static final class Node {
 /** 共享 */
 static final Node SHARED = new Node();

 /** 獨(dú)占 */
 static final Node EXCLUSIVE = null;

 /**
 * 因?yàn)槌瑫r或者中斷，節(jié)點(diǎn)會被設(shè)置為取消狀態(tài)，被取消的節(jié)點(diǎn)時不會參與到競爭中的，他會一直保持取消狀態(tài)不會轉(zhuǎn)變?yōu)槠渌麪顟B(tài)；
 */
 static final int CANCELLED = 1;

 /**
 * 后繼節(jié)點(diǎn)的線程處于等待狀態(tài)，而當(dāng)前節(jié)點(diǎn)的線程如果釋放了同步狀態(tài)或者被取消，將會通知后繼節(jié)點(diǎn)，使后繼節(jié)點(diǎn)的線程得以運(yùn)行
 */
 static final int SIGNAL = -1;

 /**
 * 節(jié)點(diǎn)在等待隊(duì)列中，節(jié)點(diǎn)線程等待在Condition上，當(dāng)其他線程對Condition調(diào)用了signal()后，改節(jié)點(diǎn)將會從等待隊(duì)列中轉(zhuǎn)移到同步隊(duì)列中，加入到同步狀態(tài)的獲取中
 */
 static final int CONDITION = -2;

 /**
 * 表示下一次共享式同步狀態(tài)獲取將會無條件地傳播下去
 */
 static final int PROPAGATE = -3;

 /** 等待狀態(tài) */
 volatile int waitStatus;

 /** 前驅(qū)節(jié)點(diǎn) */
 volatile Node prev;

 /** 后繼節(jié)點(diǎn) */
 volatile Node next;

 /** 獲取同步狀態(tài)的線程 */
 volatile Thread thread;

 Node nextWaiter;

 final boolean isShared() {
 return nextWaiter == SHARED;
 }

 final Node predecessor() throws NullPointerException {
 Node p = prev;
 if (p == null)
 throw new NullPointerException();
 else
 return p;
 }

 Node() {
 }

 Node(Thread thread, Node mode) {
 this.nextWaiter = mode;
 this.thread = thread;
 }

 Node(Thread thread, int waitStatus) {
 this.waitStatus = waitStatus;
 this.thread = thread;
 }
}

 private Node addWaiter(Node mode) {
 //新建Node
 Node node = new Node(Thread.currentThread(), mode);
 //快速嘗試添加尾節(jié)點(diǎn)
 Node pred = tail;
 if (pred != null) {
 node.prev = pred;
 //CAS設(shè)置尾節(jié)點(diǎn)
 if (compareAndSetTail(pred, node)) {
 pred.next = node;
 return node;
 }
 }
 //多次嘗試
 enq(node);
 return node;
 }

 private Node enq(final Node node) {
 //多次嘗試，直到成功為止
 for (;;) {
 Node t = tail;
 //tail不存在，設(shè)置為首節(jié)點(diǎn)
 if (t == null) {
 if (compareAndSetHead(new Node()))
 tail = head;
 } else {
 //設(shè)置為尾節(jié)點(diǎn)
 node.prev = t;
 if (compareAndSetTail(t, node)) {
 t.next = node;
 return t;
 }
 }
 }
 }