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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.*; // for javadoc (till 6280605 is fixed) |
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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> </dl> |
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* |
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* <p> <b>Extension example</b>. Most extensions of this class |
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* override one or more of the protected hook methods. For example, |
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* here is a subclass that adds a simple pause/resume feature: |
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* |
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* <pre> |
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* class PausableThreadPoolExecutor extends ThreadPoolExecutor { |
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* private boolean isPaused; |
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* private ReentrantLock pauseLock = new ReentrantLock(); |
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* private Condition unpaused = pauseLock.newCondition(); |
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* |
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* public PausableThreadPoolExecutor(...) { super(...); } |
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* |
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* protected void beforeExecute(Thread t, Runnable r) { |
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* super.beforeExecute(t, r); |
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* pauseLock.lock(); |
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* try { |
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* while (isPaused) unpaused.await(); |
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* } catch (InterruptedException ie) { |
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* t.interrupt(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void pause() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = true; |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void resume() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = false; |
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* unpaused.signalAll(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* } |
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* </pre> |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class ThreadPoolExecutor extends AbstractExecutorService { |
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/** |
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* Only used to force toArray() to produce a Runnable[]. |
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*/ |
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private static final Runnable[] EMPTY_RUNNABLE_ARRAY = new Runnable[0]; |
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|
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/** |
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* Permission for checking shutdown |
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*/ |
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private static final RuntimePermission shutdownPerm = |
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new RuntimePermission("modifyThread"); |
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|
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/** |
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* Queue used for holding tasks and handing off to worker threads. |
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*/ |
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private final BlockingQueue<Runnable> workQueue; |
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|
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/** |
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* Lock held on updates to poolSize, corePoolSize, maximumPoolSize, and |
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* workers set. |
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*/ |
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private final ReentrantLock mainLock = new ReentrantLock(); |
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|
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/** |
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* Wait condition to support awaitTermination |
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*/ |
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private final Condition termination = mainLock.newCondition(); |
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|
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/** |
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* Set containing all worker threads in pool. |
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*/ |
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private final HashSet<Worker> workers = new HashSet<Worker>(); |
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|
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/** |
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* Timeout in nanoseconds for idle threads waiting for work. |
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* Threads use this timeout only when there are more than |
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* corePoolSize present. Otherwise they wait forever for new work. |
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*/ |
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private volatile long keepAliveTime; |
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|
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/** |
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* If false (default) core threads stay alive even when idle. |
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* If true, core threads use keepAliveTime to time out waiting for work. |
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*/ |
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private boolean allowCoreThreadTimeOut; |
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|
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/** |
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* Core pool size, updated only while holding mainLock, |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int corePoolSize; |
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|
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/** |
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* Maximum pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int maximumPoolSize; |
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|
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/** |
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* Current pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int poolSize; |
