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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.concurrent.locks.*; |
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import java.util.*; |
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|
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/** |
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* An {@link ExecutorService} that executes each submitted task using |
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* one of possibly several pooled threads. |
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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 hooks. For |
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* example, it can be configured to create a new thread for each task, |
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* or even to execute tasks sequentially in a single thread, in |
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* addition to its most common configuration, which reuses a pool of |
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* threads. 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 <tt>ThreadPoolExecutor</tt>: |
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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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* accomodate 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 needed by new tasks, 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}. </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 ThreadFactory}. By |
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* default, threads are created simply with the <tt>new |
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* Thread(Runnable)</tt> constructor, but by supplying a different |
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* ThreadFactory, you can alter the thread's name, thread group, |
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* priority, daemon status, etc. </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 |
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* using method {@link ThreadPoolExecutor#setKeepAliveTime}. Using |
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* a value of <tt>Long.MAX_VALUE</tt> {@link TimeUnit#NANOSECONDS} |
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* effectively disables idle threads from ever terminating prior |
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* to shut down. |
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* </dd> |
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* |
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* <dt>Queueing</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 queueing.</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, which 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 be queued in cases where 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 artifically 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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* or queueless handoffs generally requires larger pool sizes, which |
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* keeps CPUs busier but may encounter unacceptable scheduling |
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* overhead, which also 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 queueing 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.</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 |
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* to the work queue for purposes of monitoring and debugging. |
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* Use of this method for any other purpose is strongly discouraged. |
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* Two supplied methods, {@link ThreadPoolExecutor#remove} and |
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* {@link ThreadPoolExecutor#purge} are available to assist in |
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* storage reclamation when large numbers of not-yet-executed |
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* tasks become cancelled.</dd> |
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* </dl> |
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* |
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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 implements ExecutorService { |
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/** |
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* Queue used for holding tasks and handing off to worker threads. |
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*/ |
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private final BlockingQueue<Runnable> workQueue; |
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|
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/** |
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* Lock held on updates to poolSize, corePoolSize, maximumPoolSize, and |
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* workers set. |
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*/ |
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private final ReentrantLock mainLock = new ReentrantLock(); |
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|
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/** |
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* Wait condition to support awaitTermination |
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*/ |
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private final Condition termination = mainLock.newCondition(); |
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|
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/** |
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* Set containing all worker threads in pool. |
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*/ |
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private final HashSet<Worker> workers = new HashSet<Worker>(); |
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|
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/** |
