |
| |
| Worker w = new Worker(firstTask); |
| Thread t = w.thread; |
| |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| // Recheck while holding lock. |
| // Back out on ThreadFactory failure or if |
| // shut down before lock acquired. |
| int c = ctl.get(); |
| int rs = runStateOf(c); |
| |
| if (t == null || |
| (rs >= SHUTDOWN && |
| ! (rs == SHUTDOWN && |
| firstTask == null))) { |
| decrementWorkerCount(); |
| tryTerminate(); |
| return false; |
| } |
| |
| workers.add(w); |
| |
| int s = workers.size(); |
| if (s > largestPoolSize) |
| largestPoolSize = s; |
| } finally { |
| mainLock.unlock(); |
| } |
| |
| t.start(); |
| // It is possible (but unlikely) for a thread to have been |
| // added to workers, but not yet started, during transition to |
| // STOP, which could result in a rare missed interrupt, |
| // because Thread.interrupt is not guaranteed to have any effect |
| // on a non-yet-started Thread (see Thread#interrupt). |
| if (runStateOf(ctl.get()) == STOP && ! t.isInterrupted()) |
| t.interrupt(); |
| |
| return true; |
| } |
| |
| /** |
| * Performs cleanup and bookkeeping for a dying worker. Called |
| * only from worker threads. Unless completedAbruptly is set, |
| * assumes that workerCount has already been adjusted to account |
| * for exit. This method removes thread from worker set, and |
| * possibly terminates the pool or replaces the worker if either |
| * it exited due to user task exception or if fewer than |
| * corePoolSize workers are running or queue is non-empty but |
| * there are no workers. |
| * |
| * @param w the worker |
| * @param completedAbruptly if the worker died due to user exception |
| */ |
| private void processWorkerExit(Worker w, boolean completedAbruptly) { |
| if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted |
| decrementWorkerCount(); |
| |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| completedTaskCount += w.completedTasks; |
| workers.remove(w); |
| } finally { |
| mainLock.unlock(); |
| } |
| |
| tryTerminate(); |
| |
| int c = ctl.get(); |
| if (runStateLessThan(c, STOP)) { |
| if (!completedAbruptly) { |
| int min = corePoolSize; |
| if (min == 0 && ! workQueue.isEmpty()) |
| min = 1; |
| if (workerCountOf(c) >= min) |
| return; // replacement not needed |
| } |
| addWorker(null, false); |
| } |
| } |
| |
| /** |
| * Performs blocking or timed wait for a task, depending on |
| * current configuration settings, or returns null if this worker |
| * must exit because of any of: |
| * 1. There are more than maximumPoolSize workers (due to |
| * a call to setMaximumPoolSize). |
| * 2. The pool is stopped. |
| * 3. The pool is shutdown and the queue is empty. |
| * 4. This worker timed out waiting for a task, and timed-out |
| * workers are subject to termination (that is, |
| * {@code workerCount > corePoolSize}) |
| * both before and after the timed wait. |
| * |
| * @return task, or null if the worker must exit, in which case |
| * workerCount is decremented |
| */ |
| private Runnable getTask() { |
| boolean timedOut = false; // Did the last poll() time out? |
| |
| retry: |
| for (;;) { |
| int c = ctl.get(); |
| int rs = runStateOf(c); |
| |
| // Check if queue empty only if necessary. |
| if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) { |
| decrementWorkerCount(); |
| return null; |
| } |
| |
| boolean timed; // Are workers subject to culling? |
| |
| for (;;) { |
| int wc = workerCountOf(c); |
| timed = wc > corePoolSize; |
| |
| if (wc <= maximumPoolSize && ! (timedOut && timed)) |
| break; |
| if (compareAndDecrementWorkerCount(c)) |
| return null; |
| c = ctl.get(); // Re-read ctl |
| if (runStateOf(c) != rs) |
| continue retry; |
| // else CAS failed due to workerCount change; retry inner loop |
| } |
| |
| try { |
| Runnable r = timed ? |
| workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) : |
| workQueue.take(); |
| if (r != null) |
| return r; |
| timedOut = true; |
| } catch (InterruptedException retry) { |
| timedOut = false; |
| } |
| } |
| } |
| |
| /** |
| * Main worker run loop. Repeatedly gets tasks from queue and |
| * executes them, while coping with a number of issues: |
| * |
| * 1. We may start out with an initial task, in which case we |
| * don't need to get the first one. Otherwise, as long as pool is |
| * running, we get tasks from getTask. If it returns null then the |
| * worker exits due to changed pool state or configuration |
| * parameters. Other exits result from exception throws in |
