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cache: Simplify locking mechanics

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The object cache is mostly IO-bound, so it makes no sense to have a lock
per node.
This commit is contained in:
Vicent Martí 2012-01-27 18:28:02 -08:00
parent 7a6f51de6d
commit e4b4da1406
2 changed files with 39 additions and 53 deletions
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70
src/cache.c
View File

@ -13,8 +13,6 @@
int git_cache_init(git_cache *cache, size_t size, git_cached_obj_freeptr free_ptr)
{
size_t i;
if (size < 8)
size = 8;
@ -25,20 +23,19 @@ int git_cache_init(git_cache *cache, size_t size, git_cached_obj_freeptr free_pt
size |= size >> 4;
size |= size >> 8;
size |= size >> 16;
size++;
cache->size_mask = size;
cache->size_mask = size - 1;
cache->lru_count = 0;
cache->free_obj = free_ptr;
cache->nodes = git__malloc((size + 1) * sizeof(cache_node));
git_mutex_init(&cache->lock);
cache->nodes = git__malloc(size * sizeof(git_cached_obj *));
if (cache->nodes == NULL)
return GIT_ENOMEM;
for (i = 0; i < (size + 1); ++i) {
git_mutex_init(&cache->nodes[i].lock);
cache->nodes[i].ptr = NULL;
}
memset(cache->nodes, 0x0, size * sizeof(git_cached_obj *));
return GIT_SUCCESS;
}
@ -47,10 +44,8 @@ void git_cache_free(git_cache *cache)
size_t i;
for (i = 0; i < (cache->size_mask + 1); ++i) {
if (cache->nodes[i].ptr)
git_cached_obj_decref(cache->nodes[i].ptr, cache->free_obj);
git_mutex_free(&cache->nodes[i].lock);
if (cache->nodes[i] != NULL)
git_cached_obj_decref(cache->nodes[i], cache->free_obj);
}
git__free(cache->nodes);
@ -59,53 +54,54 @@ void git_cache_free(git_cache *cache)
void *git_cache_get(git_cache *cache, const git_oid *oid)
{
uint32_t hash;
cache_node *node = NULL;
void *result = NULL;
git_cached_obj *node = NULL, *result = NULL;
memcpy(&hash, oid->id, sizeof(hash));
node = &cache->nodes[hash & cache->size_mask];
git_mutex_lock(&node->lock);
git_mutex_lock(&cache->lock);
{
if (node->ptr && git_cached_obj_compare(node->ptr, oid) == 0) {
git_cached_obj_incref(node->ptr);
result = node->ptr;
node = cache->nodes[hash & cache->size_mask];
if (node != NULL && git_oid_cmp(&node->oid, oid) == 0) {
git_cached_obj_incref(node);
result = node;
}
}
git_mutex_unlock(&node->lock);
git_mutex_unlock(&cache->lock);
return result;
}
void *git_cache_try_store(git_cache *cache, void *entry)
void *git_cache_try_store(git_cache *cache, void *_entry)
{
git_cached_obj *entry = _entry;
uint32_t hash;
const git_oid *oid;
cache_node *node = NULL;
oid = &((git_cached_obj*)entry)->oid;
memcpy(&hash, oid->id, sizeof(hash));
node = &cache->nodes[hash & cache->size_mask];
memcpy(&hash, &entry->oid, sizeof(hash));
/* increase the refcount on this object, because
* the cache now owns it */
git_cached_obj_incref(entry);
git_mutex_lock(&node->lock);
if (node->ptr == NULL) {
node->ptr = entry;
} else if (git_cached_obj_compare(node->ptr, oid) == 0) {
git_cached_obj_decref(entry, cache->free_obj);
entry = node->ptr;
} else {
git_cached_obj_decref(node->ptr, cache->free_obj);
node->ptr = entry;
git_mutex_lock(&cache->lock);
{
git_cached_obj *node = cache->nodes[hash & cache->size_mask];
if (node == NULL) {
cache->nodes[hash & cache->size_mask] = entry;
} else if (git_oid_cmp(&node->oid, &entry->oid) == 0) {
git_cached_obj_decref(entry, cache->free_obj);
entry = node;
} else {
git_cached_obj_decref(node, cache->free_obj);
cache->nodes[hash & cache->size_mask] = entry;
}
}
git_mutex_unlock(&cache->lock);
/* increase the refcount again, because we are
* returning it to the user */
git_cached_obj_incref(entry);
git_mutex_unlock(&node->lock);
return entry;
}

22
src/cache.h
View File

@ -23,42 +23,32 @@ typedef struct {
} git_cached_obj;
typedef struct {
git_cached_obj *ptr;
git_cached_obj **nodes;
git_mutex lock;
} cache_node;
typedef struct {
cache_node *nodes;
unsigned int lru_count;
size_t size_mask;
git_cached_obj_freeptr free_obj;
} git_cache;
int git_cache_init(git_cache *cache, size_t size, git_cached_obj_freeptr free_ptr);
void git_cache_free(git_cache *cache);
void *git_cache_try_store(git_cache *cache, void *entry);
void *git_cache_get(git_cache *cache, const git_oid *oid);
GIT_INLINE(int) git_cached_obj_compare(git_cached_obj *obj, const git_oid *oid)
{
return git_oid_cmp(&obj->oid, oid);
}
GIT_INLINE(void) git_cached_obj_incref(git_cached_obj *obj)
GIT_INLINE(void) git_cached_obj_incref(void *_obj)
{
git_cached_obj *obj = _obj;
git_atomic_inc(&obj->refcount);
}
GIT_INLINE(void) git_cached_obj_decref(git_cached_obj *obj, git_cached_obj_freeptr free_obj)
GIT_INLINE(void) git_cached_obj_decref(void *_obj, git_cached_obj_freeptr free_obj)
{
git_cached_obj *obj = _obj;
if (git_atomic_dec(&obj->refcount) == 0)
free_obj(obj);
}
#endif