Improvements to task processing

* Moves clean up to separate function for organization
* moves the `self.dequeued.append(item)` immediately after `self.queue.get()` so that we don't wait for it to show up

(cherry picked from commit bc9372e88f0c8855694431f811702d7fb899a97e)

cps/services/worker.py

@@ -82,33 +82,37 @@ class WorkerThread(threading.Thread):
             tasks = self.queue.to_list() + self.dequeued
             return sorted(tasks, key=lambda x: x.num)
 
+    def cleanup_tasks(self):
+        with self.doLock:
+            dead = []
+            alive = []
+            for x in self.dequeued:
+                (dead if x.task.dead else alive).append(x)
+
+            # if the ones that we need to keep are within the trigger, do nothing else
+            delta = len(self.dequeued) - len(dead)
+            if delta > TASK_CLEANUP_TRIGGER:
+                ret = alive
+            else:
+                # otherwise, lop off the oldest dead tasks until we hit the target trigger
+                ret = sorted(dead, key=lambda x: x.task.end_time)[-TASK_CLEANUP_TRIGGER:] + alive
+
+            self.dequeued = sorted(ret, key=lambda x: x.num)
 
     # Main thread loop starting the different tasks
     def run(self):
         main_thread = _get_main_thread()
         while main_thread.is_alive():
+            # this blocks until something is available
             item = self.queue.get()
-
             with self.doLock:
-                # once we hit our trigger, start cleaning up dead tasks
-                if len(self.dequeued) > TASK_CLEANUP_TRIGGER:
-                    dead = []
-                    alive = []
-                    for x in self.dequeued:
-                        (dead if x.task.dead else alive).append(x)
-
-                    # if the ones that we need to keep are within the trigger, do nothing else
-                    delta = len(self.dequeued) - len(dead)
-                    if delta > TASK_CLEANUP_TRIGGER:
-                        ret = alive
-                    else:
-                        # otherwise, lop off the oldest dead tasks until we hit the target trigger
-                        ret = sorted(dead, key=lambda x: x.task.end_time)[-TASK_CLEANUP_TRIGGER:] + alive
-
-                    self.dequeued = sorted(ret, key=lambda x: x.num)
                 # add to list so that in-progress tasks show up
                 self.dequeued.append(item)
 
+            # once we hit our trigger, start cleaning up dead tasks
+            if len(self.dequeued) > TASK_CLEANUP_TRIGGER:
+                self.cleanup_tasks()
+
             # sometimes tasks (like Upload) don't actually have work to do and are created as already finished
             if item.task.stat is STAT_WAITING:
                 # CalibreTask.start() should wrap all exceptions in it's own error handling