Main thread lock: add double-check

Author: HardNorth

reportportal_client/core/worker.py

@@ -179,10 +179,14 @@ def __perform_stop(self, stop_command):
         if not self.is_alive():
             # Already stopped or already dead or not even started
             return
-        # Do not release main thread until worker process all requests, since
-        # main thread might forcibly quit python interpreter
         with self._stop_lock:
+            if not self.is_alive():
+                # Already stopped by previous thread
+                return
             self.send(stop_command)
+            # Do not release main thread until worker process all requests,
+            # since main thread might forcibly quit python interpreter as in
+            # pytest
             self._stop_lock.wait(THREAD_TIMEOUT)
 
     def stop(self):