common/cache.c

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/*
    This file is part of darktable,
    Copyright (C) 2011-2021 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/>.
*/
 
#include "config.h"
 
#include "common/cache.h"
#include "common/darktable.h"
#include "common/dtpthread.h"
 
#include <assert.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
 
// this implements a concurrent LRU cache
 
void dt_cache_init(
    dt_cache_t *cache,
    size_t entry_size,
    size_t cost_quota)
{
  cache->cost = 0;
  cache->lru = 0;
  cache->entry_size = entry_size;
  cache->cost_quota = cost_quota;
  dt_pthread_mutex_init(&cache->lock, 0);
  cache->allocate = 0;
  cache->allocate_data = 0;
  cache->cleanup = 0;
  cache->cleanup_data = 0;
  cache->hashtable = g_hash_table_new(0, 0);
}
 
void dt_cache_cleanup(dt_cache_t *cache)
{
  g_hash_table_destroy(cache->hashtable);
  for(GList *l = cache->lru; l; l = g_list_next(l))
  {
    dt_cache_entry_t *entry = (dt_cache_entry_t *)l->data;
 
    if(cache->cleanup)
    {
      assert(entry->data_size);
      ASAN_UNPOISON_MEMORY_REGION(entry->data, entry->data_size);
 
      cache->cleanup(cache->cleanup_data, entry);
    }
    else
      dt_free_align(entry->data);
 
    dt_pthread_rwlock_destroy(&entry->lock);
    g_slice_free1(sizeof(*entry), entry);
  }
  g_list_free(cache->lru);
  dt_pthread_mutex_destroy(&cache->lock);
}
 
int32_t dt_cache_contains(dt_cache_t *cache, const uint32_t key)
{
  dt_pthread_mutex_lock(&cache->lock);
  int32_t result = g_hash_table_contains(cache->hashtable, GINT_TO_POINTER(key));
  dt_pthread_mutex_unlock(&cache->lock);
  return result;
}
 
int dt_cache_for_all(
    dt_cache_t *cache,
    int (*process)(const uint32_t key, const void *data, void *user_data),
    void *user_data)
{
  dt_pthread_mutex_lock(&cache->lock);
  GHashTableIter iter;
  gpointer key, value;
 
  g_hash_table_iter_init (&iter, cache->hashtable);
  while (g_hash_table_iter_next (&iter, &key, &value))
  {
    dt_cache_entry_t *entry = (dt_cache_entry_t *)value;
    const int err = process(GPOINTER_TO_INT(key), entry->data, user_data);
    if(err)
    {
      dt_pthread_mutex_unlock(&cache->lock);
      return err;
    }
  }
  dt_pthread_mutex_unlock(&cache->lock);
  return 0;
}
 
// return read locked bucket, or NULL if it's not already there.
// never attempt to allocate a new slot.
dt_cache_entry_t *dt_cache_testget(dt_cache_t *cache, const uint32_t key, char mode)
{
  gpointer orig_key, value;
  gboolean res;
  dt_pthread_mutex_lock(&cache->lock);
  res = g_hash_table_lookup_extended(
      cache->hashtable, GINT_TO_POINTER(key), &orig_key, &value);
  if(res)
  {
    dt_cache_entry_t *entry = (dt_cache_entry_t *)value;
    // lock the cache entry
    const int result
        = (mode == 'w') ? dt_pthread_rwlock_trywrlock(&entry->lock) : dt_pthread_rwlock_tryrdlock(&entry->lock);
    if(result)
    { // need to give up mutex so other threads have a chance to get in between and
      // free the lock we're trying to acquire:
      dt_pthread_mutex_unlock(&cache->lock);
      return 0;
    }
    // bubble up in lru list:
    cache->lru = g_list_remove_link(cache->lru, entry->link);
    cache->lru = g_list_concat(cache->lru, entry->link);
    dt_pthread_mutex_unlock(&cache->lock);
 
    if(mode == 'w')
    {
      assert(entry->data_size);
      ASAN_POISON_MEMORY_REGION(entry->data, entry->data_size);
    }
 
    // WARNING: do *NOT* unpoison here. it must be done by the caller!
 
