88 lines
2.8 KiB
C++
88 lines
2.8 KiB
C++
/* SPDX-License-Identifier: GPL-2.0-or-later */
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#pragma once
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/** \file
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* \ingroup bli
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*
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* An `Allocator` can allocate and deallocate memory. It is used by containers such as
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* blender::Vector. The allocators defined in this file do not work with standard library
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* containers such as std::vector.
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*
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* Every allocator has to implement two methods:
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* void *allocate(size_t size, size_t alignment, const char *name);
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* void deallocate(void *ptr);
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*
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* We don't use the std::allocator interface, because it does more than is really necessary for an
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* allocator and has some other quirks. It mixes the concepts of allocation and construction. It is
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* essentially forced to be a template, even though the allocator should not care about the type.
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* Also see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2271.html#std_allocator. Some
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* of these aspects have been improved in new versions of C++, so we might have to reevaluate the
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* strategy later on.
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*
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* The allocator interface dictated by this file is very simplistic, but for now that is all we
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* need. More complexity can be added when it seems necessary.
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*/
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#include <algorithm>
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#include <stdlib.h>
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#include "MEM_guardedalloc.h"
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#include "BLI_math_base.h"
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#include "BLI_utildefines.h"
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namespace blender {
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/**
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* Use Blender's guarded allocator (aka MEM_*). This should always be used except there is a
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* good reason not to use it.
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*/
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class GuardedAllocator {
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public:
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void *allocate(size_t size, size_t alignment, const char *name)
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{
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/* Should we use MEM_mallocN, when alignment is small? If yes, how small must alignment be? */
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return MEM_mallocN_aligned(size, alignment, name);
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}
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void deallocate(void *ptr)
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{
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MEM_freeN(ptr);
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}
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};
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/**
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* This is a wrapper around malloc/free. Only use this when the GuardedAllocator cannot be
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* used. This can be the case when the allocated memory might live longer than Blender's
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* allocator. For example, when the memory is owned by a static variable.
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*/
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class RawAllocator {
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private:
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struct MemHead {
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int offset;
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};
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public:
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void *allocate(size_t size, size_t alignment, const char * /*name*/)
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{
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BLI_assert(is_power_of_2_i(int(alignment)));
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void *ptr = malloc(size + alignment + sizeof(MemHead));
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void *used_ptr = reinterpret_cast<void *>(
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uintptr_t(POINTER_OFFSET(ptr, alignment + sizeof(MemHead))) & ~(uintptr_t(alignment) - 1));
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int offset = int(intptr_t(used_ptr) - intptr_t(ptr));
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BLI_assert(offset >= int(sizeof(MemHead)));
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(static_cast<MemHead *>(used_ptr) - 1)->offset = offset;
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return used_ptr;
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}
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void deallocate(void *ptr)
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{
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MemHead *head = static_cast<MemHead *>(ptr) - 1;
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int offset = -head->offset;
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void *actual_pointer = POINTER_OFFSET(ptr, offset);
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free(actual_pointer);
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}
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};
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} // namespace blender
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