From 74c04d79c91fb58d4725c77876d6c6cde0559e66 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Mon, 30 Oct 2023 11:21:25 +0200
Subject: [PATCH] gtk4: Use async-channel instead of the glib MainContext
 channel

The latter will be removed in favour of using async code in the future,
and async code generally allows for more flexible message handling than the
callback based MainContext channel.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1375>
---
 video/gtk4/Cargo.toml      |  1 +
 video/gtk4/src/sink/imp.rs | 46 +++++++++++++++++++++++---------------
 2 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/video/gtk4/Cargo.toml b/video/gtk4/Cargo.toml
index b9f6b394..b380303d 100644
--- a/video/gtk4/Cargo.toml
+++ b/video/gtk4/Cargo.toml
@@ -21,6 +21,7 @@ gst_gl = { package = "gstreamer-gl", git = "https://gitlab.freedesktop.org/gstre
 gst_gl_wayland = { package = "gstreamer-gl-wayland", git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs", features = ["v1_16"], optional = true }
 gst_gl_x11 = { package = "gstreamer-gl-x11", git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs", features = ["v1_16"], optional = true }
 gst_gl_egl = { package = "gstreamer-gl-egl", git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs", features = ["v1_16"], optional = true }
+async-channel = "2.0.0"
 
 
 [target.'cfg(target_os = "macos")'.dependencies]
diff --git a/video/gtk4/src/sink/imp.rs b/video/gtk4/src/sink/imp.rs
index 3a1059d6..fd5b7fd4 100644
--- a/video/gtk4/src/sink/imp.rs
+++ b/video/gtk4/src/sink/imp.rs
@@ -13,7 +13,7 @@ use super::SinkEvent;
 use crate::sink::frame::Frame;
 use crate::sink::paintable::Paintable;
 
-use glib::{thread_guard::ThreadGuard, Sender};
+use glib::thread_guard::ThreadGuard;
 use gtk::prelude::*;
 use gtk::{gdk, glib};
 
@@ -60,7 +60,7 @@ static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
 pub struct PaintableSink {
     paintable: Mutex<Option<ThreadGuard<Paintable>>>,
     info: Mutex<Option<gst_video::VideoInfo>>,
-    sender: Mutex<Option<Sender<SinkEvent>>>,
+    sender: Mutex<Option<async_channel::Sender<SinkEvent>>>,
     pending_frame: Mutex<Option<Frame>>,
     cached_caps: Mutex<Option<gst::Caps>>,
 }
@@ -449,10 +449,16 @@ impl VideoSinkImpl for PaintableSink {
             gst::FlowError::Flushing
         })?;
 
-        sender.send(SinkEvent::FrameChanged).map_err(|_| {
-            gst::error!(CAT, imp: self, "Have main thread receiver shut down");
-            gst::FlowError::Flushing
-        })?;
+        match sender.try_send(SinkEvent::FrameChanged) {
+            Ok(_) => (),
+            Err(async_channel::TrySendError::Full(_)) => {
+                gst::warning!(CAT, imp: self, "Have too many pending frames");
+            }
+            Err(async_channel::TrySendError::Closed(_)) => {
+                gst::error!(CAT, imp: self, "Have main thread receiver shut down");
+                return Err(gst::FlowError::Flushing);
+            }
+        }
 
         Ok(gst::FlowSuccess::Ok)
     }
@@ -521,20 +527,24 @@ impl PaintableSink {
         gst::debug!(CAT, imp: self, "Initializing paintable");
 
         // The channel for the SinkEvents
-        let (sender, receiver) = glib::MainContext::channel(glib::Priority::DEFAULT);
-        let self_ = self.to_owned();
+        let (sender, receiver) = async_channel::bounded(3);
 
+        // Spawn an async task on the main context to handle the channel messages
+        let main_context = glib::MainContext::default();
+
+        let self_ = self.downgrade();
+        main_context.spawn(async move {
+            while let Ok(action) = receiver.recv().await {
+                let Some(self_) = self_.upgrade() else {
+                    break;
+                };
+
+                self_.do_action(action);
+            }
+        });
+
+        // Create the paintable from the main thread
         let paintable = utils::invoke_on_main_thread(move || {
-            // Attach the receiver from the main thread to make sure it is called
-            // from a place where it can acquire the default main context.
-            receiver.attach(
-                Some(&glib::MainContext::default()),
-                glib::clone!(
-                    @weak self_ => @default-return glib::ControlFlow::Break,
-                    move |action| self_.do_action(action)
-                ),
-            );
-
             #[cfg(any(target_os = "macos", target_os = "windows", feature = "gst_gl"))]
             {
                 let gdk_context = if let GLContext::Initialized { gdk_context, .. } =