process did not exit when calling sys.exit with privsep

[Sean Pang]

In our product, we found when calling sys.exit using a new thread under privsep, the process did not exit and hang there forever, thus the process became a zombie process.

Monitor did not find the process is dead and not trying to restart it.

node_agent_pri = priv_context_factory(priv_ctx_name='node_agent_pri', pyfile='main')

def priv_context_factory(lock_name=None, priv_ctx_name=None, pyfile=None):
    _errors = []
    if priv_ctx_name is None:
        _errors.append('priv_ctx_name')
    if pyfile is None:
        _errors.append('pyfile')
    if _errors:
        exception_msg = 'Missing arguments: %s' % ', '.join(_errors)
        raise Exception(exception_msg)
    priv_context.init(root_helper=PRIVSEP_ROOT_HELPER)
    return PrivContextPlus(pyfile, lock_name=lock_name,
                           pypath=__name__ + '.' + priv_ctx_name,
                           capabilities=PRIVSEP_CAPS)

in main.py

@privilege.node_agent_pri.entrypoint
def main():
    some_logic() <------- call threading.Thread to generate a new thread A here.

A.start():
    when something wrong:
       sys.exit(1) <--------- here it will not exit and hang for ever.

There is not error logs or exception tracestack when this issue happens