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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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import java.util.concurrent.locks.*; |
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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. A good default is to use queueless synchronous |
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* channels to to hand off work to threads. This is a safe, |
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* conservative policy that avoids lockups when handling sets of |
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* requests that might have internal dependencies. Using an unbounded |
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* queue (for example a LinkedBlockingQueue) which will cause new |
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* tasks to be queued in cases where all corePoolSize threads are |
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* busy, so no more that corePoolSize threads will be craated. This |
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* may be appropriate when each task is completely independent of |
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* others, so tasks cannot affect each others execution. For example, |
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* in an http server. When given a choice, this pool always prefers |
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* adding a new thread rather than queueing if there are currently |
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* fewer than the current getCorePoolSize threads running, but |
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* otherwise always prefers queuing a request rather than adding a new |
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* 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: 2003/08/09 19:55:30 $ |
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* @editor $Author: dl $ |
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* @author Doug Lea |
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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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* Lifecycle state |
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*/ |
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private volatile int runState; |
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|
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// Special values for runState |
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/** Normal, not-shutdown mode */ |
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private static final int RUNNING = 0; |
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/** Controlled shutdown mode */ |
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private static final int SHUTDOWN = 1; |
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/** Immediate shutdown mode */ |
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private static final int STOP = 2; |
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/** Final state */ |
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private static final int TERMINATED = 3; |
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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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/** |
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* The default thread factory |
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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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/** |
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* The default rejectect execution handler |
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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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* Invoke the rejected execution handler for the give command. |
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*/ |
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void reject(Runnable command) { |
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handler.rejectedExecution(command, this); |
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} |
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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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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return the new thread |
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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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|
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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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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return true if successful. |
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*/ |
