Quoting myself from some earlier emails - not sure if there have been any code changes since these emails:

> I think the implementation is supposed to be synchronous, but it looks like on windows it might not be. Were you seeing async behavior on windows only?
> In particular according to the GetExitCodeProcess doc it looks like GetExitCodeProcess may return true before the process has stopped.

...

> Should be easy to fix by checking if the status returned by GetExitCodeProcess is STILL_ACTIVE or not and only returning true in wait_for_pid if it is not.
> <http://msdn.microsoft.com/en-us/library/ms683189(v=vs.85).aspx>
> I can try to fix if you want, but I don't have windows so will have to debug any failures by looking at buildbot.