    return entry;
  }
  dt_pthread_mutex_unlock(&cache->lock);
  return 0;
}
 
// if found, the data void* is returned. if not, it is set to be
// the given *data and a new hash table entry is created, which can be
// found using the given key later on.
dt_cache_entry_t *dt_cache_get_with_caller(dt_cache_t *cache, const uint32_t key, char mode, const char *file, int line)
{
  gpointer orig_key, value;
  gboolean res;
  int result;
restart:
  dt_pthread_mutex_lock(&cache->lock);
  res = g_hash_table_lookup_extended(
      cache->hashtable, GINT_TO_POINTER(key), &orig_key, &value);
  if(res)
  { // yay, found. read lock and pass on.
    dt_cache_entry_t *entry = (dt_cache_entry_t *)value;
    if(mode == 'w') result = dt_pthread_rwlock_trywrlock_with_caller(&entry->lock, file, line);
    else            result = dt_pthread_rwlock_tryrdlock_with_caller(&entry->lock, file, line);
    if(result)
    { // need to give up mutex so other threads have a chance to get in between and
      // free the lock we're trying to acquire:
      dt_pthread_mutex_unlock(&cache->lock);
      g_usleep(5);
      goto restart;
    }
    // bubble up in lru list:
    cache->lru = g_list_remove_link(cache->lru, entry->link);
    cache->lru = g_list_concat(cache->lru, entry->link);
    dt_pthread_mutex_unlock(&cache->lock);
 
#ifdef _DEBUG
    const pthread_t writer = dt_pthread_rwlock_get_writer(&entry->lock);
    if(mode == 'w')
    {
      assert(pthread_equal(writer, pthread_self()));
    }
    else
    {
      assert(!pthread_equal(writer, pthread_self()));
    }
#endif
 
    if(mode == 'w')
    {
      assert(entry->data_size);
      ASAN_POISON_MEMORY_REGION(entry->data, entry->data_size);
    }
 
    // WARNING: do *NOT* unpoison here. it must be done by the caller!
 
    return entry;
  }
 
  // else, not found, need to allocate.
 
  // first try to clean up.
  // also wait if we can't free more than the requested fill ratio.
  if(cache->cost > 0.8f * cache->cost_quota)
  {
    // need to roll back all the way to get a consistent lock state:
    dt_cache_gc(cache, 0.8f);
  }
 
  // here dies your 32-bit system:
  dt_cache_entry_t *entry = (dt_cache_entry_t *)g_slice_alloc(sizeof(dt_cache_entry_t));
  entry->data = 0;
  entry->data_size = cache->entry_size;
  entry->cost = 1;
  entry->link = g_list_append(0, entry);
  entry->key = key;
  entry->_lock_demoting = 0;
 
  if(cache->allocate)
    cache->allocate(cache->allocate_data, entry);
  else
    entry->data = dt_alloc_align(entry->data_size);
 
  if(!entry->data)
  {
    g_free(entry);
    dt_pthread_mutex_unlock(&cache->lock);
    return NULL;
  }
 
  int ret = dt_pthread_rwlock_init(&entry->lock, 0);
  if(ret) fprintf(stderr, "rwlock init: %d\n", ret);
 
  g_hash_table_insert(cache->hashtable, GINT_TO_POINTER(key), entry);
  assert(cache->allocate || entry->data_size);
 
  assert(entry->data_size);
  ASAN_POISON_MEMORY_REGION(entry->data, entry->data_size);
 
  // if allocate callback is given, always return a write lock
  const int write = ((mode == 'w') || cache->allocate);
 
  // write lock in case the caller requests it:
  if(write) dt_pthread_rwlock_wrlock_with_caller(&entry->lock, file, line);
  else      dt_pthread_rwlock_rdlock_with_caller(&entry->lock, file, line);
 
  cache->cost += entry->cost;
 
  // put at end of lru list (most recently used):
  cache->lru = g_list_concat(cache->lru, entry->link);
 
  dt_pthread_mutex_unlock(&cache->lock);
  // WARNING: do *NOT* unpoison here. it must be done by the caller!
 
  return entry;
}
 
int dt_cache_remove(dt_cache_t *cache, const uint32_t key)
{
  gpointer orig_key, value;
  gboolean res;
  int result;
  dt_cache_entry_t *entry;
restart:
  dt_pthread_mutex_lock(&cache->lock);
 
  res = g_hash_table_lookup_extended(
      cache->hashtable, GINT_TO_POINTER(key), &orig_key, &value);
  entry = (dt_cache_entry_t *)value;
  if(!res)
  { // not found in cache, not deleting.
    dt_pthread_mutex_unlock(&cache->lock);
    return 1;
  }
  // need write lock to be able to delete:
  result = dt_pthread_rwlock_trywrlock(&entry->lock);
  if(result)
  {
    dt_pthread_mutex_unlock(&cache->lock);
    g_usleep(5);
    goto restart;
  }
 
