Motown: Framework parts for mojo transport (producer/consumer/mediapipe) and control (audiotrack).

services/media/framework_mojo/mojo_pull_mode_producer.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 "base/logging.h"
+#include "services/media/framework_mojo/mojo_pull_mode_producer.h"
+
+namespace mojo {
+namespace media {
+
+MojoPullModeProducer::MojoPullModeProducer() :
+    state_(MediaState::UNPREPARED),
+    demand_(Demand::kNegative),
+    presentation_time_(0),
+    cached_packet_(nullptr) {}
+
+MojoPullModeProducer::~MojoPullModeProducer() {
+  base::AutoLock lock(lock_);
+}
+
+void MojoPullModeProducer::AddBinding(
+    InterfaceRequest<MediaPullModeProducer> producer) {
+  bindings_.AddBinding(this, producer.Pass());
+}
+
+void MojoPullModeProducer::GetBuffer(const GetBufferCallback& callback) {
+  if (!mojo_allocator_.initialized()) {
+    mojo_allocator_.InitNew(256 * 1024); // TODO(dalesat): Made up!
+  }
+
+  {
+    base::AutoLock lock(lock_);
+    if (state_ == MediaState::UNPREPARED) {
+      state_ = MediaState::PAUSED;
+    }
+  }
+
+  callback.Run(mojo_allocator_.GetDuplicateHandle());
+
+  DCHECK(!cached_packet_);
+  DCHECK(demand_callback_);
+  demand_callback_(Demand::kPositive);
+}
+
+void MojoPullModeProducer::PullPacket(
+    MediaPacketPtr to_release,
+    const PullPacketCallback& callback) {
+  if (to_release) {
+    // The client has piggy-backed a release on this pull request.
+    ReleasePacket(to_release.Pass());
+  }
+
+  {
+    base::AutoLock lock(lock_);
+
+    if (state_ == MediaState::UNPREPARED) {
+      // The consumer has yet to call GetBuffer. This request will have to wait.
+      pending_pulls_.push_back(callback);
+      return;
+    }
+
+    DCHECK(mojo_allocator_.initialized());
+
+    // If there are no pending requests, see if we can handle this now. If
+    // requests are pending, add the callback to the pending queue.
+    if (!pending_pulls_.empty() || !MaybeHandlePullUnsafe(callback)) {
+      pending_pulls_.push_back(callback);
+    }
+
+    DCHECK(!cached_packet_);
+  }
+
+  DCHECK(demand_callback_);
+  demand_callback_(Demand::kPositive);
+}
+
+void MojoPullModeProducer::ReleasePacket(MediaPacketPtr to_release) {
+  {
+    base::AutoLock lock(lock_);
+    uint64_t size = to_release->payload ? to_release->payload->length : 0;
+    void* payload = size == 0 ? nullptr :
+        mojo_allocator_.PtrFromOffset(to_release->payload->offset);
+
+    for (auto iterator = unreleased_packets_.begin(); true; ++iterator) {
+      if (iterator == unreleased_packets_.end()) {
+        DCHECK(false) << "released packet has bad offset";
+        break;
+      }
+
+      if ((*iterator)->payload() == payload) {

[johngro, 2016/02/23 00:49:42]

what happens if there are multiple payloads of 0 length inside this queue?  Can
we be sure that we are purging the proper one?

[dalesat, 2016/02/23 20:34:34]

I've changed this to look for a match on both payload pointer and size. This can
match the 'wrong' packet when there are multiple 0-sized packets in a row, but
that doesn't matter. The semantics of ReleasePacket is to signal that the shared
buffer region occupied by a packet may be reused. All zero-sized packets occupy
exactly the same shared buffer region, so we don't care which is released.

