gsqueue.cc

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

 
#include <cstring>
 
#include "MEM_guardedalloc.h"
 
#include "BLI_gsqueue.h"
#include "BLI_utildefines.h"
 
#include "BLI_strict_flags.h" /* IWYU pragma: keep. Keep last. */
 
/* target chunk size: 64kb */
#define CHUNK_SIZE_DEFAULT (1 << 16)
/* ensure we get at least this many elems per chunk */
#define CHUNK_ELEM_MIN 32
 
struct QueueChunk {
  QueueChunk *next;
  char data[0];
};
 
struct _GSQueue {
  QueueChunk *chunk_first;  /* first active chunk to pop from */
  QueueChunk *chunk_last;   /* last active chunk to push onto */
  QueueChunk *chunk_free;   /* free chunks to reuse */
  size_t chunk_first_index; /* index into 'chunk_first' */
  size_t chunk_last_index;  /* index into 'chunk_last' */
  size_t chunk_elem_max;    /* number of elements per chunk */
  size_t elem_size;         /* memory size of elements */
  size_t elem_num;          /* total number of elements */
};
 
static void *queue_get_first_elem(GSQueue *queue)
{
  return ((char *)(queue)->chunk_first->data) + ((queue)->elem_size * (queue)->chunk_first_index);
}
 
static void *queue_get_last_elem(GSQueue *queue)
{
  return ((char *)(queue)->chunk_last->data) + ((queue)->elem_size * (queue)->chunk_last_index);
}

static size_t queue_chunk_elem_max_calc(const size_t elem_size, size_t chunk_size)
{
  /* get at least this number of elems per chunk */
  const size_t elem_size_min = elem_size * CHUNK_ELEM_MIN;
 
  BLI_assert((elem_size != 0) && (chunk_size != 0));
 
  while (UNLIKELY(chunk_size <= elem_size_min)) {
    chunk_size <<= 1;
  }
 
  /* account for slop-space */
  chunk_size -= (sizeof(QueueChunk) + MEM_SIZE_OVERHEAD);
 
  return chunk_size / elem_size;
}
 
GSQueue *BLI_gsqueue_new(const size_t elem_size)
{
  GSQueue *queue = MEM_callocN<GSQueue>("BLI_gsqueue_new");
 
  queue->chunk_elem_max = queue_chunk_elem_max_calc(elem_size, CHUNK_SIZE_DEFAULT);
  queue->elem_size = elem_size;
  /* force init */
  queue->chunk_last_index = queue->chunk_elem_max - 1;
 
  return queue;
}
 
static void queue_free_chunk(QueueChunk *data)
{
  while (data) {
    QueueChunk *data_next = data->next;
    MEM_freeN(data);
    data = data_next;
  }
}
 
void BLI_gsqueue_free(GSQueue *queue)
{
  queue_free_chunk(queue->chunk_first);
  queue_free_chunk(queue->chunk_free);
  MEM_freeN(queue);
}
 
void BLI_gsqueue_push(GSQueue *queue, const void *item)
{
  queue->chunk_last_index++;
  queue->elem_num++;
 
  if (UNLIKELY(queue->chunk_last_index == queue->chunk_elem_max)) {
    QueueChunk *chunk;
    if (queue->chunk_free) {
      chunk = queue->chunk_free;
      queue->chunk_free = chunk->next;
    }
    else {
      chunk = static_cast<QueueChunk *>(
          MEM_mallocN(sizeof(*chunk) + (queue->elem_size * queue->chunk_elem_max), __func__));
    }
 
    chunk->next = nullptr;
 
    if (queue->chunk_last == nullptr) {
      queue->chunk_first = chunk;
    }
    else {
      queue->chunk_last->next = chunk;
    }
 
    queue->chunk_last = chunk;
    queue->chunk_last_index = 0;
  }
 
  BLI_assert(queue->chunk_last_index < queue->chunk_elem_max);
 
  /* Return last of queue */
  memcpy(queue_get_last_elem(queue), item, queue->elem_size);
}
 
void BLI_gsqueue_pop(GSQueue *queue, void *r_item)
{
  BLI_assert(BLI_gsqueue_is_empty(queue) == false);
 
  memcpy(r_item, queue_get_first_elem(queue), queue->elem_size);
  queue->chunk_first_index++;
  queue->elem_num--;
 
  if (UNLIKELY(queue->chunk_first_index == queue->chunk_elem_max || queue->elem_num == 0)) {
    QueueChunk *chunk_free = queue->chunk_first;
 
    queue->chunk_first = queue->chunk_first->next;
    queue->chunk_first_index = 0;
    if (queue->chunk_first == nullptr) {
      queue->chunk_last = nullptr;
      queue->chunk_last_index = queue->chunk_elem_max - 1;
    }
 
    chunk_free->next = queue->chunk_free;
    queue->chunk_free = chunk_free;
  }
}
 
size_t BLI_gsqueue_len(const GSQueue *queue)
{
  return queue->elem_num;
}
 
bool BLI_gsqueue_is_empty(const GSQueue *queue)
{
  return (queue->chunk_first == nullptr);
}