no way to compare when less than two revisions

Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== gdb ======
+Show all the backtraces:
+  (gdb) set pagination off
+  (gdb) thread apply all bt
+Other useful tips:
+  (gdb) t a a f       # thread apply all frame
+  (gdb) t a a bt 3    # thread apply all backtrace bottom three frames
+  (gdb) t a a bt -3   # thread apply all backtrace top three frames
+==== Detecting a Deadlock ====
+Get high level info on the threads:
+  (gdb) info threads
+    Id   Target Id         Frame
+  * 3    Thread 0x76c9d450 (LWP 24793) "testcode" 0x00013c38 in std::lock_guard<std::mutex>::lock_guard (this=0x76c9cd9c, __m=...) at /usr/include/c++/4.9/mutex:377
+    Thread 0x7649d450 (LWP 24794) "testcode" 0x76ded780 in __lll_lock_wait (futex=futex@entry=0x31464 <(anonymous namespace)::left_chopstick>, private=<optimized out>) at ../ports/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c:46
+    Thread 0x76fdd000 (LWP 24792) "testcode" 0x76de7274 in pthread_join (threadid=<optimized out>, thread_return=0x0) at pthread_join.c:92
+Make notes of those Thread IDs at LWP, and choose the thread you want, and choose a stack frame that shows the mutex of interest.
+   (gdb) thread 3
+   [Switching to thread 3 (Thread 0x76c9d450 (LWP 24793))]
+   #0  0x76ded780 in __lll_lock_wait (futex=futex@entry=0x3147c <(anonymous namespace)::right_chopstick>, private=<optimized out>) at ../ports/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c:46
+      ../ports/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c: No such file or directory.
+   (gdb) bt
+   #0  0x76ded780 in __lll_lock_wait (futex=futex@entry=0x3147c <(anonymous namespace)::right_chopstick>, private=<optimized out>) at ../ports/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c:46
+   #1  0x76de81a4 in __GI___pthread_mutex_lock (mutex=0x3147c <(anonymous namespace)::right_chopstick>) at pthread_mutex_lock.c:79
+   #2  0x00013868 in __gthread_mutex_lock (__mutex=0x3147c <(anonymous namespace)::right_chopstick>) at /usr/include/arm-linux-gnueabihf/c++/4.9/bits/gthr-default.h:748
+   #3  0x00013b98 in std::mutex::lock (this=0x3147c <(anonymous namespace)::right_chopstick>) at /usr/include/c++/4.9/mutex:135
+   #4  0x00013c38 in std::lock_guard<std::mutex>::lock_guard (this=0x76c9cd9c, __m=...) at /usr/include/c++/4.9/mutex:377
+   #5  0x00019e4c in (anonymous namespace)::do_work_on_right (have_left=true, tick=0) at deadlock/deadlock.cpp:43
+   ...
+   #10 0x0001b37c in std::thread::_Impl<std::_Bind_simple<deadlock()::<lambda()>()> >::_M_run(void) (this=0x5f6084) at /usr/include/c++/4.9/thread:115
+   #11 0x76f54348 in ?? () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
+   Backtrace stopped: previous frame identical to this frame (corrupt stack?)
+   (gdb) f 4
+   #4  0x00013c38 in std::lock_guard<std::mutex>::lock_guard (this=0x76c9cd9c, __m=...) at /usr/include/c++/4.9/mutex:377
+           { _M_device.lock(); }
+   (gdb) info args
+   this = 0x76c9cd9c
+   __m = @0x3147c: {<std::__mutex_base> = {_M_mutex = {__data = {__lock = 2, __count = 0, __owner = 24794, __kind = 0, __nusers = 1, {__spins = 0, __list = {__next = 0x0}}}, __size = "\002... }}, <No data fields>}
+Note the <nowiki>__owner</nowiki> of the mutex that thread 3 is waiting on. It's 24794. That's thread 2.  Likewise...
+   (gdb) t 2
+   (gdb) bt
+   (gdb) f 3
+   (gdb) p *this
+   $8 = {<std::__mutex_base> = {_M_mutex = {__data = {__lock = 2, __count = 0, __owner = 24793, __kind = 0, __nusers = 1, {__spins = 0, __list = {__next = 0x0}}}, __size = "\002... }}, <No data fields>}
+Note the <nowiki>__owner</nowiki> of the mutex that thread 2 is waiting on. It's 24793. That's thread 3. There's your deadlock.