| * external code, in which case completedAbruptly holds, which |
| * usually leads processWorkerExit to replace this thread. |
| * |
| * 2. Before running any task, the lock is acquired to prevent |
| * other pool interrupts while the task is executing, and |
| * clearInterruptsForTaskRun called to ensure that unless pool is |
| * stopping, this thread does not have its interrupt set. |
| * |
| * 3. Each task run is preceded by a call to beforeExecute, which |
| * might throw an exception, in which case we cause thread to die |
| * (breaking loop with completedAbruptly true) without processing |
| * the task. |
| * |
| * 4. Assuming beforeExecute completes normally, we run the task, |
| * gathering any of its thrown exceptions to send to |
| * afterExecute. We separately handle RuntimeException, Error |
| * (both of which the specs guarantee that we trap) and arbitrary |
| * Throwables. Because we cannot rethrow Throwables within |
| * Runnable.run, we wrap them within Errors on the way out (to the |
| * thread's UncaughtExceptionHandler). Any thrown exception also |
| * conservatively causes thread to die. |
| * |
| * 5. After task.run completes, we call afterExecute, which may |
| * also throw an exception, which will also cause thread to |
| * die. According to JLS Sec 14.20, this exception is the one that |
| * will be in effect even if task.run throws. |
| * |
| * The net effect of the exception mechanics is that afterExecute |
| * and the thread's UncaughtExceptionHandler have as accurate |
| * information as we can provide about any problems encountered by |
| * user code. |
| * |
| * @param w the worker |
| */ |
| final void runWorker(Worker w) { |
| Runnable task = w.firstTask; |
| w.firstTask = null; |
| boolean completedAbruptly = true; |
| try { |
| while (task != null || (task = getTask()) != null) { |
| w.lock(); |
| clearInterruptsForTaskRun(); |
| try { |
| beforeExecute(w.thread, task); |
| Throwable thrown = null; |
| try { |
| task.run(); |
| } catch (RuntimeException x) { |
| thrown = x; throw x; |
| } catch (Error x) { |
| thrown = x; throw x; |
| } catch (Throwable x) { |
| thrown = x; throw new Error(x); |
| } finally { |
| afterExecute(task, thrown); |
| } |
| } finally { |
| task = null; |
| w.completedTasks++; |
| w.unlock(); |
| } |
| } |
| completedAbruptly = false; |
| } finally { |
| processWorkerExit(w, completedAbruptly); |
| } |
| } |
| |
| // Public constructors and methods |
| |
| /** |
| * Creates a new {@code ThreadPoolExecutor} 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 {@code keepAliveTime} argument |
| * @param workQueue the queue to use for holding tasks before they are |
| * executed. This queue will hold only the {@code Runnable} |
| * tasks submitted by the {@code execute} method. |
| * @throws IllegalArgumentException if one of the following holds:<br> |
| * {@code corePoolSize < 0}<br> |
| * {@code keepAliveTime < 0}<br> |
| * {@code maximumPoolSize <= 0}<br> |
| * {@code maximumPoolSize < corePoolSize} |
| * @throws NullPointerException if {@code workQueue} 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 {@code ThreadPoolExecutor} 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 {@code keepAliveTime} argument |
| * @param workQueue the queue to use for holding tasks before they are |
| * executed. This queue will hold only the {@code Runnable} |
| * tasks submitted by the {@code execute} method. |
| * @param threadFactory the factory to use when the executor |
| * creates a new thread |
| * @throws IllegalArgumentException if one of the following holds:<br> |
| * {@code corePoolSize < 0}<br> |
| * {@code keepAliveTime < 0}<br> |
| * {@code maximumPoolSize <= 0}<br> |
| * {@code maximumPoolSize < corePoolSize} |
| * @throws NullPointerException if {@code workQueue} |
| * or {@code threadFactory} is 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 {@code ThreadPoolExecutor} 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 {@code keepAliveTime} argument |
| * @param workQueue the queue to use for holding tasks before they are |
| * executed. This queue will hold only the {@code Runnable} |
| * tasks submitted by the {@code execute} method. |
| * @param handler the handler to use when execution is blocked |
| * because the thread bounds and queue capacities are reached |
| * @throws IllegalArgumentException if one of the following holds:<br> |
| * {@code corePoolSize < 0}<br> |
