Executor.execute（）JMM保证 [英] Executor.execute() JMM guarantee

问题描述

请考虑以下代码snipet：

Consider the following code snipet:

public class A {

    private final Executor executor = Executors.newCachedThreadPool();
    private final Queue<Object> messageQueue = new ConcurrentLinkedQueue<M>();

    public void sendMessage(Object message) {
        messageQueue.offer(message);
        executor.execute(new Runnable() {
            @Override
            public void run() {
                final Object message = messageQueue.poll();

                // Can message == null? 
            }
        });
    }
}

是否保证messageQueue包含消息的时间当Runnable实例会尝试检索它吗？或者phraise它有点更一般：可以两个函数调用由JIT / JVM根据JMM重新排序？

Is it guaranteed that messageQueue contains the message by the time when the Runnable instance will try to retrieve it? Or to phraise it a little bit more general: can two function calls be reordered by JIT/JVM according to JMM?

推荐答案

是，如果没有其他生产者/消费者。

Yes, if there are not other producers/consumers.

Executor.execute（）建立发生先于关系。因此， offer（） 发生之前 poll（） poll（）看到 offer（）的效果。虽然没有正式指定，但是通过任何常识， poll（）应该返回刚刚添加到队列中的对象。

Executor.execute() establish a happens-before relationship. Therefore everything in offer() happens-before poll(). poll() sees the effect of offer(). Although not formally specified, by any common sense, poll() should then return the object just added to the queue.

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