janwas
0fa54bc56a
thanks to daniel.santos for reporting and alex for creating the ticket/notifying me. fixes #992 [heh, the amount of comments are proportional to the trouble caused by this code :S ran into VC++ compile errors when __declspec came after void* return type *sigh*] This was SVN commit r10385.
100 lines
3.6 KiB
C++
100 lines
3.6 KiB
C++
/* Copyright (c) 2010 Wildfire Games
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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/*
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* (header-less) pool-based heap allocator
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*/
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#ifndef INCLUDED_ALLOCATORS_HEADERLESS
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#define INCLUDED_ALLOCATORS_HEADERLESS
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/**
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* (header-less) pool-based heap allocator
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* provides Allocate and Deallocate without requiring in-band headers;
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* this is useful when allocating page-aligned I/O buffers
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* (headers would waste an entire page per buffer)
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*
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* policy:
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* - allocation: first exhaust the freelist, then allocate more
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* - freelist: address-ordered good fit, always split blocks
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* - coalescing: immediate
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* mechanism:
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* - coalescing: boundary tags in freed memory with distinct bit patterns
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* - freelist: segregated range lists of power-of-two size classes
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*
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* note: this module basically implements a (rather complex) freelist and
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* could be made independent of the Pool allocation scheme. however, reading
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* neighboring boundary tags may cause segmentation violations; knowing the
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* bounds of valid committed memory (i.e. Pool extents) avoids this.
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**/
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class HeaderlessAllocator
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{
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public:
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// allocators must 'naturally' align pointers, i.e. ensure they are
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// multiples of the largest native type (currently __m128).
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// since there are no headers, we can guarantee alignment by
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// requiring sizes to be multiples of allocationAlignment.
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static const size_t allocationAlignment = 16;
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// allocations must be large enough to hold our boundary tags
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// when freed. (see rationale above BoundaryTagManager)
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static const size_t minAllocationSize = 128;
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/**
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* @param poolSize maximum amount of memory that can be allocated.
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* this much virtual address space is reserved up-front (see Pool).
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**/
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HeaderlessAllocator(size_t poolSize);
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/**
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* restore the original state (as if newly constructed).
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* this includes reclaiming all extant allocations.
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**/
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void Reset();
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/**
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* @param size [bytes] (= minAllocationSize + i*allocationAlignment).
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* (this allocator is designed for requests on the order of several KiB)
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* @return allocated memory or 0 if the pool is too fragmented or full.
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**/
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NOTHROW_DECLARE void* Allocate(size_t size);
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/**
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* deallocate memory.
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* @param p must be exactly as returned by Allocate (in particular,
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* evenly divisible by allocationAlignment)
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* @param size must be exactly as specified to Allocate.
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**/
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void Deallocate(void* p, size_t size);
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/**
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* perform sanity checks; ensure allocator state is consistent.
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**/
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void Validate() const;
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private:
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class Impl;
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shared_ptr<Impl> impl;
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};
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#endif // #ifndef INCLUDED_ALLOCATORS_HEADERLESS
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