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 <stddef.h>
  16 #include <stdlib.h>
  17
  18 namespace mozilla {
  19
  20 /*
  21  * Allocation policies are used to implement the standard allocation behaviors
  22  * in a customizable way.  Additionally, custom behaviors may be added to these
  23  * behaviors, such as additionally reporting an error through an out-of-band
  24  * mechanism when OOM occurs.  The concept modeled here is as follows:
  25  *
  26  *  - public copy constructor, assignment, destructor
  27  *  - void* malloc_(size_t)
  28  *      Responsible for OOM reporting when null is returned.
  29  *  - void* calloc_(size_t)
  30  *      Responsible for OOM reporting when null is returned.
  31  *  - void* realloc_(void*, size_t, size_t)
  32  *      Responsible for OOM reporting when null is returned.  The *used* bytes
  33  *      of the previous buffer is passed in (rather than the old allocation
  34  *      size), in addition to the *new* allocation size requested.
  35  *  - void free_(void*)
  36  *  - void reportAllocOverflow() const
  37  *      Called on allocation overflow (that is, an allocation implicitly tried
  38  *      to allocate more than the available memory space -- think allocating an
  39  *      array of large-size objects, where N * size overflows) before null is
  40  *      returned.
  41  *
  42  * mfbt provides (and typically uses by default) only MallocAllocPolicy, which
  43  * does nothing more than delegate to the malloc/alloc/free functions.
  44  */
  45
  46 /*
  47  * A policy that straightforwardly uses malloc/calloc/realloc/free and adds no
  48  * extra behaviors.
  49  */
  50 class MallocAllocPolicy
  51 {
  52 public:
  53   void* malloc_(size_t aBytes)
  54   {
  55     return malloc(aBytes);
  56   }
  57
  58   void* calloc_(size_t aBytes)
  59   {
  60     return calloc(aBytes, 1);
  61   }
  62
  63   void* realloc_(void* aPtr, size_t aOldBytes, size_t aBytes)
  64   {
  65     return realloc(aPtr, aBytes);
  66   }
  67
  68   void free_(void* aPtr)
  69   {
  70     free(aPtr);
  71   }
  72
  73   void reportAllocOverflow() const
  74   {
  75   }
  76 };
  77
  78 } // namespace mozilla
  79
  80 #endif /* mozilla_AllocPolicy_h */