Fix performEdit() deadlock in Ardour/Mixbus

Those DAWs would immediately call `IEditController::performEdit()` with
the same parameter change the plugin has just announced, which would
result in a deadlock. Hopefully this helps with #100.

CHANGELOG.md

@@ -71,6 +71,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Fixed _FabFilter_ VST3 plugins freezing in **Ardour** and **Mixbus** when
   trying to duplicate existing instances of the plugin while the GUI editor is
   open.
+- Fixed VST3 plugins freezing in **Ardour** and **Mixbus** when the plugin tries
+  to automate a parameter while loading a preset.
 - Fixed a regression from yabridge 3.1.0 where REAPER would freeze when opening
   a VST3 plugin context menu.
 - Fixed a potential assertion failure when setting VST3 preset data. This would

src/wine-host/bridges/vst3-impls/component-handler-proxy.cpp

@@ -47,10 +47,15 @@ Vst3ComponentHandlerProxyImpl::beginEdit(Steinberg::Vst::ParamID id) {
 tresult PLUGIN_API Vst3ComponentHandlerProxyImpl::performEdit(
     Steinberg::Vst::ParamID id,
     Steinberg::Vst::ParamValue valueNormalized) {
-    return bridge.send_message(YaComponentHandler::PerformEdit{
-        .owner_instance_id = owner_instance_id(),
-        .id = id,
-        .value_normalized = valueNormalized});
+    // HACK: Ardour/Mixbus will in some cases immediately call
+    //       `IEditController::setParamNormalized()` after this `performEdit()`,
+    //       so we need to be able to receive that
+    //       `IEditController::setParamNormalized()` on the same thread.
+    return bridge.send_mutually_recursive_message(
+        YaComponentHandler::PerformEdit{
+            .owner_instance_id = owner_instance_id(),
+            .id = id,
+            .value_normalized = valueNormalized});
 }
 
 tresult PLUGIN_API

src/wine-host/bridges/vst3.cpp

@@ -440,9 +440,16 @@ void Vst3Bridge::run() {
             },
             [&](const YaEditController::SetParamNormalized& request)
                 -> YaEditController::SetParamNormalized::Response {
-                return object_instances[request.instance_id]
-                    .edit_controller->setParamNormalized(request.id,
-                                                         request.value);
+                // HACK: Under Ardour/Mixbus, `IComponentHandler::performEdit()`
+                //       and `IEditController::setParamNormalized()` can be
+                //       mutually recursive because the host will immediately
+                //       relay the parameter change the plugin has just
+                //       announced.
+                return do_mutual_recursion_on_off_thread<tresult>([&]() {
+                    return object_instances[request.instance_id]
+                        .edit_controller->setParamNormalized(request.id,
+                                                             request.value);
+                });
             },
             [&](YaEditController::SetComponentHandler& request)
                 -> YaEditController::SetComponentHandler::Response {