Remove reference counting from media::VideoDecoder and friends.

media/filters/gpu_video_decoder.cc

Index: media/filters/gpu_video_decoder.cc
diff --git a/media/filters/gpu_video_decoder.cc b/media/filters/gpu_video_decoder.cc
index b74ba5ba82e5c8a2563b6b7f84459d7402b24c55..6904bbb763e58da767f034815bef85bfd2646c34 100644
--- a/media/filters/gpu_video_decoder.cc
+++ b/media/filters/gpu_video_decoder.cc
@@ -9,6 +9,7 @@
 #include "base/cpu.h"
 #include "base/message_loop.h"
 #include "base/stl_util.h"
+#include "base/task_runner_util.h"
 #include "media/base/bind_to_loop.h"
 #include "media/base/decoder_buffer.h"
 #include "media/base/demuxer_stream.h"
@@ -18,6 +19,114 @@
 
 namespace media {
 
+// Proxies calls to a VideoDecodeAccelerator::Client from the calling thread to
+// the client's thread.
+//
+// TODO(scherkus): VDAClientProxy should hold onto GpuVideoDecoder::Factories
+// and take care of some of the work that GpuVideoDecoder does to minimize
+// thread hopping. See following for discussion:
+//
+// https://codereview.chromium.org/12989009/diff/27035/media/filters/gpu_video_decoder.cc#newcode23
+class VDAClientProxy
+    : public base::RefCountedThreadSafe<VDAClientProxy>,
+      public VideoDecodeAccelerator::Client {
+ public:
+  explicit VDAClientProxy(VideoDecodeAccelerator::Client* client);
+
+  // Detaches the proxy. |client| will no longer be called and can be safely

[xhwang, 2013/04/18 00:40:48]

s/client/weak_client_/ ?

[scherkus (not reviewing), 2013/04/18 18:45:29]

Done.

+  // deleted. Any pending/future calls will be discarded.
+  //
+  // Must be called on |client_loop|.

[xhwang, 2013/04/18 00:40:48]

s/client_loop/client_loop_/

[scherkus (not reviewing), 2013/04/18 18:45:29]

Done.

+  void Detach();
+
+  // VideoDecodeAccelerator::Client implementation.
+  virtual void NotifyInitializeDone() OVERRIDE;
+  virtual void ProvidePictureBuffers(uint32 count,
+                                     const gfx::Size& size,
+                                     uint32 texture_target) OVERRIDE;
+  virtual void DismissPictureBuffer(int32 id) OVERRIDE;
+  virtual void PictureReady(const media::Picture& picture) OVERRIDE;
+  virtual void NotifyEndOfBitstreamBuffer(int32 id) OVERRIDE;
+  virtual void NotifyFlushDone() OVERRIDE;
+  virtual void NotifyResetDone() OVERRIDE;
+  virtual void NotifyError(media::VideoDecodeAccelerator::Error error) OVERRIDE;
+
+ private:
+  friend class base::RefCountedThreadSafe<VDAClientProxy>;
+  virtual ~VDAClientProxy();
+
+  scoped_refptr<base::MessageLoopProxy> client_loop_;
+
+  // Weak pointers are used to invalidate tasks posted to |client_loop_| that

[xhwang, 2013/04/18 00:40:48]

s/that/after ?

[scherkus (not reviewing), 2013/04/18 18:45:29]

Done.

