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devtools/create_titanic/memorypool.h

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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/>.
+ *
+ */
+
+#ifndef COMMON_MEMORYPOOL_H
+#define COMMON_MEMORYPOOL_H
+
+#include "common/array.h"
+
+
+namespace Common {
+
+/**
+ * This class provides a pool of memory 'chunks' of identical size.
+ * The size of a chunk is determined when creating the memory pool.
+ *
+ * Using a memory pool may yield better performance and memory usage
+ * when allocating and deallocating many memory blocks of equal size.
+ * E.g. the Common::String class uses a memory pool for the refCount
+ * variables (each the size of an int) it allocates for each string
+ * instance.
+ */
+class MemoryPool {
+protected:
+	MemoryPool(const MemoryPool&);
+	MemoryPool& operator=(const MemoryPool&);
+
+	struct Page {
+		void *start;
+		size_t numChunks;
+	};
+
+	const size_t	_chunkSize;
+	Array<Page>		_pages;
+	void			*_next;
+	size_t			_chunksPerPage;
+
+	void	allocPage();
+	void	addPageToPool(const Page &page);
+	bool	isPointerInPage(void *ptr, const Page &page);
+
+public:
+	/**
+	 * Constructor for a memory pool with the given chunk size.
+	 * @param chunkSize		the chunk size of this memory pool
+	 */
+	explicit MemoryPool(size_t chunkSize);
+	~MemoryPool();
+
+	/**
+	 * Allocate a new chunk from the memory pool.
+	 */
+	void	*allocChunk();
+	/**
+	 * Return a chunk to the memory pool. The given pointer must have
+	 * been obtained from calling the allocChunk() method of the very
+	 * same MemoryPool instance. Passing any other pointer (e.g. to
+	 * a chunk from another MemoryPool, or a malloc'ed memory block)
+	 * will lead to undefined behavior and may result in a crash (if
+	 * you are lucky) or in silent data corruption.
+	 */
+	void	freeChunk(void *ptr);
+
+	/**
+	 * Perform garbage collection. The memory pool stores all the
+	 * chunks it manages in memory 'pages' obtained via the classic
+	 * memory allocation APIs (i.e. malloc/free). Ordinarily, once
+	 * a page has been allocated, it won't be released again during
+	 * the life time of the memory pool. The exception is when this
+	 * method is called.
+	 */
+	void	freeUnusedPages();
+
+	/**
+	 * Return the chunk size used by this memory pool.
+	 */
+	size_t	getChunkSize() const { return _chunkSize; }
+};
+
+/**
+ * This is a memory pool which already contains in itself some storage
+ * space for a fixed number of chunks. Thus if the memory pool is only
+ * lightly used, no malloc() calls have to be made at all.
+ */
+template<size_t CHUNK_SIZE, size_t NUM_INTERNAL_CHUNKS = 32>
+class FixedSizeMemoryPool : public MemoryPool {
+private:
+	enum {
+		REAL_CHUNK_SIZE = (CHUNK_SIZE + sizeof(void *) - 1) & (~(sizeof(void *) - 1))
+	};
+
+	byte	_storage[NUM_INTERNAL_CHUNKS * REAL_CHUNK_SIZE];
+public:
+	FixedSizeMemoryPool() : MemoryPool(CHUNK_SIZE) {
+		assert(REAL_CHUNK_SIZE == _chunkSize);
+		// Insert some static storage
+		Page internalPage = { _storage, NUM_INTERNAL_CHUNKS };
+		addPageToPool(internalPage);
+	}
+};
+
+// Ensure NUM_INTERNAL_CHUNKS == 0 results in a compile error
+template<size_t CHUNK_SIZE>
+class FixedSizeMemoryPool<CHUNK_SIZE,0> : public MemoryPool {
+public:
+	FixedSizeMemoryPool() : MemoryPool(CHUNK_SIZE) {}
+};
+
+/**
+ * A memory pool for C++ objects.
+ */
+template<class T, size_t NUM_INTERNAL_CHUNKS = 32>
+class ObjectPool : public FixedSizeMemoryPool<sizeof(T), NUM_INTERNAL_CHUNKS> {
+public:
+	/**
+	 * Return the memory chunk used as storage for the given object back
+	 * to the pool, after calling its destructor.
+	 */
+	void deleteChunk(T *ptr) {
+		ptr->~T();
+		this->freeChunk(ptr);
+	}
+};
+
+} // End of namespace Common
+
+/**
+ * A custom placement new operator, using an arbitrary MemoryPool.
+ *
+ * This *should* work with all C++ implementations, but may not.
+ *
+ * For details on using placement new for custom allocators, see e.g.
+ * <https://isocpp.org/wiki/faq/dtors#memory-pools>
+ */
+inline void *operator new(size_t nbytes, Common::MemoryPool &pool) {
+	assert(nbytes <= pool.getChunkSize());
+	return pool.allocChunk();
+}
+
+inline void operator delete(void *p, Common::MemoryPool &pool) {
+	pool.freeChunk(p);
+}
+
+#endif