[英]What is the good solution for calling notifyAll?
我有一个关于wait()和notifyAll()方法的问题。 该代码正在模拟两个线程的“竞赛”。
让我们看一下代码-问题在于,notifyAll()方法对等待的线程不执行任何操作,导致main方法首先获得了锁...简单的解决方法是设置一些延迟(请参见注释行)。 但这是一个坏习惯。 这个问题有什么好的解决方案? 我只想使用wait / notifyAll / join方法。
public class TestThreads {
public static void main(String[] args) throws InterruptedException {
System.out.println("_start main");
Object lock = new Object();
Thread t1 = new Thread(new Car("Red car", lock));
Thread t2 = new Thread(new Car("Black car", lock));
t1.start();
t2.start();
//Thread.sleep(10L);
synchronized (lock){
System.out.println("Let`s go!");
lock.notifyAll();
}
t1.join();
t2.join();
System.out.println("_exiting from main...");
}
}
class Car implements Runnable {
private final String name;
private final Object lock;
public Car(String name, Object lock) {
this.name = name;
this.lock = lock;
}
@Override
public void run() {
int distance = 100;
synchronized (lock){
try{
System.out.println(name + " waiting...");
lock.wait();
}catch (InterruptedException e){
e.printStackTrace();
}
}
System.out.println(name + " started...");
while (distance != 0){
try{
Thread.sleep((long) (100 * Math.random()));
}catch (InterruptedException e){
e.printStackTrace();
break;
}
distance--;
if (distance % 20 == 0 && distance != 0){
System.out.println(name + " " + distance+ " miles left");
}
else if (distance == 0){
System.out.println(name + " finished race!!!");
}
}
System.out.println("_exiting from thread of " + name + " move simulation...");
}
}
PS。 对不起,我的英语不好。
感谢您的回答。 那么,这种解决方案是否更好?
public class TestThreads {
public static void main(String[] args) throws InterruptedException {
System.out.println("_start main");
LightSignal lock = new LightSignal();
Thread t1 = new Thread(new Car("Red car", lock));
Thread t2 = new Thread(new Car("Black car", lock));
t1.start();
t2.start();
synchronized (lock){
Thread.sleep(1000L);
lock.isGreen = true;
System.out.println("Let`s go!");
lock.notifyAll();
}
t1.join();
t2.join();
System.out.println("_exiting from main...");
}
}
class Car implements Runnable {
private final String name;
private final LightSignal lock;
public Car(String name, LightSignal lock) {
this.name = name;
this.lock = lock;
}
@Override
public void run() {
int distance = 100;
synchronized (lock){
try{
while (!lock.isGreen){
System.out.println(name + " waiting...");
lock.wait();
}
}catch (InterruptedException e){
e.printStackTrace();
}
}
System.out.println(name + " started...");
while (distance != 0){
try{
Thread.sleep((long) (100 * Math.random()));
}catch (InterruptedException e){
e.printStackTrace();
break;
}
distance--;
if (distance % 20 == 0 && distance != 0){
System.out.println(name + " " + distance + " miles left");
}
}
System.out.println(name + " finished race!!!");
System.out.println("_exiting from thread of " + name + " move simulation...");
}
}
class LightSignal {
public boolean isGreen = false;
}
调用notifyAll()时,您需要更改一个状态,而在waiting()中时,您需要循环检查该状态。 如果你不这样做
在这种情况下,最简单的解决方案就是不用担心。 您正在等待最多100毫秒的随机延迟,因此尝试同步这样一个随机系统的启动非常困难。
我认为循环退出时“竞赛结束”,您不需要if
子句。
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