cache_callbacks(3) [osx man page]

cache_callbacks(3)					   BSD Library Functions Manual 					cache_callbacks(3)

NAME

     cache_callbacks -- Pre-defined cache callbacks used to configure a cache

SYNOPSIS

     #include <cache.h>
     #include <cache_callbacks.h>

     uintptr_t
     cache_key_hash_cb_cstring(void *key, void *unused);

     uintptr_t
     cache_key_hash_cb_integer(void *key, void *unused);

     bool
     cache_key_is_equal_cb_cstring(void *key1, void *key2, void *unused);

     bool
     cache_key_is_equal_cb_integer(void *key1, void *key2, void *unused);

     void
     cache_release_cb_free(void *key_or_value, void *unused);

     void
     cache_value_make_purgeable_cb(void *value, void *unused);

     bool
     cache_value_make_nonpurgeable_cb(void *value, void *unused);

     uintptr_t
     cache_hash_byte_string(const char *data, size_t bytes);

DESCRIPTION

     These functions are intended to be used as callbacks to configure how a cache functions.  They should be set in the cache_attributes_t passed
     into cache_create. They support common key types and offer support for using purgeable memory to allocate cache values.

     cache_key_hash_cb_cstring() A key_hash_cb() function for NULL-terminated cstring keys.

     cache_key_hash_cb_integer() A key_hash_cb() function for integer keys.

     cache_key_is_equal_cb_cstring() A key_is_equal_cb() function for cstring keys.

     cache_key_is_equal_cb_integer() A key_is_equal_cb() function for integer keys.

     cache_release_cb_free() Can be used for key_release_cb() or value_release_cb() for keys/values allocated from malloc and family.

     cache_value_make_purgeable_cb() Can be used for value_make_purgeable() with values allocated from the purgeable malloc zone (see malloc/mal-
     loc.h).  Calls malloc_make_purgeable() on value when it is unreferenced in order to reduce paging under memory pressure.

     value_make_purgeable() with values allocated from the purgeable malloc zone (see malloc/malloc.h).  Calls malloc_make_purgeable() on value
     when it is unreferenced in order to reduce paging under memory pressure.

     cache_hash_byte_string() Calculates a hash from a bytes string data of length bytes.

SEE ALSO

     libcache(3) cache_create(3)

Darwin								    May 7, 2009 							    Darwin

cache_set_and_retain(3) 				   BSD Library Functions Manual 				   cache_set_and_retain(3)

NAME

     cache_set_and_retain, cache_get_and_retain, cache_release_value, cache_remove -- Routines used to manage cached values

SYNOPSIS

     #include <cache.h>

     int
     cache_set_and_retain(cache_t *cache, void *key, void *value, size_t cost);

     int
     cache_get_and_retain(cache_t *cache, void *key, void **value_out);

     int
     cache_release_value(cache_t *cache, void *value);

     int
     cache_remove(cache_t *cache, void *key);

DESCRIPTION

     These routines are used to manipulate values added to an in memory cache created by cache_create(3).

     cache_set_and_retain() Adds value with cost to cache and associates it with key.  The caller retains a reference to value that will prevent
     value from being evicted from the cache until value is released in cache_release_value().

     cache_get_and_retain() Fetches value for key from cache and places value in value_out.  The caller retains a reference to value that will
     prevent value from being evicted from the cache until value is release in cache_release_value().

     cache_release_value() Releases a reference on value back to cache so that value may be evicted.  Signals that the client is not actively
     using value and will use cache_get_and_retain() before using again.

     cache_remove() Removes the value associated with key from cache.  Note that if the value is referenced by a client, the value will not be
     finalized until the reference is released using cache_release_value().

RETURN VALUES

     All functions return 0 for success and non-zero for failure.  The value ENOENT (see errno.h) indicates that a key or value passed as an argu-
     ment does not exist in the cache.	EINVAL is used for invalid arguments.

EXAMPLE

     The following example attempts to fetch a value from a cache using a key.	If the value is not present in the cache then it is created and
     added to the cache.  The value is then used and released back to the cache to allow the cache to evict it when needed.

	   cache_t *mycache;
	   cache_create("com.mycompany.mycache", &cache_attributes, &mycache);

	   void *mykey = my_create_key();
	   void *myvalue = NULL;

	   if (cache_get_and_retain(mycache, mykey, &myvalue) != 0) {
	       myvalue = my_create_value_from_key(mykey);
	       cache_set_and_retain(mycache, mykey, myvalue, 0);
	   }

	   my_use_value(value);
	   cache_release_value(mycache, myvalue);

SEE ALSO

     cache(3)

Darwin								    May 7, 2009 							    Darwin