When to use recursive mutex?

Question

I understand recursive mutex allows mutex to be locked more than once without getting to a deadlock and should be unlocked the same number of times. But in what specific sit

Answer 1

I encountered the need for a recursive mutex today, and I think it's maybe the simplest example among the posted answers so far: This is a class that exposes two API functions, Process(...) and reset().

public void Process(...)
{
  acquire_mutex(mMutex);
  // Heavy processing
  ...
  reset();
  ...
  release_mutex(mMutex);
}

public void reset()
{
  acquire_mutex(mMutex);
  // Reset
  ...
  release_mutex(mMutex);
}

Both functions must not run concurrently because they modify internals of the class, so I wanted to use a mutex. Problem is, Process() calls reset() internally, and it would create a deadlock because mMutex is already acquired. Locking them with a recursive lock instead fixes the problem.