Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
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.
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?
UPDATE 1
Are there any examples of waiting which does not include a memory barrier?
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.
For example, posix makes such a guarantee for
pthread_join(): https://stackoverflow.com/a/3208140/12711And 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