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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 man-age manage
     age 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.  Sig-nals Signals
     nals 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 argument 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