Threading issue with startPollingThread (sanitizer report)

Hello,

The following program (minimal reproducible example) is causing ThreadSanitizer warnings:

#include "fmtlog/fmtlog.h"

int main(int argc, char** argv)
{
  fmtlog::startPollingThread();
  fmtlog::setLogLevel(fmtlog::DBG);
  logd("test: reloading");
  fmtlog::stopPollingThread();

  return 0;
}

Compiled with the following line:

clang++-12 -DFMTLOG_HEADER_ONLY -DFMT_HEADER_ONLY -stdlib=libc++ -fno-omit-frame-pointer -fsanitize=thread -g -std=c++20 -o main main.cpp

Output:

% ./main
==================
WARNING: ThreadSanitizer: data race (pid=21198)
  Read of size 1 at 0x00000100d370 by thread T1:
    #0 fmtlogDetailT<0>::startPollingThread(long)::'lambda'()::operator()() const /home/matthijs/t5/./fmtlog/fmtlog-inl.h:331:14 (main+0x5146b9)
    #1 decltype(std::__1::forward<0>(fp)(std::__1::forward<fmtlogDetailT<0>::startPollingThread(long)::'lambda'()>(fp0)...)) std::__1::__invoke<fmtlogDetailT<0>::startPollingThread(long)::'lambda'()>(0&&, fmtlogDetailT<0>::startPollingThread(long)::'lambda'()&&...) /usr/lib/llvm-12/bin/../include/c++/v1/type_traits:3694:1 (main+0x5145cd)
    #2 void std::__1::__thread_execute<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, fmtlogDetailT<0>::startPollingThread(long)::'lambda'()>(std::__1::tuple<0, fmtlogDetailT<0>::startPollingThread(long)::'lambda'()>&, std::__1::__tuple_indices<>) /usr/lib/llvm-12/bin/../include/c++/v1/thread:280:5 (main+0x5144e5)
    #3 void* std::__1::__thread_proxy<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, fmtlogDetailT<0>::startPollingThread(long)::'lambda'()> >(void*) /usr/lib/llvm-12/bin/../include/c++/v1/thread:291:5 (main+0x513a35)

  Previous write of size 1 at 0x00000100d370 by main thread:
    #0 fmtlogDetailT<0>::stopPollingThread() /home/matthijs/t5/./fmtlog/fmtlog-inl.h:345:19 (main+0x4c23e7)
    #1 fmtlogT<0>::stopPollingThread() /home/matthijs/t5/./fmtlog/fmtlog-inl.h:607:31 (main+0x4c2376)
    #2 main /home/matthijs/t5/main.cpp:8:2 (main+0x4bf462)

  Location is global 'fmtlogDetailWrapper<0>::impl' of size 10496 at 0x00000100aa80 (main+0x00000100d370)

  Thread T1 (tid=21200, running) created by main thread at:
    #0 pthread_create <null> (main+0x44d02b)
    #1 std::__1::__libcpp_thread_create(unsigned long*, void* (*)(void*), void*) /usr/lib/llvm-12/bin/../include/c++/v1/__threading_support:509:10 (main+0x5139a9)
    #2 std::__1::thread::thread<fmtlogDetailT<0>::startPollingThread(long)::'lambda'(), void>(0&&, fmtlogDetailT<0>::startPollingThread(long)::'lambda'()&&...) /usr/lib/llvm-12/bin/../include/c++/v1/thread:307:16 (main+0x513581)
    #3 fmtlogDetailT<0>::startPollingThread(long) /home/matthijs/t5/./fmtlog/fmtlog-inl.h:330:11 (main+0x4c231e)
    #4 fmtlogT<0>::startPollingThread(long) /home/matthijs/t5/./fmtlog/fmtlog-inl.h:602:31 (main+0x4c228a)
    #5 main /home/matthijs/t5/main.cpp:5:2 (main+0x4bf456)

SUMMARY: ThreadSanitizer: data race /home/matthijs/t5/./fmtlog/fmtlog-inl.h:331:14 in fmtlogDetailT<0>::startPollingThread(long)::'lambda'()::operator()() const
==================
ThreadSanitizer: reported 1 warnings

Is this something to worry about?

Regards, Matthijs

MengRao / fmtlog

Threading issue with startPollingThread (sanitizer report) #24