Java上调用Object.wait()函数后，当前线程是否还拿着Object对象锁？
一、 在synchronized代码块中，调用Object.wait()后， 对象锁是否会释放？
答案是： yes, 对象锁被释放了。
如下为测试用例：
// 用来做同步的对象
final Object object = new Object();
// 执行Object.wait()的 runnable对象
Runnable runnable = new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread()+" run1");
synchronized (object) {
try {
System.out.println(Thread.currentThread()+" run2");
object.wait();
System.out.println(Thread.currentThread()+" run3");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
};
new Thread(runnable, "wait_thread_1").start();
new Thread(runnable, "wait_thread_2").start();
// sleep
Thread.sleep(3000);
new Thread( new Runnable() {
@Override
public void run() {
synchronized (object) {
System.out.println(Thread.currentThread()+" notifyAll");
object.notifyAll();
}
}
}, "notifyAll_thread").start();
执行结果：
Thread[wait_thread_1,5,main] run1
// 第一个线程进入同步块
Thread[wait_thread_1,5,main] run2
Thread[wait_thread_2,5,main] run1
// 第二个线程进入同步块
Thread[wait_thread_2,5,main] run2
// 唤醒第一个和第二个线程
Thread[notifyAll_thread,5,main] notifyAll
// 第一个和第二个线程被唤醒
Thread[wait_thread_2,5,main] run3
Thread[wait_thread_1,5,main] run3
二、在synchronized代码块中，调用Thread.sleep()后，对象锁是否被释放？
答案是： no, 对象锁没有被释放。
如下为测试用例：
// 用来做同步的对象
final Object object = new Object();
// 执行Sleep的 runnable对象
Runnable runnable = new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread()+" run1");
synchronized (object) {
try {
System.out.println(Thread.currentThread()+" run2");
Thread.sleep(10*1000);
System.out.println(Thread.currentThread()+" run3");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
};
new Thread(runnable, "wait_thread_1").start();
new Thread(runnable, "wait_thread_2").start();
// sleep
Thread.sleep(3000);
new Thread( new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread()+" notifyAll 1");
synchronized (object) {
System.out.println(Thread.currentThread()+" notifyAll 2");
object.notifyAll();
System.out.println(Thread.currentThread()+" notifyAll 3");
}
}
}, "notifyAll_thread").start();
执行结果：
Thread[wait_thread_2,5,main] run1
Thread[wait_thread_1,5,main] run1
// 第一个线程进入同步块，并sleep
Thread[wait_thread_2,5,main] run2
Thread[notifyAll_thread,5,main] notifyAll 1
// 第一个线程sleep结束
Thread[wait_thread_2,5,main] run3
// 第三个线程抢到同步锁，进入同步块
Thread[notifyAll_thread,5,main] notifyAll 2
Thread[notifyAll_thread,5,main] notifyAll 3
// 第二个线程抢到同步锁，进入同步块
Thread[wait_thread_1,5,main] run2
Thread[wait_thread_1,5,main] run3