RE: p4p timeout on get() in broadcastless network

[Freddie Akeroyd - STFC UKRI via Tech-talk <tech-talk at aps.anl.gov>]

Hi Ulrik,

 

Does setting

 

    EPICS_PVA_NAME_SERVERS=10.0.0.12

 

For the client help?

 

Regards,

 

Freddie

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Ulrik Pedersen via Tech-talk
Sent: 23 January 2026 16:44
To: Tech talk <tech-talk at aps.anl.gov>
Subject: p4p timeout on get() in broadcastless network

 

Hello,

 

I am having some trouble getting p4p working reliably in a cloud based network where UDP broadcasts are not possible. I am only using a single VM, running both the IOC and the p4p client on the same VM. The setup works well with Phoebus, archiver, and pvget/pvput/pvmonitor from EPICS base, just not with p4p...

 

I am running an EPICS IOC with PVXS and QSRV2 and just a few PVs. The IOC is running with the following EPICS environment to work around the fact that we can't use broadcast (the 10.0.0.12 is the VMs IP on a private network with archiver, etc.):

 

user02@uservm02:~$ env | grep -i pva | sort

EPICS_PVAS_AUTO_BEACON_ADDR_LIST=NO

EPICS_PVAS_BEACON_ADDR_LIST=10.0.0.12

EPICS_PVAS_BROADCAST_PORT=5076

EPICS_PVAS_SERVER_PORT=5075

EPICS_PVA_ADDR_LIST=10.0.0.12

EPICS_PVA_AUTO_ADDR_LIST=NO

EPICS_PVA_BROADCAST_PORT=5076

 

Then on for the p4p client, I am running with this environment:

 

(epics-training-env) user02@uservm02:~$ env | grep -i pva | sort

EPICS_PVAS_AUTO_BEACON_ADDR_LIST=NO

EPICS_PVAS_BEACON_ADDR_LIST=10.0.0.12

EPICS_PVA_ADDR_LIST=10.0.0.12

EPICS_PVA_AUTO_ADDR_LIST=NO

EPICS_PVA_BROADCAST_PORT=5076

 

(I know the PVAS variables are not needed on the client. I have been tinkering a lot with these today)

 

My python script with p4p looks like this:

 

(epics-training-env) user02@uservm02:~$ cat small.py 

from p4p.client.thread import Context

ctxt = Context('pva')

print(ctxt.get('user02:va:01:gauge:pressure'))

ctxt.close()

 

Sometimes the script will run successfully once or twice, but then it will mostly timeout with this error dump:

 

(epics-training-env) user02@uservm02:~$ python small.py 

Traceback (most recent call last):

  File "/opt/epics/python/.venv/lib/python3.12/site-packages/p4p/client/thread.py", line 264, in get

    value, i = done.get(timeout=timeout)

               ^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/usr/lib/python3.12/queue.py", line 179, in get

    raise Empty

_queue.Empty

 

During handling of the above exception, another exception occurred:

 

Traceback (most recent call last):

  File "/home/user02/small.py", line 3, in <module>

    print(ctxt.get('user02:va:01:gauge:pressure'))

          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/opt/epics/python/.venv/lib/python3.12/site-packages/p4p/client/thread.py", line 268, in get

    raise TimeoutError()

TimeoutError

 

I am on an Ubuntu 24.04 VM. Using system python 3.12.3, p4p==4.2.2

 

Hope someone can point out my silly mistake here... 

 

Cheers,

Ulrik