This is also peripheral to what _build_command needs, can be improved
and tested independently, and so makes more sense in a separate method.
This commit doesn't change any functionality (and I've verified that it
works with the various combinations: control_path set in ansible.cfg,
ssh_args adding or not adding ControlMaster/ControlPersist, etc.).
Also get pipelining working for people who look to chroot as an example
for their own connection plugins
Note: In the latest v2 API, action handles become but chroot doesn't
reliably handle become. Maybe we need to add a has_become attribute
that the action can display an appropriate error.
Due to the way we're now calculating delegate_to, if that value is based
on a loop variable ('item') we need to calculate all of the possible
delegated_to variables for that loop.
Fixes#12499
There doesn't appear to be anything that actually uses tmp_path in the
connection plugins so we don't need to pass that in to exec_command.
That change also means that we don't need to pass tmp_path around in
many places in the action plugins any more. there may be more cleanup
that can be done there as well (the action plugin's public run() method
takes tmp as a keyword arg but that may not be necessary).
As a sideeffect of this patch, some potential problems with chmod and
the patch, assemble, copy, and template modules has been fixed (those
modules called _remote_chmod() with the wrong order for their
parameters. Removing the tmp parameter fixed them.)
The process is already gone, so there's not going to be any new data
showing up on its stderr; we only want to make sure that we haven't
missed something that was already written. So polling once is enough.
This change is motivated by an ssh oddity: when ControlPersist is
enabled, the first (i.e. master) connection goes into the background; we
see EOF on its stdout and the process exits, but we never see EOF on its
stderr. So if we ran a command like this:
ANSIBLE_SSH_PIPELINING=1 ansible -T 30 -vvv somehost -u someuser -m command -a whoami
We would first do select([stdout,stderr], timeout) and read the command
module output, then select([stdout,stderr], timeout) again and read EOF
on stdout, then select([stderr], timeout) AGAIN (though the process has
exited), and select() would wait for the full timeout before returning
rfd=[], and then we would exit. The use of a very short timeout in the
code masked the underlying problem (that we don't see EOF on stderr).
It's always preferable to call select() with a long timeout so that the
process doesn't use any CPU until one of the events it's interested in
happens (and then select will return independent of elapsed time).
(A long timeout value means "if nothing happens, sleep for up to <x>";
omitting the timeout value means "if nothing happens, sleep forever";
specifying a zero timeout means "don't sleep at all", i.e. poll for
events and return immediately.)
This commit uses a long timeout, but explicitly detects the condition
where we've seen EOF on stdout and the process has exited, but we have
not seen EOF on stderr. If and only if that happens, it reruns select()
with a short timeout (in practice it could just exit at that point, but
I chose to be extra cautious). As a result, we end up calling select()
far less often, and use less CPU while waiting, but don't sleep for a
long time waiting for something that will never happen.
Note that we don't omit the timeout to select() altogether because if
we're waiting for an escalation prompt, we DO want to give up with an
error after some time. We also don't set exceptfds, because we're not
actually acting on any notifications of exceptional conditions.
