（jdk12）addWorker源代码分析

（jdk12）addWorker源代码分析：

private boolean addWorker(Runnable firstTask, boolean core) {
retry:
for (int c = ctl.get(); {

    // Check if queue empty only if necessary.

    if (runStateAtLeast(c, SHUTDOWN)
        && (runStateAtLeast(c, STOP)
  //⬆️判断当前的线程池处于STOP状态或TIDYING状态或TERMINATED状态
            || firstTask != null

//当前线程池没有任务
|| workQueue.isEmpty()))
//当前阻塞队列中没有待执行任务
return false;

    for (;;) {
        if (workerCountOf(c)
            >= ((core ? corePoolSize : maximumPoolSize) & COUNT_MASK))

return false;

        c = ctl.get();  // Re-read ctl
        if (runStateAtLeast(c, SHUTDOWN))

//如果clt的高三位没有变成RUNNING，即c>=SHUTDOWN那么返回true，表示线程池状态变更失败，retry
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
}

//线程池状态clt修改完毕，开始添加线程

boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;

//⬆️设置线程添加判断位（workerAdded）和 线程运行位（workerStarted）创建新线程Worker w = null

try {
    w = new Worker(firstTask);

//⬆️将传入的runnable类作为新建线程的firstTask

    final Thread t = w.thread;

//⬆️将w的Runnable类的线程传给t
//thread方法说明：Thread this worker is running in. Null if factory fails.

    if (t != null) {

//⬆️判断w线程所使用的Runnable能否成功运行，如果不行返回null

//确认新建线程t和Worker类w创建初始化成功之后，开始创建锁
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
//⬆️创建并持有锁

        try {
            // Recheck while holding lock.
            // Back out on ThreadFactory failure or if
            // shut down before lock acquired.

//⬆️try的目的是在持有锁的期间再次确认，当线程t的Runnable类是否出错，在持有锁的期间这个线程池是否被关闭，如果出现其中一种情况，退出添加线程池的方法
int c = ctl.get();

            if (isRunning(c) ||
                (runStateLessThan(c, STOP) && firstTask == null)) {

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;
}
//⬆️在线程池中添加的Worker类，即新建线程，修改相关参数：线程池的容量参数largestPoolSize，注意这个largestPoolSize只能在持有锁mainLock的状态下访问
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
//⬆️放弃锁mainLock的持有权，判断线程池中添加新线程的操作是否成功，如果成功，线程开始运行，线程池也开始运行，如果失败调用，调用addWorkerFailed方法，即删除Worker类的w，修改WorkerCount（线程池房钱线程数量wc）并尝试关闭线程池的方法，返回线程是否开始运行的判断值workerStarted;。