Revert daemon in favor of timeout

cps/services/worker.py

@@ -3,6 +3,7 @@ from __future__ import division, print_function, unicode_literals
 import threading
 import abc
 import uuid
+import time
 
 try:
     import queue
@@ -59,7 +60,7 @@ class WorkerThread(threading.Thread):
         threading.Thread.__init__(self)
 
         self.dequeued = list()
-        self.daemon = True
+
         self.doLock = threading.Lock()
         self.queue = ImprovedQueue()
         self.num = 0
@@ -101,23 +102,33 @@ class WorkerThread(threading.Thread):
 
     # Main thread loop starting the different tasks
     def run(self):
-        # this blocks until something is available
-        item = self.queue.get()
-
-        with self.doLock:
-            # 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
-            item.task.start(self)
-
-        self.queue.task_done()
+        main_thread = _get_main_thread()
+        while main_thread.is_alive():
+            try:
+                # this blocks until something is available. This can cause issues when the main thread dies - this
+                # thread will remain alive. We implement a timeout to unblock every second which allows us to check if
+                # the main thread is still alive.
+                # We don't use a daemon here because we don't want the tasks to just be abruptly halted, leading to
+                # possible file / database corruption
+                item = self.queue.get(timeout=1)
+            except queue.Empty as ex:
+                time.sleep(1)
+                continue
+
+            with self.doLock:
+                # 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
+                item.task.start(self)
+
+            self.queue.task_done()
 
 
 class CalibreTask: