AtomicBoolean中getAndSet和compareAndSet之间的区别 [英] Difference between getAndSet and compareAndSet in AtomicBoolean

问题描述

主题标题应该是自我探索的...我在 AtomicBoolean 类：

The thread title should be self-explnatory... I'm a bit confused between the specification of below methos from AtomicBoolean class:

• java.util.concurrent.atomic.AtomicBoolean＃compareAndSet


• java.util.concurrent.atomic.AtomicBoolean #getAndSet

• java.util.concurrent.atomic.AtomicBoolean#compareAndSet
• java.util.concurrent.atomic.AtomicBoolean#getAndSet

我的断言是当在 if 条件中用作布尔子句时，两者都会产生相同的行为：

My assemption is that both would result in the same behavior when used as a boolean clause in an if condition:

public class Test {
  private AtomicBoolean flag = AtomicBoolean(false);

  public void processSomeAction() {
    if (flag.getAndSet(false)) { // Shouldn't this be similar to flag.compareAndSet(false)
      // process some action
    }
  }
  //...
  private void internalMutatorMethod() {
    // do some staff then update the atomic flag
    flas.set(true);
  }
}

假设我想要检索当前的标志值并且自动更新它，两种方法都不应该产生相同的行为吗？

Assuming that I want to retrieve the current flag value and update it automaticlly, shouldn't both methods produce the same behavior?

如果我缺少内部的话，我会非常感谢有关如何以及何时使用这些方法的任何解释差异。

I would much appreciate any explanations regarding how and when to use each of those if I'm missing internal differences.

推荐答案

文档非常清楚。

• getAndSet - >原子设置为给定值并返回上一个值。


• compareAndSet - >如果当前值==期望值，则以原子方式将值设置为给定的更新值。

• getAndSet --> "Atomically sets to the given value and returns the previous value."
• compareAndSet --> "Atomically sets the value to the given updated value if the current value == the expected value."

毫不奇怪， compareAndSet 有两个参数。

Not surprisingly, compareAndSet takes two arguments.

在您的具体情况中：

• if（flag.getAndSet（ false））将 flag 设置为 false 仅当前一个值为<$ c时$ c> true


• 这相当于 if（flag.compareAndSet（true，false））

• if (flag.getAndSet(false)) will set flag to false only if its previous value was true
• That would be the equivalent of if (flag.compareAndSet(true, false))

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