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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, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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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 using |
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* one of possibly several pooled threads, normally configured |
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* using {@link Executors} factory methods. |
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* |
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* <p>Thread pools address two different problems: they usually |
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* provide improved performance when executing large numbers of |
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* asynchronous tasks, due to reduced per-task invocation overhead, |
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* and they provide a means of bounding and managing the resources, |
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* including threads, consumed when executing a collection of tasks. |
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* Each <tt>ThreadPoolExecutor</tt> also maintains some basic |
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* statistics, such as the number of completed tasks. |
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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 |
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* hooks. However, programmers are urged to use the more convenient |
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* {@link Executors} factory methods {@link |
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* Executors#newCachedThreadPool} (unbounded thread pool, with |
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* automatic thread reclamation), {@link Executors#newFixedThreadPool} |
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* (fixed size thread pool) and {@link |
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* Executors#newSingleThreadExecutor} (single background thread), that |
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* preconfigure settings for the most common usage |
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* scenarios. Otherwise, use the following guide when manually |
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* configuring and tuning this class: |
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* |
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* <dl> |
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* |
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* <dt>Core and maximum pool sizes</dt> |
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* |
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* <dd>A <tt>ThreadPoolExecutor</tt> will automatically adjust the |
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* pool size |
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* (see {@link ThreadPoolExecutor#getPoolSize}) |
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* according to the bounds set by corePoolSize |
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* (see {@link ThreadPoolExecutor#getCorePoolSize}) |
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* and |
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* maximumPoolSize |
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* (see {@link ThreadPoolExecutor#getMaximumPoolSize}). |
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* When a new task is submitted in method {@link |
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* ThreadPoolExecutor#execute}, 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 |
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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. By setting maximumPoolSize to an essentially unbounded |
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* value such as <tt>Integer.MAX_VALUE</tt>, you allow the pool to |
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* accommodate an arbitrary number of concurrent tasks. Most typically, |
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* core and maximum pool sizes are set only upon construction, but they |
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* may also be changed dynamically using {@link |
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* ThreadPoolExecutor#setCorePoolSize} and {@link |
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* ThreadPoolExecutor#setMaximumPoolSize}. <dd> |
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* |
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* <dt> On-demand construction |
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* |
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* <dd> By default, even core threads are initially created and |
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* started only when new tasks arrive, but this can be overridden |
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* dynamically using method {@link |
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* ThreadPoolExecutor#prestartCoreThread} or |
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* {@link ThreadPoolExecutor#prestartAllCoreThreads}. |
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* You probably want to prestart threads if you construct the |
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* pool with a non-empty queue. </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 {@link |
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* java.util.concurrent.ThreadFactory}. If not otherwise specified, a |
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* {@link Executors#defaultThreadFactory} is used, that creates threads to all |
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* be in the same {@link ThreadGroup} and with the same |
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* <tt>NORM_PRIORITY</tt> priority and non-daemon status. By supplying |
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* a different ThreadFactory, you can alter the thread's name, thread |
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* group, priority, daemon status, etc. If a <tt>ThreadFactory</tt> fails to create |
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* a thread when asked by returning null from <tt>newThread</tt>, |
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* the executor will continue, but might |
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* not be able to execute any tasks. </dd> |
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* |
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* <dt>Keep-alive times</dt> |
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* |
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* <dd>If the pool currently has more than corePoolSize threads, |
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* excess threads will be terminated if they have been idle for more |
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* than the keepAliveTime (see {@link |
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* ThreadPoolExecutor#getKeepAliveTime}). This provides a means of |
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* reducing resource consumption when the pool is not being actively |
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* used. If the pool becomes more active later, new threads will be |
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* constructed. This parameter can also be changed dynamically using |
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* method {@link ThreadPoolExecutor#setKeepAliveTime}. Using a value |
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* of <tt>Long.MAX_VALUE</tt> {@link TimeUnit#NANOSECONDS} effectively |
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* disables idle threads from ever terminating prior to shut down. By |
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* default, the keep-alive policy applies only when there are more |
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* than corePoolSizeThreads. But method {@link |
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* ThreadPoolExecutor#allowCoreThreadTimeOut} can be used to apply |
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* this time-out policy to core threads as well, so long as |
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* the keepAliveTime value is non-zero. </dd> |
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* |
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* <dt>Queuing</dt> |