  if(entry->_lock_demoting)
  {
    // oops, we are currently demoting (rw -> r) lock to this entry in some thread. do not touch!
    dt_pthread_rwlock_unlock(&entry->lock);
    dt_pthread_mutex_unlock(&cache->lock);
    g_usleep(5);
    goto restart;
  }
 
  gboolean removed = g_hash_table_remove(cache->hashtable, GINT_TO_POINTER(key));
  (void)removed; // make non-assert compile happy
  assert(removed);
  cache->lru = g_list_delete_link(cache->lru, entry->link);
 
  if(cache->cleanup)
  {
    assert(entry->data_size);
    ASAN_UNPOISON_MEMORY_REGION(entry->data, entry->data_size);
 
    cache->cleanup(cache->cleanup_data, entry);
  }
  else
    dt_free_align(entry->data);
 
  dt_pthread_rwlock_unlock(&entry->lock);
  dt_pthread_rwlock_destroy(&entry->lock);
  cache->cost -= entry->cost;
  g_slice_free1(sizeof(*entry), entry);
 
  dt_pthread_mutex_unlock(&cache->lock);
  return 0;
}
 
// best-effort garbage collection. never blocks, never fails. well, sometimes it just doesn't free anything.
void dt_cache_gc(dt_cache_t *cache, const float fill_ratio)
{
  GList *l = cache->lru;
  while(l)
  {
    dt_cache_entry_t *entry = (dt_cache_entry_t *)l->data;
    assert(entry->link->data == entry);
    l = g_list_next(l); // we might remove this element, so walk to the next one while we still have the pointer..
    if(cache->cost < cache->cost_quota * fill_ratio) break;
 
    // if still locked by anyone else give up:
    if(dt_pthread_rwlock_trywrlock(&entry->lock)) continue;
 
    if(entry->_lock_demoting)
    {
      // oops, we are currently demoting (rw -> r) lock to this entry in some thread. do not touch!
      dt_pthread_rwlock_unlock(&entry->lock);
      continue;
    }
 
    // delete!
    g_hash_table_remove(cache->hashtable, GINT_TO_POINTER(entry->key));
    cache->lru = g_list_delete_link(cache->lru, entry->link);
    cache->cost -= entry->cost;
 
    if(cache->cleanup)
    {
      assert(entry->data_size);
      ASAN_UNPOISON_MEMORY_REGION(entry->data, entry->data_size);
 
      cache->cleanup(cache->cleanup_data, entry);
    }
    else
      dt_free_align(entry->data);
 
    dt_pthread_rwlock_unlock(&entry->lock);
    dt_pthread_rwlock_destroy(&entry->lock);
    g_slice_free1(sizeof(*entry), entry);
  }
}
 
void dt_cache_release_with_caller(dt_cache_t *cache, dt_cache_entry_t *entry, const char *file, int line)
{
#if((__has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)) && 1)
  // yes, this is *HIGHLY* unportable and is accessing implementation details.
#ifdef _DEBUG
 
# if defined(HAVE_THREAD_RWLOCK_ARCH_T_READERS)
  if (entry->lock.lock.__data.__readers <= 1)
# elif defined(HAVE_THREAD_RWLOCK_ARCH_T_NR_READERS)
  if (entry->lock.lock.__data.__nr_readers <= 1)
# else /* HAVE_THREAD_RWLOCK_ARCH_T_(NR_)READERS */
#  error "No valid reader member"
# endif /* HAVE_THREAD_RWLOCK_ARCH_T_(NR_)READERS */
 
#else /* _DEBUG */
 
# if defined(HAVE_THREAD_RWLOCK_ARCH_T_READERS)
  if (entry->lock.__data.__readers <= 1)
# elif defined(HAVE_THREAD_RWLOCK_ARCH_T_NR_READERS)
  if(entry->lock.__data.__nr_readers <= 1)
# else /* HAVE_THREAD_RWLOCK_ARCH_T_(NR_)READERS */
#  error "No valid reader member"
# endif /* HAVE_THREAD_RWLOCK_ARCH_T_(NR_)READERS */
 
#endif /* _DEBUG */
  {
    // only if there are no other reades we may poison.
    assert(entry->data_size);
    ASAN_POISON_MEMORY_REGION(entry->data, entry->data_size);
  }
#endif
 
  dt_pthread_rwlock_unlock(&entry->lock);
}
 
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