scheduler.py: Respect priority when scheduling jobs

#75

buildgrid/server/scheduler.py

@@ -43,7 +43,7 @@ class Scheduler:
 
         self._action_cache = action_cache
         self.jobs = {}
-        self.queue = deque()
+        self.__queue = deque()
 
         self._is_instrumented = monitor
 
@@ -76,6 +76,18 @@ class Scheduler:
                 self.__leases_by_state[LeaseState.COMPLETED].discard(job_name)
 
     def queue_job(self, job, skip_cache_lookup=False):
+        def __queue_job(jobs_queue, new_job):
+            index = 0
+            for queued_job in reversed(jobs_queue):
+                if new_job.priority < queued_job.priority:
+                    index += 1
+                else:
+                    break
+
+            index = len(jobs_queue) - index
+
+            jobs_queue.insert(index, new_job)
+
         self.jobs[job.name] = job
 
         operation_stage = None
@@ -84,7 +96,7 @@ class Scheduler:
                 action_result = self._action_cache.get_action_result(job.action_digest)
             except NotFoundError:
                 operation_stage = OperationStage.QUEUED
-                self.queue.append(job)
+                __queue_job(self.__queue, job)
 
             else:
                 job.set_cached_result(action_result)
@@ -95,7 +107,7 @@ class Scheduler:
 
         else:
             operation_stage = OperationStage.QUEUED
-            self.queue.append(job)
+            __queue_job(self.__queue, job)
 
         self._update_job_operation_stage(job.name, operation_stage)
 
@@ -111,7 +123,7 @@ class Scheduler:
         else:
             operation_stage = OperationStage.QUEUED
             job.update_lease_state(LeaseState.PENDING)
-            self.queue.append(job)
+            self.__queue.append(job)
 
         self._update_job_operation_stage(job_name, operation_stage)
 
@@ -126,10 +138,10 @@ class Scheduler:
                 worker properties, configuration and state at the time of the
                 request.
         """
-        if not self.queue:
+        if not self.__queue:
             return []
 
-        job = self.queue.popleft()
+        job = self.__queue.popleft()
 
         lease = job.lease