On Tue, Nov 12, 2019 at 2:11 PM Florian Weimer <fw@xxxxxxxxxxxxx> wrote: > > * enh: > > > On Tue, Nov 12, 2019 at 1:52 PM Florian Weimer <fw@xxxxxxxxxxxxx> wrote: > >> > >> * enh: > >> > >> > On Tue, Nov 12, 2019 at 1:38 PM Florian Weimer <fw@xxxxxxxxxxxxx> wrote: > >> >> > >> >> * enh: > >> >> > >> >> > POSIX removed ESRCH years ago. > >> >> > > >> >> > In resolving http://austingroupbugs.net/view.php?id=1214 it was made > >> >> > clear that callers can't rely on using signal 0 to test for the > >> >> > continued existence of a thread. Update the man page to make it clearer > >> >> > that this doesn't generally work (even if it sometimes seems to). > >> >> > > >> >> > See also the long explanation of why this is the case (and how to fix > >> >> > your code) here: > >> >> > > >> >> > https://android.googlesource.com/platform/bionic/+/master/docs/status.md#invalid-handling-targetsdkversion-o > >> >> > >> >> Well, if you fix the thread exit race (like musl did, and glibc should > >> >> as well, see bug 12889), you could get a reliable ESRCH as a side > >> >> effect. Pity that POSIX doesn't allow that. > >> > > >> > this isn't about the tid stored *in* the object that the pthread_t > >> > points to. > >> > > >> > like i (briefly) said in the commit message, this is because a > >> > pthread_t is a pointer, so if you have an old pthread_t that's been > >> > recycled... boom! > >> > >> Backing storage for a pthread_t object denoting a joinable thread > >> cannot be recycled, so that's not the case here. POSIX mandates > >> returning success even if the implementation has detected that it must > >> not send the signal because the thread has already terminated. > > > > who said anything about joinable? > > That determines whether the pthread_t object is still valid. but this is all about *invalid* threads, which obviously can't be joinable. i'm really not sure what you're trying to say. > > the cases we've seen in practice are that folks incorrectly believe > > that pthread_kill(3) with a signal of 0 is a reliable way to test > > whether a thread is still running. > > Right, that's not working according to (future) POSIX. Which I > dislike because a correct implementation of pthread_kill has to do all > the work to support this usage (or something like it; after all, only > testing for termination gives stable results), and then is forced by > POSIX to discard the data.
