On Saturday 28 February 2009 17:06:49 Jamie Lokier wrote: > Mike Frysinger wrote: > > On Saturday 28 February 2009 14:16:30 Jamie Lokier wrote: > > > (I still haven't figured out if it's safe to use vfork with shared > > > libraries and lazy procedure lookup... doesn't apply for Jan's ARM > > > with no shared libraries of course). > > > > why wouldnt it ? there isnt any locking or such in the resolver, and it > > isnt like there are "speculative lookups" done randomly. there is an > > issue on Blackfin with thread safety, but that is only because we lack > > 64bit atomic load/stores and the FDPIC PLT is a 64bit descriptor. > > What about when another thread is calling dlopen(RTLD_GLOBAL)? > Doesn't that update a global list of DSOs to search?
in a completely unrelated project, i revisited this. turns out, same exact thing can happen with fork(). POSIX even has quite a bit of explanation on the topic: http://www.opengroup.org/onlinepubs/9699919799/functions/pthread_atfork.html#tag_16_402_08 the very last paragraph is such a nice summary: only async-signal-safe functions are safe after a fork/vfork in a threaded environment. none of the dl* functions show up in that list (scroll down a page or two): http://www.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04_03_03 i'm not sure glibc even supports this. i know their libdl is thread safe, but POSIX is clear that threads + fork safe is screwed and that's just A-OK :). -mike
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