Motown: Add ActiveMultistreamSource model in preparation for the ffmpeg demux with async I/O

services/media/framework/stages/active_multistream_source_stage.cc

Index: services/media/framework/stages/active_multistream_source_stage.cc
diff --git a/services/media/framework/stages/active_multistream_source_stage.cc b/services/media/framework/stages/active_multistream_source_stage.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a6859bbb4ba9bd8b3c78621a0b487d5279107d33
--- /dev/null
+++ b/services/media/framework/stages/active_multistream_source_stage.cc
@@ -0,0 +1,117 @@
+// 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 "services/media/framework/stages/active_multistream_source_stage.h"
+#include "services/media/framework/stages/util.h"
+
+namespace mojo {
+namespace media {
+
+ActiveMultistreamSourceStage::ActiveMultistreamSourceStage(
+    std::shared_ptr<ActiveMultistreamSource> source)
+    : source_(source) {
+  DCHECK(source);
+  outputs_.resize(source->stream_count());
+
+  supply_function_ = [this](size_t output_index, PacketPtr packet) {
+    DCHECK(!cached_packet_) << "source supplied unrequested packet";
+    DCHECK(output_index < outputs_.size());
+    DCHECK(packet);
+
+    cached_packet_output_index_ = output_index;
+    cached_packet_ = std::move(packet);
+
+    if (cached_packet_->end_of_stream()) {
+      ended_streams_++;
+    }
+
+    Output& output = outputs_[cached_packet_output_index_];
+    if (output.demand() != Demand::kNegative) {
+      RequestUpdate();
+    }
+  };
+
+  source_->SetSupplyCallback(supply_function_);
+}
+
+ActiveMultistreamSourceStage::~ActiveMultistreamSourceStage() {}
+
+size_t ActiveMultistreamSourceStage::input_count() const {
+  return 0;
+};
+
+Input& ActiveMultistreamSourceStage::input(size_t index) {
+  CHECK(false) << "input requested from source";
+  abort();
+}
+
+size_t ActiveMultistreamSourceStage::output_count() const {
+  return outputs_.size();
+}
+
+Output& ActiveMultistreamSourceStage::output(size_t index) {
+  DCHECK(index < outputs_.size());
+  return outputs_[index];
+}
+
+PayloadAllocator* ActiveMultistreamSourceStage::PrepareInput(size_t index) {
+  CHECK(false) << "PrepareInput called on source";
+  return nullptr;
+}
+
+void ActiveMultistreamSourceStage::PrepareOutput(
+    size_t index,
+    PayloadAllocator* allocator,
+    const UpstreamCallback& callback) {
+  DCHECK(index < outputs_.size());
+
+  if (allocator != nullptr) {
+    // Currently, we don't support a source that uses provided allocators. If
+    // we're provided an allocator, the output must have it so supplied packets
+    // can be copied.
+    outputs_[index].SetCopyAllocator(allocator);
+  }
+}
+
+void ActiveMultistreamSourceStage::UnprepareOutput(
+    size_t index,
+    const UpstreamCallback& callback) {
+  DCHECK(index < outputs_.size());
+  outputs_[index].SetCopyAllocator(nullptr);
+}
+
+void ActiveMultistreamSourceStage::Update(Engine* engine) {
+  DCHECK(engine);
+
+  if (cached_packet_) {
+    Output& output = outputs_[cached_packet_output_index_];
+    if (output.demand() != Demand::kNegative) {
+      // cached_packet_ is intended for an output which will accept packets.
+      output.SupplyPacket(std::move(cached_packet_), engine);
+    }
+  }
+
+  if (!cached_packet_ && HasPositiveDemand(outputs_)) {
+    // We have no cached packet and positive demand. Request a packet.
+    source_->RequestPacket();
+  }
+}
+
+void ActiveMultistreamSourceStage::FlushInput(
+    size_t index,
+    const DownstreamCallback& callback) {
+  CHECK(false) << "FlushInput called on source";
+}
+
+void ActiveMultistreamSourceStage::FlushOutput(size_t index) {
+  DCHECK(index < outputs_.size());
+  DCHECK(source_);
+  outputs_[index].Flush();
+  cached_packet_.reset(nullptr);
+  cached_packet_output_index_ = 0;
+  ended_streams_ = 0;
+}
+
+}  // namespace media
+}  // namespace mojo