+  // Detach() has been called.
+  base::WeakPtrFactory<VideoDecodeAccelerator::Client> weak_client_factory_;
+  base::WeakPtr<VideoDecodeAccelerator::Client> weak_client_;
+
+  DISALLOW_COPY_AND_ASSIGN(VDAClientProxy);
+};
+
+VDAClientProxy::VDAClientProxy(VideoDecodeAccelerator::Client* client)
+    : client_loop_(base::MessageLoopProxy::current()),
+      weak_client_factory_(client),
+      weak_client_(weak_client_factory_.GetWeakPtr()) {
+  DCHECK(weak_client_);
+}
+
+VDAClientProxy::~VDAClientProxy() {
+  DCHECK(!weak_client_) << "Detach() was not called";
+}
+
+void VDAClientProxy::Detach() {
+  DCHECK(client_loop_->BelongsToCurrentThread());
+  DCHECK(weak_client_) << "Detach() already called";
+  weak_client_factory_.InvalidateWeakPtrs();
+}
+
+void VDAClientProxy::NotifyInitializeDone() {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::NotifyInitializeDone, weak_client_));
+}
+
+void VDAClientProxy::ProvidePictureBuffers(uint32 count,
+                                           const gfx::Size& size,
+                                           uint32 texture_target) {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::ProvidePictureBuffers, weak_client_,
+      count, size, texture_target));
+}
+
+void VDAClientProxy::DismissPictureBuffer(int32 id) {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::DismissPictureBuffer, weak_client_, id));
+}
+
+void VDAClientProxy::PictureReady(const media::Picture& picture) {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::PictureReady, weak_client_, picture));
+}
+
+void VDAClientProxy::NotifyEndOfBitstreamBuffer(int32 id) {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::NotifyEndOfBitstreamBuffer, weak_client_,
+      id));
+}
+
+void VDAClientProxy::NotifyFlushDone() {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::NotifyFlushDone, weak_client_));
+}
+
+void VDAClientProxy::NotifyResetDone() {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::NotifyResetDone, weak_client_));
+}
+
+void VDAClientProxy::NotifyError(media::VideoDecodeAccelerator::Error error) {
+  client_loop_->PostTask(FROM_HERE, base::Bind(
+      &VideoDecodeAccelerator::Client::NotifyError, weak_client_, error));
+}
+
+
 // Maximum number of concurrent VDA::Decode() operations GVD will maintain.
 // Higher values allow better pipelining in the GPU, but also require more
 // resources.
@@ -54,6 +163,7 @@ GpuVideoDecoder::GpuVideoDecoder(
     const scoped_refptr<base::MessageLoopProxy>& message_loop,
     const scoped_refptr<Factories>& factories)
     : gvd_loop_proxy_(message_loop),
+      weak_factory_(this),
       vda_loop_proxy_(factories->GetMessageLoop()),
       factories_(factories),
       state_(kNormal),
@@ -71,7 +181,7 @@ void GpuVideoDecoder::Reset(const base::Closure& closure)  {
 
   if (state_ == kDrainingDecoder && !factories_->IsAborted()) {
     gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::Reset, this, closure));
+        &GpuVideoDecoder::Reset, weak_this_, closure));
     // NOTE: if we're deferring Reset() until a Flush() completes, return
     // queued pictures to the VDA so they can be used to finish that Flush().
     if (pending_read_cb_.is_null())
@@ -115,6 +225,8 @@ void GpuVideoDecoder::Initialize(const scoped_refptr<DemuxerStream>& stream,
                                  const PipelineStatusCB& orig_status_cb,
                                  const StatisticsCB& statistics_cb) {
   DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
+  weak_this_ = weak_factory_.GetWeakPtr();
+
   PipelineStatusCB status_cb = CreateUMAReportingPipelineCB(
       "Media.GpuVideoDecoderInitializeStatus",
       BindToCurrentLoop(orig_status_cb));
@@ -152,8 +264,9 @@ void GpuVideoDecoder::Initialize(const scoped_refptr<DemuxerStream>& stream,
     }
   }
 
+  client_proxy_ = new VDAClientProxy(this);
   VideoDecodeAccelerator* vda =
-      factories_->CreateVideoDecodeAccelerator(config.profile(), this);
+      factories_->CreateVideoDecodeAccelerator(config.profile(), client_proxy_);
   if (!vda) {
     status_cb.Run(DECODER_ERROR_NOT_SUPPORTED);
     return;
@@ -166,17 +279,21 @@ void GpuVideoDecoder::Initialize(const scoped_refptr<DemuxerStream>& stream,
   statistics_cb_ = statistics_cb;
 
   DVLOG(1) << "GpuVideoDecoder::Initialize() succeeded.";
-  vda_loop_proxy_->PostTaskAndReply(
-      FROM_HERE,
-      base::Bind(&GpuVideoDecoder::SetVDA, this, vda),
-      base::Bind(status_cb, PIPELINE_OK));
+  PostTaskAndReplyWithResult(
+      vda_loop_proxy_, FROM_HERE,
+      base::Bind(&VideoDecodeAccelerator::AsWeakPtr, base::Unretained(vda)),
+      base::Bind(&GpuVideoDecoder::SetVDA, weak_this_, status_cb, vda));
 }
 
