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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.util.*; |
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|
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/** |
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* An {@link ExecutorService} that executes each submitted task on one |
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* of several pooled threads. |
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* |
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* <p>Thread pools address two different problems at the same time: |
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* they usually provide improved performance when executing large |
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* numbers of asynchronous tasks, due to reduced per-task invocation |
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* overhead, and they provide a means of bounding and managing the |
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* resources, including threads, consumed in executing a collection of |
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* tasks. |
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* |
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* <p>This class is very configurable and can be configured to create |
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* a new thread for each task, or even to execute tasks sequentially |
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* in a single thread, in addition to its most common configuration, |
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* which reuses a pool of threads. |
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* |
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* <p>To be useful across a wide range of contexts, this class |
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* provides many adjustable parameters and extensibility hooks. |
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* However, programmers are urged to use the more convenient factory |
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* methods <tt>newCachedThreadPool</tt> (unbounded thread pool, with |
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* automatic thread reclamation), <tt>newFixedThreadPool</tt> (fixed |
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* size thread pool), <tt>newSingleThreadPoolExecutor</tt> (single |
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* background thread for execution of tasks), and |
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* <tt>newThreadPerTaskExeceutor</tt> (execute each task in a new |
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* thread), that preconfigure settings for the most common usage |
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* scenarios. |
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* |
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* <p>This class also maintain some basic statistics, such as the |
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* number of completed tasks, that may be useful for monitoring and |
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* tuning executors. |
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* |
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* <h3>Tuning guide</h3> |
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* <dl> |
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* |
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* <dt>Core and maximum pool size</dt> |
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* |
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* <dd>A ThreadPoolExecutor will automatically adjust the pool size |
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* according to the bounds set by corePoolSize and maximumPoolSize. |
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* When a new task is submitted, and fewer than corePoolSize threads |
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* are running, a new thread is created to handle the request, even if |
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* other worker threads are idle. If there are more than the |
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* corePoolSize but less than maximumPoolSize threads running, a new |
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* thread will be created only if the queue is full. By setting |
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* corePoolSize and maximumPoolSize the same, you create a fixed-size |
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* thread pool.</dd> |
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* |
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* <dt>Keep-alive</dt> |
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* |
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* <dd>The keepAliveTime determines what happens to idle threads. If |
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* the pool currently has more than the core number of threads, excess |
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* threads will be terminated if they have been idle for more than the |
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* keepAliveTime.</dd> |
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* |
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* <dt>Queueing</dt> |
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* |
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* <dd>You are free to specify the queuing mechanism used to handle |
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* submitted tasks. The newCachedThreadPool factory method uses |
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* queueless synchronous channels to to hand off work to threads. |
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* This is a safe, conservative policy that avoids lockups when |
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* handling sets of requests that might have internal dependencies. |
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* The newFixedThreadPool factory method uses a LinkedBlockingQueue, |
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* which will cause new tasks to be queued in cases where all |
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* MaximumPoolSize threads are busy. Queues are sometimes appropriate |
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* when each task is completely independent of others, so tasks cannot |
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* affect each others execution. For example, in an http server. When |
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* given a choice, this pool always prefers adding a new thread rather |
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* than queueing if there are currently fewer than the current |
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* getCorePoolSize threads running, but otherwise always prefers |
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* queuing a request rather than adding a new thread. |
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* |
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* <p>While queuing can be useful in smoothing out transient bursts of |
