JDK的java.util.concurrent.ThreadPoolExecutor允許您將任務提交到線程池，并使用BlockingQueue來保存提交的任務。 如果您要提交數千個任務，請指定一個“綁定”隊列（即最大容量的隊列），否則JVM可能會耗盡內存。 您可以設置RejectedExecutionHandler來處理隊列已滿時發生的情況，但是仍然有待提交的任務。

這里是你展示如何使用一個簡單的例子ThreadPoolExecutor具有BlockingQueue容量1000 CallerRunsPolicy確保，當隊列已滿時，其他任務將由提交線程處理。

int numThreads = 5; ExecutorService exec = new ThreadPoolExecutor(5, 5, 0L, TimeUnit.MILLISECONDS,new ArrayBlockingQueue<Runnable>(1000),new ThreadPoolExecutor.CallerRunsPolicy());

這種方法的問題在于，當隊列已滿時，向池提交任務的線程會變得忙于執行任務本身，在此期間，隊列可能會變空并且池中的線程可能會變得空閑。 這不是很有效。 我們希望一直保持線程池繁忙，并且工作隊列始終處于飽和狀態。

有多種解決方案。 其中之一是使用自定義的Executor ，該Executor在隊列已滿時會阻塞（從而阻止其他任務提交到池）。 BlockingExecutor的代碼如下所示。 它基于Brian Goetz，2006年的BoundedExecutor示例。Java Concurrency in Practice。 1版。 Addison-Wesley專業。 （第8.3.3節） 。

import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.RejectedExecutionException; import java.util.concurrent.Semaphore; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit;import org.slf4j.Logger; import org.slf4j.LoggerFactory;/*** An executor which blocks and prevents further tasks from* being submitted to the pool when the queue is full.* <p>* Based on the BoundedExecutor example in:* Brian Goetz, 2006. Java Concurrency in Practice. (Listing 8.4)*/ public class BlockingExecutor extends ThreadPoolExecutor {private static final Logger LOGGER = LoggerFactory.getLogger(BlockingExecutor.class);private final Semaphore semaphore;/*** Creates a BlockingExecutor which will block and prevent further* submission to the pool when the specified queue size has been reached.** @param poolSize the number of the threads in the pool* @param queueSize the size of the queue*/public BlockingExecutor(final int poolSize, final int queueSize) {super(poolSize, poolSize, 0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());// the semaphore is bounding both the number of tasks currently executing// and those queued upsemaphore = new Semaphore(poolSize + queueSize);}/*** Executes the given task.* This method will block when the semaphore has no permits* i.e. when the queue has reached its capacity.*/@Overridepublic void execute(final Runnable task) {boolean acquired = false;do {try {semaphore.acquire();acquired = true;} catch (final InterruptedException e) {LOGGER.warn("InterruptedException whilst aquiring semaphore", e);}} while (!acquired);try {super.execute(task);} catch (final RejectedExecutionException e) {semaphore.release();throw e;}}/*** Method invoked upon completion of execution of the given Runnable,* by the thread that executed the task.* Releases a semaphore permit.*/@Overrideprotected void afterExecute(final Runnable r, final Throwable t) {super.afterExecute(r, t);semaphore.release();} }

參考：我們的JCG合作伙伴 Fahd Shariff在fahd.blog博客上使用BlockingExecutor進行節流任務提交 。

翻譯自: https://www.javacodegeeks.com/2013/11/throttling-task-submission-with-a-blockingexecutor-2.html

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