adjusted scheduler prioritization algorithm (#45367) (cherry-pick to preview) (#45370)

zed-zippy[bot] and Yara 🏳️‍⚧️ created 1 week ago

Cherry-pick of #45367 to preview

----
This fixes a number of issues where zed depends on the order of polling
which changed when switching scheduler. We have adjusted the algorithm
so it matches the previous order while keeping the prioritization
feature.

Release Notes:
- N/A

Co-authored-by: Yara 🏳️‍⚧️ <[e-mail]>

Change summary

crates/gpui/src/queue.rs | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)

Detailed changes

crates/gpui/src/queue.rs

@@ -1,4 +1,5 @@
 use std::{
+    collections::VecDeque,
     fmt,
     iter::FusedIterator,
     sync::{Arc, atomic::AtomicUsize},
@@ -9,9 +10,9 @@ use rand::{Rng, SeedableRng, rngs::SmallRng};
 use crate::Priority;
 
 struct PriorityQueues<T> {
-    high_priority: Vec<T>,
-    medium_priority: Vec<T>,
-    low_priority: Vec<T>,
+    high_priority: VecDeque<T>,
+    medium_priority: VecDeque<T>,
+    low_priority: VecDeque<T>,
 }
 
 impl<T> PriorityQueues<T> {
@@ -42,9 +43,9 @@ impl<T> PriorityQueueState<T> {
         let mut queues = self.queues.lock();
         match priority {
             Priority::Realtime(_) => unreachable!(),
-            Priority::High => queues.high_priority.push(item),
-            Priority::Medium => queues.medium_priority.push(item),
-            Priority::Low => queues.low_priority.push(item),
+            Priority::High => queues.high_priority.push_back(item),
+            Priority::Medium => queues.medium_priority.push_back(item),
+            Priority::Low => queues.low_priority.push_back(item),
         };
         self.condvar.notify_one();
         Ok(())
@@ -141,9 +142,9 @@ impl<T> PriorityQueueReceiver<T> {
     pub(crate) fn new() -> (PriorityQueueSender<T>, Self) {
         let state = PriorityQueueState {
             queues: parking_lot::Mutex::new(PriorityQueues {
-                high_priority: Vec::new(),
-                medium_priority: Vec::new(),
-                low_priority: Vec::new(),
+                high_priority: VecDeque::new(),
+                medium_priority: VecDeque::new(),
+                low_priority: VecDeque::new(),
             }),
             condvar: parking_lot::Condvar::new(),
             receiver_count: AtomicUsize::new(1),
@@ -226,7 +227,7 @@ impl<T> PriorityQueueReceiver<T> {
         if !queues.high_priority.is_empty() {
             let flip = self.rand.random_ratio(P::High.probability(), mass);
             if flip {
-                return Ok(queues.high_priority.pop());
+                return Ok(queues.high_priority.pop_front());
             }
             mass -= P::High.probability();
         }
@@ -234,7 +235,7 @@ impl<T> PriorityQueueReceiver<T> {
         if !queues.medium_priority.is_empty() {
             let flip = self.rand.random_ratio(P::Medium.probability(), mass);
             if flip {
-                return Ok(queues.medium_priority.pop());
+                return Ok(queues.medium_priority.pop_front());
             }
             mass -= P::Medium.probability();
         }
@@ -242,7 +243,7 @@ impl<T> PriorityQueueReceiver<T> {
         if !queues.low_priority.is_empty() {
             let flip = self.rand.random_ratio(P::Low.probability(), mass);
             if flip {
-                return Ok(queues.low_priority.pop());
+                return Ok(queues.low_priority.pop_front());
             }
         }