Caches

Caches — caches allow sharing of complex data structures to save resources

Synopsis

#include <glib.h>

                    GCache;
GCache*             g_cache_new                         (GCacheNewFunc value_new_func,
                                                         GCacheDestroyFunc value_destroy_func,
                                                         GCacheDupFunc key_dup_func,
                                                         GCacheDestroyFunc key_destroy_func,
                                                         GHashFunc hash_key_func,
                                                         GHashFunc hash_value_func,
                                                         GEqualFunc key_equal_func);
gpointer            g_cache_insert                      (GCache *cache,
                                                         gpointer key);
void                g_cache_remove                      (GCache *cache,
                                                         gconstpointer value);
void                g_cache_destroy                     (GCache *cache);

void                g_cache_key_foreach                 (GCache *cache,
                                                         GHFunc func,
                                                         gpointer user_data);
void                g_cache_value_foreach               (GCache *cache,
                                                         GHFunc func,
                                                         gpointer user_data);

void                (*GCacheDestroyFunc)                (gpointer value);
gpointer            (*GCacheDupFunc)                    (gpointer value);
gpointer            (*GCacheNewFunc)                    (gpointer key);

Description

A GCache allows sharing of complex data structures, in order to save system resources.

GTK+ uses caches for GtkStyles and GdkGCs. These consume a lot of resources, so a GCache is used to see if a GtkStyle or GdkGC with the required properties already exists. If it does, then the existing object is used instead of creating a new one.

GCache uses keys and values. A GCache key describes the properties of a particular resource. A GCache value is the actual resource.

Details

GCache

typedef struct _GCache GCache;

The GCache struct is an opaque data structure containing information about a GCache. It should only be accessed via the following functions.

g_cache_new ()

GCache*             g_cache_new                         (GCacheNewFunc value_new_func,
                                                         GCacheDestroyFunc value_destroy_func,
                                                         GCacheDupFunc key_dup_func,
                                                         GCacheDestroyFunc key_destroy_func,
                                                         GHashFunc hash_key_func,
                                                         GHashFunc hash_value_func,
                                                         GEqualFunc key_equal_func);

Creates a new GCache.

`value_new_func` :	a function to create a new object given a key. This is called by `g_cache_insert()` if an object with the given key does not already exist.
`value_destroy_func` :	a function to destroy an object. It is called by `g_cache_remove()` when the object is no longer needed (i.e. its reference count drops to 0).
`key_dup_func` :	a function to copy a key. It is called by `g_cache_insert()` if the key does not already exist in the GCache.
`key_destroy_func` :	a function to destroy a key. It is called by `g_cache_remove()` when the object is no longer needed (i.e. its reference count drops to 0).
`hash_key_func` :	a function to create a hash value from a key.
`hash_value_func` :	a function to create a hash value from a value.
`key_equal_func` :	a function to compare two keys. It should return `TRUE` if the two keys are equivalent.
Returns :	a new GCache.

g_cache_insert ()

gpointer            g_cache_insert                      (GCache *cache,
                                                         gpointer key);

Gets the value corresponding to the given key, creating it if necessary. It first checks if the value already exists in the GCache, by using the key_equal_func function passed to g_cache_new(). If it does already exist it is returned, and its reference count is increased by one. If the value does not currently exist, if is created by calling the value_new_func. The key is duplicated by calling key_dup_func and the duplicated key and value are inserted into the GCache.

`cache` :	a GCache.
`key` :	a key describing a GCache object.
Returns :	a pointer to a GCache value.

g_cache_remove ()

void                g_cache_remove                      (GCache *cache,
                                                         gconstpointer value);

Decreases the reference count of the given value. If it drops to 0 then the value and its corresponding key are destroyed, using the value_destroy_func and key_destroy_func passed to g_cache_new().

`cache` :	a GCache.
`value` :	the value to remove.

g_cache_destroy ()

void                g_cache_destroy                     (GCache *cache);

Frees the memory allocated for the GCache.

Note that it does not destroy the keys and values which were contained in the GCache.

cache :

a GCache.

g_cache_key_foreach ()

void                g_cache_key_foreach                 (GCache *cache,
                                                         GHFunc func,
                                                         gpointer user_data);

Calls the given function for each of the keys in the GCache.

NOTE func is passed three parameters, the value and key of a cache entry and the user_data. The order of value and key is different from the order in which g_hash_table_foreach() passes key-value pairs to its callback function !

`cache` :	a GCache.
`func` :	the function to call with each GCache key.
`user_data` :	user data to pass to the function.

g_cache_value_foreach ()

void                g_cache_value_foreach               (GCache *cache,
                                                         GHFunc func,
                                                         gpointer user_data);

Warning

g_cache_value_foreach has been deprecated since version 2.10 and should not be used in newly-written code. The reason is that it passes pointers to internal data structures to func; use g_cache_key_foreach() instead

Calls the given function for each of the values in the GCache.

`cache` :	a GCache.
`func` :	the function to call with each GCache value.
`user_data` :	user data to pass to the function.

GCacheDestroyFunc ()

void                (*GCacheDestroyFunc)                (gpointer value);

Specifies the type of the value_destroy_func and key_destroy_func functions passed to g_cache_new(). The functions are passed a pointer to the GCache key or GCache value and should free any memory and other resources associated with it.

value :

the GCache value to destroy.

GCacheDupFunc ()

gpointer            (*GCacheDupFunc)                    (gpointer value);

Specifies the type of the key_dup_func function passed to g_cache_new(). The function is passed a key (not a value as the prototype implies) and should return a duplicate of the key.

`value` :	the GCache key to destroy (not a GCache value as it seems).
Returns :	a copy of the GCache key.

GCacheNewFunc ()

gpointer            (*GCacheNewFunc)                    (gpointer key);

Specifies the type of the value_new_func function passed to g_cache_new(). It is passed a GCache key and should create the value corresponding to the key.

`key` :	a GCache key.
Returns :	a new GCache value corresponding to the key.

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