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* |
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* <dd>Any {@link BlockingQueue} may be used to transfer and hold |
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* submitted tasks. The use of this queue interacts with pool sizing: |
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* |
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* <ul> |
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* |
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* <li> If fewer than corePoolSize threads are running, the Executor |
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* always prefers adding a new thread |
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* rather than queuing.</li> |
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* |
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* <li> If corePoolSize or more threads are running, the Executor |
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* always prefers queuing a request rather than adding a new |
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* thread.</li> |
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* |
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* <li> If a request cannot be queued, a new thread is created unless |
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* this would exceed maximumPoolSize, in which case, the task will be |
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* rejected.</li> |
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* |
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* </ul> |
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* |
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* There are three general strategies for queuing: |
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* <ol> |
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* |
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* <li> <em> Direct handoffs.</em> A good default choice for a work |
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* queue is a {@link SynchronousQueue} that hands off tasks to threads |
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* without otherwise holding them. Here, an attempt to queue a task |
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* will fail if no threads are immediately available to run it, so a |
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* new thread will be constructed. This policy avoids lockups when |
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* handling sets of requests that might have internal dependencies. |
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* Direct handoffs generally require unbounded maximumPoolSizes to |
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* avoid rejection of new submitted tasks. This in turn admits the |
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* possibility of unbounded thread growth when commands continue to |
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* arrive on average faster than they can be processed. </li> |
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* |
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* <li><em> Unbounded queues.</em> Using an unbounded queue (for |
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* example a {@link LinkedBlockingQueue} without a predefined |
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* capacity) will cause new tasks to wait in the queue when all |
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* corePoolSize threads are busy. Thus, no more than corePoolSize |
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* threads will ever be created. (And the value of the maximumPoolSize |
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* therefore doesn't have any effect.) This may be appropriate when |
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* each task is completely independent of others, so tasks cannot |
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* affect each others execution; for example, in a web page server. |
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* While this style of queuing can be useful in smoothing out |
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* transient bursts of requests, it admits the possibility of |
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* unbounded work queue growth when commands continue to arrive on |
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* average faster than they can be processed. </li> |
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* |
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* <li><em>Bounded queues.</em> A bounded queue (for example, an |
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* {@link ArrayBlockingQueue}) helps prevent resource exhaustion when |
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* used with finite maximumPoolSizes, but can be more difficult to |
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* tune and control. Queue sizes and maximum pool sizes may be traded |
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* off for each other: Using large queues and small pools minimizes |
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* CPU usage, OS resources, and context-switching overhead, but can |
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* lead to artificially low throughput. If tasks frequently block (for |
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* example if they are I/O bound), a system may be able to schedule |
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* time for more threads than you otherwise allow. Use of small queues |
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* generally requires larger pool sizes, which keeps CPUs busier but |
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* may encounter unacceptable scheduling overhead, which also |
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* decreases throughput. </li> |
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* |
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* </ol> |
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* |
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* </dd> |
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* |
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* <dt>Rejected tasks</dt> |
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* |
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* <dd> New tasks submitted in method {@link |
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* ThreadPoolExecutor#execute} will be <em>rejected</em> when the |
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* Executor has been shut down, and also when the Executor uses finite |
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* bounds for both maximum threads and work queue capacity, and is |
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* saturated. In either case, the <tt>execute</tt> method invokes the |
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* {@link RejectedExecutionHandler#rejectedExecution} method of its |
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* {@link RejectedExecutionHandler}. Four predefined handler policies |
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* are provided: |
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* |
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* <ol> |
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* |
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* <li> In the |
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* default {@link ThreadPoolExecutor.AbortPolicy}, the handler throws a |
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* runtime {@link RejectedExecutionException} upon rejection. </li> |
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* |
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* <li> In {@link |
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* ThreadPoolExecutor.CallerRunsPolicy}, the thread that invokes |
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* <tt>execute</tt> itself runs the task. This provides a simple |
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* feedback control mechanism that will slow down the rate that new |
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* tasks are submitted. </li> |
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* |
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* <li> In {@link ThreadPoolExecutor.DiscardPolicy}, |
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* a task that cannot be executed is simply dropped. </li> |
