mfbt/AllocPolicy.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * An allocation policy concept, usable for structures and algorithms to
   9  * control how memory is allocated and how failures are handled.
  10  */
  11
  12 #ifndef mozilla_AllocPolicy_h
  13 #define mozilla_AllocPolicy_h
  14
  15 #include "mozilla/TemplateLib.h"
  16
  17 #include <stddef.h>
  18 #include <stdlib.h>
  19
  20 namespace mozilla {
  21
  22 /*
  23  * Allocation policies are used to implement the standard allocation behaviors
  24  * in a customizable way.  Additionally, custom behaviors may be added to these
  25  * behaviors, such as additionally reporting an error through an out-of-band
  26  * mechanism when OOM occurs.  The concept modeled here is as follows:
  27  *
  28  *  - public copy constructor, assignment, destructor
  29  *  - template <typename T> T* pod_malloc(size_t)
  30  *      Responsible for OOM reporting when null is returned.
  31  *  - template <typename T> T* pod_calloc(size_t)
  32  *      Responsible for OOM reporting when null is returned.
  33  *  - template <typename T> T* pod_realloc(T*, size_t, size_t)
  34  *      Responsible for OOM reporting when null is returned.  The old allocation
  35  *      size is passed in, in addition to the new allocation size requested.
  36  *  - void free_(void*)
  37  *  - void reportAllocOverflow() const
  38  *      Called on allocation overflow (that is, an allocation implicitly tried
  39  *      to allocate more than the available memory space -- think allocating an
  40  *      array of large-size objects, where N * size overflows) before null is
  41  *      returned.
  42  *
  43  * mfbt provides (and typically uses by default) only MallocAllocPolicy, which
  44  * does nothing more than delegate to the malloc/alloc/free functions.
  45  */
  46
  47 /*
  48  * A policy that straightforwardly uses malloc/calloc/realloc/free and adds no
  49  * extra behaviors.
  50  */
  51 class MallocAllocPolicy
  52 {
  53 public:
  54   template <typename T>
  55   T* pod_malloc(size_t aNumElems)
  56   {
  57     if (aNumElems & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
  58       return nullptr;
  59     }
  60     return static_cast<T*>(malloc(aNumElems * sizeof(T)));
  61   }
  62
  63   template <typename T>
  64   T* pod_calloc(size_t aNumElems)
  65   {
  66     return static_cast<T*>(calloc(aNumElems, sizeof(T)));
  67   }
  68
  69   template <typename T>
  70   T* pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize)
  71   {
  72     if (aNewSize & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
  73       return nullptr;
  74     }
  75     return static_cast<T*>(realloc(aPtr, aNewSize * sizeof(T)));
  76   }
  77
  78   void free_(void* aPtr)
  79   {
  80     free(aPtr);
  81   }
  82
  83   void reportAllocOverflow() const
  84   {
  85   }
  86 };
  87
  88 } // namespace mozilla
  89
  90 #endif /* mozilla_AllocPolicy_h */