Bug 891177 - Add AllocPolicy.h to define an implementation policy con…

…cept for use in mfbt. r=terrence

--HG--
extra : rebase_source : f6336b5ba3298bbf9c5418b4e9d993b9173f7926

js/src/jsalloc.h

@@ -4,9 +4,13 @@
  * 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/. */
 
+/* JS allocation policies. */
+
 #ifndef jsalloc_h
 #define jsalloc_h
 
+#include "mozilla/AllocPolicy.h"
+
 #include "js/Utility.h"
 
 struct JSContext;
@@ -15,23 +19,6 @@ namespace js {
 
 class ContextFriendFields;
 
-/*
- * Allocation policies.  These model the concept:
- *  - public copy constructor, assignment, destructor
- *  - void *malloc_(size_t)
- *      Responsible for OOM reporting on NULL return value.
- *  - void *calloc_(size_t)
- *      Responsible for OOM reporting on NULL return value.
- *  - void *realloc_(size_t)
- *      Responsible for OOM reporting on NULL return value.
- *      The *used* bytes of the previous buffer is passed in
- *      (rather than the old allocation size), in addition to
- *      the *new* allocation size requested.
- *  - void free_(void *)
- *  - reportAllocOverflow()
- *      Called on overflow before the container returns NULL.
- */
-
 /* Policy for using system memory functions and doing no error reporting. */
 class SystemAllocPolicy
 {

mfbt/AllocPolicy.h

@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 <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
+ *  - void* malloc_(size_t)
+ *      Responsible for OOM reporting when null is returned.
+ *  - void* calloc_(size_t)
+ *      Responsible for OOM reporting when null is returned.
+ *  - void* realloc_(void*, size_t, size_t)
+ *      Responsible for OOM reporting when null is returned.  The *used* bytes
+ *      of the previous buffer is passed in (rather than the old allocation
+ *      size), 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.
+ *
+ * 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:
+    void* malloc_(size_t bytes) { return malloc(bytes); }
+    void* calloc_(size_t bytes) { return calloc(bytes, 1); }
+    void* realloc_(void* p, size_t oldBytes, size_t bytes) { return realloc(p, bytes); }
+    void free_(void* p) { free(p); }
+    void reportAllocOverflow() const {}
+};
+
+
+} // namespace mozilla
+
+#endif // mozilla_AllocPolicy_h_

mfbt/exported_headers.mk

@@ -9,6 +9,7 @@
 EXPORTS_NAMESPACES += mozilla
 
 EXPORTS_mozilla += \
+  AllocPolicy.h \
   Assertions.h \
   Atomics.h \
   Attributes.h \