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* |
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* <li>In {@link |
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* ThreadPoolExecutor.DiscardOldestPolicy}, if the executor is not |
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* shut down, the task at the head of the work queue is dropped, and |
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* then execution is retried (which can fail again, causing this to be |
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* repeated.) </li> |
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* |
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* </ol> |
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* |
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* It is possible to define and use other kinds of {@link |
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* RejectedExecutionHandler} classes. Doing so requires some care |
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* especially when policies are designed to work only under particular |
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* capacity or queuing policies. </dd> |
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* |
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* <dt>Hook methods</dt> |
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* |
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* <dd>This class provides <tt>protected</tt> overridable {@link |
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* ThreadPoolExecutor#beforeExecute} and {@link |
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* ThreadPoolExecutor#afterExecute} methods that are called before and |
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* after execution of each task. These can be used to manipulate the |
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* execution environment; for example, reinitializing ThreadLocals, |
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* gathering statistics, or adding log entries. Additionally, method |
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* {@link ThreadPoolExecutor#terminated} can be overridden to perform |
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* any special processing that needs to be done once the Executor has |
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* fully terminated. |
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* |
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* <p>If hook or callback methods throw |
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* exceptions, internal worker threads may in turn fail and |
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* abruptly terminate.</dd> |
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* |
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* <dt>Queue maintenance</dt> |
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* |
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* <dd> Method {@link ThreadPoolExecutor#getQueue} allows access to |
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* the work queue for purposes of monitoring and debugging. Use of |
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* this method for any other purpose is strongly discouraged. Two |
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* supplied methods, {@link ThreadPoolExecutor#remove} and {@link |
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* ThreadPoolExecutor#purge} are available to assist in storage |
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* reclamation when large numbers of queued tasks become |
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* cancelled.</dd> |
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* |
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* <dt>Finalization</dt> |
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* |
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* <dd> A pool that is no longer referenced in a program <em>AND</em> |
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* has no remaining threads will be <tt>shutdown</tt> |
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* automatically. If you would like to ensure that unreferenced pools |
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* are reclaimed even if users forget to call {@link |
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* ThreadPoolExecutor#shutdown}, then you must arrange that unused |
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* threads eventually die, by setting appropriate keep-alive times, |
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* using a lower bound of zero core threads and/or setting {@link |
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* ThreadPoolExecutor#allowCoreThreadTimeOut}. </dd> </dl> |
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* |
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* <p> <b>Extension example</b>. Most extensions of this class |
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* override one or more of the protected hook methods. For example, |
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* here is a subclass that adds a simple pause/resume feature: |
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* |
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* <pre> |
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* class PausableThreadPoolExecutor extends ThreadPoolExecutor { |
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* private boolean isPaused; |
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* private ReentrantLock pauseLock = new ReentrantLock(); |
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* private Condition unpaused = pauseLock.newCondition(); |
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* |
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* public PausableThreadPoolExecutor(...) { super(...); } |
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* |
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* protected void beforeExecute(Thread t, Runnable r) { |
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* super.beforeExecute(t, r); |
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* pauseLock.lock(); |
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* try { |
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* while (isPaused) unpaused.await(); |
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* } catch (InterruptedException ie) { |
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* t.interrupt(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void pause() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = true; |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void resume() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = false; |
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* unpaused.signalAll(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* } |
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* </pre> |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class ThreadPoolExecutor extends AbstractExecutorService { |
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/** |
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* Only used to force toArray() to produce a Runnable[]. |
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*/ |
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private static final Runnable[] EMPTY_RUNNABLE_ARRAY = new Runnable[0]; |
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|
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/** |
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* Permission for checking shutdown |
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*/ |
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private static final RuntimePermission shutdownPerm = |
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new RuntimePermission("modifyThread"); |
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|
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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 HashSet<Worker> workers = new HashSet<Worker>(); |
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|
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/** |
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* Timeout in nanoseconds 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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* If false (default) core threads stay alive even when idle. |
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* If true, core threads use keepAliveTime to time out waiting for work. |
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*/ |
