Replace AsyncExecutor with simple closure

This makes everything much simpler. The task type is now defined
directly on `Plugin`.

BREAKING_CHANGES.md

@@ -14,13 +14,12 @@ code then it will not be listed here.
   changed to `&mut impl InitContext<Self>`.
 - NIH-plug has gained support for asynchronously running background tasks in a
   simple, type-safe, and realtime-safe way. This sadly does mean that every
-  `Plugin` instance now needs to define an `AsyncExecutor` type definition and
+  `Plugin` instance now needs to define a `BackgroundTask` type definition and
   constructor function as Rust does not yet support defaults for associated
   types (Rust issue [#29661](https://github.com/rust-lang/rust/issues/29661)):
 
   ```rust
-  type AsyncExecutor = ();
-  fn async_executor(&self) -> Self::AsyncExecutor {}
+  type BackgroundTask = ();
   ```
 
 - The `Editor` trait and the `ParentWindowHandle` struct have been moved from

plugins/crisp/src/lib.rs

@@ -307,8 +307,7 @@ impl Plugin for Crisp {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/crossover/src/lib.rs

@@ -183,8 +183,7 @@ impl Plugin for Crossover {
         aux_outputs: Some(&["Band 1", "Band 2", "Band 3", "Band 4", "Band 5"]),
     };
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/diopser/src/lib.rs

@@ -252,8 +252,7 @@ impl Plugin for Diopser {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/gain/src/lib.rs

@@ -132,11 +132,10 @@ impl Plugin for Gain {
     // splits.
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    // More advanced plugins can use this to run expensive background tasks. See the `AsyncExecutor`
-    // trait's documentation for more information. `()` means that the plugin does not have any
-    // background tasks.
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    // More advanced plugins can use this to run expensive background tasks. See the field's
+    // documentation for more information. `()` means that the plugin does not have any background
+    // tasks.
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/gain_gui_egui/src/lib.rs

@@ -83,8 +83,7 @@ impl Plugin for Gain {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/gain_gui_iced/src/lib.rs

@@ -80,8 +80,7 @@ impl Plugin for Gain {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/gain_gui_vizia/src/lib.rs

@@ -79,8 +79,7 @@ impl Plugin for Gain {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/midi_inverter/src/lib.rs

@@ -33,8 +33,7 @@ impl Plugin for MidiInverter {
     const MIDI_OUTPUT: MidiConfig = MidiConfig::MidiCCs;
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/poly_mod_synth/src/lib.rs

@@ -155,8 +155,7 @@ impl Plugin for PolyModSynth {
     const MIDI_INPUT: MidiConfig = MidiConfig::Basic;
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/sine/src/lib.rs

@@ -111,8 +111,7 @@ impl Plugin for Sine {
     const MIDI_INPUT: MidiConfig = MidiConfig::Basic;
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/examples/stft/src/lib.rs

@@ -95,8 +95,7 @@ impl Plugin for Stft {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/loudness_war_winner/src/lib.rs

@@ -123,8 +123,7 @@ impl Plugin for LoudnessWarWinner {
     const DEFAULT_INPUT_CHANNELS: u32 = 2;
     const DEFAULT_OUTPUT_CHANNELS: u32 = 2;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/puberty_simulator/src/lib.rs

@@ -168,8 +168,7 @@ impl Plugin for PubertySimulator {
     const DEFAULT_INPUT_CHANNELS: u32 = 2;
     const DEFAULT_OUTPUT_CHANNELS: u32 = 2;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/safety_limiter/src/lib.rs

@@ -157,8 +157,7 @@ impl Plugin for SafetyLimiter {
     const DEFAULT_INPUT_CHANNELS: u32 = 2;
     const DEFAULT_OUTPUT_CHANNELS: u32 = 2;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

plugins/spectral_compressor/src/lib.rs

@@ -272,8 +272,7 @@ impl Plugin for SpectralCompressor {
 
     const SAMPLE_ACCURATE_AUTOMATION: bool = true;
 