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* requests, especially in socket-based services, it is not very well |
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* behaved when commands continue to arrive on average faster than |
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* they can be processed. |
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* |
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* Queue sizes and maximum pool sizes can often be traded off for each |
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* other. Using large queues and small pools minimizes CPU usage, OS |
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* resources, and context-switching overhead, but can lead to |
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* artifically low throughput. If tasks frequently block (for example |
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* if they are I/O bound), a JVM and underlying OS may be able to |
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* schedule time for more threads than you otherwise allow. Use of |
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* small queues or queueless handoffs generally requires larger pool |
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* sizes, which keeps CPUs busier but may encounter unacceptable |
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* scheduling overhead, which also decreases throughput. |
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* </dd> |
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* |
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* <dt>Creating new threads</dt> |
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* |
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* <dd>New threads are created using a ThreadFactory. By default, |
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* threads are created simply with the new Thread(Runnable) |
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* constructor, but by supplying a different ThreadFactory, you can |
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* alter the thread's name, thread group, priority, daemon status, |
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* etc. </dd> |
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* |
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* <dt>Before and after intercepts</dt> |
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* |
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* <dd>This class has overridable methods that which are called before |
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* and after execution of each task. These can be used to manipulate |
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* the execution environment (for example, reinitializing |
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* ThreadLocals), gather statistics, or perform logging. </dd> |
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* |
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* <dt>Blocked execution</dt> |
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* |
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* <dd>There are a number of factors which can bound the number of |
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* tasks which can execute at once, including the maximum pool size |
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* and the queuing mechanism used. If the executor determines that a |
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* task cannot be executed because it has been refused by the queue |
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* and no threads are available, or because the executor has been shut |
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* down, the RejectedExecutionHandler's rejectedExecution method is |
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* invoked. </dd> |
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* |
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* <dt>Termination</dt> |
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* |
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* <dd>ThreadPoolExecutor supports two shutdown options, immediate and |
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* graceful. In an immediate shutdown, any threads currently |
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* executing are interrupted, and any tasks not yet begun are returned |
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* from the shutdownNow call. In a graceful shutdown, all queued |
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* tasks are allowed to run, but new tasks may not be submitted. |
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* </dd> |
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* |
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* </dl> |
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* |
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* @since 1.5 |
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* @see RejectedExecutionHandler |
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* @see Executors |
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* @see ThreadFactory |
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* |
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* @spec JSR-166 |
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* @revised $Date: 2003/05/28 23:00:40 $ |
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* @editor $Author: dl $ |
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* |
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*/ |
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public class ThreadPoolExecutor implements ExecutorService { |
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/** |
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* Queue used for holding tasks and handing off to worker threads. |
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*/ |
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private final BlockingQueue<Runnable> workQueue; |
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|
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/** |
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* Lock held on updates to poolSize, corePoolSize, maximumPoolSize, and |
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* workers set. |
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*/ |
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private final ReentrantLock mainLock = new ReentrantLock(); |
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|
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/** |
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* Wait condition to support awaitTermination |
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*/ |
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private final Condition termination = mainLock.newCondition(); |
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|
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/** |
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* Set containing all worker threads in pool. |
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*/ |