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* Timeout in nanosecods for idle threads waiting for work. |
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* Threads use this timeout only when there are more than |
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* corePoolSize present. Otherwise they wait forever for new work. |
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*/ |
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private volatile long keepAliveTime; |
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|
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/** |
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* Core pool size, updated only while holding mainLock, |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int corePoolSize; |
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|
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/** |
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* Maximum pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int maximumPoolSize; |
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|
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/** |
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* Current pool size, updated only while holding mainLock |
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* but volatile to allow concurrent readability even |
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* during updates. |
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*/ |
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private volatile int poolSize; |
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|
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/** |
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* Lifecycle state |
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*/ |
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private volatile int runState; |
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|
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// Special values for runState |
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/** Normal, not-shutdown mode */ |
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private static final int RUNNING = 0; |
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/** Controlled shutdown mode */ |
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private static final int SHUTDOWN = 1; |
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/** Immediate shutdown mode */ |
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private static final int STOP = 2; |
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/** Final state */ |
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private static final int TERMINATED = 3; |
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|
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/** |
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* Handler called when saturated or shutdown in execute. |
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*/ |
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private volatile RejectedExecutionHandler handler = defaultHandler; |
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|
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/** |
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* Factory for new threads. |
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*/ |
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private volatile ThreadFactory threadFactory = defaultThreadFactory; |
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|
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/** |
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* Tracks largest attained pool size. |
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*/ |
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private int largestPoolSize; |
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|
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/** |
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* Counter for completed tasks. Updated only on termination of |
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* worker threads. |
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*/ |
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private long completedTaskCount; |
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|
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/** |
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* The default thread factory |
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*/ |
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private static final ThreadFactory defaultThreadFactory = |
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new ThreadFactory() { |
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public Thread newThread(Runnable r) { |
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return new Thread(r); |
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} |
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}; |
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|
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/** |
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* The default rejectect execution handler |
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*/ |
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private static final RejectedExecutionHandler defaultHandler = |
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new AbortPolicy(); |
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|
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/** |
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* Invoke the rejected execution handler for the 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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* Create and return a new thread running firstTask as its first |
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* task. Call only while holding mainLock |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return the new thread |
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*/ |
