AtomicInteger.incrementAndGet线程安全吗? [英] Is AtomicInteger.incrementAndGet thread safe?

问题描述

例如，如果我在多个线程中运行此代码并且每个线程多次运行，是否会发生数据争用?

For example, if I run this code from multiple threads and each thread for many times, will there be potentially a data race?

   public boolean swap(int i, int j) {
    if (value.get(i) <= 0 || value.get(j) >= maxval) {
        return false;
    }
    value.decrementAndGet(i);
    value.incrementAndGet(j);
    return true;
}

顺便说一句，如果我在这里使用decrementAndGet或getAndDecrement有什么区别吗?

BTW, is there any difference if I use decrementAndGet or getAndDecrement here?

值是一个AtomicIntegerArray.我需要在不同的同步方法之间进行性能测试.因此，我交换了elemtents的值，看看输出的总和是否与预期的相同

value here is an AtomicIntegerArray. I need to do performance test among different synchronization method. So I swap elemtents in value and see if the output sum the same to what is expected

我的任务是找到一种不应为DRF"但仍必须无死锁"的方法，并且该方法也比ReentrantLock快得多.所以我很难找到一种具有数据竞争的方法...

My task is to find a method that "should not be DRF," but "must still be deadlock-free", and is also much faster than ReentrantLock. So I'm troubling with finding a method that has data race...

推荐答案

是的，incrementAndGet是线程安全的.

incrementAndGet和getAndIncrement与++i和i++相同.即

int i = 0;
i++ // <- expression returns 0, i is now 1
++i // <- expression return 2, i is now 2

Ditto与decrement.

但是，您在if中的||上两次调用get时，您的代码不是不是线程安全的.因此，无论value是什么，都可以在value.get(i)和value.get(j)之间更改 值.

Your code, however, is not threadsafe as you call get twice across the || in the if. So the value could be changed between value.get(i) and value.get(j), whatever value is.

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