self-profiling: Switch query-blocking measurements to RAII-style API.

src/librustc/ty/query/plumbing.rs

@@ -90,6 +90,10 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
                 }
                 return TryGetJob::JobCompleted(result);
             }
+
+            #[cfg(parallel_compiler)]
+            let query_blocked_prof_timer;
+
             let job = match lock.active.entry((*key).clone()) {
                 Entry::Occupied(entry) => {
                     match *entry.get() {
@@ -98,7 +102,9 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
                             // in another thread has completed. Record how long we wait in the
                             // self-profiler.
                             #[cfg(parallel_compiler)]
-                            tcx.prof.query_blocked_start(Q::NAME);
+                            {
+                                query_blocked_prof_timer = tcx.prof.query_blocked(Q::NAME);
+                            }
 
                             job.clone()
                         },
@@ -140,7 +146,11 @@ impl<'a, 'tcx, Q: QueryDescription<'tcx>> JobOwner<'a, 'tcx, Q> {
             #[cfg(parallel_compiler)]
             {
                 let result = job.r#await(tcx, span);
-                tcx.prof.query_blocked_end(Q::NAME);
+
+                // This `drop()` is not strictly necessary as the binding
+                // would go out of scope anyway. But it's good to have an
+                // explicit marker of how far the measurement goes.
+                drop(query_blocked_prof_timer);
 
                 if let Err(cycle) = result {
                     return TryGetJob::Cycle(Q::handle_cycle_error(tcx, cycle));

src/librustc/util/profiling.rs

@@ -156,26 +156,14 @@ impl SelfProfilerRef {
     }
 
     /// Start profiling a query being blocked on a concurrent execution.
-    /// Profiling continues until `query_blocked_end` is called.
+    /// Profiling continues until the TimingGuard returned from this call is
+    /// dropped.
     #[inline(always)]
-    pub fn query_blocked_start(&self, query_name: QueryName) {
-        self.non_guard_query_event(
-            |profiler| profiler.query_blocked_event_kind,
-            query_name,
-            EventFilter::QUERY_BLOCKED,
-            TimestampKind::Start,
-        );
-    }
-
-    /// End profiling a query being blocked on a concurrent execution.
-    #[inline(always)]
-    pub fn query_blocked_end(&self, query_name: QueryName) {
-        self.non_guard_query_event(
-            |profiler| profiler.query_blocked_event_kind,
-            query_name,
-            EventFilter::QUERY_BLOCKED,
-            TimestampKind::End,
-        );
+    pub fn query_blocked(&self, query_name: QueryName) -> TimingGuard<'_> {
+        self.exec(EventFilter::QUERY_BLOCKED, |profiler| {
+            let event_id = SelfProfiler::get_query_name_string_id(query_name);
+            TimingGuard::start(profiler, profiler.query_blocked_event_kind, event_id)
+        })
     }
 
     /// Start profiling how long it takes to load a query result from the