The GRWLock struct is an opaque data structure to represent a reader-writer lock. It is similar to a #GMutex 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 g_rw_lock_writer_lock()), multiple threads can gain simultaneous read-only access (by holding the reader lock via g_rw_lock_reader_lock()).

Here is an example for an array with access functions: |[language="C" -- 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 #GRWLock is allocated in static storage then it can be used without initialisation. Otherwise, you should call g_rw_lock_init() on it and g_rw_lock_clear() when done.

A GRWLock should only be accessed with the g_rw_lock_ functions.