错误示例:
1 public class Test { 2 public static void main(String[] args){ 3 thread1.start(); 4 thread2.start(); 5 thread3.start(); 6 } 7 8 static Thread thread1 = new Thread(new Runnable() { 9 @Override 10 public void run() { 11 System.out.println("thread1"); 12 } 13 }); 14 15 static Thread thread2 = new Thread(new Runnable() { 16 @Override 17 public void run() { 18 System.out.println("thread2"); 19 } 20 }); 21 22 static Thread thread3 = new Thread(new Runnable() { 23 @Override 24 public void run() { 25 System.out.println("thread3"); 26 } 27 }); 28 }
执行结果:
1 thread2 2 thread1 3 thread3
原因:start()方法只是让子线程处于就绪状态,最终执行状态是不可控的
方案一:
1 public class Test { 2 public static void main(String[] args) throws InterruptedException { 3 thread1.start(); 4 thread1.join();//主线程放弃cpu执行权,让给子线程执行 5 thread2.start(); 6 thread2.join(); 7 thread3.start(); 8 thread3.join(); 9 } 10 11 static Thread thread1 = new Thread(new Runnable() { 12 @Override 13 public void run() { 14 System.out.println("thread1"); 15 } 16 }); 17 18 static Thread thread2 = new Thread(new Runnable() { 19 @Override 20 public void run() { 21 System.out.println("thread2"); 22 } 23 }); 24 25 static Thread thread3 = new Thread(new Runnable() { 26 @Override 27 public void run() { 28 System.out.println("thread3"); 29 } 30 }); 31 }
结果:
1 thread1 2 thread2 3 thread3
join方法的原理就是调用相应线程的wait方法进行等待操作的,例如A线程中调用了B线程的join方法,则相当于在A线程中调用了B线程的wait方法,当B线程执行完(或者到达等待时间),B线程会自动调用自身的notifyAll方法唤醒A线程,从而达到同步的目的。
源码:
1 public final synchronized void join(long millis) 2 throws InterruptedException { 3 long base = System.currentTimeMillis(); 4 long now = 0; 5 6 if (millis < 0) { 7 throw new IllegalArgumentException("timeout value is negative"); 8 } 9 10 if (millis == 0) { 11 while (isAlive()) { 12 wait(0); 13 } 14 } else { 15 while (isAlive()) { 16 long delay = millis - now; 17 if (delay <= 0) { 18 break; 19 } 20 wait(delay); 21 now = System.currentTimeMillis() - base; 22 } 23 } 24 }
wait(0)是当前主线程进入等待
方案二:
1 public class Test { 2 public static void main(String[] args) throws InterruptedException { 3 executorService.submit(thread1); 4 executorService.submit(thread2); 5 executorService.submit(thread3); 6 } 7 8 static ExecutorService executorService = Executors.newSingleThreadExecutor(); 9 10 static Thread thread1 = new Thread(new Runnable() { 11 @Override 12 public void run() { 13 System.out.println("thread1"); 14 } 15 }); 16 17 static Thread thread2 = new Thread(new Runnable() { 18 @Override 19 public void run() { 20 System.out.println("thread2"); 21 } 22 }); 23 24 static Thread thread3 = new Thread(new Runnable() { 25 @Override 26 public void run() { 27 System.out.println("thread3"); 28 } 29 }); 30 }
执行结果:
thread1 thread2 thread3
单线程化线程池(newSingleThreadExecutor)的优点,串行执行所有任务
原文地址:https://www.cnblogs.com/chinano1/p/9981368.html
时间: 2024-10-08 08:37:31