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|
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/** |
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* Lifecycle state |
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*/ |
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volatile int runState; |
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|
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// Special values for runState |
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/** Normal, not-shutdown mode */ |
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static final int RUNNING = 0; |
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/** Controlled shutdown mode */ |
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static final int SHUTDOWN = 1; |
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/** Immediate shutdown mode */ |
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static final int STOP = 2; |
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/** Final state */ |
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static final int TERMINATED = 3; |
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|
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/** |
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* Handler called when saturated or shutdown in execute. |
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*/ |
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private volatile RejectedExecutionHandler handler; |
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|
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/** |
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* Factory for new threads. |
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*/ |
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private volatile ThreadFactory threadFactory; |
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|
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/** |
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* Tracks largest attained pool size. |
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*/ |
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private int largestPoolSize; |
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|
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/** |
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* Counter for completed tasks. Updated only on termination of |
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* worker threads. |
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*/ |
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private long completedTaskCount; |
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|
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/** |
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* The default rejected execution handler |
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*/ |
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private static final RejectedExecutionHandler defaultHandler = |
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new AbortPolicy(); |
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|
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/** |
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* Invokes the rejected execution handler for the given command. |
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*/ |
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void reject(Runnable command) { |
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handler.rejectedExecution(command, this); |
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} |
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|
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/** |
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* Creates and returns a new thread running firstTask as its first |
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* task. Call only while holding mainLock. |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return the new thread, or null if threadFactory fails to create thread |
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*/ |
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private Thread addThread(Runnable firstTask) { |
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Worker w = new Worker(firstTask); |
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Thread t = threadFactory.newThread(w); |
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if (t != null) { |
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w.thread = t; |
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workers.add(w); |
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int nt = ++poolSize; |
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if (nt > largestPoolSize) |
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largestPoolSize = nt; |
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} |
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return t; |
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} |
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|
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/** |
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* Creates and starts a new thread running firstTask as its first |
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* task, only if fewer than corePoolSize threads are running. |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return true if successful. |
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*/ |
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private boolean addIfUnderCorePoolSize(Runnable firstTask) { |
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Thread t = null; |
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final ReentrantLock mainLock = this.mainLock; |
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mainLock.lock(); |
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try { |
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if (poolSize < corePoolSize) |
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t = addThread(firstTask); |
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} finally { |
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mainLock.unlock(); |
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} |
435 |
if (t == null) |
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return false; |
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t.start(); |
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return true; |
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} |
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|
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/** |
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* Creates and starts a new thread only if fewer than maximumPoolSize |
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* threads are running. The new thread runs as its first task the |
