AtomicBoolean介绍与使用

java.util.concurrent.atomic.AtomicBoolean

继承自Object。

 

• 介绍：

           

       在这个Boolean值的变化的时候不允许在之间插入，保持操作的原子性

• 方法和举例
• compareAndSet(boolean expect, boolean update)

        这个方法主要两个作用        

1. 比较AtomicBoolean和expect的值，如果一致，执行方法内的语句。其实就是一个if语句        

2. 把AtomicBoolean的值设成update        

比较最要的是这两件事是一气呵成的，这连个动作之间不会被打断，任何内部或者外部的语句都不可能在两个动作之间运行。

为多线程的控制提供了解决的方案。

使用：

private static class BarWorker implements Runnable {

 private static boolean exists = false;

 private String name;

 public BarWorker(String name) {
 　　this.name = name;
 }

 public void run() {
   if (!exists) {
        exists = true;
 　　  System.out.println(name + " enter");
        System.out.println(name + " working");
        System.out.println(name + " leave");
        exists = false;
  }else {
     System.out.println(name + " give up");
  }
 }
}

 

static变量exists用来实现同一时间只有一个worker在工作.

但是假设exists的判断和exists = true;之间有了 其他指令呢？

Java代码

 

private static class BarWorker implements Runnable {

 private static boolean exists = false;

 private String name;

 public BarWorker(String name) {
  this.name = name;
 }

 public void run() {
  if (!exists) {
   try {
    TimeUnit.SECONDS.sleep(1);
   } catch (InterruptedException e1) {
    // do nothing
   }
   exists = true;
   System.out.println(name + " enter");
   try {
    System.out.println(name + " working");
    TimeUnit.SECONDS.sleep(2);
   } catch (InterruptedException e) {
    // do nothing
   }
   System.out.println(name + " leave");
   exists = false;
  } else {
   System.out.println(name + " give up");
  }
 }

}

 

private static class BarWorker implements Runnable {

  private static boolean exists = false;

  private String name;

  public BarWorker(String name) {
   this.name = name;
  }

  public void run() {
   if (!exists) {
    try {
     TimeUnit.SECONDS.sleep(1);
    } catch (InterruptedException e1) {
     // do nothing
    }
    exists = true;
    System.out.println(name + " enter");
    try {
     System.out.println(name + " working");
     TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException e) {
     // do nothing
    }
    System.out.println(name + " leave");
    exists = false;
   } else {
    System.out.println(name + " give up");
   }
  }

 }

这时输出是 bar2 enter bar2 working bar1 enter bar1 working bar1 leave bar2 leave 看到两个线程同时工作了. 这时可以用AtomicBoolean Java代码

 

private static class BarWorker implements Runnable {

  private static AtomicBoolean exists = new AtomicBoolean(false);

  private String name;

  public BarWorker(String name) {
   this.name = name;
  }

  public void run() {
   if (exists.compareAndSet(false, true)) {
    System.out.println(name + " enter");
    try {
     System.out.println(name + " working");
     TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException e) {
     // do nothing
    }
    System.out.println(name + " leave");
    exists.set(false);
   }else{
    System.out.println(name + " give up");
   }
  }

 }

 

private static class BarWorker implements Runnable {

  private static AtomicBoolean exists = new AtomicBoolean(false);

  private String name;

  public BarWorker(String name) {
   this.name = name;
  }

  public void run() {
   if (exists.compareAndSet(false, true)) {
    System.out.println(name + " enter");
    try {
     System.out.println(name + " working");
     TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException e) {
     // do nothing
    }
    System.out.println(name + " leave");
    exists.set(false);
   }else{
    System.out.println(name + " give up");
   }
  }

 }

因为它提供了原子性操作,其中exists.compareAndSet(false, true)这个操作把比较和赋值操作组成了一个原子操作, 中间不会提供可乘之机.输出为 bar1 enter bar1 working bar2 give up