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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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/** |
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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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* A ThreadPoolExecutor manages a largish set of control fields. |
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* State changes in fields that affect execution control |
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* guarantees only occur within mainLock regions. These include |
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* fields runState, poolSize, corePoolSize, and maximumPoolSize |
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* However, these fields are also declared volatile, so can be |
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* read outside of locked regions. (Also, the workers Set is |
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* accessed only under lock). |
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* |
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* The other fields representing user control parameters do not |
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* affect execution invariants, so are declared volatile and |
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* allowed to change (via user methods) asynchronously with |
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* execution. These fields: allowCoreThreadTimeOut, keepAliveTime, |
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* the rejected execution handler, and threadFactory, are not |
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* updated within locks. |
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* |
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* The extensive use of volatiles here enables the most |
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* performance-critical actions, such as enqueuing and dequeuing |
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* tasks in the workQueue, to normally proceed without holding the |
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* mainLock when they see that the state allows actions, although, |
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* as described below, sometimes at the expense of re-checks |
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* following these actions. |
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*/ |
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|
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/** |
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* runState provides the main lifecyle control, taking on values: |
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* |
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* RUNNING: Accept new tasks and process queued tasks |
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* SHUTDOWN: Don't accept new tasks, but process queued tasks |
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* STOP: Don't accept new tasks, don't process queued tasks, |
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* and interrupt in-progress tasks |
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* TERMINATED: Same as STOP, plus all threads have terminated |
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* |
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* The numerical order among these values matters, to allow |
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* ordered comparisons. The runState monotonically increases over |
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* time, but need not hit each state. The transitions are: |
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* |
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* RUNNING -> SHUTDOWN |
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* On invocation of shutdown(), perhaps implicitly in finalize() |
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* (RUNNING or SHUTDOWN) -> STOP |
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* On invocation of shutdownNow() |
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* SHUTDOWN -> TERMINATED |
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* When both queue and pool are empty |
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* STOP -> TERMINATED |
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* When pool is empty |
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*/ |
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volatile int runState; |
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static final int RUNNING = 0; |
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static final int SHUTDOWN = 1; |
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static final int STOP = 2; |
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static final int TERMINATED = 3; |
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|
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/** |
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* The queue used for holding tasks and handing off to worker |
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* threads. Note that when using this queue, we do not require |
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* that workQueue.poll() returning null necessarily means that |
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* workQueue.isEmpty(), so must sometimes check both. This |
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* accommodates special-purpose queues such as DelayQueues for |
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* which poll() is allowed to return null even if it may later |
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* return non-null when delays expire. |
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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, |
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* maximumPoolSize, runState, and 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. Accessed only when |
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* holding mainLock. |
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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 when there are more than corePoolSize |
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* present or if allowCoreThreadTimeOut. Otherwise they wait |
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* 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. If |
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* true, core threads use keepAliveTime to time out waiting for |
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* 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, but |
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* volatile to allow concurrent readability even 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 but |
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* volatile to allow concurrent readability even 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 but |
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* volatile to allow concurrent readability even 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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* 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. All threads are created using this |
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* factory (via method addThread). All callers must be prepared |
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* for addThread to fail by returning null, which may reflect a |
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* system or user's policy limiting the number of threads. Even |
