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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program 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 2
* of the License, or (at your option) any later version.
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL$
* $Id$
*
*/
#include "common/memorypool.h"
#include "common/util.h"
namespace Common {
MemoryPool::MemoryPool(size_t chunkSize) {
// You must at least fit the pointer in the node (technically unneeded considering the next rounding statement)
_chunkSize = MAX(chunkSize, sizeof(void*));
// There might be an alignment problem on some platforms when trying to load a void* on a non natural boundary
// so we round to the next sizeof(void*)
_chunkSize = (_chunkSize + sizeof(void*) - 1) & (~(sizeof(void*) - 1));
_next = NULL;
_chunksPerPage = 8;
}
MemoryPool::~MemoryPool() {
for (size_t i = 0; i < _pages.size(); ++i)
::free(_pages[i].start);
}
void MemoryPool::allocPage() {
Page page;
// Allocate a new page
page.numChunks = _chunksPerPage;
page.start = ::malloc(page.numChunks * _chunkSize);
assert(page.start);
_pages.push_back(page);
// Next time, we'll alocate a page twice as big as this one.
_chunksPerPage *= 2;
// Add the page to the pool of free chunk
addPageToPool(page);
}
void MemoryPool::addPageToPool(const Page &page) {
// Add all chunks of the new page to the linked list (pool) of free chunks
void *current = page.start;
for (size_t i = 1; i < page.numChunks; ++i) {
void *next = ((char*)current + _chunkSize);
*(void **)current = next;
current = next;
}
// Last chunk points to the old _next
*(void**)current = _next;
// From now on, the first free chunk is the first chunk of the new page
_next = page.start;
}
void *MemoryPool::malloc() {
if (!_next) // No free chunks left? Allocate a new page
allocPage();
assert(_next);
void *result = _next;
_next = *(void**)result;
return result;
}
void MemoryPool::free(void* ptr) {
// Add the chunk back to (the start of) the list of free chunks
*(void**)ptr = _next;
_next = ptr;
}
// Technically not compliant C++ to compare unrelated pointers. In practice...
bool MemoryPool::isPointerInPage(void *ptr, const Page &page) {
return (ptr >= page.start) && (ptr < (char*)page.start + page.numChunks * _chunkSize);
}
void MemoryPool::freeUnusedPages() {
//std::sort(_pages.begin(), _pages.end());
Array<size_t> numberOfFreeChunksPerPage;
numberOfFreeChunksPerPage.resize(_pages.size());
for (size_t i = 0; i < numberOfFreeChunksPerPage.size(); ++i) {
numberOfFreeChunksPerPage[i] = 0;
}
// Compute for each page how many chunks in it are still in use.
void *iterator = _next;
while (iterator) {
// TODO: This should be a binary search (requiring us to keep _pages sorted)
for (size_t i = 0; i < _pages.size(); ++i) {
if (isPointerInPage(iterator, _pages[i])) {
++numberOfFreeChunksPerPage[i];
break;
}
}
iterator = *(void**)iterator;
}
// Free all pages which are not in use.
// TODO: Might want to reset _chunksPerPage here (e.g. to the largest
// _pages[i].numChunks value still in use).
size_t freedPagesCount = 0;
for (size_t i = 0; i < _pages.size(); ++i) {
if (numberOfFreeChunksPerPage[i] == _pages[i].numChunks) {
// Remove all chunks of this page from the list of free chunks
void **iter2 = &_next;
while (*iter2) {
if (isPointerInPage(*iter2, _pages[i]))
*iter2 = **(void***)iter2;
else
iter2 = *(void***)iter2;
}
::free(_pages[i].start);
++freedPagesCount;
_pages[i].start = NULL;
}
}
for (size_t i = 0; i < _pages.size(); ) {
if (_pages[i].start == NULL) {
_pages.remove_at(i);
// We just removed an entry, so we do not advance "i"
} else {
++i;
}
}
//printf("%d freed pages\n", freedPagesCount);
}
} // End of namespace Common
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