Add an AsyncExecutor trait for background tasks

src/async_executor.rs

@@ -0,0 +1,23 @@
+//! 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 {
+    /// 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;
+
+    /// 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/lib.rs

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

src/prelude.rs

@@ -10,6 +10,7 @@ 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