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private final Set<Worker> workers = new HashSet<Worker>(); |
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|
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/** |
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* Timeout in nanosecods for idle threads waiting for work. |
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* Threads use this timeout only when there are more than |
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* corePoolSize present. Otherwise they wait forever for new work. |
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*/ |
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private volatile long keepAliveTime; |
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|
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/** |
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* Core pool size, updated only while holding mainLock, |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int corePoolSize; |
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|
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/** |
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* Maximum pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int maximumPoolSize; |
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|
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/** |
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* Current pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int poolSize; |
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|
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/** |
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* Shutdown status, becomes (and remains) nonzero when shutdown called. |
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*/ |
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private volatile int shutdownStatus; |
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|
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// Special values for status |
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private static final int NOT_SHUTDOWN = 0; |
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private static final int SHUTDOWN_WHEN_IDLE = 1; |
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private static final int SHUTDOWN_NOW = 2; |
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|
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/** |
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* Latch that becomes true when all threads terminate after shutdown. |
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*/ |
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private volatile boolean isTerminated; |
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|
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/** |
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* Handler called when saturated or shutdown in execute. |
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*/ |
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private volatile RejectedExecutionHandler handler = defaultHandler; |
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|
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/** |
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* Factory for new threads. |
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*/ |
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private volatile ThreadFactory threadFactory = defaultThreadFactory; |
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|
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/** |
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* Tracks largest attained pool size. |
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*/ |
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private int largestPoolSize; |
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|
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/** |
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* Counter for completed tasks. Updated only on termination of |
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* worker threads. |
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*/ |
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private long completedTaskCount; |
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|
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private static final ThreadFactory defaultThreadFactory = |
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new ThreadFactory() { |
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public Thread newThread(Runnable r) { |
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return new Thread(r); |
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} |
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}; |
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|
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private static final RejectedExecutionHandler defaultHandler = |
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new AbortPolicy(); |
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|
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/** |
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* Create and return a new thread running firstTask as its first |
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* task. Call only while holding mainLock |
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*/ |
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private Thread addThread(Runnable firstTask) { |
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Worker w = new Worker(firstTask); |
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Thread t = threadFactory.newThread(w); |
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w.thread = t; |
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workers.add(w); |
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int nt = ++poolSize; |
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if (nt > largestPoolSize) |
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largestPoolSize = nt; |
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return t; |
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} |
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|
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/** |
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* Create and start a new thread running firstTask as its first |
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* task, only if less than corePoolSize threads are running. |
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* @return true if successful. |
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*/ |
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boolean addIfUnderCorePoolSize(Runnable task) { |
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Thread t = null; |
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mainLock.lock(); |
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try { |
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if (poolSize < corePoolSize) |
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t = addThread(task); |
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} |
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finally { |
