Does a mutex still need to be released if it times-out?

Question

Using the WaitForSingleObject Function.

If the function is called and times out, does it still need to release the mutex?

i.e. should ReleaseMutex be in position 1. or 2. if the five seconds elapse?

WaitForSingleObject(5 second time out)
{
  //access shared resource

  //1. - ReleaseMutex() here?
}
  //2. - ReleaseMutex() here?

Answer 1

No. If the call to WaitForSingleObject times out then you have not acquired the mutex, so should not release it.

i.e. you only need ReleaseMutex at position 1.

Answer 2

Your case #1 is correct. If you time out on that call, it means the resource was not acquired and you should not attempt to release it.