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* though it is not treated as an error, failure to create threads |
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* may result in new tasks being rejected or existing ones |
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* remaining stuck in the queue. On the other hand, no special |
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* precautions exist to handle OutOfMemoryErrors that might be |
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* thrown while trying to create threads, since there is generally |
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* no recourse from within this class. |
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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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// Constructors |
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|
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/** |
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* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
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* parameters and default thread factory and rejected execution handler. |
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* It may be more convenient to use one of the {@link Executors} factory |
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* methods instead of this general purpose constructor. |
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* |
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* @param corePoolSize the number of threads to keep in the |
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* pool, even if they are idle. |
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* @param maximumPoolSize the maximum number of threads to allow in the |
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* pool. |
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* @param keepAliveTime when the number of threads is greater than |
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* the core, this is the maximum time that excess idle threads |
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* will wait for new tasks before terminating. |
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* @param unit the time unit for the keepAliveTime |
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* argument. |
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* @param workQueue the queue to use for holding tasks before they |
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* are executed. This queue will hold only the <tt>Runnable</tt> |
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* tasks submitted by the <tt>execute</tt> method. |
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* @throws IllegalArgumentException if corePoolSize, or |
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* keepAliveTime less than zero, or if maximumPoolSize less than or |
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* equal to zero, or if corePoolSize greater than maximumPoolSize. |
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* @throws NullPointerException if <tt>workQueue</tt> is null |
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*/ |
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public ThreadPoolExecutor(int corePoolSize, |
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int maximumPoolSize, |
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long keepAliveTime, |
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TimeUnit unit, |
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BlockingQueue<Runnable> workQueue) { |
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this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
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Executors.defaultThreadFactory(), defaultHandler); |
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} |
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|
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/** |
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* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
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* parameters and default rejected execution handler. |
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* |
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* @param corePoolSize the number of threads to keep in the |
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* pool, even if they are idle. |
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* @param maximumPoolSize the maximum number of threads to allow in the |
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* pool. |
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* @param keepAliveTime when the number of threads is greater than |
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* the core, this is the maximum time that excess idle threads |
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* will wait for new tasks before terminating. |
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* @param unit the time unit for the keepAliveTime |
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* argument. |
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* @param workQueue the queue to use for holding tasks before they |
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* are executed. This queue will hold only the <tt>Runnable</tt> |
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* tasks submitted by the <tt>execute</tt> method. |
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* @param threadFactory the factory to use when the executor |
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* creates a new thread. |
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* @throws IllegalArgumentException if corePoolSize, or |
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* keepAliveTime less than zero, or if maximumPoolSize less than or |
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* equal to zero, or if corePoolSize greater than maximumPoolSize. |
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* @throws NullPointerException if <tt>workQueue</tt> |
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* or <tt>threadFactory</tt> are null. |
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*/ |
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public ThreadPoolExecutor(int corePoolSize, |
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int maximumPoolSize, |
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long keepAliveTime, |
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TimeUnit unit, |
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BlockingQueue<Runnable> workQueue, |
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ThreadFactory threadFactory) { |
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this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
514 |
threadFactory, defaultHandler); |
515 |
} |
516 |
|
517 |
/** |
518 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
519 |
* parameters and default thread factory. |
520 |
* |
521 |
* @param corePoolSize the number of threads to keep in the |
522 |
* pool, even if they are idle. |
523 |
* @param maximumPoolSize the maximum number of threads to allow in the |
524 |
* pool. |
525 |
* @param keepAliveTime when the number of threads is greater than |
526 |
* the core, this is the maximum time that excess idle threads |
527 |
* will wait for new tasks before terminating. |
528 |
* @param unit the time unit for the keepAliveTime |
529 |
* argument. |
530 |
* @param workQueue the queue to use for holding tasks before they |
531 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
532 |
* tasks submitted by the <tt>execute</tt> method. |
533 |