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* next task in queue, or if there is none, the given task. |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return 0 if a new thread cannot be created, a positive number |
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* if firstTask will be run in a new thread, or a negative number |
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* if a new thread was created but is running some other task, in |
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* which case the caller must try some other way to run firstTask |
451 |
* (perhaps by calling this method again). |
452 |
*/ |
453 |
private int addIfUnderMaximumPoolSize(Runnable firstTask) { |
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Thread t = null; |
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int status = 0; |
456 |
final ReentrantLock mainLock = this.mainLock; |
457 |
mainLock.lock(); |
458 |
try { |
459 |
if (poolSize < maximumPoolSize) { |
460 |
Runnable next = workQueue.poll(); |
461 |
if (next == null) { |
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next = firstTask; |
463 |
status = 1; |
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} else |
465 |
status = -1; |
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t = addThread(next); |
467 |
} |
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} finally { |
469 |
mainLock.unlock(); |
470 |
} |
471 |
if (t == null) |
472 |
return 0; |
473 |
t.start(); |
474 |
return status; |
475 |
} |
476 |
|
477 |
|
478 |
/** |
479 |
* Gets the next task for a worker thread to run. |
480 |
* @return the task |
481 |
*/ |
482 |
Runnable getTask() { |
483 |
for (;;) { |
484 |
try { |
485 |
switch (runState) { |
486 |
case RUNNING: { |
487 |
// untimed wait if core and not allowing core timeout |
488 |
if (poolSize <= corePoolSize && !allowCoreThreadTimeOut) |
489 |
return workQueue.take(); |
490 |
|
491 |
long timeout = keepAliveTime; |
492 |
if (timeout <= 0) // die immediately for 0 timeout |
493 |
return null; |
494 |
Runnable r = workQueue.poll(timeout, TimeUnit.NANOSECONDS); |
495 |
if (r != null) |
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return r; |
497 |
if (poolSize > corePoolSize || allowCoreThreadTimeOut) |
498 |
return null; // timed out |
499 |
// Else, after timeout, the pool shrank. Retry |
500 |
break; |
501 |
} |
502 |
|
503 |
case SHUTDOWN: { |
504 |
// Help drain queue |
505 |
Runnable r = workQueue.poll(); |
506 |
if (r != null) |
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return r; |
508 |
|
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// Check if can terminate |
510 |
if (workQueue.isEmpty()) { |
511 |
interruptIdleWorkers(); |
512 |
return null; |
513 |
} |
514 |
|
515 |
// Else there could still be delayed tasks in queue. |
516 |
return workQueue.take(); |
517 |
} |
518 |
|
519 |
case STOP: |
520 |
return null; |
521 |
default: |
522 |
assert false; |
523 |
} |
524 |
} catch (InterruptedException ie) { |
525 |
// On interruption, re-check runstate |
526 |
} |
527 |
} |
528 |
} |
529 |
|
530 |
/** |
531 |
* Wakes up all threads that might be waiting for tasks. |
532 |
*/ |
533 |
void interruptIdleWorkers() { |
534 |
final ReentrantLock mainLock = this.mainLock; |
535 |
mainLock.lock(); |
536 |
try { |
537 |
for (Worker w : workers) |
538 |
w.interruptIfIdle(); |
539 |
} finally { |
540 |
mainLock.unlock(); |
541 |
} |
542 |
} |
543 |
|
544 |
/** |
545 |
* Performs bookkeeping for a terminated worker thread. |
546 |
* @param w the worker |
547 |
*/ |
548 |
void workerDone(Worker w) { |
549 |
final ReentrantLock mainLock = this.mainLock; |
550 |
mainLock.lock(); |
551 |
try { |
552 |
completedTaskCount += w.completedTasks; |
553 |
workers.remove(w); |
554 |
if (--poolSize > 0) |
555 |
return; |
556 |
|
557 |
// Else, this is the last thread. Deal with potential shutdown. |
558 |
|
559 |
int state = runState; |
560 |
assert state != TERMINATED; |
561 |
|
562 |
if (state != STOP) { |
563 |
// If there are queued tasks but no threads, create |
564 |
// replacement thread. We must create it initially |
565 |
// idle to avoid orphaned tasks in case addThread |
566 |
// fails. This also handles case of delayed tasks |
567 |
// that will sometime later become runnable. |
568 |
if (!workQueue.isEmpty()) { |
569 |
Thread t = addThread(null); |
570 |
if (t != null) |
571 |
t.start(); |
572 |
return; |
573 |
} |
574 |
|
575 |
// Otherwise, we can exit without replacement |
576 |
if (state == RUNNING) |
577 |
return; |
578 |
} |
579 |
|
580 |
// Either state is STOP, or state is SHUTDOWN and there is |
581 |
// no work to do. So we can terminate. |
582 |
termination.signalAll(); |
583 |
runState = TERMINATED; |
584 |
// fall through to call terminate() outside of lock. |
585 |
} finally { |
586 |
mainLock.unlock(); |
587 |
} |
588 |
|
589 |
assert runState == TERMINATED; |
590 |
terminated(); |
591 |
} |
592 |
|
593 |
/** |
594 |
* Worker threads |
595 |
*/ |
596 |
private class Worker implements Runnable { |
597 |
|
598 |
/** |
599 |
* The runLock is acquired and released surrounding each task |
600 |
* execution. It mainly protects against interrupts that are |
601 |
* intended to cancel the worker thread from instead |
602 |
* interrupting the task being run. |
603 |
*/ |
604 |
private final ReentrantLock runLock = new ReentrantLock(); |
605 |
|
606 |
/** |
607 |
* Initial task to run before entering run loop |
608 |
*/ |
609 |
private Runnable firstTask; |
610 |
|
611 |
/** |
612 |
* Per thread completed task counter; accumulated |
613 |
* into completedTaskCount upon termination. |
614 |
*/ |
615 |
volatile long completedTasks; |
616 |
|
617 |
/** |
618 |
* Thread this worker is running in. Acts as a final field, |
619 |
* but cannot be set until thread is created. |
620 |
*/ |
621 |
Thread thread; |
622 |
|
623 |
Worker(Runnable firstTask) { |
624 |
this.firstTask = firstTask; |
625 |
} |
626 |
|
627 |
boolean isActive() { |
628 |
return runLock.isLocked(); |
629 |
} |
630 |
|
631 |
/** |
632 |
* Interrupts thread if not running a task. |
633 |
*/ |
634 |
void interruptIfIdle() { |
635 |
final ReentrantLock runLock = this.runLock; |
636 |
if (runLock.tryLock()) { |
637 |
try { |
638 |
thread.interrupt(); |
639 |
} finally { |
640 |
runLock.unlock(); |
641 |
} |
642 |
} |
643 |
} |
644 |
|
645 |
/** |
646 |
* Interrupts thread even if running a task. |
647 |
*/ |
648 |
void interruptNow() { |
649 |
thread.interrupt(); |
650 |
} |
651 |
|
652 |
/** |
653 |
* Runs a single task between before/after methods. |
654 |
*/ |
655 |
private void runTask(Runnable task) { |
656 |
final ReentrantLock runLock = this.runLock; |
657 |
runLock.lock(); |
658 |
try { |
659 |
Thread.interrupted(); // clear interrupt status on entry |
660 |
// Abort now if immediate cancel. Otherwise, we have |
661 |
// committed to run this task. |
662 |
if (runState == STOP) |
663 |
return; |
664 |
|
665 |
boolean ran = false; |
