Add hook/event system

.cargo/config.toml

@@ -1,3 +1,17 @@
+# we use tokio_unstable to enable runtime::Handle::id so we can separate
+# globals from multiple parallel tests. If that function ever does get removed
+# its possible to replace (with some additional overhead and effort)
+# Annoyingly build.rustflags doesn't work here because it gets overwritten
+# if people have their own global target.<..> config (for example to enable mold)
+# specifying flags this way is more robust as they get merged
+# This still gets overwritten by RUST_FLAGS though, luckily it shouldn't be necessary
+# to set those most of the time. If downstream does overwrite this its not a huge
+# deal since it will only break tests anyway
+[target."cfg(all())"]
+rustflags = ["--cfg", "tokio_unstable", "-C", "target-feature=-crt-static"]
+
+
 [alias]
 xtask = "run --package xtask --"
 integration-test = "test --features integration --profile integration --workspace --test integration"
+

helix-event/Cargo.toml

@@ -12,5 +12,18 @@ homepage.workspace = true
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-tokio = { version = "1", features = ["rt", "rt-multi-thread", "time", "sync", "parking_lot"] }
-parking_lot = { version = "0.12", features = ["send_guard"] }
+ahash = "0.8.3"
+hashbrown = "0.14.0"
+tokio = { version = "1", features = ["rt", "rt-multi-thread", "time", "sync", "parking_lot", "macros"] }
+# the event registry is essentially read only but must be an rwlock so we can
+# setup new events on initialization, hardware-lock-elision hugely benefits this case
+# as it essentially makes the lock entirely free as long as there is no writes 
+parking_lot = { version = "0.12", features = ["hardware-lock-elision"] }
+once_cell = "1.18"
+
+anyhow = "1"
+log = "0.4"
+futures-executor = "0.3.28"
+
+[features]
+integration_test = []

helix-event/src/cancel.rs

@@ -0,0 +1,19 @@
+use std::future::Future;
+
+pub use oneshot::channel as cancelation;
+use tokio::sync::oneshot;
+
+pub type CancelTx = oneshot::Sender<()>;
+pub type CancelRx = oneshot::Receiver<()>;
+
+pub async fn cancelable_future<T>(future: impl Future<Output = T>, cancel: CancelRx) -> Option<T> {
+    tokio::select! {
+        biased;
+        _ = cancel => {
+            None
+        }
+        res = future => {
+            Some(res)
+        }
+    }
+}

helix-event/src/debounce.rs

@@ -0,0 +1,67 @@
+//! Utilities for declaring an async (usually debounced) hook
+
+use std::time::Duration;
+
+use futures_executor::block_on;
+use tokio::sync::mpsc::{self, error::TrySendError, Sender};
+use tokio::time::Instant;
+
+/// Async hooks provide a convenient framework for implementing (debounced)
+/// async event handlers. Most synchronous event hooks will likely need to
+/// debounce their events, coordinate multiple different hooks and potentially
+/// track some state. `AsyncHooks` facilitate these use cases by running as
+/// a background tokio task that waits for events (usually an enum) to be
+/// sent through a channel.
+pub trait AsyncHook: Sync + Send + 'static + Sized {
+    type Event: Sync + Send + 'static;
+    /// Called immediately whenever an event is received, this function can
+    /// consume the event immediately or debounce it. In case of debouncing,
+    /// it can either define a new debounce timeout or continue the current one
+    fn handle_event(&mut self, event: Self::Event, timeout: Option<Instant>) -> Option<Instant>;
+
+    /// Called whenever the debounce timeline is reached
+    fn finish_debounce(&mut self);
+
+    fn spawn(self) -> mpsc::Sender<Self::Event> {
+        // the capacity doesn't matter too much here, unless the cpu is totally overwhelmed
+        // the cap will never be reached since we always immediately drain the channel
+        // so it should only be reached in case of total CPU overload.
+        // However, a bounded channel is much more efficient so it's nice to use here
+        let (tx, rx) = mpsc::channel(128);
+        tokio::spawn(run(self, rx));
+        tx
+    }
+}
+
+async fn run<Hook: AsyncHook>(mut hook: Hook, mut rx: mpsc::Receiver<Hook::Event>) {
+    let mut deadline = None;
+    loop {
+        let event = match deadline {
+            Some(deadline_) => {
+                let res = tokio::time::timeout_at(deadline_, rx.recv()).await;
+                match res {
+                    Ok(event) => event,
+                    Err(_) => {
+                        hook.finish_debounce();
+                        deadline = None;
+                        continue;
+                    }
+                }
+            }
+            None => rx.recv().await,
+        };
+        let Some(event) = event else {
+            break;
+        };
+        deadline = hook.handle_event(event, deadline);
+    }
+}
+
+pub fn send_blocking<T>(tx: &Sender<T>, data: T) {
+    // block_on has some overhead and in practice the channel should basically
+    // never be full anyway so first try sending without blocking
+    if let Err(TrySendError::Full(data)) = tx.try_send(data) {
+        // set a timeout so that we just drop a message instead of freezing the editor in the worst case
+        let _ = block_on(tx.send_timeout(data, Duration::from_millis(10)));
+    }
+}

