Move Pipeline permanent callbacks into Pipeline::Client interface.

media/base/pipeline_impl.cc

 // Copyright (c) 2012 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 "media/base/pipeline_impl.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram.h"
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
-#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/thread_task_runner_handle.h"
+#include "media/base/bind_to_current_loop.h"
 #include "media/base/media_log.h"
 #include "media/base/media_switches.h"
 #include "media/base/renderer.h"
 #include "media/base/text_renderer.h"
 #include "media/base/text_track_config.h"
 #include "media/base/timestamp_constants.h"
 #include "media/base/video_decoder_config.h"
 
 using base::TimeDelta;
 
 namespace media {
 
 PipelineImpl::PipelineImpl(
-    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+    const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner,
     MediaLog* media_log)
-    : task_runner_(task_runner),
+    : main_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      media_task_runner_(media_task_runner),
       media_log_(media_log),
       running_(false),
       did_loading_progress_(false),
       volume_(1.0f),
       playback_rate_(0.0),
       status_(PIPELINE_OK),
       state_(kCreated),
       suspend_timestamp_(kNoTimestamp()),
       renderer_ended_(false),
       text_renderer_ended_(false),
       demuxer_(NULL),
       cdm_context_(nullptr),
       weak_factory_(this) {
   weak_this_ = weak_factory_.GetWeakPtr();
   media_log_->AddEvent(media_log_->CreatePipelineStateChangedEvent(kCreated));
 }
 
 PipelineImpl::~PipelineImpl() {
-  DCHECK(thread_checker_.CalledOnValidThread())
+  DCHECK(main_task_runner_->BelongsToCurrentThread())
       << "Pipeline must be destroyed on same thread that created it";
   DCHECK(!running_) << "Stop() must complete before destroying object";
-  DCHECK(stop_cb_.is_null());
   DCHECK(seek_cb_.is_null());
 }
 
 void PipelineImpl::Start(Demuxer* demuxer,
                          std::unique_ptr<Renderer> renderer,
-                         const base::Closure& ended_cb,
-                         const PipelineStatusCB& error_cb,
-                         const PipelineStatusCB& seek_cb,
-                         const PipelineMetadataCB& metadata_cb,
-                         const BufferingStateCB& buffering_state_cb,
-                         const base::Closure& duration_change_cb,
-                         const AddTextTrackCB& add_text_track_cb,
-                         const base::Closure& waiting_for_decryption_key_cb) {
-  DCHECK(!ended_cb.is_null());
-  DCHECK(!error_cb.is_null());
+                         Client* client,
+                         const PipelineStatusCB& seek_cb) {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+  DCHECK(client);
   DCHECK(!seek_cb.is_null());
-  DCHECK(!metadata_cb.is_null());
-  DCHECK(!buffering_state_cb.is_null());
 
   base::AutoLock auto_lock(lock_);
   CHECK(!running_) << "Media pipeline is already running";
   running_ = true;
 
   demuxer_ = demuxer;
   renderer_ = std::move(renderer);
-  ended_cb_ = ended_cb;
-  error_cb_ = error_cb;
-  seek_cb_ = seek_cb;
-  metadata_cb_ = metadata_cb;
-  buffering_state_cb_ = buffering_state_cb;
-  duration_change_cb_ = duration_change_cb;
-  add_text_track_cb_ = add_text_track_cb;
-  waiting_for_decryption_key_cb_ = waiting_for_decryption_key_cb;
-
-  task_runner_->PostTask(FROM_HERE,
-                         base::Bind(&PipelineImpl::StartTask, weak_this_));
+  client_weak_factory_.reset(new base::WeakPtrFactory<Client>(client));
+  seek_cb_ = media::BindToCurrentLoop(seek_cb);
+  media_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PipelineImpl::StartTask, weak_this_));
 }
 
