如何根据条件更新Atomic？

Question

如何更新AtomicInteger当前值是否小于给定值？这个想法是:

AtomicInteger ai = new AtomicInteger(0);
...
ai.update(threadInt); // this call happens concurrently
...
// inside AtomicInteger atomic operation
synchronized {
    if (ai.currentvalue < threadInt)
        ai.currentvalue = threadInt;
}

Answer 1

如果您使用的是Java 8,则可以使用其中一种新的更新方法AtomicInteger,您可以传递lambda表达式.例如:

AtomicInteger ai = new AtomicInteger(0);

int threadInt = ...

// Update ai atomically, but only if the current value is less than threadInt
ai.updateAndGet(value -> value < threadInt ? threadInt : value);

Answer 2

如果我没有 Java 8，我可能会创建一个实用方法，例如：

public static boolean setIfIncreases(AtomicInteger ai, int newValue) {
    int currentValue;
    do {
        currentValue = ai.get();
        if (currentValue >= newValue) {
            return false;
        } 
     } while (!ai.compareAndSet(currentValue, newValue));
     return true;
}

从OP的代码中，它将被这样调用：

AtomicInteger ai = new AtomicInteger(0);

int threadInt = ...

// Update ai atomically, but only if the current value is less than threadInt
setIfIncreases(ai, threadInt);