Add an is_gui_thread flag to MainThreadExecutor

We'll also use the EventLoop for running background tasks completely
decoupled from the GUI.

src/event_loop.rs

@@ -55,11 +55,7 @@ where
 
 /// Something that can execute tasks of type `T`.
 pub(crate) trait MainThreadExecutor<T>: Send + Sync {
-    /// Execute a task on the current thread. This should only be called from the main thread.
-    ///
-    /// # Safety
-    ///
-    /// This is not actually unsafe in the typical Rust sense. But the implemnting function will
-    /// assume (and can only assume) that this is called from the main thread.
-    unsafe fn execute(&self, task: T);
+    /// Execute a task on the current thread. This is either called from the GUI thread or from
+    /// another background thread, depending on how the task was scheduled in the [`EventContext`].
+    fn execute(&self, task: T, is_gui_thread: bool);
 }

src/event_loop/linux.rs

@@ -66,7 +66,7 @@ where
 
     fn do_maybe_async(&self, task: T) -> bool {
         if self.is_main_thread() {
-            unsafe { self.executor.execute(task) };
+            self.executor.execute(task, true);
             true
         } else {
             self.worker_thread_channel
@@ -103,7 +103,7 @@ where
     loop {
         match receiver.recv() {
             Ok(Message::Task(task)) => match executor.upgrade() {
-                Some(e) => unsafe { e.execute(task) },
+                Some(e) => e.execute(task, true),
                 None => {
                     nih_trace!(
                         "Received a new task but the executor is no longer alive, shutting down \

src/event_loop/windows.rs

@@ -97,7 +97,7 @@ where
                 };
 
                 while let Some(task) = tasks.pop() {
-                    unsafe { executor.execute(task) };
+                    executor.execute(task, true);
                 }
             })
         };
@@ -134,7 +134,7 @@ where
 
     fn do_maybe_async(&self, task: T) -> bool {
         if self.is_main_thread() {
-            unsafe { e.execute(task) };
+            self.executor.execute(task, true);
             true
         } else {
             let success = self.tasks.push(task).is_ok();

src/wrapper/clap/wrapper.rs

@@ -322,7 +322,7 @@ impl<P: ClapPlugin> EventLoop<Task<P>, Wrapper<P>> for Wrapper<P> {
 
     fn do_maybe_async(&self, task: Task<P>) -> bool {
         if self.is_main_thread() {
-            unsafe { self.execute(task) };
+            self.execute(task, true);
             true
         } else {
             let success = self.tasks.push(task).is_ok();
@@ -351,33 +351,37 @@ impl<P: ClapPlugin> EventLoop<Task<P>, Wrapper<P>> for Wrapper<P> {
 }
 
 impl<P: ClapPlugin> MainThreadExecutor<Task<P>> for Wrapper<P> {
-    unsafe fn execute(&self, task: Task<P>) {
+    fn execute(&self, task: Task<P>, is_gui_thread: bool) {
         // This function is always called from the main thread, from [Self::on_main_thread].
         match task {
             Task::PluginTask(task) => (self.task_executor.lock())(task),
             Task::LatencyChanged => match &*self.host_latency.borrow() {
                 Some(host_latency) => {
+                    nih_debug_assert!(is_gui_thread);
+
                     // XXX: The CLAP docs mention that you should request a restart if this happens
                     //      while the plugin is activated (which is not entirely the same thing as
                     //      is processing, but we'll treat it as the same thing). In practice just
                     //      calling the latency changed function also seems to work just fine.
                     if self.is_processing.load(Ordering::SeqCst) {
-                        clap_call! { &*self.host_callback=>request_restart(&*self.host_callback) };
+                        unsafe_clap_call! { &*self.host_callback=>request_restart(&*self.host_callback) };
                     } else {
-                        clap_call! { host_latency=>changed(&*self.host_callback) };
+                        unsafe_clap_call! { host_latency=>changed(&*self.host_callback) };
                     }
                 }
                 None => nih_debug_assert_failure!("Host does not support the latency extension"),
             },
             Task::VoiceInfoChanged => match &*self.host_voice_info.borrow() {
                 Some(host_voice_info) => {
-                    clap_call! { host_voice_info=>changed(&*self.host_callback) };
+                    nih_debug_assert!(is_gui_thread);
+                    unsafe_clap_call! { host_voice_info=>changed(&*self.host_callback) };
                 }
                 None => nih_debug_assert_failure!("Host does not support the voice-info extension"),
             },
             Task::RescanParamValues => match &*self.host_params.borrow() {
                 Some(host_params) => {
-                    clap_call! { host_params=>rescan(&*self.host_callback, CLAP_PARAM_RESCAN_VALUES) };
+                    nih_debug_assert!(is_gui_thread);
+                    unsafe_clap_call! { host_params=>rescan(&*self.host_callback, CLAP_PARAM_RESCAN_VALUES) };
                 }
                 None => nih_debug_assert_failure!("The host does not support parameters? What?"),
             },
@@ -2352,7 +2356,7 @@ impl<P: ClapPlugin> Wrapper<P> {
         // [Self::do_maybe_async] posts a task to the queue and asks the host to call this function
         // on the main thread, so once that's done we can just handle all requests here
         while let Some(task) = wrapper.tasks.pop() {
-            wrapper.execute(task);
+            wrapper.execute(task, true);
         }
     }
 