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mainLock.unlock(); |
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} |
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if (t == null) |
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return false; |
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t.start(); |
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return true; |
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} |
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|
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/** |
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* Create and start a new thread only if less than maximumPoolSize |
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* threads are running. The new thread runs as its first task the |
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* next task in queue, or if there is none, the given task. |
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* @return null on failure, else the first task to be run by new thread. |
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*/ |
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private Runnable addIfUnderMaximumPoolSize(Runnable task) { |
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Thread t = null; |
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Runnable next = null; |
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mainLock.lock(); |
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try { |
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if (poolSize < maximumPoolSize) { |
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next = workQueue.poll(); |
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if (next == null) |
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next = task; |
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t = addThread(next); |
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} |
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} |
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finally { |
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mainLock.unlock(); |
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} |
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if (t == null) |
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return null; |
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t.start(); |
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return next; |
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} |
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|
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|
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/** |
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* Get the next task for a worker thread to run. |
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*/ |
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private Runnable getTask() throws InterruptedException { |
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for (;;) { |
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int stat = shutdownStatus; |
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if (stat == SHUTDOWN_NOW) |
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return null; |
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long timeout = keepAliveTime; |
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if (timeout <= 0) // must die immediately for 0 timeout |
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return null; |
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if (stat == SHUTDOWN_WHEN_IDLE) // help drain queue before dying |
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return workQueue.poll(); |
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if (poolSize <= corePoolSize) // untimed wait if core |
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return workQueue.take(); |
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Runnable task = workQueue.poll(timeout, TimeUnit.NANOSECONDS); |
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if (task != null) |
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return task; |
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if (poolSize > corePoolSize) // timed out |
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return null; |
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// else, after timeout, pool shrank so shouldn't die, so retry |
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} |
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} |
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|
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/** |
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* Perform bookkeeping for a terminated worker thread. |
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*/ |
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private void workerDone(Worker w) { |
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boolean allDone = false; |
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mainLock.lock(); |
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try { |
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completedTaskCount += w.completedTasks; |
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workers.remove(w); |
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|
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if (--poolSize > 0) |
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return; |
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|
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// If this was last thread, deal with potential shutdown |
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int stat = shutdownStatus; |
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|
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// If there are queued tasks but no threads, create replacement. |
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if (stat != SHUTDOWN_NOW) { |
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Runnable r = workQueue.poll(); |
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if (r != null) { |
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addThread(r).start(); |
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return; |
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} |
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} |
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|
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// if no tasks and not shutdown, can exit without replacement |
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if (stat == NOT_SHUTDOWN) |
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return; |
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|
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allDone = true; |
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isTerminated = true; |
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termination.signalAll(); |
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} |
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finally { |
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mainLock.unlock(); |
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} |
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|
