Blimp: Add BlobChannelReceiver and bindings interface.

blimp/net/blob_channel/blob_channel_receiver.h

+// 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.
+
+#ifndef BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_
+#define BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "blimp/common/blob_cache/blob_cache.h"
+#include "blimp/net/blimp_message_processor.h"
+#include "blimp/net/blimp_net_export.h"
+#include "blimp/net/blob_channel/blob_channel_bindings.h"
+
+namespace blimp {
+
+class BlobCache;
+
+class BLIMP_NET_EXPORT BlobChannelReceiver
+    : public BlobReceiverBindings::Delegate {
+ public:
+  typedef base::Callback<void(const std::string&,
+                              scoped_refptr<RefCountedVector>)>
+      BlobReceivedCallback;
+
+  // Caller must ensure that |cache| and |bindings| outlive |this|.
+  BlobChannelReceiver(BlobCache* cache, BlobReceiverBindings* bindings);

[Wez, 2016/04/15 17:27:43]

See comments on BlobChannelSender re the naming & structure of these APIs.

[Kevin M, 2016/04/15 23:53:43]

Done.

+  ~BlobChannelReceiver();
+
+  // Gets a blob from the BlobChannel, first pulling from a local cache and
+  // falling back to requesting the data from a remote cache.
+  // If blob |id| is already available, then it is returned synchronously and
+  // |callback| is discarded.

[Wez, 2016/04/15 17:27:43]

Do we need the synchronous path? Or can we just have the asynchronous path but
require that the current impl call the callback before returning?

[Kevin M, 2016/04/15 23:53:44]

The synchronous path is pretty essential for getting bits out to Skia - the
caller gets the image bits synchronously and we don't have the ability to slip
them in asynchronously at arbitrary points after rendering has completed.

+  // If blob |id| has not yet been received, then a null refptr is returned,
+  // and |callback| is invoked later when the blob arrives.
+  // Can be called on any thread. Holds |lock_|.

[Wez, 2016/04/15 17:27:43]

This object isn't ref-counted; how can it "be called on any thread"?  Is the
caller required to ensure some special lifetime constraints of this class?

[Kevin M, 2016/04/15 23:53:44]

This is meant to support concurrent calls by a number of raster working threads.
I'm not sure if we have guarantees that the raster threads will finish execution
before the BlimpClientSession is torn down, but it _seems_ like a safe bet? O_o

[Wez, 2016/04/18 22:44:47]

Best to state such assumptions up-front!

+  scoped_refptr<RefCountedVector> Get(const std::string& id,
+                                      const BlobReceivedCallback& callback);
+
+ protected:
+  // BlobReceiverBindings::Delegate implementation.
+  // Holds |lock_|.
+  void OnBlobReceived(const std::string& id,
+                      std::unique_ptr<std::vector<uint8_t>> data) override;
+
+ private:
+  BlobCache* cache_ = nullptr;
+  BlobReceiverBindings* bindings_ = nullptr;
+
+  // Callbacks waiting to be invoked on read completion, keyed by blob ID.
+  std::multimap<std::string, BlobReceivedCallback> active_read_callbacks_;
+
+  // Guards concurrent access to |cache_| and |active_read_callbacks_|.
+  base::Lock lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlobChannelReceiver);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_RECEIVER_H_