Java 队列已满时ThreadPoolExecutor块？
我正在尝试使用ThreadPoolExecutor执行许多任务。下面是一个假设的例子：Java 队列已满时ThreadPoolExecutor块？,java,multithreading,concurrency,executorservice,executor,Java,Multithreading,Concurrency,Executorservice,Executor,我正在尝试使用ThreadPoolExecutor执行许多任务。下面是一个假设的例子： def workQueue = new ArrayBlockingQueue<Runnable>(3, false) def threadPoolExecutor = new ThreadPoolExecutor(3, 3, 1L, TimeUnit.HOURS, workQueue) for(int i = 0; i < 100000; i++) threadPoolExecuto
def workQueue = new ArrayBlockingQueue<Runnable>(3, false)
def threadPoolExecutor = new ThreadPoolExecutor(3, 3, 1L, TimeUnit.HOURS, workQueue)
for(int i = 0; i < 100000; i++)
threadPoolExecutor.execute(runnable)
def workQueue=new ArrayBlockingQueue（3，false）
def threadPoolExecutor=新的threadPoolExecutor（3,3,1L，TimeUnit.HOURS，workQueue）
对于（int i=0；i<100000；i++）
threadPoolExecutor.execute（可运行）
问题是我很快得到了一个
java.util.concurrent.RejectedExecutionExceptionRejectedExecutionHandler block = new RejectedExecutionHandler() {
rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
executor.getQueue().put( r );
}
};
ThreadPoolExecutor pool = new ...
pool.setRejectedExecutionHandler(block);
- 它很容易死锁，因为池中的所有线程都可能在您放入队列的内容可见之前死亡。通过设置合理的保持活动时间来缓解此问题
- 任务没有按照执行者预期的方式包装。许多执行器实现在执行之前将其任务包装在某种跟踪对象中。看看你的来源
- API强烈反对通过getQueue（）进行添加，在某些情况下可能会被禁止
- 只有一个线程调用execute（）
- 您必须（或希望）有一个非常小的队列长度
- 您绝对需要限制运行这项工作的线程数量（通常是出于外部原因），调用方运行策略将打破这一限制
- 您的任务大小不可预测，因此，如果池暂时忙于4个短任务，而调用execute的单线程被一个大任务卡住，则调用程序运行可能会导致饥饿
祝你好运。这是我在本例中的代码片段：
public void executeBlocking( Runnable command ) {
if ( threadPool == null ) {
logger.error( "Thread pool '{}' not initialized.", threadPoolName );
return;
}
ThreadPool threadPoolMonitor = this;
boolean accepted = false;
do {
try {
threadPool.execute( new Runnable() {
@Override
public void run() {
try {
command.run();
}
// to make sure that the monitor is freed on exit
finally {
// Notify all the threads waiting for the resource, if any.
synchronized ( threadPoolMonitor ) {
threadPoolMonitor.notifyAll();
}
}
}
} );
accepted = true;
}
catch ( RejectedExecutionException e ) {
// Thread pool is full
try {
// Block until one of the threads finishes its job and exits.
synchronized ( threadPoolMonitor ) {
threadPoolMonitor.wait();
}
}
catch ( InterruptedException ignored ) {
// return immediately
break;
}
}
} while ( !accepted );
}
threadPool是已经初始化的java.util.concurrent.ExecutorService的本地实例。我使用一个自定义的RejectedExecutionHandler解决了这个问题，它只是暂时阻止调用线程，然后再次尝试提交任务：
public class BlockWhenQueueFull implements RejectedExecutionHandler {
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
// The pool is full. Wait, then try again.
try {
long waitMs = 250;
Thread.sleep(waitMs);
} catch (InterruptedException interruptedException) {}
executor.execute(r);
}
}
executorPool = new def threadPoolExecutor = new ThreadPoolExecutor(3, 3, 1L, TimeUnit.HOURS, workQueue, new BlockWhenQueueFull())
然而，我个人喜欢这种方法。它结构紧凑，易于理解，运行良好。我遗漏了什么重要的东西吗？您可以使用
信号量来阻止线程进入池中
执行器服务=新的线程池执行器(
3.