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if (allDone) // call outside lock |
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terminated(); |
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} |
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|
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/** |
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* Worker threads |
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*/ |
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private class Worker implements Runnable { |
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|
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/** |
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* The runLock is acquired and released surrounding each task |
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* execution. It mainly protects against interrupts that are |
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* intended to cancel the worker thread from instead |
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* interrupting the task being run. |
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*/ |
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private final ReentrantLock runLock = new ReentrantLock(); |
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|
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/** |
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* Initial task to run before entering run loop |
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*/ |
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private Runnable firstTask; |
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|
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/** |
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* Per thread completed task counter; accumulated |
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* into completedTaskCount upon termination. |
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*/ |
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volatile long completedTasks; |
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|
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/** |
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* Thread this worker is running in. Acts as a final field, |
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* but cannot be set until thread is created. |
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*/ |
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Thread thread; |
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|
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Worker(Runnable firstTask) { |
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this.firstTask = firstTask; |
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} |
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|
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boolean isActive() { |
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return runLock.isLocked(); |
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} |
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|
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/** |
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* Interrupt thread if not running a task |
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*/ |
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void interruptIfIdle() { |
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if (runLock.tryLock()) { |
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try { |
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thread.interrupt(); |
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} |
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finally { |
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runLock.unlock(); |
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} |
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} |
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} |
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|
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/** |
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* Cause thread to die even if running a task. |
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*/ |
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void interruptNow() { |
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thread.interrupt(); |
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} |
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|
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/** |
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* Run a single task between before/after methods. |
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*/ |
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private void runTask(Runnable task) { |
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runLock.lock(); |
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try { |
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// Abort now if immediate cancel. Otherwise, we have |
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// committed to run this task. |
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if (shutdownStatus == SHUTDOWN_NOW) |
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return; |
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|
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Thread.interrupted(); // clear interrupt status on entry |
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boolean ran = false; |
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beforeExecute(thread, task); |
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try { |
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task.run(); |
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ran = true; |
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afterExecute(task, null); |
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++completedTasks; |
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} |
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catch(RuntimeException ex) { |
448 |
if (!ran) |
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afterExecute(task, ex); |
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// else the exception occurred within |
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// afterExecute itself in which case we don't |
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// want to call it again. |
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throw ex; |
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} |
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} |
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finally { |
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runLock.unlock(); |
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} |
459 |
} |
460 |
|
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/** |
462 |
* Main run loop |
463 |
*/ |
464 |
public void run() { |
465 |
try { |
466 |
for (;;) { |
467 |
Runnable task; |
468 |
if (firstTask != null) { |
469 |
task = firstTask; |
470 |
firstTask = null; |
471 |
} |
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else { |
473 |
task = getTask(); |
474 |
if (task == null) |
475 |
break; |
476 |
} |
477 |