-void GpuVideoDecoder::SetVDA(VideoDecodeAccelerator* vda) {
-  DCHECK(vda_loop_proxy_->BelongsToCurrentThread());
+void GpuVideoDecoder::SetVDA(
+    const PipelineStatusCB& status_cb,
+    VideoDecodeAccelerator* vda,
+    base::WeakPtr<VideoDecodeAccelerator> weak_vda) {
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   DCHECK(!vda_.get());
   vda_.reset(vda);
-  weak_vda_ = vda->AsWeakPtr();
+  weak_vda_ = weak_vda;
+  status_cb.Run(PIPELINE_OK);
 }
 
 void GpuVideoDecoder::DestroyTextures() {
@@ -188,17 +305,24 @@ void GpuVideoDecoder::DestroyTextures() {
   picture_buffers_in_decoder_.clear();
 }
 
+static void DestroyVDAWithClientProxy(
+    const scoped_refptr<VDAClientProxy>& client_proxy,
+    base::WeakPtr<VideoDecodeAccelerator> weak_vda) {
+  DCHECK(client_proxy->HasOneRef());

[xhwang, 2013/04/18 00:40:48]

hmm, are we making assumption about vda implementation details? Can vda just
drop the reference to client_proxy if something bad happened?

Also, can there be a race condition? e.g. can this DCHECK executed before line
325 is executed?

[scherkus (not reviewing), 2013/04/18 18:45:29]

ah good catch -- fischman@ suggested this but you're right that it can race

I don't find it's a very valuable DCHECK - removed

+  if (weak_vda)

[xhwang, 2013/04/18 00:40:48]

OOC, in which case can this happen? DestroyVDA called twice in a row? In that
case shall we check on line 323?

[scherkus (not reviewing), 2013/04/18 18:45:29]

you can only check/deref a weak pointer on the thread it's bound to (hence this
task post)

IIRC fischman@ said it's possible for VDA to get destroyed by other means (e.g.,
compositor)

+    weak_vda->Destroy();

[xhwang, 2013/04/18 00:40:48]

weak_vda.reset()?

[scherkus (not reviewing), 2013/04/18 18:45:29]

Destroy() is a VDA method that takes care of deleting the VDA

.reset() would release a weak reference but leak the VDA object

Did you mean something else?

[xhwang, 2013/04/18 19:17:49]

Sorry, I meant calling .reset() after ->Destroy(). I was worrying about checking
on 312 happens again after 313 is executed (this can happen if DestroyVDA() is
called twice). But since Destroy() deletes the VDA, it should already
invalidates weak_vda_. So no need to call .reset() anymore. 

BTW, does it make sense to call DCHECK(!weak_vda) after 313?

[scherkus (not reviewing), 2013/04/18 20:21:14]

Done.

+}
+
 void GpuVideoDecoder::DestroyVDA() {
   DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
+
+  // |client_proxy| must stay alive until |weak_vda_| has been destroyed.
+  vda_loop_proxy_->PostTask(FROM_HERE, base::Bind(
+      &DestroyVDAWithClientProxy, client_proxy_, weak_vda_));
+
   VideoDecodeAccelerator* vda ALLOW_UNUSED = vda_.release();
-  // Tricky: |this| needs to stay alive until after VDA::Destroy is actually
-  // called, not just posted, so we take an artificial ref to |this| and release
-  // it as |reply| after VDA::Destroy() returns.
-  AddRef();
-  vda_loop_proxy_->PostTaskAndReply(
-      FROM_HERE,
-      base::Bind(&VideoDecodeAccelerator::Destroy, weak_vda_),
-      base::Bind(&GpuVideoDecoder::Release, this));
+  client_proxy_->Detach();
+  client_proxy_ = NULL;
 
   DestroyTextures();
 }
@@ -246,13 +370,9 @@ bool GpuVideoDecoder::CanMoreDecodeWorkBeDone() {
 void GpuVideoDecoder::RequestBufferDecode(
     DemuxerStream::Status status,
     const scoped_refptr<DecoderBuffer>& buffer) {
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   DCHECK_EQ(status != DemuxerStream::kOk, !buffer) << status;
 
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::RequestBufferDecode, this, status, buffer));
-    return;
-  }
   demuxer_read_in_progress_ = false;
 
   if (status != DemuxerStream::kOk) {
@@ -307,7 +427,7 @@ void GpuVideoDecoder::RequestBufferDecode(
   if (CanMoreDecodeWorkBeDone()) {
     // Force post here to prevent reentrancy into DemuxerStream.
     gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::EnsureDemuxOrDecode, this));
+        &GpuVideoDecoder::EnsureDemuxOrDecode, weak_this_));
   }
 }
 
