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private boolean addWorker(Runnable firstTask, boolean core);
方法参数:
firstTask – 需要执行的任务,和worker进行绑定,可以为null
core ------- 是否为核心线程,如果为true,则使用corePoolSize;否则使用maxPoolSize
private boolean addWorker(Runnable firstTask, boolean core) {
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
/*
if rs >= SHUTDOWN :
if rs != SHUTDOWN //在STOP/TIDYING/TERMINATED状态下不能添加worker
if rs == SHUTDOWN && firstTask != null // 在SHUTDOWN状态下只能添加null任务
if rs == SHUTDOWN && firstTask == null && workQueue.isEmpty // 任务队列为空,没有必要添加新的工作线程,firstTask = null是为了额外添加一个线程,消耗任务队列
*/
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;
for (;;) {
int wc = workerCountOf(c);
// 工作线程饱和
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
if (compareAndIncrementWorkerCount(c))
break retry;
//cas自增失败
c = ctl.get(); // Re-read ctl
//状态发生改变
if (runStateOf(c) != rs)
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
}
//添加任务
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
// Recheck while holding lock.
// Back out on ThreadFactory failure or if
// shut down before lock acquired.
int rs = runStateOf(ctl.get());
/*
if rs == RUNNING //线程池状态为RUNNING
if rs == SHUTDOWN && firstTask == null //线程池状态为SHUTDOWN,而且firstTask == null
*/
if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
// isAlive 返回true,说明线程非按照正常过程被启动,可以导致wokerStarted = false
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
addWorker(Runnable firstTask,bool core)只有在两种情况下会返回true
1、当线程池状态为SHUTDOWN时,且工作任务队列不为空,这时候只有addWorker(null)返回为true。
2、当线程池状态为RUNNING时,判断工作线程数量是否饱和(即判断workerCount),如果不饱和,添加并返回true。代码如下:
wc >= CAPACITY || wc >= (core ? corePoolSize : maximumPoolSize)
这里有必要解释一下addWorker(null)的用意,这种调用只会出现在SHUTDOWN状态并且工作任务队列不为空的情况,为的是新建一个工作线程从工作任务队列获取取任务执行,以尽快的结束工作任务队列的任务。