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private volatile boolean allowCoreThreadTimeOut; |
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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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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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static final int RUNNING = 0; |
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/** Controlled shutdown mode */ |
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static final int SHUTDOWN = 1; |
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/** Immediate shutdown mode */ |
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static final int STOP = 2; |
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/** Final state */ |
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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; |
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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; |
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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 rejected 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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* Invokes the rejected execution handler for the given 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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* Creates and returns 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, or null if threadFactory fails to create 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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if (t != null) { |
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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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} |
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return t; |
426 |
} |
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|
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/** |
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* Creates and starts a new thread running firstTask as its first |
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* task, only if fewer 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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final ReentrantLock mainLock = this.mainLock; |
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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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* Creates and starts a new thread only if fewer than maximumPoolSize |
453 |
* threads are running. The new thread runs as its first task the |
454 |
* 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 |
456 |
* null if none) |
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* @return 0 if a new thread cannot be created, a positive number |
458 |
* if firstTask will be run in a new thread, or a negative number |
459 |
* if a new thread was created but is running some other task, in |
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* which case the caller must try some other way to run firstTask |
461 |
* (perhaps by calling this method again). |
462 |
*/ |
463 |
private int addIfUnderMaximumPoolSize(Runnable firstTask) { |
464 |
Thread t = null; |
465 |
int status = 0; |
466 |
final ReentrantLock mainLock = this.mainLock; |
467 |
mainLock.lock(); |
468 |
try { |
469 |
if (poolSize < maximumPoolSize) { |
470 |
Runnable next = workQueue.poll(); |
471 |
if (next == null) { |
472 |
next = firstTask; |
473 |
status = 1; |
474 |
} else |
475 |
status = -1; |
476 |
t = addThread(next); |
477 |
} |
478 |
} finally { |
479 |
mainLock.unlock(); |
480 |
} |
481 |
if (t == null) |
482 |
return 0; |
483 |
t.start(); |
484 |
return status; |
485 |
} |
486 |
|
487 |
|
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/** |
489 |
* Gets the next task for a worker thread to run. |
490 |
* @return the task |
491 |
*/ |
492 |
Runnable getTask() { |
493 |
for (;;) { |
494 |
try { |
495 |
switch (runState) { |
496 |
case RUNNING: { |
497 |
// untimed wait if core and not allowing core timeout |
498 |
if (poolSize <= corePoolSize && !allowCoreThreadTimeOut) |
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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; |
504 |
Runnable r = workQueue.poll(timeout, TimeUnit.NANOSECONDS); |
505 |
if (r != null) |
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return r; |
507 |
if (poolSize > corePoolSize || allowCoreThreadTimeOut) |
508 |
return null; // timed out |
509 |
// Else, after timeout, the pool shrank. Retry |
510 |
break; |
511 |
} |
512 |
|
513 |
case SHUTDOWN: { |
514 |
// Help drain queue |
515 |
Runnable r = workQueue.poll(); |
516 |
if (r != null) |
517 |
return r; |
518 |
|
519 |
// Check if can terminate |
520 |
if (workQueue.isEmpty()) { |
521 |
interruptIdleWorkers(); |
522 |
return null; |
523 |
} |
524 |
|
525 |
// Else there could still be delayed tasks in queue. |
526 |
return workQueue.take(); |
527 |
} |
528 |
|
529 |
case STOP: |
530 |
return null; |
531 |
default: |
532 |
assert false; |
533 |
} |
534 |
} catch (InterruptedException ie) { |
535 |
// On interruption, re-check runstate |
536 |
} |
537 |
} |
538 |
} |
539 |
|
540 |
/** |
541 |
* Wakes up all threads that might be waiting for tasks. |
542 |
*/ |
543 |
void interruptIdleWorkers() { |
544 |
final ReentrantLock mainLock = this.mainLock; |
545 |
mainLock.lock(); |
546 |
try { |
547 |
for (Worker w : workers) |
548 |
w.interruptIfIdle(); |
549 |
} finally { |
550 |
mainLock.unlock(); |
551 |
} |
552 |
} |
553 |
|
554 |
/** |
555 |
* Performs bookkeeping for a terminated worker thread. |
556 |
* @param w the worker |
557 |
*/ |
558 |
void workerDone(Worker w) { |
559 |
final ReentrantLock mainLock = this.mainLock; |
560 |
mainLock.lock(); |
561 |
try { |
562 |
completedTaskCount += w.completedTasks; |
563 |
workers.remove(w); |
564 |
if (--poolSize > 0) |
565 |
return; |
566 |
|
567 |
// Else, this is the last thread. Deal with potential shutdown. |
568 |
|
569 |
int state = runState; |
570 |
assert state != TERMINATED; |
571 |
|
572 |
if (state != STOP) { |
573 |
// If there are queued tasks but no threads, create |
574 |
// replacement thread. We must create it initially |
575 |
// idle to avoid orphaned tasks in case addThread |
576 |
// fails. This also handles case of delayed tasks |
577 |
// that will sometime later become runnable. |
578 |
if (!workQueue.isEmpty()) { |
579 |
Thread t = addThread(null); |
580 |
if (t != null) |
581 |
t.start(); |
582 |
return; |
583 |
} |
584 |
|
585 |
// Otherwise, we can exit without replacement |
586 |
if (state == RUNNING) |
587 |
return; |
588 |
} |
589 |
|
590 |
// Either state is STOP, or state is SHUTDOWN and there is |
591 |
// no work to do. So we can terminate. |
592 |
termination.signalAll(); |
593 |
runState = TERMINATED; |
594 |
// fall through to call terminate() outside of lock. |
595 |
} finally { |
596 |
mainLock.unlock(); |
597 |
} |
598 |
|
599 |
assert runState == TERMINATED; |
600 |
terminated(); |
601 |
} |
602 |
|
603 |
/** |
604 |
* Worker threads |
605 |
*/ |
606 |
private class Worker implements Runnable { |
607 |
|
608 |
/** |
609 |
* The runLock is acquired and released surrounding each task |
610 |
* execution. It mainly protects against interrupts that are |
611 |
* intended to cancel the worker thread from instead |
612 |
* interrupting the task being run. |
613 |
*/ |
614 |
private final ReentrantLock runLock = new ReentrantLock(); |
615 |
|
616 |
/** |
617 |
* Initial task to run before entering run loop |
618 |
*/ |
619 |
private Runnable firstTask; |
620 |
|
621 |
/** |
622 |
* Per thread completed task counter; accumulated |
623 |
* into completedTaskCount upon termination. |
624 |
*/ |
625 |
volatile long completedTasks; |
626 |
|
627 |
/** |
628 |
* Thread this worker is running in. Acts as a final field, |
629 |
* but cannot be set until thread is created. |
630 |
*/ |
631 |
Thread thread; |
632 |
|
633 |
Worker(Runnable firstTask) { |
634 |
this.firstTask = firstTask; |
635 |
} |
636 |
|
637 |
boolean isActive() { |
638 |
return runLock.isLocked(); |
639 |
} |
640 |
|
641 |
/** |
642 |
* Interrupts thread if not running a task. |
643 |
*/ |
644 |
void interruptIfIdle() { |
645 |
final ReentrantLock runLock = this.runLock; |
646 |
if (runLock.tryLock()) { |
647 |
try { |
648 |
thread.interrupt(); |
649 |
} finally { |
650 |
runLock.unlock(); |
651 |
} |
652 |
} |
653 |
} |
654 |
|
655 |
/** |
656 |
* Interrupts thread even if running a task. |
657 |
*/ |
658 |
void interruptNow() { |
659 |
thread.interrupt(); |
660 |
} |
661 |
|
662 |
/** |
663 |
* Runs a single task between before/after methods. |
664 |
*/ |
665 |
