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/*
* Copyright © 2019 Facebook, Inc.
*
* This is part of HarfBuzz, a text shaping library.
*
* Permission is hereby granted, without written agreement and without
* license or royalty fees, to use, copy, modify, and distribute this
* software and its documentation for any purpose, provided that the
* above copyright notice and the following two paragraphs appear in
* all copies of this software.
*
* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*
* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*
* Facebook Author(s): Behdad Esfahbod
*/
#ifndef HB_POOL_HH
#define HB_POOL_HH
#include "hb.hh"
/* Memory pool for persistent allocation of small objects.
*
* Some AI musings on this, not necessarily true:
*
* This is a very simple implementation, but it's good enough for our
* purposes. It's not thread-safe. It's not very fast. It's not
* very memory efficient. It's not very cache efficient. It's not
* very anything efficient. But it's simple and it works. And it's
* good enough for our purposes. If you need something more
* sophisticated, use a real allocator. Or use a real language. */
template <typename T, unsigned ChunkLen = 32>
struct hb_pool_t
{
hb_pool_t () : next (nullptr) {}
~hb_pool_t ()
{
next = nullptr;
+ hb_iter (chunks)
| hb_apply (hb_free)
;
}
T* alloc ()
{
if (unlikely (!next))
{
if (unlikely (!chunks.alloc (chunks.length + 1))) return nullptr;
chunk_t *chunk = (chunk_t *) hb_malloc (sizeof (chunk_t));
if (unlikely (!chunk)) return nullptr;
chunks.push (chunk);
next = chunk->thread ();
}
T* obj = next;
next = * ((T**) next);
hb_memset (obj, 0, sizeof (T));
return obj;
}
void release (T* obj)
{
* (T**) obj = next;
next = obj;
}
private:
static_assert (ChunkLen > 1, "");
static_assert (sizeof (T) >= sizeof (void *), "");
static_assert (alignof (T) % alignof (void *) == 0, "");
struct chunk_t
{
T* thread ()
{
for (unsigned i = 0; i < ARRAY_LENGTH (arrayZ) - 1; i++)
* (T**) &arrayZ[i] = &arrayZ[i + 1];
* (T**) &arrayZ[ARRAY_LENGTH (arrayZ) - 1] = nullptr;
return arrayZ;
}
T arrayZ[ChunkLen];
};
T* next;
hb_vector_t<chunk_t *> chunks;
};
#endif /* HB_POOL_HH */