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private Thread addThread(Runnable firstTask) { |
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Worker w = new Worker(firstTask); |
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Thread t = threadFactory.newThread(w); |
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w.thread = t; |
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workers.add(w); |
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int nt = ++poolSize; |
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if (nt > largestPoolSize) |
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largestPoolSize = nt; |
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return t; |
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} |
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|
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|
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|
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/** |
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* Create and start a new thread running firstTask as its first |
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* task, only if less than corePoolSize threads are running. |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return true if successful. |
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*/ |
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private boolean addIfUnderCorePoolSize(Runnable firstTask) { |
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Thread t = null; |
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mainLock.lock(); |
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try { |
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if (poolSize < corePoolSize) |
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t = addThread(firstTask); |
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} finally { |
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mainLock.unlock(); |
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} |
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if (t == null) |
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return false; |
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t.start(); |
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return true; |
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} |
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|
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/** |
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* Create and start a new thread only if less than maximumPoolSize |
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* threads are running. The new thread runs as its first task the |
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* next task in queue, or if there is none, the given task. |
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* @param firstTask the task the new thread should run first (or |
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* null if none) |
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* @return null on failure, else the first task to be run by new thread. |
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*/ |
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private Runnable addIfUnderMaximumPoolSize(Runnable firstTask) { |
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Thread t = null; |
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Runnable next = null; |
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mainLock.lock(); |
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try { |
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if (poolSize < maximumPoolSize) { |
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next = workQueue.poll(); |
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if (next == null) |
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next = firstTask; |
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t = addThread(next); |
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} |
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} finally { |
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mainLock.unlock(); |
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} |
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if (t == null) |
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return null; |
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t.start(); |
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return next; |
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} |
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|
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|
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/** |
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* Get the next task for a worker thread to run. |
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* @return the task |
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* @throws InterruptedException if interrupted while waiting for task |
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*/ |
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private Runnable getTask() throws InterruptedException { |
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for (;;) { |
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switch(runState) { |
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case RUNNING: { |
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if (poolSize <= corePoolSize) // untimed wait if core |
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return workQueue.take(); |
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|
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long timeout = keepAliveTime; |
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if (timeout <= 0) // die immediately for 0 timeout |
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return null; |
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Runnable r = workQueue.poll(timeout, TimeUnit.NANOSECONDS); |
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if (r != null) |
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return r; |
