Example

The example below will end in a deadlock: a thread calls the member function MyClass::DoIt. This member function acquires the class its only mutex. Then, MyClass::DoIt calls MyClass::DoItAgain, which starts by acquiring the same mutex. Because this mutex is already in use, the program will wait infinitely.

Download the Qt Creator project 'CppDeadlock' (zip)


#include <iostream>

#include <thread>

#include <regex>

#include <boost/bind.hpp>



struct MyClass

{

  void DoIt()

  {

    ///Acquire single access

    std::lock_guard<std::mutex> lock(m_mutex);



    ///Use of std::clog to write to screen directly

    std::clog << __func__ << '\n';



    ///Causes deadlock: DoItAgain wants to acquire m_mutex, which is in use already!

    DoItAgain();

  }



  private:

  void DoItAgain()

  {

    ///Causes deadlock: m_mutex is in use already!

    std::lock_guard<std::mutex> lock(m_mutex);



    ///Use of std::clog to write to screen directly

    std::clog << __func__ << '\n';

  }



  ///The MyClass mutex

  static std::mutex m_mutex;

};



std::mutex MyClass::m_mutex;



int main()

{

  ///Create the class that will cause a deadlock

  MyClass my_class;



  ///Create a thread that calls the class its method that will cause a deadlock

  std::thread t(boost::bind(&MyClass::DoIt,my_class));



  ///Due to deadlock, it will take forever to wait until t has finished

  t.join();

}

Screen output:


DoIt

The problem in this example can be solved by using a std::recursive_mutex instead.

Detecting a deadlock using DRD

Detecting a deadlock using DRD gives an indication of the problem. DRD calls the program like this:


#!/bin/sh

valgrind --tool=drd --log-file=helgrind.txt ../CppDeadlock-build-desktop/./CppDeadlock

After terminating the program by CTRL-C, the following output is generated by DRD:


==8958== drd, a thread error detector

==8958== Copyright (C) 2006-2010, and GNU GPL'd, by Bart Van Assche.

==8958== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info

==8958== Command: ../CppDeadlock-build-desktop/./CppDeadlock

==8958== Parent PID: 8957

==8958== 

==8958== Thread 2:

==8958== Recursive locking not allowed: mutex 0x804c194, recursion count 1, owner 2.

==8958==    at 0x40295E0: pthread_mutex_lock (drd_pthread_intercepts.c:584)

==8958==    by 0x80494EF: MyClass::DoIt() (in /home/richel/Projects/Website/CppDeadlock-build-desktop/CppDeadlock)

==8958==    by 0x4399265: ??? (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.14)

==8958==    by 0x4027E8B: vgDrd_thread_wrapper (drd_pthread_intercepts.c:281)

==8958==    by 0x4027E8B: vgDrd_thread_wrapper (drd_pthread_intercepts.c:281)

==8958==    by 0x42E1E98: start_thread (pthread_create.c:304)

==8958==    by 0x44F273D: clone (clone.S:130)

==8958== mutex 0x804c194 was first observed at:

==8958==    at 0x40295E0: pthread_mutex_lock (drd_pthread_intercepts.c:584)

==8958==    by 0x804949C: MyClass::DoIt() (in /home/richel/Projects/Website/CppDeadlock-build-desktop/CppDeadlock)

==8958==    by 0x4399265: ??? (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.14)

==8958==    by 0x4027E8B: vgDrd_thread_wrapper (drd_pthread_intercepts.c:281)

==8958==    by 0x4027E8B: vgDrd_thread_wrapper (drd_pthread_intercepts.c:281)

==8958==    by 0x42E1E98: start_thread (pthread_create.c:304)

==8958==    by 0x44F273D: clone (clone.S:130)

==8958==

Detecting a deadlock using helgrind

Detecting a deadlock using helgrind fails. helgrind calls the program like this:


#!/bin/sh

valgrind --tool=helgrind --log-file=helgrind.txt ../CppDeadlock-build-desktop/./CppDeadlock

After terminating the program by CTRL-C, the following output is generated by helgrind:


==1649== Helgrind, a thread error detector

==1649== Copyright (C) 2007-2010, and GNU GPL'd, by OpenWorks LLP et al.

