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<== Date ==> <== Thread ==>
Subject: Re: warnings.warn from raspberry pyepics
From: Matt Newville via Tech-talk <tech-talk at aps.anl.gov>
To: LE-DANIEL Erwann <erwann.le-daniel at alstomgroup.com>
Cc: "tech-talk-request at aps.anl.gov" <tech-talk-request at aps.anl.gov>, "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Date: Mon, 19 Sep 2022 11:25:20 -0500
Hi,

On Mon, Sep 19, 2022 at 10:57 AM LE-DANIEL Erwann <erwann.le-daniel at alstomgroup.com> wrote:

True, It works and return values from network during few seconds and after the loop speed decrease and the error message occures.

 


OK.  Then, I'm less sure about what is going on.  Creating multiple instances of a PV in a loop would be an odd thing to do, though it will not create completely new connections to the CA Channel: `epics.ca._cache` should only have one Channel in it, though it will retain a large number of callbacks that are no longer accessible.  I don't know if there is a limit on the number of PVs that can be created - your script runs to at least 3000 times for me, though I did not test with raspberry pi.

But: For sure, creating a PV and then fetching its value repeatedly is recommended:

p = epics.PV(‘TL_AN_Input’)

while True:

               val = p.get()

               print (val)

               time.sleep(0.1)


There is also `epics.get_pv` which will get a cached PV or create one if needed:


while True:

               p = epics.get_(‘TL_AN_Input’)

               val = p.get()

               print (val)

               time.sleep(0.1)

this will prevent the creation of thousands of useless callbacks.

--Matt

Replies:
Re: warnings.warn from raspberry pyepics Matt Newville via Tech-talk
RE: warnings.warn from raspberry pyepics LE-DANIEL Erwann via Tech-talk
References:
warnings.warn from raspberry pyepics LE-DANIEL Erwann via Tech-talk
Re: warnings.warn from raspberry pyepics Matt Newville via Tech-talk
Re: warnings.warn from raspberry pyepics Mark Rivers via Tech-talk
RE: warnings.warn from raspberry pyepics LE-DANIEL Erwann via Tech-talk
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