-    type AsyncExecutor = ();
-    fn async_executor(&self) -> Self::AsyncExecutor {}
+    type BackgroundTask = ();
 
     fn params(&self) -> Arc<dyn Params> {
         self.params.clone()

src/async_executor.rs

@@ -1,23 +0,0 @@
-//! Traits for running background tasks from a [`Plugin`][crate::prelude::Plugin].
-//!
-//! This should not be confused with the `async` language features and ecosystem in Rust.
-
-/// Something that can run tasks of type [`Task`][Self::Task]. This can be used to defer expensive
-/// computations to a background thread. Tasks can be spawned through the methods on the various
-/// [`*Context`][crate::context] types.
-pub trait AsyncExecutor: Send + Sync {
-    /// The type of task this executor can execute. This is usually an enum type. The task type
-    /// should not contain any heap allocated data like [`Vec`]s and [`Box`]es.
-    type Task: Send;
-
-    /// Run `task` on the current thread. This is usually called from the operating system's main
-    /// thread or a similar thread.
-    fn execute(&self, task: Self::Task);
-}
-
-/// A default implementation for plugins that don't need asynchronous background tasks.
-impl AsyncExecutor for () {
-    type Task = ();
-
-    fn execute(&self, _task: Self::Task) {}
-}

src/context.rs

@@ -5,7 +5,7 @@ use std::fmt::Display;
 use crate::midi::NoteEvent;
 use crate::params::internals::ParamPtr;
 use crate::params::Param;
-use crate::prelude::{AsyncExecutor, Plugin};
+use crate::plugin::Plugin;
 use crate::wrapper::state::PluginState;
 
 /// Callbacks the plugin can make while it is being initialized. This is passed to the plugin during
@@ -23,7 +23,7 @@ pub trait InitContext<P: Plugin> {
     ///
     /// There is no asynchronous alternative for this function as that may result in incorrect
     /// behavior when doing offline rendering.
-    fn execute(&self, task: <P::AsyncExecutor as AsyncExecutor>::Task);
+    fn execute(&self, task: P::BackgroundTask);
 
     /// Get the current plugin API.
     fn plugin_api(&self) -> PluginApi;
@@ -53,7 +53,7 @@ pub trait InitContext<P: Plugin> {
 pub trait ProcessContext<P: Plugin> {
     /// Run a task on a background thread. This allows defering expensive background tasks for
     /// alter. As long as creating the `task` is realtime-safe, this operation is too.
-    fn execute_async(&self, task: <P::AsyncExecutor as AsyncExecutor>::Task);
+    fn execute_async(&self, task: P::BackgroundTask);
 
     /// Get the current plugin API.
     fn plugin_api(&self) -> PluginApi;

src/event_loop.rs

@@ -10,8 +10,6 @@ mod linux;
 #[cfg(target_os = "windows")]
 mod windows;
 
-use crate::prelude::AsyncExecutor;
-
 #[cfg(all(target_family = "unix", not(target_os = "macos")))]
 pub(crate) use self::linux::LinuxEventLoop as OsEventLoop;
 // For now, also use the Linux event loop on macOS so it at least compiles
@@ -68,11 +66,3 @@ pub(crate) trait MainThreadExecutor<T>: Send + Sync {
     /// assume (and can only assume) that this is called from the main thread.
     unsafe fn execute(&self, task: T);
 }
-
-/// An adapter implementation to allow any [`AsyncExecutor`] to function as a
-/// [`MainThreadExecutor`]. Used only in the standalone wrapper.
-impl<T: Send, E: AsyncExecutor<Task = T>> MainThreadExecutor<T> for E {
-    unsafe fn execute(&self, task: T) {
-        AsyncExecutor::execute(self, task);
-    }
-}

src/lib.rs

@@ -101,7 +101,6 @@ pub mod prelude;
 pub mod formatters;
 pub mod util;
 
-pub mod async_executor;
 pub mod buffer;
 pub mod context;
 pub mod editor;

src/plugin.rs

@@ -2,7 +2,6 @@
 
 use std::sync::Arc;
 