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private boolean addIfUnderCorePoolSize(Runnable firstTask) { |
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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(firstTask); |
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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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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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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 firstTask) { |
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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 = firstTask; |
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t = addThread(next); |
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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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* @return the task |
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* @throws InterruptedException if interrupted while waiting for task |
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*/ |
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private Runnable getTask() throws InterruptedException { |
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for (;;) { |
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switch(runState) { |
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case RUNNING: { |
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if (poolSize <= corePoolSize) // untimed wait if core |
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return workQueue.take(); |
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|
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long timeout = keepAliveTime; |
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if (timeout <= 0) // die immediately for 0 timeout |
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return null; |
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Runnable r = workQueue.poll(timeout, TimeUnit.NANOSECONDS); |
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if (r != null) |
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return r; |
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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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break; |
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} |
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|
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case SHUTDOWN: { |
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// Help drain queue |
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Runnable r = workQueue.poll(); |
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if (r != null) |
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return r; |
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|
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// Check if can terminate |
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if (workQueue.isEmpty()) { |
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interruptIdleWorkers(); |
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return null; |
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} |
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|
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// There could still be delayed tasks in queue. |
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// Wait for one, re-checking state upon interruption |
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try { |
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return workQueue.take(); |
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} |
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catch(InterruptedException ignore) { |
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} |
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break; |
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} |
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|
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case STOP: |
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return null; |
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default: |
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assert false; |
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} |
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} |
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} |
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|
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/** |
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* Wake up all threads that might be waiting for tasks. |
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*/ |
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void interruptIdleWorkers() { |
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mainLock.lock(); |
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try { |
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for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
