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/* -*- 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
/*
* 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/Assertions.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.
* - template <typename T> void free_(T*, size_t)
* The capacity passed in must match the old allocation size.
* - template <typename T> void free_(T*)
* Frees a buffer without knowing its allocated size. This might not be
* implemented by allocation policies that need the allocation size.
* - 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);
}
template <typename T>
void free_(T* aPtr, size_t aNumElems = 0) {
free(aPtr);
}
void reportAllocOverflow() const {}
[[nodiscard]] bool checkSimulatedOOM() const { return true; }
};
/*
* A policy which always fails to allocate memory, returning nullptr. Methods
* which expect an existing allocation assert.
*
* This type should be used in situations where you want to use a MFBT type with
* inline storage, and don't want to allow it to allocate on the heap.
*/
class NeverAllocPolicy {
public:
template <typename T>
T* maybe_pod_malloc(size_t aNumElems) {
return nullptr;
}
template <typename T>
T* maybe_pod_calloc(size_t aNumElems) {
return nullptr;
}
template <typename T>
T* maybe_pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize) {
MOZ_CRASH("NeverAllocPolicy::maybe_pod_realloc");
}
template <typename T>
T* pod_malloc(size_t aNumElems) {
return nullptr;
}
template <typename T>
T* pod_calloc(size_t aNumElems) {
return nullptr;
}
template <typename T>
T* pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize) {
MOZ_CRASH("NeverAllocPolicy::pod_realloc");
}
template <typename T>
void free_(T* aPtr, size_t aNumElems = 0) {
MOZ_CRASH("NeverAllocPolicy::free_");
}
void reportAllocOverflow() const {}
[[nodiscard]] bool checkSimulatedOOM() const { return true; }
};
} // namespace mozilla
#endif /* mozilla_AllocPolicy_h */