Hello all,
I'm finding what appears to be a data race in the std::string class. Although I
find that hard to believe.
I am using libstdc++ 6.0.8, with g++ version 4.1.2 that is using the posix
thread model, on a Linux machine running SuSE SLES10SP1
Linux <hostname> 2.6.16.46-0.12-smp #1 SMP Thu May 17 14:00:09 UTC 2007
i686 i686 i386 GNU/Linux
My machine has 2 cores (or 4 hyper threads).
My application is a multithreaded, using boost threads, which in turn is using
posix pthreads under the sheets.
Below is one of many reports that all seem to be variations on the same
thing. If I read this correctly it is indicating that std::string in thread 1
and thread 8 are potentially racing.
thread1 and thread8 are absolutely not sharing any strings. Thread8's string is
a local stack string, and thread1's string appears to be another stack string
from inside the libboost_program_options.so-1.43.0
Am I reading this correctly? That there is a data race in the string class?
Thanks in advance for your help,
-=John
===============================================================================
Raw Data
----------------------------------------
==17936== Possible data race during write of size 4 at 0x43AF5D0 by thread #1
==17936== Locks held: none
==17936== at 0x435DD45: std::string::_M_mutate(unsigned int, unsigned int,
unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435DEA9: std::string::_M_replace_safe(unsigned int, unsigned
int, char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435DF44: std::string::assign(char const*, unsigned int) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x457F9F2:
boost::program_options::positional_options_description::add(char const*, int)
(in lib/libboost_program_options.so.1.43.0)
==17936== by 0x806D82F: process_args(int, char**, bool&)
(MyProgramDaemon.cxx:130)
==17936== by 0x806DF55: main (MyProgramDaemon.cxx:263)
==17936== by 0x440D87B: __libc_start_main (in /lib/libc-2.4.so)
==17936== by 0x806D170: ??? (in MyProgramDaemon)
==17936==
==17936== This conflicts with a previous read of size 4 by thread #8
==17936== Locks held: none
==17936== at 0x435DF2E: std::string::assign(char const*, unsigned int) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435E0C4: std::string::operator=(char const*) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x4154C96: vee_gut_log(bool, bool, char const*, int, char
const*, int, char const*, char const*, char*) (MyProgramLoggingCommon.cxx:71)
==17936== by 0x4154F6F: ee_gut_log(bool, bool, char const*, int, char
const*,
int, char const*, char const*, ...) (MyProgramLoggingCommon.cxx:144)
==17936== by 0x413CC53: sigThreadHdlr_c::sigThreadHdlr_main()
(MyProgramSignalThreads.cxx:192)
==17936== by 0x413CE02: sigThreadHdlr_c::sigThreadWrapper_main(void*)
(MyProgramSignalThreads.cxx:54)
==17936== by 0x402765D: mythread_wrapper (hg_intercepts.c:219)
==17936== by 0x402765D: mythread_wrapper (hg_intercepts.c:219)
===============================================================================
Annotated version
----------------------------------------
==17936== Possible data race during write of size 4 at 0x43AF5D0 by thread #1
==17936== Locks held: none
==17936== at 0x435DD45: std::string::_M_mutate(unsigned int, unsigned int,
unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435DEA9: std::string::_M_replace_safe(unsigned int, unsigned
int, char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435DF44: std::string::assign(char const*, unsigned int) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x457F9F2:
boost::program_options::positional_options_description::add(char const*, int)
(in lib/libboost_program_options.so.1.43.0)
==17936== by 0x806D82F: process_args(int, char**, bool&)
(MyProgramDaemon.cxx:130)
pd.add("", -1);
==17936== by 0x806DF55: main (MyProgramDaemon.cxx:263)
==17936== by 0x440D87B: __libc_start_main (in /lib/libc-2.4.so)
==17936== by 0x806D170: ??? (in MyProgramDaemon)
==17936==
==17936== This conflicts with a previous read of size 4 by thread #8
==17936== Locks held: none
==17936== at 0x435DF2E: std::string::assign(char const*, unsigned int) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x435E0C4: std::string::operator=(char const*) (in
/usr/lib/libstdc++.so.6.0.8)
==17936== by 0x4154C96: vee_gut_log(bool, bool, char const*, int, char
const*, int, char const*, char const*, char*) (MyProgramLoggingCommon.cxx:71)
std::string s_new_fmt; // this is a local string
...
...
s_new_fmt = p_func;
==17936== by 0x4154F6F: ee_gut_log(bool, bool, char const*, int, char
const*,
int, char const*, char const*, ...) (MyProgramLoggingCommon.cxx:144)
==17936== by 0x413CC53: sigThreadHdlr_c::sigThreadHdlr_main()
(MyProgramSignalThreads.cxx:192)
==17936== by 0x413CE02: sigThreadHdlr_c::sigThreadWrapper_main(void*)
(MyProgramSignalThreads.cxx:54)
==17936== by 0x402765D: mythread_wrapper (hg_intercepts.c:219)
==17936== by 0x402765D: mythread_wrapper (hg_intercepts.c:219)
------------------------------------------------------------------------------
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