Improve output buffering in the Linux tv CI test script

Author: shaoltan-amazon

scripts/tests/linux/log_line_processing.py

@@ -63,8 +63,9 @@ def _io_thread(self):
         err_wait = select.poll()
         err_wait.register(self.process.stderr, select.POLLIN | select.POLLHUP)
 
-        with open(self.output_path, "wt") as f:
+        with open(self.output_path, "wt", buffering=1) as f:
             f.write("PROCESS START: %s\n" % time.ctime())
+            f.flush()
             while not self.done:
                 changes = out_wait.poll(0.1)
                 if changes:
@@ -73,6 +74,7 @@ def _io_thread(self):
                         # stdout closed (otherwise readline should have at least \n)
                         continue
                     f.write(out_line)
+                    f.flush()
                     self.output_lines.put(out_line)
 
                 changes = err_wait.poll(0)
@@ -82,7 +84,9 @@ def _io_thread(self):
                         # stderr closed (otherwise readline should have at least \n)
                         continue
                     f.write(f"!!STDERR!! : {err_line}")
+                    f.flush()
             f.write("PROCESS END: %s\n" % time.ctime())
+            f.flush()
 
     def __enter__(self):
         self.done = False
@@ -92,6 +96,7 @@ def __enter__(self):
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             text=True,
+            bufsize=1
         )
         self.io_thread = threading.Thread(target=self._io_thread)
         self.io_thread.start()

scripts/tests/run_tv_casting_test.py

@@ -205,6 +205,8 @@ def send_input_cmd_to_subprocess(
         f"{test_sequence_name} - Sent `{input_cmd}` to the {app_name} subprocess."
     )
 
+    time.sleep(0.5)
+
 
 def handle_input_cmd(
     processes: RunningProcesses, test_sequence_name: str, test_sequence_step: Step