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

问题描述

线程标题应该是不言自明的......我对 AtomicBoolean 类的以下方法的规范有点困惑:

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

我的看法是，当在 if 条件中用作布尔子句时，两者都会导致相同的行为:

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);
  }
}

假设我想检索当前标志值并自动更新它，这两种方法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?

如果我遗漏了内部差异，我将非常感谢有关如何以及何时使用每一个的解释.

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 --> 原子地设置为给定值并返回前一个值."
• compareAndSet --> 如果当前值 == 预期值，则原子地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 需要两个参数.

Not surprisingly, compareAndSet takes two arguments.

在您的具体情况下:

• if (flag.getAndSet(false)) 只会在 flag 之前的值为 true 时将其设置为 false代码>
• 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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