-use crate::async_executor::AsyncExecutor;
 use crate::buffer::Buffer;
 use crate::context::{InitContext, ProcessContext};
 use crate::editor::Editor;
@@ -11,6 +10,8 @@ use crate::params::Params;
 use crate::wrapper::clap::features::ClapFeature;
 use crate::wrapper::state::PluginState;
 
+pub type TaskExecutor<P> = Box<dyn Fn(<P as Plugin>::BackgroundTask) + Send + Sync>;
+
 /// Basic functionality that needs to be implemented by a plugin. The wrappers will use this to
 /// expose the plugin in a particular plugin format.
 ///
@@ -90,19 +91,21 @@ pub trait Plugin: Default + Send + 'static {
     /// to do offline processing.
     const HARD_REALTIME_ONLY: bool = false;
 
-    /// The plugin's [`AsyncExecutor`] type. Use `()` if the plugin does not need to perform
-    /// expensive background tasks.
-    //
-    // This needs to be an associated type so we can have a nice type safe interface in the
-    // `*Context` traits.
+    /// A type encoding this plugin's different background tasks, if it needs those. This is usually
+    /// an enum type. The task type should not contain any heap allocated data like [`Vec`]s and
+    /// [`Box`]es. Tasks can be send using the methods on the various [`*Context`][crate::context]
+    /// objects.
+    ///
+    /// Use `()` if the plugin does not need any background tasks.
     //
     // NOTE: Sadly it's not yet possible to default this and the `async_executor()` function to
     //       `()`: https://github.com/rust-lang/rust/issues/29661
-    type AsyncExecutor: AsyncExecutor;
-
-    /// The plugin's background task executor. Use `()` if the plugin does not need this
-    /// functinlality.
-    fn async_executor(&self) -> Self::AsyncExecutor;
+    type BackgroundTask: Send;
+    /// The plugin's background task executor. See [`BackgroundTask`][Self::BackgroundTask].
+    fn task_executor(&self) -> TaskExecutor<Self> {
+        // In the default implementation we can simply ignore the value
+        Box::new(|_| ())
+    }
 
     /// The plugin's parameters. The host will update the parameter values before calling
     /// `process()`. These parameters are identified by strings that should never change when the

src/prelude.rs

@@ -10,7 +10,6 @@ pub use crate::wrapper::standalone::{nih_export_standalone, nih_export_standalon
 pub use crate::formatters;
 pub use crate::util;
 
-pub use crate::async_executor::AsyncExecutor;
 pub use crate::buffer::Buffer;
 pub use crate::context::{GuiContext, InitContext, ParamSetter, PluginApi, ProcessContext};
 // This also includes the derive macro
@@ -24,7 +23,7 @@ pub use crate::params::Params;
 pub use crate::params::{BoolParam, FloatParam, IntParam, Param, ParamFlags};
 pub use crate::plugin::{
     AuxiliaryBuffers, AuxiliaryIOConfig, BufferConfig, BusConfig, ClapPlugin, Plugin,
-    PolyModulationConfig, PortNames, ProcessMode, ProcessStatus, Vst3Plugin,
+    PolyModulationConfig, PortNames, ProcessMode, ProcessStatus, TaskExecutor, Vst3Plugin,
 };
 pub use crate::wrapper::clap::features::ClapFeature;
 pub use crate::wrapper::state::PluginState;

src/wrapper/clap/context.rs

@@ -3,7 +3,6 @@ use std::collections::VecDeque;
 use std::sync::Arc;
 
 use super::wrapper::{OutputParamEvent, Task, Wrapper};
-use crate::async_executor::AsyncExecutor;
 use crate::context::{GuiContext, InitContext, PluginApi, ProcessContext, Transport};
 use crate::event_loop::EventLoop;
 use crate::midi::NoteEvent;
@@ -115,8 +114,8 @@ impl<P: ClapPlugin> GuiContext for WrapperGuiContext<P> {
 }
 