* @param handler the handler to use when execution is blocked |
534 |
* because the thread bounds and queue capacities are reached. |
535 |
* @throws IllegalArgumentException if corePoolSize, or |
536 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
537 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
538 |
* @throws NullPointerException if <tt>workQueue</tt> |
539 |
* or <tt>handler</tt> are null. |
540 |
*/ |
541 |
public ThreadPoolExecutor(int corePoolSize, |
542 |
int maximumPoolSize, |
543 |
long keepAliveTime, |
544 |
TimeUnit unit, |
545 |
BlockingQueue<Runnable> workQueue, |
546 |
RejectedExecutionHandler handler) { |
547 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
548 |
Executors.defaultThreadFactory(), handler); |
549 |
} |
550 |
|
551 |
/** |
552 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
553 |
* parameters. |
554 |
* |
555 |
* @param corePoolSize the number of threads to keep in the |
556 |
* pool, even if they are idle. |
557 |
* @param maximumPoolSize the maximum number of threads to allow in the |
558 |
* pool. |
559 |
* @param keepAliveTime when the number of threads is greater than |
560 |
* the core, this is the maximum time that excess idle threads |
561 |
* will wait for new tasks before terminating. |
562 |
* @param unit the time unit for the keepAliveTime |
563 |
* argument. |
564 |
* @param workQueue the queue to use for holding tasks before they |
565 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
566 |
* tasks submitted by the <tt>execute</tt> method. |
567 |
* @param threadFactory the factory to use when the executor |
568 |
* creates a new thread. |
569 |
* @param handler the handler to use when execution is blocked |
570 |
* because the thread bounds and queue capacities are reached. |
571 |
* @throws IllegalArgumentException if corePoolSize, or |
572 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
573 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
574 |
* @throws NullPointerException if <tt>workQueue</tt> |
575 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
576 |
*/ |
577 |
public ThreadPoolExecutor(int corePoolSize, |
578 |
int maximumPoolSize, |
579 |
long keepAliveTime, |
580 |
TimeUnit unit, |
581 |
BlockingQueue<Runnable> workQueue, |
582 |
ThreadFactory threadFactory, |
583 |
RejectedExecutionHandler handler) { |
584 |
if (corePoolSize < 0 || |
585 |
maximumPoolSize <= 0 || |
586 |
maximumPoolSize < corePoolSize || |
587 |
keepAliveTime < 0) |
588 |
throw new IllegalArgumentException(); |
589 |
if (workQueue == null || threadFactory == null || handler == null) |
590 |
throw new NullPointerException(); |
591 |
this.corePoolSize = corePoolSize; |
592 |
this.maximumPoolSize = maximumPoolSize; |
593 |
this.workQueue = workQueue; |
594 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
595 |
this.threadFactory = threadFactory; |
596 |
this.handler = handler; |
597 |
} |
598 |
|
599 |
/* |
600 |
* Support for execute(). |
601 |
* |
602 |
* Method execute() and its helper methods handle the various |
603 |
* cases encountered when new tasks are submitted. The main |
604 |
* execute() method proceeds in 3 steps: |
605 |
* |
606 |
* 1. If it appears that fewer than corePoolSize threads are |
607 |
* running, try to start a new thread with the given command as |
608 |
* its first task. The check here errs on the side of caution. |
609 |
* The call to addIfUnderCorePoolSize rechecks runState and pool |
610 |
* size under lock (they change only under lock) so prevents false |
611 |
* alarms that would add threads when it shouldn't, but may also |
612 |
* fail to add them when they should. This is compensated within |
613 |
* the following steps. |
614 |
* |
615 |
* 2. If a task can be successfully queued, then we are done, but |
616 |
* still need to compensate for missing the fact that we should |
617 |
* have added a thread (because existing ones died) or that |
618 |
* shutdown occurred since entry into this method. So we recheck |
619 |
* state to and if necessary (in ensureQueuedTaskHandled) roll |
620 |
* back the enqueuing if shut down, or start a new thread if there |
621 |
* are none. |
622 |
* |
623 |
* 3. If we cannot queue task, then we try to add a new |
624 |
* thread. There's no guesswork here (addIfUnderMaximumPoolSize) |
625 |
* since it is performed under lock. If it fails, we know we are |
626 |
* shut down or saturated. |
627 |
* |
628 |
* The reason for taking this overall approach is to normally |
629 |
* avoid holding mainLock during this method, which would be a |
630 |
* serious scalability bottleneck. After warmup, almost all calls |
631 |
* take step 2 in a way that entails no locking. |
632 |
*/ |
633 |
|
634 |
/** |
635 |
* Executes the given task sometime in the future. The task |
636 |
* may execute in a new thread or in an existing pooled thread. |
637 |
* |
638 |
* If the task cannot be submitted for execution, either because this |
639 |
* executor has been shutdown or because its capacity has been reached, |
640 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
641 |
* |
642 |
* @param command the task to execute |
643 |
* @throws RejectedExecutionException at discretion of |
644 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
645 |
* for execution |
646 |
* @throws NullPointerException if command is null |
647 |
*/ |
648 |
public void execute(Runnable command) { |
649 |
if (command == null) |
650 |
throw new NullPointerException(); |
651 |
if (poolSize >= corePoolSize || !addIfUnderCorePoolSize(command)) { |
652 |
if (runState == RUNNING && workQueue.offer(command)) { |
653 |
if (runState != RUNNING || poolSize == 0) |
654 |
ensureQueuedTaskHandled(command); |
655 |
} |
656 |
else if (!addIfUnderMaximumPoolSize(command)) |
657 |
reject(command); // is shutdown or saturated |
658 |
} |
659 |
} |
660 |
|
661 |
/** |
662 |
* Creates and returns a new thread running firstTask as its first |
663 |
* task. Call only while holding mainLock. |
664 |
* |
665 |
* @param firstTask the task the new thread should run first (or |
666 |
* null if none) |
667 |
* @return the new thread, or null if threadFactory fails to create thread |
668 |
*/ |
669 |
private Thread addThread(Runnable firstTask) { |
670 |
Worker w = new Worker(firstTask); |
671 |
Thread t = threadFactory.newThread(w); |
672 |
if (t != null) { |
673 |
w.thread = t; |
674 |
workers.add(w); |
675 |
int nt = ++poolSize; |
676 |
if (nt > largestPoolSize) |
677 |
largestPoolSize = nt; |
678 |
} |
679 |
return t; |
680 |
} |
681 |
|
682 |
/** |
683 |
* Creates and starts a new thread running firstTask as its first |
684 |
* task, only if fewer than corePoolSize threads are running |
685 |
* and the pool is not shut down. |
686 |
* @param firstTask the task the new thread should run first (or |
687 |
* null if none) |
688 |
* @return true if successful |
689 |
*/ |
690 |
private boolean addIfUnderCorePoolSize(Runnable firstTask) { |
691 |
Thread t = null; |
692 |
final ReentrantLock mainLock = this.mainLock; |
693 |
mainLock.lock(); |
694 |
try { |
695 |
if (poolSize < corePoolSize && runState == RUNNING) |
696 |
t = addThread(firstTask); |
697 |
} finally { |
698 |
mainLock.unlock(); |
699 |
} |
700 |
if (t == null) |
701 |
return false; |
702 |
t.start(); |
703 |
return true; |
704 |
} |
705 |
|
706 |
/** |
707 |
* Creates and starts a new thread running firstTask as its first |
708 |
* task, only if fewer than maximumPoolSize threads are running |
709 |
* and pool is not shut down. |
710 |
* @param firstTask the task the new thread should run first (or |
711 |
* null if none) |
712 |
* @return true if successful |
713 |
*/ |
714 |
private boolean addIfUnderMaximumPoolSize(Runnable firstTask) { |
715 |
Thread t = null; |
716 |
final ReentrantLock mainLock = this.mainLock; |
717 |
mainLock.lock(); |
718 |
try { |
719 |
if (poolSize < maximumPoolSize && runState == RUNNING) |