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it.next().interruptIfIdle(); |
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} finally { |
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mainLock.unlock(); |
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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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* @param w the worker |
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*/ |
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private void workerDone(Worker w) { |
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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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if (--poolSize > 0) |
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return; |
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|
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// Else, this is the last thread. Deal with potential shutdown. |
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|
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int state = runState; |
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assert state != TERMINATED; |
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|
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if (state != STOP) { |
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// If there are queued tasks but no threads, create |
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// replacement. |
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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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// If there are some (presumably delayed) tasks but |
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// none pollable, create an idle replacement to wait. |
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if (!workQueue.isEmpty()) { |
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addThread(null).start(); |
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return; |
422 |
} |
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|
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// Otherwise, we can exit without replacement |
425 |
if (state == RUNNING) |
426 |
return; |
427 |
} |
428 |
|
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// Either state is STOP, or state is SHUTDOWN and there is |
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// no work to do. So we can terminate. |
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runState = TERMINATED; |
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termination.signalAll(); |
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// fall through to call terminate() outside of lock. |
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} finally { |
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mainLock.unlock(); |
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} |
437 |
|
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assert runState == TERMINATED; |
439 |
terminated(); |
440 |
} |
441 |
|
442 |
/** |
443 |
* Worker threads |
444 |
*/ |
445 |
private class Worker implements Runnable { |
446 |
|
447 |
/** |
448 |
* The runLock is acquired and released surrounding each task |
449 |
* execution. It mainly protects against interrupts that are |
450 |
* intended to cancel the worker thread from instead |
451 |
* interrupting the task being run. |
452 |
*/ |
453 |
private final ReentrantLock runLock = new ReentrantLock(); |
454 |
|
455 |
/** |
456 |
* Initial task to run before entering run loop |
457 |
*/ |
458 |
private Runnable firstTask; |
459 |
|
460 |
/** |
461 |
* Per thread completed task counter; accumulated |
462 |
* into completedTaskCount upon termination. |
463 |
*/ |
464 |
volatile long completedTasks; |
465 |
|
466 |
/** |
467 |
* Thread this worker is running in. Acts as a final field, |
468 |
* but cannot be set until thread is created. |
469 |
*/ |
470 |
Thread thread; |
471 |
|
472 |
Worker(Runnable firstTask) { |
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this.firstTask = firstTask; |
474 |
} |
475 |
|
476 |
boolean isActive() { |
477 |
return runLock.isLocked(); |
478 |
} |
479 |
|
480 |
/** |
481 |
* Interrupt thread if not running a task |
482 |
*/ |
483 |
void interruptIfIdle() { |
484 |
if (runLock.tryLock()) { |
485 |
try { |
486 |
thread.interrupt(); |
487 |
} finally { |
488 |
runLock.unlock(); |
489 |
} |
490 |
} |
491 |
} |
492 |
|
493 |
/** |
494 |
* Cause thread to die even if running a task. |
495 |
*/ |
496 |
void interruptNow() { |
497 |
thread.interrupt(); |
498 |
} |
499 |
|
500 |
/** |
501 |
* Run a single task between before/after methods. |
502 |
*/ |
503 |
private void runTask(Runnable task) { |
504 |
runLock.lock(); |
505 |
try { |
506 |
// Abort now if immediate cancel. Otherwise, we have |
507 |
// committed to run this task. |
508 |
if (runState == STOP) |
509 |
return; |
510 |
|
511 |
Thread.interrupted(); // clear interrupt status on entry |
512 |