src/wrapper/standalone/wrapper.rs

@@ -146,7 +146,7 @@ pub struct TaskExecutorWrapper<P: Plugin> {
 }
 
 impl<P: Plugin> MainThreadExecutor<P::BackgroundTask> for TaskExecutorWrapper<P> {
-    unsafe fn execute(&self, task: P::BackgroundTask) {
+    fn execute(&self, task: P::BackgroundTask, _is_gui_thread: bool) {
         (self.task_executor.lock())(task)
     }
 }

src/wrapper/vst3/inner.rs

@@ -377,7 +377,7 @@ impl<P: Vst3Plugin> WrapperInner<P> {
         let event_loop = self.event_loop.borrow();
         let event_loop = event_loop.as_ref().unwrap();
         if event_loop.is_main_thread() {
-            unsafe { self.execute(task) };
+            self.execute(task, true);
             true
         } else {
             // If the editor is open, and the host exposes the `IRunLoop` interface, then we'll run
@@ -535,25 +535,22 @@ impl<P: Vst3Plugin> WrapperInner<P> {
 }
 
 impl<P: Vst3Plugin> MainThreadExecutor<Task<P>> for WrapperInner<P> {
-    unsafe fn execute(&self, task: Task<P>) {
+    fn execute(&self, task: Task<P>, is_gui_thread: bool) {
         // This function is always called from the main thread
-        // TODO: When we add GUI resizing and context menus, this should propagate those events to
-        //       `IRunLoop` on Linux to keep REAPER happy. That does mean a double spool, but we can
-        //       come up with a nicer solution to handle that later (can always add a separate
-        //       function for checking if a to be scheduled task can be handled right there and
-        //       then).
         match task {
             Task::PluginTask(task) => (self.task_executor.lock())(task),
             Task::TriggerRestart(flags) => match &*self.component_handler.borrow() {
-                Some(handler) => {
+                Some(handler) => unsafe {
+                    nih_debug_assert!(is_gui_thread);
                     handler.restart_component(flags);
-                }
+                },
                 None => nih_debug_assert_failure!("Component handler not yet set"),
             },
             Task::RequestResize => match &*self.plug_view.read() {
-                Some(plug_view) => {
+                Some(plug_view) => unsafe {
+                    nih_debug_assert!(is_gui_thread);
                     plug_view.request_resize();
-                }
+                },
                 None => nih_debug_assert_failure!("Can't resize a closed editor"),
             },
         }

src/wrapper/vst3/view.rs

@@ -486,7 +486,7 @@ impl<P: Vst3Plugin> IEventHandler for RunLoopEventHandler<P> {
         // This gets called from the host's UI thread because we wrote some bytes to the Unix domain
         // socket. We'll read that data from the socket again just to make REAPER happy.
         while let Some(task) = self.tasks.pop() {
-            self.inner.execute(task);
+            self.inner.execute(task, true);
 
             let mut notify_value = 1i8;
             const NOTIFY_VALUE_SIZE: usize = std::mem::size_of::<i8>();