核心参数解析
核心线程
非核心线程及存活时间
任务队列
线程工厂
拒绝策略
默认实现有四种:
CallerRunsPolicy
AbortPolicy
DiscardPolicy
DiscardOldestPolicy
任务提交
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@Override public void execute(Runnable command) {
// 不可提交空任务
if (command == null) throw new NullPointerException();
int c = ctl.get();
// 工作线程数目小于核心线程数，则初始化核心线程
if (workerCountOf(c) < corePoolSize) {
// 添加核心工作线程，Worker#thread
if (addWorker(command/*firstTask*/, true/*core*/)) return;
c = ctl.get();
}
// 工作线程大于核心线程，则尝试向队列中提交任务
if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();
if (!isRunning(recheck) && remove(command)) {
reject(command);
} else if (workerCountOf(recheck) == 0) {
// 添加非核心工作线程
addWorker(null, false);
}
}
// 尝试添加非核心线程，若添加失败则执行拒绝策略
else if (!addWorker(command, false)) {
reject(command);
}
}
任务执行
Worker#run() -> runWorker()
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final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
try {
// getTask() 为阻塞方法，任务队列无任务时会阻塞，从而达到核心线程保活
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 interrupt
if ((runStateAtLeast(ctl.get(), STOP) ||
(Thread.interrupted() && runStateAtLeast(ctl.get(), STOP))) &&
!wt.isInterrupted())
wt.interrupt();
try {
beforeExecute(wt, task);
Throwable thrown = null;
try {
task.run(); // 任务执行
} finally {
afterExecute(task, thrown);
}
} finally {
task = null;
w.completedTasks++;
w.unlock();
}
}
completedAbruptly = false;
} finally {
processWorkerExit(w, completedAbruptly);
}
}