runTask(task); |
478 |
task = null; // unnecessary but can help GC |
479 |
} |
480 |
} |
481 |
catch(InterruptedException ie) { |
482 |
// fall through |
483 |
} |
484 |
finally { |
485 |
workerDone(this); |
486 |
} |
487 |
} |
488 |
} |
489 |
|
490 |
private static class DequeuableFutureTask<V> extends FutureTask<V> { |
491 |
private final ThreadPoolExecutor tpe; |
492 |
public DequeuableFutureTask(Callable<V> callable, ThreadPoolExecutor tpe) { |
493 |
super(callable); |
494 |
this.tpe = tpe; |
495 |
} |
496 |
|
497 |
public DequeuableFutureTask(final Runnable runnable, final V result, ThreadPoolExecutor tpe) { |
498 |
super(runnable, result); |
499 |
this.tpe = tpe; |
500 |
} |
501 |
|
502 |
public boolean cancel(boolean mayInterruptIfRunning) { |
503 |
if (!isDone()) |
504 |
tpe.dequeue(this); |
505 |
return super.cancel(mayInterruptIfRunning); |
506 |
} |
507 |
} |
508 |
|
509 |
/** |
510 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
511 |
* parameters. It may be more convenient to use one of the factory |
512 |
* methods instead of this general purpose constructor. |
513 |
* |
514 |
* @param corePoolSize the number of threads to keep in the |
515 |
* pool, even if they are idle. |
516 |
* @param maximumPoolSize the maximum number of threads to allow in the |
517 |
* pool. |
518 |
* @param keepAliveTime when the number of threads is greater than |
519 |
* the core, this is the maximum time that excess idle threads |
520 |
* will wait for new tasks before terminating. |
521 |
* @param unit the time unit for the keepAliveTime |
522 |
* argument. |
523 |
* @param workQueue the queue to use for holding tasks before the |
524 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
525 |
* tasks submitted by the <tt>execute</tt> method. |
526 |
* @throws IllegalArgumentException if corePoolSize, or |
527 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
528 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
529 |
* @throws NullPointerException if <tt>workQueue</tt> is null |
530 |
*/ |
531 |
public ThreadPoolExecutor(int corePoolSize, |
532 |
int maximumPoolSize, |
533 |
long keepAliveTime, |
534 |
TimeUnit unit, |
535 |
BlockingQueue<Runnable> workQueue) { |
536 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
537 |
defaultThreadFactory, defaultHandler); |
538 |
} |
539 |
|
540 |
/** |
541 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
542 |
* parameters. |
543 |
* |
544 |
* @param corePoolSize the number of threads to keep in the |
545 |
* pool, even if they are idle. |
546 |
* @param maximumPoolSize the maximum number of threads to allow in the |
547 |
* pool. |
548 |
* @param keepAliveTime when the number of threads is greater than |
549 |
* the core, this is the maximum time that excess idle threads |
550 |
* will wait for new tasks before terminating. |
551 |
* @param unit the time unit for the keepAliveTime |
552 |
* argument. |
553 |
* @param workQueue the queue to use for holding tasks before the |
554 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
555 |
* tasks submitted by the <tt>execute</tt> method. |
556 |
* @param threadFactory the factory to use when the executor |
557 |
* creates a new thread. |
558 |
* @throws IllegalArgumentException if corePoolSize, or |
559 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
560 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
561 |
* @throws NullPointerException if <tt>workQueue</tt> |
562 |
* or <tt>threadFactory</tt> are null. |
563 |
*/ |
564 |
public ThreadPoolExecutor(int corePoolSize, |
565 |
int maximumPoolSize, |
566 |
long keepAliveTime, |
567 |
TimeUnit unit, |
568 |
BlockingQueue<Runnable> workQueue, |
569 |
ThreadFactory threadFactory) { |
570 |
|
571 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
572 |
threadFactory, defaultHandler); |
573 |
} |
574 |
|
575 |
/** |
576 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
577 |
* parameters. |
578 |
* |
579 |
* @param corePoolSize the number of threads to keep in the |
580 |
* pool, even if they are idle. |
581 |
* @param maximumPoolSize the maximum number of threads to allow in the |
582 |
* pool. |
583 |
* @param keepAliveTime when the number of threads is greater than |
584 |
* the core, this is the maximum time that excess idle threads |
585 |
* will wait for new tasks before terminating. |
586 |
* @param unit the time unit for the keepAliveTime |
587 |
* argument. |
588 |
* @param workQueue the queue to use for holding tasks before the |
589 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
590 |
* tasks submitted by the <tt>execute</tt> method. |
591 |
* @param handler the handler to use when execution is blocked |
592 |
* because the thread bounds and queue capacities are reached. |
593 |
* @throws IllegalArgumentException if corePoolSize, or |
594 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
595 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
596 |
* @throws NullPointerException if <tt>workQueue</tt> |
597 |
* or <tt>handler</tt> are null. |
598 |
*/ |
599 |
public ThreadPoolExecutor(int corePoolSize, |
600 |
int maximumPoolSize, |
601 |
long keepAliveTime, |
602 |
TimeUnit unit, |
603 |
BlockingQueue<Runnable> workQueue, |
604 |
RejectedExecutionHandler handler) { |
605 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
606 |
defaultThreadFactory, handler); |
607 |
} |
608 |
|
609 |
/** |
610 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
611 |
* parameters. |
612 |
* |
613 |
* @param corePoolSize the number of threads to keep in the |
614 |
* pool, even if they are idle. |
615 |
* @param maximumPoolSize the maximum number of threads to allow in the |
616 |
* pool. |
617 |
* @param keepAliveTime when the number of threads is greater than |
618 |
* the core, this is the maximum time that excess idle threads |
619 |
* will wait for new tasks before terminating. |
620 |
* @param unit the time unit for the keepAliveTime |
621 |
* argument. |
622 |
* @param workQueue the queue to use for holding tasks before the |
623 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
624 |
* tasks submitted by the <tt>execute</tt> method. |
625 |
* @param threadFactory the factory to use when the executor |
626 |
* creates a new thread. |
627 |
* @param handler the handler to use when execution is blocked |
628 |
* because the thread bounds and queue capacities are reached. |
629 |
* @throws IllegalArgumentException if corePoolSize, or |
630 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
631 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
632 |
* @throws NullPointerException if <tt>workQueue</tt> |
633 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
634 |
*/ |
635 |
public ThreadPoolExecutor(int corePoolSize, |
636 |
int maximumPoolSize, |
637 |
long keepAliveTime, |
638 |
TimeUnit unit, |
639 |
BlockingQueue<Runnable> workQueue, |
640 |
ThreadFactory threadFactory, |
641 |
RejectedExecutionHandler handler) { |
642 |
if (corePoolSize < 0 || |
643 |
maximumPoolSize <= 0 || |
644 |
maximumPoolSize < corePoolSize || |
645 |
keepAliveTime < 0) |
646 |
throw new IllegalArgumentException(); |
647 |
if (workQueue == null || threadFactory == null || handler == null) |
648 |
throw new NullPointerException(); |
649 |
this.corePoolSize = corePoolSize; |
650 |
this.maximumPoolSize = maximumPoolSize; |
651 |
this.workQueue = workQueue; |
