:right-sidebar: True RWLock =================================================================== .. currentmodule:: gi.repository.GLib .. versionadded:: 2.32 .. class:: RWLock(*args, **kwargs) :no-contents-entry: The GRWLock struct is an opaque data structure to represent a reader-writer lock. It is similar to a :obj:`~gi.repository.GLib.Mutex` in that it allows multiple threads to coordinate access to a shared resource. The difference to a mutex is that a reader-writer lock discriminates between read-only ('reader') and full ('writer') access. While only one thread at a time is allowed write access (by holding the 'writer' lock via :func:`~gi.repository.GLib.RWLock.writer_lock`), multiple threads can gain simultaneous read-only access (by holding the 'reader' lock via :func:`~gi.repository.GLib.RWLock.reader_lock`). It is unspecified whether readers or writers have priority in acquiring the lock when a reader already holds the lock and a writer is queued to acquire it. Here is an example for an array with access functions: .. code-block:: C :dedent: GRWLock lock; GPtrArray *array; gpointer my_array_get (guint index) { gpointer retval = NULL; if (!array) return NULL; g_rw_lock_reader_lock (&lock); if (index < array->len) retval = g_ptr_array_index (array, index); g_rw_lock_reader_unlock (&lock); return retval; } void my_array_set (guint index, gpointer data) { g_rw_lock_writer_lock (&lock); if (!array) array = g_ptr_array_new (); if (index >= array->len) g_ptr_array_set_size (array, index+1); g_ptr_array_index (array, index) = data; g_rw_lock_writer_unlock (&lock); } This example shows an array which can be accessed by many readers (the my_array_get() function) simultaneously, whereas the writers (the my_array_set() function) will only be allowed one at a time and only if no readers currently access the array. This is because of the potentially dangerous resizing of the array. Using these functions is fully multi-thread safe now. If a :obj:`~gi.repository.GLib.RWLock` is allocated in static storage then it can be used without initialisation. Otherwise, you should call :func:`~gi.repository.GLib.RWLock.init` on it and :func:`~gi.repository.GLib.RWLock.clear` when done. A GRWLock should only be accessed with the ``g_rw_lock_`` functions. Methods ------- .. rst-class:: interim-class .. class:: RWLock :no-index: .. method:: clear() -> None Frees the resources allocated to a lock with :func:`~gi.repository.GLib.RWLock.init`. This function should not be used with a :obj:`~gi.repository.GLib.RWLock` that has been statically allocated. Calling :func:`~gi.repository.GLib.RWLock.clear` when any thread holds the lock leads to undefined behaviour. .. versionadded:: 2.32 .. method:: init() -> None Initializes a :obj:`~gi.repository.GLib.RWLock` so that it can be used. This function is useful to initialize a lock that has been allocated on the stack, or as part of a larger structure. It is not necessary to initialise a reader-writer lock that has been statically allocated. .. code-block:: C :dedent: typedef struct { GRWLock l; ... } Blob; Blob *b; b = g_new (Blob, 1); g_rw_lock_init (&b->l); To undo the effect of :func:`~gi.repository.GLib.RWLock.init` when a lock is no longer needed, use :func:`~gi.repository.GLib.RWLock.clear`. Calling :func:`~gi.repository.GLib.RWLock.init` on an already initialized :obj:`~gi.repository.GLib.RWLock` leads to undefined behaviour. .. versionadded:: 2.32 .. method:: reader_lock() -> None Obtain a read lock on ``rw_lock``\. If another thread currently holds the write lock on ``rw_lock``\, the current thread will block until the write lock was (held and) released. If another thread does not hold the write lock, but is waiting for it, it is implementation defined whether the reader or writer will block. Read locks can be taken recursively. Calling :func:`~gi.repository.GLib.RWLock.reader_lock` while the current thread already owns a write lock leads to undefined behaviour. Read locks however can be taken recursively, in which case you need to make sure to call :func:`~gi.repository.GLib.RWLock.reader_unlock` the same amount of times. It is implementation-defined how many read locks are allowed to be held on the same lock simultaneously. If the limit is hit, or if a deadlock is detected, a critical warning will be emitted. .. versionadded:: 2.32 .. method:: reader_trylock() -> bool Tries to obtain a read lock on ``rw_lock`` and returns :const:`True` if the read lock was successfully obtained. Otherwise it returns :const:`False`. .. versionadded:: 2.32 .. method:: reader_unlock() -> None Release a read lock on ``rw_lock``\. Calling :func:`~gi.repository.GLib.RWLock.reader_unlock` on a lock that is not held by the current thread leads to undefined behaviour. .. versionadded:: 2.32 .. method:: writer_lock() -> None Obtain a write lock on ``rw_lock``\. If another thread currently holds a read or write lock on ``rw_lock``\, the current thread will block until all other threads have dropped their locks on ``rw_lock``\. Calling :func:`~gi.repository.GLib.RWLock.writer_lock` while the current thread already owns a read or write lock on ``rw_lock`` leads to undefined behaviour. .. versionadded:: 2.32 .. method:: writer_trylock() -> bool Tries to obtain a write lock on ``rw_lock``\. If another thread currently holds a read or write lock on ``rw_lock``\, it immediately returns :const:`False`. Otherwise it locks ``rw_lock`` and returns :const:`True`. .. versionadded:: 2.32 .. method:: writer_unlock() -> None Release a write lock on ``rw_lock``\. Calling :func:`~gi.repository.GLib.RWLock.writer_unlock` on a lock that is not held by the current thread leads to undefined behaviour. .. versionadded:: 2.32 Fields ------ .. rst-class:: interim-class .. class:: RWLock :no-index: .. attribute:: i .. attribute:: p