-void PipelineImpl::Stop(const base::Closure& stop_cb) {
+void PipelineImpl::Stop() {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
   DVLOG(2) << __FUNCTION__;
-  task_runner_->PostTask(
-      FROM_HERE, base::Bind(&PipelineImpl::StopTask, weak_this_, stop_cb));
+
+  if (media_task_runner_ != main_task_runner_) {
+    // This path is executed by production code where the two task runners -
+    // main and media - live on different threads.
+    // TODO(alokp): It may be possible to not have to wait for StopTask by
+    // moving the members accessed on media thread into a class/struct and
+    // DeleteSoon the instance on the media thread.
+    base::WaitableEvent waiter(false, false);
+    base::Closure stop_cb =
+        base::Bind(&base::WaitableEvent::Signal, base::Unretained(&waiter));
+    media_task_runner_->PostTask(

[sandersd (OOO until July 31), 2016/05/02 22:45:52]

At a minimum, DCHECK() the result of posting. (Better would be to signal the
event if the posted task is deleted, but that may take rather more code.)

[alokp, 2016/05/02 23:00:59]

Good idea. Added a CHECK.

+        FROM_HERE, base::Bind(&PipelineImpl::StopTask, weak_this_, stop_cb));
+    waiter.Wait();
+  } else {
+    // This path is executed by unittests that share media and main threads.
+    StopTask(base::Bind(&base::DoNothing));
+  }
+  // Invalidate client weak pointer effectively canceling all pending client
+  // notifications in the message queue.
+  client_weak_factory_.reset();
 }
 
 void PipelineImpl::Seek(TimeDelta time, const PipelineStatusCB& seek_cb) {
-  base::AutoLock auto_lock(lock_);
-  if (!running_) {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
+  if (!IsRunning()) {
     DLOG(ERROR) << "Media pipeline isn't running. Ignoring Seek().";
     return;
   }
 
-  task_runner_->PostTask(FROM_HERE, base::Bind(&PipelineImpl::SeekTask,
-                                               weak_this_, time, seek_cb));
+  media_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PipelineImpl::SeekTask, weak_this_, time,
+                            media::BindToCurrentLoop(seek_cb)));
 }
 
 bool PipelineImpl::IsRunning() const {
+  // TODO(alokp): Add thread DCHECK after removing the internal usage on
+  // media thread.
   base::AutoLock auto_lock(lock_);
   return running_;
 }
 
 double PipelineImpl::GetPlaybackRate() const {
+  // TODO(alokp): Add thread DCHECK after removing the internal usage on
+  // media thread.
   base::AutoLock auto_lock(lock_);
   return playback_rate_;
 }
 
 void PipelineImpl::SetPlaybackRate(double playback_rate) {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   if (playback_rate < 0.0)
     return;
 
   base::AutoLock auto_lock(lock_);
   playback_rate_ = playback_rate;
   if (running_) {
-    task_runner_->PostTask(FROM_HERE,
-                           base::Bind(&PipelineImpl::PlaybackRateChangedTask,
-                                      weak_this_, playback_rate));
+    media_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&PipelineImpl::PlaybackRateChangedTask,
+                              weak_this_, playback_rate));
   }
 }
 
 void PipelineImpl::Suspend(const PipelineStatusCB& suspend_cb) {
-  task_runner_->PostTask(FROM_HERE, base::Bind(&PipelineImpl::SuspendTask,
-                                               weak_this_, suspend_cb));
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
+  media_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PipelineImpl::SuspendTask, weak_this_,
+                            media::BindToCurrentLoop(suspend_cb)));
 }
 
 void PipelineImpl::Resume(std::unique_ptr<Renderer> renderer,
                           base::TimeDelta timestamp,
                           const PipelineStatusCB& seek_cb) {
-  task_runner_->PostTask(
-      FROM_HERE, base::Bind(&PipelineImpl::ResumeTask, weak_this_,
-                            base::Passed(&renderer), timestamp, seek_cb));
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
+  media_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&PipelineImpl::ResumeTask, weak_this_, base::Passed(&renderer),
+                 timestamp, media::BindToCurrentLoop(seek_cb)));
 }
 
 float PipelineImpl::GetVolume() const {
+  // TODO(alokp): Add thread DCHECK after removing the internal usage on
+  // media thread.
   base::AutoLock auto_lock(lock_);
   return volume_;
 }
 
 void PipelineImpl::SetVolume(float volume) {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   if (volume < 0.0f || volume > 1.0f)
     return;
 
   base::AutoLock auto_lock(lock_);
   volume_ = volume;
   if (running_) {
-    task_runner_->PostTask(
+    media_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&PipelineImpl::VolumeChangedTask, weak_this_, volume));
   }
 }
 
