多线程-wait/notify方法

wait方法

作用

1.结合以下例子进行叙述。

lock.wait();这句执行后线程a会释放锁，线程a会进入阻塞状态，等待线程b的lock.notify()执行后，才可以尝试获取锁，a线程等待获取锁，当b线程锁住的lock对象代码块执行完并释放锁后，a线程才可以得到锁进入运行状态。

2.如下图

step	图
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MyList.java

public class MyList {
	private static List<String> list = new ArrayList<String>();

	public static void add() {
		list.add("anyString");
	}

	public static int size() {
		return list.size();
	}

}

ThreadA.java

public class ThreadA extends Thread {

	private Object lock;

	public ThreadA(Object lock) {
		super();
		this.lock = lock;
	}

	@Override
	public void run() {
		try {
			synchronized (lock) {
				if (MyList.size() != 5) {
					System.out.println("wait begin "
							+ System.currentTimeMillis());
					lock.wait();
					System.out.println("wait end  "
							+ System.currentTimeMillis());
				}
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

ThreadB.java

public class ThreadB extends Thread {
	private Object lock;

	public ThreadB(Object lock) {
		super();
		this.lock = lock;
	}

	@Override
	public void run() {
		try {
			synchronized (lock) {
				for (int i = 0; i < 10; i++) {
					MyList.add();
					if (MyList.size() == 5) {
						lock.notify();
                        /*
                        发出通知后，b线程并不会释放锁，必须等待synchronized (lock){...}执行完才会释放锁，a线程才可以获得锁。
                        */
						System.out.println("已发出通知！");
					}
					System.out.println("添加了" + (i + 1) + "个元素!");
					Thread.sleep(1000);
				}
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

Run.java

public class Run {

	public static void main(String[] args) {

		try {
			Object lock = new Object();

			ThreadA a = new ThreadA(lock);
			a.start();

			Thread.sleep(50);//等待线程a进入阻塞状态，释放锁。

			ThreadB b = new ThreadB(lock);
			b.start();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}

	}

}

运行结果：