private void runTask(Runnable task) { |
666 |
final ReentrantLock runLock = this.runLock; |
667 |
runLock.lock(); |
668 |
try { |
669 |
// If not shutting down then clear an outstanding interrupt. |
670 |
if (runState != STOP && |
671 |
Thread.interrupted() && |
672 |
runState == STOP) // Re-interrupt if stopped after clearing |
673 |
thread.interrupt(); |
674 |
boolean ran = false; |
675 |
beforeExecute(thread, task); |
676 |
try { |
677 |
task.run(); |
678 |
ran = true; |
679 |
afterExecute(task, null); |
680 |
++completedTasks; |
681 |
} catch (RuntimeException ex) { |
682 |
if (!ran) |
683 |
afterExecute(task, ex); |
684 |
// Else the exception occurred within |
685 |
// afterExecute itself in which case we don't |
686 |
// want to call it again. |
687 |
throw ex; |
688 |
} |
689 |
} finally { |
690 |
runLock.unlock(); |
691 |
} |
692 |
} |
693 |
|
694 |
/** |
695 |
* Main run loop |
696 |
*/ |
697 |
public void run() { |
698 |
try { |
699 |
Runnable task = firstTask; |
700 |
firstTask = null; |
701 |
while (task != null || (task = getTask()) != null) { |
702 |
runTask(task); |
703 |
task = null; // unnecessary but can help GC |
704 |
} |
705 |
} finally { |
706 |
workerDone(this); |
707 |
} |
708 |
} |
709 |
} |
710 |
|
711 |
// Public methods |
712 |
|
713 |
/** |
714 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
715 |
* parameters and default thread factory and rejected execution handler. |
716 |
* It may be more convenient to use one of the {@link Executors} factory |
717 |
* methods instead of this general purpose constructor. |
718 |
* |
719 |
* @param corePoolSize the number of threads to keep in the |
720 |
* pool, even if they are idle. |
721 |
* @param maximumPoolSize the maximum number of threads to allow in the |
722 |
* pool. |
723 |
* @param keepAliveTime when the number of threads is greater than |
724 |
* the core, this is the maximum time that excess idle threads |
725 |
* will wait for new tasks before terminating. |
726 |
* @param unit the time unit for the keepAliveTime |
727 |
* argument. |
728 |
* @param workQueue the queue to use for holding tasks before they |
729 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
730 |
* tasks submitted by the <tt>execute</tt> method. |
731 |
* @throws IllegalArgumentException if corePoolSize, or |
732 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
733 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
734 |
* @throws NullPointerException if <tt>workQueue</tt> is null |
735 |
*/ |
736 |
public ThreadPoolExecutor(int corePoolSize, |
737 |
int maximumPoolSize, |
738 |
long keepAliveTime, |
739 |
TimeUnit unit, |
740 |
BlockingQueue<Runnable> workQueue) { |
741 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
742 |
Executors.defaultThreadFactory(), defaultHandler); |
743 |
} |
744 |
|
745 |
/** |
746 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
747 |
* parameters and default rejected execution handler. |
748 |
* |
749 |
* @param corePoolSize the number of threads to keep in the |
750 |
* pool, even if they are idle. |
751 |
* @param maximumPoolSize the maximum number of threads to allow in the |
752 |
* pool. |
753 |
* @param keepAliveTime when the number of threads is greater than |
754 |
* the core, this is the maximum time that excess idle threads |
755 |
* will wait for new tasks before terminating. |
756 |
* @param unit the time unit for the keepAliveTime |
757 |
* argument. |
758 |
* @param workQueue the queue to use for holding tasks before they |
759 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
760 |
* tasks submitted by the <tt>execute</tt> method. |
761 |
* @param threadFactory the factory to use when the executor |
762 |
* creates a new thread. |
763 |
* @throws IllegalArgumentException if corePoolSize, or |
764 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
765 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
766 |
* @throws NullPointerException if <tt>workQueue</tt> |
767 |
* or <tt>threadFactory</tt> are null. |
768 |
*/ |
769 |
public ThreadPoolExecutor(int corePoolSize, |
770 |
int maximumPoolSize, |
771 |
long keepAliveTime, |
772 |
TimeUnit unit, |
773 |
BlockingQueue<Runnable> workQueue, |
774 |
ThreadFactory threadFactory) { |
775 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
776 |
threadFactory, defaultHandler); |
777 |
} |
778 |
|
779 |
/** |
780 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
781 |
* parameters and default thread factory. |
782 |
* |
783 |
* @param corePoolSize the number of threads to keep in the |
784 |
* pool, even if they are idle. |
785 |
* @param maximumPoolSize the maximum number of threads to allow in the |
786 |
* pool. |
787 |
* @param keepAliveTime when the number of threads is greater than |
788 |
* the core, this is the maximum time that excess idle threads |
789 |
* will wait for new tasks before terminating. |
790 |
* @param unit the time unit for the keepAliveTime |
791 |
* argument. |
792 |
* @param workQueue the queue to use for holding tasks before they |
793 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
794 |
* tasks submitted by the <tt>execute</tt> method. |
795 |
* @param handler the handler to use when execution is blocked |
796 |
* because the thread bounds and queue capacities are reached. |
797 |
* @throws IllegalArgumentException if corePoolSize, or |
798 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
799 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
800 |
* @throws NullPointerException if <tt>workQueue</tt> |
801 |
* or <tt>handler</tt> are null. |
802 |
*/ |
803 |
public ThreadPoolExecutor(int corePoolSize, |
804 |
int maximumPoolSize, |
805 |
long keepAliveTime, |
806 |
TimeUnit unit, |
807 |
BlockingQueue<Runnable> workQueue, |
808 |
RejectedExecutionHandler handler) { |
809 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
810 |
Executors.defaultThreadFactory(), handler); |
811 |
} |
812 |
|
813 |
/** |
814 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
815 |
* parameters. |
816 |
* |
817 |
* @param corePoolSize the number of threads to keep in the |
818 |
* pool, even if they are idle. |
819 |
* @param maximumPoolSize the maximum number of threads to allow in the |
820 |
* pool. |
821 |
* @param keepAliveTime when the number of threads is greater than |
822 |
* the core, this is the maximum time that excess idle threads |
823 |
* will wait for new tasks before terminating. |
824 |
* @param unit the time unit for the keepAliveTime |
825 |
* argument. |
826 |
* @param workQueue the queue to use for holding tasks before they |
827 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
828 |
* tasks submitted by the <tt>execute</tt> method. |
829 |
* @param threadFactory the factory to use when the executor |
830 |
* creates a new thread. |
831 |
* @param handler the handler to use when execution is blocked |
832 |
* because the thread bounds and queue capacities are reached. |
833 |
* @throws IllegalArgumentException if corePoolSize, or |
834 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
835 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
836 |
* @throws NullPointerException if <tt>workQueue</tt> |
837 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
838 |
*/ |
839 |
public ThreadPoolExecutor(int corePoolSize, |
840 |
int maximumPoolSize, |
841 |
long keepAliveTime, |
842 |
TimeUnit unit, |
843 |
BlockingQueue<Runnable> workQueue, |
844 |
ThreadFactory threadFactory, |
845 |
RejectedExecutionHandler handler) { |
846 |
if (corePoolSize < 0 || |
847 |
maximumPoolSize <= 0 || |
848 |
maximumPoolSize < corePoolSize || |
849 |
keepAliveTime < 0) |
850 |
throw new IllegalArgumentException(); |
851 |
if (workQueue == null || threadFactory == null || handler == null) |
852 |
throw new NullPointerException(); |
853 |
this.corePoolSize = corePoolSize; |
854 |
this.maximumPoolSize = maximumPoolSize; |
855 |
this.workQueue = workQueue; |
856 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
857 |
this.threadFactory = threadFactory; |
858 |
this.handler = handler; |
859 |
} |
860 |
|
861 |
|
862 |
/** |
863 |
* Executes the given task sometime in the future. The task |
864 |
* may execute in a new thread or in an existing pooled thread. |
865 |
* |
866 |
* If the task cannot be submitted for execution, either because this |
867 |
* executor has been shutdown or because its capacity has been reached, |
868 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
869 |
* |
870 |
* @param command the task to execute |
871 |
* @throws RejectedExecutionException at discretion of |
872 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
873 |
* for execution |
874 |
* @throws NullPointerException if command is null |
875 |
*/ |
876 |
public void execute(Runnable command) { |
877 |
