Comment 32 for bug 903212

> FYI, been down this path with the glibc maintainers. Their claim is that
> localtime_r while reentrant cannot be used in threaded programs, because it is
> not thread safe according to POSIX.

IIUC the issue here is not one of "thread safety", but rather whether the function is "async signal safe".

If you have a multi-threaded application, and you fork a child process, then you are only allowed to use async-signal safe functions, until you execve(). The reason is as you describe

 1. Thread A acquires lock L
 2. Thread B forks process process C
 3. Child process C attempts to acquire lock L
 4. Thread A releases lock L

....child process C can never see results of step 4, since it is no longer in the same memory address space as Thread A.

Unfortunately libvirt is not complying for the async signal safety rules here.