 TimeDelta PipelineImpl::GetMediaTime() const {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   base::AutoLock auto_lock(lock_);
   if (suspend_timestamp_ != kNoTimestamp())
     return suspend_timestamp_;
   return renderer_ ? std::min(renderer_->GetMediaTime(), duration_)
                    : TimeDelta();
 }
 
 Ranges<TimeDelta> PipelineImpl::GetBufferedTimeRanges() const {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   base::AutoLock auto_lock(lock_);
   return buffered_time_ranges_;
 }
 
 TimeDelta PipelineImpl::GetMediaDuration() const {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   base::AutoLock auto_lock(lock_);
   return duration_;
 }
 
 bool PipelineImpl::DidLoadingProgress() {
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
   base::AutoLock auto_lock(lock_);
   bool ret = did_loading_progress_;
   did_loading_progress_ = false;
   return ret;
 }
 
 PipelineStatistics PipelineImpl::GetStatistics() const {
+  // TODO(alokp): Add thread DCHECK after removing the internal usage on
+  // media thread.
   base::AutoLock auto_lock(lock_);
   return statistics_;
 }
 
 void PipelineImpl::SetCdm(CdmContext* cdm_context,
                           const CdmAttachedCB& cdm_attached_cb) {
-  task_runner_->PostTask(
+  DCHECK(main_task_runner_->BelongsToCurrentThread());
+
+  media_task_runner_->PostTask(
       FROM_HERE, base::Bind(&PipelineImpl::SetCdmTask, weak_this_, cdm_context,
                             cdm_attached_cb));
 }
 
 void PipelineImpl::SetErrorForTesting(PipelineStatus status) {
   OnError(status);
 }
 
 bool PipelineImpl::HasWeakPtrsForTesting() const {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   return weak_factory_.HasWeakPtrs();
 }
 
 void PipelineImpl::SetState(State next_state) {
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DVLOG(1) << GetStateString(state_) << " -> " << GetStateString(next_state);
 
   state_ = next_state;
   media_log_->AddEvent(media_log_->CreatePipelineStateChangedEvent(next_state));
 }
 
 #define RETURN_STRING(state) \
   case state:                \
     return #state;
 
@@ skipping 10 matching lines @@
     RETURN_STRING(kSuspended);
     RETURN_STRING(kResuming);
   }
   NOTREACHED();
   return "INVALID";
 }
 
 #undef RETURN_STRING
 
 PipelineImpl::State PipelineImpl::GetNextState() const {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(stop_cb_.is_null()) << "State transitions don't happen when stopping";
   DCHECK_EQ(status_, PIPELINE_OK)
       << "State transitions don't happen when there's an error: " << status_;
 
   switch (state_) {
     case kCreated:
       return kInitDemuxer;
 
     case kInitDemuxer:
       return kInitRenderer;
@@ skipping 14 matching lines @@
     case kPlaying:
     case kStopping:
     case kStopped:
       break;
   }
   NOTREACHED() << "State has no transition: " << state_;
   return state_;
 }
 
 void PipelineImpl::OnDemuxerError(PipelineStatus error) {
-  task_runner_->PostTask(FROM_HERE, base::Bind(&PipelineImpl::ErrorChangedTask,
-                                               weak_this_, error));
+  // TODO(alokp): Add thread DCHECK after ensuring that all Demuxer
+  // implementations call DemuxerHost on the media thread.
+  media_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&PipelineImpl::ErrorChangedTask, weak_this_, error));
 }
 