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if (poolSize > corePoolSize) // timed out |
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return null; |
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// else, after timeout, pool shrank so shouldn't die, so retry |
427 |
break; |
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} |
429 |
|
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case SHUTDOWN: { |
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// Help drain queue |
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Runnable r = workQueue.poll(); |
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if (r != null) |
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return r; |
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|
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// Check if can terminate |
437 |
if (workQueue.isEmpty()) { |
438 |
interruptIdleWorkers(); |
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return null; |
440 |
} |
441 |
|
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// There could still be delayed tasks in queue. |
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// Wait for one, re-checking state upon interruption |
444 |
try { |
445 |
return workQueue.take(); |
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} |
447 |
catch(InterruptedException ignore) { |
448 |
} |
449 |
break; |
450 |
} |
451 |
|
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case STOP: |
453 |
return null; |
454 |
default: |
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assert false; |
456 |
} |
457 |
} |
458 |
} |
459 |
|
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/** |
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* Wake up all threads that might be waiting for tasks. |
462 |
*/ |
463 |
void interruptIdleWorkers() { |
464 |
mainLock.lock(); |
465 |
try { |
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for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
467 |
it.next().interruptIfIdle(); |
468 |
} finally { |
469 |
mainLock.unlock(); |
470 |
} |
471 |
} |
472 |
|
473 |
/** |
474 |
* Perform bookkeeping for a terminated worker thread. |
475 |
* @param w the worker |
476 |
*/ |
477 |
private void workerDone(Worker w) { |
478 |
mainLock.lock(); |
479 |
try { |
480 |
completedTaskCount += w.completedTasks; |
481 |
workers.remove(w); |
482 |
if (--poolSize > 0) |
483 |
return; |
484 |
|
485 |
// Else, this is the last thread. Deal with potential shutdown. |
486 |
|
487 |
int state = runState; |
488 |
assert state != TERMINATED; |
489 |
|
490 |
if (state != STOP) { |
491 |
// If there are queued tasks but no threads, create |
492 |
// replacement. |
493 |
Runnable r = workQueue.poll(); |
494 |
if (r != null) { |
495 |
addThread(r).start(); |
496 |
return; |
497 |
} |
498 |
|
499 |
// If there are some (presumably delayed) tasks but |
500 |
// none pollable, create an idle replacement to wait. |
501 |
if (!workQueue.isEmpty()) { |
502 |
addThread(null).start(); |
503 |
return; |
504 |
} |
505 |
|
506 |
// Otherwise, we can exit without replacement |
507 |
if (state == RUNNING) |
508 |
return; |
509 |
} |
510 |
|
511 |
// Either state is STOP, or state is SHUTDOWN and there is |
512 |
// no work to do. So we can terminate. |
513 |
runState = TERMINATED; |
514 |
termination.signalAll(); |
515 |
// fall through to call terminate() outside of lock. |
516 |
} finally { |
517 |
mainLock.unlock(); |
518 |
} |
519 |
|
520 |
assert runState == TERMINATED; |
521 |
terminated(); |
522 |
} |
523 |
|
524 |
/** |
525 |
* Worker threads |
526 |
*/ |
527 |
private class Worker implements Runnable { |
528 |
|
529 |
/** |
530 |
* The runLock is acquired and released surrounding each task |
531 |
* execution. It mainly protects against interrupts that are |
532 |
* intended to cancel the worker thread from instead |
533 |
* interrupting the task being run. |
534 |
*/ |
535 |
private final ReentrantLock runLock = new ReentrantLock(); |
536 |
|
537 |
/** |
538 |
* Initial task to run before entering run loop |
539 |
*/ |
540 |
private Runnable firstTask; |
541 |
|
542 |
/** |
543 |
* Per thread completed task counter; accumulated |
544 |
* into completedTaskCount upon termination. |
545 |
*/ |
546 |
volatile long completedTasks; |
547 |
|
548 |
/** |
549 |
* Thread this worker is running in. Acts as a final field, |
550 |
* but cannot be set until thread is created. |
551 |
*/ |
552 |
Thread thread; |
553 |
|
554 |
Worker(Runnable firstTask) { |
555 |
this.firstTask = firstTask; |
556 |
} |
557 |
|
558 |
boolean isActive() { |
559 |
return runLock.isLocked(); |
560 |
} |
561 |
|
562 |
/** |
563 |
* Interrupt thread if not running a task |
564 |
*/ |
565 |
void interruptIfIdle() { |
566 |
if (runLock.tryLock()) { |
567 |
try { |
568 |
thread.interrupt(); |
569 |
} finally { |
570 |
runLock.unlock(); |
571 |
} |
572 |
} |
573 |
} |
574 |
|
575 |
/** |
576 |
* Cause thread to die even if running a task. |
577 |
*/ |
578 |
void interruptNow() { |
579 |
thread.interrupt(); |
580 |
} |
581 |
|
582 |
/** |
583 |
* Run a single task between before/after methods. |
584 |
*/ |
585 |
private void runTask(Runnable task) { |
586 |
runLock.lock(); |
587 |
try { |
588 |
// Abort now if immediate cancel. Otherwise, we have |
589 |
// committed to run this task. |
590 |
if (runState == STOP) |
591 |
return; |
592 |
|
593 |
Thread.interrupted(); // clear interrupt status on entry |
594 |
boolean ran = false; |
595 |
beforeExecute(thread, task); |
596 |
try { |
597 |
task.run(); |
598 |
ran = true; |
599 |
afterExecute(task, null); |
600 |
++completedTasks; |
601 |
} catch(RuntimeException ex) { |
602 |
if (!ran) |
603 |
afterExecute(task, ex); |
604 |
// Else the exception occurred within |
605 |
// afterExecute itself in which case we don't |
606 |
// want to call it again. |
607 |
throw ex; |
608 |
} |
609 |
} finally { |
610 |
runLock.unlock(); |
611 |
} |
612 |
} |
613 |
|
614 |
/** |
615 |
* Main run loop |
616 |
*/ |
617 |
public void run() { |
618 |
try { |
619 |
for (;;) { |
620 |
Runnable task; |
621 |
if (firstTask != null) { |
622 |
task = firstTask; |
623 |
firstTask = null; |
624 |
