AtomicBoolean 介绍与使用

7. ?????private?static?boolean?exists?=?false;????

8. ?????private?String?name;????

9. ?????public?BarWorker(String?name)?{?????

10. ??????????this.name?=?name;????

11. ?????}????

12. ?????@Override????

13. ?????public?void?run()?{?????

14. ?????????if?(!exists)?{????

15. ?????????????????try?{????

16. ??????????????????TimeUnit.SECONDS.sleep(1);????

17. ?????????????????}?catch?(InterruptedException?e1)?{????

18. ??????????????????//?do?nothing????

19. ?????????????????}????

20. ?????????????????exists?=?true;????

21. ?????????????????System.out.println(name?+?"?enter");????

22. ?????????????????try?{????

23. ??????????????????System.out.println(name?+?"?working");????

24. ??????????????????TimeUnit.SECONDS.sleep(2);????

25. ?????????????????}?catch?(InterruptedException?e)?{????

26. ??????????????????//?do?nothing????

27. ?????????????????}????

28. ?????????????????System.out.println(name?+?"?leave");????

29. ?????????????????exists?=?false;????

30. ????????}?else?{????

31. ?????????System.out.println(name?+?"?give?up");????

32. ????????}????

33. ????}???

34. ?????public?static?void?main(String[]?args)?{??

35. ?????????BarWorker?bar1?=?new?BarWorker("bar1");??

36. ?????????BarWorker?bar2?=?new?BarWorker("bar2");??

37. ?????????new?Thread(bar1).start();??

38. ?????????new?Thread(bar2).start();??

39. ????}??

40. }??

该代码使用 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？ 输出如下：

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1. bar1?enter??

2. bar2?enter??

3. bar1?working??

4. bar2?working??

5. bar1?leave??

6. bar2?leave??

可以看到两个线程同时工作了。这时可以用 AtomicBoolean 进行线程同步，代码如下：

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1. package?zmx.atomic.test;??

2. import?java.util.concurrent.TimeUnit;??

3. import?java.util.concurrent.atomic.AtomicBoolean;??

4. public?class?BarWorker2?implements?Runnable?{??

5. ????private?static?AtomicBoolean?exists?=?new?AtomicBoolean(false);????

6. ?????private?String?name;????

7. ?????public?BarWorker2(String?name)?{?????

8. ??????????this.name?=?name;????

9. ?????}????

10. ?????@Override????

11. ?????public?void?run()?{?????

12. ?????????if?(exists.compareAndSet(false,?true))?{????

13. ?????????????System.out.println(name?+?"?enter");????

14. ?????????????try?{????

15. ??????????????????System.out.println(name?+?"?working");????

16. ??????????????????TimeUnit.SECONDS.sleep(2);????

17. ?????????????}?catch?(InterruptedException?e)?{????

18. ??????????????????//?do?nothing????

19. ?????????????}????

20. ?????????????System.out.println(name?+?"?leave");????

21. ?????????????exists.set(false);??????

22. ????????}?else?{????