GLib.Mutex¶

union

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 Mutex.init.

A Mutex should only be accessed via g_mutex_ functions.

Methods¶

clear¶

def clear(self) -> None

Frees the resources allocated to a mutex with Mutex.init.

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

Calling Mutex.clear on a locked mutex leads to undefined behaviour.

init¶

def init(self) -> 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 Mutex.init when a mutex is no longer needed, use Mutex.clear.

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

lock¶

def lock(self) -> 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 Mutex.lock on a Mutex that has already been locked by the same thread results in undefined behaviour (including but not limited to deadlocks).

trylock¶

def trylock(self) -> 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 Mutex.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¶

def unlock(self) -> None

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

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

Properties¶

p¶

p: int  # read/write

i¶

i: list[int]  # read/write