cache.h

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/*
    This file is part of darktable,
    Copyright (C) 2011-2020 darktable developers.
 
    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    darktable 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 darktable.  If not, see <http://www.gnu.org/licenses/>.
*/
 
#pragma once
 
#include "common/dtpthread.h"
#include <glib.h>
#include <inttypes.h>
#include <stddef.h>
 
typedef struct dt_cache_entry_t
{
  void *data;
  size_t data_size;
  size_t cost;
  GList *link;
  dt_pthread_rwlock_t lock;
  int _lock_demoting;
  uint32_t key;
}
dt_cache_entry_t;
 
typedef void((*dt_cache_allocate_t)(void *userdata, dt_cache_entry_t *entry));
typedef void((*dt_cache_cleanup_t)(void *userdata, dt_cache_entry_t *entry));
 
typedef struct dt_cache_t
{
  dt_pthread_mutex_t lock; // big fat lock. we're only expecting a couple hand full of cpu threads to use this concurrently.
 
  size_t entry_size; // cache line allocation
  size_t cost;       // user supplied cost per cache line (bytes?)
  size_t cost_quota; // quota to try and meet. but don't use as hard limit.
 
  GHashTable *hashtable; // stores (key, entry) pairs
  GList *lru;            // last element is most recently used, first is about to be kicked from cache.
 
  // callback functions for cache misses/garbage collection
  dt_cache_allocate_t allocate;
  dt_cache_allocate_t cleanup;
  void *allocate_data;
  void *cleanup_data;
}
dt_cache_t;
 
// entry size is only used if alloc callback is 0
void dt_cache_init(dt_cache_t *cache, size_t entry_size, size_t cost_quota);
void dt_cache_cleanup(dt_cache_t *cache);
 
static inline void dt_cache_set_allocate_callback(dt_cache_t *cache, dt_cache_allocate_t allocate_cb,
                                                  void *allocate_data)
{
  cache->allocate = allocate_cb;
  cache->allocate_data = allocate_data;
}
static inline void dt_cache_set_cleanup_callback(dt_cache_t *cache, dt_cache_cleanup_t cleanup_cb,
                                                 void *cleanup_data)
{
  cache->cleanup = cleanup_cb;
  cache->cleanup_data = cleanup_data;
}
 
// returns a slot in the cache for this key (newly allocated if need be), locked according to mode (r, w)
#define dt_cache_get(A, B, C)  dt_cache_get_with_caller(A, B, C, __FILE__, __LINE__)
dt_cache_entry_t *dt_cache_get_with_caller(dt_cache_t *cache, const uint32_t key, char mode, const char *file, int line);
// same but returns 0 if not allocated yet (both will block and wait for entry rw locks to be released)
dt_cache_entry_t *dt_cache_testget(dt_cache_t *cache, const uint32_t key, char mode);
// release a lock on a cache entry. the cache knows which one you mean (r or w).
#define dt_cache_release(A, B) dt_cache_release_with_caller(A, B, __FILE__, __LINE__)
void dt_cache_release_with_caller(dt_cache_t *cache, dt_cache_entry_t *entry, const char *file, int line);
 
// 0: not contained
int32_t dt_cache_contains(dt_cache_t *cache, const uint32_t key);
// returns 0 on success, 1 if the key was not found.
int32_t dt_cache_remove(dt_cache_t *cache, const uint32_t key);
// removes from the tip of the lru list, until the fill ratio of the hashtable
// goes below the given parameter, in terms of the user defined cost measure.
// will never lock and never fail, but sometimes not free memory (in case all
// is locked)
void dt_cache_gc(dt_cache_t *cache, const float fill_ratio);
 
// iterate over all currently contained data blocks.
// not thread safe! only use this for init/cleanup!
// returns non zero the first time process() returns non zero.
int dt_cache_for_all(dt_cache_t *cache,
    int (*process)(const uint32_t key, const void *data, void *user_data),
    void *user_data);
 
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