==1649== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info

==1649== Command: ../CppDeadlock-build-desktop/./CppDeadlock

==1649== Parent PID: 1648

==1649==

Detecting a deadlock using memcheck

Detecting a deadlock using memcheck fails. memcheck calls the program like this:


#!/bin/sh

valgrind --leak-check=full -v --show-reachable=yes --log-file=memcheck.txt ../CppDeadlock-build-desktop/./CppDeadlock

After terminating the program by CTRL-C, the following output is generated by memcheck:


==8769== Memcheck, a memory error detector

==8769== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.

==8769== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info

==8769== Command: ../CppDeadlock-build-desktop/./CppDeadlock

==8769== Parent PID: 8768

==8769== 

--8769-- 

--8769-- Valgrind options:

--8769--    --suppressions=/usr/lib/valgrind/debian-libc6-dbg.supp

--8769--    --leak-check=full

--8769--    -v

--8769--    --show-reachable=yes

--8769--    --log-file=memcheck.txt

--8769-- Contents of /proc/version:

--8769--   Linux version 2.6.38-11-generic-pae (buildd@rothera) (gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) ) #48-Ubuntu SMP Fri Jul 29 20:51:21 UTC 2011

--8769-- Arch and hwcaps: X86, x86-sse1-sse2

--8769-- Page sizes: currently 4096, max supported 4096

--8769-- Valgrind library directory: /usr/lib/valgrind

--8769-- Reading syms from /lib/i386-linux-gnu/ld-2.13.so (0x4000000)

--8769--   Considering /lib/i386-linux-gnu/ld-2.13.so ..

--8769--   .. CRC mismatch (computed 2a2c2799 wanted 1e351f1f)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/ld-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /home/richel/Projects/Website/CppDeadlock-build-desktop/CppDeadlock (0x8048000)

--8769-- Reading syms from /usr/lib/valgrind/memcheck-x86-linux (0x38000000)

--8769--    object doesn't have a dynamic symbol table

--8769-- Reading suppressions file: /usr/lib/valgrind/debian-libc6-dbg.supp

--8769-- Reading suppressions file: /usr/lib/valgrind/default.supp

--8769-- REDIR: 0x4016a80 (index) redirected to 0x3803f82b (vgPlain_x86_linux_REDIR_FOR_index)

--8769-- Reading syms from /usr/lib/valgrind/vgpreload_core-x86-linux.so (0x4020000)

--8769-- Reading syms from /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so (0x4023000)

==8769== WARNING: new redirection conflicts with existing -- ignoring it

--8769--     new: 0x04016a80 (index               ) R-> 0x04026c78 index

--8769-- REDIR: 0x4016c20 (strlen) redirected to 0x4027048 (strlen)

--8769-- Reading syms from /usr/lib/libQtCore.so.4.7.2 (0x4044000)

--8769--   Considering /usr/lib/libQtCore.so.4.7.2 ..

--8769--   .. CRC mismatch (computed 5d0d89bc wanted b4e02a1a)

--8769--   Considering /usr/lib/debug/usr/lib/libQtCore.so.4.7.2 ..

--8769--   .. CRC is valid

--8769-- Reading syms from /lib/i386-linux-gnu/libpthread-2.13.so (0x42d7000)

--8769--   Considering /lib/i386-linux-gnu/libpthread-2.13.so ..

--8769--   .. CRC mismatch (computed 87269ed5 wanted 7df95f2f)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/libpthread-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /usr/lib/i386-linux-gnu/libstdc++.so.6.0.14 (0x42f0000)

--8769--    object doesn't have a symbol table

--8769-- Reading syms from /lib/i386-linux-gnu/libm-2.13.so (0x43db000)

--8769--   Considering /lib/i386-linux-gnu/libm-2.13.so ..

