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/*
* 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.
*
* Author(s): Behdad Esfahbod
*/
#ifndef HB_ALLOC_POOL_HH
#define HB_ALLOC_POOL_HH
#include "hb-vector.hh"
/* Memory pool for persistent small- to medium-sized allocations.
*
* 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. */
struct hb_alloc_pool_t
{
unsigned ChunkSize = 65536 - 2 * sizeof (void *);
void *alloc (size_t size, unsigned alignment = 2 * sizeof (void *))
{
if (unlikely (chunks.in_error ())) return nullptr;
assert (alignment > 0);
assert (alignment <= 2 * sizeof (void *));
assert ((alignment & (alignment - 1)) == 0); /* power of two */
if (size > (ChunkSize) / 4)
{
/* Big chunk, allocate separately. */
hb_vector_t<char> chunk;
if (unlikely (!chunk.resize (size))) return nullptr;
void *ret = chunk.arrayZ;
chunks.push (std::move (chunk));
if (chunks.in_error ()) return nullptr;
if (chunks.length > 1)
{
// Bring back the previous last chunk to the end, so that
// we can continue to allocate from it.
hb_swap (chunks.arrayZ[chunks.length - 1], chunks.arrayZ[chunks.length - 2]);
}
return ret;
}
unsigned pad = current_chunk.length & (alignment - 1);
if (pad) pad = alignment - pad;
// Small chunk, allocate from the last chunk.
if (current_chunk.length < pad + size)
{
chunks.push ();
if (unlikely (chunks.in_error ())) return nullptr;
hb_vector_t<char> &chunk = chunks.arrayZ[chunks.length - 1];
if (unlikely (!chunk.resize (ChunkSize))) return nullptr;
current_chunk = chunk;
}
else
current_chunk += pad;
assert (current_chunk.length >= size);
void *ret = current_chunk.arrayZ;
current_chunk += size;
return ret;
}
void discard (void *p_, size_t size)
{
// Reclaim memory if we can.
char *p = (char *) p_;
if (current_chunk.arrayZ == p + size && current_chunk.backwards_length >= size)
current_chunk -= size;
}
private:
hb_vector_t<hb_vector_t<char>> chunks;
hb_array_t<char> current_chunk;
};
#endif /* HB_ALLOC_POOL_HH */