 void PipelineImpl::AddTextStream(DemuxerStream* text_stream,
                                  const TextTrackConfig& config) {
-  task_runner_->PostTask(
+  // TODO(alokp): Add thread DCHECK after ensuring that all Demuxer
+  // implementations call DemuxerHost on the media thread.
+  media_task_runner_->PostTask(
       FROM_HERE, base::Bind(&PipelineImpl::AddTextStreamTask, weak_this_,
                             text_stream, config));
 }
 
 void PipelineImpl::RemoveTextStream(DemuxerStream* text_stream) {
-  task_runner_->PostTask(
+  // TODO(alokp): Add thread DCHECK after ensuring that all Demuxer
+  // implementations call DemuxerHost on the media thread.
+  media_task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&PipelineImpl::RemoveTextStreamTask, weak_this_, text_stream));
 }
 
 void PipelineImpl::OnError(PipelineStatus error) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(IsRunning());
   DCHECK_NE(PIPELINE_OK, error);
   VLOG(1) << "Media pipeline error: " << error;
 
-  task_runner_->PostTask(FROM_HERE, base::Bind(&PipelineImpl::ErrorChangedTask,
-                                               weak_this_, error));
+  media_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&PipelineImpl::ErrorChangedTask, weak_this_, error));
 }
 
 void PipelineImpl::SetDuration(TimeDelta duration) {
+  // TODO(alokp): Add thread DCHECK after ensuring that all Demuxer
+  // implementations call DemuxerHost on the media thread.
   DCHECK(IsRunning());
   media_log_->AddEvent(media_log_->CreateTimeEvent(MediaLogEvent::DURATION_SET,
                                                    "duration", duration));
   UMA_HISTOGRAM_LONG_TIMES("Media.Duration", duration);
 
   base::AutoLock auto_lock(lock_);
   duration_ = duration;
-  if (!duration_change_cb_.is_null())
-    duration_change_cb_.Run();
+  main_task_runner_->PostTask(FROM_HERE,
+                              base::Bind(&Pipeline::Client::OnDurationChange,
+                                         client_weak_factory_->GetWeakPtr()));
 }
 
 void PipelineImpl::StateTransitionTask(PipelineStatus status) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   // No-op any state transitions if we're stopping.
   if (state_ == kStopping || state_ == kStopped)
     return;
 
-  // Preserve existing abnormal status, otherwise update based on the result of
-  // the previous operation.
-  status_ = (status_ != PIPELINE_OK ? status_ : status);
-
-  if (status_ != PIPELINE_OK) {
-    ErrorChangedTask(status_);
+  // Report error from the previous operation.
+  if (status != PIPELINE_OK) {
+    ErrorChangedTask(status);
     return;
   }
 
   // Guard against accidentally clearing |pending_callbacks_| for states that
   // use it as well as states that should not be using it.
   DCHECK_EQ(pending_callbacks_.get() != NULL,
             state_ == kSeeking || state_ == kSuspending || state_ == kResuming);
 
   pending_callbacks_.reset();
 
@@ skipping 55 matching lines @@
   }
 }
 
 // Note that the usage of base::Unretained() with the renderers is considered
 // safe as they are owned by |pending_callbacks_| and share the same lifetime.
 //
 // That being said, deleting the renderers while keeping |pending_callbacks_|
 // running on the media thread would result in crashes.
 void PipelineImpl::DoSeek(TimeDelta seek_timestamp,
                           const PipelineStatusCB& done_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(!pending_callbacks_.get());
   DCHECK_EQ(state_, kSeeking);
   SerialRunner::Queue bound_fns;
 
   // Pause.
   if (text_renderer_) {
     bound_fns.Push(base::Bind(&TextRenderer::Pause,
                               base::Unretained(text_renderer_.get())));
   }
 
