store jobs priorities in the pending queue

This cleans up the priority-sorted scheduling by removing the need
for a priority accessor that would hash the nodes, and allows inserting
in the queue at the correctly sorted position to remove the insert +
sort combination.

src/cargo/core/compiler/job_queue.rs

@@ -162,7 +162,7 @@ struct DrainState<'cfg> {
     /// The list of jobs that we have not yet started executing, but have
     /// retrieved from the `queue`. We eagerly pull jobs off the main queue to
     /// allow us to request jobserver tokens pretty early.
-    pending_queue: Vec<(Unit, Job)>,
+    pending_queue: Vec<(Unit, Job, usize)>,
     print: DiagnosticPrinter<'cfg>,
 
     /// How many jobs we've finished
@@ -576,26 +576,29 @@ impl<'cfg> DrainState<'cfg> {
         // possible that can run. Note that this is also the point where we
         // start requesting job tokens. Each job after the first needs to
         // request a token.
-        while let Some((unit, job)) = self.queue.dequeue() {
-            self.pending_queue.push((unit, job));
+        while let Some((unit, job, priority)) = self.queue.dequeue() {
+            // We want to keep the pieces of work in the `pending_queue` sorted
+            // by their priorities, and insert the current job at its correctly
+            // sorted position: following the lower priority jobs, and the ones
+            // with the same priority (since they were dequeued before the
+            // current one, we also keep that relation).
+            let idx = self
+                .pending_queue
+                .partition_point(|&(_, _, p)| p <= priority);
+            self.pending_queue.insert(idx, (unit, job, priority));
             if self.active.len() + self.pending_queue.len() > 1 {
                 jobserver_helper.request_token();
             }
         }
 
-        // If multiple pieces of work are waiting in the pending queue, we can
-        // sort it according to their priorities: higher priorities should be
-        // scheduled sooner.
-        self.pending_queue
-            .sort_by_cached_key(|(unit, _)| self.queue.priority(unit));
-
         // Now that we've learned of all possible work that we can execute
         // try to spawn it so long as we've got a jobserver token which says
         // we're able to perform some parallel work.
-        // The `pending_queue` is sorted in ascending priority order, and we're
-        // removing the highest priority items from its end.
+        // The `pending_queue` is sorted in ascending priority order, and we
+        // remove items from its end to schedule the highest priority items
+        // sooner.
         while self.has_extra_tokens() && !self.pending_queue.is_empty() {
-            let (unit, job) = self.pending_queue.pop().unwrap();
+            let (unit, job, _) = self.pending_queue.pop().unwrap();
             *self.counts.get_mut(&unit.pkg.package_id()).unwrap() -= 1;
             if !cx.bcx.build_config.build_plan {
                 // Print out some nice progress information.

src/cargo/util/dependency_queue.rs

@@ -149,15 +149,15 @@ impl<N: Hash + Eq + Clone, E: Eq + Hash + Clone, V> DependencyQueue<N, E, V> {
     ///
     /// A package is ready to be built when it has 0 un-built dependencies. If
     /// `None` is returned then no packages are ready to be built.
-    pub fn dequeue(&mut self) -> Option<(N, V)> {
-        let key = self
+    pub fn dequeue(&mut self) -> Option<(N, V, usize)> {
+        let (key, priority) = self
             .dep_map
             .iter()
             .filter(|(_, (deps, _))| deps.is_empty())
-            .map(|(key, _)| key.clone())
-            .max_by_key(|k| self.priority[k])?;
+            .map(|(key, _)| (key.clone(), self.priority[key]))
+            .max_by_key(|(_, priority)| *priority)?;
         let (_, data) = self.dep_map.remove(&key).unwrap();
-        Some((key, data))
+        Some((key, data, priority))
     }
 
     /// Returns `true` if there are remaining packages to be built.
@@ -170,13 +170,6 @@ impl<N: Hash + Eq + Clone, E: Eq + Hash + Clone, V> DependencyQueue<N, E, V> {
         self.dep_map.len()
     }
 
-    /// Returns the relative priority of a node. Higher priorities should be scheduled sooner.
-    /// Currently computed as the transitive cost of the given node: its own, plus the cost of its
-    /// reverse dependencies.
-    pub(crate) fn priority(&self, node: &N) -> usize {
-        self.priority[node]
-    }
-
     /// Indicate that something has finished.
     ///
     /// Calling this function indicates that the `node` has produced `edge`. All
@@ -220,19 +213,19 @@ mod test {
         q.queue(5, (), vec![(4, ()), (3, ())], 1);
         q.queue_finished();
 
-        assert_eq!(q.dequeue(), Some((1, ())));
-        assert_eq!(q.dequeue(), Some((3, ())));
+        assert_eq!(q.dequeue(), Some((1, (), 5)));
+        assert_eq!(q.dequeue(), Some((3, (), 4)));
         assert_eq!(q.dequeue(), None);
         q.finish(&3, &());
         assert_eq!(q.dequeue(), None);
         q.finish(&1, &());
-        assert_eq!(q.dequeue(), Some((2, ())));
+        assert_eq!(q.dequeue(), Some((2, (), 4)));
         assert_eq!(q.dequeue(), None);
         q.finish(&2, &());
-        assert_eq!(q.dequeue(), Some((4, ())));
+        assert_eq!(q.dequeue(), Some((4, (), 3)));
         assert_eq!(q.dequeue(), None);
         q.finish(&4, &());
-        assert_eq!(q.dequeue(), Some((5, ())));
+        assert_eq!(q.dequeue(), Some((5, (), 2)));
     }
 
     #[test]
@@ -245,16 +238,16 @@ mod test {
         q.queue(4, (), vec![(2, ()), (3, ())], 1);
         q.queue_finished();
 
-        assert_eq!(q.dequeue(), Some((3, ())));
-        assert_eq!(q.dequeue(), Some((1, ())));
+        assert_eq!(q.dequeue(), Some((3, (), 9)));
+        assert_eq!(q.dequeue(), Some((1, (), 4)));
         assert_eq!(q.dequeue(), None);
         q.finish(&3, &());
         assert_eq!(q.dequeue(), None);
         q.finish(&1, &());
-        assert_eq!(q.dequeue(), Some((2, ())));
+        assert_eq!(q.dequeue(), Some((2, (), 3)));
         assert_eq!(q.dequeue(), None);
         q.finish(&2, &());
-        assert_eq!(q.dequeue(), Some((4, ())));
+        assert_eq!(q.dequeue(), Some((4, (), 2)));
         assert_eq!(q.dequeue(), None);
         q.finish(&4, &());
         assert_eq!(q.dequeue(), None);