Use try_lock in collect_active_jobs

src/librustc/ty/maps/plumbing.rs

@@ -659,7 +659,9 @@ macro_rules! define_maps {
             pub fn collect_active_jobs(&self) -> Vec<Lrc<QueryJob<$tcx>>> {
                 let mut jobs = Vec::new();
 
-                $(for v in self.$name.lock().active.values() {
+                // We use try_lock here since we are only called from the
+                // deadlock handler, and this shouldn't be locked
+                $(for v in self.$name.try_lock().unwrap().active.values() {
                     match *v {
                         QueryResult::Started(ref job) => jobs.push(job.clone()),
                         _ => (),

src/librustc_data_structures/sync.rs

@@ -519,6 +519,18 @@ impl<T> Lock<T> {
         self.0.get_mut()
     }
 
+    #[cfg(parallel_queries)]
+    #[inline(always)]
+    pub fn try_lock(&self) -> Option<LockGuard<T>> {
+        self.0.try_lock()
+    }
+
+    #[cfg(not(parallel_queries))]
+    #[inline(always)]
+    pub fn try_lock(&self) -> Option<LockGuard<T>> {
+        self.0.try_borrow_mut().ok()
+    }
+
     #[cfg(parallel_queries)]
     #[inline(always)]
     pub fn lock(&self) -> LockGuard<T> {