Created
May 19, 2018 11:59
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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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