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Add hook/event system
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pascalkuthe authored and archseer committed Jan 23, 2024

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1 parent 7d7ace5 commit 13ed4f6
Showing 26 changed files with 1,024 additions and 50 deletions.
14 changes: 14 additions & 0 deletions .cargo/config.toml
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@@ -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"

6 changes: 6 additions & 0 deletions Cargo.lock

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17 changes: 15 additions & 2 deletions helix-event/Cargo.toml
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@@ -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 = []
19 changes: 19 additions & 0 deletions helix-event/src/cancel.rs
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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)
}
}
}
67 changes: 67 additions & 0 deletions helix-event/src/debounce.rs
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//! 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)));
}
}
91 changes: 91 additions & 0 deletions helix-event/src/hook.rs
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//! 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 {}
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