boolean ran = false; |
513 |
beforeExecute(thread, task); |
514 |
try { |
515 |
task.run(); |
516 |
ran = true; |
517 |
afterExecute(task, null); |
518 |
++completedTasks; |
519 |
} catch(RuntimeException ex) { |
520 |
if (!ran) |
521 |
afterExecute(task, ex); |
522 |
// else the exception occurred within |
523 |
// afterExecute itself in which case we don't |
524 |
// want to call it again. |
525 |
throw ex; |
526 |
} |
527 |
} finally { |
528 |
runLock.unlock(); |
529 |
} |
530 |
} |
531 |
|
532 |
/** |
533 |
* Main run loop |
534 |
*/ |
535 |
public void run() { |
536 |
try { |
537 |
for (;;) { |
538 |
Runnable task; |
539 |
if (firstTask != null) { |
540 |
task = firstTask; |
541 |
firstTask = null; |
542 |
} else { |
543 |
task = getTask(); |
544 |
if (task == null) |
545 |
break; |
546 |
} |
547 |
runTask(task); |
548 |
task = null; // unnecessary but can help GC |
549 |
} |
550 |
} catch(InterruptedException ie) { |
551 |
// fall through |
552 |
} finally { |
553 |
workerDone(this); |
554 |
} |
555 |
} |
556 |
} |
557 |
|
558 |
/** |
559 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
560 |
* parameters. It may be more convenient to use one of the factory |
561 |
* methods instead of this general purpose constructor. |
562 |
* |
563 |
* @param corePoolSize the number of threads to keep in the |
564 |
* pool, even if they are idle. |
565 |
* @param maximumPoolSize the maximum number of threads to allow in the |
566 |
* pool. |
567 |
* @param keepAliveTime when the number of threads is greater than |
568 |
* the core, this is the maximum time that excess idle threads |
569 |
* will wait for new tasks before terminating. |
570 |
* @param unit the time unit for the keepAliveTime |
571 |
* argument. |
572 |
* @param workQueue the queue to use for holding tasks before the |
573 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
574 |
* tasks submitted by the <tt>execute</tt> method. |
575 |
* @throws IllegalArgumentException if corePoolSize, or |
576 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
577 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
578 |
* @throws NullPointerException if <tt>workQueue</tt> is null |
579 |
*/ |
580 |
public ThreadPoolExecutor(int corePoolSize, |
581 |
int maximumPoolSize, |
582 |
long keepAliveTime, |
583 |
TimeUnit unit, |
584 |
BlockingQueue<Runnable> workQueue) { |
585 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
586 |
defaultThreadFactory, defaultHandler); |
587 |
} |
588 |
|
589 |
/** |
590 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
591 |
* parameters. |
592 |
* |
593 |
* @param corePoolSize the number of threads to keep in the |
594 |
* pool, even if they are idle. |
595 |
* @param maximumPoolSize the maximum number of threads to allow in the |
596 |
* pool. |
597 |
* @param keepAliveTime when the number of threads is greater than |
598 |
* the core, this is the maximum time that excess idle threads |
599 |
* will wait for new tasks before terminating. |
600 |
* @param unit the time unit for the keepAliveTime |
601 |
* argument. |
602 |
* @param workQueue the queue to use for holding tasks before the |
603 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
604 |
* tasks submitted by the <tt>execute</tt> method. |
605 |
* @param threadFactory the factory to use when the executor |
606 |
* creates a new thread. |
607 |
* @throws IllegalArgumentException if corePoolSize, or |
608 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
609 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
610 |
* @throws NullPointerException if <tt>workQueue</tt> |
611 |
* or <tt>threadFactory</tt> are null. |
612 |
*/ |
613 |
public ThreadPoolExecutor(int corePoolSize, |
614 |
int maximumPoolSize, |
615 |
long keepAliveTime, |
616 |
TimeUnit unit, |
617 |
BlockingQueue<Runnable> workQueue, |
618 |
ThreadFactory threadFactory) { |
619 |
|
620 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
621 |
threadFactory, defaultHandler); |
622 |
} |
623 |
|
624 |
/** |
625 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
626 |
* parameters. |
627 |
* |
628 |
* @param corePoolSize the number of threads to keep in the |
629 |
* pool, even if they are idle. |
630 |
* @param maximumPoolSize the maximum number of threads to allow in the |
631 |
* pool. |
632 |
* @param keepAliveTime when the number of threads is greater than |
633 |
* the core, this is the maximum time that excess idle threads |
634 |
* will wait for new tasks before terminating. |
635 |
* @param unit the time unit for the keepAliveTime |
636 |
* argument. |
637 |
* @param workQueue the queue to use for holding tasks before the |
638 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
639 |
* tasks submitted by the <tt>execute</tt> method. |
640 |
* @param handler the handler to use when execution is blocked |
641 |
* because the thread bounds and queue capacities are reached. |
642 |
* @throws IllegalArgumentException if corePoolSize, or |
643 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
644 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