652 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
653 |
this.threadFactory = threadFactory; |
654 |
this.handler = handler; |
655 |
} |
656 |
|
657 |
|
658 |
/** |
659 |
* Executes the given task sometime in the future. The task |
660 |
* may execute in a new thread or in an existing pooled thread. |
661 |
* |
662 |
* If the task cannot be submitted for execution, either because this |
663 |
* executor has been shutdown or because its capacity has been reached, |
664 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
665 |
* |
666 |
* @param command the task to execute |
667 |
* @throws RejectedExecutionException at discretion of |
668 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted for execution |
669 |
*/ |
670 |
public void execute(Runnable command) { |
671 |
for (;;) { |
672 |
if (shutdownStatus != NOT_SHUTDOWN) { |
673 |
handler.rejectedExecution(command, this); |
674 |
return; |
675 |
} |
676 |
if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) |
677 |
return; |
678 |
if (workQueue.offer(command)) |
679 |
return; |
680 |
Runnable r = addIfUnderMaximumPoolSize(command); |
681 |
if (r == command) |
682 |
return; |
683 |
if (r == null) { |
684 |
handler.rejectedExecution(command, this); |
685 |
return; |
686 |
} |
687 |
// else retry |
688 |
} |
689 |
} |
690 |
|
691 |
public <T> FutureTask<T> executeAsFuture(Callable<T> task) { |
692 |
FutureTask<T> future = new DequeuableFutureTask<T>(task, this); |
693 |
execute(future); |
694 |
return future; |
695 |
} |
696 |
|
697 |
public <T> FutureTask<T> executeAsFuture(Runnable task, T returnValue) { |
698 |
FutureTask<T> future = new DequeuableFutureTask<T>(task, returnValue, this); |
699 |
execute(future); |
700 |
return future; |
701 |
} |
702 |
|
703 |
|
704 |
|
705 |
public void shutdown() { |
706 |
mainLock.lock(); |
707 |
try { |
708 |
if (shutdownStatus == NOT_SHUTDOWN) // don't override shutdownNow |
709 |
shutdownStatus = SHUTDOWN_WHEN_IDLE; |
710 |
|
711 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
712 |
it.next().interruptIfIdle(); |
713 |
} |
714 |
finally { |
715 |
mainLock.unlock(); |
716 |
} |
717 |
} |
718 |
|
719 |
public List shutdownNow() { |
720 |
mainLock.lock(); |
721 |
try { |
722 |
shutdownStatus = SHUTDOWN_NOW; |
723 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
724 |
it.next().interruptNow(); |
725 |
} |
726 |
finally { |
727 |
mainLock.unlock(); |
728 |
} |
729 |
return Arrays.asList(workQueue.toArray()); |
730 |
} |
731 |
|
732 |
public boolean isShutdown() { |
733 |
return shutdownStatus != NOT_SHUTDOWN; |
734 |
} |
735 |
|
736 |
public boolean isTerminated() { |
737 |
return isTerminated; |
738 |
} |
739 |
|
740 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
741 |
throws InterruptedException { |
742 |
mainLock.lock(); |
743 |
try { |
744 |
return termination.await(timeout, unit); |
745 |
} |
746 |
finally { |
747 |
mainLock.unlock(); |
748 |
} |
749 |
} |
750 |
|
751 |
/** |
752 |
* Sets the thread factory used to create new threads. |
753 |
* |
754 |
* @param threadFactory the new thread factory |
755 |
*/ |
756 |
public void setThreadFactory(ThreadFactory threadFactory) { |
757 |
this.threadFactory = threadFactory; |
758 |
} |
759 |
|
760 |
/** |
761 |
* Returns the thread factory used to create new threads. |
762 |
* |
763 |
* @return the current thread factory |
764 |
*/ |
765 |
public ThreadFactory getThreadFactory() { |
766 |
return threadFactory; |
767 |
} |
768 |
|
769 |
/** |
770 |
* Sets a new handler for unexecutable tasks. |
771 |
* |
772 |
* @param handler the new handler |
773 |
*/ |
774 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
775 |
this.handler = handler; |
776 |
} |
777 |
|
778 |
/** |
779 |
* Returns the current handler for unexecutable tasks. |
780 |
* |
781 |
* @return the current handler |
782 |
*/ |
783 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
784 |
return handler; |
785 |
} |
786 |
|
787 |
/** |
788 |
* Returns the task queue used by this executor. Note that |
789 |
* this queue may be in active use. Retrieveing the task queue |
790 |
* does not prevent queued tasks from executing. |
791 |
* |
792 |
* @return the task queue |
793 |
*/ |
794 |
public BlockingQueue<Runnable> getQueue() { |
795 |
return workQueue; |
796 |
} |
797 |
|
798 |
/** |
799 |
* Removes this task from internal queue if it is present, thus |
800 |
* causing it not to be run if it has not already started. This |
801 |
* method may be useful as one part of a cancellation scheme. |
802 |
* |
803 |
* #return true if the task was removed |
804 |
*/ |
805 |
public boolean dequeue(Runnable task) { |
806 |
return getQueue().remove(task); |
807 |
} |
808 |
|
809 |
|
810 |
/** |
811 |
* Sets the core number of threads. This overrides any value set |
812 |
* in the constructor. If the new value is smaller than the |
813 |
* current value, excess existing threads will be terminated when |
814 |
* they next become idle. |
815 |
* |
816 |
* @param corePoolSize the new core size |
817 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> less than zero |
818 |
*/ |
819 |
public void setCorePoolSize(int corePoolSize) { |
820 |
if (corePoolSize < 0) |
821 |
throw new IllegalArgumentException(); |
822 |
mainLock.lock(); |
823 |
try { |
824 |
int extra = this.corePoolSize - corePoolSize; |
825 |
this.corePoolSize = corePoolSize; |
826 |
if (extra > 0 && poolSize > corePoolSize) { |
827 |
Iterator<Worker> it = workers.iterator(); |
828 |
while (it.hasNext() && |
829 |
extra > 0 && |
830 |
poolSize > corePoolSize && |
831 |
workQueue.remainingCapacity() == 0) { |
832 |
it.next().interruptIfIdle(); |
833 |
--extra; |
834 |
} |
835 |
} |
836 |
|
837 |
} |
838 |
finally { |
839 |
mainLock.unlock(); |
840 |
} |
841 |
} |
842 |
|
843 |
/** |
844 |
* Returns the core number of threads. |
845 |
* |
846 |
* @return the core number of threads |
847 |
*/ |
848 |
public int getCorePoolSize() { |
849 |
return corePoolSize; |
850 |
} |
851 |
|
852 |
/** |
853 |
* Sets the maximum allowed number of threads. This overrides any |
854 |
* value set in the constructor. If the new value is smaller than |
855 |
* the current value, excess existing threads will be |
856 |
* terminated when they next become idle. |
857 |
* |
858 |
* @param maximumPoolSize the new maximum |
859 |
* @throws IllegalArgumentException if maximumPoolSize less than zero or |
860 |
* the {@link #getCorePoolSize core pool size} |
861 |
*/ |
862 |
public void setMaximumPoolSize(int maximumPoolSize) { |
863 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
864 |
throw new IllegalArgumentException(); |
865 |
mainLock.lock(); |
866 |
try { |
867 |
int extra = this.maximumPoolSize - maximumPoolSize; |
868 |
this.maximumPoolSize = maximumPoolSize; |
869 |
if (extra > 0 && poolSize > maximumPoolSize) { |
870 |
Iterator<Worker> it = workers.iterator(); |
871 |
while (it.hasNext() && |
872 |
extra > 0 && |
873 |
poolSize > maximumPoolSize) { |
874 |
it.next().interruptIfIdle(); |
875 |
--extra; |
876 |
} |
877 |
} |
878 |
} |
879 |
finally { |
880 |
mainLock.unlock(); |
881 |
} |
882 |
} |
883 |
|
884 |
/** |
885 |
* Returns the maximum allowed number of threads. |
886 |
* |
887 |
* @return the maximum allowed number of threads |
888 |
*/ |
889 |
public int getMaximumPoolSize() { |
890 |
return maximumPoolSize; |
891 |
} |
892 |
|
893 |