666 |
beforeExecute(thread, task); |
667 |
try { |
668 |
task.run(); |
669 |
ran = true; |
670 |
afterExecute(task, null); |
671 |
++completedTasks; |
672 |
} catch (RuntimeException ex) { |
673 |
if (!ran) |
674 |
afterExecute(task, ex); |
675 |
// Else the exception occurred within |
676 |
// afterExecute itself in which case we don't |
677 |
// want to call it again. |
678 |
throw ex; |
679 |
} |
680 |
} finally { |
681 |
runLock.unlock(); |
682 |
} |
683 |
} |
684 |
|
685 |
/** |
686 |
* Main run loop |
687 |
*/ |
688 |
public void run() { |
689 |
try { |
690 |
Runnable task = firstTask; |
691 |
firstTask = null; |
692 |
while (task != null || (task = getTask()) != null) { |
693 |
runTask(task); |
694 |
task = null; // unnecessary but can help GC |
695 |
} |
696 |
} finally { |
697 |
workerDone(this); |
698 |
} |
699 |
} |
700 |
} |
701 |
|
702 |
// Public methods |
703 |
|
704 |
/** |
705 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
706 |
* parameters and default thread factory and rejected execution handler. |
707 |
* It may be more convenient to use one of the {@link Executors} factory |
708 |
* methods instead of this general purpose constructor. |
709 |
* |
710 |
* @param corePoolSize the number of threads to keep in the |
711 |
* pool, even if they are idle. |
712 |
* @param maximumPoolSize the maximum number of threads to allow in the |
713 |
* pool. |
714 |
* @param keepAliveTime when the number of threads is greater than |
715 |
* the core, this is the maximum time that excess idle threads |
716 |
* will wait for new tasks before terminating. |
717 |
* @param unit the time unit for the keepAliveTime |
718 |
* argument. |
719 |
* @param workQueue the queue to use for holding tasks before they |
720 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
721 |
* tasks submitted by the <tt>execute</tt> method. |
722 |
* @throws IllegalArgumentException if corePoolSize, or |
723 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
724 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
725 |
* @throws NullPointerException if <tt>workQueue</tt> is null |
726 |
*/ |
727 |
public ThreadPoolExecutor(int corePoolSize, |
728 |
int maximumPoolSize, |
729 |
long keepAliveTime, |
730 |
TimeUnit unit, |
731 |
BlockingQueue<Runnable> workQueue) { |
732 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
733 |
Executors.defaultThreadFactory(), defaultHandler); |
734 |
} |
735 |
|
736 |
/** |
737 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
738 |
* parameters and default rejected execution handler. |
739 |
* |
740 |
* @param corePoolSize the number of threads to keep in the |
741 |
* pool, even if they are idle. |
742 |
* @param maximumPoolSize the maximum number of threads to allow in the |
743 |
* pool. |
744 |
* @param keepAliveTime when the number of threads is greater than |
745 |
* the core, this is the maximum time that excess idle threads |
746 |
* will wait for new tasks before terminating. |
747 |
* @param unit the time unit for the keepAliveTime |
748 |
* argument. |
749 |
* @param workQueue the queue to use for holding tasks before they |
750 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
751 |
* tasks submitted by the <tt>execute</tt> method. |
752 |
* @param threadFactory the factory to use when the executor |
753 |
* creates a new thread. |
754 |
* @throws IllegalArgumentException if corePoolSize, or |
755 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
756 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
757 |
* @throws NullPointerException if <tt>workQueue</tt> |
758 |
* or <tt>threadFactory</tt> are null. |
759 |
*/ |
760 |
public ThreadPoolExecutor(int corePoolSize, |
761 |
int maximumPoolSize, |
762 |
long keepAliveTime, |
763 |
TimeUnit unit, |
764 |
BlockingQueue<Runnable> workQueue, |
765 |
ThreadFactory threadFactory) { |
766 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
767 |
threadFactory, defaultHandler); |
768 |
} |
769 |
|
770 |
/** |
771 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
772 |
* parameters and default thread factory. |
773 |
* |
774 |
* @param corePoolSize the number of threads to keep in the |
775 |
* pool, even if they are idle. |
776 |
* @param maximumPoolSize the maximum number of threads to allow in the |
777 |
* pool. |
778 |
* @param keepAliveTime when the number of threads is greater than |
779 |
* the core, this is the maximum time that excess idle threads |
780 |
* will wait for new tasks before terminating. |
781 |
* @param unit the time unit for the keepAliveTime |
782 |
* argument. |
783 |
* @param workQueue the queue to use for holding tasks before they |
784 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
785 |
* tasks submitted by the <tt>execute</tt> method. |
786 |
* @param handler the handler to use when execution is blocked |
787 |
* because the thread bounds and queue capacities are reached. |
788 |
* @throws IllegalArgumentException if corePoolSize, or |
789 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
790 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
791 |
* @throws NullPointerException if <tt>workQueue</tt> |
792 |
* or <tt>handler</tt> are null. |
793 |
*/ |
794 |
public ThreadPoolExecutor(int corePoolSize, |
795 |
int maximumPoolSize, |
796 |
long keepAliveTime, |
797 |
TimeUnit unit, |
798 |
BlockingQueue<Runnable> workQueue, |
799 |
RejectedExecutionHandler handler) { |
800 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
801 |
Executors.defaultThreadFactory(), handler); |
802 |
} |
803 |
|
804 |
/** |
805 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
806 |
* parameters. |
807 |
* |
808 |
* @param corePoolSize the number of threads to keep in the |
809 |
* pool, even if they are idle. |
810 |
* @param maximumPoolSize the maximum number of threads to allow in the |
811 |
* pool. |
812 |
* @param keepAliveTime when the number of threads is greater than |
813 |
* the core, this is the maximum time that excess idle threads |
814 |
* will wait for new tasks before terminating. |
815 |
* @param unit the time unit for the keepAliveTime |
816 |
* argument. |
817 |
* @param workQueue the queue to use for holding tasks before they |
818 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
819 |
* tasks submitted by the <tt>execute</tt> method. |
820 |
* @param threadFactory the factory to use when the executor |
821 |
* creates a new thread. |
822 |
* @param handler the handler to use when execution is blocked |
823 |
* because the thread bounds and queue capacities are reached. |
824 |
* @throws IllegalArgumentException if corePoolSize, or |
825 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
826 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
827 |
* @throws NullPointerException if <tt>workQueue</tt> |
828 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
829 |
*/ |
830 |
public ThreadPoolExecutor(int corePoolSize, |
831 |
int maximumPoolSize, |
832 |
long keepAliveTime, |
833 |
TimeUnit unit, |
834 |