 impl<P: ClapPlugin> InitContext<P> for WrapperInitContext<'_, P> {
-    fn execute(&self, task: <P::AsyncExecutor as crate::prelude::AsyncExecutor>::Task) {
-        self.wrapper.async_executor.execute(task);
+    fn execute(&self, task: P::BackgroundTask) {
+        (self.wrapper.task_executor)(task);
     }
 
     fn plugin_api(&self) -> PluginApi {
@@ -133,10 +132,7 @@ impl<P: ClapPlugin> InitContext<P> for WrapperInitContext<'_, P> {
 }
 
 impl<P: ClapPlugin> ProcessContext<P> for WrapperProcessContext<'_, P> {
-    fn execute_async(
-        &self,
-        task: <<P as crate::prelude::Plugin>::AsyncExecutor as AsyncExecutor>::Task,
-    ) {
+    fn execute_async(&self, task: P::BackgroundTask) {
         let task_posted = self.wrapper.do_maybe_async(Task::PluginTask(task));
         nih_debug_assert!(task_posted, "The task queue is full, dropping task...");
     }

src/wrapper/clap/wrapper.rs

@@ -76,7 +76,6 @@ use std::time::Duration;
 use super::context::{WrapperGuiContext, WrapperInitContext, WrapperProcessContext};
 use super::descriptor::PluginDescriptor;
 use super::util::ClapPtr;
-use crate::async_executor::AsyncExecutor;
 use crate::buffer::Buffer;
 use crate::context::Transport;
 use crate::editor::{Editor, ParentWindowHandle};
@@ -86,6 +85,7 @@ use crate::params::internals::ParamPtr;
 use crate::params::{ParamFlags, Params};
 use crate::plugin::{
     AuxiliaryBuffers, BufferConfig, BusConfig, ClapPlugin, Plugin, ProcessMode, ProcessStatus,
+    TaskExecutor,
 };
 use crate::util::permit_alloc;
 use crate::wrapper::clap::util::{read_stream, write_stream};
@@ -106,8 +106,8 @@ pub struct Wrapper<P: ClapPlugin> {
 
     /// The wrapped plugin instance.
     plugin: Mutex<P>,
-    /// The plugin's background task executor.
-    pub async_executor: P::AsyncExecutor,
+    /// The plugin's background task executor closure.
+    pub task_executor: TaskExecutor<P>,
     /// The plugin's parameters. These are fetched once during initialization. That way the
     /// `ParamPtr`s are guaranteed to live at least as long as this object and we can interact with
     /// the `Params` object without having to acquire a lock on `plugin`.
@@ -272,7 +272,7 @@ pub struct Wrapper<P: ClapPlugin> {
 #[allow(clippy::enum_variant_names)]
 pub enum Task<P: Plugin> {
     /// Execute one of the plugin's background tasks.
-    PluginTask(<P::AsyncExecutor as AsyncExecutor>::Task),
+    PluginTask(P::BackgroundTask),
     /// Inform the host that the latency has changed.
     LatencyChanged,
     /// Inform the host that the voice info has changed.
@@ -353,7 +353,7 @@ impl<P: ClapPlugin> MainThreadExecutor<Task<P>> for Wrapper<P> {
     unsafe fn execute(&self, task: Task<P>) {
         // This function is always called from the main thread, from [Self::on_main_thread].
         match task {
-            Task::PluginTask(task) => AsyncExecutor::execute(&self.async_executor, task),
+            Task::PluginTask(task) => (self.task_executor)(task),
             Task::LatencyChanged => match &*self.host_latency.borrow() {
                 Some(host_latency) => {
                     // XXX: The CLAP docs mention that you should request a restart if this happens
@@ -387,7 +387,7 @@ impl<P: ClapPlugin> MainThreadExecutor<Task<P>> for Wrapper<P> {
 impl<P: ClapPlugin> Wrapper<P> {
     pub fn new(host_callback: *const clap_host) -> Arc<Self> {
         let plugin = P::default();
-        let async_executor = plugin.async_executor();
+        let task_executor = plugin.task_executor();
         let editor = plugin.editor().map(Mutex::new);
 
