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+[[!meta copyright="Copyright © 2011, 2012, 2013, 2014 Free Software Foundation,
+Inc."]]
+
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
+
+[[!tag open_issue_libpthread]]
+
+[[!toc]]
+
+# [[FAQ entry|faq/libpthread_dlopen]]
+
+# IRC, freenode, #hurd, 2010-01-24
+
+    <pinotree> youpi: hm, thought about the pthread/stubs issue w/ dlopen'ed
+      libraries
+    <pinotree> currently looks like libstdc++ on hurd links to pthread-stubs,
+      we're the only one with such configuration
+    <pinotree> i was looking at the gcc 4.4 patch hurd-pthread.diff, could it
+      be it does not set THREADLIBS in the configure.ac switch case?
+    <youpi> that's expected
+    <youpi> on linux the libc provides hooks itself, on hurd-i386 it's
+      pthread-stubs
+    <pinotree> why not explicitly link to pthread though?
+    <youpi> because there is no strict need to, for applications that don't
+      need libpthread
+    <youpi> the dlopen case is a tricky case that pthread-stubs had not thought
+      about
+    <pinotree> hm
+    <pinotree> what if the pthread stubs would be moved in our glibc?
+    <youpi> that's what we should do yes
+    <youpi> (ideally)
+    <youpi> but for this we need to build libpthread along glibc, to get it
+      really working
+
+[[Packaging_libpthread]].
+
+    <youpi> and that's the tricky part (Makefile & such) which hasn't been done
+      yet
+    <pinotree> why both (stubs + actual libpthread)?
+    <youpi> because you need the stubs to be able to call the actual libpthread
+    <youpi> as soon libpthread gets dlopened for instance
+    <youpi> +as
+    <pinotree> i see
+    <youpi> (remember that nptl does this if you want to see how)
+    <youpi> (it's the libc files in nptl/)
+    <youpi> (and forward.c)
+    <guillem> also if libpthreads gets integrated with glibc don't we need to
+      switch the hurd from cthreads then? Which has been the blocker all this
+      time AFAIR?
+    <youpi> we don't _need_ to
+    <guillem> ok
+
+
+# IRC, OFTC, #debian-hurd, 2011-07-21
+
+    <youpi> there's one known issue with pthreads
+    <youpi> you can't dlopen() it
+
+... if the main application is not already linked against it.
+
+    <youpi> which also means you can't dlopen() a module which depends on it if
+      the main application hasn't used -lpthread already
+    <youpi> (so as to get libpthread initialized early, not at the dlopen()
+      call)
+    <lucas> I get this while building simgrid:
+    <lucas> cd /home/lucas/simgrid-3.6.1/obj-i486-gnu/examples/gras/console &&
+      /usr/bin/cmake -E create_symlink
+      /home/lucas/simgrid-3.6.1/obj-i486-gnu/lib/libsimgrid.so
+      /home/lucas/simgrid-3.6.1/obj-i486-gnu/examples/gras/console/simgrid.so
+    <lucas> cd /home/lucas/simgrid-3.6.1/obj-i486-gnu/examples/gras/console &&
+      lua /home/lucas/simgrid-3.6.1/examples/gras/console/ping_generator.lua
+    <lucas> lua:
+      /home/buildd/build/chroot-sid/home/buildd/byhand/hurd/./libpthread/sysdeps/generic/pt-mutex-timedlock.c:68:
+      __pthread_mutex_timedlock_internal: Assertion `__pthread_threads' failed.
+    <lucas> Aborted (core dumped)
+    <youpi> that's it, yes
+    <youpi> (or at least it has the same symptoms)
+    <lucas> it would need fixing in lua, not in SG, then, right?
+    <youpi> yes
+    <lucas> ok, thanks
+
+The fix thus being: link the main application with -lpthread.
+
+IRC, freenode, #hurd, 2011-08-17
+
+    < youpi> i.e. openjade apparently dlopen()s modules which use pthreads, but
+      openjade itself is not liked against libpthread
+    < youpi> which means unexpectedly  loading pthreads on the fly, which is
+      not implemented
+    < youpi> (and hard to implement of course)
+    < youpi> gnu_srs: so simply tell openjade people to link it with -lpthread
+    < gnu_srs> Shuoldn't missing linking with pthread create an error when
+      building openjade then?
+    < youpi> no
+    < youpi> because it's just a module which needs pthread
+    < youpi> and that module _is_ linked with -lpthread
+    < youpi> and dlopen() loads libpthreads too due to that
+    < youpi> but that's unexpected, for the libpthread initialization stuff
+    < youpi> (and too late to fix initlaization)
+    < gnu_srs> How come that other OSes build opensp w/o problems?
+    < youpi> because there are stubs in the libc
+    < gnu_srs> Sorry for the delay: What hinders stubs to be present also in
+      the Hurd libc parts too, to cope with this problem?
+    < youpi> doing it
+    < youpi> which is hard because you need libpthread bits inside the libc
+    < youpi> making it simpler would need building libpthread at the same time
+      as libc
+
+[[packaging_libpthread]]
+
+
+# IRC, freenode, #hurd, 2013-09-03
+
+    <gnu_srs> iceweasel: ./pthread/../sysdeps/generic/pt-mutex-timedlock.c:70:
+      __pthread_mutex_timedlock_internal: Assertion `__pthread_threads' failed.
+    <pinotree> LD_PRELOAD libpthread
+    <gnu_srs> why
+    <pinotree> missing link to pthread?
