java中Atomic类之AtomicBoolean
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java.lang.Object
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
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