thodg/libgit2/src/cache.c

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• Hash : 335d6c99
  Author :
  Date : 2011-05-17T01:46:07
  

  cache: Drop cuckoo hashing
  
  Now we use a simple closed-addressing cache. Cuckoo hashing was creating
  too many issues with race conditions. Fuck that.
  
  Let's see what happens performance wise, we may have to roll back or
  come up with another way to implement an efficient multi-threaded cache.
  

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• src/cache.c

• /*
   * This file is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License, version 2,
   * as published by the Free Software Foundation.
   *
   * In addition to the permissions in the GNU General Public License,
   * the authors give you unlimited permission to link the compiled
   * version of this file into combinations with other programs,
   * and to distribute those combinations without any restriction
   * coming from the use of this file.  (The General Public License
   * restrictions do apply in other respects; for example, they cover
   * modification of the file, and distribution when not linked into
   * a combined executable.)
   *
   * This file is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; see the file COPYING.  If not, write to
   * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
   * Boston, MA 02110-1301, USA.
   */
  
  #include "common.h"
  #include "repository.h"
  #include "commit.h"
  #include "thread-utils.h"
  #include "cache.h"
  
  int git_cache_init(git_cache *cache, size_t size, git_cached_obj_freeptr free_ptr)
  {
  	size_t i;
  
  	if (size < 8)
  		size = 8;
  
  	/* round up size to closest power of 2 */
  	size--;
  	size |= size >> 1;
  	size |= size >> 2;
  	size |= size >> 4;
  	size |= size >> 8;
  	size |= size >> 16;
  
  	cache->size_mask = size;
  	cache->lru_count = 0;
  	cache->free_obj = free_ptr;
  
  	cache->nodes = git__malloc((size + 1) * sizeof(cache_node));
  	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;
  	}
  
  	return GIT_SUCCESS;
  }
  
  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);
  	}
  
  	free(cache->nodes);
  }
  
  void *git_cache_get(git_cache *cache, const git_oid *oid)
  {
  	const uint32_t *hash;
  	cache_node *node = NULL;
  	void *result = NULL;
  
  	hash = (const uint32_t *)oid->id;
  	node = &cache->nodes[hash[0] & cache->size_mask];
  
  	git_mutex_lock(&node->lock);
  	{
  		if (node->ptr && git_cached_obj_compare(node->ptr, oid) == 0) {
  			git_cached_obj_incref(node->ptr);
  			result = node->ptr;
  		}
  	}
  	git_mutex_unlock(&node->lock);
  
  	return result;
  }
  
  void *git_cache_try_store(git_cache *cache, void *entry)
  {
  	const uint32_t *hash;
  	const git_oid *oid;
  	cache_node *node = NULL;
  
  	oid = &((git_cached_obj*)entry)->oid;
  	hash = (const uint32_t *)oid->id;
  	node = &cache->nodes[hash[0] & cache->size_mask];
  
  	/* 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;
  	}
  
  	/* increase the refcount again, because we are
  	 * returning it to the user */
  	git_cached_obj_incref(entry);
  	git_mutex_unlock(&node->lock);
  
  	return entry;
  }
  

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