/**
* Executes the given task sometime in the future. The task
* may execute in a new thread or in an existing pooled thread.
*
* If the task cannot be submitted for execution, either because this
* executor has been shutdown or because its capacity has been reached,
* the task is handled by the current {@code RejectedExecutionHandler}.
*
* @param command the task to execute
* @throws RejectedExecutionException at discretion of
* {@code RejectedExecutionHandler}, if the task
* cannot be accepted for execution
* @throws NullPointerException if {@code command} is null
*/publicvoidexecute(Runnable command){if(command == null)thrownewNullPointerException();/*
* 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);elseif(workerCountOf(recheck)==0)addWorker(null,false);}elseif(!addWorker(command,false))reject(command);}
/**
* Main worker run loop. Repeatedly gets tasks from queue and
* executes them, while coping with a number of issues:
*
* 1. We may start out with an initial task, in which case we
* don't need to get the first one. Otherwise, as long as pool is
* running, we get tasks from getTask. If it returns null then the
* worker exits due to changed pool state or configuration
* parameters. Other exits result from exception throws in
* external code, in which case completedAbruptly holds, which
* usually leads processWorkerExit to replace this thread.
*
* 2. Before running any task, the lock is acquired to prevent
* other pool interrupts while the task is executing, and then we
* ensure that unless pool is stopping, this thread does not have
* its interrupt set.
*
* 3. Each task run is preceded by a call to beforeExecute, which
* might throw an exception, in which case we cause thread to die
* (breaking loop with completedAbruptly true) without processing
* the task.
*
* 4. Assuming beforeExecute completes normally, we run the task,
* gathering any of its thrown exceptions to send to afterExecute.
* We separately handle RuntimeException, Error (both of which the
* specs guarantee that we trap) and arbitrary Throwables.
* Because we cannot rethrow Throwables within Runnable.run, we
* wrap them within Errors on the way out (to the thread's
* UncaughtExceptionHandler). Any thrown exception also
* conservatively causes thread to die.
*
* 5. After task.run completes, we call afterExecute, which may
* also throw an exception, which will also cause thread to
* die. According to JLS Sec 14.20, this exception is the one that
* will be in effect even if task.run throws.
*
* The net effect of the exception mechanics is that afterExecute
* and the thread's UncaughtExceptionHandler have as accurate
* information as we can provide about any problems encountered by
* user code.
*
* @param w the worker
*/finalvoidrunWorker(Worker w){
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock();// allow interruptsboolean completedAbruptly =true;try{while(task != null ||(task =getTask())!= null){
w.lock();// If pool is stopping, ensure thread is interrupted;// if not, ensure thread is not interrupted. This// requires a recheck in second case to deal with// shutdownNow race while clearing interruptif((runStateAtLeast(ctl.get(), STOP)||(Thread.interrupted()&&runStateAtLeast(ctl.get(), STOP)))&&!wt.isInterrupted())
wt.interrupt();try{beforeExecute(wt, task);
Throwable thrown = null;try{
task.run();}catch(RuntimeException x){
thrown = x;throw x;}catch(Error x){
thrown = x;throw x;}catch(Throwable x){
thrown = x;thrownewError(x);}finally{afterExecute(task, thrown);}}finally{
task = null;
w.completedTasks++;
w.unlock();}}
completedAbruptly =false;}finally{processWorkerExit(w, completedAbruptly);}}
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