我正在寻找一个 ThreadPoolExecutor，当它的任务队列已满时会阻塞 - 如果底层队列已满，当前的 Java 实现会拒绝新任务 -
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);
}
会改变这一行：
if (isRunning(c) && workQueue.offer(command)) {
到
if (isRunning(c) && workQueue.put(command)) {
做伎俩？我错过了什么吗？
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();
}
}