wait()、notify()、notifyAll()是三个定义在Object类里的方法,可以用来控制线程的状态。
这三个方法最终调用的都是jvm级的native方法。随着jvm运行平台的不同可能有些许差异。
- 如果对象调用了wait方法就会使持有该对象的线程把该对象的控制权交出去,然后处于等待状态。
- 如果对象调用了notify方法就会通知某个正在等待这个对象的控制权的线程可以继续运行。
- 如果对象调用了notifyAll方法就会通知所有等待这个对象控制权的线程继续运行。
其中wait方法有三个over load方法:
wait()
wait(long)
wait(long,int)
wait方法通过参数可以指定等待的时长。如果没有指定参数,默认一直等待直到被通知。
和synchronize结合使用
http://longdick.iteye.com/blog/453615 讲解的异常java.lang.IllegalMonitorStateException。
- 任何一个时刻,对象的控制权(monitor)只能被一个线程拥有。
- 无论是执行对象的wait、notify还是notifyAll方法,必须保证当前运行的线程取得了该对象的控制权(monitor)
- 如果在没有控制权的线程里执行对象的以上三种方法,就会报java.lang.IllegalMonitorStateException异常。
- JVM基于多线程,默认情况下不能保证运行时线程的时序性
package com.swntek.czm.myzxingdemo; public class NotifyTest { private Boolean flag = true; private Object obj = new Object(); class NotifyThread extends Thread { public NotifyThread(String name) { super(name); } public void run() { try { sleep(3000);//推迟3秒钟通知 } catch (InterruptedException e) { e.printStackTrace(); } synchronized (obj) { flag = false; obj.notifyAll(); } } } class WaitThread extends Thread { public WaitThread(String name) { super(name); } public void run() { synchronized (obj) { while (flag) { System.out.println(getName() + " begin waiting!"); long waitTime = System.currentTimeMillis(); try { obj.wait(); } catch (InterruptedException e) { e.printStackTrace(); } waitTime = System.currentTimeMillis() - waitTime; System.out.println("wait time :" + waitTime); } System.out.println(getName() + " end waiting!"); } } } public static void main(String[] args) throws InterruptedException { System.out.println("Main Thread Run!"); NotifyTest test = new NotifyTest(); NotifyThread notifyThread = test.new NotifyThread("notify01"); WaitThread waitThread01 = test.new WaitThread("waiter01"); WaitThread waitThread02 = test.new WaitThread("waiter02"); WaitThread waitThread03 = test.new WaitThread("waiter03"); notifyThread.start(); waitThread01.start(); waitThread02.start(); waitThread03.start(); } }
jdk1.5Lock取代了synchronized
Condition替代了wait notify
newCondition() |
private Lock lock=new ReentrantLock();
private Lock lock=new ReentrantLock();
Condition con=lock.newCondition();
con.await();con.signal();con.signalAll()
http://ifeve.com/understand-condition/
package com.swntek.czm.myzxingdemo; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; public class NotifyTest { private static Lock reentrantLock = new ReentrantLock(); private static Condition condition; private Boolean flag = true; class NotifyThread extends Thread { public NotifyThread(String name) { super(name); } public void run() { try { sleep(3000);//推迟3秒钟通知 } catch (InterruptedException e) { e.printStackTrace(); } reentrantLock.lock(); flag = false; condition.signalAll(); reentrantLock.unlock(); } } class WaitThread extends Thread { public WaitThread(String name) { super(name); } public void run() { reentrantLock.lock(); while (flag) { System.out.println(getName() + " begin waiting!"); long waitTime = System.currentTimeMillis(); try { condition.await(); } catch (InterruptedException e) { e.printStackTrace(); } waitTime = System.currentTimeMillis() - waitTime; System.out.println("wait time :" + waitTime); } System.out.println(getName() + " end waiting!"); reentrantLock.unlock(); } } public static void main(String[] args) throws InterruptedException { System.out.println("Main Thread Run!"); condition = reentrantLock.newCondition(); NotifyTest test = new NotifyTest(); NotifyThread notifyThread = test.new NotifyThread("notify01"); WaitThread waitThread01 = test.new WaitThread("waiter01"); WaitThread waitThread02 = test.new WaitThread("waiter02"); WaitThread waitThread03 = test.new WaitThread("waiter03"); notifyThread.start(); waitThread01.start(); waitThread02.start(); waitThread03.start(); } }