Data race in CalcGmtOffset according to Thread Sanitizer

[aidangoettsch]

I'm working on a program which has several threads that log. When running under thread sanitizer, we see races related to google::LogMessageTime::CalcGmtOffset(), frequently with this malloc/free pattern. It seems like glog is intended to behave well under thread sanitizer and my understanding is that locking outside glog is not necessary. I would appreciate any advice to understand why this is happening. We can suppress this location, but it would be nice to have a better understanding of what is going on here.

WARNING: ThreadSanitizer: data race (pid=700438)
  Write of size 8 at 0x7204000002b0 by thread T18:
    #0 free <null> (binary_name+0x9c8d4) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #1 tzset_internal /usr/src/debug/glibc/glibc/time/tzset.c:401:3 (libc.so.6+0xd5ff5) (BuildId: 98b3d8e0b8c534c769cb871c438b4f8f3a8e4bf3)
    #2 google::LogMessageTime::CalcGmtOffset() <null> (binary_name+0x2dada8) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #3 google::LogMessageTime::init(tm const&, long, double) <null> (binary_name+0x2dac60) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #4 google::LogMessageTime::LogMessageTime(long, double) <null> (binary_name+0x2dad07) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #5 google::LogMessage::Init(char const*, int, int, void (google::LogMessage::*)()) <null> (binary_name+0x2d5cc0) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #6 google::LogMessage::LogMessage(char const*, int) <null> (binary_name+0x2d6c7b) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
...user code, std::thread launch routines

  Previous write of size 8 at 0x7204000002b0 by main thread:
    #0 malloc <null> (binary_name+0x9bebc) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #1 strdup /usr/src/debug/glibc/glibc/string/strdup.c:42:15 (libc.so.6+0xabcdf) (BuildId: 98b3d8e0b8c534c769cb871c438b4f8f3a8e4bf3)
    #2 google::LogMessageTime::CalcGmtOffset() <null> (binary_name+0x2dada8) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #3 google::LogMessageTime::init(tm const&, long, double) <null> (binary_name+0x2dac60) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #4 google::LogMessageTime::LogMessageTime(long, double) <null> (binary_name+0x2dad07) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #5 google::LogMessage::Init(char const*, int, int, void (google::LogMessage::*)()) <null> (binary_name+0x2d5cc0) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #6 google::LogMessage::LogMessage(char const*, int) <null> (binary_name+0x2d6c7b) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
...user code

  Thread T18 (tid=700465, running) created by main thread at:
    #0 pthread_create <null> (binary_name+0x9d759) (BuildId: 2b3461021462dd0c9b963684d29b6a32fc66bc4b)
    #1 __gthread_create /usr/src/debug/gcc/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu/bits/gthr-default.h:676:35 (libstdc++.so.6+0xe1d31) (BuildId: 4c06d605b755e81d6c346bb8a1be8bc85f13f81f)
    #2 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State>>, void (*)()) /usr/src/debug/gcc/gcc/libstdc++-v3/src/c++11/thread.cc:172:37 (libstdc++.so.6+0xe1d31)
...user code

[sergiud]

You are using an old and unsupported version of glog. In 0.7.x google::LogMessageTime::CalcGmtOffset no longer exists.