1 files changed, 54 insertions, 0 deletions
diff --git a/dom/ipc/MemMapSnapshot.h b/dom/ipc/MemMapSnapshot.h
new file mode 100644
index 0000000000..12b4d353ad
--- /dev/null
+++ b/dom/ipc/MemMapSnapshot.h
@@ -0,0 +1,54 @@
+/* -*- 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/. */
+
+#ifndef dom_ipc_MemMapSnapshot_h
+#define dom_ipc_MemMapSnapshot_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/RangedPtr.h"
+#include "mozilla/Result.h"
+#include "base/shared_memory.h"
+#include "ErrorList.h"
+
+namespace mozilla {
+namespace loader {
+class AutoMemMap;
+}
+
+namespace ipc {
+
+/**
+ * A helper class for creating a read-only snapshot of memory-mapped data.
+ *
+ * The Init() method initializes a read-write memory mapped region of the given
+ * size, which can be initialized with arbitrary data. The Finalize() method
+ * remaps that region as read-only (and backs it with a read-only file
+ * descriptor), and initializes an AutoMemMap with the new contents.
+ *
+ * The file descriptor for the resulting AutoMemMap can be shared among
+ * processes, to safely access a shared, read-only copy of the data snapshot.
+ */
+class MOZ_RAII MemMapSnapshot {
+ public:
+  Result<Ok, nsresult> Init(size_t aSize);
+  Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap);
+
+  template <typename T>
+  RangedPtr<T> Get() {
+    MOZ_ASSERT(mInitialized);
+    return {static_cast<T*>(mMem.memory()), mMem.max_size() / sizeof(T)};
+  }
+
+ private:
+  base::SharedMemory mMem;
+  bool mInitialized = false;
+};
+
+}  // namespace ipc
+}  // namespace mozilla
+
+#endif  // dom_ipc_MemMapSnapshot_h