Use lowest tier judge only and hold the rest in reserve

judge/bridge/judge_handler.py

@@ -59,6 +59,7 @@ def __init__(self, request, client_address, server, judges):
         self.load = 1e100
         self.name = None
         self.is_disabled = False
+        self.tier = None
         self.batch_id = None
         self.in_batch = False
         self._stop_ping = threading.Event()
@@ -107,6 +108,9 @@ def _authenticate(self, id, key):
             json_log.warning(self._make_json_log(action='auth', judge=id, info='judge authenticated but is blocked'))
             return False
 
+        # Cache judge tier for use by JudgeList
+        self.tier = judge.tier
+
         return True
 
     def _connected(self):

judge/bridge/judge_list.py

@@ -25,16 +25,19 @@ def __init__(self):
         self.node_map = {}
         self.submission_map = {}
         self.lock = RLock()
+        self.min_tier = None
 
     def _handle_free_judge(self, judge):
         with self.lock:
+            if judge.tier > self.min_tier:
+                return
+
             node = self.queue.first
             priority = 0
             while node:
                 if isinstance(node.value, PriorityMarker):
                     priority = node.value.priority + 1
-                elif priority >= REJUDGE_PRIORITY and self.count_not_disabled() > 1 and sum(
-                        not judge.working and not judge.is_disabled for judge in self.judges) <= 1:
+                elif priority >= REJUDGE_PRIORITY and self.should_reserve_judge():
                     return
                 else:
                     id, problem, language, source, judge_id = node.value
@@ -52,14 +55,42 @@ def _handle_free_judge(self, judge):
                         break
                 node = node.next
 
-    def count_not_disabled(self):
-        return sum(not judge.is_disabled for judge in self.judges)
+    def _update_min_tier(self):
+        with self.lock:
+            old = self.min_tier
+            try:
+                self.min_tier = min(judge.tier for judge in self.judges if judge.tier is not None and not judge.is_disabled)
+            except ValueError:
+                self.min_tier = None
+
+            # We must be adding a judge, let register handle the new judge.
+            if old is None:
+                return
+
+            # If the new min tier is larger, then we should treat all judges of the new tier as free and start grading.
+            # This is only possible when removing a judge.
+            if self.min_tier is None and self.min_tier > old:
+                for judge in self.current_tier_judges():
+                    if not judge.working:
+                        self._handle_free_judge(judge)
+
+    def current_tier_judges(self):
+        return [judge for judge in self.judges if judge.tier == self.min_tier and not judge.is_disabled]
+
+    def should_reserve_judge(self):
+        judges = self.current_tier_judges()
+        if len(judges) <= 1:
+            return False
+
+        free_judges = sum(not judge.working for judge in judges)
+        return free_judges <= 1
 
     def register(self, judge):
         with self.lock:
             # Disconnect all judges with the same name, see <https://github.com/DMOJ/online-judge/issues/828>
             self.disconnect(judge, force=True)
             self.judges.add(judge)
+            self._update_min_tier()
             self._handle_free_judge(judge)
 
     def disconnect(self, judge_id, force=False):
@@ -77,6 +108,7 @@ def update_disable_judge(self, judge_id, is_disabled):
             for judge in self.judges:
                 if judge.name == judge_id:
                     judge.is_disabled = is_disabled
+            self._update_min_tier()
 
     def remove(self, judge):
         with self.lock:
@@ -87,11 +119,13 @@ def remove(self, judge):
                 except KeyError:
                     pass
             self.judges.discard(judge)
+            self._update_min_tier()
 
             # Since we reserve a judge for high priority submissions when there are more than one,
             # we'll need to start judging if there is exactly one judge and it's free.
-            if len(self.judges) == 1:
-                judge = next(iter(self.judges))
+            current_tier = self.current_tier_judges()
+            if len(current_tier) == 1:
+                judge = next(iter(current_tier))
                 if not judge.working:
                     self._handle_free_judge(judge)
 
@@ -131,7 +165,7 @@ def judge(self, id, problem, language, source, judge_id, priority):
                 # idempotent.
                 return
 
-            candidates = [judge for judge in self.judges if judge.can_judge(problem, language, judge_id)]
+            candidates = [judge for judge in self.current_tier_judges() if judge.can_judge(problem, language, judge_id)]
             available = [judge for judge in candidates if not judge.working and not judge.is_disabled]
             if judge_id:
                 logger.info('Specified judge %s is%savailable', judge_id, ' ' if available else ' not ')