720 |
t = addThread(firstTask); |
721 |
} finally { |
722 |
mainLock.unlock(); |
723 |
} |
724 |
if (t == null) |
725 |
return false; |
726 |
t.start(); |
727 |
return true; |
728 |
} |
729 |
|
730 |
/** |
731 |
* Rechecks state after queuing a task. Called from execute when |
732 |
* pool state has been observed to change after queuing a task. If |
733 |
* the task was queued concurrently with a call to shutdownNow, |
734 |
* and is still present in the queue, this task must be removed |
735 |
* and rejected to preserve shutdownNow guarantees. Otherwise, |
736 |
* this method ensures (unless addThread fails) that there is at |
737 |
* least one live thread to handle this task |
738 |
* @param command the task |
739 |
*/ |
740 |
private void ensureQueuedTaskHandled(Runnable command) { |
741 |
final ReentrantLock mainLock = this.mainLock; |
742 |
mainLock.lock(); |
743 |
boolean reject = false; |
744 |
Thread t = null; |
745 |
try { |
746 |
int state = runState; |
747 |
if (state != RUNNING && workQueue.remove(command)) |
748 |
reject = true; |
749 |
else if (state < STOP && |
750 |
poolSize < Math.max(corePoolSize, 1) && |
751 |
!workQueue.isEmpty()) |
752 |
t = addThread(null); |
753 |
} finally { |
754 |
mainLock.unlock(); |
755 |
} |
756 |
if (reject) |
757 |
reject(command); |
758 |
else if (t != null) |
759 |
t.start(); |
760 |
} |
761 |
|
762 |
/** |
763 |
* Invokes the rejected execution handler for the given command. |
764 |
*/ |
765 |
void reject(Runnable command) { |
766 |
handler.rejectedExecution(command, this); |
767 |
} |
768 |
|
769 |
|
770 |
/** |
771 |
* Worker threads. |
772 |
* |
773 |
* Worker threads can start out life either with an initial first |
774 |
* task, or without one. Normally, they are started with a first |
775 |
* task. This enables execute(), etc to bypass queuing when there |
776 |
* are fewer than corePoolSize threads (in which case we always |
777 |
* start one), or when the queue is full.(in which case we must |
778 |
* bypass queue.) Initially idle threads are created either by |
779 |
* users (prestartCoreThread and setCorePoolSize) or when methods |
780 |
* ensureQueuedTaskHandled and tryTerminate notice that the queue |
781 |
* is not empty but there are no active threads to handle them. |
782 |
* |
783 |
* After completing a task, workers try to get another one, |
784 |
* via method getTask. If they cannot (i.e., getTask returns |
785 |
* null), they exit, calling workerDone to update pool state. |
786 |
* |
787 |
* When starting to run a task, unless the pool is stopped, each |
788 |
* worker thread ensures that it is not interrupted, and uses |
789 |
* runLock to prevent the pool from interrupting it in the midst |
790 |
* of execution. This shields user tasks from any interrupts that |
791 |
* may otherwise be needed during shutdown (see method |
792 |
* interruptIdleWorkers), unless the pool is stopping (via |
793 |
* shutdownNow) in which case interrupts are let through to affect |
794 |
* both tasks and workers. However, this shielding does not |
795 |
* necessarily protect the workers from lagging interrupts from |
796 |
* other user threads directed towards tasks that have already |
797 |
* been completed. Thus, a worker thread may be interrupted |
798 |
* needlessly (for example in getTask), in which case it rechecks |
799 |
* pool state to see if it should exit. |
800 |
* |
801 |
*/ |
802 |
private final class Worker implements Runnable { |
803 |
/** |
804 |
* The runLock is acquired and released surrounding each task |
805 |
* execution. It mainly protects against interrupts that are |
806 |
* intended to cancel the worker thread from instead |
807 |
* interrupting the task being run. |
808 |
*/ |
809 |
private final ReentrantLock runLock = new ReentrantLock(); |
810 |
|
811 |
/** |
812 |
* Initial task to run before entering run loop. Possibly null. |
813 |
*/ |
814 |
private Runnable firstTask; |
815 |
|
816 |
/** |
817 |
* Per thread completed task counter; accumulated |
818 |
* into completedTaskCount upon termination. |
819 |
*/ |
820 |
volatile long completedTasks; |
821 |
|
822 |
/** |
823 |
* Thread this worker is running in. Acts as a final field, |
824 |
* but cannot be set until thread is created. |
825 |
*/ |
826 |
Thread thread; |
827 |
|
828 |
Worker(Runnable firstTask) { |
829 |
this.firstTask = firstTask; |
830 |
} |
831 |
|
832 |
boolean isActive() { |
833 |
return runLock.isLocked(); |
834 |
} |
835 |
|
836 |
/** |
837 |
* Interrupts thread if not running a task. |
838 |
*/ |
839 |
void interruptIfIdle() { |
840 |
final ReentrantLock runLock = this.runLock; |
841 |
if (runLock.tryLock()) { |
842 |
try { |
843 |
thread.interrupt(); |
844 |
} finally { |
845 |
runLock.unlock(); |
846 |
} |
847 |
} |
848 |
} |
849 |
|
850 |
/** |
851 |
* Interrupts thread even if running a task. |
852 |
*/ |
853 |
void interruptNow() { |
854 |
thread.interrupt(); |
855 |
} |
856 |
|
857 |
/** |
858 |
* Runs a single task between before/after methods. |
859 |
*/ |
860 |
private void runTask(Runnable task) { |
861 |
final ReentrantLock runLock = this.runLock; |
862 |
runLock.lock(); |
863 |
try { |
864 |
/* |
865 |
* Ensure that unless pool is stopping, this thread |
866 |
* does not have its interrupt set. This requires a |
867 |
* double-check of state in case the interrupt was |
868 |
* cleared concurrently with a shutdownNow -- if so, |
869 |
* the interrupt is re-enabled. |
870 |
*/ |
871 |
if (runState < STOP && |
872 |
Thread.interrupted() && |
873 |
runState >= STOP) |
874 |
thread.interrupt(); |
875 |
/* |
876 |
* Track execution state to ensure that afterExecute |
877 |
* is called only if task completed or threw |
878 |
* exception. Otherwise, the caught runtime exception |
879 |
* will have been thrown by afterExecute itself, in |
880 |
* which case we don't want to call it again. |
881 |
*/ |
882 |
boolean ran = false; |
883 |
beforeExecute(thread, task); |
884 |
try { |
885 |
task.run(); |
886 |
ran = true; |
887 |
afterExecute(task, null); |
888 |
++completedTasks; |
889 |
} catch (RuntimeException ex) { |
890 |
if (!ran) |
891 |
afterExecute(task, ex); |
892 |
throw ex; |
893 |
} |
894 |
} finally { |
895 |
runLock.unlock(); |
896 |
} |
897 |
} |
898 |
|
899 |
/** |
900 |
* Main run loop |
901 |
*/ |
902 |
public void run() { |
903 |
try { |
904 |
Runnable task = firstTask; |
905 |
firstTask = null; |
906 |
while (task != null || (task = getTask()) != null) { |
907 |
runTask(task); |
908 |
task = null; |
909 |
} |
910 |
} finally { |
911 |
workerDone(this); |
912 |
} |
913 |
} |
914 |
} |
915 |
|
916 |
/* Utilities for worker thread control */ |
917 |
|
918 |
/** |
919 |
* Gets the next task for a worker thread to run. The general |
920 |
* approach is similar to execute() in that worker threads trying |
921 |
* to get a task to run do so on the basis of prevailing state |
922 |
* accessed outside of locks. This may cause them to choose the |
923 |
* "wrong" action, such as or trying to exit because no tasks |
924 |
* appear to be available, or entering a take when the pool is in |
925 |
* the process of being shut down. These potential problems are |
926 |
* countered by (1) rechecking pool state (in workerCanExit) |
927 |
* before giving up, and (2) interrupting other workers upon |
928 |
* shutdown, so they can recheck state. All other user-based state |
929 |
* changes (to allowCoreThreadTimeOut etc) are OK even when |
930 |
* performed asynchronously wrt getTask. |
931 |
* |
932 |
* @return the task |
933 |
*/ |
934 |
Runnable getTask() { |
935 |
for (;;) { |
936 |
try { |
937 |
int state = runState; |
938 |
if (state > SHUTDOWN) |
939 |
return null; |
940 |
Runnable r; |
941 |
if (state == SHUTDOWN) // Help drain queue |
942 |
r = workQueue.poll(); |
943 |
else if (poolSize > corePoolSize || allowCoreThreadTimeOut) |
944 |
r = workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS); |
945 |
else |
946 |
r = workQueue.take(); |
947 |
if (r != null) |
948 |
return r; |
949 |
if (workerCanExit()) { |
950 |
if (runState >= SHUTDOWN) // Wake up others |
951 |
interruptIdleWorkers(); |
952 |
return null; |
953 |
} |
954 |
// Else retry |
955 |
} catch (InterruptedException ie) { |
956 |
// On interruption, re-check runState |
957 |
} |
958 |
} |
959 |
} |
960 |
|
961 |
/** |
962 |
* Check whether a worker thread that fails to get a task can |
963 |
* exit. We allow a worker thread to die if the pool is stopping, |
964 |
* or the queue is empty, or there is at least one thread to |
965 |
* handle possibly non-empty queue, even if core timeouts are |
966 |
* allowed. |
967 |
*/ |
968 |
private boolean workerCanExit() { |
969 |
final ReentrantLock mainLock = this.mainLock; |
970 |
mainLock.lock(); |
971 |
boolean canExit; |
972 |
try { |
973 |
canExit = runState >= STOP || |
974 |
workQueue.isEmpty() || |
975 |
(allowCoreThreadTimeOut && |
976 |
poolSize > Math.max(1, corePoolSize)); |
977 |
} finally { |
978 |
mainLock.unlock(); |
979 |
} |
980 |
return canExit; |
981 |
} |
982 |
|
983 |
/** |
984 |
* Wakes up all threads that might be waiting for tasks so they |
985 |
* can check for termination. Note: this method is also called by |
986 |
* ScheduledThreadPoolExecutor. |
987 |
*/ |
988 |
void interruptIdleWorkers() { |
989 |
final ReentrantLock mainLock = this.mainLock; |
990 |
mainLock.lock(); |
991 |
try { |
992 |
for (Worker w : workers) |
993 |
w.interruptIfIdle(); |
994 |
} finally { |
995 |
mainLock.unlock(); |
996 |
} |
997 |
} |
998 |
|
999 |
/** |
1000 |
* Performs bookkeeping for an exiting worker thread. |
1001 |
* @param w the worker |
1002 |
*/ |
1003 |
void workerDone(Worker w) { |
1004 |
final ReentrantLock mainLock = this.mainLock; |
1005 |
mainLock.lock(); |
1006 |
try { |
1007 |
completedTaskCount += w.completedTasks; |
1008 |
workers.remove(w); |
1009 |
if (--poolSize == 0) |
1010 |
tryTerminate(); |
1011 |
} finally { |
1012 |
mainLock.unlock(); |
1013 |
} |
1014 |
} |
1015 |
|
1016 |
/* Termination support. */ |
1017 |
|
1018 |
/** |
1019 |
* Transitions to TERMINATED state if either (SHUTDOWN and pool |
1020 |
* and queue empty) or (STOP and pool empty), otherwise unless |
1021 |
* stopped, ensuring that there is at least one live thread to |
1022 |
* handle queued tasks. |
1023 |
* |
1024 |
* This method is called from the three places in which |
1025 |
* termination can occur: in workerDone on exit of the last thread |
1026 |
* after pool has been shut down, or directly within calls to |
1027 |
* shutdown or shutdownNow, if there are no live threads. |
1028 |
*/ |
1029 |
private void tryTerminate() { |
1030 |
if (poolSize == 0) { |
1031 |
int state = runState; |
1032 |
if (state < STOP && !workQueue.isEmpty()) { |
1033 |
state = RUNNING; // disable termination check below |
1034 |
Thread t = addThread(null); |
1035 |
if (t != null) |
1036 |
t.start(); |
1037 |
} |
1038 |
if (state == STOP || state == SHUTDOWN) { |
1039 |
runState = TERMINATED; |
1040 |
termination.signalAll(); |
1041 |
terminated(); |
1042 |
} |
1043 |
} |
1044 |
} |
1045 |
|
1046 |
/** |
1047 |
* Initiates an orderly shutdown in which previously submitted |
1048 |
* tasks are executed, but no new tasks will be |
1049 |
* accepted. Invocation has no additional effect if already shut |
1050 |
* down. |
1051 |
* @throws SecurityException if a security manager exists and |
1052 |
* shutting down this ExecutorService may manipulate threads that |
1053 |
* the caller is not permitted to modify because it does not hold |
1054 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
1055 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
1056 |
*/ |
1057 |
public void shutdown() { |
1058 |
/* |
1059 |
* Conceptually, shutdown is just a matter of changing the |
1060 |
* runState to SHUTDOWN, and then interrupting any worker |
1061 |
* threads that might be blocked in getTask() to wake them up |
1062 |
* so they can exit. Then, if there happen not to be any |
1063 |
* threads or tasks, we can directly terminate pool via |
1064 |
* tryTerminate. |
1065 |
* |
1066 |
* But this is made more delicate because we must cooperate |
1067 |
* with the security manager (if present), which may implement |
1068 |
* policies that make more sense for operations on Threads |
1069 |
* than they do for ThreadPools. This requires 3 steps: |
1070 |
* |
1071 |
* 1. Making sure caller has permission to shut down threads |
1072 |
* in general (see shutdownPerm). |
1073 |
* |
1074 |
* 2. If (1) passes, making sure the caller is allowed to |
1075 |
* modify each of our threads. This might not be true even if |
1076 |
* first check passed, if the SecurityManager treats some |
1077 |
* threads specially. If this check passes, then we can try |
1078 |
* to set runState. |
1079 |
* |
1080 |
* 3. If both (1) and (2) pass, dealing with inconsistent |
1081 |
* security managers that allow checkAccess but then throw a |
1082 |
* SecurityException when interrupt() is invoked. In this |
1083 |
* third case, because we have already set runState, we can |
1084 |
* only try to back out from the shutdown.as cleanly as |
1085 |
* possible. Some threads may have been killed but we remain |
1086 |
* in non-shutdown state (which may entail tryTerminate |
1087 |
* starting a thread to maintain liveness.) |
1088 |
*/ |
1089 |
|
1090 |
SecurityManager security = System.getSecurityManager(); |
1091 |
if (security != null) |
1092 |
security.checkPermission(shutdownPerm); |
1093 |
|
1094 |
final ReentrantLock mainLock = this.mainLock; |
1095 |
mainLock.lock(); |
1096 |
try { |
1097 |
if (security != null) { // Check if caller can modify our threads |
1098 |
for (Worker w: workers) |
1099 |
security.checkAccess(w.thread); |
1100 |
} |
1101 |
|
1102 |
int state = runState; |
1103 |
if (state < SHUTDOWN) |
1104 |
runState = SHUTDOWN; |
1105 |
|
1106 |
try { |
1107 |
for (Worker w: workers) { |
1108 |
w.interruptIfIdle(); |
1109 |
} |
1110 |
} catch (SecurityException se) { // Try to back out |
1111 |
runState = state; |
1112 |
tryTerminate(); |
1113 |
throw se; |
1114 |
} |
1115 |
|
1116 |
tryTerminate(); // Terminate now if pool and queue empty |
1117 |
} finally { |
1118 |
mainLock.unlock(); |
1119 |
} |
1120 |
} |
1121 |
|
1122 |
/** |
1123 |
* Attempts to stop all actively executing tasks, halts the |
1124 |
* processing of waiting tasks, and returns a list of the tasks |
1125 |
* that were awaiting execution. These tasks are drained (removed) |
1126 |
* from the task queue upon return from this method. |
1127 |
* |
1128 |
* <p>There are no guarantees beyond best-effort attempts to stop |
1129 |
* processing actively executing tasks. This implementation |
1130 |
* cancels tasks via {@link Thread#interrupt}, so any task that |
1131 |
* fails to respond to interrupts may never terminate. |
1132 |
* |
1133 |
* @return list of tasks that never commenced execution |
1134 |
* @throws SecurityException if a security manager exists and |
1135 |
* shutting down this ExecutorService may manipulate threads that |
1136 |
* the caller is not permitted to modify because it does not hold |
1137 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
1138 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
1139 |
*/ |
1140 |
public List<Runnable> shutdownNow() { |
1141 |
/* |
1142 |
* shutdownNow differs from shutdown only in that |
1143 |
* (1) runState is set to STOP, (2) All worker threads |
1144 |
* are interrupted, not just the idle ones, and (3) |
1145 |
* the queue is drained and returned. |
1146 |
*/ |
1147 |
SecurityManager security = System.getSecurityManager(); |
1148 |
if (security != null) |
1149 |
security.checkPermission(shutdownPerm); |
1150 |
|
1151 |
final ReentrantLock mainLock = this.mainLock; |
1152 |
