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[[!tag open_issue_libpthread]]

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]]

---

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.