--8769--   .. CRC mismatch (computed e686ed93 wanted a0f1e52c)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/libm-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /lib/i386-linux-gnu/libgcc_s.so.1 (0x4401000)

--8769--   Considering /lib/i386-linux-gnu/libgcc_s.so.1 ..

--8769--   .. CRC mismatch (computed 3fa6d24f wanted 8b2bf89f)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/libgcc_s.so.1 ..

--8769--   .. CRC is valid

--8769-- Reading syms from /lib/i386-linux-gnu/libc-2.13.so (0x441d000)

--8769--   Considering /lib/i386-linux-gnu/libc-2.13.so ..

--8769--   .. CRC mismatch (computed 97e88cd2 wanted 4635a554)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/libc-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /lib/i386-linux-gnu/libz.so.1.2.3.4 (0x457f000)

--8769--   Considering /lib/i386-linux-gnu/libz.so.1.2.3.4 ..

--8769--   .. CRC mismatch (computed 995eb12f wanted 33a06a21)

--8769--    object doesn't have a symbol table

--8769-- Reading syms from /lib/i386-linux-gnu/libdl-2.13.so (0x4594000)

--8769--   Considering /lib/i386-linux-gnu/libdl-2.13.so ..

--8769--   .. CRC mismatch (computed 608d0daf wanted 983d6578)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/libdl-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /usr/lib/i386-linux-gnu/libgthread-2.0.so.0.2800.6 (0x4598000)

--8769--   Considering /usr/lib/i386-linux-gnu/libgthread-2.0.so.0.2800.6 ..

--8769--   .. CRC mismatch (computed 244482a3 wanted 61a9cd3c)

--8769--    object doesn't have a symbol table

--8769-- Reading syms from /lib/i386-linux-gnu/librt-2.13.so (0x459d000)

--8769--   Considering /lib/i386-linux-gnu/librt-2.13.so ..

--8769--   .. CRC mismatch (computed 680ec6ea wanted 247d4d27)

--8769--   Considering /usr/lib/debug/lib/i386-linux-gnu/librt-2.13.so ..

--8769--   .. CRC is valid

--8769-- Reading syms from /lib/i386-linux-gnu/libglib-2.0.so.0.2800.6 (0x45a6000)

--8769--   Considering /lib/i386-linux-gnu/libglib-2.0.so.0.2800.6 ..

--8769--   .. CRC mismatch (computed 2312631e wanted e21a44de)

--8769--    object doesn't have a symbol table

--8769-- Reading syms from /lib/i386-linux-gnu/libpcre.so.3.12.1 (0x467e000)

--8769--   Considering /lib/i386-linux-gnu/libpcre.so.3.12.1 ..

--8769--   .. CRC mismatch (computed 9e5ab3c1 wanted 29aaf7e3)

--8769--    object doesn't have a symbol table

--8769-- REDIR: 0x4490fb0 (strncmp) redirected to 0x4020479 (_vgnU_ifunc_wrapper)

--8769-- REDIR: 0x4498140 (strstr) redirected to 0x4020479 (_vgnU_ifunc_wrapper)

--8769-- REDIR: 0x4497db0 (__GI_strstr) redirected to 0x4028ef1 (strstr)

--8769-- REDIR: 0x44910b0 (rindex) redirected to 0x4026acc (rindex)

--8769-- REDIR: 0x439c650 (operator new(unsigned int)) redirected to 0x4026398 (operator new(unsigned int))

--8769-- REDIR: 0x448cef0 (malloc) redirected to 0x40267df (malloc)

--8769-- REDIR: 0x4490d80 (__GI_strlen) redirected to 0x402702d (__GI_strlen)

--8769-- REDIR: 0x4490740 (strcmp) redirected to 0x4020479 (_vgnU_ifunc_wrapper)

--8769-- REDIR: 0x4539cb0 (__strcmp_ssse3) redirected to 0x40279d0 (strcmp)

--8769-- REDIR: 0x448de70 (calloc) redirected to 0x4025235 (calloc)

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.

(C++) deadlock

Example

Detecting a deadlock using DRD

Detecting a deadlock using helgrind

Detecting a deadlock using memcheck