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diff --git a/mfbt/AllocPolicy.h b/mfbt/AllocPolicy.h
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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
+ * 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/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 */