BlockingQueue<Runnable> workQueue, |
835 |
ThreadFactory threadFactory, |
836 |
RejectedExecutionHandler handler) { |
837 |
if (corePoolSize < 0 || |
838 |
maximumPoolSize <= 0 || |
839 |
maximumPoolSize < corePoolSize || |
840 |
keepAliveTime < 0) |
841 |
throw new IllegalArgumentException(); |
842 |
if (workQueue == null || threadFactory == null || handler == null) |
843 |
throw new NullPointerException(); |
844 |
this.corePoolSize = corePoolSize; |
845 |
this.maximumPoolSize = maximumPoolSize; |
846 |
this.workQueue = workQueue; |
847 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
848 |
this.threadFactory = threadFactory; |
849 |
this.handler = handler; |
850 |
} |
851 |
|
852 |
|
853 |
/** |
854 |
* Executes the given task sometime in the future. The task |
855 |
* may execute in a new thread or in an existing pooled thread. |
856 |
* |
857 |
* If the task cannot be submitted for execution, either because this |
858 |
* executor has been shutdown or because its capacity has been reached, |
859 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
860 |
* |
861 |
* @param command the task to execute |
862 |
* @throws RejectedExecutionException at discretion of |
863 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
864 |
* for execution |
865 |
* @throws NullPointerException if command is null |
866 |
*/ |
867 |
public void execute(Runnable command) { |
868 |
if (command == null) |
869 |
throw new NullPointerException(); |
870 |
for (;;) { |
871 |
if (runState != RUNNING) { |
872 |
reject(command); |
873 |
return; |
874 |
} |
875 |
if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) |
876 |
return; |
877 |
if (workQueue.offer(command)) |
878 |
return; |
879 |
int status = addIfUnderMaximumPoolSize(command); |
880 |
if (status > 0) // created new thread |
881 |
return; |
882 |
if (status == 0) { // failed to create thread |
883 |
reject(command); |
884 |
return; |
885 |
} |
886 |
// Retry if created a new thread but it is busy with another task |
887 |
} |
888 |
} |
889 |
|
890 |
/** |
891 |
* Initiates an orderly shutdown in which previously submitted |
892 |
* tasks are executed, but no new tasks will be |
893 |
* accepted. Invocation has no additional effect if already shut |
894 |
* down. |
895 |
* @throws SecurityException if a security manager exists and |
896 |
* shutting down this ExecutorService may manipulate threads that |
897 |
* the caller is not permitted to modify because it does not hold |
898 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
899 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
900 |
*/ |
901 |
public void shutdown() { |
902 |
// Fail if caller doesn't have modifyThread permission. We |
903 |
// explicitly check permissions directly because we can't trust |
904 |
// implementations of SecurityManager to correctly override |
905 |
// the "check access" methods such that our documented |
906 |
// security policy is implemented. |
907 |
SecurityManager security = System.getSecurityManager(); |
908 |
if (security != null) |
909 |
java.security.AccessController.checkPermission(shutdownPerm); |
910 |
|
911 |
boolean fullyTerminated = false; |
912 |
final ReentrantLock mainLock = this.mainLock; |
913 |
mainLock.lock(); |
914 |
try { |
915 |
if (workers.size() > 0) { |
916 |
// Check if caller can modify worker threads. This |
917 |
// might not be true even if passed above check, if |
918 |
// the SecurityManager treats some threads specially. |
919 |
if (security != null) { |
920 |
for (Worker w: workers) |
921 |
security.checkAccess(w.thread); |
922 |
} |
923 |
|
924 |
int state = runState; |
925 |
if (state == RUNNING) // don't override shutdownNow |
926 |
runState = SHUTDOWN; |
927 |
|
928 |
try { |
929 |
for (Worker w: workers) |
930 |
w.interruptIfIdle(); |
931 |
} catch (SecurityException se) { |
932 |
// If SecurityManager allows above checks, but |
933 |
// then unexpectedly throws exception when |
934 |
// interrupting threads (which it ought not do), |
935 |
// back out as cleanly as we can. Some threads may |
936 |
// have been killed but we remain in non-shutdown |
937 |
// state. |
938 |
runState = state; |
939 |
throw se; |
940 |
} |
941 |
} |
942 |
else { // If no workers, trigger full termination now |
943 |
fullyTerminated = true; |
944 |
runState = TERMINATED; |
945 |
termination.signalAll(); |
946 |
} |
947 |
} finally { |
948 |
mainLock.unlock(); |
949 |
} |
950 |
if (fullyTerminated) |
951 |
terminated(); |
952 |
} |
953 |
|
954 |
|
955 |
/** |
956 |
* Attempts to stop all actively executing tasks, halts the |
957 |
* processing of waiting tasks, and returns a list of the tasks that were |
958 |
* awaiting execution. |
959 |
* |
960 |
* <p>This implementation cancels tasks via {@link |
961 |
* Thread#interrupt}, so if any tasks mask or fail to respond to |
962 |
* interrupts, they may never terminate. |
963 |
* |
964 |
* @return list of tasks that never commenced execution |
965 |
* @throws SecurityException if a security manager exists and |
966 |
* shutting down this ExecutorService may manipulate threads that |
967 |
* the caller is not permitted to modify because it does not hold |
968 |
* {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
969 |
* or the security manager's <tt>checkAccess</tt> method denies access. |
970 |
*/ |
971 |
public List<Runnable> shutdownNow() { |
972 |
// Almost the same code as shutdown() |
973 |
SecurityManager security = System.getSecurityManager(); |
974 |
if (security != null) |
975 |
java.security.AccessController.checkPermission(shutdownPerm); |
976 |
|
977 |
boolean fullyTerminated = false; |
978 |
final ReentrantLock mainLock = this.mainLock; |
979 |
mainLock.lock(); |
980 |
try { |
981 |
if (workers.size() > 0) { |
982 |
if (security != null) { |
983 |
for (Worker w: workers) |
984 |
security.checkAccess(w.thread); |
985 |
} |
986 |
|
987 |
int state = runState; |
988 |
if (state != TERMINATED) |
989 |
runState = STOP; |
990 |
try { |
991 |
for (Worker w : workers) |
992 |
w.interruptNow(); |
993 |
} catch (SecurityException se) { |
994 |
runState = state; // back out; |
995 |
throw se; |
996 |
} |
997 |
} |
998 |
else { // If no workers, trigger full termination now |
999 |
fullyTerminated = true; |
1000 |
runState = TERMINATED; |
1001 |
termination.signalAll(); |
1002 |
} |
1003 |
} finally { |
1004 |
mainLock.unlock(); |
1005 |
} |
1006 |
if (fullyTerminated) |
1007 |
terminated(); |
1008 |
return Arrays.asList(workQueue.toArray(EMPTY_RUNNABLE_ARRAY)); |
1009 |
} |
1010 |
|
1011 |
public boolean isShutdown() { |
1012 |
return runState != RUNNING; |
1013 |
} |
1014 |
|
1015 |
/** |
1016 |
* Returns true if this executor is in the process of terminating |
1017 |
* after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not |
1018 |
* completely terminated. This method may be useful for |
1019 |
* debugging. A return of <tt>true</tt> reported a sufficient |
1020 |
* period after shutdown may indicate that submitted tasks have |
1021 |