         // This is used to allow the plugin to restore preset data from its editor, see the comment
@@ -549,7 +549,7 @@ impl<P: ClapPlugin> Wrapper<P> {
             this: AtomicRefCell::new(Weak::new()),
 
             plugin: Mutex::new(plugin),
-            async_executor,
+            task_executor,
             params,
             editor,
             editor_handle: Mutex::new(None),

src/wrapper/standalone/context.rs

@@ -3,7 +3,6 @@ use std::sync::Arc;
 
 use super::backend::Backend;
 use super::wrapper::{GuiTask, Wrapper};
-use crate::async_executor::AsyncExecutor;
 use crate::context::{GuiContext, InitContext, PluginApi, ProcessContext, Transport};
 use crate::event_loop::EventLoop;
 use crate::midi::NoteEvent;
@@ -80,8 +79,8 @@ impl<P: Plugin, B: Backend> GuiContext for WrapperGuiContext<P, B> {
 }
 
 impl<P: Plugin, B: Backend> InitContext<P> for WrapperInitContext<'_, P, B> {
-    fn execute(&self, task: <<P as Plugin>::AsyncExecutor as crate::prelude::AsyncExecutor>::Task) {
-        self.wrapper.async_executor.execute(task);
+    fn execute(&self, task: P::BackgroundTask) {
+        (self.wrapper.task_executor_wrapper.task_executor)(task);
     }
 
     fn plugin_api(&self) -> PluginApi {
@@ -98,7 +97,7 @@ impl<P: Plugin, B: Backend> InitContext<P> for WrapperInitContext<'_, P, B> {
 }
 
 impl<P: Plugin, B: Backend> ProcessContext<P> for WrapperProcessContext<'_, P, B> {
-    fn execute_async(&self, task: <P::AsyncExecutor as AsyncExecutor>::Task) {
+    fn execute_async(&self, task: P::BackgroundTask) {
         let task_posted = self.wrapper.event_loop.do_maybe_async(task);
         nih_debug_assert!(task_posted, "The task queue is full, dropping task...");
     }

src/wrapper/standalone/wrapper.rs

@@ -13,16 +13,15 @@ use std::thread;
 use super::backend::Backend;
 use super::config::WrapperConfig;
 use super::context::{WrapperGuiContext, WrapperInitContext, WrapperProcessContext};
-use crate::async_executor::AsyncExecutor;
 use crate::context::Transport;
 use crate::editor::{Editor, ParentWindowHandle};
-use crate::event_loop::{EventLoop, OsEventLoop};
+use crate::event_loop::{EventLoop, MainThreadExecutor, OsEventLoop};
 use crate::midi::NoteEvent;
 use crate::params::internals::ParamPtr;
 use crate::params::{ParamFlags, Params};
 use crate::plugin::{
     AuxiliaryBuffers, AuxiliaryIOConfig, BufferConfig, BusConfig, Plugin, ProcessMode,
-    ProcessStatus,
+    ProcessStatus, TaskExecutor,
 };
 use crate::util::permit_alloc;
 use crate::wrapper::state::{self, PluginState};
@@ -37,8 +36,9 @@ pub struct Wrapper<P: Plugin, B: Backend> {
 
     /// The wrapped plugin instance.
     plugin: Mutex<P>,
-    /// The plugin's background task executor.
-    pub async_executor: Arc<P::AsyncExecutor>,
+    /// The plugin's background task executor closure. Wrapped in another struct so it can be used
+    /// as a [`MainContext`] with [`EventLoop`].
+    pub task_executor_wrapper: Arc<TaskExecutorWrapper<P>>,
     /// The plugin's parameters. These are fetched once during initialization. That way the
     /// `ParamPtr`s are guaranteed to live at least as long as this object and we can interact with
     /// the `Params` object without having to acquire a lock on `plugin`.
@@ -60,7 +60,7 @@ pub struct Wrapper<P: Plugin, B: Backend> {
     ///
     /// This is only used for executing [`AsyncExecutor`] tasks, so it's parameterized directly over
     /// that using a special `MainThreadExecutor` wrapper around `AsyncExecutor`.
-    pub(crate) event_loop: OsEventLoop<<P::AsyncExecutor as AsyncExecutor>::Task, P::AsyncExecutor>,
+    pub(crate) event_loop: OsEventLoop<P::BackgroundTask, TaskExecutorWrapper<P>>,
 