/** |
894 |
* Sets the time limit for which threads may remain idle before |
895 |
* being terminated. If there are more than the core number of |
896 |
* threads currently in the pool, after waiting this amount of |
897 |
* time without processing a task, excess threads will be |
898 |
* terminated. This overrides any value set in the constructor. |
899 |
* @param time the time to wait. A time value of zero will cause |
900 |
* excess threads to terminate immediately after executing tasks. |
901 |
* @param unit the time unit of the time argument |
902 |
* @throws IllegalArgumentException if msecs less than zero |
903 |
*/ |
904 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
905 |
if (time < 0) |
906 |
throw new IllegalArgumentException(); |
907 |
this.keepAliveTime = unit.toNanos(time); |
908 |
} |
909 |
|
910 |
/** |
911 |
* Returns the thread keep-alive time, which is the amount of time |
912 |
* which threads in excess of the core pool size may remain |
913 |
* idle before being terminated. |
914 |
* |
915 |
* @param unit the desired time unit of the result |
916 |
* @return the time limit |
917 |
*/ |
918 |
public long getKeepAliveTime(TimeUnit unit) { |
919 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
920 |
} |
921 |
|
922 |
/* Statistics */ |
923 |
|
924 |
/** |
925 |
* Returns the current number of threads in the pool. |
926 |
* |
927 |
* @return the number of threads |
928 |
*/ |
929 |
public int getPoolSize() { |
930 |
return poolSize; |
931 |
} |
932 |
|
933 |
/** |
934 |
* Returns the approximate number of threads that are actively |
935 |
* executing tasks. |
936 |
* |
937 |
* @return the number of threads |
938 |
*/ |
939 |
public int getActiveCount() { |
940 |
mainLock.lock(); |
941 |
try { |
942 |
int n = 0; |
943 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
944 |
if (it.next().isActive()) |
945 |
++n; |
946 |
} |
947 |
return n; |
948 |
} |
949 |
finally { |
950 |
mainLock.unlock(); |
951 |
} |
952 |
} |
953 |
|
954 |
/** |
955 |
* Returns the largest number of threads that have ever |
956 |
* simultaneously been in the pool. |
957 |
* |
958 |
* @return the number of threads |
959 |
*/ |
960 |
public int getLargestPoolSize() { |
961 |
mainLock.lock(); |
962 |
try { |
963 |
return largestPoolSize; |
964 |
} |
965 |
finally { |
966 |
mainLock.unlock(); |
967 |
} |
968 |
} |
969 |
|
970 |
/** |
971 |
* Returns the approximate total number of tasks that have been |
972 |
* scheduled for execution. Because the states of tasks and |
973 |
* threads may change dynamically during computation, the returned |
974 |
* value is only an approximation. |
975 |
* |
976 |
* @return the number of tasks |
977 |
*/ |
978 |
public long getTaskCount() { |
979 |
mainLock.lock(); |
980 |
try { |
981 |
long n = completedTaskCount; |
982 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
983 |
Worker w = it.next(); |
984 |
n += w.completedTasks; |
985 |
if (w.isActive()) |
986 |
++n; |
987 |
} |
988 |
return n + workQueue.size(); |
989 |
} |
990 |
finally { |
991 |
mainLock.unlock(); |
992 |
} |
993 |
} |
994 |
|
995 |
/** |
996 |
* Returns the approximate total number of tasks that have |
997 |
* completed execution. Because the states of tasks and threads |
998 |
* may change dynamically during computation, the returned value |
999 |
* is only an approximation. |
1000 |
* |
1001 |
* @return the number of tasks |
1002 |
*/ |
1003 |
public long getCompletedTaskCount() { |
1004 |
mainLock.lock(); |
1005 |
try { |
1006 |
long n = completedTaskCount; |
1007 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
1008 |
n += it.next().completedTasks; |
1009 |
return n; |
1010 |
} |
1011 |
finally { |
1012 |
mainLock.unlock(); |
1013 |
} |
1014 |
} |
1015 |
|
1016 |
/** |
1017 |
* Method invoked prior to executing the given Runnable in given |
1018 |
* thread. This method may be used to re-initialize ThreadLocals, |
1019 |
* or to perform logging. |
1020 |
* |
1021 |
* @param t the thread that will run task r. |
1022 |
* @param r the task that will be executed. |
1023 |
*/ |
1024 |
protected void beforeExecute(Thread t, Runnable r) { } |
1025 |
|
1026 |
/** |
1027 |
* Method invoked upon completion of execution of the given |
1028 |
* Runnable. If non-null, the Throwable is the uncaught exception |
1029 |
* that caused execution to terminate abruptly. |
1030 |
* |
1031 |
* @param r the runnable that has completed. |
1032 |
* @param t the exception that cause termination, or null if |
1033 |
* execution completed normally. |
1034 |
*/ |
1035 |
protected void afterExecute(Runnable r, Throwable t) { } |
1036 |
|
1037 |
/** |
1038 |
* Method invoked when the Executor has terminated. Default |
1039 |
* implementation does nothing. |
1040 |
*/ |
1041 |
protected void terminated() { } |
1042 |
|
1043 |
/** |
1044 |
* A handler for unexecutable tasks that runs these tasks directly in the |
1045 |
* calling thread of the <tt>execute</tt> method. This is the default |
1046 |
* <tt>RejectedExecutionHandler</tt>. |
1047 |
*/ |
1048 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1049 |
|
1050 |
/** |
1051 |
* Constructs a <tt>CallerRunsPolicy</tt>. |
1052 |
*/ |
1053 |
public CallerRunsPolicy() { } |
1054 |
|
1055 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1056 |
if (!e.isShutdown()) { |
1057 |
r.run(); |
1058 |
} |
1059 |
} |
1060 |
} |
1061 |
|
1062 |
/** |
1063 |
* A handler for unexecutable tasks that throws a <tt>RejectedExecutionException</tt>. |
1064 |
*/ |
1065 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1066 |
|
1067 |
/** |
1068 |
* Constructs a <tt>AbortPolicy</tt>. |
1069 |
*/ |
1070 |
public AbortPolicy() { } |
1071 |
|
1072 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1073 |
throw new RejectedExecutionException(); |
1074 |
} |
1075 |
} |
1076 |
|
1077 |
/** |
1078 |
* A handler for unexecutable tasks that waits until the task can be |
1079 |
* submitted for execution. |
1080 |
*/ |
1081 |
public static class WaitPolicy implements RejectedExecutionHandler { |
1082 |
/** |
1083 |
* Constructs a <tt>WaitPolicy</tt>. |
1084 |
*/ |
1085 |
public WaitPolicy() { } |
1086 |
|
1087 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1088 |
if (!e.isShutdown()) { |
1089 |
try { |
1090 |
e.getQueue().put(r); |
1091 |
} |
1092 |
catch (InterruptedException ie) { |
1093 |
Thread.currentThread().interrupt(); |
1094 |
throw new RejectedExecutionException(ie); |
1095 |
} |
1096 |
} |
1097 |
} |
1098 |
} |
1099 |
|
1100 |
/** |
1101 |
* A handler for unexecutable tasks that silently discards these tasks. |
1102 |
*/ |
1103 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1104 |
|
1105 |
/** |
1106 |
* Constructs <tt>DiscardPolicy</tt>. |
1107 |
*/ |
1108 |
public DiscardPolicy() { } |
1109 |
|
1110 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1111 |
} |
1112 |
} |
1113 |
|
1114 |
/** |
1115 |
* A handler for unexecutable tasks that discards the oldest unhandled request. |
1116 |
*/ |
1117 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1118 |
/** |
1119 |
* Constructs a <tt>DiscardOldestPolicy</tt> for the given executor. |
1120 |
*/ |
1121 |
public DiscardOldestPolicy() { } |
1122 |
|
1123 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1124 |
if (!e.isShutdown()) { |
1125 |
e.getQueue().poll(); |
1126 |
e.execute(r); |
1127 |
} |
1128 |
} |
1129 |
} |
1130 |
} |