public void lock() throws InterruptedException {
QueueObject queueObject = new QueueObject();
synchronized (this) {
waitingThreads.add(queueObject);
}
boolean mustWait = true;
while (mustWait) {
// 对局部变量mustWait的检查与赋值是在同一个同步块中完成的
synchronized (this) {
mustWait = isLocked || waitingThreads.get(0) != queueObject;
if (!mustWait) {
waitingThreads.remove(queueObject);
isLocked = true;
lockingThread = Thread.currentThread();
// 如果一个线程肯定不会等待（即mustWait为false），那么就没必要让它进入到
// synchronized(queueObject)同步块中和执行if(mustWait)子句了
return;
}
}
synchronized (queueObject) {
if (mustWait) {
try {
queueObject.wait();
} catch (InterruptedException e) {
waitingThreads.remove(queueObject);
throw e;
}
}
}
}
}
public synchronized void unlock() {
if (this.lockingThread != Thread.currentThread()) {
throw new IllegalMonitorStateException("Calling thread has not locked this lock");
}
isLocked = false;
lockingThread = null;
if (waitingThreads.size() > 0) {
QueueObject queueObject = waitingThreads.get(0);
synchronized (queueObject) {
queueObject.notify();
}
}
}