Rename JobOwner to ActiveJobGuard

This commit also adds and updates some relevant comments.

Author: Zalathar

compiler/rustc_middle/src/ty/context/tls.rs

@@ -16,8 +16,7 @@ pub struct ImplicitCtxt<'a, 'tcx> {
     /// The current `TyCtxt`.
     pub tcx: TyCtxt<'tcx>,
 
-    /// The current query job, if any. This is updated by `JobOwner::start` in
-    /// `ty::query::plumbing` when executing a query.
+    /// The current query job, if any.
     pub query: Option<QueryJobId>,
 
     /// Used to prevent queries from calling too deeply.

compiler/rustc_query_impl/src/execution.rs

@@ -83,9 +83,12 @@ pub(crate) fn gather_active_jobs_inner<'tcx, K: Copy>(
     Some(())
 }
 
-/// A type representing the responsibility to execute the job in the `job` field.
-/// This will poison the relevant query if dropped.
-struct JobOwner<'tcx, K>
+/// Guard object representing the responsibility to execute a query job and
+/// mark it as completed.
+///
+/// This will poison the relevant query key if it is dropped without calling
+/// [`Self::complete`].
+struct ActiveJobGuard<'tcx, K>
 where
     K: Eq + Hash + Copy,
 {
@@ -139,12 +142,12 @@ where
     }
 }
 
-impl<'tcx, K> JobOwner<'tcx, K>
+impl<'tcx, K> ActiveJobGuard<'tcx, K>
 where
     K: Eq + Hash + Copy,
 {
     /// Completes the query by updating the query cache with the `result`,
-    /// signals the waiter and forgets the JobOwner, so it won't poison the query
+    /// signals the waiter, and forgets the guard so it won't poison the query.
     fn complete<C>(self, cache: &C, key_hash: u64, result: C::Value, dep_node_index: DepNodeIndex)
     where
         C: QueryCache<Key = K>,
@@ -176,7 +179,7 @@ where
     }
 }
 
-impl<'tcx, K> Drop for JobOwner<'tcx, K>
+impl<'tcx, K> Drop for ActiveJobGuard<'tcx, K>
 where
     K: Eq + Hash + Copy,
 {
@@ -356,11 +359,13 @@ fn execute_job<'tcx, Q, const INCR: bool>(
 where
     Q: QueryDispatcher<'tcx, Qcx = QueryCtxt<'tcx>>,
 {
-    // Use `JobOwner` so the query will be poisoned if executing it panics.
-    let job_owner = JobOwner { state, key };
+    // Set up a guard object that will automatically poison the query if a
+    // panic occurs while executing the query (or any intermediate plumbing).
+    let job_guard = ActiveJobGuard { state, key };
 
     debug_assert_eq!(qcx.tcx.dep_graph.is_fully_enabled(), INCR);
 
+    // Delegate to another function to actually execute the query job.
     let (result, dep_node_index) = if INCR {
         execute_job_incr(query, qcx, qcx.tcx.dep_graph.data().unwrap(), key, dep_node, id)
     } else {
@@ -402,7 +407,9 @@ where
             }
         }
     }
-    job_owner.complete(cache, key_hash, result, dep_node_index);
+
+    // Tell the guard to perform completion bookkeeping, and also to not poison the query.
+    job_guard.complete(cache, key_hash, result, dep_node_index);
 
     (result, Some(dep_node_index))
 }