} else { |
625 |
task = getTask(); |
626 |
if (task == null) |
627 |
break; |
628 |
} |
629 |
runTask(task); |
630 |
task = null; // unnecessary but can help GC |
631 |
} |
632 |
} catch(InterruptedException ie) { |
633 |
// fall through |
634 |
} finally { |
635 |
workerDone(this); |
636 |
} |
637 |
} |
638 |
} |
639 |
|
640 |
// Public methods |
641 |
|
642 |
/** |
643 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given |
644 |
* initial parameters. It may be more convenient to use one of |
645 |
* the {@link Executors} factory methods instead of this general |
646 |
* purpose constructor. |
647 |
* |
648 |
* @param corePoolSize the number of threads to keep in the |
649 |
* pool, even if they are idle. |
650 |
* @param maximumPoolSize the maximum number of threads to allow in the |
651 |
* pool. |
652 |
* @param keepAliveTime when the number of threads is greater than |
653 |
* the core, this is the maximum time that excess idle threads |
654 |
* will wait for new tasks before terminating. |
655 |
* @param unit the time unit for the keepAliveTime |
656 |
* argument. |
657 |
* @param workQueue the queue to use for holding tasks before the |
658 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
659 |
* tasks submitted by the <tt>execute</tt> method. |
660 |
* @throws IllegalArgumentException if corePoolSize, or |
661 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
662 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
663 |
* @throws NullPointerException if <tt>workQueue</tt> is null |
664 |
*/ |
665 |
public ThreadPoolExecutor(int corePoolSize, |
666 |
int maximumPoolSize, |
667 |
long keepAliveTime, |
668 |
TimeUnit unit, |
669 |
BlockingQueue<Runnable> workQueue) { |
670 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
671 |
defaultThreadFactory, defaultHandler); |
672 |
} |
673 |
|
674 |
/** |
675 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
676 |
* parameters. |
677 |
* |
678 |
* @param corePoolSize the number of threads to keep in the |
679 |
* pool, even if they are idle. |
680 |
* @param maximumPoolSize the maximum number of threads to allow in the |
681 |
* pool. |
682 |
* @param keepAliveTime when the number of threads is greater than |
683 |
* the core, this is the maximum time that excess idle threads |
684 |
* will wait for new tasks before terminating. |
685 |
* @param unit the time unit for the keepAliveTime |
686 |
* argument. |
687 |
* @param workQueue the queue to use for holding tasks before the |
688 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
689 |
* tasks submitted by the <tt>execute</tt> method. |
690 |
* @param threadFactory the factory to use when the executor |
691 |
* creates a new thread. |
692 |
* @throws IllegalArgumentException if corePoolSize, or |
693 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
694 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
695 |
* @throws NullPointerException if <tt>workQueue</tt> |
696 |
* or <tt>threadFactory</tt> are null. |
697 |
*/ |
698 |
public ThreadPoolExecutor(int corePoolSize, |
699 |
int maximumPoolSize, |
700 |
long keepAliveTime, |
701 |
TimeUnit unit, |
702 |
BlockingQueue<Runnable> workQueue, |
703 |
ThreadFactory threadFactory) { |
704 |
|
705 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
706 |
threadFactory, defaultHandler); |
707 |
} |
708 |
|
709 |
/** |
710 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
711 |
* parameters. |
712 |
* |
713 |
* @param corePoolSize the number of threads to keep in the |
714 |
* pool, even if they are idle. |
715 |
* @param maximumPoolSize the maximum number of threads to allow in the |
716 |
* pool. |
717 |
* @param keepAliveTime when the number of threads is greater than |
718 |
* the core, this is the maximum time that excess idle threads |
719 |
* will wait for new tasks before terminating. |
720 |
* @param unit the time unit for the keepAliveTime |
721 |
* argument. |
722 |
* @param workQueue the queue to use for holding tasks before the |
723 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
724 |
* tasks submitted by the <tt>execute</tt> method. |
725 |
* @param handler the handler to use when execution is blocked |
726 |
* because the thread bounds and queue capacities are reached. |
727 |
* @throws IllegalArgumentException if corePoolSize, or |
728 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
729 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
730 |
* @throws NullPointerException if <tt>workQueue</tt> |
731 |
* or <tt>handler</tt> are null. |
732 |
*/ |
733 |
public ThreadPoolExecutor(int corePoolSize, |
734 |
int maximumPoolSize, |
735 |
long keepAliveTime, |
736 |
TimeUnit unit, |
737 |
BlockingQueue<Runnable> workQueue, |
738 |
RejectedExecutionHandler handler) { |
739 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
740 |
defaultThreadFactory, handler); |
741 |
} |
742 |
|
743 |
/** |
744 |
* Creates a new <tt>ThreadPoolExecutor</tt> with the given initial |
745 |
* parameters. |
746 |
* |
747 |
* @param corePoolSize the number of threads to keep in the |
748 |
* pool, even if they are idle. |
749 |
* @param maximumPoolSize the maximum number of threads to allow in the |
750 |
* pool. |
751 |
* @param keepAliveTime when the number of threads is greater than |
752 |
* the core, this is the maximum time that excess idle threads |
753 |
* will wait for new tasks before terminating. |
754 |
* @param unit the time unit for the keepAliveTime |
755 |
* argument. |
756 |
* @param workQueue the queue to use for holding tasks before the |
757 |
* are executed. This queue will hold only the <tt>Runnable</tt> |
758 |
* tasks submitted by the <tt>execute</tt> method. |
759 |
* @param threadFactory the factory to use when the executor |
760 |
* creates a new thread. |
761 |
* @param handler the handler to use when execution is blocked |
762 |
* because the thread bounds and queue capacities are reached. |
763 |
* @throws IllegalArgumentException if corePoolSize, or |
764 |
* keepAliveTime less than zero, or if maximumPoolSize less than or |
765 |
* equal to zero, or if corePoolSize greater than maximumPoolSize. |
766 |
* @throws NullPointerException if <tt>workQueue</tt> |