helix-event/src/hook.rs

@@ -0,0 +1,91 @@
+//! rust dynamic dispatch is extremely limited so we have to build our
+//! own vtable implementation. Otherwise implementing the event system would not be possible.
+//! A nice bonus of this approach is that we can optimize the vtable a bit more. Normally
+//! a dyn Trait fat pointer contains two pointers: A pointer to the data itself and a
+//! pointer to a global (static) vtable entry which itself contains multiple other pointers
+//! (the various functions of the trait, drop, size and align). That makes dynamic
+//! dispatch pretty slow (double pointer indirections). However, we only have a single function
+//! in the hook trait and don't need a drop implementation (event system is global anyway
+//! and never dropped) so we can just store the entire vtable inline.
+
+use anyhow::Result;
+use std::ptr::{self, NonNull};
+
+use crate::Event;
+
+/// Opaque handle type that represents an erased type parameter.
+///
+/// If extern types were stable, this could be implemented as `extern { pub type Opaque; }` but
+/// until then we can use this.
+///
+/// Care should be taken that we don't use a concrete instance of this. It should only be used
+/// through a reference, so we can maintain something else's lifetime.
+struct Opaque(());
+
+pub(crate) struct ErasedHook {
+    data: NonNull<Opaque>,
+    call: unsafe fn(NonNull<Opaque>, NonNull<Opaque>, NonNull<Opaque>),
+}
+
+impl ErasedHook {
+    pub(crate) fn new_dynamic<H: Fn() -> Result<()> + 'static + Send + Sync>(
+        hook: H,
+    ) -> ErasedHook {
+        unsafe fn call<F: Fn() -> Result<()> + 'static + Send + Sync>(
+            hook: NonNull<Opaque>,
+            _event: NonNull<Opaque>,
+            result: NonNull<Opaque>,
+        ) {
+            let hook: NonNull<F> = hook.cast();
+            let result: NonNull<Result<()>> = result.cast();
+            let hook: &F = hook.as_ref();
+            let res = hook();
+            ptr::write(result.as_ptr(), res)
+        }
+
+        unsafe {
+            ErasedHook {
+                data: NonNull::new_unchecked(Box::into_raw(Box::new(hook)) as *mut Opaque),
+                call: call::<H>,
+            }
+        }
+    }
+
+    pub(crate) fn new<E: Event, F: Fn(&mut E) -> Result<()>>(hook: F) -> ErasedHook {
+        unsafe fn call<E: Event, F: Fn(&mut E) -> Result<()>>(
+            hook: NonNull<Opaque>,
+            event: NonNull<Opaque>,
+            result: NonNull<Opaque>,
+        ) {
+            let hook: NonNull<F> = hook.cast();
+            let mut event: NonNull<E> = event.cast();
+            let result: NonNull<Result<()>> = result.cast();
+            let hook: &F = hook.as_ref();
+            let res = hook(event.as_mut());
+            ptr::write(result.as_ptr(), res)
+        }
+
+        unsafe {
+            ErasedHook {
+                data: NonNull::new_unchecked(Box::into_raw(Box::new(hook)) as *mut Opaque),
+                call: call::<E, F>,
+            }
+        }
+    }
+
+    pub(crate) unsafe fn call<E: Event>(&self, event: &mut E) -> Result<()> {
+        let mut res = Ok(());
+
+        unsafe {
+            (self.call)(
+                self.data,
+                NonNull::from(event).cast(),
+                NonNull::from(&mut res).cast(),
+            );
+        }
+        res
+    }
+}
+
+unsafe impl Sync for ErasedHook {}
+unsafe impl Send for ErasedHook {}