+    <pinotree> and yes, it's known already, just nobody worked on solving it
+
+
+# IRC, freenode, #hurd, 2014-01-28
+
+    <gnu_srs> braunr: Is this fixed by your recent patches? test_dbi:
+      ./pthread/../sysdeps/generic/pt-mutex-timedlock.c:70: 
+    <gnu_srs> __pthread_mutex_timedlock_internal: Assertion `__pthread_threads'
+      failed.
+    <youpi> faq/libpthread_dlopen.mdwn:
+      ./pthread/../sysdeps/generic/pt-mutex-timedlock.c:70:
+      __pthread_mutex_time
+    <gnu_srs> youpi: tks. A workaround seems to be available:
+      LD_PRELOAD=/lib/i386-gnu/libpthread.so.0.3
+    <gnu_srs> Is that possible on a buildd?
+    <youpi> it would be simpler to just make the package explicitly link
+      libpthread
+    <gnu_srs> Package is libdbi-drivers, providing libdbd-sqlite3 needed by
+      gnucash
+
+
+# IRC, freenode, #hurd, 2014-02-17
+
+    <braunr> hm ok, looks like iceweasel errors all have something to do with
+      the libc dns resolver
+    <braunr> http://darnassus.sceen.net/~rbraun/iceweasel_crash
+    <braunr> apparently, it's simply because the memory chunk isn't page
+      aligned ..
+    <braunr> looks like not preloading libpthread tirggers lots of tricky
+      issues
+    <braunr> anyway, apparently, the malloc/free calls in libresolv don't use
+      locks if libpthread isn't preloaded, which explains why the program state
+      looked impossible to reach and why crashes look random
+    <congzhang> debian linux does not have the pthread load problem.
+    <braunr> congzhang: it had it
+    <braunr> maybe not debian but i've found one such report for opensuse
+
+    <braunr> ok the bug is simple
+    <braunr> for some reason, our glibc still uses a global _res state for dns
+      resolution instead of per thread ones
+    <braunr> uh, apparently, it's libpthread's job to define a __res_state
+      function for that :(
+
+## IRC, freenode, #hurd, 2014-02-18
+
+    <braunr> usually when i say it, it crashes soon after, so let's try it :
+    <braunr> i've been running iceweasel 27 fine for like 10 minutes with a
+      patched libpthread
+    <braunr> still no crash ;p
+    <braunr> with luck this extremely lightweight patch will fix all
+      multithreaded applications doing concurrent name resolution .... :)
+    <teythoon> nice :)
+    <braunr> let's try gnash ....
+    <braunr> uh, segfault on termination
+    <braunr> gnash works :)
+    <teythoon> sweet :)
+    <braunr> i'm very surprised we could live so long with that resolv bug
+
+
+## IRC, freenode, #hurd, 2014-02-19
+
+    <braunr> youpi: the eglibc bug is about libresolv
+    <braunr> it uses a global resolver state even in multithreaded applications
+    <youpi> libresolv is a horrible part of glibc :)
+    <braunr> which is obviously bad
+    <braunr> yes .. :)
+    <braunr> here is the patch :
+      http://darnassus.sceen.net/~rbraun/0001-libpthread-per-thread-resolver-states.patch
+    <braunr> it's very short, it basically allocates a resolver state per
+      thread in the pthread struct, and sets the TLS variable __resp when the
+      thread starts
+    <braunr> should we make that hurd-specific ?
+    <braunr> or enclose that assignment with #ifdef ENABLE_TLS ?
+    <youpi> well, ENABLE_TLS is now always 1, iirc :)
+    <braunr> for the hurd, yes
+    <youpi> I'm surprised linux never had the issue
+    <youpi> no, not for the hurd
+    <braunr> ah
+    <youpi> I *had* to implement TLS for hurd because it was always 1 for
+      everybody :)
+    <braunr> ok
+    <braunr> so all those ifdefs could be removed and libpthread can assume tls
+      is enabled
+    <braunr> in which case my patch looks fine
+    <youpi> ah, thats a libpthread patch, not glibc patch
+    <braunr> yes
+    <braunr> nptl obviously did that from the start . :)
+    <braunr> linuxthreads had the problem a looong time ago
+    <youpi> ok
+    <braunr> i'm surprised we overlooked it for so long
+    <braunr> but anyway, that's a good fix
+    <youpi> indeed
+    <youpi> it seems all good to me
+    <braunr> well, __resp is a __thread variable
+    <braunr> i could add #ifdef ENABLE_TLS, but then what of the case where TLS
+      isn't enabled, and do we actually care ?
+    <braunr> #error maybe ?
+    <braunr> or #warning ?
+    <youpi> I don't think we care about the non-TLS case any more
+    <braunr> ok
+    <braunr> topgit branch i suppose ?
+    <youpi> well, not, hurd libpthread repo :)
+    <braunr> oh right ... :)
+
+
+# libthreads vs. libpthread
+
+The same symptom appears in an odd case, for instance:
+
+    buildd@hurd:~$ ldd /usr/bin/openjade
+            libthreads.so.0.3 => /lib/libthreads.so.0.3 (0x0103d000)
+            libosp.so.5 => /usr/lib/libosp.so.5 (0x01044000)
+            libpthread.so.0.3 => /lib/libpthread.so.0.3 (0x01221000)
+            libnsl.so.1 => /lib/i386-gnu/libnsl.so.1 (0x01232000)
+    [...]
+
+openjade links against *both* libthreads and libpthread. The result is that libc
+early-initializes libthreads only, and thus libpthread is not early-initialized,
+and later on raises assertions. The solution is to just get rid of libthreads,
+to have only one threading library.