mainLock.lock(); |
1153 |
try { |
1154 |
if (security != null) { // Check if caller can modify our threads |
1155 |
for (Worker w: workers) |
1156 |
security.checkAccess(w.thread); |
1157 |
} |
1158 |
|
1159 |
int state = runState; |
1160 |
if (state < STOP) |
1161 |
runState = STOP; |
1162 |
|
1163 |
try { |
1164 |
for (Worker w : workers) { |
1165 |
w.interruptNow(); |
1166 |
} |
1167 |
} catch (SecurityException se) { // Try to back out |
1168 |
runState = state; |
1169 |
tryTerminate(); |
1170 |
throw se; |
1171 |
} |
1172 |
|
1173 |
List<Runnable> tasks = drainQueue(); |
1174 |
tryTerminate(); // Terminate now if pool and queue empty |
1175 |
return tasks; |
1176 |
} finally { |
1177 |
mainLock.unlock(); |
1178 |
} |
1179 |
} |
1180 |
|
1181 |
/** |
1182 |
* Drains the task queue into a new list. Used by shutdownNow. |
1183 |
* Call only while holding main lock. |
1184 |
*/ |
1185 |
private List<Runnable> drainQueue() { |
1186 |
List<Runnable> taskList = new ArrayList<Runnable>(); |
1187 |
workQueue.drainTo(taskList); |
1188 |
/* |
1189 |
* If the queue is a DelayQueue or any other kind of queue |
1190 |
* for which poll or drainTo may fail to remove some elements, |
1191 |
* we need to manually traverse and remove remaining tasks. |
1192 |
* To guarantee atomicity wrt other threads using this queue, |
1193 |
* we need to create a new iterator for each element removed. |
1194 |
*/ |
1195 |
while (!workQueue.isEmpty()) { |
1196 |
Iterator<Runnable> it = workQueue.iterator(); |
1197 |
try { |
1198 |
if (it.hasNext()) { |
1199 |
Runnable r = it.next(); |
1200 |
if (workQueue.remove(r)) |
1201 |
taskList.add(r); |
1202 |
} |
1203 |
} catch(ConcurrentModificationException ignore) { |
1204 |
} |
1205 |
} |
1206 |
return taskList; |
1207 |
} |
1208 |
|
1209 |
public boolean isShutdown() { |
1210 |
return runState != RUNNING; |
1211 |
} |
1212 |
|
1213 |
/** |
1214 |
* Returns true if this executor is in the process of terminating |
1215 |
* after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not |
1216 |
* completely terminated. This method may be useful for |
1217 |
* debugging. A return of <tt>true</tt> reported a sufficient |
1218 |
* period after shutdown may indicate that submitted tasks have |
1219 |
* ignored or suppressed interruption, causing this executor not |
1220 |
* to properly terminate. |
1221 |
* @return true if terminating but not yet terminated. |
1222 |
*/ |
1223 |
public boolean isTerminating() { |
1224 |
return runState == STOP; |
1225 |
} |
1226 |
|
1227 |
public boolean isTerminated() { |
1228 |
return runState == TERMINATED; |
1229 |
} |
1230 |
|
1231 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1232 |
throws InterruptedException { |
1233 |
long nanos = unit.toNanos(timeout); |
1234 |
final ReentrantLock mainLock = this.mainLock; |
1235 |
mainLock.lock(); |
1236 |
try { |
1237 |
for (;;) { |
1238 |
if (runState == TERMINATED) |
1239 |
return true; |
1240 |
if (nanos <= 0) |
1241 |
return false; |
1242 |
nanos = termination.awaitNanos(nanos); |
1243 |
} |
1244 |
} finally { |
1245 |
mainLock.unlock(); |
1246 |
} |
1247 |
} |
1248 |
|
1249 |
/** |
1250 |
* Invokes <tt>shutdown</tt> when this executor is no longer |
1251 |
* referenced. |
1252 |
*/ |
1253 |
protected void finalize() { |
1254 |
shutdown(); |
1255 |
} |
1256 |
|
1257 |
/* Getting and setting tunable parameters */ |
1258 |
|
1259 |
/** |
1260 |
* Sets the thread factory used to create new threads. |
1261 |
* |
1262 |
* @param threadFactory the new thread factory |
1263 |
* @throws NullPointerException if threadFactory is null |
1264 |
* @see #getThreadFactory |
1265 |
*/ |
1266 |
public void setThreadFactory(ThreadFactory threadFactory) { |
1267 |
if (threadFactory == null) |
1268 |
throw new NullPointerException(); |
1269 |
this.threadFactory = threadFactory; |
1270 |
} |
1271 |
|
1272 |
/** |
1273 |
* Returns the thread factory used to create new threads. |
1274 |
* |
1275 |
* @return the current thread factory |
1276 |
* @see #setThreadFactory |
1277 |
*/ |
1278 |
public ThreadFactory getThreadFactory() { |
1279 |
return threadFactory; |
1280 |
} |
1281 |
|
1282 |
/** |
1283 |
* Sets a new handler for unexecutable tasks. |
1284 |
* |
1285 |
* @param handler the new handler |
1286 |
* @throws NullPointerException if handler is null |
1287 |
* @see #getRejectedExecutionHandler |
1288 |
*/ |
1289 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
1290 |
if (handler == null) |
1291 |
throw new NullPointerException(); |
1292 |
this.handler = handler; |
1293 |
} |
1294 |
|
1295 |
/** |
1296 |
* Returns the current handler for unexecutable tasks. |
1297 |
* |
1298 |
* @return the current handler |
1299 |
* @see #setRejectedExecutionHandler |
1300 |
*/ |
1301 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
1302 |
return handler; |
1303 |
} |
1304 |
|
1305 |
/** |
1306 |
* Sets the core number of threads. This overrides any value set |
1307 |
* in the constructor. If the new value is smaller than the |
1308 |
* current value, excess existing threads will be terminated when |
1309 |
* they next become idle. If larger, new threads will, if needed, |
1310 |
* be started to execute any queued tasks. |
1311 |
* |
1312 |
* @param corePoolSize the new core size |
1313 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> |
1314 |
* less than zero |
1315 |
* @see #getCorePoolSize |
1316 |
*/ |
1317 |
public void setCorePoolSize(int corePoolSize) { |
1318 |
if (corePoolSize < 0) |
1319 |
throw new IllegalArgumentException(); |
1320 |
final ReentrantLock mainLock = this.mainLock; |
1321 |
mainLock.lock(); |
1322 |
try { |
1323 |
int extra = this.corePoolSize - corePoolSize; |
1324 |
this.corePoolSize = corePoolSize; |
1325 |
if (extra < 0) { |
1326 |
int n = workQueue.size(); // don't add more threads than tasks |
1327 |
while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize) { |
1328 |
Thread t = addThread(null); |
1329 |
if (t != null) |
1330 |
t.start(); |
1331 |
else |
1332 |
break; |
1333 |
} |
1334 |
} |
1335 |
else if (extra > 0 && poolSize > corePoolSize) { |
1336 |
try { |
1337 |
Iterator<Worker> it = workers.iterator(); |
1338 |
while (it.hasNext() && |
1339 |
extra-- > 0 && |
1340 |
poolSize > corePoolSize && |
1341 |
workQueue.remainingCapacity() == 0) |
1342 |
it.next().interruptIfIdle(); |
1343 |
} catch(SecurityException ignore) { |
1344 |
// Not an error; it is OK if the threads stay live |
1345 |
} |
1346 |
} |
1347 |
} finally { |
1348 |
mainLock.unlock(); |
1349 |
} |
1350 |
} |
1351 |
|
1352 |
/** |
1353 |
* Returns the core number of threads. |
1354 |
* |
1355 |
* @return the core number of threads |
1356 |
* @see #setCorePoolSize |
1357 |
*/ |
1358 |
public int getCorePoolSize() { |
1359 |
return corePoolSize; |
1360 |
} |
1361 |
|
1362 |
/** |
1363 |
* Starts a core thread, causing it to idly wait for work. This |
1364 |
* overrides the default policy of starting core threads only when |
1365 |
* new tasks are executed. This method will return <tt>false</tt> |
1366 |
* if all core threads have already been started. |
1367 |
* @return true if a thread was started |
1368 |
*/ |
1369 |
public boolean prestartCoreThread() { |
1370 |
return addIfUnderCorePoolSize(null); |
1371 |
} |
1372 |
|
1373 |
/** |
1374 |
* Starts all core threads, causing them to idly wait for work. This |
1375 |
* overrides the default policy of starting core threads only when |
1376 |
* new tasks are executed. |
1377 |
* @return the number of threads started |
1378 |
*/ |
1379 |
public int prestartAllCoreThreads() { |
1380 |
int n = 0; |
1381 |
while (addIfUnderCorePoolSize(null)) |
1382 |
++n; |
1383 |
return n; |
1384 |
} |
1385 |
|
1386 |
/** |
1387 |
* Returns true if this pool allows core threads to time out and |
1388 |
* terminate if no tasks arrive within the keepAlive time, being |
1389 |