   // Flush.
   DCHECK(renderer_);
   bound_fns.Push(
       base::Bind(&Renderer::Flush, base::Unretained(renderer_.get())));
 
   if (text_renderer_) {
     bound_fns.Push(base::Bind(&TextRenderer::Flush,
                               base::Unretained(text_renderer_.get())));
   }
 
   // Seek demuxer.
   bound_fns.Push(
       base::Bind(&Demuxer::Seek, base::Unretained(demuxer_), seek_timestamp));
 
   pending_callbacks_ = SerialRunner::Run(bound_fns, done_cb);
 }
 
-void PipelineImpl::DoStop(const PipelineStatusCB& done_cb) {
+void PipelineImpl::DoStop() {
   DVLOG(2) << __FUNCTION__;
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+  DCHECK_EQ(state_, kStopping);
   DCHECK(!pending_callbacks_.get());
 
   // TODO(scherkus): Enforce that Renderer is only called on a single thread,
   // even for accessing media time http://crbug.com/370634
   std::unique_ptr<Renderer> renderer;
   {
     base::AutoLock auto_lock(lock_);
     renderer.swap(renderer_);
   }
   renderer.reset();
   text_renderer_.reset();
 
   if (demuxer_) {
     demuxer_->Stop();
     demuxer_ = NULL;
   }
 
-  task_runner_->PostTask(FROM_HERE, base::Bind(done_cb, PIPELINE_OK));
-}
-
-void PipelineImpl::OnStopCompleted(PipelineStatus status) {
-  DVLOG(2) << __FUNCTION__;
-  DCHECK(task_runner_->BelongsToCurrentThread());
-  DCHECK_EQ(state_, kStopping);
-  DCHECK(!renderer_);
-  DCHECK(!text_renderer_);
-
   {
     base::AutoLock auto_lock(lock_);
     running_ = false;
   }
-
   SetState(kStopped);
-  demuxer_ = NULL;
 
   // If we stop during initialization/seeking/suspending we don't want to leave
-  // outstanding callbacks around.
-  if (!seek_cb_.is_null()) {
-    base::ResetAndReturn(&seek_cb_).Run(status_);
-    error_cb_.Reset();
-  }
-  if (!suspend_cb_.is_null()) {
-    base::ResetAndReturn(&suspend_cb_).Run(status_);
-    error_cb_.Reset();
-  }
+  // outstanding callbacks around. The callbacks also do not get run if the
+  // pipeline is stopped before it had a chance to complete outstanding tasks.
+  seek_cb_.Reset();
+  suspend_cb_.Reset();
+
   if (!stop_cb_.is_null()) {
-    error_cb_.Reset();
-
     // Invalid all weak pointers so it's safe to destroy |this| on the render
     // main thread.
     weak_factory_.InvalidateWeakPtrs();
 
     base::ResetAndReturn(&stop_cb_).Run();
 
     // NOTE: pipeline may be deleted at this point in time as a result of
     // executing |stop_cb_|.
     return;
   }
-  if (!error_cb_.is_null()) {
-    DCHECK_NE(status_, PIPELINE_OK);
-    base::ResetAndReturn(&error_cb_).Run(status_);
-  }
 }
 
 void PipelineImpl::OnBufferedTimeRangesChanged(
     const Ranges<base::TimeDelta>& ranges) {
+  // TODO(alokp): Add thread DCHECK after ensuring that all Demuxer
+  // implementations call DemuxerHost on the media thread.
   base::AutoLock auto_lock(lock_);
   buffered_time_ranges_ = ranges;
   did_loading_progress_ = true;
 }
 
 // Called from any thread.
 void PipelineImpl::OnUpdateStatistics(const PipelineStatistics& stats_delta) {
   base::AutoLock auto_lock(lock_);
   statistics_.audio_bytes_decoded += stats_delta.audio_bytes_decoded;
   statistics_.video_bytes_decoded += stats_delta.video_bytes_decoded;
   statistics_.video_frames_decoded += stats_delta.video_frames_decoded;
   statistics_.video_frames_dropped += stats_delta.video_frames_dropped;
   statistics_.audio_memory_usage += stats_delta.audio_memory_usage;
   statistics_.video_memory_usage += stats_delta.video_memory_usage;
 }
 