645 |
* @throws NullPointerException if <tt>workQueue</tt> |
646 |
* or <tt>handler</tt> are null. |
647 |
*/ |
648 |
public ThreadPoolExecutor(int corePoolSize, |
649 |
int maximumPoolSize, |
650 |
long keepAliveTime, |
651 |
TimeUnit unit, |
652 |
BlockingQueue<Runnable> workQueue, |
653 |
RejectedExecutionHandler handler) { |
654 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
655 |
defaultThreadFactory, handler); |
656 |
} |
657 |
|
658 |
/** |
659 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
660 |
* parameters. |
661 |
* |
662 |
* @param corePoolSize the number of threads to keep in the |
663 |
* pool, even if they are idle. |
664 |
* @param maximumPoolSize the maximum number of threads to allow in the |
665 |
* pool. |
666 |
* @param keepAliveTime when the number of threads is greater than |
667 |
* the core, this is the maximum time that excess idle threads |
668 |
* will wait for new tasks before terminating. |
669 |
* @param unit the time unit for the keepAliveTime |
670 |
* argument. |
671 |
* @param workQueue the queue to use for holding tasks before the |
672 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
673 |
* tasks submitted by the <tt>execute</tt> method. |
674 |
* @param threadFactory the factory to use when the executor |
675 |
* creates a new thread. |
676 |
* @param handler the handler to use when execution is blocked |
677 |
* because the thread bounds and queue capacities are reached. |
678 |
* @throws IllegalArgumentException if corePoolSize, or |
679 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
680 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
681 |
* @throws NullPointerException if <tt>workQueue</tt> |
682 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
683 |
*/ |
684 |
public ThreadPoolExecutor(int corePoolSize, |
685 |
int maximumPoolSize, |
686 |
long keepAliveTime, |
687 |
TimeUnit unit, |
688 |
BlockingQueue<Runnable> workQueue, |
689 |
ThreadFactory threadFactory, |
690 |
RejectedExecutionHandler handler) { |
691 |
if (corePoolSize < 0 || |
692 |
maximumPoolSize <= 0 || |
693 |
maximumPoolSize < corePoolSize || |
694 |
keepAliveTime < 0) |
695 |
throw new IllegalArgumentException(); |
696 |
if (workQueue == null || threadFactory == null || handler == null) |
697 |
throw new NullPointerException(); |
698 |
this.corePoolSize = corePoolSize; |
699 |
this.maximumPoolSize = maximumPoolSize; |
700 |
this.workQueue = workQueue; |
701 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
702 |
this.threadFactory = threadFactory; |
703 |
this.handler = handler; |
704 |
} |
705 |
|
706 |
|
707 |
/** |
708 |
* Executes the given task sometime in the future. The task |
709 |
* may execute in a new thread or in an existing pooled thread. |
710 |
* |
711 |
* If the task cannot be submitted for execution, either because this |
712 |
* executor has been shutdown or because its capacity has been reached, |
713 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
714 |
* |
715 |
* @param command the task to execute |
716 |
* @throws RejectedExecutionException at discretion of |
717 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
718 |
* for execution |
719 |
*/ |
720 |
public void execute(Runnable command) { |
721 |
for (;;) { |
722 |
if (runState != RUNNING) { |
723 |
reject(command); |
724 |
return; |
725 |
} |
726 |
if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) |
727 |
return; |
728 |
if (workQueue.offer(command)) |
729 |
return; |
730 |
Runnable r = addIfUnderMaximumPoolSize(command); |
731 |
if (r == command) |
732 |
return; |
733 |
if (r == null) { |
734 |
reject(command); |
735 |
return; |
736 |
} |
737 |
// else retry |
738 |
} |
739 |
} |
740 |
|
741 |
public void shutdown() { |
742 |
mainLock.lock(); |
743 |
try { |
744 |
if (runState == RUNNING) // don't override shutdownNow |
745 |
runState = SHUTDOWN; |
746 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
747 |
it.next().interruptIfIdle(); |
748 |
} finally { |
749 |
mainLock.unlock(); |
750 |
} |
751 |
} |
752 |
|
753 |
|
754 |
public List shutdownNow() { |
755 |
mainLock.lock(); |
756 |
try { |
757 |
if (runState != TERMINATED) |
758 |
runState = STOP; |
759 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
760 |
it.next().interruptNow(); |
761 |
} finally { |
762 |
mainLock.unlock(); |
763 |
} |
764 |
return Arrays.asList(workQueue.toArray()); |
765 |
} |
766 |
|
767 |
public boolean isShutdown() { |
768 |
return runState != RUNNING; |
769 |
} |
770 |
|
771 |
/** |
772 |
* Return true if this executor is in the process of terminating |
773 |
* after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not |
774 |
* completely terminated. This method may be useful for |
775 |
* debugging. A return of <tt>true</tt> reported a sufficient |
776 |
* period after shutdown may indicate that submitted tasks have |
777 |
* ignored or suppressed interruption, causing this executor not |
778 |
* to properly terminate. |
779 |
* @return true if terminating but not yet terminated. |
780 |
