问题描述
假设线程Alpha在不锁定的情况下正在写入变量A.第二个线程Beta正在等待Alpha终止，然后依次读取变量A.
Suppose that thread Alpha is writing to variable A without locking. A second thread Beta is waiting for Alpha to terminate, then reads the variable A in turn.
A的内容是否可能不是新鲜的?可以将内存写入延迟到线程生存期之后吗?等待线程Alpha终止的标准机制是否会隐式地充当内存屏障?
Is it possible that the contents of A will not be fresh? Can memory writes be delayed beyond the thread lifetime? Won't the standard mechanism of waiting for thread Alpha termination implicitly work as a memory barrier?
更新1
有没有没有记忆障碍的等待示例?
Are there any examples of waiting which does not include a memory barrier?
推荐答案
几乎可以肯定(用于等待线程终止的API需要出于自身目的使用内存屏障)，但是我想为您提供一个明确的答案需要谈论所使用的特定线程API.
Almost certainly (the API used to wait for thread termination would need to use memory barriers for its own purposes), but I think for a definitive answer you'll need to talk about the specific threading API being used.
例如，posix为pthread_join()提供了这样的保证: https://stackoverflow.com/a/3208140/12711
For example, posix makes such a guarantee for pthread_join(): https://stackoverflow.com/a/3208140/12711
并且Win32文档证明，它是等待对象(例如，线程句柄)的同步API施加了内存障碍: http://msdn.microsoft.com/en-us/library/ms686355.aspx
And Win32 documents that it's synchronization APIs to wait on an object (for example, a thread handle) impose memory barriers: http://msdn.microsoft.com/en-us/library/ms686355.aspx
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