+void PipelineImpl::OnWaitingForDecryptionKey() {
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
+  main_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&Pipeline::Client::OnWaitingForDecryptionKey,
+                            client_weak_factory_->GetWeakPtr()));
+}
+
 void PipelineImpl::StartTask() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   CHECK_EQ(kCreated, state_)
       << "Media pipeline cannot be started more than once";
 
   text_renderer_ = CreateTextRenderer();
   if (text_renderer_) {
     text_renderer_->Initialize(
         base::Bind(&PipelineImpl::OnTextRendererEnded, weak_this_));
   }
 
   StateTransitionTask(PIPELINE_OK);
 }
 
 void PipelineImpl::StopTask(const base::Closure& stop_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(stop_cb_.is_null());
 
   if (state_ == kStopped) {
     // Invalid all weak pointers so it's safe to destroy |this| on the render
     // main thread.
     weak_factory_.InvalidateWeakPtrs();
 
     // NOTE: pipeline may be deleted at this point in time as a result of
     // executing |stop_cb|.
     stop_cb.Run();
@@ skipping 12 matching lines @@
       state_ == kSuspended || state_ == kResuming) {
     PipelineStatistics stats = GetStatistics();
     if (stats.video_frames_decoded > 0) {
       UMA_HISTOGRAM_COUNTS("Media.DroppedFrameCount",
                            stats.video_frames_dropped);
     }
   }
 
   SetState(kStopping);
   pending_callbacks_.reset();
-  DoStop(base::Bind(&PipelineImpl::OnStopCompleted, weak_this_));
+  DoStop();
 }
 
 void PipelineImpl::ErrorChangedTask(PipelineStatus error) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK_NE(PIPELINE_OK, error) << "PIPELINE_OK isn't an error!";
 
+  // Preserve existing abnormal status.
+  if (status_ != PIPELINE_OK)
+    return;
+
   // Don't report pipeline error events to the media log here. The embedder will
   // log this when |error_cb_| is called. If the pipeline is already stopped or
   // stopping we also don't want to log any event. In case we are suspending or
   // suspended, the error may be recoverable, so don't propagate it now, instead
   // let the subsequent seek during resume propagate it if it's unrecoverable.
-
   if (state_ == kStopping || state_ == kStopped || state_ == kSuspending ||
       state_ == kSuspended) {
     return;
   }
 
+  // Once we enter |kStopping| state, nothing is reported back to the client.
+  // If we encounter an error during initialization/seeking/suspending,
+  // report the error using the completion callbacks for those tasks.
+  status_ = error;
+  bool error_reported = false;
+  if (!seek_cb_.is_null()) {
+    base::ResetAndReturn(&seek_cb_).Run(status_);
+    error_reported = true;
+  }
+  if (!suspend_cb_.is_null()) {
+    base::ResetAndReturn(&suspend_cb_).Run(status_);
+    error_reported = true;
+  }
+  if (!error_reported) {
+    DCHECK_NE(status_, PIPELINE_OK);
+    main_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&Pipeline::Client::OnError,
+                              client_weak_factory_->GetWeakPtr(), status_));
+  }
+
   SetState(kStopping);
   pending_callbacks_.reset();
-  status_ = error;
-
-  DoStop(base::Bind(&PipelineImpl::OnStopCompleted, weak_this_));
+  DoStop();
 }
 
 void PipelineImpl::PlaybackRateChangedTask(double playback_rate) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   // Playback rate changes are only carried out while playing.
   if (state_ != kPlaying)
     return;
 
   renderer_->SetPlaybackRate(playback_rate);
 }
 
 void PipelineImpl::VolumeChangedTask(float volume) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   // Volume changes are only carried out while playing.
   if (state_ != kPlaying)
     return;
 
   renderer_->SetVolume(volume);
 }
 
 void PipelineImpl::SeekTask(TimeDelta time, const PipelineStatusCB& seek_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(stop_cb_.is_null());
 