     config: WrapperConfig,
 
@@ -139,12 +139,25 @@ impl WindowHandler for WrapperWindowHandler {
     }
 }
 
+/// Adapter to make `TaskExecutor<P>` work as a `MainThreadExecutor`.
+pub struct TaskExecutorWrapper<P: Plugin> {
+    pub task_executor: TaskExecutor<P>,
+}
+
+impl<P: Plugin> MainThreadExecutor<P::BackgroundTask> for TaskExecutorWrapper<P> {
+    unsafe fn execute(&self, task: P::BackgroundTask) {
+        (self.task_executor)(task)
+    }
+}
+
 impl<P: Plugin, B: Backend> Wrapper<P, B> {
     /// Instantiate a new instance of the standalone wrapper. Returns an error if the plugin does
     /// not accept the IO configuration from the wrapper config.
     pub fn new(backend: B, config: WrapperConfig) -> Result<Arc<Self>, WrapperError> {
         let plugin = P::default();
-        let async_executor = Arc::new(plugin.async_executor());
+        let task_executor_wrapper = Arc::new(TaskExecutorWrapper {
+            task_executor: plugin.task_executor(),
+        });
         let params = plugin.params();
         let editor = plugin.editor().map(|editor| Arc::new(Mutex::new(editor)));
 
@@ -191,7 +204,7 @@ impl<P: Plugin, B: Backend> Wrapper<P, B> {
             backend: AtomicRefCell::new(backend),
 
             plugin: Mutex::new(plugin),
-            async_executor: async_executor.clone(),
+            task_executor_wrapper: task_executor_wrapper.clone(),
             params,
             known_parameters: param_map.iter().map(|(_, ptr, _)| *ptr).collect(),
             param_map: param_map
@@ -200,7 +213,7 @@ impl<P: Plugin, B: Backend> Wrapper<P, B> {
                 .collect(),
             editor,
 
-            event_loop: OsEventLoop::new_and_spawn(Arc::downgrade(&async_executor)),
+            event_loop: OsEventLoop::new_and_spawn(Arc::downgrade(&task_executor_wrapper)),
 
             bus_config: BusConfig {
                 num_input_channels: config.input_channels.unwrap_or(P::DEFAULT_INPUT_CHANNELS),

src/wrapper/vst3/context.rs

@@ -5,7 +5,6 @@ use std::sync::Arc;
 use vst3_sys::vst::IComponentHandler;
 
 use super::inner::{Task, WrapperInner};
-use crate::async_executor::AsyncExecutor;
 use crate::context::{GuiContext, InitContext, PluginApi, ProcessContext, Transport};
 use crate::midi::NoteEvent;
 use crate::params::internals::ParamPtr;
@@ -117,8 +116,8 @@ impl<P: Vst3Plugin> GuiContext for WrapperGuiContext<P> {
 }
 
 impl<P: Vst3Plugin> InitContext<P> for WrapperInitContext<'_, P> {
-    fn execute(&self, task: <P::AsyncExecutor as crate::prelude::AsyncExecutor>::Task) {
-        self.inner.async_executor.execute(task);
+    fn execute(&self, task: P::BackgroundTask) {
+        (self.inner.task_executor)(task);
     }
 
     fn plugin_api(&self) -> PluginApi {
@@ -135,7 +134,7 @@ impl<P: Vst3Plugin> InitContext<P> for WrapperInitContext<'_, P> {
 }
 
 impl<P: Vst3Plugin> ProcessContext<P> for WrapperProcessContext<'_, P> {
-    fn execute_async(&self, task: <P::AsyncExecutor as AsyncExecutor>::Task) {
+    fn execute_async(&self, task: P::BackgroundTask) {
         let task_posted = self.inner.do_maybe_async(Task::PluginTask(task));
         nih_debug_assert!(task_posted, "The task queue is full, dropping task...");
     }

src/wrapper/vst3/inner.rs

@@ -14,7 +14,6 @@ use super::note_expressions::NoteExpressionController;
 use super::param_units::ParamUnits;
 use super::util::{ObjectPtr, VstPtr, VST3_MIDI_PARAMS_END, VST3_MIDI_PARAMS_START};
 use super::view::WrapperView;
-use crate::async_executor::AsyncExecutor;
 use crate::buffer::Buffer;
 use crate::context::Transport;
 use crate::editor::Editor;
@@ -22,7 +21,9 @@ use crate::event_loop::{EventLoop, MainThreadExecutor, OsEventLoop};
 use crate::midi::{MidiConfig, NoteEvent};
 use crate::params::internals::ParamPtr;
 use crate::params::{ParamFlags, Params};
-use crate::plugin::{BufferConfig, BusConfig, Plugin, ProcessMode, ProcessStatus, Vst3Plugin};
+use crate::plugin::{
+    BufferConfig, BusConfig, Plugin, ProcessMode, ProcessStatus, TaskExecutor, Vst3Plugin,
+};
 use crate::wrapper::state::{self, PluginState};
 use crate::wrapper::util::{hash_param_id, process_wrapper};
 
@@ -32,8 +33,8 @@ use crate::wrapper::util::{hash_param_id, process_wrapper};
 pub(crate) struct WrapperInner<P: Vst3Plugin> {
     /// The wrapped plugin instance.
     pub plugin: Mutex<P>,
-    /// The plugin's background task executor.
-    pub async_executor: P::AsyncExecutor,
+    /// The plugin's background task executor closure.
+    pub task_executor: TaskExecutor<P>,
     /// The plugin's parameters. These are fetched once during initialization. That way the
     /// `ParamPtr`s are guaranteed to live at least as long as this object and we can interact with
     /// the `Params` object without having to acquire a lock on `plugin`.
@@ -154,7 +155,7 @@ pub(crate) struct WrapperInner<P: Vst3Plugin> {
 #[allow(clippy::enum_variant_names)]
 pub enum Task<P: Plugin> {
     /// Execute one of the plugin's background tasks.
-    PluginTask(<P::AsyncExecutor as AsyncExecutor>::Task),
+    PluginTask(P::BackgroundTask),
     /// Trigger a restart with the given restart flags. This is a bit set of the flags from
     /// [`vst3_sys::vst::RestartFlags`].
     TriggerRestart(i32),
@@ -196,7 +197,7 @@ impl<P: Vst3Plugin> WrapperInner<P> {
     #[allow(unused_unsafe)]
     pub fn new() -> Arc<Self> {
         let plugin = P::default();
-        let async_executor = plugin.async_executor();
+        let task_executor = plugin.task_executor();
         let editor = plugin.editor().map(|editor| Arc::new(Mutex::new(editor)));
 
         // This is used to allow the plugin to restore preset data from its editor, see the comment
@@ -280,7 +281,7 @@ impl<P: Vst3Plugin> WrapperInner<P> {
 
         let wrapper = Self {
             plugin: Mutex::new(plugin),
-            async_executor,
+            task_executor,
             params,
             editor,
 
@@ -526,7 +527,7 @@ impl<P: Vst3Plugin> MainThreadExecutor<Task<P>> for WrapperInner<P> {
         //       function for checking if a to be scheduled task can be handled right there and
         //       then).
         match task {
-            Task::PluginTask(task) => AsyncExecutor::execute(&self.async_executor, task),
+            Task::PluginTask(task) => (self.task_executor)(task),
             Task::TriggerRestart(flags) => match &*self.component_handler.borrow() {
                 Some(handler) => {
                     handler.restart_component(flags);