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- 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);
- }
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