wait-notify简介：
程序测试：
public class WaitNotify {
static boolean flag =
true;
static Object lock =
new Object();
public static void main(String[] args) throws InterruptedException {
Thread waitThread =
new Thread(
new Wait(),
"waitThread");
waitThread.start();
try {
TimeUnit.SECONDS.sleep(
2);
}
catch (InterruptedException e) {
e.printStackTrace();
}
Thread notifyThread =
new Thread(
new Notify(),
"notifyThread");
notifyThread.start();
}
static class Wait implements Runnable {
@Override
public void run() {
synchronized (lock) {
while (flag) {
System.out.println(Thread.currentThread() +
" flag is true. release lock and wait@ " + LocalDateTime.now());
try {
lock.wait();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread() +
" flag is false. return@ " + LocalDateTime.now());
}
}
}
static class Notify implements Runnable {
@Override
public void run() {
synchronized (lock) {
System.out.println(Thread.currentThread() +
" hold lock. notify @ " + LocalDateTime.now());
lock.notifyAll();
flag =
false;
try {
TimeUnit.SECONDS.sleep(
5);
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
synchronized (lock) {
System.out.println(Thread.currentThread() +
" hold lock again. notify @ " + LocalDateTime.now());
try {
TimeUnit.SECONDS.sleep(
5);
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
测试结果：
Thread[waitThread,
5,main] flag
is true.release
lock and wait@
2017-
03-
10T11:
05:
56.710
Thread[notifyThread,
5,main] hold
lock. notify @
2017-
03-
10T11:
05:
58.584
Thread[notifyThread,
5,main] hold
lock again. notify @
2017-
03-
10T11:
06:
03.584
Thread[waitThread,
5,main] flag
is false.
return@
2017-
03-
10T11:
06:
08.584
运行过程原理：
原理说明：
使用wait()、notify（）和notifyAll时需要先对对象加锁，否则会报异常：“java.lang.IllegalMonitorStateException”调用wait()方法后，程序状态由running变为waiting，并将当前线程放置到对象的等待队列notify()或notifyAll()方法返回后，等待线程依旧不会从wait返回，需要调用notfiy()或notifyAll的线程释放锁以后，等待线程才【有机会】从wait返回notify()将等待队列中的一个线程从“等待队列”中移到“同步队列”中，而notifyAll方法则将等待队列中的所有线程全部移到“同步队列“中，被移动的线程由waiting变为blocked从wait（）方法返回的前提是获得调用对象的锁，由程序的打印结果可以证实
从上述细节可看出，等待/通知依托于同步机制，目的就是确保等待线程从wait()方法返回时，能够感知通知线程对变量做的修改
摘录：《Java并发编程的艺术》
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