Inside AbstractQueuedSynchronizer (3)

Inside AbstractQueuedSynchronizer (1)

Inside AbstractQueuedSynchronizer (2)

Inside AbstractQueuedSynchronizer (3)

Inside AbstractQueuedSynchronizer (4)

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3.4 Template Method

??? AbstractQueuedSynchronizer提供了以下几个protected方法用于子类改写

  int ws = pred.waitStatus;        if (ws == Node.SIGNAL)//下次循环判断 返回true block线程            /*             * This node has already set status asking a release             * to signal it, so it can safely park.             */            return true;        if (ws > 0) {            /*             * Predecessor was cancelled. Skip over predecessors and             * indicate retry.             */            do {                node.prev = pred = pred.prev;            } while (pred.waitStatus > 0);            pred.next = node;        } else {            /*             * waitStatus must be 0 or PROPAGATE.  Indicate that we             * need a signal, but don't park yet.  Caller will need to             * retry to make sure it cannot acquire before parking.             */            compareAndSetWaitStatus(pred, ws, Node.SIGNAL);//第一次设置，标志需要这样一个信号        }        return false;