if (command == null) |
878 |
throw new NullPointerException(); |
879 |
for (;;) { |
880 |
if (runState != RUNNING) { |
881 |
reject(command); |
882 |
return; |
883 |
} |
884 |
if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) |
885 |
return; |
886 |
if (workQueue.offer(command)) |
887 |
return; |
888 |
int status = addIfUnderMaximumPoolSize(command); |
889 |
if (status > 0) // created new thread |
890 |
return; |
891 |
if (status == 0) { // failed to create thread |
892 |
reject(command); |
893 |
return; |
894 |
} |
895 |
// Retry if created a new thread but it is busy with another task |
896 |
} |
897 |
} |
898 |
|
899 |
/** |
900 |
* Initiates an orderly shutdown in which previously submitted |
901 |
* tasks are executed, but no new tasks will be |
902 |
* accepted. Invocation has no additional effect if already shut |
903 |
* down. |
904 |
* @throws SecurityException if a security manager exists and |
905 |
* shutting down this ExecutorService may manipulate threads that |
906 |
* the caller is not permitted to modify because it does not hold |
907 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
908 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
909 |
*/ |
910 |
public void shutdown() { |
911 |
// Fail if caller doesn't have modifyThread permission. |
912 |
SecurityManager security = System.getSecurityManager(); |
913 |
if (security != null) |
914 |
security.checkPermission(shutdownPerm); |
915 |
|
916 |
boolean fullyTerminated = false; |
917 |
final ReentrantLock mainLock = this.mainLock; |
918 |
mainLock.lock(); |
919 |
try { |
920 |
if (workers.size() > 0) { |
921 |
// Check if caller can modify worker threads. This |
922 |
// might not be true even if passed above check, if |
923 |
// the SecurityManager treats some threads specially. |
924 |
if (security != null) { |
925 |
for (Worker w: workers) |
926 |
security.checkAccess(w.thread); |
927 |
} |
928 |
|
929 |
int state = runState; |
930 |
if (state == RUNNING) // don't override shutdownNow |
931 |
runState = SHUTDOWN; |
932 |
|
933 |
try { |
934 |
for (Worker w: workers) |
935 |
w.interruptIfIdle(); |
936 |
} catch (SecurityException se) { |
937 |
// If SecurityManager allows above checks, but |
938 |
// then unexpectedly throws exception when |
939 |
// interrupting threads (which it ought not do), |
940 |
// back out as cleanly as we can. Some threads may |
941 |
// have been killed but we remain in non-shutdown |
942 |
// state. |
943 |
runState = state; |
944 |
throw se; |
945 |
} |
946 |
} |
947 |
else { // If no workers, trigger full termination now |
948 |
fullyTerminated = true; |
949 |
runState = TERMINATED; |
950 |
termination.signalAll(); |
951 |
} |
952 |
} finally { |
953 |
mainLock.unlock(); |
954 |
} |
955 |
if (fullyTerminated) |
956 |
terminated(); |
957 |
} |
958 |
|
959 |
|
960 |
/** |
961 |
* Attempts to stop all actively executing tasks, halts the |
962 |
* processing of waiting tasks, and returns a list of the tasks |
963 |
* that were awaiting execution. |
964 |
* |
965 |
* <p>There are no guarantees beyond best-effort attempts to stop |
966 |
* processing actively executing tasks. This implementation |
967 |
* cancels tasks via {@link Thread#interrupt}, so any task that |
968 |
* fails to respond to interrupts may never terminate. |
969 |
* |
970 |
* @return list of tasks that never commenced execution |
971 |
* @throws SecurityException if a security manager exists and |
972 |
* shutting down this ExecutorService may manipulate threads that |
973 |
* the caller is not permitted to modify because it does not hold |
974 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
975 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
976 |
*/ |
977 |
public List<Runnable> shutdownNow() { |
978 |
// Almost the same code as shutdown() |
979 |
SecurityManager security = System.getSecurityManager(); |
980 |
if (security != null) |
981 |
security.checkPermission(shutdownPerm); |
982 |
|
983 |
boolean fullyTerminated = false; |
984 |
final ReentrantLock mainLock = this.mainLock; |
985 |
mainLock.lock(); |
986 |
try { |
987 |
if (workers.size() > 0) { |
988 |
if (security != null) { |
989 |
for (Worker w: workers) |
990 |
security.checkAccess(w.thread); |
991 |
} |
992 |
|
993 |
int state = runState; |
994 |
if (state != TERMINATED) |
995 |
runState = STOP; |
996 |
try { |
997 |
for (Worker w : workers) |
998 |
w.interruptNow(); |
999 |
} catch (SecurityException se) { |
1000 |
runState = state; // back out; |
1001 |
throw se; |
1002 |
} |
1003 |
} |
1004 |
else { // If no workers, trigger full termination now |
1005 |
fullyTerminated = true; |
1006 |
runState = TERMINATED; |
1007 |
termination.signalAll(); |
1008 |
} |
1009 |
} finally { |
1010 |
mainLock.unlock(); |
1011 |
} |
1012 |
if (fullyTerminated) |
1013 |
terminated(); |
1014 |
return Arrays.asList(workQueue.toArray(EMPTY_RUNNABLE_ARRAY)); |
1015 |
} |
1016 |
|
1017 |
public boolean isShutdown() { |
1018 |
return runState != RUNNING; |
1019 |
} |
1020 |
|
1021 |
/** |
1022 |
* Returns true if this executor is in the process of terminating |
1023 |
* after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not |
1024 |
* completely terminated. This method may be useful for |
1025 |
* debugging. A return of <tt>true</tt> reported a sufficient |
1026 |
* period after shutdown may indicate that submitted tasks have |
1027 |
* ignored or suppressed interruption, causing this executor not |
1028 |
* to properly terminate. |
1029 |
* @return true if terminating but not yet terminated. |
1030 |
*/ |
1031 |
public boolean isTerminating() { |
1032 |
return runState == STOP; |
1033 |
} |
1034 |
|
1035 |
public boolean isTerminated() { |
1036 |
return runState == TERMINATED; |
1037 |
} |
1038 |
|
1039 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1040 |
throws InterruptedException { |
1041 |
long nanos = unit.toNanos(timeout); |
1042 |
final ReentrantLock mainLock = this.mainLock; |
1043 |
mainLock.lock(); |
1044 |
try { |
1045 |
for (;;) { |
1046 |
if (runState == TERMINATED) |
1047 |
return true; |
1048 |
if (nanos <= 0) |
1049 |
return false; |
1050 |
nanos = termination.awaitNanos(nanos); |
1051 |
} |
1052 |
} finally { |
1053 |
mainLock.unlock(); |
1054 |
} |
1055 |
} |
1056 |
|
1057 |
/** |
1058 |
* Invokes <tt>shutdown</tt> when this executor is no longer |
1059 |
* referenced. |
1060 |
*/ |
1061 |
protected void finalize() { |
1062 |
shutdown(); |
1063 |
} |
1064 |
|
1065 |
/** |
1066 |
* Sets the thread factory used to create new threads. |
1067 |
* |
1068 |
* @param threadFactory the new thread factory |
1069 |
* @throws NullPointerException if threadFactory is null |
1070 |
* @see #getThreadFactory |
1071 |
*/ |
1072 |
public void setThreadFactory(ThreadFactory threadFactory) { |
1073 |
if (threadFactory == null) |
1074 |
throw new NullPointerException(); |
1075 |
this.threadFactory = threadFactory; |
1076 |
} |
1077 |
|
1078 |
/** |
1079 |
* Returns the thread factory used to create new threads. |
1080 |
* |
1081 |
* @return the current thread factory |
1082 |
* @see #setThreadFactory |
1083 |
*/ |
1084 |
public ThreadFactory getThreadFactory() { |
1085 |
return threadFactory; |
1086 |
} |
1087 |
|
1088 |
/** |
1089 |
* Sets a new handler for unexecutable tasks. |
1090 |
* |
1091 |
* @param handler the new handler |
1092 |
* @throws NullPointerException if handler is null |
1093 |
* @see #getRejectedExecutionHandler |
1094 |
*/ |
1095 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
1096 |
if (handler == null) |
1097 |
throw new NullPointerException(); |
1098 |
this.handler = handler; |
1099 |
} |
1100 |
|
1101 |
/** |
1102 |
* Returns the current handler for unexecutable tasks. |
1103 |
* |
1104 |
* @return the current handler |
1105 |
* @see #setRejectedExecutionHandler |
1106 |
*/ |
1107 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
1108 |
return handler; |
1109 |
} |
1110 |
|
1111 |
/** |
1112 |
* Returns the task queue used by this executor. Access to the |
1113 |
* task queue is intended primarily for debugging and monitoring. |
1114 |
* This queue may be in active use. Retrieving the task queue |
1115 |
* does not prevent queued tasks from executing. |
1116 |
* |
1117 |
* @return the task queue |
1118 |
*/ |
1119 |
public BlockingQueue<Runnable> getQueue() { |
1120 |
return workQueue; |
1121 |
} |
1122 |
|
1123 |
/** |
1124 |
* Removes this task from the executor's internal queue if it is |
1125 |
* present, thus causing it not to be run if it has not already |
1126 |
* started. |
1127 |
* |
1128 |
* <p> This method may be useful as one part of a cancellation |
1129 |
* scheme. It may fail to remove tasks that have been converted |
1130 |
* into other forms before being placed on the internal queue. For |
1131 |