   // Suppress seeking if we're not fully started.
   if (state_ != kPlaying) {
     DCHECK(state_ == kStopping || state_ == kStopped)
         << "Receive seek in unexpected state: " << state_;
     seek_cb.Run(PIPELINE_ERROR_INVALID_STATE);
     return;
   }
 
   DCHECK(seek_cb_.is_null());
 
   const base::TimeDelta seek_timestamp =
       std::max(time, demuxer_->GetStartTime());
 
   SetState(kSeeking);
   seek_cb_ = seek_cb;
   renderer_ended_ = false;
   text_renderer_ended_ = false;
   start_timestamp_ = seek_timestamp;
 
   DoSeek(seek_timestamp,
          base::Bind(&PipelineImpl::StateTransitionTask, weak_this_));
 }
 
 void PipelineImpl::SuspendTask(const PipelineStatusCB& suspend_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   // Suppress suspending if we're not playing.
   if (state_ != kPlaying) {
     DCHECK(state_ == kStopping || state_ == kStopped)
         << "Receive suspend in unexpected state: " << state_;
     suspend_cb.Run(PIPELINE_ERROR_INVALID_STATE);
     return;
   }
   DCHECK(renderer_);
   DCHECK(!pending_callbacks_.get());
@@ skipping 27 matching lines @@
                         base::Unretained(text_renderer_.get())));
   }
 
   pending_callbacks_ = SerialRunner::Run(
       fns, base::Bind(&PipelineImpl::StateTransitionTask, weak_this_));
 }
 
 void PipelineImpl::ResumeTask(std::unique_ptr<Renderer> renderer,
                               base::TimeDelta timestamp,
                               const PipelineStatusCB& seek_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   // Suppress resuming if we're not suspended.
   if (state_ != kSuspended) {
     DCHECK(state_ == kStopping || state_ == kStopped)
         << "Receive resume in unexpected state: " << state_;
     seek_cb.Run(PIPELINE_ERROR_INVALID_STATE);
     return;
   }
   DCHECK(!renderer_);
   DCHECK(!pending_callbacks_.get());
@@ skipping 33 matching lines @@
   }
 
   renderer_->SetCdm(cdm_context,
                     base::Bind(&PipelineImpl::OnCdmAttached, weak_this_,
                                cdm_attached_cb, cdm_context));
 }
 
 void PipelineImpl::OnCdmAttached(const CdmAttachedCB& cdm_attached_cb,
                                  CdmContext* cdm_context,
                                  bool success) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   if (success)
     cdm_context_ = cdm_context;
   cdm_attached_cb.Run(success);
 }
 
 void PipelineImpl::OnRendererEnded() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   media_log_->AddEvent(media_log_->CreateEvent(MediaLogEvent::ENDED));
 
   if (state_ != kPlaying)
     return;
 
   DCHECK(!renderer_ended_);
   renderer_ended_ = true;
 
   RunEndedCallbackIfNeeded();
 }
 
 void PipelineImpl::OnTextRendererEnded() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   media_log_->AddEvent(media_log_->CreateEvent(MediaLogEvent::TEXT_ENDED));
 
   if (state_ != kPlaying)
     return;
 
   DCHECK(!text_renderer_ended_);
   text_renderer_ended_ = true;
 
   RunEndedCallbackIfNeeded();
 }
 
 void PipelineImpl::RunEndedCallbackIfNeeded() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   if (renderer_ && !renderer_ended_)
     return;
 
   if (text_renderer_ && text_renderer_->HasTracks() && !text_renderer_ended_)
     return;
 
