backend: better handling of too many open files errors

src/scheduler/unpacking_scheduler.py

@@ -107,7 +107,8 @@ def shutdown(self):
         )
         self.stop_containers()
         self._clean_tmp_dirs()
-        self.manager.shutdown()
+        if self.manager:
+            self.manager.shutdown()
         logging.info('Unpacking scheduler offline')
 
     def _clean_tmp_dirs(self):
@@ -138,8 +139,9 @@ def create_containers(self):
             self.worker_tmp_dirs.append(tmp_dir)
 
     def stop_containers(self):
-        with ThreadPoolExecutor(max_workers=len(self.workers)) as pool:
-            pool.map(lambda container: container.stop(), self.workers)
+        if self.workers:
+            with ThreadPoolExecutor(max_workers=len(self.workers)) as pool:
+                pool.map(lambda container: container.stop(), self.workers)
 
     def extraction_loop(self):
         logging.debug(f'Starting unpacking scheduler loop (pid={os.getpid()})')

src/start_fact_backend.py

@@ -127,5 +127,11 @@ def _check_ulimit():
 
 
 if __name__ == '__main__':
-    FactBackend().main()
-    sys.exit(0)
+    backend = FactBackend()
+    try:
+        backend.main()
+        sys.exit(0)
+    except OSError as error:
+        logging.exception(f'Exception during start: {error}')
+        backend.shutdown()
+        sys.exit(1)