From: Byron Campen <docfaraday@gmail.com>
Date: Thu, 20 Jul 2023 14:24:00 +0000
Subject: Bug 1838080: Ensure that last ref to transformation_queue_ is not
 released on itself. r=pehrsons,webrtc-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D181699
Mercurial Revision: https://hg.mozilla.org/mozilla-central/rev/91d9e8b6a5c430a73561ffd2330865f04fcb1a6d
---
 .../rtp_sender_video_frame_transformer_delegate.cc       | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/modules/rtp_rtcp/source/rtp_sender_video_frame_transformer_delegate.cc b/modules/rtp_rtcp/source/rtp_sender_video_frame_transformer_delegate.cc
index c54f9f8991..a52f16077a 100644
--- a/modules/rtp_rtcp/source/rtp_sender_video_frame_transformer_delegate.cc
+++ b/modules/rtp_rtcp/source/rtp_sender_video_frame_transformer_delegate.cc
@@ -34,6 +34,7 @@
 #include "api/video_codecs/video_codec.h"
 #include "modules/rtp_rtcp/source/rtp_video_header.h"
 #include "rtc_base/checks.h"
+#include "rtc_base/event.h"
 #include "rtc_base/synchronization/mutex.h"
 
 namespace webrtc {
@@ -282,6 +283,14 @@ void RTPSenderVideoFrameTransformerDelegate::Reset() {
     MutexLock lock(&sender_lock_);
     sender_ = nullptr;
   }
+  // Wait until all pending tasks are executed, to ensure that the last ref
+  // standing is not on the transformation queue.
+  Event flush;
+  transformation_queue_->PostTask([this, &flush]() {
+    RTC_DCHECK_RUN_ON(transformation_queue_.get());
+    flush.Set();
+  });
+  flush.Wait(Event::kForever);
 }
 
 std::unique_ptr<TransformableVideoFrameInterface> CloneSenderVideoFrame(