* ignored or suppressed interruption, causing this executor not |
1022 |
* to properly terminate. |
1023 |
* @return true if terminating but not yet terminated. |
1024 |
*/ |
1025 |
public boolean isTerminating() { |
1026 |
return runState == STOP; |
1027 |
} |
1028 |
|
1029 |
public boolean isTerminated() { |
1030 |
return runState == TERMINATED; |
1031 |
} |
1032 |
|
1033 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1034 |
throws InterruptedException { |
1035 |
long nanos = unit.toNanos(timeout); |
1036 |
final ReentrantLock mainLock = this.mainLock; |
1037 |
mainLock.lock(); |
1038 |
try { |
1039 |
for (;;) { |
1040 |
if (runState == TERMINATED) |
1041 |
return true; |
1042 |
if (nanos <= 0) |
1043 |
return false; |
1044 |
nanos = termination.awaitNanos(nanos); |
1045 |
} |
1046 |
} finally { |
1047 |
mainLock.unlock(); |
1048 |
} |
1049 |
} |
1050 |
|
1051 |
/** |
1052 |
* Invokes <tt>shutdown</tt> when this executor is no longer |
1053 |
* referenced. |
1054 |
*/ |
1055 |
protected void finalize() { |
1056 |
shutdown(); |
1057 |
} |
1058 |
|
1059 |
/** |
1060 |
* Sets the thread factory used to create new threads. |
1061 |
* |
1062 |
* @param threadFactory the new thread factory |
1063 |
* @throws NullPointerException if threadFactory is null |
1064 |
* @see #getThreadFactory |
1065 |
*/ |
1066 |
public void setThreadFactory(ThreadFactory threadFactory) { |
1067 |
if (threadFactory == null) |
1068 |
throw new NullPointerException(); |
1069 |
this.threadFactory = threadFactory; |
1070 |
} |
1071 |
|
1072 |
/** |
1073 |
* Returns the thread factory used to create new threads. |
1074 |
* |
1075 |
* @return the current thread factory |
1076 |
* @see #setThreadFactory |
1077 |
*/ |
1078 |
public ThreadFactory getThreadFactory() { |
1079 |
return threadFactory; |
1080 |
} |
1081 |
|
1082 |
/** |
1083 |
* Sets a new handler for unexecutable tasks. |
1084 |
* |
1085 |
* @param handler the new handler |
1086 |
* @throws NullPointerException if handler is null |
1087 |
* @see #getRejectedExecutionHandler |
1088 |
*/ |
1089 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
1090 |
if (handler == null) |
1091 |
throw new NullPointerException(); |
1092 |
this.handler = handler; |
1093 |
} |
1094 |
|
1095 |
/** |
1096 |
* Returns the current handler for unexecutable tasks. |
1097 |
* |
1098 |
* @return the current handler |
1099 |
* @see #setRejectedExecutionHandler |
1100 |
*/ |
1101 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
1102 |
return handler; |
1103 |
} |
1104 |
|
1105 |
/** |
1106 |
* Returns the task queue used by this executor. Access to the |
1107 |
* task queue is intended primarily for debugging and monitoring. |
1108 |
* This queue may be in active use. Retrieving the task queue |
1109 |
* does not prevent queued tasks from executing. |
1110 |
* |
1111 |
* @return the task queue |
1112 |
*/ |
1113 |
public BlockingQueue<Runnable> getQueue() { |
1114 |
return workQueue; |
1115 |
} |
1116 |
|
1117 |
/** |
1118 |
* Removes this task from the executor's internal queue if it is |
1119 |
* present, thus causing it not to be run if it has not already |
1120 |
* started. |
1121 |
* |
1122 |
* <p> This method may be useful as one part of a cancellation |
1123 |
* scheme. It may fail to remove tasks that have been converted |
1124 |
* into other forms before being placed on the internal queue. For |
1125 |
* example, a task entered using <tt>submit</tt> might be |
1126 |
* converted into a form that maintains <tt>Future</tt> status. |
1127 |
* However, in such cases, method {@link ThreadPoolExecutor#purge} |
1128 |
* may be used to remove those Futures that have been cancelled. |
1129 |
* |
1130 |
* |
1131 |
* @param task the task to remove |
1132 |
* @return true if the task was removed |
1133 |
*/ |
1134 |
public boolean remove(Runnable task) { |
1135 |
return getQueue().remove(task); |
1136 |
} |
1137 |
|
1138 |
|
1139 |
/** |
1140 |
* Tries to remove from the work queue all {@link Future} |
1141 |
* tasks that have been cancelled. This method can be useful as a |
1142 |
* storage reclamation operation, that has no other impact on |
1143 |
* functionality. Cancelled tasks are never executed, but may |
1144 |
* accumulate in work queues until worker threads can actively |
1145 |
* remove them. Invoking this method instead tries to remove them now. |
1146 |
* However, this method may fail to remove tasks in |
1147 |
* the presence of interference by other threads. |
1148 |
*/ |
1149 |
public void purge() { |
1150 |
// Fail if we encounter interference during traversal |
1151 |
try { |
1152 |
Iterator<Runnable> it = getQueue().iterator(); |
1153 |
while (it.hasNext()) { |
1154 |
Runnable r = it.next(); |
1155 |
if (r instanceof Future<?>) { |
1156 |
Future<?> c = (Future<?>)r; |
1157 |
if (c.isCancelled()) |
1158 |
it.remove(); |
1159 |
} |
1160 |
} |
1161 |
} |
1162 |
catch (ConcurrentModificationException ex) { |
1163 |
return; |
1164 |
} |
1165 |
} |
1166 |
|
1167 |
/** |
1168 |
* Sets the core number of threads. This overrides any value set |
1169 |
* in the constructor. If the new value is smaller than the |
1170 |
* current value, excess existing threads will be terminated when |
1171 |
* they next become idle. If larger, new threads will, if needed, |
1172 |
* be started to execute any queued tasks. |
1173 |
* |
1174 |
* @param corePoolSize the new core size |
1175 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> |
1176 |
* less than zero |
1177 |
* @see #getCorePoolSize |
1178 |
*/ |
1179 |
public void setCorePoolSize(int corePoolSize) { |
1180 |
if (corePoolSize < 0) |
1181 |
throw new IllegalArgumentException(); |
1182 |
final ReentrantLock mainLock = this.mainLock; |
1183 |
mainLock.lock(); |
1184 |
try { |
1185 |
int extra = this.corePoolSize - corePoolSize; |
1186 |
this.corePoolSize = corePoolSize; |
1187 |
if (extra < 0) { |
1188 |
int n = workQueue.size(); |
1189 |
// We have to create initially-idle threads here |
1190 |
// because we otherwise have no recourse about |
1191 |
// what to do with a dequeued task if addThread fails. |
1192 |
while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize ) { |
1193 |
Thread t = addThread(null); |
1194 |
if (t != null) |
1195 |
t.start(); |
1196 |
else |
1197 |
break; |
1198 |
} |
1199 |
} |
1200 |
else if (extra > 0 && poolSize > corePoolSize) { |
1201 |
Iterator<Worker> it = workers.iterator(); |
1202 |
while (it.hasNext() && |
1203 |
extra-- > 0 && |
1204 |
poolSize > corePoolSize && |
1205 |
workQueue.remainingCapacity() == 0) |
1206 |
it.next().interruptIfIdle(); |
1207 |
} |
1208 |
} finally { |
1209 |
mainLock.unlock(); |
1210 |
} |
1211 |
} |
1212 |
|
1213 |
/** |
1214 |
* Returns the core number of threads. |
1215 |
* |
1216 |
* @return the core number of threads |
1217 |
* @see #setCorePoolSize |
1218 |
*/ |
1219 |
public int getCorePoolSize() { |
1220 |
return corePoolSize; |
1221 |
} |
1222 |
|
1223 |
/** |
1224 |
* Starts a core thread, causing it to idly wait for work. This |
