The previous fix (dbcc7cb5) only added os.waitpid() to _kill_process(),
covering the timeout/cancel path of one-shot exec. Zombies continued to
accumulate because several other exit paths never reaped children:
- _ExecSession.kill(): sent SIGKILL + process.wait(5s) but had no
os.waitpid() fallback if the wait timed out
- ExecTool.execute() generic exception handler: leaked the subprocess
if communicate() raised an unexpected error
- Normal completion paths: relied entirely on asyncio's child-watcher,
which can miss exits inside Docker containers (pidfd/SIGCHLD gaps)
Changes:
- Extract _reap_pid() helper for consistent, safe os.waitpid(WNOHANG)
- Add _reap_pid() fallback to _ExecSession.kill() via try/finally
- Add _reap_pid() safety-net after normal process exit in both
ExecTool.execute() and _ExecSession.poll()
- Kill + reap subprocess in the generic except Exception handler
- Add periodic zombie reaper background task (every 30s) in the
gateway as a last line of defense
Eric YangandXubin Ren