Java Concurrency 简明教程

Java Concurrency - AtomicBoolean Class

java.util.concurrent.atomic.AtomicBoolean 类在可以读取和写入原子的底层布尔值上提供操作，还包含高级原子操作。AtomicBoolean 支持对底层布尔变量的原子操作。它具有像读写 volatile 变量那样的 get 和 set 方法。也就是说，一个 set 与对同一变量的任何后续 get 都具有 happens-before 关系。atomic compareAndSet 方法还具有这些内存一致性特性。

AtomicBoolean Methods

以下是 AtomicBoolean 类中可用的重要方法列表。

Sr.No.	Method & Description
1	public boolean compareAndSet(boolean expect, boolean update) 如果当前值 == 预期值，则以原子方式将值设置给定的更新后值。
2	public boolean get() 返回当前值。
3	public boolean getAndSet(boolean newValue) 以原子方式设置为给定的值并返回前一个值。
4	public void lazySet(boolean newValue) 最终设置为给定的值。
5	public void set(boolean newValue) 无条件设置为给定的值。
6	public String toString() 返回当前值的 String 表示形式。
7	public boolean weakCompareAndSet(boolean expect, boolean update) 如果当前值 == 预期值，则以原子方式将值设置给定的更新后值。

Example

以下 TestThread 程序显示了在基于线程的环境中使用 AtomicBoolean 变量。

import java.util.concurrent.atomic.AtomicBoolean;

public class TestThread {

   public static void main(final String[] arguments) throws InterruptedException {
      final AtomicBoolean atomicBoolean = new AtomicBoolean(false);

      new Thread("Thread 1") {

         public void run() {

            while(true) {
               System.out.println(Thread.currentThread().getName()
                  +" Waiting for Thread 2 to set Atomic variable to true. Current value is "
                  + atomicBoolean.get());

               if(atomicBoolean.compareAndSet(true, false)) {
                  System.out.println("Done!");
                  break;
               }
            }
         };
      }.start();

      new Thread("Thread 2") {

         public void run() {
            System.out.println(Thread.currentThread().getName() +
               ", Atomic Variable: " +atomicBoolean.get());
            System.out.println(Thread.currentThread().getName() +
               " is setting the variable to true ");
            atomicBoolean.set(true);
            System.out.println(Thread.currentThread().getName() +
               ", Atomic Variable: " +atomicBoolean.get());
         };
      }.start();
   }
}

这将产生以下结果。

Output

Thread 1 Waiting for Thread 2 to set Atomic variable to true. Current value is false
Thread 1 Waiting for Thread 2 to set Atomic variable to true. Current value is false
Thread 1 Waiting for Thread 2 to set Atomic variable to true. Current value is false
Thread 2, Atomic Variable: false
Thread 1 Waiting for Thread 2 to set Atomic variable to true. Current value is false
Thread 2 is setting the variable to true
Thread 2, Atomic Variable: true
Thread 1 Waiting for Thread 2 to set Atomic variable to true. Current value is false
Done!