Strange dead lock with g_threads_enter

[Wei-Ning Huang <aitjcize gmail com>]

Hi everyone,

I am working on a multi-threaded application. The thing is, it working
perfectly for a while, but after that it fall into a deadlock.

Here is the code layout:

// Thread function
// It is signaled to wake up for every 1 second
gpointer motion_compile_thread(gpointer data) {
...
   while (TRUE) {
     if (!g_mutex_trylock(cp_mutex)) continue;
     g_cond_wait(compile_cv, cp_mutex);
     ....
     ....
     g_mutex_unlock(mutex);

     gdk_threads_enter();
     // do somethin
     do_refresh(xxxx)
     gdk_threads_leave();
}

void do_refresh(void) {
   if (!g_mutex_trylock(cp_mutex)) continue;
   // do something, but guarantee won't cause recursive call to do_refresh
   g_mutex_unlock(cp_mutex);
}

The program worked without problem for a while(about 5 minute)
but after that it hangs. Here is the gdb backtrace.

(gdb) bt
#0  0xb7fe1424 in __kernel_vsyscall ()
#1  0xb74c9e82 in __lll_lock_wait () from /lib/libpthread.so.0
#2  0xb74c535b in _L_lock_505 () from /lib/libpthread.so.0
#3  0xb74c5181 in pthread_mutex_lock () from /lib/libpthread.so.0
#4  0xb79475b6 in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#5  0xb7985e3e in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#6  0xb7515096 in g_main_context_prepare () from /usr/lib/libglib-2.0.so.0
#7  0xb7515f33 in ?? () from /usr/lib/libglib-2.0.so.0
#8  0xb7516a1b in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#9  0xb7af95b9 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#10 0x080536b3 in gui_main (builder=0x80e0828) at gui/gui-main.c:185
#11 0x08052e15 in main (argc=1, argv=0xbffff1e4) at main.c:127
(gdb) thread 2
[Switching to thread 2 (Thread 0xb322cb70 (LWP 24441))]#0  0xb7fe1424 in
__kernel_vsyscall ()
(gdb) bt
#0  0xb7fe1424 in __kernel_vsyscall ()
#1  0xb74c9e82 in __lll_lock_wait () from /lib/libpthread.so.0
#2  0xb74c535b in _L_lock_505 () from /lib/libpthread.so.0
#3  0xb74c5181 in pthread_mutex_lock () from /lib/libpthread.so.0
#4  0xb79475b6 in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#5  0xb7947b80 in gdk_threads_enter () from /usr/lib/libgdk-x11-2.0.so.0
#6  0x0805b676 in motion_compile_thread (data=0x8117330) at motion.c:96
#7  0xb753ebcf in ?? () from /usr/lib/libglib-2.0.so.0
#8  0xb74c2df0 in start_thread () from /lib/libpthread.so.0
#9  0xb743f98e in clone () from /lib/libc.so.6

> From what I can see, the program is stuck because the main thread locked a
mutex in #3.
But from the backtrace, the mutex seems to be locked by gtk_main_loop_run()
which is something I can't control,
and somehow it locked the same mutex as gdk_threads_enter()? any ideas?

Thanks,
Wei-Ning Huang