Improve CommandEventHandler error detection (avoid polling)

lib/tfw/components/pipe_io_event_handler.py

@@ -6,7 +6,6 @@ from os import getpgid, killpg
 from os.path import join
 from signal import SIGTERM
 from secrets import token_urlsafe
-from time import sleep
 from threading import Thread
 from contextlib import suppress
 
@@ -113,26 +112,22 @@ class CommandEventHandler(PipeIOEventHandler):
             stdin=self._proc_stdin, stdout=self._proc_stdout, stderr=PIPE,
             start_new_session=True
         )
-        self._poll_check_proc_thread = self._start_poll_check_proc()
+        self._monitor_proc_thread = self._start_monitor_proc()
 
     def _generate_tempfilename(self):
         # pylint: disable=no-self-use
         random_filename = partial(token_urlsafe, 10)
         return join('/tmp', f'{type(self).__name__}.{random_filename()}')
 
-    def _start_poll_check_proc(self):
-        thread = Thread(target=self._poll_check_proc, daemon=True)
+    def _start_monitor_proc(self):
+        thread = Thread(target=self._monitor_proc, daemon=True)
         thread.start()
         return thread
 
     @terminate_process_on_failure
-    def _poll_check_proc(self):
-        while True:
-            self.check_proc()
-            sleep(1)
-
-    def check_proc(self):
-        if self._proc.poll() is not None:
+    def _monitor_proc(self):
+        return_code = self._proc.wait()
+        if return_code != 0:
             _, stderr = self._proc.communicate()
             raise RuntimeError(f'Subprocess failed: {stderr.decode()}')