diff -r 000000000000 -r 6474c204b198 ipc/glue/SharedMemory.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/glue/SharedMemory.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,111 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* 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/. */
+
+#ifndef mozilla_ipc_SharedMemory_h
+#define mozilla_ipc_SharedMemory_h
+
+#include "nsDebug.h"
+#include "nsISupportsImpl.h"    // NS_INLINE_DECL_REFCOUNTING
+#include "mozilla/Attributes.h"
+
+//
+// This is a low-level wrapper around platform shared memory.  Don't
+// use it directly; use Shmem allocated through IPDL interfaces.
+//
+namespace {
+enum Rights {
+  RightsNone = 0,
+  RightsRead = 1 << 0,
+  RightsWrite = 1 << 1
+};
+}
+
+namespace mozilla {
+namespace ipc {
+
+class SharedMemory
+{
+public:
+  virtual ~SharedMemory()
+  {
+    MOZ_COUNT_DTOR(SharedMemory);
+    Unmapped();
+    Destroyed();
+  }
+
+  enum SharedMemoryType {
+    TYPE_BASIC,
+    TYPE_SYSV,
+    TYPE_UNKNOWN
+  };
+
+  size_t Size() const { return mMappedSize; }
+
+  virtual void* memory() const = 0;
+
+  virtual bool Create(size_t size) = 0;
+  virtual bool Map(size_t nBytes) = 0;
+
+  virtual SharedMemoryType Type() const = 0;
+
+  void
+  Protect(char* aAddr, size_t aSize, int aRights)
+  {
+    char* memStart = reinterpret_cast<char*>(memory());
+    if (!memStart)
+      NS_RUNTIMEABORT("SharedMemory region points at NULL!");
+    char* memEnd = memStart + Size();
+
+    char* protStart = aAddr;
+    if (!protStart)
+      NS_RUNTIMEABORT("trying to Protect() a NULL region!");
+    char* protEnd = protStart + aSize;
+
+    if (!(memStart <= protStart
+          && protEnd <= memEnd))
+      NS_RUNTIMEABORT("attempt to Protect() a region outside this SharedMemory");
+
+    // checks alignment etc.
+    SystemProtect(aAddr, aSize, aRights);
+  }
+
+  NS_INLINE_DECL_REFCOUNTING(SharedMemory)
+
+  static void SystemProtect(char* aAddr, size_t aSize, int aRights);
+  static size_t SystemPageSize();
+  static size_t PageAlignedSize(size_t aSize);
+
+protected:
+  SharedMemory();
+
+  // Implementations should call these methods on shmem usage changes,
+  // but *only if* the OS-specific calls are known to have succeeded.
+  // The methods are expected to be called in the pattern
+  //
+  //   Created (Mapped Unmapped)* Destroy
+  //
+  // but this isn't checked.
+  void Created(size_t aNBytes);
+  void Mapped(size_t aNBytes);
+  void Unmapped();
+  void Destroyed();
+
+  // The size of the shmem region requested in Create(), if
+  // successful.  SharedMemory instances that are opened from a
+  // foreign handle have an alloc size of 0, even though they have
+  // access to the alloc-size information.
+  size_t mAllocSize;
+  // The size of the region mapped in Map(), if successful.  All
+  // SharedMemorys that are mapped have a non-zero mapped size.
+  size_t mMappedSize;
+};
+
+} // namespace ipc
+} // namespace mozilla
+
+
+#endif // ifndef mozilla_ipc_SharedMemory_h