*/ |
781 |
public boolean isTerminating() { |
782 |
return runState == STOP; |
783 |
} |
784 |
|
785 |
public boolean isTerminated() { |
786 |
return runState == TERMINATED; |
787 |
} |
788 |
|
789 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
790 |
throws InterruptedException { |
791 |
mainLock.lock(); |
792 |
try { |
793 |
return termination.await(timeout, unit); |
794 |
} finally { |
795 |
mainLock.unlock(); |
796 |
} |
797 |
} |
798 |
|
799 |
/** |
800 |
* Invokes <tt>shutdown</tt> when this executor is no longer |
801 |
* referenced. |
802 |
*/ |
803 |
protected void finalize() { |
804 |
shutdown(); |
805 |
} |
806 |
|
807 |
/** |
808 |
* Sets the thread factory used to create new threads. |
809 |
* |
810 |
* @param threadFactory the new thread factory |
811 |
* @see #getThreadFactory |
812 |
*/ |
813 |
public void setThreadFactory(ThreadFactory threadFactory) { |
814 |
this.threadFactory = threadFactory; |
815 |
} |
816 |
|
817 |
/** |
818 |
* Returns the thread factory used to create new threads. |
819 |
* |
820 |
* @return the current thread factory |
821 |
* @see #setThreadFactory |
822 |
*/ |
823 |
public ThreadFactory getThreadFactory() { |
824 |
return threadFactory; |
825 |
} |
826 |
|
827 |
/** |
828 |
* Sets a new handler for unexecutable tasks. |
829 |
* |
830 |
* @param handler the new handler |
831 |
* @see #getRejectedExecutionHandler |
832 |
*/ |
833 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
834 |
this.handler = handler; |
835 |
} |
836 |
|
837 |
/** |
838 |
* Returns the current handler for unexecutable tasks. |
839 |
* |
840 |
* @return the current handler |
841 |
* @see #setRejectedExecutionHandler |
842 |
*/ |
843 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
844 |
return handler; |
845 |
} |
846 |
|
847 |
/** |
848 |
* Returns the task queue used by this executor. Note that |
849 |
* this queue may be in active use. Retrieveing the task queue |
850 |
* does not prevent queued tasks from executing. |
851 |
* |
852 |
* @return the task queue |
853 |
*/ |
854 |
public BlockingQueue<Runnable> getQueue() { |
855 |
return workQueue; |
856 |
} |
857 |
|
858 |
/** |
859 |
* Removes this task from internal queue if it is present, thus |
860 |
* causing it not to be run if it has not already started. This |
861 |
* method may be useful as one part of a cancellation scheme. |
862 |
* |
863 |
* @param task the task to remove |
864 |
* @return true if the task was removed |
865 |
*/ |
866 |
public boolean remove(Runnable task) { |
867 |
return getQueue().remove(task); |
868 |
} |
869 |
|
870 |
|
871 |
/** |
872 |
* Tries to remove from the work queue all {@link Cancellable} |
873 |
* tasks that have been cancelled. This method can be useful as a |
874 |
* storage reclamation operation, that has no other impact on |
875 |
* functionality. Cancelled tasks are never executed, but may |
876 |
* accumulate in work queues until worker threads can actively |
877 |
* remove them. Invoking this method instead tries to remove them now. |
878 |
* However, this method may fail to remove all such tasks in |
879 |
* the presence of interference by other threads. |
880 |
*/ |
881 |
|
882 |
public void purge() { |
883 |
// Fail if we encounter interference during traversal |
884 |
try { |
885 |
Iterator<Runnable> it = getQueue().iterator(); |
886 |
while (it.hasNext()) { |
887 |
Runnable r = it.next(); |
888 |
if (r instanceof Cancellable) { |
889 |
Cancellable c = (Cancellable)r; |
890 |
if (c.isCancelled()) |
891 |
it.remove(); |
892 |
} |
893 |
} |
894 |
} |
895 |
catch(ConcurrentModificationException ex) { |
896 |
return; |
897 |
} |
898 |
} |
899 |
|
900 |
/** |
901 |
* Sets the core number of threads. This overrides any value set |
902 |
* in the constructor. If the new value is smaller than the |
903 |
* current value, excess existing threads will be terminated when |
904 |
* they next become idle. |
905 |
* |
906 |
* @param corePoolSize the new core size |
907 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> |
908 |
* less than zero |
909 |
* @see #getCorePoolSize |
910 |
*/ |
911 |
public void setCorePoolSize(int corePoolSize) { |
912 |
if (corePoolSize < 0) |
913 |
throw new IllegalArgumentException(); |
914 |
mainLock.lock(); |
915 |
try { |
916 |
int extra = this.corePoolSize - corePoolSize; |
917 |
this.corePoolSize = corePoolSize; |
918 |
if (extra > 0 && poolSize > corePoolSize) { |
919 |
Iterator<Worker> it = workers.iterator(); |
920 |
while (it.hasNext() && |
921 |
extra > 0 && |
922 |
poolSize > corePoolSize && |
923 |
workQueue.remainingCapacity() == 0) { |
924 |
it.next().interruptIfIdle(); |
925 |
--extra; |
926 |
} |
927 |
} |
928 |
|
929 |
} finally { |
930 |
mainLock.unlock(); |
931 |
} |
932 |
} |
933 |
|
934 |
/** |
935 |
* Returns the core number of threads. |
936 |
* |
937 |
* @return the core number of threads |
938 |
* @see #setCorePoolSize |
939 |
*/ |
940 |
public int getCorePoolSize() { |
941 |
return corePoolSize; |
942 |
} |
943 |
|
944 |
/** |
945 |
* Start a core thread, causing it to idly wait for work. This |
