测试条件然后锁定然后重新测试条件是否好 [英] Is it good to test a condition then lock then re-test the condition

问题描述

可能重复:
对.net中的双重检查锁定

Possible Duplicate:
Double-checked locking in .net

编辑:为澄清该问题与单例无关的大量修改

lots of edits to clarify this question is not about singleton

我发现自己正在编写如下代码:

I find myself writing code like this:

    if(resourceOnDiskNeedsUpdating)
    {
        lock(lockObject)
        {
            if(resourceOnDiskNeedsUpdating) // has a previous thread already done this?
                UpdateResourceOnDisk();
        }
    }
    return LoadResourceFromDisk();

UpdateResource()是一个缓慢的操作. 这种模式有意义吗?
有更好的选择吗?

UpdateResource() is a slow operation. Does this pattern make sense?
Are there better alternatives?

推荐答案

这称为双重检查锁定".

This called "double-checked locking".

您需要一个内存围栏以使其正确.

You need a memory fence to make it correct.

请参见有关.NET中双重检查锁定的维基百科文章.

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