3.
1.
时间单位：小时，
新建ArrayBlockingQueue（6，false）
);
信号量锁=新信号量（6）；//等于队列容量
对于（int i=0；i<100000；i++）{
试一试{
lock.acquire（）；
服务提交（（）->{
试一试{
task.run（）；
}最后{
锁定。释放（）；
}
});
}捕捉（中断异常e）{
抛出新的运行时异常（e）；
}
}
- 仅在固定线程池中使用此模式。队列不太可能经常满，因此不会创建新线程。查看ThreadPoolExecutor上的java文档了解更多详细信息：有一种方法可以解决这个问题，但它超出了这个答案的范围
- 队列大小应大于核心线程数。如果我们将队列大小设为3，最终会发生以下情况：
- T0：所有三个线程都在工作，队列为空，没有可用的许可证
- T1：螺纹1完成，释放许可证
- T2：线程1轮询队列中的新工作，未找到任何工作，等待
- T3：主线程将工作提交到池中，线程1开始工作
private static class BlockingExecutor implements Executor {
final Semaphore semaphore;
final Executor delegate;
private BlockingExecutor(final int concurrentTasksLimit, final Executor delegate) {
semaphore = new Semaphore(concurrentTasksLimit);
this.delegate = delegate;
}
@Override
public void execute(final Runnable command) {
try {
semaphore.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
return;
}
final Runnable wrapped = () -> {
try {
command.run();
} finally {
semaphore.release();
}
};
delegate.execute(wrapped);
}
}
您可以将concurrentTasksLimit调整为您的委托执行者的threadPoolSize+queueSize，这将基本上解决您的问题
int NUM_THREADS = 6;
Semaphore lock = new Semaphore(NUM_THREADS);
ExecutorService pool = Executors.newCachedThreadPool();
for (int i = 0; i < 100000; i++) {
try {
lock.acquire();
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
pool.execute(() -> {
try {
// Task logic
} finally {
lock.release();
}
});
}
int NUM_THREADS=6；
信号量锁=新信号量（NUM_线程）；
ExecutorService池=Executors.newCachedThreadPool（）；
对于（int i=0；i<100000；i++）{
试一试{
lock.acquire（）；
}捕捉（中断异常e）{
抛出新的运行时异常（e）；
}
pool.execute（（）->{
试一试{
//任务逻辑
}最后{
锁定。释放（）；
}
});
}
offer（…）put（…）BlockingQueuepublic class BlockOnOfferAdapter<T> implements BlockingQueue<T> {
(..)
public boolean offer(E o) {
try {
delegate.put(o);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
return false;
}
return true;
}
(.. implement all other methods simply by delegating ..)
}
没有捕获被拒绝的执行异常或需要复杂的锁定。好的，旧线程，但这是我在搜索时发现的
/**
* Inserts the specified element into this queue, waiting if necessary
* for space to become available.
*
* @param e the element to add
* @throws InterruptedException if interrupted while waiting
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this queue
*/
void put(E e) throws InterruptedException;
class BlockingThreadPoolTaskExecutor(concurrency: Int) : ThreadPoolTaskExecutor() {
companion object {
lateinit var semaphore: Semaphore
}
init {
semaphore = Semaphore(concurrency)
val semaphoreTaskDecorator = SemaphoreTaskDecorator()
this.setTaskDecorator(semaphoreTaskDecorator)
}
override fun <T> submit(task: Callable<T>): Future<T> {
log.debug("submit")
semaphore.acquire()
return super.submit(task)
}
}
private class SemaphoreTaskDecorator : TaskDecorator {
override fun decorate(runnable: Runnable): Runnable {
log.debug("decorate")
return Runnable {
try {
runnable.run()
} finally {
log.debug("decorate done")
semaphore.release()
}
}
}
}