767 |
* or <tt>threadFactory</tt> or <tt>handler</tt> are null. |
768 |
*/ |
769 |
public ThreadPoolExecutor(int corePoolSize, |
770 |
int maximumPoolSize, |
771 |
long keepAliveTime, |
772 |
TimeUnit unit, |
773 |
BlockingQueue<Runnable> workQueue, |
774 |
ThreadFactory threadFactory, |
775 |
RejectedExecutionHandler handler) { |
776 |
if (corePoolSize < 0 || |
777 |
maximumPoolSize <= 0 || |
778 |
maximumPoolSize < corePoolSize || |
779 |
keepAliveTime < 0) |
780 |
throw new IllegalArgumentException(); |
781 |
if (workQueue == null || threadFactory == null || handler == null) |
782 |
throw new NullPointerException(); |
783 |
this.corePoolSize = corePoolSize; |
784 |
this.maximumPoolSize = maximumPoolSize; |
785 |
this.workQueue = workQueue; |
786 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
787 |
this.threadFactory = threadFactory; |
788 |
this.handler = handler; |
789 |
} |
790 |
|
791 |
|
792 |
/** |
793 |
* Executes the given task sometime in the future. The task |
794 |
* may execute in a new thread or in an existing pooled thread. |
795 |
* |
796 |
* If the task cannot be submitted for execution, either because this |
797 |
* executor has been shutdown or because its capacity has been reached, |
798 |
* the task is handled by the current <tt>RejectedExecutionHandler</tt>. |
799 |
* |
800 |
* @param command the task to execute |
801 |
* @throws RejectedExecutionException at discretion of |
802 |
* <tt>RejectedExecutionHandler</tt>, if task cannot be accepted |
803 |
* for execution |
804 |
*/ |
805 |
public void execute(Runnable command) { |
806 |
for (;;) { |
807 |
if (runState != RUNNING) { |
808 |
reject(command); |
809 |
return; |
810 |
} |
811 |
if (poolSize < corePoolSize && addIfUnderCorePoolSize(command)) |
812 |
return; |
813 |
if (workQueue.offer(command)) |
814 |
return; |
815 |
Runnable r = addIfUnderMaximumPoolSize(command); |
816 |
if (r == command) |
817 |
return; |
818 |
if (r == null) { |
819 |
reject(command); |
820 |
return; |
821 |
} |
822 |
// else retry |
823 |
} |
824 |
} |
825 |
|
826 |
public void shutdown() { |
827 |
mainLock.lock(); |
828 |
try { |
829 |
if (runState == RUNNING) // don't override shutdownNow |
830 |
runState = SHUTDOWN; |
831 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
832 |
it.next().interruptIfIdle(); |
833 |
} finally { |
834 |
mainLock.unlock(); |
835 |
} |
836 |
} |
837 |
|
838 |
|
839 |
public List shutdownNow() { |
840 |
mainLock.lock(); |
841 |
try { |
842 |
if (runState != TERMINATED) |
843 |
runState = STOP; |
844 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
845 |
it.next().interruptNow(); |
846 |
} finally { |
847 |
mainLock.unlock(); |
848 |
} |
849 |
return Arrays.asList(workQueue.toArray()); |
850 |
} |
851 |
|
852 |
public boolean isShutdown() { |
853 |
return runState != RUNNING; |
854 |
} |
855 |
|
856 |
/** |
857 |
* Return true if this executor is in the process of terminating |
858 |
* after <tt>shutdown</tt> or <tt>shutdownNow</tt> but has not |
859 |
* completely terminated. This method may be useful for |
860 |
* debugging. A return of <tt>true</tt> reported a sufficient |
861 |
* period after shutdown may indicate that submitted tasks have |
862 |
* ignored or suppressed interruption, causing this executor not |
863 |
* to properly terminate. |
864 |
* @return true if terminating but not yet terminated. |
865 |
*/ |
866 |
public boolean isTerminating() { |
867 |
return runState == STOP; |
868 |
} |
869 |
|
870 |
public boolean isTerminated() { |
871 |
return runState == TERMINATED; |
872 |
} |
873 |
|
874 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
875 |
throws InterruptedException { |
876 |
mainLock.lock(); |
877 |
try { |
878 |
return termination.await(timeout, unit); |
879 |
} finally { |
880 |
mainLock.unlock(); |
881 |
} |
882 |
} |
883 |
|
884 |
/** |
885 |
* Invokes <tt>shutdown</tt> when this executor is no longer |
886 |
* referenced. |
887 |
*/ |
888 |
protected void finalize() { |
889 |
shutdown(); |
890 |
} |
891 |
|
892 |
/** |
893 |
* Sets the thread factory used to create new threads. |
894 |
* |
895 |
* @param threadFactory the new thread factory |
896 |
* @see #getThreadFactory |
897 |
*/ |
898 |
public void setThreadFactory(ThreadFactory threadFactory) { |
899 |
this.threadFactory = threadFactory; |
900 |
} |
901 |
|
902 |
/** |
903 |
* Returns the thread factory used to create new threads. |
904 |
* |
905 |
* @return the current thread factory |
906 |
* @see #setThreadFactory |
907 |
*/ |
908 |
public ThreadFactory getThreadFactory() { |
909 |
return threadFactory; |
910 |
} |
911 |
|
912 |
/** |
913 |
* Sets a new handler for unexecutable tasks. |
914 |
* |
915 |
* @param handler the new handler |
916 |
* @see #getRejectedExecutionHandler |
917 |
*/ |
918 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
919 |
this.handler = handler; |
920 |
} |
921 |
|
922 |
/** |
923 |
* Returns the current handler for unexecutable tasks. |
924 |
* |
925 |
* @return the current handler |
926 |
* @see #setRejectedExecutionHandler |
927 |
*/ |
928 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
929 |
return handler; |
930 |
} |
931 |
|
932 |
/** |
933 |
* Returns the task queue used by this executor. Access to the |
934 |
* task queue is intended primarily for debugging and monitoring. |
935 |
* This queue may be in active use. Retrieveing the task queue |
936 |
* does not prevent queued tasks from executing. |
937 |
* |
938 |
* @return the task queue |
939 |
*/ |
940 |
public BlockingQueue<Runnable> getQueue() { |
941 |
return workQueue; |
942 |
} |
943 |
|
944 |
/** |
945 |
* Removes this task from internal queue if it is present, thus |
946 |
* causing it not to be run if it has not already started. This |
947 |
* method may be useful as one part of a cancellation scheme. |
948 |
* |
949 |
* @param task the task to remove |
950 |
* @return true if the task was removed |
951 |
*/ |
952 |
public boolean remove(Runnable task) { |
953 |
return getQueue().remove(task); |
954 |
} |
955 |
|
956 |
|
957 |
/** |
958 |
* Tries to remove from the work queue all {@link Cancellable} |
959 |
* tasks that have been cancelled. This method can be useful as a |