   DCHECK_EQ(status_, PIPELINE_OK);
-  ended_cb_.Run();
+  main_task_runner_->PostTask(FROM_HERE,
+                              base::Bind(&Pipeline::Client::OnEnded,
+                                         client_weak_factory_->GetWeakPtr()));
 }
 
 std::unique_ptr<TextRenderer> PipelineImpl::CreateTextRenderer() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   const base::CommandLine* cmd_line = base::CommandLine::ForCurrentProcess();
   if (!cmd_line->HasSwitch(switches::kEnableInbandTextTracks))
     return nullptr;
 
   return base::WrapUnique(new media::TextRenderer(
-      task_runner_, base::Bind(&PipelineImpl::OnAddTextTrack, weak_this_)));
+      media_task_runner_,
+      base::Bind(&PipelineImpl::OnAddTextTrack, weak_this_)));
 }
 
 void PipelineImpl::AddTextStreamTask(DemuxerStream* text_stream,
                                      const TextTrackConfig& config) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
   // TODO(matthewjheaney): fix up text_ended_ when text stream
   // is added (http://crbug.com/321446).
   if (text_renderer_)
     text_renderer_->AddTextStream(text_stream, config);
 }
 
 void PipelineImpl::RemoveTextStreamTask(DemuxerStream* text_stream) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
   if (text_renderer_)
     text_renderer_->RemoveTextStream(text_stream);
 }
 
 void PipelineImpl::OnAddTextTrack(const TextTrackConfig& config,
                                   const AddTextTrackDoneCB& done_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
-  add_text_track_cb_.Run(config, done_cb);
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
+  main_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&Pipeline::Client::OnAddTextTrack,
+                 client_weak_factory_->GetWeakPtr(), config, done_cb));
 }
 
 void PipelineImpl::InitializeDemuxer(const PipelineStatusCB& done_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
   demuxer_->Initialize(this, done_cb, !!text_renderer_);
 }
 
 void PipelineImpl::InitializeRenderer(const PipelineStatusCB& done_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
 
   if (!demuxer_->GetStream(DemuxerStream::AUDIO) &&
       !demuxer_->GetStream(DemuxerStream::VIDEO)) {
     {
       base::AutoLock auto_lock(lock_);
       renderer_.reset();
     }
     OnError(PIPELINE_ERROR_COULD_NOT_RENDER);
     return;
   }
 
   if (cdm_context_)
     renderer_->SetCdm(cdm_context_, base::Bind(&IgnoreCdmAttached));
 
   renderer_->Initialize(
       demuxer_, done_cb,
       base::Bind(&PipelineImpl::OnUpdateStatistics, weak_this_),
       base::Bind(&PipelineImpl::BufferingStateChanged, weak_this_),
       base::Bind(&PipelineImpl::OnRendererEnded, weak_this_),
       base::Bind(&PipelineImpl::OnError, weak_this_),
-      waiting_for_decryption_key_cb_);
+      base::Bind(&PipelineImpl::OnWaitingForDecryptionKey, weak_this_));
 }
 
 void PipelineImpl::ReportMetadata() {
-  DCHECK(task_runner_->BelongsToCurrentThread());
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
   PipelineMetadata metadata;
   metadata.timeline_offset = demuxer_->GetTimelineOffset();
   DemuxerStream* stream = demuxer_->GetStream(DemuxerStream::VIDEO);
   if (stream) {
     metadata.has_video = true;
     metadata.natural_size = stream->video_decoder_config().natural_size();
     metadata.video_rotation = stream->video_rotation();
   }
   if (demuxer_->GetStream(DemuxerStream::AUDIO)) {
     metadata.has_audio = true;
   }
-  metadata_cb_.Run(metadata);
+
+  main_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&Pipeline::Client::OnMetadata,
+                            client_weak_factory_->GetWeakPtr(), metadata));
 }
 
 void PipelineImpl::BufferingStateChanged(BufferingState new_buffering_state) {
   DVLOG(1) << __FUNCTION__ << "(" << new_buffering_state << ") ";
-  DCHECK(task_runner_->BelongsToCurrentThread());
-  buffering_state_cb_.Run(new_buffering_state);
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
+  main_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&Pipeline::Client::OnBufferingStateChange,
+                 client_weak_factory_->GetWeakPtr(), new_buffering_state));
 }
 
 }  // namespace media