* example, a task entered using <tt>submit</tt> might be |
1132 |
* converted into a form that maintains <tt>Future</tt> status. |
1133 |
* However, in such cases, method {@link ThreadPoolExecutor#purge} |
1134 |
* may be used to remove those Futures that have been cancelled. |
1135 |
* |
1136 |
* @param task the task to remove |
1137 |
* @return true if the task was removed |
1138 |
*/ |
1139 |
public boolean remove(Runnable task) { |
1140 |
return getQueue().remove(task); |
1141 |
} |
1142 |
|
1143 |
|
1144 |
/** |
1145 |
* Tries to remove from the work queue all {@link Future} |
1146 |
* tasks that have been cancelled. This method can be useful as a |
1147 |
* storage reclamation operation, that has no other impact on |
1148 |
* functionality. Cancelled tasks are never executed, but may |
1149 |
* accumulate in work queues until worker threads can actively |
1150 |
* remove them. Invoking this method instead tries to remove them now. |
1151 |
* However, this method may fail to remove tasks in |
1152 |
* the presence of interference by other threads. |
1153 |
*/ |
1154 |
public void purge() { |
1155 |
// Fail if we encounter interference during traversal |
1156 |
try { |
1157 |
Iterator<Runnable> it = getQueue().iterator(); |
1158 |
while (it.hasNext()) { |
1159 |
Runnable r = it.next(); |
1160 |
if (r instanceof Future<?>) { |
1161 |
Future<?> c = (Future<?>)r; |
1162 |
if (c.isCancelled()) |
1163 |
it.remove(); |
1164 |
} |
1165 |
} |
1166 |
} |
1167 |
catch (ConcurrentModificationException ex) { |
1168 |
return; |
1169 |
} |
1170 |
} |
1171 |
|
1172 |
/** |
1173 |
* Sets the core number of threads. This overrides any value set |
1174 |
* in the constructor. If the new value is smaller than the |
1175 |
* current value, excess existing threads will be terminated when |
1176 |
* they next become idle. If larger, new threads will, if needed, |
1177 |
* be started to execute any queued tasks. |
1178 |
* |
1179 |
* @param corePoolSize the new core size |
1180 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> |
1181 |
* less than zero |
1182 |
* @see #getCorePoolSize |
1183 |
*/ |
1184 |
public void setCorePoolSize(int corePoolSize) { |
1185 |
if (corePoolSize < 0) |
1186 |
throw new IllegalArgumentException(); |
1187 |
final ReentrantLock mainLock = this.mainLock; |
1188 |
mainLock.lock(); |
1189 |
try { |
1190 |
int extra = this.corePoolSize - corePoolSize; |
1191 |
this.corePoolSize = corePoolSize; |
1192 |
if (extra < 0) { |
1193 |
int n = workQueue.size(); |
1194 |
// We have to create initially-idle threads here |
1195 |
// because we otherwise have no recourse about |
1196 |
// what to do with a dequeued task if addThread fails. |
1197 |
while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize ) { |
1198 |
Thread t = addThread(null); |
1199 |
if (t != null) |
1200 |
t.start(); |
1201 |
else |
1202 |
break; |
1203 |
} |
1204 |
} |
1205 |
else if (extra > 0 && poolSize > corePoolSize) { |
1206 |
Iterator<Worker> it = workers.iterator(); |
1207 |
while (it.hasNext() && |
1208 |
extra-- > 0 && |
1209 |
poolSize > corePoolSize && |
1210 |
workQueue.remainingCapacity() == 0) |
1211 |
it.next().interruptIfIdle(); |
1212 |
} |
1213 |
} finally { |
1214 |
mainLock.unlock(); |
1215 |
} |
1216 |
} |
1217 |
|
1218 |
/** |
1219 |
* Returns the core number of threads. |
1220 |
* |
1221 |
* @return the core number of threads |
1222 |
* @see #setCorePoolSize |
1223 |
*/ |
1224 |
public int getCorePoolSize() { |
1225 |
return corePoolSize; |
1226 |
} |
1227 |
|
1228 |
/** |
1229 |
* Starts a core thread, causing it to idly wait for work. This |
1230 |
* overrides the default policy of starting core threads only when |
1231 |
* new tasks are executed. This method will return <tt>false</tt> |
1232 |
* if all core threads have already been started. |
1233 |
* @return true if a thread was started |
1234 |
*/ |
1235 |
public boolean prestartCoreThread() { |
1236 |
return addIfUnderCorePoolSize(null); |
1237 |
} |
1238 |
|
1239 |
/** |
1240 |
* Starts all core threads, causing them to idly wait for work. This |
1241 |
* overrides the default policy of starting core threads only when |
1242 |
* new tasks are executed. |
1243 |
* @return the number of threads started. |
1244 |
*/ |
1245 |
public int prestartAllCoreThreads() { |
1246 |
int n = 0; |
1247 |
while (addIfUnderCorePoolSize(null)) |
1248 |
++n; |
1249 |
return n; |
1250 |
} |
1251 |
|
1252 |
/** |
1253 |
* Returns true if this pool allows core threads to time out and |
1254 |
* terminate if no tasks arrive within the keepAlive time, being |
1255 |
* replaced if needed when new tasks arrive. When true, the same |
1256 |
* keep-alive policy applying to non-core threads applies also to |
1257 |
* core threads. When false (the default), core threads are never |
1258 |
* terminated due to lack of incoming tasks. |
1259 |
* @return <tt>true</tt> if core threads are allowed to time out, |
1260 |
* else <tt>false</tt> |
1261 |
* |
1262 |
* @since 1.6 |
1263 |
*/ |
1264 |
public boolean allowsCoreThreadTimeOut() { |
1265 |
return allowCoreThreadTimeOut; |
1266 |
} |
1267 |
|
1268 |
/** |
1269 |
* Sets the policy governing whether core threads may time out and |
1270 |
* terminate if no tasks arrive within the keep-alive time, being |
1271 |
* replaced if needed when new tasks arrive. When false, core |
1272 |
* threads are never terminated due to lack of incoming |
1273 |
* tasks. When true, the same keep-alive policy applying to |
1274 |
* non-core threads applies also to core threads. To avoid |
1275 |
* continual thread replacement, the keep-alive time must be |
1276 |
* greater than zero when setting <tt>true</tt>. This method |
1277 |
* should in general be called before the pool is actively used. |
1278 |
* @param value <tt>true</tt> if should time out, else <tt>false</tt> |
1279 |
* @throws IllegalArgumentException if value is <tt>true</tt> |
1280 |
* and the current keep-alive time is not greater than zero. |
1281 |
* |
1282 |
* @since 1.6 |
1283 |
*/ |
1284 |
public void allowCoreThreadTimeOut(boolean value) { |
1285 |
if (value && keepAliveTime <= 0) |
1286 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1287 |
|
1288 |
allowCoreThreadTimeOut = value; |
1289 |
} |
1290 |
|
1291 |
/** |
1292 |
* Sets the maximum allowed number of threads. This overrides any |
1293 |
* value set in the constructor. If the new value is smaller than |
1294 |
* the current value, excess existing threads will be |
1295 |
* terminated when they next become idle. |
1296 |
* |
1297 |
* @param maximumPoolSize the new maximum |
1298 |
* @throws IllegalArgumentException if maximumPoolSize less than zero or |
1299 |
* the {@link #getCorePoolSize core pool size} |
1300 |
* @see #getMaximumPoolSize |
1301 |
*/ |
1302 |
public void setMaximumPoolSize(int maximumPoolSize) { |
1303 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
1304 |
throw new IllegalArgumentException(); |
1305 |
final ReentrantLock mainLock = this.mainLock; |
1306 |
mainLock.lock(); |
1307 |
try { |
1308 |
int extra = this.maximumPoolSize - maximumPoolSize; |
1309 |
this.maximumPoolSize = maximumPoolSize; |
1310 |
if (extra > 0 && poolSize > maximumPoolSize) { |
1311 |
Iterator<Worker> it = workers.iterator(); |
1312 |
while (it.hasNext() && |
1313 |
extra > 0 && |
1314 |
poolSize > maximumPoolSize) { |
1315 |
it.next().interruptIfIdle(); |
1316 |
--extra; |
1317 |
} |
1318 |
} |
1319 |
} finally { |
1320 |
mainLock.unlock(); |
1321 |
} |
1322 |
} |
1323 |
|
1324 |
/** |
1325 |
* Returns the maximum allowed number of threads. |
1326 |
* |
1327 |
* @return the maximum allowed number of threads |
1328 |
* @see #setMaximumPoolSize |
1329 |
*/ |
1330 |
public int getMaximumPoolSize() { |
1331 |
return maximumPoolSize; |
1332 |
} |
1333 |
|
1334 |
/** |
1335 |
* Sets the time limit for which threads may remain idle before |
1336 |
* being terminated. If there are more than the core number of |
1337 |
* threads currently in the pool, after waiting this amount of |
1338 |
* time without processing a task, excess threads will be |
1339 |
* terminated. This overrides any value set in the constructor. |
1340 |
* @param time the time to wait. A time value of zero will cause |
1341 |
* excess threads to terminate immediately after executing tasks. |
1342 |
* @param unit the time unit of the time argument |
1343 |
* @throws IllegalArgumentException if time less than zero or |
1344 |
* if time is zero and allowsCoreThreadTimeOut |
1345 |
* @see #getKeepAliveTime |
1346 |
*/ |
1347 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
1348 |
if (time < 0) |
1349 |
throw new IllegalArgumentException(); |
1350 |
if (time == 0 && allowsCoreThreadTimeOut()) |
1351 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1352 |
this.keepAliveTime = unit.toNanos(time); |
