cpp-mutex-playground

To debug in VSCode

• Open (single-click) the built .exe in VSCode and press F5

TODOs

• study how to replace dangling mutex belongs to crashed / terminated process by new mutex
  • c++ - interprocess::named_upgradable_mutex - remains locked if process is killed - Stack Overflow
    • boost-single-application
    • win32-single-application
  • UPDATE
    • atexit in normal termination (Ctrl + C) can clean up mutex
    • Signal handlers may also work for normal termination
      • How to use signal handlers in C language?
    • Anyway, process killing cannot trigger any cleaning, dangling mutex still there
  • UPDATE 2023

    • OS can tell us if a system mutex is dangling:

      • 1. Obtain a handle to the mutex: If you know the name of the mutex, you can use the OpenMutex function to obtain a handle to it. This function takes the desired access rights and the name of the mutex as parameters and returns a handle to the mutex if it exists.

      HANDLE hMutex = OpenMutex(SYNCHRONIZE, FALSE, L"MutexName");

      • 2. Check if the handle is valid: The OpenMutex function will return a valid handle if the mutex exists and you have the necessary access rights. You can check if the handle is valid by comparing it to the NULL value.

      if (hMutex != NULL)
      {
          // Mutex exists and handle is valid
          // The mutex is still active
      }
      else
      {
          // Mutex does not exist or handle is invalid
          // The mutex is not active
      }

      • 3. Close the handle: After you have finished checking the mutex's status, it's important to close the handle using the CloseHandle function to release system resources.

      CloseHandle(hMutex);

  • UPDATE 2024
    • don't trust chatgpt code above
    • C++多线程之使用Mutex和Critical_Section_std::mutex ccriticalsection-CSDN博客
      • query mutex state function can be non-waiting
    • 使用 Mutex 物件 - Win32 apps | Microsoft Learn
      • implemented and working
      • this article tells everything
        • We can query mutex state

By following these steps, you can determine if a mutex is still active on Windows using the Win32 API. Remember to handle errors appropriately and ensure that you have the necessary access rights to open the mutex.

• compare boost mutex to std::mutex

Reference

• Synchronization mechanisms - 1.79.0
• Locking in C++
• Synchronization - 1.79.0