* replaced if needed when new tasks arrive. When true, the same |
1390 |
* keep-alive policy applying to non-core threads applies also to |
1391 |
* core threads. When false (the default), core threads are never |
1392 |
* terminated due to lack of incoming tasks. |
1393 |
* @return <tt>true</tt> if core threads are allowed to time out, |
1394 |
* else <tt>false</tt> |
1395 |
* |
1396 |
* @since 1.6 |
1397 |
*/ |
1398 |
public boolean allowsCoreThreadTimeOut() { |
1399 |
return allowCoreThreadTimeOut; |
1400 |
} |
1401 |
|
1402 |
/** |
1403 |
* Sets the policy governing whether core threads may time out and |
1404 |
* terminate if no tasks arrive within the keep-alive time, being |
1405 |
* replaced if needed when new tasks arrive. When false, core |
1406 |
* threads are never terminated due to lack of incoming |
1407 |
* tasks. When true, the same keep-alive policy applying to |
1408 |
* non-core threads applies also to core threads. To avoid |
1409 |
* continual thread replacement, the keep-alive time must be |
1410 |
* greater than zero when setting <tt>true</tt>. This method |
1411 |
* should in general be called before the pool is actively used. |
1412 |
* @param value <tt>true</tt> if should time out, else <tt>false</tt> |
1413 |
* @throws IllegalArgumentException if value is <tt>true</tt> |
1414 |
* and the current keep-alive time is not greater than zero. |
1415 |
* |
1416 |
* @since 1.6 |
1417 |
*/ |
1418 |
public void allowCoreThreadTimeOut(boolean value) { |
1419 |
if (value && keepAliveTime <= 0) |
1420 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1421 |
|
1422 |
allowCoreThreadTimeOut = value; |
1423 |
} |
1424 |
|
1425 |
/** |
1426 |
* Sets the maximum allowed number of threads. This overrides any |
1427 |
* value set in the constructor. If the new value is smaller than |
1428 |
* the current value, excess existing threads will be |
1429 |
* terminated when they next become idle. |
1430 |
* |
1431 |
* @param maximumPoolSize the new maximum |
1432 |
* @throws IllegalArgumentException if the new maximum is |
1433 |
* less than or equal to zero, or |
1434 |
* less than the {@linkplain #getCorePoolSize core pool size} |
1435 |
* @see #getMaximumPoolSize |
1436 |
*/ |
1437 |
public void setMaximumPoolSize(int maximumPoolSize) { |
1438 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
1439 |
throw new IllegalArgumentException(); |
1440 |
final ReentrantLock mainLock = this.mainLock; |
1441 |
mainLock.lock(); |
1442 |
try { |
1443 |
int extra = this.maximumPoolSize - maximumPoolSize; |
1444 |
this.maximumPoolSize = maximumPoolSize; |
1445 |
if (extra > 0 && poolSize > maximumPoolSize) { |
1446 |
try { |
1447 |
Iterator<Worker> it = workers.iterator(); |
1448 |
while (it.hasNext() && |
1449 |
extra > 0 && |
1450 |
poolSize > maximumPoolSize) { |
1451 |
it.next().interruptIfIdle(); |
1452 |
--extra; |
1453 |
} |
1454 |
} catch(SecurityException ignore) { |
1455 |
// Not an error; it is OK if the threads stay live |
1456 |
} |
1457 |
} |
1458 |
} finally { |
1459 |
mainLock.unlock(); |
1460 |
} |
1461 |
} |
1462 |
|
1463 |
/** |
1464 |
* Returns the maximum allowed number of threads. |
1465 |
* |
1466 |
* @return the maximum allowed number of threads |
1467 |
* @see #setMaximumPoolSize |
1468 |
*/ |
1469 |
public int getMaximumPoolSize() { |
1470 |
return maximumPoolSize; |
1471 |
} |
1472 |
|
1473 |
/** |
1474 |
* Sets the time limit for which threads may remain idle before |
1475 |
* being terminated. If there are more than the core number of |
1476 |
* threads currently in the pool, after waiting this amount of |
1477 |
* time without processing a task, excess threads will be |
1478 |
* terminated. This overrides any value set in the constructor. |
1479 |
* @param time the time to wait. A time value of zero will cause |
1480 |
* excess threads to terminate immediately after executing tasks. |
1481 |
* @param unit the time unit of the time argument |
1482 |
* @throws IllegalArgumentException if time less than zero or |
1483 |
* if time is zero and allowsCoreThreadTimeOut |
1484 |
* @see #getKeepAliveTime |
1485 |
*/ |
1486 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
1487 |
if (time < 0) |
1488 |
throw new IllegalArgumentException(); |
1489 |
if (time == 0 && allowsCoreThreadTimeOut()) |
1490 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1491 |
this.keepAliveTime = unit.toNanos(time); |
1492 |
} |
1493 |
|
1494 |
/** |
1495 |
* Returns the thread keep-alive time, which is the amount of time |
1496 |
* which threads in excess of the core pool size may remain |
1497 |
* idle before being terminated. |
1498 |
* |
1499 |
* @param unit the desired time unit of the result |
1500 |
* @return the time limit |
1501 |
* @see #setKeepAliveTime |
1502 |
*/ |
1503 |
public long getKeepAliveTime(TimeUnit unit) { |
1504 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
1505 |
} |
1506 |
|
1507 |
/* User-level queue utilities */ |
1508 |
|
1509 |
/** |
1510 |
* Returns the task queue used by this executor. Access to the |
1511 |
* task queue is intended primarily for debugging and monitoring. |
1512 |
* This queue may be in active use. Retrieving the task queue |
1513 |
* does not prevent queued tasks from executing. |
1514 |
* |
1515 |
* @return the task queue |
1516 |
*/ |
1517 |
public BlockingQueue<Runnable> getQueue() { |
1518 |
return workQueue; |
1519 |
} |
1520 |
|
1521 |
/** |
1522 |
* Removes this task from the executor's internal queue if it is |
1523 |
* present, thus causing it not to be run if it has not already |
1524 |
* started. |
1525 |
* |
1526 |
* <p> This method may be useful as one part of a cancellation |
1527 |
* scheme. It may fail to remove tasks that have been converted |
1528 |
* into other forms before being placed on the internal queue. For |
1529 |
* example, a task entered using <tt>submit</tt> might be |
1530 |
* converted into a form that maintains <tt>Future</tt> status. |
1531 |
* However, in such cases, method {@link ThreadPoolExecutor#purge} |
1532 |
* may be used to remove those Futures that have been cancelled. |
1533 |
* |
1534 |
* @param task the task to remove |
1535 |
* @return true if the task was removed |
1536 |
*/ |
1537 |
public boolean remove(Runnable task) { |
1538 |
return getQueue().remove(task); |
1539 |
} |
1540 |
|
1541 |
/** |
1542 |
* Tries to remove from the work queue all {@link Future} |
1543 |
* tasks that have been cancelled. This method can be useful as a |
1544 |
* storage reclamation operation, that has no other impact on |
1545 |
* functionality. Cancelled tasks are never executed, but may |
1546 |
* accumulate in work queues until worker threads can actively |
1547 |
* remove them. Invoking this method instead tries to remove them now. |
1548 |
* However, this method may fail to remove tasks in |
1549 |
* the presence of interference by other threads. |
1550 |
*/ |
1551 |
public void purge() { |
1552 |
// Fail if we encounter interference during traversal |
1553 |
try { |
1554 |
Iterator<Runnable> it = getQueue().iterator(); |
1555 |
while (it.hasNext()) { |
1556 |
Runnable r = it.next(); |
1557 |
if (r instanceof Future<?>) { |
1558 |
Future<?> c = (Future<?>)r; |
1559 |
if (c.isCancelled()) |
1560 |
it.remove(); |
1561 |
} |
1562 |
} |
1563 |
} |
1564 |
catch (ConcurrentModificationException ex) { |
1565 |
return; |
1566 |
} |
1567 |
} |
1568 |
|
1569 |
/* Statistics */ |
1570 |
|
1571 |
/** |
1572 |
* Returns the current number of threads in the pool. |
1573 |
* |
1574 |
* @return the number of threads |
1575 |
*/ |
1576 |
public int getPoolSize() { |
1577 |
return poolSize; |
1578 |
} |
1579 |
|
1580 |
/** |
1581 |
* Returns the approximate number of threads that are actively |
1582 |
* executing tasks. |
1583 |
* |
1584 |
* @return the number of threads |
1585 |
*/ |
1586 |
public int getActiveCount() { |
1587 |
final ReentrantLock mainLock = this.mainLock; |
