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       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/Attributes.h"
      16             : #include "mozilla/TemplateLib.h"
      17             : 
      18             : #include <stddef.h>
      19             : #include <stdlib.h>
      20             : 
      21             : namespace mozilla {
      22             : 
      23             : /*
      24             :  * Allocation policies are used to implement the standard allocation behaviors
      25             :  * in a customizable way.  Additionally, custom behaviors may be added to these
      26             :  * behaviors, such as additionally reporting an error through an out-of-band
      27             :  * mechanism when OOM occurs.  The concept modeled here is as follows:
      28             :  *
      29             :  *  - public copy constructor, assignment, destructor
      30             :  *  - template <typename T> T* maybe_pod_malloc(size_t)
      31             :  *      Fallible, but doesn't report an error on OOM.
      32             :  *  - template <typename T> T* maybe_pod_calloc(size_t)
      33             :  *      Fallible, but doesn't report an error on OOM.
      34             :  *  - template <typename T> T* maybe_pod_realloc(T*, size_t, size_t)
      35             :  *      Fallible, but doesn't report an error on OOM.  The old allocation
      36             :  *      size is passed in, in addition to the new allocation size requested.
      37             :  *  - template <typename T> T* pod_malloc(size_t)
      38             :  *      Responsible for OOM reporting when null is returned.
      39             :  *  - template <typename T> T* pod_calloc(size_t)
      40             :  *      Responsible for OOM reporting when null is returned.
      41             :  *  - template <typename T> T* pod_realloc(T*, size_t, size_t)
      42             :  *      Responsible for OOM reporting when null is returned.  The old allocation
      43             :  *      size is passed in, in addition to the new allocation size requested.
      44             :  *  - void free_(void*)
      45             :  *  - void reportAllocOverflow() const
      46             :  *      Called on allocation overflow (that is, an allocation implicitly tried
      47             :  *      to allocate more than the available memory space -- think allocating an
      48             :  *      array of large-size objects, where N * size overflows) before null is
      49             :  *      returned.
      50             :  *  - bool checkSimulatedOOM() const
      51             :  *      Some clients generally allocate memory yet in some circumstances won't
      52             :  *      need to do so. For example, appending to a vector with a small amount of
      53             :  *      inline storage generally allocates memory, but no allocation occurs
      54             :  *      unless appending exceeds inline storage. But for testing purposes, it
      55             :  *      can be useful to treat *every* operation as allocating.
      56             :  *      Clients (such as this hypothetical append method implementation) should
      57             :  *      call this method in situations that don't allocate, but could generally,
      58             :  *      to support this. The default behavior should return true; more
      59             :  *      complicated behavior might be to return false only after a certain
      60             :  *      number of allocations-or-check-simulated-OOMs (coordinating with the
      61             :  *      other AllocPolicy methods) have occurred.
      62             :  *
      63             :  * mfbt provides (and typically uses by default) only MallocAllocPolicy, which
      64             :  * does nothing more than delegate to the malloc/alloc/free functions.
      65             :  */
      66             : 
      67             : /*
      68             :  * A policy that straightforwardly uses malloc/calloc/realloc/free and adds no
      69             :  * extra behaviors.
      70             :  */
      71           7 : class MallocAllocPolicy
      72             : {
      73             : public:
      74             :   template <typename T>
      75         231 :   T* maybe_pod_malloc(size_t aNumElems)
      76             :   {
      77         101 :     if (aNumElems & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
      78           0 :       return nullptr;
      79             :     }
      80         231 :     return static_cast<T*>(malloc(aNumElems * sizeof(T)));
      81             :   }
      82             : 
      83             :   template <typename T>
      84             :   T* maybe_pod_calloc(size_t aNumElems)
      85             :   {
      86             :     return static_cast<T*>(calloc(aNumElems, sizeof(T)));
      87             :   }
      88             : 
      89             :   template <typename T>
      90         712 :   T* maybe_pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize)
      91             :   {
      92          38 :     if (aNewSize & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
      93           0 :       return nullptr;
      94             :     }
      95         712 :     return static_cast<T*>(realloc(aPtr, aNewSize * sizeof(T)));
      96             :   }
      97             : 
      98             :   template <typename T>
      99         231 :   T* pod_malloc(size_t aNumElems)
     100             :   {
     101         231 :     return maybe_pod_malloc<T>(aNumElems);
     102             :   }
     103             : 
     104             :   template <typename T>
     105             :   T* pod_calloc(size_t aNumElems)
     106             :   {
     107             :     return maybe_pod_calloc<T>(aNumElems);
     108             :   }
     109             : 
     110             :   template <typename T>
     111         689 :   T* pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize)
     112             :   {
     113         689 :     return maybe_pod_realloc<T>(aPtr, aOldSize, aNewSize);
     114             :   }
     115             : 
     116        1302 :   void free_(void* aPtr)
     117             :   {
     118        1302 :     free(aPtr);
     119        1302 :   }
     120             : 
     121           0 :   void reportAllocOverflow() const
     122             :   {
     123           0 :   }
     124             : 
     125      255958 :   MOZ_MUST_USE bool checkSimulatedOOM() const
     126             :   {
     127      255958 :     return true;
     128             :   }
     129             : };
     130             : 
     131             : } // namespace mozilla
     132             : 
     133             : #endif /* mozilla_AllocPolicy_h */