From 3e1e831ae391ae3df62d7770bea2b478d2747c1a Mon Sep 17 00:00:00 2001
From: Peter Hanspers <peterhanspers@webrtc.org>
Date: Tue, 5 Sep 2023 17:55:34 +0200
Subject: [PATCH] Reland "ConnectionContext: remove media engine without
 blocking."

This reverts commit 2d71807fe09aad67efcd660fe286044ff10982ba.

Reason for revert: With the new AsyncAudioProcessing API, the issue that was introduced can now be worked around.

Original change's description:
> Revert "ConnectionContext: remove media engine without blocking."
>
> This reverts commit 2ba941e6bc1d20acb9cfda4b87ba53c80640bbcb.
>
> Reason for revert: Temporarily reverting due to b/269628432.
>
> Original change's description:
> > ConnectionContext: remove media engine without blocking.
> >
> > Bug: webrtc:14449
> > Change-Id: I445114c14f4d440a5a8cac003266047fe4588dab
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/288580
> > Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> > Commit-Queue: Markus Handell <handellm@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#38928}
>
> Bug: webrtc:14449
> Change-Id: If2f23662e486a1c1f85c318fc98c441aab9ace31
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/295862
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Auto-Submit: Markus Handell <handellm@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#39454}

Bug: webrtc:14449
Change-Id: I43bb7a3b366eb60b3dc4b88dd9d47d570bb99bc2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/311941
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Markus Handell <handellm@webrtc.org>
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40705}
---
 pc/connection_context.cc | 11 ++---------
 pc/connection_context.h  |  4 +++-
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/pc/connection_context.cc b/pc/connection_context.cc
index 661550e2d4..f436e27c0a 100644
--- a/pc/connection_context.cc
+++ b/pc/connection_context.cc
@@ -174,15 +174,8 @@ ConnectionContext::ConnectionContext(
 
 ConnectionContext::~ConnectionContext() {
   RTC_DCHECK_RUN_ON(signaling_thread_);
-  worker_thread_->BlockingCall([&] {
-    RTC_DCHECK_RUN_ON(worker_thread());
-    // While `media_engine_` is const throughout the ConnectionContext's
-    // lifetime, it requires destruction to happen on the worker thread. Instead
-    // of marking the pointer as non-const, we live with this const_cast<> in
-    // the destructor.
-    const_cast<std::unique_ptr<cricket::MediaEngineInterface>&>(media_engine_)
-        .reset();
-  });
+  // `media_engine_` requires destruction to happen on the worker thread.
+  worker_thread_->PostTask([media_engine = std::move(media_engine_)] {});
 
   // Make sure `worker_thread()` and `signaling_thread()` outlive
   // `default_socket_factory_` and `default_network_manager_`.
diff --git a/pc/connection_context.h b/pc/connection_context.h
index 38a6f8e514..399e7c2b45 100644
--- a/pc/connection_context.h
+++ b/pc/connection_context.h
@@ -125,7 +125,9 @@ class ConnectionContext final
   // Accessed both on signaling thread and worker thread.
   std::unique_ptr<FieldTrialsView> const trials_;
 
-  const std::unique_ptr<cricket::MediaEngineInterface> media_engine_;
+  // This object is const over the lifetime of the ConnectionContext, and is
+  // only altered in the destructor.
+  std::unique_ptr<cricket::MediaEngineInterface> media_engine_;
 
   // This object should be used to generate any SSRC that is not explicitly
   // specified by the user (or by the remote party).