946 |
* overrides the default policy of starting core threads only when |
947 |
* new tasks are executed. This method will return <tt>false</tt> |
948 |
* if all core threads have already been started. |
949 |
* @return true if a thread was started |
950 |
*/ |
951 |
public boolean prestartCoreThread() { |
952 |
return addIfUnderCorePoolSize(null); |
953 |
} |
954 |
|
955 |
/** |
956 |
* Start all core threads, causing them to idly wait for work. This |
957 |
* overrides the default policy of starting core threads only when |
958 |
* new tasks are executed. |
959 |
* @return the number of threads started. |
960 |
*/ |
961 |
public int prestartAllCoreThreads() { |
962 |
int n = 0; |
963 |
while (addIfUnderCorePoolSize(null)) |
964 |
++n; |
965 |
return n; |
966 |
} |
967 |
|
968 |
/** |
969 |
* Sets the maximum allowed number of threads. This overrides any |
970 |
* value set in the constructor. If the new value is smaller than |
971 |
* the current value, excess existing threads will be |
972 |
* terminated when they next become idle. |
973 |
* |
974 |
* @param maximumPoolSize the new maximum |
975 |
* @throws IllegalArgumentException if maximumPoolSize less than zero or |
976 |
* the {@link #getCorePoolSize core pool size} |
977 |
* @see #getMaximumPoolSize |
978 |
*/ |
979 |
public void setMaximumPoolSize(int maximumPoolSize) { |
980 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
981 |
throw new IllegalArgumentException(); |
982 |
mainLock.lock(); |
983 |
try { |
984 |
int extra = this.maximumPoolSize - maximumPoolSize; |
985 |
this.maximumPoolSize = maximumPoolSize; |
986 |
if (extra > 0 && poolSize > maximumPoolSize) { |
987 |
Iterator<Worker> it = workers.iterator(); |
988 |
while (it.hasNext() && |
989 |
extra > 0 && |
990 |
poolSize > maximumPoolSize) { |
991 |
it.next().interruptIfIdle(); |
992 |
--extra; |
993 |
} |
994 |
} |
995 |
} finally { |
996 |
mainLock.unlock(); |
997 |
} |
998 |
} |
999 |
|
1000 |
/** |
1001 |
* Returns the maximum allowed number of threads. |
1002 |
* |
1003 |
* @return the maximum allowed number of threads |
1004 |
* @see #setMaximumPoolSize |
1005 |
*/ |
1006 |
public int getMaximumPoolSize() { |
1007 |
return maximumPoolSize; |
1008 |
} |
1009 |
|
1010 |
/** |
1011 |
* Sets the time limit for which threads may remain idle before |
1012 |
* being terminated. If there are more than the core number of |
1013 |
* threads currently in the pool, after waiting this amount of |
1014 |
* time without processing a task, excess threads will be |
1015 |
* terminated. This overrides any value set in the constructor. |
1016 |
* @param time the time to wait. A time value of zero will cause |
1017 |
* excess threads to terminate immediately after executing tasks. |
1018 |
* @param unit the time unit of the time argument |
1019 |
* @throws IllegalArgumentException if msecs less than zero |
1020 |
* @see #getKeepAliveTime |
1021 |
*/ |
1022 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
1023 |
if (time < 0) |
1024 |
throw new IllegalArgumentException(); |
1025 |
this.keepAliveTime = unit.toNanos(time); |
1026 |
} |
1027 |
|
1028 |
/** |
1029 |
* Returns the thread keep-alive time, which is the amount of time |
1030 |
* which threads in excess of the core pool size may remain |
1031 |
* idle before being terminated. |
1032 |
* |
1033 |
* @param unit the desired time unit of the result |
1034 |
* @return the time limit |
1035 |
* @see #setKeepAliveTime |
1036 |
*/ |
1037 |
public long getKeepAliveTime(TimeUnit unit) { |
1038 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
1039 |
} |
1040 |
|
1041 |
/* Statistics */ |
1042 |
|
1043 |
/** |
1044 |
* Returns the current number of threads in the pool. |
1045 |
* |
1046 |
* @return the number of threads |
1047 |
*/ |
1048 |
public int getPoolSize() { |
1049 |
return poolSize; |
1050 |
} |
1051 |
|
1052 |
/** |
1053 |
* Returns the approximate number of threads that are actively |
1054 |
* executing tasks. |
1055 |
* |
1056 |
* @return the number of threads |
1057 |
*/ |
1058 |
public int getActiveCount() { |
1059 |
mainLock.lock(); |
1060 |
try { |
1061 |
int n = 0; |
1062 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
1063 |
if (it.next().isActive()) |
1064 |
++n; |
1065 |
} |
1066 |
return n; |
1067 |
} finally { |
1068 |
mainLock.unlock(); |
1069 |
} |
1070 |
} |
1071 |
|
1072 |
/** |
1073 |
* Returns the largest number of threads that have ever |
1074 |
* simultaneously been in the pool. |
1075 |
* |
1076 |
* @return the number of threads |
1077 |
*/ |
1078 |
public int getLargestPoolSize() { |
1079 |
mainLock.lock(); |
1080 |
try { |
1081 |
return largestPoolSize; |
1082 |
} finally { |
1083 |
mainLock.unlock(); |
1084 |
} |
1085 |
} |
1086 |
|
1087 |
/** |
1088 |
* Returns the approximate total number of tasks that have been |
1089 |
* scheduled for execution. Because the states of tasks and |
1090 |
* threads may change dynamically during computation, the returned |
1091 |
* value is only an approximation. |
1092 |
* |
1093 |
