GMutex

The #GMutex struct is an opaque data structure to represent a mutex (mutual exclusion). It can be used to protect data against shared access.

Take for example the following function:

int
give_me_next_number (void)
{
  static int current_number = 0;

  // now do a very complicated calculation to calculate the new
  // number, this might for example be a random number generator
  current_number = calc_next_number (current_number);

  return current_number;
}

It is easy to see that this won't work in a multi-threaded application. There current_number must be protected against shared access. A #GMutex can be used as a solution to this problem:

int
give_me_next_number (void)
{
  static GMutex mutex;
  static int current_number = 0;
  int ret_val;

  g_mutex_lock (&mutex);
  ret_val = current_number = calc_next_number (current_number);
  g_mutex_unlock (&mutex);

  return ret_val;
}

Notice that the #GMutex is not initialised to any particular value. Its placement in static storage ensures that it will be initialised to all-zeros, which is appropriate.

If a #GMutex is placed in other contexts (eg: embedded in a struct) then it must be explicitly initialised using glib.mutex.Mutex.init_.

A #GMutex should only be accessed via g_mutex_ functions.