Initial commit

common/memorypool.cpp

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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 3 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "common/memorypool.h"
+#include "common/util.h"
+
+namespace Common {
+
+enum {
+	INITIAL_CHUNKS_PER_PAGE = 8
+};
+
+static size_t adjustChunkSize(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));
+
+	return chunkSize;
+}
+
+
+MemoryPool::MemoryPool(size_t chunkSize)
+	: _chunkSize(adjustChunkSize(chunkSize)) {
+
+	_next = nullptr;
+
+	_chunksPerPage = INITIAL_CHUNKS_PER_PAGE;
+}
+
+MemoryPool::~MemoryPool() {
+#if 0
+	freeUnusedPages();
+	if (!_pages.empty())
+		warning("Memory leak found in pool");
+#endif
+
+	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;
+	assert(page.numChunks * _chunkSize < 16*1024*1024); // Refuse to allocate pages bigger than 16 MB
+
+	page.start = ::malloc(page.numChunks * _chunkSize);
+	assert(page.start);
+	_pages.push_back(page);
+
+
+	// Next time, we'll allocate 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 = (byte *)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::allocChunk() {
+	// No free chunks left? Allocate a new page
+	if (!_next)
+		allocPage();
+
+	assert(_next);
+	void *result = _next;
+	_next = *(void **)result;
+	return result;
+}
+
+void MemoryPool::freeChunk(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.
+	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);
+			_pages[i].start = nullptr;
+		}
+	}
+
+	// Remove all now unused pages
+	size_t newSize = 0;
+	for (size_t i = 0; i < _pages.size(); ++i) {
+		if (_pages[i].start != nullptr) {
+			if (newSize != i)
+				_pages[newSize] = _pages[i];
+			++newSize;
+		}
+	}
+	_pages.resize(newSize);
+
+	// Reset _chunksPerPage
+	_chunksPerPage = INITIAL_CHUNKS_PER_PAGE;
+	for (size_t i = 0; i < _pages.size(); ++i) {
+		if (_chunksPerPage < _pages[i].numChunks)
+			_chunksPerPage = _pages[i].numChunks;
+	}
+}
+
+} // End of namespace Common