+        DCHECK_EQ(size, (*iterator)->size()) << "released packet has bad size";
+        unreleased_packets_.erase(iterator);
+        break;
+      }
+    }
+
+    // TODO(dalesat): What if the allocator has starved?
+  }
+
+  DCHECK(demand_callback_);
+  demand_callback_(cached_packet_ ? Demand::kNegative : Demand::kPositive);
+}
+
+PayloadAllocator* MojoPullModeProducer::allocator() {
+  return mojo_allocator_.initialized() ? &mojo_allocator_ : nullptr;
+}
+
+void MojoPullModeProducer::SetDemandCallback(
+    const DemandCallback& demand_callback) {
+  demand_callback_ = demand_callback;
+}
+
+void MojoPullModeProducer::Prime() {
+  DCHECK(demand_callback_);
+  demand_callback_(Demand::kNeutral);
+}
+
+Demand MojoPullModeProducer::SupplyPacket(PacketPtr packet) {
+  base::AutoLock lock(lock_);
+  DCHECK(demand_ != Demand::kNegative) << "packet pushed with negative demand";
+  DCHECK(state_ != MediaState::ENDED) << "packet pushed after end-of-stream";
+
+  DCHECK(!cached_packet_);
+
+  // If there's no binding on the stream, throw the packet away. This can
+  // happen if a pull client disconnects unexpectedly.
+  if (bindings_.size() == 0) {
+    demand_ = Demand::kNegative;
+    state_ = MediaState::UNPREPARED;
+    // TODO(dalesat): More shutdown?
+    return demand_;
+  }
+
+  // Accept the packet and handle pending pulls with it.
+  cached_packet_ = std::move(packet);
+
+  HandlePendingPullsUnsafe();
+
+  demand_ = cached_packet_ ? Demand::kNegative : Demand::kPositive;
+  return demand_;
+}
+
+void MojoPullModeProducer::HandlePendingPullsUnsafe() {
+  lock_.AssertAcquired();
+
+  while (!pending_pulls_.empty()) {
+    DCHECK(mojo_allocator_.initialized());
+
+    if (MaybeHandlePullUnsafe(pending_pulls_.front())) {
+      pending_pulls_.pop_front();
+    } else {
+      break;
+    }
+  }
+}
+
+bool MojoPullModeProducer::MaybeHandlePullUnsafe(
+    const PullPacketCallback& callback) {
+  DCHECK(!callback.is_null());
+  lock_.AssertAcquired();
+
+  if (state_ == MediaState::ENDED) {

[johngro, 2016/02/23 00:49:42]

If we are in State::ENDED, and there are N pending pulls, and
HandlePendingPullsUnsafe is called, this is going to create and send N empty EOS
packets down the line.  Is this the right thing to do?  This seems like a case
where we can end up sticking multiple 0 length packets into the unreleased
queue.

Also, if we are ended, why are we holding onto the cached supplied packet?  Can
we just release it at this point (and ASSERT that our demand is Negative while
we do?)

[dalesat, 2016/02/23 20:34:34]

This behavior is correct, I think. Keep in mind that this is the pull-mode
producer, which isn't used for connecting to a consumer. This method is called
both from HandlePendingPullsUnsafe and from PullPacket, so we don't put packets
in the pending queue once we know we've hit EOS.

+    // At end-of-stream. Respond with empty end-of-stream packet.
+    HandlePullWithPacketUnsafe(
+        callback,
+        Packet::CreateEndOfStream(presentation_time_));
+    return true;
+  }
+
+  if (!cached_packet_) {
+    // Waiting for packet or end-of-stream indication.
+    return false;
+  }
+
+  HandlePullWithPacketUnsafe(callback, std::move(cached_packet_));
+  return true;
+}
+
+void MojoPullModeProducer::HandlePullWithPacketUnsafe(
+    const PullPacketCallback& callback,
+    PacketPtr packet) {
+  DCHECK(packet);
+  lock_.AssertAcquired();
+
+  // TODO(dalesat): Use TaskRunner for this callback.
+  callback.Run(CreateMediaPacket(packet));
+  unreleased_packets_.push_back(std::move(packet));
+}
+
+MediaPacketPtr MojoPullModeProducer::CreateMediaPacket(
+    const PacketPtr& packet) {
+  DCHECK(packet);
+
+  MediaPacketRegionPtr region = MediaPacketRegion::New();
+  region->offset = mojo_allocator_.OffsetFromPtr(packet->payload());
+  region->length = packet->size();
+
+  MediaPacketPtr media_packet = MediaPacket::New();
+  media_packet->pts = packet->presentation_time();
+  media_packet->duration = packet->duration();
+  media_packet->end_of_stream = packet->end_of_stream();
+  media_packet->payload = region.Pass();
+  presentation_time_ = packet->presentation_time() + packet->duration();
+
+  return media_packet.Pass();
+}
+
+} // namespace media
+} // namespace mojo