mfbt/AllocPolicy.h
author Dustin J. Mitchell <dustin@mozilla.com>
Wed, 07 Sep 2016 00:10:51 +0000
changeset 354971 1627fd341fc154d4fb771366676b7101204362df
parent 338367 010987e0dc81f5021cf3b200ceab78d742783d21
child 419590 0318e26f75c82bf5c0938e1b616f623e2f55a5f9
permissions -rw-r--r--
Bug 1286075: allow optimization of tasks whose dependencies have not been optimized; r=armenzg MikeLing initially did this in bug 1287018. The intent of this conditional was to make optimization faster by not even checking most tasks, based on the assumption that if the prerequisite to a task has changed (for example, a docker image or a build), then naturally we will want to execute that task. However, as we have developed actual optimization methods, this has proven not to be the case: we might want to optimize a test out if its inputs have not changed, even if a new installer has been built. Similarly, SETA may optimize tasks out even if their inputs have changed. MozReview-Commit-ID: LgHET3Z84GB

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
 * An allocation policy concept, usable for structures and algorithms to
 * control how memory is allocated and how failures are handled.
 */

#ifndef mozilla_AllocPolicy_h
#define mozilla_AllocPolicy_h

#include "mozilla/Attributes.h"
#include "mozilla/TemplateLib.h"

#include <stddef.h>
#include <stdlib.h>

namespace mozilla {

/*
 * Allocation policies are used to implement the standard allocation behaviors
 * in a customizable way.  Additionally, custom behaviors may be added to these
 * behaviors, such as additionally reporting an error through an out-of-band
 * mechanism when OOM occurs.  The concept modeled here is as follows:
 *
 *  - public copy constructor, assignment, destructor
 *  - template <typename T> T* maybe_pod_malloc(size_t)
 *      Fallible, but doesn't report an error on OOM.
 *  - template <typename T> T* maybe_pod_calloc(size_t)
 *      Fallible, but doesn't report an error on OOM.
 *  - template <typename T> T* maybe_pod_realloc(T*, size_t, size_t)
 *      Fallible, but doesn't report an error on OOM.  The old allocation
 *      size is passed in, in addition to the new allocation size requested.
 *  - template <typename T> T* pod_malloc(size_t)
 *      Responsible for OOM reporting when null is returned.
 *  - template <typename T> T* pod_calloc(size_t)
 *      Responsible for OOM reporting when null is returned.
 *  - template <typename T> T* pod_realloc(T*, size_t, size_t)
 *      Responsible for OOM reporting when null is returned.  The old allocation
 *      size is passed in, in addition to the new allocation size requested.
 *  - void free_(void*)
 *  - void reportAllocOverflow() const
 *      Called on allocation overflow (that is, an allocation implicitly tried
 *      to allocate more than the available memory space -- think allocating an
 *      array of large-size objects, where N * size overflows) before null is
 *      returned.
 *  - bool checkSimulatedOOM() const
 *      Some clients generally allocate memory yet in some circumstances won't
 *      need to do so. For example, appending to a vector with a small amount of
 *      inline storage generally allocates memory, but no allocation occurs
 *      unless appending exceeds inline storage. But for testing purposes, it
 *      can be useful to treat *every* operation as allocating.
 *      Clients (such as this hypothetical append method implementation) should
 *      call this method in situations that don't allocate, but could generally,
 *      to support this. The default behavior should return true; more
 *      complicated behavior might be to return false only after a certain
 *      number of allocations-or-check-simulated-OOMs (coordinating with the
 *      other AllocPolicy methods) have occurred.
 *
 * mfbt provides (and typically uses by default) only MallocAllocPolicy, which
 * does nothing more than delegate to the malloc/alloc/free functions.
 */

/*
 * A policy that straightforwardly uses malloc/calloc/realloc/free and adds no
 * extra behaviors.
 */
class MallocAllocPolicy
{
public:
  template <typename T>
  T* maybe_pod_malloc(size_t aNumElems)
  {
    if (aNumElems & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
      return nullptr;
    }
    return static_cast<T*>(malloc(aNumElems * sizeof(T)));
  }

  template <typename T>
  T* maybe_pod_calloc(size_t aNumElems)
  {
    return static_cast<T*>(calloc(aNumElems, sizeof(T)));
  }

  template <typename T>
  T* maybe_pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize)
  {
    if (aNewSize & mozilla::tl::MulOverflowMask<sizeof(T)>::value) {
      return nullptr;
    }
    return static_cast<T*>(realloc(aPtr, aNewSize * sizeof(T)));
  }

  template <typename T>
  T* pod_malloc(size_t aNumElems)
  {
    return maybe_pod_malloc<T>(aNumElems);
  }

  template <typename T>
  T* pod_calloc(size_t aNumElems)
  {
    return maybe_pod_calloc<T>(aNumElems);
  }

  template <typename T>
  T* pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize)
  {
    return maybe_pod_realloc<T>(aPtr, aOldSize, aNewSize);
  }

  void free_(void* aPtr)
  {
    free(aPtr);
  }

  void reportAllocOverflow() const
  {
  }

  MOZ_MUST_USE bool checkSimulatedOOM() const
  {
    return true;
  }
};

} // namespace mozilla

#endif /* mozilla_AllocPolicy_h */