1588 |
mainLock.lock(); |
1589 |
try { |
1590 |
int n = 0; |
1591 |
for (Worker w : workers) { |
1592 |
if (w.isActive()) |
1593 |
++n; |
1594 |
} |
1595 |
return n; |
1596 |
} finally { |
1597 |
mainLock.unlock(); |
1598 |
} |
1599 |
} |
1600 |
|
1601 |
/** |
1602 |
* Returns the largest number of threads that have ever |
1603 |
* simultaneously been in the pool. |
1604 |
* |
1605 |
* @return the number of threads |
1606 |
*/ |
1607 |
public int getLargestPoolSize() { |
1608 |
final ReentrantLock mainLock = this.mainLock; |
1609 |
mainLock.lock(); |
1610 |
try { |
1611 |
return largestPoolSize; |
1612 |
} finally { |
1613 |
mainLock.unlock(); |
1614 |
} |
1615 |
} |
1616 |
|
1617 |
/** |
1618 |
* Returns the approximate total number of tasks that have ever been |
1619 |
* scheduled for execution. Because the states of tasks and |
1620 |
* threads may change dynamically during computation, the returned |
1621 |
* value is only an approximation, but one that does not ever |
1622 |
* decrease across successive calls. |
1623 |
* |
1624 |
* @return the number of tasks |
1625 |
*/ |
1626 |
public long getTaskCount() { |
1627 |
final ReentrantLock mainLock = this.mainLock; |
1628 |
mainLock.lock(); |
1629 |
try { |
1630 |
long n = completedTaskCount; |
1631 |
for (Worker w : workers) { |
1632 |
n += w.completedTasks; |
1633 |
if (w.isActive()) |
1634 |
++n; |
1635 |
} |
1636 |
return n + workQueue.size(); |
1637 |
} finally { |
1638 |
mainLock.unlock(); |
1639 |
} |
1640 |
} |
1641 |
|
1642 |
/** |
1643 |
* Returns the approximate total number of tasks that have |
1644 |
* completed execution. Because the states of tasks and threads |
1645 |
* may change dynamically during computation, the returned value |
1646 |
* is only an approximation, but one that does not ever decrease |
1647 |
* across successive calls. |
1648 |
* |
1649 |
* @return the number of tasks |
1650 |
*/ |
1651 |
public long getCompletedTaskCount() { |
1652 |
final ReentrantLock mainLock = this.mainLock; |
1653 |
mainLock.lock(); |
1654 |
try { |
1655 |
long n = completedTaskCount; |
1656 |
for (Worker w : workers) |
1657 |
n += w.completedTasks; |
1658 |
return n; |
1659 |
} finally { |
1660 |
mainLock.unlock(); |
1661 |
} |
1662 |
} |
1663 |
|
1664 |
/* Extension hooks */ |
1665 |
|
1666 |
/** |
1667 |
* Method invoked prior to executing the given Runnable in the |
1668 |
* given thread. This method is invoked by thread <tt>t</tt> that |
1669 |
* will execute task <tt>r</tt>, and may be used to re-initialize |
1670 |
* ThreadLocals, or to perform logging. |
1671 |
* |
1672 |
* <p>This implementation does nothing, but may be customized in |
1673 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1674 |
* should generally invoke <tt>super.beforeExecute</tt> at the end of |
1675 |
* this method. |
1676 |
* |
1677 |
* @param t the thread that will run task r. |
1678 |
* @param r the task that will be executed. |
1679 |
*/ |
1680 |
protected void beforeExecute(Thread t, Runnable r) { } |
1681 |
|
1682 |
/** |
1683 |
* Method invoked upon completion of execution of the given Runnable. |
1684 |
* This method is invoked by the thread that executed the task. If |
1685 |
* non-null, the Throwable is the uncaught <tt>RuntimeException</tt> |
1686 |
* or <tt>Error</tt> that caused execution to terminate abruptly. |
1687 |
* |
1688 |
* <p><b>Note:</b> When actions are enclosed in tasks (such as |
1689 |
* {@link FutureTask}) either explicitly or via methods such as |
1690 |
* <tt>submit</tt>, these task objects catch and maintain |
1691 |
* computational exceptions, and so they do not cause abrupt |
1692 |
* termination, and the internal exceptions are <em>not</em> |
1693 |
* passed to this method. |
1694 |
* |
1695 |
* <p>This implementation does nothing, but may be customized in |
1696 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1697 |
* should generally invoke <tt>super.afterExecute</tt> at the |
1698 |
* beginning of this method. |
1699 |
* |
1700 |
* @param r the runnable that has completed. |
1701 |
* @param t the exception that caused termination, or null if |
1702 |
* execution completed normally. |
1703 |
*/ |
1704 |
protected void afterExecute(Runnable r, Throwable t) { } |
1705 |
|
1706 |
/** |
1707 |
* Method invoked when the Executor has terminated. Default |
1708 |
* implementation does nothing. Note: To properly nest multiple |
1709 |
* overridings, subclasses should generally invoke |
1710 |
* <tt>super.terminated</tt> within this method. |
1711 |
*/ |
1712 |
protected void terminated() { } |
1713 |
|
1714 |
/* Predefined RejectedExecutionHandlers */ |
1715 |
|
1716 |
/** |
1717 |
* A handler for rejected tasks that runs the rejected task |
1718 |
* directly in the calling thread of the <tt>execute</tt> method, |
1719 |
* unless the executor has been shut down, in which case the task |
1720 |
* is discarded. |
1721 |
*/ |
1722 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1723 |
/** |
1724 |
* Creates a <tt>CallerRunsPolicy</tt>. |
1725 |
*/ |
1726 |
public CallerRunsPolicy() { } |
1727 |
|
1728 |
/** |
1729 |
* Executes task r in the caller's thread, unless the executor |
1730 |
* has been shut down, in which case the task is discarded. |
1731 |
* @param r the runnable task requested to be executed |
1732 |
* @param e the executor attempting to execute this task |
1733 |
*/ |
1734 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1735 |
if (!e.isShutdown()) { |
1736 |
r.run(); |
1737 |
} |
1738 |
} |
1739 |
} |
1740 |
|
1741 |
/** |
1742 |
* A handler for rejected tasks that throws a |
1743 |
* <tt>RejectedExecutionException</tt>. |
1744 |
*/ |
1745 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1746 |
/** |
1747 |
* Creates an <tt>AbortPolicy</tt>. |
1748 |
*/ |
1749 |
public AbortPolicy() { } |
1750 |
|
1751 |
/** |
1752 |
* Always throws RejectedExecutionException. |
1753 |
* @param r the runnable task requested to be executed |
1754 |
* @param e the executor attempting to execute this task |
1755 |
* @throws RejectedExecutionException always. |
1756 |
*/ |
1757 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1758 |
throw new RejectedExecutionException(); |
1759 |
} |
1760 |
} |
1761 |
|
1762 |
/** |
1763 |
* A handler for rejected tasks that silently discards the |
1764 |
* rejected task. |
1765 |
*/ |
1766 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1767 |
/** |
1768 |
* Creates a <tt>DiscardPolicy</tt>. |
1769 |
*/ |
1770 |
public DiscardPolicy() { } |
1771 |
|
1772 |
/** |
1773 |
* Does nothing, which has the effect of discarding task r. |
1774 |
* @param r the runnable task requested to be executed |
1775 |
* @param e the executor attempting to execute this task |
1776 |
*/ |
1777 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1778 |
} |
1779 |
} |
1780 |
|
1781 |
/** |
1782 |
* A handler for rejected tasks that discards the oldest unhandled |
1783 |
* request and then retries <tt>execute</tt>, unless the executor |
1784 |
* is shut down, in which case the task is discarded. |
1785 |
*/ |
1786 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1787 |
/** |
1788 |
* Creates a <tt>DiscardOldestPolicy</tt> for the given executor. |
1789 |
*/ |
1790 |
public DiscardOldestPolicy() { } |
1791 |
|
1792 |
/** |
1793 |
* Obtains and ignores the next task that the executor |
1794 |
* would otherwise execute, if one is immediately available, |
1795 |
* and then retries execution of task r, unless the executor |
1796 |
* is shut down, in which case task r is instead discarded. |
1797 |
* @param r the runnable task requested to be executed |
1798 |
* @param e the executor attempting to execute this task |
1799 |
*/ |
1800 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1801 |
if (!e.isShutdown()) { |
1802 |
e.getQueue().poll(); |
1803 |
e.execute(r); |
1804 |
} |
1805 |
} |
1806 |
} |
1807 |
} |