| * {@code keepAliveTime < 0}<br> |
| * {@code maximumPoolSize <= 0}<br> |
| * {@code maximumPoolSize < corePoolSize} |
| * @throws NullPointerException if {@code workQueue} |
| * or {@code handler} is 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 {@code ThreadPoolExecutor} with the given initial |
| * parameters. |
| * |
| * @param corePoolSize the number of threads to keep in the pool, even |
| * if they are idle |
| * @param maximumPoolSize the maximum number of threads to allow in the |
| * pool |
| * @param keepAliveTime when the number of threads is greater than |
| * the core, this is the maximum time that excess idle threads |
| * will wait for new tasks before terminating. |
| * @param unit the time unit for the {@code keepAliveTime} argument |
| * @param workQueue the queue to use for holding tasks before they are |
| * executed. This queue will hold only the {@code Runnable} |
| * tasks submitted by the {@code execute} method. |
| * @param threadFactory the factory to use when the executor |
| * creates a new thread |
| * @param handler the handler to use when execution is blocked |
| * because the thread bounds and queue capacities are reached |
| * @throws IllegalArgumentException if one of the following holds:<br> |
| * {@code corePoolSize < 0}<br> |
| * {@code keepAliveTime < 0}<br> |
| * {@code maximumPoolSize <= 0}<br> |
| * {@code maximumPoolSize < corePoolSize} |
| * @throws NullPointerException if {@code workQueue} |
| * or {@code threadFactory} or {@code handler} is 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 {@code RejectedExecutionHandler}. |
| * |
| * @param command the task to execute |
| * @throws RejectedExecutionException at discretion of |
| * {@code RejectedExecutionHandler}, if the task |
| * cannot be accepted for execution |
| * @throws NullPointerException if {@code command} is null |
| */ |
| public void execute(Runnable command) { |
| if (command == null) |
| throw new NullPointerException(); |
| /* |
| * Proceed in 3 steps: |
| * |
| * 1. If fewer than corePoolSize threads are running, try to |
| * start a new thread with the given command as its first |
| * task. The call to addWorker atomically checks runState and |
| * workerCount, and so prevents false alarms that would add |
| * threads when it shouldn't, by returning false. |
| * |
| * 2. If a task can be successfully queued, then we still need |
| * to double-check whether we should have added a thread |
| * (because existing ones died since last checking) or that |
| * the pool shut down since entry into this method. So we |
| * recheck state and if necessary roll back the enqueuing if |
| * stopped, or start a new thread if there are none. |
| * |
| * 3. If we cannot queue task, then we try to add a new |
| * thread. If it fails, we know we are shut down or saturated |
| * and so reject the task. |
| */ |
| int c = ctl.get(); |
| if (workerCountOf(c) < corePoolSize) { |
| if (addWorker(command, true)) |
| return; |
| c = ctl.get(); |
| } |
| if (isRunning(c) && workQueue.offer(command)) { |
| int recheck = ctl.get(); |
| if (! isRunning(recheck) && remove(command)) |
| reject(command); |
| else if (workerCountOf(recheck) == 0) |
| addWorker(null, false); |
| } |
| else if (!addWorker(command, false)) |
| reject(command); |
| } |
| |
| /** |
| * 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. |
| * |
| * <p>This method does not wait for previously submitted tasks to |
| * complete execution. Use {@link #awaitTermination awaitTermination} |
| * to do that. |
| * |
| * @throws SecurityException {@inheritDoc} |
| */ |
| public void shutdown() { |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| checkShutdownAccess(); |
| advanceRunState(SHUTDOWN); |
| interruptIdleWorkers(); |
| onShutdown(); // hook for ScheduledThreadPoolExecutor |
| } finally { |
| mainLock.unlock(); |
| } |
| tryTerminate(); |
| } |
| |
| /** |
| * Attempts to stop all actively executing tasks, halts the |
| * processing of waiting tasks, and returns a list of the tasks |
| * that were awaiting execution. These tasks are drained (removed) |
| * from the task queue upon return from this method. |
| * |
| * <p>This method does not wait for actively executing tasks to |
| * terminate. Use {@link #awaitTermination awaitTermination} to |
| * do that. |
| * |
| * <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. |
| * |
| * @throws SecurityException {@inheritDoc} |
| */ |
| public List<Runnable> shutdownNow() { |