960 |
* storage reclamation operation, that has no other impact on |
961 |
* functionality. Cancelled tasks are never executed, but may |
962 |
* accumulate in work queues until worker threads can actively |
963 |
* remove them. Invoking this method instead tries to remove them now. |
964 |
* However, this method may fail to remove tasks in |
965 |
* the presence of interference by other threads. |
966 |
*/ |
967 |
|
968 |
public void purge() { |
969 |
// Fail if we encounter interference during traversal |
970 |
try { |
971 |
Iterator<Runnable> it = getQueue().iterator(); |
972 |
while (it.hasNext()) { |
973 |
Runnable r = it.next(); |
974 |
if (r instanceof Cancellable) { |
975 |
Cancellable c = (Cancellable)r; |
976 |
if (c.isCancelled()) |
977 |
it.remove(); |
978 |
} |
979 |
} |
980 |
} |
981 |
catch(ConcurrentModificationException ex) { |
982 |
return; |
983 |
} |
984 |
} |
985 |
|
986 |
/** |
987 |
* Sets the core number of threads. This overrides any value set |
988 |
* in the constructor. If the new value is smaller than the |
989 |
* current value, excess existing threads will be terminated when |
990 |
* they next become idle. |
991 |
* |
992 |
* @param corePoolSize the new core size |
993 |
* @throws IllegalArgumentException if <tt>corePoolSize</tt> |
994 |
* less than zero |
995 |
* @see #getCorePoolSize |
996 |
*/ |
997 |
public void setCorePoolSize(int corePoolSize) { |
998 |
if (corePoolSize < 0) |
999 |
throw new IllegalArgumentException(); |
1000 |
mainLock.lock(); |
1001 |
try { |
1002 |
int extra = this.corePoolSize - corePoolSize; |
1003 |
this.corePoolSize = corePoolSize; |
1004 |
if (extra > 0 && poolSize > corePoolSize) { |
1005 |
Iterator<Worker> it = workers.iterator(); |
1006 |
while (it.hasNext() && |
1007 |
extra > 0 && |
1008 |
poolSize > corePoolSize && |
1009 |
workQueue.remainingCapacity() == 0) { |
1010 |
it.next().interruptIfIdle(); |
1011 |
--extra; |
1012 |
} |
1013 |
} |
1014 |
|
1015 |
} finally { |
1016 |
mainLock.unlock(); |
1017 |
} |
1018 |
} |
1019 |
|
1020 |
/** |
1021 |
* Returns the core number of threads. |
1022 |
* |
1023 |
* @return the core number of threads |
1024 |
* @see #setCorePoolSize |
1025 |
*/ |
1026 |
public int getCorePoolSize() { |
1027 |
return corePoolSize; |
1028 |
} |
1029 |
|
1030 |
/** |
1031 |
* Start a core thread, causing it to idly wait for work. This |
1032 |
* overrides the default policy of starting core threads only when |
1033 |
* new tasks are executed. This method will return <tt>false</tt> |
1034 |
* if all core threads have already been started. |
1035 |
* @return true if a thread was started |
1036 |
*/ |
1037 |
public boolean prestartCoreThread() { |
1038 |
return addIfUnderCorePoolSize(null); |
1039 |
} |
1040 |
|
1041 |
/** |
1042 |
* Start all core threads, causing them to idly wait for work. This |
1043 |
* overrides the default policy of starting core threads only when |
1044 |
* new tasks are executed. |
1045 |
* @return the number of threads started. |
1046 |
*/ |
1047 |
public int prestartAllCoreThreads() { |
1048 |
int n = 0; |
1049 |
while (addIfUnderCorePoolSize(null)) |
1050 |
++n; |
1051 |
return n; |
1052 |
} |
1053 |
|
1054 |
/** |
1055 |
* Sets the maximum allowed number of threads. This overrides any |
1056 |
* value set in the constructor. If the new value is smaller than |
1057 |
* the current value, excess existing threads will be |
1058 |
* terminated when they next become idle. |
1059 |
* |
1060 |
* @param maximumPoolSize the new maximum |
1061 |
* @throws IllegalArgumentException if maximumPoolSize less than zero or |
1062 |
* the {@link #getCorePoolSize core pool size} |
1063 |
* @see #getMaximumPoolSize |
1064 |
*/ |
1065 |
public void setMaximumPoolSize(int maximumPoolSize) { |
1066 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
1067 |
throw new IllegalArgumentException(); |
1068 |
mainLock.lock(); |
1069 |
try { |
1070 |
int extra = this.maximumPoolSize - maximumPoolSize; |
1071 |
this.maximumPoolSize = maximumPoolSize; |
1072 |
if (extra > 0 && poolSize > maximumPoolSize) { |
1073 |
Iterator<Worker> it = workers.iterator(); |
1074 |
while (it.hasNext() && |
1075 |
extra > 0 && |
1076 |
poolSize > maximumPoolSize) { |
1077 |
it.next().interruptIfIdle(); |
1078 |
--extra; |
1079 |
} |
1080 |
} |
1081 |
} finally { |
1082 |
mainLock.unlock(); |
1083 |
} |
1084 |
} |
1085 |
|
1086 |
/** |
1087 |
* Returns the maximum allowed number of threads. |
1088 |
* |
1089 |
* @return the maximum allowed number of threads |
1090 |
* @see #setMaximumPoolSize |
1091 |
*/ |
1092 |
public int getMaximumPoolSize() { |
1093 |
return maximumPoolSize; |
1094 |
} |
1095 |
|
1096 |
/** |
1097 |
* Sets the time limit for which threads may remain idle before |
1098 |
* being terminated. If there are more than the core number of |
1099 |
* threads currently in the pool, after waiting this amount of |
1100 |
* time without processing a task, excess threads will be |
1101 |
* terminated. This overrides any value set in the constructor. |
1102 |
* @param time the time to wait. A time value of zero will cause |
1103 |
* excess threads to terminate immediately after executing tasks. |
1104 |
* @param unit the time unit of the time argument |
1105 |
* @throws IllegalArgumentException if time less than zero |
1106 |
* @see #getKeepAliveTime |
1107 |
*/ |
1108 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
1109 |
if (time < 0) |
1110 |
throw new IllegalArgumentException(); |
1111 |
this.keepAliveTime = unit.toNanos(time); |
1112 |
} |
1113 |
|
1114 |
/** |
1115 |
* Returns the thread keep-alive time, which is the amount of time |
1116 |
* which threads in excess of the core pool size may remain |
1117 |
* idle before being terminated. |
1118 |
* |
1119 |
* @param unit the desired time unit of the result |
1120 |
* @return the time limit |
1121 |
* @see #setKeepAliveTime |
1122 |
*/ |
1123 |
public long getKeepAliveTime(TimeUnit unit) { |
1124 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
1125 |
} |
1126 |
|
1127 |
/* Statistics */ |
1128 |
|
1129 |
/** |
1130 |
* Returns the current number of threads in the pool. |
1131 |
* |
1132 |
