Implements JS bindings for mojo shared buffer.

third_party/WebKit/Source/core/mojo/MojoHandle.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/mojo/MojoHandle.h"
 
 #include "bindings/core/v8/ArrayBufferOrArrayBufferView.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "core/dom/DOMArrayBuffer.h"
 #include "core/dom/DOMArrayBufferView.h"
+#include "core/mojo/MojoMapBufferResult.h"
 #include "core/mojo/MojoReadMessageFlags.h"
 #include "core/mojo/MojoReadMessageResult.h"
+#include "core/mojo/MojoSharedBuffer.h"
 #include "core/mojo/MojoWatcher.h"
 
 // Mojo messages typically do not contain many handles. In fact most
 // messages do not contain any handle. An inline capacity of 4 should avoid
 // heap allocation in vast majority of cases.
 static const size_t kHandleVectorInlineCapacity = 4;
 
 namespace blink {
 
 MojoHandle* MojoHandle::create(mojo::ScopedHandle handle) {
@@ skipping 62 matching lines @@
   for (size_t i = 0; i < numHandles; ++i) {
     handles[i] =
         MojoHandle::create(mojo::MakeScopedHandle(mojo::Handle(rawHandles[i])));
   }
 
   resultDict.setResult(result);
   resultDict.setBuffer(buffer);
   resultDict.setHandles(handles);
 }
 
+void MojoHandle::mapBuffer(unsigned offset,
+                           unsigned numBytes,
+                           MojoMapBufferResult& resultDict) {
+  void* data = nullptr;
+  MojoResult result = MojoMapBuffer(m_handle->value(), offset, numBytes, &data,
+                                    MOJO_MAP_BUFFER_FLAG_NONE);
+  resultDict.setResult(result);
+  if (result == MOJO_RESULT_OK) {
+    // TODO(alokp): Check if we need to track all mappings so that they can be

[alokp, 2017/02/27 19:50:45]

yzshen@: The current js-binding implementation does not track the various
mappings for a shared buffer. But I think we should. Otherwise the mappings
would keep holding on to invalid memory when the handle gets closed. I am
assuming that shared buffer associated with a handle gets destroyed on
MojoClose?

[yzshen1, 2017/02/27 21:05:27]

The lifetime of mappings is not tied to that of the mojo handle. Actually mojo
keeps a duplicated shared memory handle for each mapping internally.

+    // unmapped when this handle is closed.
+    resultDict.setBuffer(new MojoSharedBuffer(data, numBytes));
+  }
+}
+
 }  // namespace blink