Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Mon, 18 Dec 2017 11:21:25 +0100

Hi Mark,

The database and subroutine are stripped down to a state that shows the

effect without the complexity of the original code. My question is not

so much how to optimize the subroutine but how to deal with such a

situation which may always happen.

The user actually wants to tell the aSub "do something special (and time

consuming) once"

The only solution I found was to make the slow part asynchronous, which

is a bit complicated but the only "correct" way.

Dirk

On 15.12.2017 17:17, Mark Engbretson wrote:

Wouldn't the actual database file be more useful to post? I.e., there may be a more optimal way to process the record that doesn't take so long (what makes for a slow calculation)?

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Dirk Zimoch
Sent: Friday, December 15, 2017 10:03 AM
To: EPICS <[email protected]>
Subject: Puzzled with lockset(?) problem

Hi Folks,

A colleague puzzled me with a db that shows surprising behavior.

An aSub record is triggered periodically though a CP input link. It looks up if it needs re-initialization (the user can press a button to request that). If yes it does an additional calculation. After processing it resets the record that requested the re-initialization.

See the attached .db file.

Usually when the user presses the button to re-initialize, the aSub does the additional calculation once and then goes back to normal processing.

But the calculation may may take a bit too long -- longer than the rate of the CP input link monitors. In that case, the record never leaves initialization mode!

I have simulated the slow calculation with the attached subroutine code which simply waits. (I know that is is a bad idea to wait in a synchronous subroutine. The original code does not wait but calculates.)

I think that this is an effect of lock sets because the "mode" record is as well input being processed by a caput as well as output of the aSub record. But is this the intended behavior?

The CP monitor finds the record busy (PACT=1) and arranges for re-processing when the record is done. But should not the FLNK be processed and the mode record go to 1 before the aSub runs again?

Any idea how to fix this? Is it necessary to make the subroutine asynchonous? Making the links from and to "mode" CA links does not fix it. Scanning the aSub itself with ".1 second" does not show the strange behavior, it simply delays the scan thread.

Puzzle for the weekend...
Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System