1225 |
* overrides the default policy of starting core threads only when |
1226 |
* new tasks are executed. This method will return <tt>false</tt> |
1227 |
* if all core threads have already been started. |
1228 |
* @return true if a thread was started |
1229 |
*/ |
1230 |
public boolean prestartCoreThread() { |
1231 |
return addIfUnderCorePoolSize(null); |
1232 |
} |
1233 |
|
1234 |
/** |
1235 |
* Starts all core threads, causing them to idly wait for work. This |
1236 |
* overrides the default policy of starting core threads only when |
1237 |
* new tasks are executed. |
1238 |
* @return the number of threads started. |
1239 |
*/ |
1240 |
public int prestartAllCoreThreads() { |
1241 |
int n = 0; |
1242 |
while (addIfUnderCorePoolSize(null)) |
1243 |
++n; |
1244 |
return n; |
1245 |
} |
1246 |
|
1247 |
/** |
1248 |
* Returns true if this pool allows core threads to time out and |
1249 |
* terminate if no tasks arrive within the keepAlive time, being |
1250 |
* replaced if needed when new tasks arrive. When true, the same |
1251 |
* keep-alive policy applying to non-core threads applies also to |
1252 |
* core threads. When false (the default), core threads are never |
1253 |
* terminated due to lack of incoming tasks. |
1254 |
* @return <tt>true</tt> if core threads are allowed to time out, |
1255 |
* else <tt>false</tt> |
1256 |
* |
1257 |
* @since 1.6 |
1258 |
*/ |
1259 |
public boolean allowsCoreThreadTimeOut() { |
1260 |
return allowCoreThreadTimeOut; |
1261 |
} |
1262 |
|
1263 |
/** |
1264 |
* Sets the policy governing whether core threads may time out and |
1265 |
* terminate if no tasks arrive within the keep-alive time, being |
1266 |
* replaced if needed when new tasks arrive. When false, core |
1267 |
* threads are never terminated due to lack of incoming |
1268 |
* tasks. When true, the same keep-alive policy applying to |
1269 |
* non-core threads applies also to core threads. To avoid |
1270 |
* continual thread replacement, the keep-alive time must be |
1271 |
* greater than zero when setting <tt>true</tt>. This method |
1272 |
* should in general be called before the pool is actively used. |
1273 |
* @param value <tt>true</tt> if should time out, else <tt>false</tt> |
1274 |
* @throws IllegalArgumentException if value is <tt>true</tt> |
1275 |
* and the current keep-alive time is not greater than zero. |
1276 |
* |
1277 |
* @since 1.6 |
1278 |
*/ |
1279 |
public void allowCoreThreadTimeOut(boolean value) { |
1280 |
if (value && keepAliveTime <= 0) |
1281 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1282 |
|
1283 |
allowCoreThreadTimeOut = value; |
1284 |
} |
1285 |
|
1286 |
/** |
1287 |
* Sets the maximum allowed number of threads. This overrides any |
1288 |
* value set in the constructor. If the new value is smaller than |
1289 |
* the current value, excess existing threads will be |
1290 |
* terminated when they next become idle. |
1291 |
* |
1292 |
* @param maximumPoolSize the new maximum |
1293 |
* @throws IllegalArgumentException if maximumPoolSize less than zero or |
1294 |
* the {@link #getCorePoolSize core pool size} |
1295 |
* @see #getMaximumPoolSize |
1296 |
*/ |
1297 |
public void setMaximumPoolSize(int maximumPoolSize) { |
1298 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
1299 |
throw new IllegalArgumentException(); |
1300 |
final ReentrantLock mainLock = this.mainLock; |
1301 |
mainLock.lock(); |
1302 |
try { |
1303 |
int extra = this.maximumPoolSize - maximumPoolSize; |
1304 |
this.maximumPoolSize = maximumPoolSize; |
1305 |
if (extra > 0 && poolSize > maximumPoolSize) { |
1306 |
Iterator<Worker> it = workers.iterator(); |
1307 |
while (it.hasNext() && |
1308 |
extra > 0 && |
1309 |
poolSize > maximumPoolSize) { |
1310 |
it.next().interruptIfIdle(); |
1311 |
--extra; |
1312 |
} |
1313 |
} |
1314 |
} finally { |
1315 |
mainLock.unlock(); |
1316 |
} |
1317 |
} |
1318 |
|
1319 |
/** |
1320 |
* Returns the maximum allowed number of threads. |
1321 |
* |
1322 |
* @return the maximum allowed number of threads |
1323 |
* @see #setMaximumPoolSize |
1324 |
*/ |
1325 |
public int getMaximumPoolSize() { |
1326 |
return maximumPoolSize; |
1327 |
} |
1328 |
|
1329 |
/** |
1330 |
* Sets the time limit for which threads may remain idle before |
1331 |
* being terminated. If there are more than the core number of |
1332 |
* threads currently in the pool, after waiting this amount of |
1333 |
* time without processing a task, excess threads will be |
1334 |
* terminated. This overrides any value set in the constructor. |
1335 |
* @param time the time to wait. A time value of zero will cause |
1336 |
* excess threads to terminate immediately after executing tasks. |
1337 |
* @param unit the time unit of the time argument |
1338 |
* @throws IllegalArgumentException if time less than zero or |
1339 |
* if time is zero and allowsCoreThreadTimeOut |
1340 |
* @see #getKeepAliveTime |
1341 |
*/ |
1342 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
1343 |
if (time < 0) |
1344 |
throw new IllegalArgumentException(); |
1345 |
if (time == 0 && allowsCoreThreadTimeOut()) |
1346 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
1347 |
this.keepAliveTime = unit.toNanos(time); |
1348 |
} |
1349 |
|
1350 |
/** |
1351 |
* Returns the thread keep-alive time, which is the amount of time |
1352 |
* which threads in excess of the core pool size may remain |
1353 |
* idle before being terminated. |
1354 |
* |
1355 |
* @param unit the desired time unit of the result |
1356 |
* @return the time limit |
1357 |
* @see #setKeepAliveTime |
1358 |
*/ |
1359 |
public long getKeepAliveTime(TimeUnit unit) { |
1360 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
1361 |
} |
1362 |
|
1363 |
/* Statistics */ |
1364 |
|
1365 |
/** |
1366 |
* Returns the current number of threads in the pool. |
1367 |
* |
1368 |
* @return the number of threads |
1369 |
*/ |
1370 |
public int getPoolSize() { |
1371 |
return poolSize; |
1372 |
} |
1373 |
|
1374 |
/** |
1375 |
* Returns the approximate number of threads that are actively |
1376 |
* executing tasks. |
1377 |
* |
1378 |
* @return the number of threads |
1379 |
*/ |
1380 |
public int getActiveCount() { |
1381 |
final ReentrantLock mainLock = this.mainLock; |
1382 |
mainLock.lock(); |
1383 |
try { |
1384 |
int n = 0; |
1385 |
for (Worker w : workers) { |
1386 |
if (w.isActive()) |
1387 |
++n; |
1388 |
} |
1389 |
return n; |
1390 |
} finally { |
1391 |
mainLock.unlock(); |
1392 |
} |
1393 |
} |
1394 |
|
1395 |
/** |
1396 |
* Returns the largest number of threads that have ever |
1397 |
* simultaneously been in the pool. |
1398 |
* |
1399 |
* @return the number of threads |
1400 |
*/ |
1401 |
public int getLargestPoolSize() { |
1402 |
final ReentrantLock mainLock = this.mainLock; |
1403 |
mainLock.lock(); |
1404 |
try { |
1405 |
return largestPoolSize; |
1406 |
} finally { |
1407 |
mainLock.unlock(); |
1408 |
} |
1409 |
} |
1410 |
|
1411 |
/** |
1412 |
* Returns the approximate total number of tasks that have been |
