private boolean addWorker(Runnable firstTask, boolean core) {//firstTask:新增一個執行緒並執行這個任務，可空，增加的執行緒從佇列獲取任務；core：是否使用corePoolSize作為上限，否則使用maxmunPoolSize</span>
        retry: //較少使用到的識別符號，用於重試
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);

            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))//執行緒狀態非執行並且當非shutdown狀態下任務為空且佇列非空；
                return false;  //判斷條件有點難理解，其實是非執行狀態下（>=SHUTDOWN）或者SHUTDOWN狀態下任務非空(新提交任務)、任務佇列為空，就不可以再新增執行緒了（return false）,即SHUTDOWN狀態是可以新增執行緒去執行佇列中的任務；
            for (;;) {
                int wc = workerCountOf(c);
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize)) //實際最大執行緒數是CAPACITY;
                    return false;
                if (compareAndIncrementWorkerCount(c)) //AtomicInteger的CAS操作;
                    break retry;                       //新增執行緒數成功，結束retry(retry下的for迴圈)
                c = ctl.get();  // Re-read ctl
                if (runStateOf(c) != rs) //狀態發生改變，重試retry;
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }

        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            final ReentrantLock mainLock = this.mainLock;
            w = new Worker(firstTask); // Worker為內部類，封裝了執行緒和任務，通過ThreadFactory建立執行緒，可能失敗拋異常或者返回null
            final Thread t = w.thread;
            if (t != null) {
                mainLock.lock();
                try {
                    int c = ctl.get();
                    int rs = runStateOf(c);

                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        if (t.isAlive()) // SHUTDOWN以後的狀態和SHUTDOWN狀態下firstTask為null，不可新增執行緒
                            throw new IllegalThreadStateException();
                        workers.add(w); //儲存到一個HashSet中
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s; //記錄最大執行緒數
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);//失敗回退,從wokers移除w,執行緒數減一，嘗試結束執行緒池(呼叫tryTerminate方法，後續解析)
        }
        return workerStarted;
    }