1353 |
} |
1354 |
|
1355 |
/** |
1356 |
* Returns the thread keep-alive time, which is the amount of time |
1357 |
* which threads in excess of the core pool size may remain |
1358 |
* idle before being terminated. |
1359 |
* |
1360 |
* @param unit the desired time unit of the result |
1361 |
* @return the time limit |
1362 |
* @see #setKeepAliveTime |
1363 |
*/ |
1364 |
public long getKeepAliveTime(TimeUnit unit) { |
1365 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
1366 |
} |
1367 |
|
1368 |
/* Statistics */ |
1369 |
|
1370 |
/** |
1371 |
* Returns the current number of threads in the pool. |
1372 |
* |
1373 |
* @return the number of threads |
1374 |
*/ |
1375 |
public int getPoolSize() { |
1376 |
return poolSize; |
1377 |
} |
1378 |
|
1379 |
/** |
1380 |
* Returns the approximate number of threads that are actively |
1381 |
* executing tasks. |
1382 |
* |
1383 |
* @return the number of threads |
1384 |
*/ |
1385 |
public int getActiveCount() { |
1386 |
final ReentrantLock mainLock = this.mainLock; |
1387 |
mainLock.lock(); |
1388 |
try { |
1389 |
int n = 0; |
1390 |
for (Worker w : workers) { |
1391 |
if (w.isActive()) |
1392 |
++n; |
1393 |
} |
1394 |
return n; |
1395 |
} finally { |
1396 |
mainLock.unlock(); |
1397 |
} |
1398 |
} |
1399 |
|
1400 |
/** |
1401 |
* Returns the largest number of threads that have ever |
1402 |
* simultaneously been in the pool. |
1403 |
* |
1404 |
* @return the number of threads |
1405 |
*/ |
1406 |
public int getLargestPoolSize() { |
1407 |
final ReentrantLock mainLock = this.mainLock; |
1408 |
mainLock.lock(); |
1409 |
try { |
1410 |
return largestPoolSize; |
1411 |
} finally { |
1412 |
mainLock.unlock(); |
1413 |
} |
1414 |
} |
1415 |
|
1416 |
/** |
1417 |
* Returns the approximate total number of tasks that have been |
1418 |
* scheduled for execution. Because the states of tasks and |
1419 |
* threads may change dynamically during computation, the returned |
1420 |
* value is only an approximation, but one that does not ever |
1421 |
* decrease across successive calls. |
1422 |
* |
1423 |
* @return the number of tasks |
1424 |
*/ |
1425 |
public long getTaskCount() { |
1426 |
final ReentrantLock mainLock = this.mainLock; |
1427 |
mainLock.lock(); |
1428 |
try { |
1429 |
long n = completedTaskCount; |
1430 |
for (Worker w : workers) { |
1431 |
n += w.completedTasks; |
1432 |
if (w.isActive()) |
1433 |
++n; |
1434 |
} |
1435 |
return n + workQueue.size(); |
1436 |
} finally { |
1437 |
mainLock.unlock(); |
1438 |
} |
1439 |
} |
1440 |
|
1441 |
/** |
1442 |
* Returns the approximate total number of tasks that have |
1443 |
* completed execution. Because the states of tasks and threads |
1444 |
* may change dynamically during computation, the returned value |
1445 |
* is only an approximation, but one that does not ever decrease |
1446 |
* across successive calls. |
1447 |
* |
1448 |
* @return the number of tasks |
1449 |
*/ |
1450 |
public long getCompletedTaskCount() { |
1451 |
final ReentrantLock mainLock = this.mainLock; |
1452 |
mainLock.lock(); |
1453 |
try { |
1454 |
long n = completedTaskCount; |
1455 |
for (Worker w : workers) |
1456 |
n += w.completedTasks; |
1457 |
return n; |
1458 |
} finally { |
1459 |
mainLock.unlock(); |
1460 |
} |
1461 |
} |
1462 |
|
1463 |
/** |
1464 |
* Method invoked prior to executing the given Runnable in the |
1465 |
* given thread. This method is invoked by thread <tt>t</tt> that |
1466 |
* will execute task <tt>r</tt>, and may be used to re-initialize |
1467 |
* ThreadLocals, or to perform logging. |
1468 |
* |
1469 |
* <p>This implementation does nothing, but may be customized in |
1470 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1471 |
* should generally invoke <tt>super.beforeExecute</tt> at the end of |
1472 |
* this method. |
1473 |
* |
1474 |
* @param t the thread that will run task r. |
1475 |
* @param r the task that will be executed. |
1476 |
*/ |
1477 |
protected void beforeExecute(Thread t, Runnable r) { } |
1478 |
|
1479 |
/** |
1480 |
* Method invoked upon completion of execution of the given Runnable. |
1481 |
* This method is invoked by the thread that executed the task. If |
1482 |
* non-null, the Throwable is the uncaught <tt>RuntimeException</tt> |
1483 |
* or <tt>Error</tt> that caused execution to terminate abruptly. |
1484 |
* |
1485 |
* <p><b>Note:</b> When actions are enclosed in tasks (such as |
1486 |
* {@link FutureTask}) either explicitly or via methods such as |
1487 |
* <tt>submit</tt>, these task objects catch and maintain |
1488 |
* computational exceptions, and so they do not cause abrupt |
1489 |
* termination, and the internal exceptions are <em>not</em> |
1490 |
* passed to this method. |
1491 |
* |
1492 |
* <p>This implementation does nothing, but may be customized in |
1493 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1494 |
* should generally invoke <tt>super.afterExecute</tt> at the |
1495 |
* beginning of this method. |
1496 |
* |
1497 |
* @param r the runnable that has completed. |
1498 |
* @param t the exception that caused termination, or null if |
1499 |
* execution completed normally. |
1500 |
*/ |
1501 |
protected void afterExecute(Runnable r, Throwable t) { } |
1502 |
|
1503 |
/** |
1504 |
* Method invoked when the Executor has terminated. Default |
1505 |
* implementation does nothing. Note: To properly nest multiple |
1506 |
* overridings, subclasses should generally invoke |
1507 |
* <tt>super.terminated</tt> within this method. |
1508 |
*/ |
1509 |
protected void terminated() { } |
1510 |
|
1511 |
/** |
1512 |
* A handler for rejected tasks that runs the rejected task |
1513 |
* directly in the calling thread of the <tt>execute</tt> method, |
1514 |
* unless the executor has been shut down, in which case the task |
1515 |
* is discarded. |
1516 |
*/ |
1517 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1518 |
/** |
1519 |
* Creates a <tt>CallerRunsPolicy</tt>. |
1520 |
*/ |
1521 |
public CallerRunsPolicy() { } |
1522 |
|
1523 |
/** |
1524 |
* Executes task r in the caller's thread, unless the executor |
1525 |
* has been shut down, in which case the task is discarded. |
1526 |
* @param r the runnable task requested to be executed |
1527 |
* @param e the executor attempting to execute this task |
1528 |
*/ |
1529 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1530 |
if (!e.isShutdown()) { |
1531 |
r.run(); |
1532 |
} |
1533 |
} |
1534 |
} |
1535 |
|
1536 |
/** |
1537 |
* A handler for rejected tasks that throws a |
1538 |
* <tt>RejectedExecutionException</tt>. |
1539 |
*/ |
1540 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1541 |
/** |
1542 |
* Creates an <tt>AbortPolicy</tt>. |
1543 |
*/ |
1544 |
public AbortPolicy() { } |
1545 |
|
1546 |
/** |
1547 |
* Always throws RejectedExecutionException. |
1548 |
* @param r the runnable task requested to be executed |
1549 |
* @param e the executor attempting to execute this task |
1550 |
* @throws RejectedExecutionException always. |
1551 |
*/ |
1552 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1553 |
throw new RejectedExecutionException(); |
1554 |
} |
1555 |
} |
1556 |
|
1557 |
/** |
1558 |
* A handler for rejected tasks that silently discards the |
1559 |
* rejected task. |
1560 |
*/ |
1561 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1562 |
/** |
1563 |
* Creates a <tt>DiscardPolicy</tt>. |
1564 |
*/ |
1565 |
public DiscardPolicy() { } |
1566 |
|
1567 |
/** |
1568 |
* Does nothing, which has the effect of discarding task r. |
1569 |
* @param r the runnable task requested to be executed |
1570 |
* @param e the executor attempting to execute this task |
1571 |
*/ |
1572 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1573 |
} |
1574 |
} |
1575 |
|
1576 |
/** |
1577 |
* A handler for rejected tasks that discards the oldest unhandled |
1578 |
* request and then retries <tt>execute</tt>, unless the executor |
1579 |
* is shut down, in which case the task is discarded. |
1580 |
*/ |
1581 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1582 |
/** |
1583 |
* Creates a <tt>DiscardOldestPolicy</tt> for the given executor. |
1584 |
*/ |
1585 |
public DiscardOldestPolicy() { } |
1586 |
|
1587 |
/** |
1588 |
* Obtains and ignores the next task that the executor |
1589 |
* would otherwise execute, if one is immediately available, |
1590 |
* and then retries execution of task r, unless the executor |
1591 |
* is shut down, in which case task r is instead discarded. |
1592 |
* @param r the runnable task requested to be executed |
1593 |
* @param e the executor attempting to execute this task |
1594 |
*/ |
1595 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1596 |
if (!e.isShutdown()) { |
1597 |
e.getQueue().poll(); |
1598 |
e.execute(r); |
1599 |
} |
1600 |
} |
1601 |
} |
1602 |
} |