chobjcaches.c File Reference

Objects Caches code. More...

#include "ch.h"

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Functions
static oc_object_t *	hash_get_s (objects_cache_t *ocp, uint32_t group, uint32_t key)
	Returns an object pointer from the cache, if present. More...
static oc_object_t *	lru_get_last_s (objects_cache_t *ocp)
	Gets the least recently used object buffer from the LRU list. More...
void	chCacheObjectInit (objects_cache_t *ocp, ucnt_t hashn, oc_hash_header_t *hashp, ucnt_t objn, size_t objsz, void *objvp, oc_readf_t readf, oc_writef_t writef)
	Initializes a objects_cache_t object. More...
oc_object_t *	chCacheGetObject (objects_cache_t *ocp, uint32_t group, uint32_t key)
	Retrieves an object from the cache. More...
void	chCacheReleaseObjectI (objects_cache_t *ocp, oc_object_t *objp)
	Releases an object into the cache. More...
bool	chCacheReadObject (objects_cache_t *ocp, oc_object_t *objp, bool async)
	Reads object data from the storage. More...
bool	chCacheWriteObject (objects_cache_t *ocp, oc_object_t *objp, bool async)
	Writes the object data back to storage. More...

Detailed Description

Objects Caches code.

Objects caches.

Operation mode

An object cache allows to retrieve and release objects from a slow media, for example a disk or flash.
The most recently used objects are kept in a series of RAM buffers making access faster. Objects are identified by a pair <group, key> which could be mapped, for example, to a disk drive identifier and sector identifier.
Read and write operations are performed using externally-supplied functions, the cache is device-agnostic.
The cache uses internally an hash table, the size of the table should be dimensioned to minimize the risk of hash collisions, a factor of two is usually acceptable, it depends on the specific application requirements.
Operations defined for caches:

• Get Object: Retrieves an object from cache, if not present then an empty buffer is returned.
• Read Object: Retrieves an object from cache, if not present a buffer is allocated and the object is read from the media.
• Release Object: Releases an object to the cache handling the media update, if required.

Precondition

In order to use the pipes APIs the CH_CFG_USE_OBJ_CACHES option must be enabled in chconf.h.

Note

Compatible with RT and NIL.

Definition in file chobjcaches.c.