Object中线程阻塞及唤醒方法的使用

Object中线程阻塞及唤醒方法使用

使用说明

调用对象的这些方法(wait/notify)，必须先持有对象的监视器（monitor）；否则会抛出IllegalMonitorStateException异常

例1：

public static void main(String[] args) {
	Thread th1 = new Thread(){
		@Override
		public void run() {
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	};
	
	th1.start();
}

运行结果：

Exception in thread "Thread-0" java.lang.IllegalMonitorStateException

	at java.lang.Object.wait(Native Method)

	at java.lang.Object.wait(Object.java:503)

	at com.falco.src.verify.ObjectVerification$1.run(ObjectVerification.java:11)

当调用对象的wait方法后，线程处于阻塞状态，对应的监视器（monitor）也被释放，其他线程可以获得此监视器来唤醒该线程。当线程重新被唤醒时，它会再次获取该监视器（monitor），然后被唤醒

唤醒方式

调用wait方法后，线程处于阻塞状态。可以通过以下四种唤醒方式：

调用notify/notifyAll方法唤醒

例二：

public static void main(String[] args) {
		final Object bt = new Object();
		Thread th1 = new Thread() {
			@Override
			public void run() {
				try {
					synchronized (bt) {
						bt.wait();
						System.out.println("the thread has been woke up.");
					}
				} catch (InterruptedException e) {
					System.out.println("the current thread has been interupted.");
					e.printStackTrace();
				}
			}
		};
		th1.start();
	
		Thread th2 = new Thread() {
			@Override
			public void run() {
				synchronized (bt) {
					bt.notify();
					System.out.println("finish waking up.");
				}
			}
		};
		th2.start();
		System.out.println("wait the program exit.");
	}

结果：

wait the program exit.
finish waking up.
the thread has been woke up.

超时自动唤醒，即：wait方法指定一个超时时间，达到这个超时时间且没有被唤醒的线程将自动唤醒

例三：

	public static void main(String[] args) {
		final Object bt = new Object();
		Thread th1 = new Thread() {
			@Override
			public void run() {
				try {
					synchronized (bt) {
						bt.wait(10,1);
						System.out.println("the thread has been woke up.");
					}
				} catch (InterruptedException e) {
					System.out.println("the current thread has been interupted.");
					e.printStackTrace();
				}
			}
		};
		th1.start();
		System.out.println("wait the program exit.");
	}

运行结果：

wait the program exit.
the thread has been woke up.

中断唤醒，在其他线程中，调用阻塞线程的中断方法，从而唤醒阻塞的线程

例四：

public static void main(String[] args) {
		Thread th1 = new Thread() {
			@Override
			public void run() {
				try {
					synchronized (this) {
						this.wait();
					}
				} catch (InterruptedException e) {
					System.out.println("the current thread has been interupted.");
					e.printStackTrace();
				}
			}
		};

		th1.start();
		System.out.println("before interrupting,the interrupt flag:"+th1.isInterrupted());
		th1.interrupt();
		System.out.println("after interrupting,the interrupt flag:"+th1.isInterrupted());
	}

运行结果：

before interrupting,the interrupt flag:false
after interrupting,the interrupt flag:true
the current thread has been interupted.
java.lang.InterruptedException
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:503)
	at com.falco.src.verify.ObjectVerification$1.run(ObjectVerification.java:11)

假醒（spurious wakeup），除了以上三种方式外，处于阻塞中的线程还可能自动被唤醒

由于假醒的存在，因此需要自行处理假醒的场景，通过下面的形式排出假醒，避免程序出错
```
...
synchronized (bt) {
    while (condition) {//condition为不满足唤醒条件，即不满足唤醒条件时执行循环
    	bt.wait();
    }
}
...
```
假醒相关内容就不在这里介绍了，如果有兴趣，请自行研究

假醒wiki地址

Object中线程阻塞及唤醒方法的使用

Object中线程阻塞及唤醒方法使用

相关方法

使用说明

唤醒方式