* @return the number of tasks |
1094 |
*/ |
1095 |
public long getTaskCount() { |
1096 |
mainLock.lock(); |
1097 |
try { |
1098 |
long n = completedTaskCount; |
1099 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
1100 |
Worker w = it.next(); |
1101 |
n += w.completedTasks; |
1102 |
if (w.isActive()) |
1103 |
++n; |
1104 |
} |
1105 |
return n + workQueue.size(); |
1106 |
} finally { |
1107 |
mainLock.unlock(); |
1108 |
} |
1109 |
} |
1110 |
|
1111 |
/** |
1112 |
* Returns the approximate total number of tasks that have |
1113 |
* completed execution. Because the states of tasks and threads |
1114 |
* may change dynamically during computation, the returned value |
1115 |
* is only an approximation. |
1116 |
* |
1117 |
* @return the number of tasks |
1118 |
*/ |
1119 |
public long getCompletedTaskCount() { |
1120 |
mainLock.lock(); |
1121 |
try { |
1122 |
long n = completedTaskCount; |
1123 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
1124 |
n += it.next().completedTasks; |
1125 |
return n; |
1126 |
} finally { |
1127 |
mainLock.unlock(); |
1128 |
} |
1129 |
} |
1130 |
|
1131 |
/** |
1132 |
* Method invoked prior to executing the given Runnable in given |
1133 |
* thread. This method may be used to re-initialize ThreadLocals, |
1134 |
* or to perform logging. Note: To properly nest multiple |
1135 |
* overridings, subclasses should generally invoke |
1136 |
* <tt>super.beforeExecute</tt> at the end of this method. |
1137 |
* |
1138 |
* @param t the thread that will run task r. |
1139 |
* @param r the task that will be executed. |
1140 |
*/ |
1141 |
protected void beforeExecute(Thread t, Runnable r) { } |
1142 |
|
1143 |
/** |
1144 |
* Method invoked upon completion of execution of the given |
1145 |
* Runnable. If non-null, the Throwable is the uncaught exception |
1146 |
* that caused execution to terminate abruptly. Note: To properly |
1147 |
* nest multiple overridings, subclasses should generally invoke |
1148 |
* <tt>super.afterExecute</tt> at the beginning of this method. |
1149 |
* |
1150 |
* @param r the runnable that has completed. |
1151 |
* @param t the exception that cause termination, or null if |
1152 |
* execution completed normally. |
1153 |
*/ |
1154 |
protected void afterExecute(Runnable r, Throwable t) { } |
1155 |
|
1156 |
/** |
1157 |
* Method invoked when the Executor has terminated. Default |
1158 |
* implementation does nothing. |
1159 |
*/ |
1160 |
protected void terminated() { } |
1161 |
|
1162 |
/** |
1163 |
* A handler for unexecutable tasks that runs these tasks directly in the |
1164 |
* calling thread of the <tt>execute</tt> method. This is the default |
1165 |
* <tt>RejectedExecutionHandler</tt>. |
1166 |
*/ |
1167 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1168 |
|
1169 |
/** |
1170 |
* Constructs a <tt>CallerRunsPolicy</tt>. |
1171 |
*/ |
1172 |
public CallerRunsPolicy() { } |
1173 |
|
1174 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1175 |
if (!e.isShutdown()) { |
1176 |
r.run(); |
1177 |
} |
1178 |
} |
1179 |
} |
1180 |
|
1181 |
/** |
1182 |
* A handler for unexecutable tasks that throws a |
1183 |
* <tt>RejectedExecutionException</tt>. |
1184 |
*/ |
1185 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1186 |
|
1187 |
/** |
1188 |
* Constructs a <tt>AbortPolicy</tt>. |
1189 |
*/ |
1190 |
public AbortPolicy() { } |
1191 |
|
1192 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1193 |
throw new RejectedExecutionException(); |
1194 |
} |
1195 |
} |
1196 |
|
1197 |
/** |
1198 |
* A handler for unexecutable tasks that waits until the task can be |
1199 |
* submitted for execution. |
1200 |
*/ |
1201 |
public static class WaitPolicy implements RejectedExecutionHandler { |
1202 |
/** |
1203 |
* Constructs a <tt>WaitPolicy</tt>. |
1204 |
*/ |
1205 |
public WaitPolicy() { } |
1206 |
|
1207 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1208 |
if (!e.isShutdown()) { |
1209 |
try { |
1210 |
e.getQueue().put(r); |
1211 |
} catch (InterruptedException ie) { |
1212 |
Thread.currentThread().interrupt(); |
1213 |
throw new RejectedExecutionException(ie); |
1214 |
} |
1215 |
} |
1216 |
} |
1217 |
} |
1218 |
|
1219 |
/** |
1220 |
* A handler for unexecutable tasks that silently discards these tasks. |
1221 |
*/ |
1222 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1223 |
|
1224 |
/** |
1225 |
* Constructs <tt>DiscardPolicy</tt>. |
1226 |
*/ |
1227 |
public DiscardPolicy() { } |
1228 |
|
1229 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1230 |
} |
1231 |
} |
1232 |
|
1233 |
/** |
1234 |
* A handler for unexecutable tasks that discards the oldest |
1235 |
* unhandled request. |
1236 |
*/ |
1237 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1238 |
/** |
1239 |
* Constructs a <tt>DiscardOldestPolicy</tt> for the given executor. |
1240 |
*/ |
1241 |
public DiscardOldestPolicy() { } |
1242 |
|
1243 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1244 |
if (!e.isShutdown()) { |
1245 |
e.getQueue().poll(); |
1246 |
e.execute(r); |
1247 |
} |
1248 |
} |
1249 |
} |
1250 |
} |