The program racing.cpp is incrementing a shared integer many times, within several threads, which should lead to race conditions if no specific protection is used. The values of the global parameters nThread, nInc and nRepeat can be custommized for your own computer.

Tasks

• Compile and run the executable, check it races.
• If you have a bash shell, try ./run ./racing, which keeps invoking the executable until a race condition is detected.
• (Optional) You can use valgrind --tool=helgrind ./racing to prove your assumption
• (Optional) If your operating system supports it, recompile with thread sanitizer. With Makefile, use e.g. make CXXFLAGS="-fsanitize=thread"
• Use a std::mutex to fix the issue.
• See the difference in execution time, for example with time ./racing. You might have to increase nRepeat if it completes too fast, or lower it if it takes too long.
• (Optional) Check again with valgrind or thread sanitizer if the problem is fixed.
• Try to use std::atomic instead of the mutex, and compare the execution time.