* @return the number of threads |
1133 |
*/ |
1134 |
public int getPoolSize() { |
1135 |
return poolSize; |
1136 |
} |
1137 |
|
1138 |
/** |
1139 |
* Returns the approximate number of threads that are actively |
1140 |
* executing tasks. |
1141 |
* |
1142 |
* @return the number of threads |
1143 |
*/ |
1144 |
public int getActiveCount() { |
1145 |
mainLock.lock(); |
1146 |
try { |
1147 |
int n = 0; |
1148 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
1149 |
if (it.next().isActive()) |
1150 |
++n; |
1151 |
} |
1152 |
return n; |
1153 |
} finally { |
1154 |
mainLock.unlock(); |
1155 |
} |
1156 |
} |
1157 |
|
1158 |
/** |
1159 |
* Returns the largest number of threads that have ever |
1160 |
* simultaneously been in the pool. |
1161 |
* |
1162 |
* @return the number of threads |
1163 |
*/ |
1164 |
public int getLargestPoolSize() { |
1165 |
mainLock.lock(); |
1166 |
try { |
1167 |
return largestPoolSize; |
1168 |
} finally { |
1169 |
mainLock.unlock(); |
1170 |
} |
1171 |
} |
1172 |
|
1173 |
/** |
1174 |
* Returns the approximate total number of tasks that have been |
1175 |
* scheduled for execution. Because the states of tasks and |
1176 |
* threads may change dynamically during computation, the returned |
1177 |
* value is only an approximation, but one that does not ever |
1178 |
* decrease across successive calls. |
1179 |
* |
1180 |
* @return the number of tasks |
1181 |
*/ |
1182 |
public long getTaskCount() { |
1183 |
mainLock.lock(); |
1184 |
try { |
1185 |
long n = completedTaskCount; |
1186 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) { |
1187 |
Worker w = it.next(); |
1188 |
n += w.completedTasks; |
1189 |
if (w.isActive()) |
1190 |
++n; |
1191 |
} |
1192 |
return n + workQueue.size(); |
1193 |
} finally { |
1194 |
mainLock.unlock(); |
1195 |
} |
1196 |
} |
1197 |
|
1198 |
/** |
1199 |
* Returns the approximate total number of tasks that have |
1200 |
* completed execution. Because the states of tasks and threads |
1201 |
* may change dynamically during computation, the returned value |
1202 |
* is only an approximation, but one that does not ever decrease |
1203 |
* across successive calls. |
1204 |
* |
1205 |
* @return the number of tasks |
1206 |
*/ |
1207 |
public long getCompletedTaskCount() { |
1208 |
mainLock.lock(); |
1209 |
try { |
1210 |
long n = completedTaskCount; |
1211 |
for (Iterator<Worker> it = workers.iterator(); it.hasNext(); ) |
1212 |
n += it.next().completedTasks; |
1213 |
return n; |
1214 |
} finally { |
1215 |
mainLock.unlock(); |
1216 |
} |
1217 |
} |
1218 |
|
1219 |
/** |
1220 |
* Method invoked prior to executing the given Runnable in the |
1221 |
* given thread. This method may be used to re-initialize |
1222 |
* ThreadLocals, or to perform logging. Note: To properly nest |
1223 |
* multiple overridings, subclasses should generally invoke |
1224 |
* <tt>super.beforeExecute</tt> at the end of this method. |
1225 |
* |
1226 |
* @param t the thread that will run task r. |
1227 |
* @param r the task that will be executed. |
1228 |
*/ |
1229 |
protected void beforeExecute(Thread t, Runnable r) { } |
1230 |
|
1231 |
/** |
1232 |
* Method invoked upon completion of execution of the given |
1233 |
* Runnable. If non-null, the Throwable is the uncaught exception |
1234 |
* that caused execution to terminate abruptly. Note: To properly |
1235 |
* nest multiple overridings, subclasses should generally invoke |
1236 |
* <tt>super.afterExecute</tt> at the beginning of this method. |
1237 |
* |
1238 |
* @param r the runnable that has completed. |
1239 |
* @param t the exception that cause termination, or null if |
1240 |
* execution completed normally. |
1241 |
*/ |
1242 |
protected void afterExecute(Runnable r, Throwable t) { } |
1243 |
|
1244 |
/** |
1245 |
* Method invoked when the Executor has terminated. Default |
1246 |
* implementation does nothing. Note: To properly nest multiple |
1247 |
* overridings, subclasses should generally invoke |
1248 |
* <tt>super.terminated</tt> within this method. |
1249 |
*/ |
1250 |
protected void terminated() { } |
1251 |
|
1252 |
/** |
1253 |
* A handler for rejected tasks that runs the rejected task |
1254 |
* directly in the calling thread of the <tt>execute</tt> method, |
1255 |
* unless the executor has been shut down, in which case the task |
1256 |
* is discarded. |
1257 |
*/ |
1258 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
1259 |
|
1260 |
/** |
1261 |
* Constructs a <tt>CallerRunsPolicy</tt>. |
1262 |
*/ |
1263 |
public CallerRunsPolicy() { } |
1264 |
|
1265 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1266 |
if (!e.isShutdown()) { |
1267 |
r.run(); |
1268 |
} |
1269 |
} |
1270 |
} |
1271 |
|
1272 |
/** |
1273 |
* A handler for rejected tasks that throws a |
1274 |
* <tt>RejectedExecutionException</tt>. |
1275 |
*/ |
1276 |
public static class AbortPolicy implements RejectedExecutionHandler { |
1277 |
|
1278 |
/** |
1279 |
* Constructs a <tt>AbortPolicy</tt>. |
1280 |
*/ |
1281 |
public AbortPolicy() { } |
1282 |
|
1283 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1284 |
throw new RejectedExecutionException(); |
1285 |
} |
1286 |
} |
1287 |
|
1288 |
/** |
1289 |
* A handler for rejected tasks that silently discards the |
1290 |
* rejected task. |
1291 |
*/ |
1292 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
1293 |
|
1294 |
/** |
1295 |
* Constructs <tt>DiscardPolicy</tt>. |
1296 |
*/ |
1297 |
public DiscardPolicy() { } |
1298 |
|
1299 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1300 |
} |
1301 |
} |
1302 |
|
1303 |
/** |
1304 |
* A handler for rejected tasks that discards the oldest unhandled |
1305 |
* request and then retries <tt>execute</tt>, unless the executor |
1306 |
* is shut down, in which case the task is discarded. |
1307 |
*/ |
1308 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
1309 |
/** |
1310 |
* Constructs a <tt>DiscardOldestPolicy</tt> for the given executor. |
1311 |
*/ |
1312 |
public DiscardOldestPolicy() { } |
1313 |
|
1314 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
1315 |
if (!e.isShutdown()) { |
1316 |
e.getQueue().poll(); |
1317 |
e.execute(r); |
1318 |
} |
1319 |
} |
1320 |
} |
1321 |
} |