Fix for failure in the benchmark_launch when using Process.wait twice (#2076)

- Address failure:
 "child process pid 116528 exit status already read:
  will report returncode 255" by avoiding usage Process.wait twice.
- Note: the second time Process.wait calling from the
def test_proc_terminates(self, last_benchmark):
# Wait for the last benchmark to complete before processing the results
self.proc_info.assertWaitForShutdown(process=last_benchmark,timeout=600)

- Explanation and RCA:
 In Python 3.12, the internal implementation of process management and
 resource cleanup (especially around wait() and exit status handling)
 has become stricter and more robust. Double-waiting on a process
 (calling wait() twice) can now trigger errors or warnings, such as
 "exit status already read," because the exit status is only meant to be
 consumed once.  In Python 3.8, this was more permissive or silent,
 but in newer versions, the subprocess module may raise exceptions or
 log messages if you try to wait for a process whose exit status has
 already been collected.

Signed-off-by: Michael Orlov <[email protected]>

Author: MichaelOrlov

rosbag2_performance/rosbag2_performance_benchmarking/launch/benchmark_launch.py

@@ -51,6 +51,7 @@
 import shutil
 import signal
 import sys
+import time
 
 from ament_index_python import get_package_share_directory
 import launch
@@ -267,9 +268,19 @@ def _producer_node_exited(event, context):
             ]
         _recorder_cpu_usage = _rosbag_process.cpu_percent()
         os.kill(_rosbag_pid, signal.SIGINT)
-        # Wait for rosbag2 process to exit for 10 seconds
-        rosbag_return_code = _rosbag_process.wait(10)
         _rosbag_pid = None
+        # Wait for rosbag2 process to exit for 10 seconds
+        timeout = 10
+        start_time = time.time()
+        rosbag_return_code = None
+        # Note: we cant use _rosbag_process.wait(10) because wait shall be called only once.
+        # We will have to call wait one more time in the test_proc_terminates(self, last_benchmark)
+        while time.time() - start_time < timeout:
+            if not _rosbag_process.is_running():
+                rosbag_return_code = _rosbag_process.returncode()
+                break
+            time.sleep(0.1)
+
         if rosbag_return_code is not None and rosbag_return_code != 0:
             return [
                 launch.actions.LogInfo(msg='Rosbag2 record error. Shutting down benchmark. '