Use `try_lock` in `diff_handle` for Diff gutter (#11092)

* Use `try_lock` in `diff_handle` for Diff gutter
- Add the method `try_load() -> Option<Diff>` to `DiffHandle`, using `try_lock` to avoid deadlocks.
- Use said method in `gutter.rs diff()`, which will use a blank `GutterFn` instead when met with a locked `Diff`.

* Revert changes

* Replace `Mutex` with `RwLock` in `Diff`

---------

Co-authored-by: Kaniel Kirby <pirate7007@runbox.com>

helix-vcs/src/diff.rs

@@ -5,7 +5,7 @@ use std::sync::Arc;
 use helix_core::Rope;
 use helix_event::RenderLockGuard;
 use imara_diff::Algorithm;
-use parking_lot::{Mutex, MutexGuard};
+use parking_lot::{RwLock, RwLockReadGuard};
 use tokio::sync::mpsc::{unbounded_channel, UnboundedSender};
 use tokio::task::JoinHandle;
 use tokio::time::Instant;
@@ -37,7 +37,7 @@ struct DiffInner {
 #[derive(Clone, Debug)]
 pub struct DiffHandle {
     channel: UnboundedSender<Event>,
-    diff: Arc<Mutex<DiffInner>>,
+    diff: Arc<RwLock<DiffInner>>,
     inverted: bool,
 }
 
@@ -48,7 +48,7 @@ impl DiffHandle {
 
     fn new_with_handle(diff_base: Rope, doc: Rope) -> (DiffHandle, JoinHandle<()>) {
         let (sender, receiver) = unbounded_channel();
-        let diff: Arc<Mutex<DiffInner>> = Arc::default();
+        let diff: Arc<RwLock<DiffInner>> = Arc::default();
         let worker = DiffWorker {
             channel: receiver,
             diff: diff.clone(),
@@ -70,7 +70,7 @@ impl DiffHandle {
 
     pub fn load(&self) -> Diff {
         Diff {
-            diff: self.diff.lock(),
+            diff: self.diff.read(),
             inverted: self.inverted,
         }
     }
@@ -164,7 +164,7 @@ impl Hunk {
 /// non-overlapping order
 #[derive(Debug)]
 pub struct Diff<'a> {
-    diff: MutexGuard<'a, DiffInner>,
+    diff: RwLockReadGuard<'a, DiffInner>,
     inverted: bool,
 }
 

helix-vcs/src/diff/worker.rs

@@ -4,7 +4,7 @@ use std::sync::Arc;
 
 use helix_core::{Rope, RopeSlice};
 use imara_diff::intern::InternedInput;
-use parking_lot::Mutex;
+use parking_lot::RwLock;
 use tokio::sync::mpsc::UnboundedReceiver;
 use tokio::sync::Notify;
 use tokio::time::{timeout, timeout_at, Duration};
@@ -21,7 +21,7 @@ mod test;
 
 pub(super) struct DiffWorker {
     pub channel: UnboundedReceiver<Event>,
-    pub diff: Arc<Mutex<DiffInner>>,
+    pub diff: Arc<RwLock<DiffInner>>,
     pub new_hunks: Vec<Hunk>,
     pub diff_finished_notify: Arc<Notify>,
 }
@@ -73,7 +73,7 @@ impl DiffWorker {
     /// `self.new_hunks` is always empty after this function runs.
     /// To improve performance this function tries to reuse the allocation of the old diff previously stored in `self.line_diffs`
     fn apply_hunks(&mut self, diff_base: Rope, doc: Rope) {
-        let mut diff = self.diff.lock();
+        let mut diff = self.diff.write();
         diff.diff_base = diff_base;
         diff.doc = doc;
         swap(&mut diff.hunks, &mut self.new_hunks);

helix-vcs/src/diff/worker/test.rs

@@ -12,7 +12,7 @@ impl DiffHandle {
         // dropping the channel terminates the task
         drop(self.channel);
         handle.await.unwrap();
-        let diff = diff.lock();
+        let diff = diff.read();
         Vec::clone(&diff.hunks)
     }
 }