DeviceProxy in green mode: wait for ...

[woutdenolf]

Is there a better way of doing this without the two while loops? (Maybe something with threadpool and AsyncResult.wait?)

def wait_tango_online(uri, timeout=10, initial_state=None):
    """
    Wait until Tango device is online
    """
    error = RuntimeError(f"{uri} not online in {timeout} seconds")
    with gevent.Timeout(timeout, error):
        while True:
            try:
                dev_proxy = DeviceProxy(uri)  # raises when database is not online yet
                dev_proxy.ping()   # raises when device is not online yet
            except DevFailed as e:
                gevent.sleep(0.5)
            else:
                break
        if initial_state is not None:
            while dev_proxy.state() != initial_state:
                gevent.sleep(0.1)
        return dev_proxy

[tiagocoutinho]

To wait for a device to be online, one trick would be to subscribe to the state attribute configuration changed event:

import gevent.event
import tango.gevent


def wait(name, timeout=None):
  evt = gevent.event.Event()
  d = tango.gevent.DeviceProxy(name)
  sid = d.subscribe_event("state", tango.EventType.ATTR_CONF_EVENT,
                          lambda e: not e.err and evt.set(), [], True)
  try:
    return evt.wait(timeout)
  finally:
    d.unsubscribe_event(sid)


r = wait('a/b/c', 10)
print('Alive!' if r else 'Timed out!')

So this would get rid of your first while loop.

[tiagocoutinho]

If you are sure your device state attribute fires events you can catch two birds with one stone
by comparing the state event value with the one you are interested:

import gevent.event
import tango.gevent

def wait_state(name, state=None, timeout=None):
  evt = gevent.event.Event()
  d = tango.gevent.DeviceProxy(name)
  def cb(e):
    if not e.err and state in {None, e.attr_value.value}:
      evt.set()

  sid = d.subscribe_event("state", tango.EventType.CHANGE_EVENT, cb, [], True)
  try:
    return evt.wait(timeout)
  finally:
    d.unsubscribe_event(sid)

r = wait_state('a/b/c', timeout=10)
print('Alive!' if r else 'Timed out!')

[mguijarr]

I had the information from @bourtemb that the ADMIN device is always instantiated last - so, we should also ping or do the state query on this one in case a server has multiple devices and we want to know when they are all "ready"/"online".

This is the case for Lima servers, for example.

[ajoubertza]

@woutdenolf Can we close this ticket?