Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/renderer/blob_channel_sender_proxy.cc

Index: blimp/engine/renderer/blob_channel_sender_proxy.cc
diff --git a/blimp/engine/renderer/blob_channel_sender_proxy.cc b/blimp/engine/renderer/blob_channel_sender_proxy.cc
index 8b689d36c73dd840878105bb72a926845ebe97be..79c8c2f5465c1a02dc8553bff062625fac6f8e92 100644
--- a/blimp/engine/renderer/blob_channel_sender_proxy.cc
+++ b/blimp/engine/renderer/blob_channel_sender_proxy.cc
@@ -4,6 +4,7 @@
 
 #include "blimp/engine/renderer/blob_channel_sender_proxy.h"
 
+#include "blimp/common/blob_cache/id_util.h"
 #include "content/public/common/service_registry.h"
 #include "content/public/renderer/render_thread.h"
 
@@ -19,30 +20,96 @@ mojom::BlobChannelPtr GetConnectedBlobChannel() {
   return blob_channel_ptr;
 }
 
+// Manages the creation and lifetime of Mojo shared memory buffers for blobs.
+// Cleans up the shared memory state when deleted.
+// The SharedMemoryBlob must not be deleted until the data consumer has
+// acknowledged that it is finished using the buffer.
+class SharedMemoryBlob {
+ public:
+  explicit SharedMemoryBlob(BlobDataPtr data);
+  ~SharedMemoryBlob();
+
+  mojo::ScopedSharedBufferHandle take_remote_handle();
+
+ private:
+  mojo::ScopedSharedBufferHandle local_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryBlob);
+};
+
+SharedMemoryBlob::SharedMemoryBlob(BlobDataPtr data) {
+  local_handle_ = mojo::SharedBufferHandle::Create(data->data.size());

[dcheng, 2016/06/25 01:06:31]

Any idea how likely it is to run into shared memory limits with this?

[Kevin M, 2016/06/27 17:31:12]

Added size check. Done.

+  CHECK(local_handle_.is_valid()) << "Mojo error when creating shared buffer.";

[dcheng, 2016/06/25 01:06:31]

IMO, DCHECK() if this is something that should "never happen" or if () if it can
happen. CHECK() should be quite rare.

[Kevin M, 2016/06/27 17:31:12]

Done.

+
+  auto mapped = local_handle_->Map(data->data.size());
+  CHECK(mapped) << "Mojo error when memory mapping shared buffer.";
+  memcpy(mapped.get(), data->data.data(), data->data.size());
+}
+
+SharedMemoryBlob::~SharedMemoryBlob() {}
+
+mojo::ScopedSharedBufferHandle SharedMemoryBlob::take_remote_handle() {

[dcheng, 2016/06/25 01:06:31]

Take implies that this is destructive, but I don't think it is?

Style guide also dictates NamingLikeThis for this sort of method.

[Kevin M, 2016/06/27 17:31:12]

Done.

+  auto remote_handle =
+      local_handle_->Clone(mojo::SharedBufferHandle::AccessMode::READ_ONLY);
+  CHECK(remote_handle.is_valid())
+      << "Mojo error when creating read-only buffer handle.";
+  return remote_handle;
+}
+
 }  // namespace
 
 BlobChannelSenderProxy::BlobChannelSenderProxy()
-    : blob_channel_(GetConnectedBlobChannel()) {}
+    : BlobChannelSenderProxy(GetConnectedBlobChannel()) {}
 
 BlobChannelSenderProxy::~BlobChannelSenderProxy() {}
 
+BlobChannelSenderProxy::BlobChannelSenderProxy(
+    mojom::BlobChannelPtr blob_channel)
+    : blob_channel_(std::move(blob_channel)) {}
+
+// static
+std::unique_ptr<BlobChannelSenderProxy> BlobChannelSenderProxy::CreateForTest(
+    mojom::BlobChannelPtr blob_channel) {
+  return base::WrapUnique(new BlobChannelSenderProxy(std::move(blob_channel)));

[dcheng, 2016/06/25 01:06:31]

Nit: base::MakeUnique

[Kevin M, 2016/06/27 17:31:12]

This is a cool method, but N/A in this case. The ctor that this method is
calling is private, and therefore is inaccessible to MakeUnique().

+}
+
 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;
+  auto found = replication_state_.find(id);
+  return found != replication_state_.end() && found->second;
 }
 
 void BlobChannelSenderProxy::PutBlob(const BlobId& id, BlobDataPtr data) {
-  DCHECK(!IsInEngineCache(id));

[dcheng, 2016/06/25 01:06:31]

How come these (and other checks) changed from DCHECKs()?

[Kevin M, 2016/06/27 17:31:12]

So that these conditions are correctly handled by release builds, and so that we
can develop unit tests for it.

[dcheng, 2016/06/28 06:26:18]

Right, but violating these conditions means that the consumer of this class is
violating the expected preconditions, right? Can we fix the consumer, since it's
all in the same process?

[Kevin M, 2016/06/28 18:18:53]

Good point... done.

+  if (IsInEngineCache(id)) {
+    DLOG(FATAL) << "Redundant blob put attempted: " << BlobIdToString(id);
+    return;
+  }
+
+  size_t size = data->data.size();
+  if (size == 0) {
+    DLOG(FATAL) << "Zero length blob sent: " << BlobIdToString(id);
+    return;
+  }
 
   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);
 }
 
 void BlobChannelSenderProxy::DeliverBlob(const std::string& id) {
-  DCHECK(!IsInClientCache(id));
+  if (!IsInEngineCache(id)) {
+    DLOG(FATAL) << "Attempted to deliver an invalid blob: "
+                << BlobIdToString(id);
+    return;
+  }
+  if (IsInClientCache(id)) {
+    DVLOG(1) << "Blob is already in the remote cache:" << BlobIdToString(id);
+    return;
+  }
 
   // We assume that the client will have the blob if we push it.
   // TODO(kmarshall): Revisit this assumption when asynchronous blob transport