From d3b403afdf6b3cb2d1f6d1af1810a6b82164870b Mon Sep 17 00:00:00 2001
From: Quantum <quantum2048@gmail.com>
Date: Sat, 12 Feb 2022 23:53:20 -0500
Subject: [PATCH] Leave a spare judge when rejudging if possible

---
 judge/bridge/judge_list.py | 21 ++++++++++++++++++++-
 judge/judge_priority.py    |  4 ++++
 judge/judgeapi.py          |  6 +-----
 3 files changed, 25 insertions(+), 6 deletions(-)
 create mode 100644 judge/judge_priority.py

diff --git a/judge/bridge/judge_list.py b/judge/bridge/judge_list.py
index 3b65f4771..7d44c89a3 100644
--- a/judge/bridge/judge_list.py
+++ b/judge/bridge/judge_list.py
@@ -3,6 +3,8 @@ from collections import namedtuple
 from random import random
 from threading import RLock
 
+from judge.judge_priority import REJUDGE_PRIORITY
+
 try:
     from llist import dllist
 except ImportError:
@@ -27,8 +29,14 @@ class JudgeList(object):
     def _handle_free_judge(self, judge):
         with self.lock:
             node = self.queue.first
+            priority = 0
             while node:
-                if not isinstance(node.value, PriorityMarker):
+                if isinstance(node.value, PriorityMarker):
+                    priority = node.value.priority + 1
+                elif priority >= REJUDGE_PRIORITY and len(self.judges) > 1 and sum(
+                        not judge.working for judge in self.judges) <= 1:
+                    return
+                else:
                     id, problem, language, source, judge_id = node.value
                     if judge.can_judge(problem, language, judge_id):
                         self.submission_map[id] = judge
@@ -71,6 +79,13 @@ class JudgeList(object):
                     pass
             self.judges.discard(judge)
 
+            # 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))
+                if not judge.working:
+                    self._handle_free_judge(judge)
+
     def __iter__(self):
         return iter(self.judges)
 
@@ -114,6 +129,10 @@ class JudgeList(object):
                 logger.info('Specified judge %s is%savailable', judge_id, ' ' if candidates else ' not ')
             else:
                 logger.info('Free judges: %d', len(candidates))
+
+            if len(candidates) == 1 and priority >= REJUDGE_PRIORITY:
+                candidates = []
+
             if candidates:
                 # Schedule the submission on the judge reporting least load.
                 judge = min(candidates, key=lambda judge: (judge.load, random()))
diff --git a/judge/judge_priority.py b/judge/judge_priority.py
new file mode 100644
index 000000000..c7ea61f56
--- /dev/null
+++ b/judge/judge_priority.py
@@ -0,0 +1,4 @@
+CONTEST_SUBMISSION_PRIORITY = 0
+DEFAULT_PRIORITY = 1
+REJUDGE_PRIORITY = 2
+BATCH_REJUDGE_PRIORITY = 3
diff --git a/judge/judgeapi.py b/judge/judgeapi.py
index df781206b..42bc000f5 100644
--- a/judge/judgeapi.py
+++ b/judge/judgeapi.py
@@ -8,6 +8,7 @@ from django.conf import settings
 from django.utils import timezone
 
 from judge import event_poster as event
+from judge.judge_priority import BATCH_REJUDGE_PRIORITY, CONTEST_SUBMISSION_PRIORITY, DEFAULT_PRIORITY, REJUDGE_PRIORITY
 
 logger = logging.getLogger('judge.judgeapi')
 size_pack = struct.Struct('!I')
@@ -52,11 +53,6 @@ def judge_request(packet, reply=True):
 def judge_submission(submission, rejudge=False, batch_rejudge=False, judge_id=None):
     from .models import ContestSubmission, Submission, SubmissionTestCase
 
-    CONTEST_SUBMISSION_PRIORITY = 0
-    DEFAULT_PRIORITY = 1
-    REJUDGE_PRIORITY = 2
-    BATCH_REJUDGE_PRIORITY = 3
-
     updates = {'time': None, 'memory': None, 'points': None, 'result': None, 'case_points': 0, 'case_total': 0,
                'error': None, 'rejudged_date': timezone.now() if rejudge or batch_rejudge else None, 'status': 'QU'}
     try: