ThreadPoolExecutor中的java Override execute（）

Question

我正在寻找一个ThreadPoolExecutor，当它的任务队列已满时，它将被阻止——如果底层队列已满，当前的Java实现将拒绝新任务-

public void execute(Runnable command) {
    if (command == null)
        throw new NullPointerException();
    /*
     * Proceed in 3 steps:
     *
     * 1. If fewer than corePoolSize threads are running, try to
     * start a new thread with the given command as its first
     * task.  The call to addWorker atomically checks runState and
     * workerCount, and so prevents false alarms that would add
     * threads when it shouldn't, by returning false.
     *
     * 2. If a task can be successfully queued, then we still need
     * to double-check whether we should have added a thread
     * (because existing ones died since last checking) or that
     * the pool shut down since entry into this method. So we
     * recheck state and if necessary roll back the enqueuing if
     * stopped, or start a new thread if there are none.
     *
     * 3. If we cannot queue task, then we try to add a new
     * thread.  If it fails, we know we are shut down or saturated
     * and so reject the task.
     */
    int c = ctl.get();
    if (workerCountOf(c) < corePoolSize) {
        if (addWorker(command, true))
            return;
        c = ctl.get();
    }
    if (isRunning(c) && workQueue.offer(command)) {
        int recheck = ctl.get();
        if (! isRunning(recheck) && remove(command))
            reject(command);
        else if (workerCountOf(recheck) == 0)
            addWorker(null, false);
    }
    else if (!addWorker(command, false))
        reject(command);
}

如果改变这一行：

 if (isRunning(c) && workQueue.offer(command)) {

到

 if (isRunning(c) && workQueue.put(command)) {

玩这个把戏吗？我错过什么了吗

解决方案（可能会帮助下一个人）：

public class BlockingThreadPoolExecutor extends ThreadPoolExecutor {

    private final Semaphore runLock;

    public BlockingThreadPoolExecutor(int corePoolSize, int maximumPoolSize,
            long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, int maxTasks) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
        runLock = new Semaphore(maxTasks);
    }

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        runLock.acquireUninterruptibly();
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        runLock.release();
    }

}

Answer 1

取决于ThreadPoolExecutor状态和设置，因为并非所有任务提交都通过BlockingQueue。通常，您只想将ThreadPoolExecutor的RejectedExecutionHandler更改为ThreadPoolExecutor.CallerRunsPolicy，这将限制提交。如果你真的想在提交时阻止，那么你应该使用CompletionService，并在想要阻止时调用'take'方法。还可以创建一个子类，并使用Semaphore来阻止execute方法。有关更多信息，请参见JDK-6648211 : Need for blocking ThreadPoolExecutor