等待(wait) 和通知(notify)
这两个方法来自Object类, 使用前必须先获得目标的锁.
wait()使用场景必须包含在synchronzied语句中., 当调用后,线程释放锁, 进入object对象的等待队列, 等待notify() .notifyAll()去唤醒.
package threads;
public class WaitAndNotify {
final static Object ob = new Object();
public static class T1 extends Thread {
@Override
public void run() {
synchronized (ob) {
System.out.println(System.currentTimeMillis() + " : " + "T1.start");
try {
System.out.println(System.currentTimeMillis() + " : " + "T1.wait");
ob.wait();//放开锁,停止继续执行下一步
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(System.currentTimeMillis() + " : " + "T1.end");
}
}
}
public static class T2 extends Thread {
@Override
public void run() {
synchronized (ob) {
System.out.println(System.currentTimeMillis() + " : " + "T2.start");
ob.notify();// 提示其他进程去获取锁
System.out.println(System.currentTimeMillis() + " : " + "T2.end");
try {
Thread.sleep(2000);//占用锁没有放开.导致t2end比t1end早两秒
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
Thread t1 = new T1();
Thread t2 = new T2();
t1.start();
t2.start();
}
}
1568212250034 : T1.start
1568212250034 : T1.wait
1568212250034 : T2.start
1568212250034 : T2.end 两秒
1568212252034 : T1.end
等待线程结束join() 和 谦让yield()
有些时候我们需要一个线程依赖其他线程执行完毕才能,才能操作这是使用join()
join 分为2种 , 第一种是无限等待阻塞进程,直到目标线程执行完毕,
第二种是有时间限制, 过了时间就不等了,继续执行下一步.
private volatile static int i = 0;
public static class Nums extends Thread{
@Override
public void run() {
for ( i = 0; i < 10000999; i++);
}
}
public static void main(String[] args) throws InterruptedException {
Nums nums = new Nums(); // 选择目标线程对象, 而不是Thread
nums.start(); //0
nums.join(); //10000999
System.out.println(i);
}
yiled()是静态方法,使用后 当前线程让出CPU,继续参与CPU的争夺适用于优先级低,害怕占用太多资源的线程.
public class YieldA {
public static class RunCPU extends Thread{
public RunCPU(String name) {
super.setName(name);
}
@Override
public void run() {
for (int i = 0; i < 50; i++) {
System.out.println(Thread.currentThread().getName() + ": " + i);
if(i == 30) {
Thread.yield();
try {
Thread.sleep(5);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
public static void main(String[] args) {
RunCPU runCPU = new RunCPU("run111111");
RunCPU runCPU2 = new RunCPU("run222222");
runCPU.start(); // 到30让出cpu给runCPU2
runCPU2.start();// 到30让出cpu给runCPU
}
}
原文：https://www.cnblogs.com/zkfly/p/11509381.html