1413 |
* scheduled for execution. Because the states of tasks and |
1414 |
* threads may change dynamically during computation, the returned |
1415 |
* value is only an approximation, but one that does not ever |
1416 |
* decrease across successive calls. |
1417 |
* |
1418 |
* @return the number of tasks |
1419 |
*/ |
1420 |
public long getTaskCount() { |
1421 |
final ReentrantLock mainLock = this.mainLock; |
1422 |
mainLock.lock(); |
1423 |
try { |
1424 |
long n = completedTaskCount; |
1425 |
for (Worker w : workers) { |
1426 |
n += w.completedTasks; |
1427 |
if (w.isActive()) |
1428 |
++n; |
1429 |
} |
1430 |
return n + workQueue.size(); |
1431 |
} finally { |
1432 |
mainLock.unlock(); |
1433 |
} |
1434 |
} |
1435 |
|
1436 |
/** |
1437 |
* Returns the approximate total number of tasks that have |
1438 |
* completed execution. Because the states of tasks and threads |
1439 |
* may change dynamically during computation, the returned value |
1440 |
* is only an approximation, but one that does not ever decrease |
1441 |
* across successive calls. |
1442 |
* |
1443 |
* @return the number of tasks |
1444 |
*/ |
1445 |
public long getCompletedTaskCount() { |
1446 |
final ReentrantLock mainLock = this.mainLock; |
1447 |
mainLock.lock(); |
1448 |
try { |
1449 |
long n = completedTaskCount; |
1450 |
for (Worker w : workers) |
1451 |
n += w.completedTasks; |
1452 |
return n; |
1453 |
} finally { |
1454 |
mainLock.unlock(); |
1455 |
} |
1456 |
} |
1457 |
|
1458 |
/** |
1459 |
* Method invoked prior to executing the given Runnable in the |
1460 |
* given thread. This method is invoked by thread <tt>t</tt> that |
1461 |
* will execute task <tt>r</tt>, and may be used to re-initialize |
1462 |
* ThreadLocals, or to perform logging. |
1463 |
* |
1464 |
* <p>This implementation does nothing, but may be customized in |
1465 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1466 |
* should generally invoke <tt>super.beforeExecute</tt> at the end of |
1467 |
* this method. |
1468 |
* |
1469 |
* @param t the thread that will run task r. |
1470 |
* @param r the task that will be executed. |
1471 |
*/ |
1472 |
protected void beforeExecute(Thread t, Runnable r) { } |
1473 |
|
1474 |
/** |
1475 |
* Method invoked upon completion of execution of the given Runnable. |
1476 |
* This method is invoked by the thread that executed the task. If |
1477 |
* non-null, the Throwable is the uncaught <tt>RuntimeException</tt> |
1478 |
* or <tt>Error</tt> that caused execution to terminate abruptly. |
1479 |
* |
1480 |
* <p><b>Note:</b> When actions are enclosed in tasks (such as |
1481 |
* {@link FutureTask}) either explicitly or via methods such as |
1482 |
* <tt>submit</tt>, these task objects catch and maintain |
1483 |
* computational exceptions, and so they do not cause abrupt |
1484 |
* termination, and the internal exceptions are <em>not</em> |
1485 |
* passed to this method. |
1486 |
* |
1487 |
* <p>This implementation does nothing, but may be customized in |
1488 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
1489 |
* should generally invoke <tt>super.afterExecute</tt> at the |
1490 |
* beginning of this method. |
1491 |
* |
1492 |
* @param r the runnable that has completed. |
1493 |
* @param t the exception that caused termination, or null if |
1494 |
* execution completed normally. |
1495 |
*/ |
1496 |
protected void afterExecute(Runnable r, Throwable t) { } |
1497 |
|
1498 |
/** |
1499 |
* Method invoked when the Executor has terminated. Default |
1500 |
* implementation does nothing. Note: To properly nest multiple |
1501 |
* overridings, subclasses should generally invoke |
1502 |
* <tt>super.terminated</tt> within this method. |
1503 |
*/ |
1504 |
protected void terminated() { } |
1505 |
|
1506 |
/** |
1507 |
* A handler for rejected tasks that runs the rejected task |
1508 |
* directly in the calling thread of the <tt>execute</tt> method, |
1509 |
* unless the executor has been shut down, in which case the task |
1510 |
* is discarded. |
1511 |
*/ |
1512 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1513 |
/** |
1514 |
* Creates a <tt>CallerRunsPolicy</tt>. |
1515 |
*/ |
1516 |
public CallerRunsPolicy() { } |
1517 |
|
1518 |
/** |
1519 |
* Executes task r in the caller's thread, unless the executor |
1520 |
* has been shut down, in which case the task is discarded. |
1521 |
* @param r the runnable task requested to be executed |
1522 |
* @param e the executor attempting to execute this task |
1523 |
*/ |
1524 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1525 |
if (!e.isShutdown()) { |
1526 |
r.run(); |
1527 |
} |
1528 |
} |
1529 |
} |
1530 |
|
1531 |
/** |
1532 |
* A handler for rejected tasks that throws a |
1533 |
* <tt>RejectedExecutionException</tt>. |
1534 |
*/ |
1535 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1536 |
/** |
1537 |
* Creates an <tt>AbortPolicy</tt>. |
1538 |
*/ |
1539 |
public AbortPolicy() { } |
1540 |
|
1541 |
/** |
1542 |
* Always throws RejectedExecutionException. |
1543 |
* @param r the runnable task requested to be executed |
1544 |
* @param e the executor attempting to execute this task |
1545 |
* @throws RejectedExecutionException always. |
1546 |
*/ |
1547 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1548 |
throw new RejectedExecutionException(); |
1549 |
} |
1550 |
} |
1551 |
|
1552 |
/** |
1553 |
* A handler for rejected tasks that silently discards the |
1554 |
* rejected task. |
1555 |
*/ |
1556 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1557 |
/** |
1558 |
* Creates a <tt>DiscardPolicy</tt>. |
1559 |
*/ |
1560 |
public DiscardPolicy() { } |
1561 |
|
1562 |
/** |
1563 |
* Does nothing, which has the effect of discarding task r. |
1564 |
* @param r the runnable task requested to be executed |
1565 |
* @param e the executor attempting to execute this task |
1566 |
*/ |
1567 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1568 |
} |
1569 |
} |
1570 |
|
1571 |
/** |
1572 |
* A handler for rejected tasks that discards the oldest unhandled |
1573 |
* request and then retries <tt>execute</tt>, unless the executor |
1574 |
* is shut down, in which case the task is discarded. |
1575 |
*/ |
1576 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1577 |
/** |
1578 |
* Creates a <tt>DiscardOldestPolicy</tt> for the given executor. |
1579 |
*/ |
1580 |
public DiscardOldestPolicy() { } |
1581 |
|
1582 |
/** |
1583 |
* Obtains and ignores the next task that the executor |
1584 |
* would otherwise execute, if one is immediately available, |
1585 |
* and then retries execution of task r, unless the executor |
1586 |
* is shut down, in which case task r is instead discarded. |
1587 |
* @param r the runnable task requested to be executed |
1588 |
* @param e the executor attempting to execute this task |
1589 |
*/ |
1590 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1591 |
if (!e.isShutdown()) { |
1592 |
e.getQueue().poll(); |
1593 |
e.execute(r); |
1594 |
} |
1595 |
} |
1596 |
} |
1597 |
} |