| List<Runnable> tasks; |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| checkShutdownAccess(); |
| advanceRunState(STOP); |
| interruptWorkers(); |
| tasks = drainQueue(); |
| } finally { |
| mainLock.unlock(); |
| } |
| tryTerminate(); |
| return tasks; |
| } |
| |
| public boolean isShutdown() { |
| return ! isRunning(ctl.get()); |
| } |
| |
| /** |
| * Returns true if this executor is in the process of terminating |
| * after {@link #shutdown} or {@link #shutdownNow} but has not |
| * completely terminated. This method may be useful for |
| * debugging. A return of {@code true} reported a sufficient |
| * period after shutdown may indicate that submitted tasks have |
| * ignored or suppressed interruption, causing this executor not |
| * to properly terminate. |
| * |
| * @return true if terminating but not yet terminated |
| */ |
| public boolean isTerminating() { |
| int c = ctl.get(); |
| return ! isRunning(c) && runStateLessThan(c, TERMINATED); |
| } |
| |
| public boolean isTerminated() { |
| return runStateAtLeast(ctl.get(), 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 (runStateAtLeast(ctl.get(), TERMINATED)) |
| return true; |
| if (nanos <= 0) |
| return false; |
| nanos = termination.awaitNanos(nanos); |
| } |
| } finally { |
| mainLock.unlock(); |
| } |
| } |
| |
| /** |
| * Invokes {@code shutdown} when this executor is no longer |
| * referenced and it has no threads. |
| */ |
| 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; |
| } |
| |
| /** |
| * 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 {@code corePoolSize < 0} |
| * @see #getCorePoolSize |
| */ |
| public void setCorePoolSize(int corePoolSize) { |
| if (corePoolSize < 0) |
| throw new IllegalArgumentException(); |
| int delta = corePoolSize - this.corePoolSize; |
| this.corePoolSize = corePoolSize; |
| if (workerCountOf(ctl.get()) > corePoolSize) |
| interruptIdleWorkers(); |
| else if (delta > 0) { |
| // We don't really know how many new threads are "needed". |
| // As a heuristic, prestart enough new workers (up to new |
| // core size) to handle the current number of tasks in |
| // queue, but stop if queue becomes empty while doing so. |
| int k = Math.min(delta, workQueue.size()); |
| while (k-- > 0 && addWorker(null, true)) { |
| if (workQueue.isEmpty()) |
| break; |
| } |
| } |
| } |
| |
| /** |
| * 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 {@code false} |
| * if all core threads have already been started. |
| * |
| * @return {@code true} if a thread was started |
| */ |
| public boolean prestartCoreThread() { |
| return workerCountOf(ctl.get()) < corePoolSize && |
| addWorker(null, true); |
| } |
| |
| /** |
| * 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 (addWorker(null, true)) |
| ++n; |
| return n; |
| } |
| |
| /** |
| * 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(); |
| this.maximumPoolSize = maximumPoolSize; |
| if (workerCountOf(ctl.get()) > maximumPoolSize) |
| interruptIdleWorkers(); |
| } |
| |
| /** |
| * 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 {@code time} argument |
| * @throws IllegalArgumentException if {@code time} less than zero or |
| * if {@code time} is zero and {@code allowsCoreThreadTimeOut} |
| * @see #getKeepAliveTime |
| */ |
| public void setKeepAliveTime(long time, TimeUnit unit) { |
| if (time < 0) |
| throw new IllegalArgumentException(); |
| long keepAliveTime = unit.toNanos(time); |
| long delta = keepAliveTime - this.keepAliveTime; |
| this.keepAliveTime = keepAliveTime; |
| if (delta < 0) |
| interruptIdleWorkers(); |
| } |
| |
| /** |
| * Returns the thread keep-alive time, which is the amount of time |
| * that 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); |
| } |
| |
| /* User-level queue utilities */ |
| |
| /** |
| * 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 {@code submit} might be |
| * converted into a form that maintains {@code Future} status. |
| * However, in such cases, method {@link #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) { |
| boolean removed = workQueue.remove(task); |
| tryTerminate(); // In case SHUTDOWN and now empty |
| return removed; |
| } |
| |
| /** |
| * 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() { |
| final BlockingQueue<Runnable> q = workQueue; |
| try { |
| Iterator<Runnable> it = q.iterator(); |
| while (it.hasNext()) { |
| Runnable r = it.next(); |
| if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
| it.remove(); |
| } |
