Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/renderer/blob_channel_sender_proxy.cc

 // Copyright 2016 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 "blimp/engine/renderer/blob_channel_sender_proxy.h"
 
 #include "content/public/common/service_registry.h"
 #include "content/public/renderer/render_thread.h"
 
 namespace blimp {
 namespace engine {
 namespace {
 
 mojom::BlobChannelPtr GetConnectedBlobChannel() {
   mojom::BlobChannelPtr blob_channel_ptr;
   content::RenderThread::Get()->GetServiceRegistry()->ConnectToRemoteService(
       mojo::GetProxy(&blob_channel_ptr));
   CHECK(blob_channel_ptr) << "Could not connect to BlobChannel Mojo service.";
   return blob_channel_ptr;
 }
 
+// Manages the creation and lifetime of Mojo shared memory buffers for blobs.
+// Cleans up the shared memory state when deleted.
+// Caller is responsible for ensuring that |this| is not deleted until the
+// remote side has acknowledged that it is finished using the buffer.
+class SharedMemoryBlob {
+ public:
+  explicit SharedMemoryBlob(BlobDataPtr data) {
+    mojo::ScopedSharedBufferHandle local_handle;
+    MojoResult result =
+        mojo::CreateSharedBuffer(NULL, data->data.size(), &local_handle);
+    CHECK_EQ(MOJO_RESULT_OK, result)
+        << "Mojo error when creating shared buffer: " << result;
+
+    result = mojo::MapBuffer(local_handle.get(), 0, data->data.size(),
+                             &mapped_data_, MOJO_MAP_BUFFER_FLAG_NONE);
+    CHECK_EQ(MOJO_RESULT_OK, result)
+        << "Mojo error when memory mapping shared buffer: " << result;
+    memcpy(mapped_data_, data->data.data(), data->data.size());
+
+    // Create read-only handle for browser-side consumption.
+    MojoDuplicateBufferHandleOptions options{
+        sizeof(MojoDuplicateBufferHandleOptions),
+        MOJO_DUPLICATE_BUFFER_HANDLE_OPTIONS_FLAG_READ_ONLY};
+    result =
+        mojo::DuplicateBuffer(local_handle.get(), &options, &remote_handle_);
+    CHECK_EQ(MOJO_RESULT_OK, result)
+        << "Mojo error when creating read-only buffer handle.";
+    DCHECK(remote_handle_.is_valid());
+  }
+
+  ~SharedMemoryBlob() {
+    MojoResult result = mojo::UnmapBuffer(mapped_data_);
+    CHECK_EQ(MOJO_RESULT_OK, result);
+  }
+
+  mojo::ScopedSharedBufferHandle take_remote_handle() {
+    return std::move(remote_handle_);
+  }
+
+ private:
+  // Pointer to shared memory buffer.
+  void* mapped_data_;
+
+  // Handle to be passed to the remote end of the BlobChannel Mojo service.
+  mojo::ScopedSharedBufferHandle remote_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryBlob);
+};
+
+void PutComplete(std::unique_ptr<SharedMemoryBlob>) {
+  // Allow the blob to go out of scope and be deleted.
+}
+
 }  // namespace
 
 BlobChannelSenderProxy::BlobChannelSenderProxy()
     : blob_channel_(GetConnectedBlobChannel()) {}
 
 BlobChannelSenderProxy::~BlobChannelSenderProxy() {}
 
 bool BlobChannelSenderProxy::IsInEngineCache(const std::string& id) const {
   return replication_state_.find(id) != replication_state_.end();
 }
 
 bool BlobChannelSenderProxy::IsInClientCache(const std::string& id) const {
   return replication_state_.find(id)->second;
 }
 
 void BlobChannelSenderProxy::PutBlob(const BlobId& id, BlobDataPtr data) {
   DCHECK(!IsInEngineCache(id));
 
+  if (data->data.size() == 0) {
+    return;
+  }
+
+  size_t size = data->data.size();
   replication_state_[id] = false;
-  blob_channel_->PutBlob(id, data->data);
+  std::unique_ptr<SharedMemoryBlob> shared_mem_blob(
+      new SharedMemoryBlob(std::move(data)));
+  blob_channel_->PutBlob(
+      id, shared_mem_blob->take_remote_handle(), size,
+      base::Bind(&PutComplete, base::Passed(std::move(shared_mem_blob))));
 }
 
 void BlobChannelSenderProxy::DeliverBlob(const std::string& id) {
   DCHECK(!IsInClientCache(id));
 
   // We assume that the client will have the blob if we push it.
   // TODO(kmarshall): Revisit this assumption when asynchronous blob transport
   // is supported.
   replication_state_[id] = true;
 
   blob_channel_->DeliverBlob(id);
 }
 
 }  // namespace engine
 }  // namespace blimp