In the shutdown system test multiple queries are sent to a resolver
instance, in the meantime we terminate the same resolver process for
which the queries were sent to, either via rndc stop or a SIGTERM
signal, that means the resolver may not be able to answer all those
queries, since it has initiated the shutdown process.
The dnspython library raises a dns.resolver.NoNameservers exception when
a resolver object fails to receive an answer from the specified list
of nameservers (resolver.nameservers list), we need to handle this
exception as this is something that may happen since we asked the
resolver to terminate, as a result it may not answer clients even if
an answer is available, as the operation will be canceled.
PyLint 2.8.2 reports the following suggestions for two Python scripts
used in the system test suite:
************* Module tests_rndc_deadlock
bin/tests/system/addzone/tests_rndc_deadlock.py:71:4: R1732: Consider using 'with' for resource-allocating operations (consider-using-with)
************* Module tests-shutdown
bin/tests/system/shutdown/tests-shutdown.py:68:4: R1732: Consider using 'with' for resource-allocating operations (consider-using-with)
bin/tests/system/shutdown/tests-shutdown.py:154:8: R1732: Consider using 'with' for resource-allocating operations (consider-using-with)
Implement the above suggestions by using
concurrent.futures.ThreadPoolExecutor() and subprocess.Popen() as
context managers.
The $SYSTEMTESTTOP shell variable if often set to .. in various shell
scripts inside bin/tests/system/, but most of the time it is only
used one line later, while sourcing conf.sh. This hardly improves
code readability.
$SYSTEMTESTTOP is also used for the purpose of referencing
scripts/files living in bin/tests/system/, but given that the
variable is always set to a short, relative path, we can drop it and
replace all of its occurrences with the relative path without adversely
affecting code readability.
This test ensures that named will correctly shutdown
when receiving multiple control connections after processing
of either "rncd stop" or "kill -SIGTERM" commands.
Before the fix, named was crashing due to a race condition happening
between two threads, one running shutdown logic in named/server.c
and other handling control logic in controlconf.c.
This test tries to reproduce the above scenario by issuing multiple
queries to a target named instance, issuing either rndc stop or kill
-SIGTERM command to the same named instance, then starting multiple rndc
status connections to ensure it is not crashing anymore.