| } catch (ConcurrentModificationException fallThrough) { |
| // Take slow path if we encounter interference during traversal. |
| // Make copy for traversal and call remove for cancelled entries. |
| // The slow path is more likely to be O(N*N). |
| for (Object r : q.toArray()) |
| if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
| q.remove(r); |
| } |
| |
| tryTerminate(); // In case SHUTDOWN and now empty |
| } |
| |
| /* Statistics */ |
| |
| /** |
| * Returns the current number of threads in the pool. |
| * |
| * @return the number of threads |
| */ |
| public int getPoolSize() { |
| final ReentrantLock mainLock = this.mainLock; |
| mainLock.lock(); |
| try { |
| // Remove rare and surprising possibility of |
| // isTerminated() && getPoolSize() > 0 |
| return runStateAtLeast(ctl.get(), TIDYING) ? 0 |
| : workers.size(); |
| } finally { |
| mainLock.unlock(); |
| } |
| } |
| |
| /** |
| * 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.isLocked()) |
| ++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 ever been |
| * scheduled for execution. Because the states of tasks and |
| * threads may change dynamically during computation, the returned |
| * value is only an approximation. |
| * |
| * @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.isLocked()) |
| ++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(); |
| } |
| } |
| |
| /* Extension hooks */ |
| |
| /** |
| * Method invoked prior to executing the given Runnable in the |
| * given thread. This method is invoked by thread {@code t} that |
| * will execute task {@code r}, 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 {@code super.beforeExecute} at the end of |
| * this method. |
| * |
| * @param t the thread that will run task {@code 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 {@code RuntimeException} |
| * or {@code Error} that caused execution to terminate abruptly. |
| * |
| * <p>This implementation does nothing, but may be customized in |
| * subclasses. Note: To properly nest multiple overridings, subclasses |
| * should generally invoke {@code super.afterExecute} at the |
| * beginning of this method. |
| * |
| * <p><b>Note:</b> When actions are enclosed in tasks (such as |
| * {@link FutureTask}) either explicitly or via methods such as |
| * {@code submit}, 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. If you would like to trap both kinds of |
| * failures in this method, you can further probe for such cases, |
| * as in this sample subclass that prints either the direct cause |
| * or the underlying exception if a task has been aborted: |
| * |
| * <pre> {@code |
| * class ExtendedExecutor extends ThreadPoolExecutor { |
| * // ... |
| * protected void afterExecute(Runnable r, Throwable t) { |
| * super.afterExecute(r, t); |
| * if (t == null && r instanceof Future<?>) { |
| * try { |
| * Object result = ((Future<?>) r).get(); |
| * } catch (CancellationException ce) { |
| * t = ce; |
| * } catch (ExecutionException ee) { |
| * t = ee.getCause(); |
| * } catch (InterruptedException ie) { |
| * Thread.currentThread().interrupt(); // ignore/reset |
| * } |
| * } |
| * if (t != null) |
| * System.out.println(t); |
| * } |
| * }}</pre> |
| * |
| * @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 |
| * {@code super.terminated} within this method. |
| */ |
| protected void terminated() { } |
| |
| /* Predefined RejectedExecutionHandlers */ |
| |
| /** |
| * A handler for rejected tasks that runs the rejected task |
| * directly in the calling thread of the {@code execute} method, |
| * unless the executor has been shut down, in which case the task |
| * is discarded. |
| */ |
| public static class CallerRunsPolicy implements RejectedExecutionHandler { |
| /** |
| * Creates a {@code CallerRunsPolicy}. |
| */ |
| 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 |
| * {@code RejectedExecutionException}. |
| */ |
| public static class AbortPolicy implements RejectedExecutionHandler { |
| /** |
| * Creates an {@code AbortPolicy}. |
| */ |
| 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 {@code DiscardPolicy}. |
| */ |
| 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 {@code execute}, unless the executor |
| * is shut down, in which case the task is discarded. |
| */ |
| public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
| /** |
| * Creates a {@code DiscardOldestPolicy} 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); |
| } |
| } |
| } |
| } |