Mutex

class Mutex(*args, **kwargs)

The Mutex 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 Mutex 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 Mutex 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 Mutex is placed in other contexts (eg: embedded in a struct) then it must be explicitly initialised using init().

A Mutex should only be accessed via g_mutex_ functions.

Methods

class Mutex

clear() → None

Frees the resources allocated to a mutex with init().

This function should not be used with a Mutex that has been statically allocated.

Calling clear() on a locked mutex leads to undefined behaviour.

Added in version 2.32.

init() → None

Initializes a Mutex so that it can be used.

This function is useful to initialize a mutex that has been allocated on the stack, or as part of a larger structure. It is not necessary to initialize a mutex that has been statically allocated.

  typedef struct {
    GMutex m;
    ...
  } Blob;

Blob *b;

b = g_new (Blob, 1);
g_mutex_init (&b->m);

To undo the effect of init() when a mutex is no longer needed, use clear().

Calling init() on an already initialized Mutex leads to undefined behaviour.

Added in version 2.32.

lock() → None

Locks mutex. If mutex is already locked by another thread, the current thread will block until mutex is unlocked by the other thread.

Mutex is neither guaranteed to be recursive nor to be non-recursive. As such, calling lock() on a Mutex that has already been locked by the same thread results in undefined behaviour (including but not limited to deadlocks).

trylock() → bool

Tries to lock mutex. If mutex is already locked by another thread, it immediately returns False. Otherwise it locks mutex and returns True.

Mutex is neither guaranteed to be recursive nor to be non-recursive. As such, calling lock() on a Mutex that has already been locked by the same thread results in undefined behaviour (including but not limited to deadlocks or arbitrary return values).

unlock() → None

Unlocks mutex. If another thread is blocked in a lock() call for mutex, it will become unblocked and can lock mutex itself.

Calling unlock() on a mutex that is not locked by the current thread leads to undefined behaviour.

Fields

class Mutex

i

p