@@ -360,12 +480,7 @@ void GpuVideoDecoder::NotifyInitializeDone() {
 void GpuVideoDecoder::ProvidePictureBuffers(uint32 count,
                                             const gfx::Size& size,
                                             uint32 texture_target) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::ProvidePictureBuffers, this, count, size,
-        texture_target));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
 
   std::vector<uint32> texture_ids;
   decoder_texture_target_ = texture_target;
@@ -395,11 +510,8 @@ void GpuVideoDecoder::ProvidePictureBuffers(uint32 count,
 }
 
 void GpuVideoDecoder::DismissPictureBuffer(int32 id) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::DismissPictureBuffer, this, id));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
+
   std::map<int32, PictureBuffer>::iterator it =
       picture_buffers_in_decoder_.find(id);
   if (it == picture_buffers_in_decoder_.end()) {
@@ -411,11 +523,8 @@ void GpuVideoDecoder::DismissPictureBuffer(int32 id) {
 }
 
 void GpuVideoDecoder::PictureReady(const media::Picture& picture) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::PictureReady, this, picture));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
+
   std::map<int32, PictureBuffer>::iterator it =
       picture_buffers_in_decoder_.find(picture.picture_buffer_id());
   if (it == picture_buffers_in_decoder_.end()) {
@@ -439,8 +548,9 @@ void GpuVideoDecoder::PictureReady(const media::Picture& picture) {
           base::Bind(&Factories::ReadPixels, factories_, pb.texture_id(),
                      decoder_texture_target_,
                      gfx::Size(visible_rect.width(), visible_rect.height())),
-          base::Bind(&GpuVideoDecoder::ReusePictureBuffer, this,
-                     picture.picture_buffer_id())));
+          BindToCurrentLoop(base::Bind(
+              &GpuVideoDecoder::ReusePictureBuffer, weak_this_,
+              picture.picture_buffer_id()))));
   CHECK_GT(available_pictures_, 0);
   available_pictures_--;
 
@@ -469,11 +579,7 @@ void GpuVideoDecoder::EnqueueFrameAndTriggerFrameDelivery(
 }
 
 void GpuVideoDecoder::ReusePictureBuffer(int64 picture_buffer_id) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::ReusePictureBuffer, this, picture_buffer_id));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   CHECK_GE(available_pictures_, 0);
   available_pictures_++;
 
@@ -506,11 +612,7 @@ void GpuVideoDecoder::PutSHM(SHMBuffer* shm_buffer) {
 }
 
 void GpuVideoDecoder::NotifyEndOfBitstreamBuffer(int32 id) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::NotifyEndOfBitstreamBuffer, this, id));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
 
   std::map<int32, BufferPair>::iterator it =
       bitstream_buffers_in_decoder_.find(id);
@@ -565,27 +667,18 @@ void GpuVideoDecoder::EnsureDemuxOrDecode() {
 
   demuxer_read_in_progress_ = true;
   demuxer_stream_->Read(base::Bind(
-      &GpuVideoDecoder::RequestBufferDecode, this));
+      &GpuVideoDecoder::RequestBufferDecode, weak_this_));
 }
 
 void GpuVideoDecoder::NotifyFlushDone() {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::NotifyFlushDone, this));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   DCHECK_EQ(state_, kDrainingDecoder);
   state_ = kDecoderDrained;
   EnqueueFrameAndTriggerFrameDelivery(VideoFrame::CreateEmptyFrame());
 }
 
 void GpuVideoDecoder::NotifyResetDone() {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::NotifyResetDone, this));
-    return;
-  }
-
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   DCHECK(ready_video_frames_.empty());
 
   // This needs to happen after the Reset() on vda_ is done to ensure pictures
@@ -600,11 +693,7 @@ void GpuVideoDecoder::NotifyResetDone() {
 }
 
 void GpuVideoDecoder::NotifyError(media::VideoDecodeAccelerator::Error error) {
-  if (!gvd_loop_proxy_->BelongsToCurrentThread()) {
-    gvd_loop_proxy_->PostTask(FROM_HERE, base::Bind(
-        &GpuVideoDecoder::NotifyError, this, error));
-    return;
-  }
+  DCHECK(gvd_loop_proxy_->BelongsToCurrentThread());
   if (!vda_.get())
     return;