Re: SSEQ record does not "appear" to be demanding callback completion from an asynchronous record forward-linked to another asynchronous record

["Hu, Yong via Tech-talk" <tech-talk at aps.anl.gov>]

Another thing I just noticed that you are using field(PRIO, "HIGH") for SET_PROP. I am not sure if this has an unexpected effect on the record processing chains.

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Hu, Yong via Tech-talk <tech-talk at aps.anl.gov>
Date: Thursday, March 30, 2023 at 8:44 AM
To: Wang, Andrew <wang126 at llnl.gov>, Mark Rivers <rivers at cars.uchicago.edu>, EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: Re: SSEQ record does not "appear" to be demanding callback completion from an asynchronous record forward-linked to another asynchronous record

Hi Andy,

Please take a look at the documentation: https://epics.anl.gov/bcda/synApps/std/sseqRecord.html. Specifically, this snippet “Finally, if the sseq record successfully waits for targetRecord to finish processing, … , and the sseq record cannot wait for this indirectly caused processing to finish unless …”.

I think this explains why DOL1/LNK1/WAIT1 does not work as you expect (you probably think that ‘FLNK’ will cause GET_PROP to be completely processed when SET_PROP gets processed) and you need additional DOL2/LNK2/WAIT2 to make GET_PROP completely processed.

As always, it is tricky to make asynchronous records (i.e. SET_PROP, GET_PROP) get processed as you expect.

Cheers,
Yong

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Wang, Andrew via Tech-talk <tech-talk at aps.anl.gov>
Date: Tuesday, March 28, 2023 at 6:00 PM
To: Mark Rivers <rivers at cars.uchicago.edu>, EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: RE: SSEQ record does not "appear" to be demanding callback completion from an asynchronous record forward-linked to another asynchronous record

Hi Mark,

 

I totally forgot about that. Thank you for bringing that to my attention.

 

I attempted your suggestion by doing the following:

 

record(ao, “VAL”)

{

                field(SCAN, “Passive”)

}

record(sseq, “PROCESS_INST")

{

                field(SCAN,  "Passive")

                field(SELM,  "All")

field(DOL1, “VAL”)

                field(LNK1,  "SET_PROP CA")

                field(WAIT1, "Wait")

                field(FLNK, “PRINT_SET_AND_GET”)

}

 

record(aSub, “PRINT_SET_AND_GET")

{

                field(SCAN,  "Passive")

                field(SNAM, “print_set_and_get”)

                field(INPA, “SET_PROP”)

                field(INPB, “GET_PROP”)

}

 

However, the values for SET_PROP and GET_PROP are still different when PRINT_SET_AND_GET processes.

 

To make it a little clearer, suppose that SET_PROP and GET_PROP both contain 25 initially. Then, I set VAL to be 55. Then, my hope would be that both SET_PROP and GET_PROP would both be 55 before PRINT_SET_AND_GET processes after I process PROCESS_INST. However, when PRINT_SET_AND_GET processes, SET_PROP is 55 but GET_PROP is still 25. If I process PROCESS_INST again, then both SET_PROP and GET_PROP are 55. My current workaround is doing the following, but it is very verbose. I still feel like the former method you proposed (if I understood it correctly) should work.

 

record(ao, “VAL”)

{

                field(SCAN, “Passive”)

}

record(sseq, “PROCESS_INST")

{

                field(SCAN,  "Passive")

                field(SELM,  "All")

                field(DOL1, “VAL”)

                field(LNK1,  "SET_PROP CA")

                field(WAIT1, "Wait")

                field(DOL2, “1”)

                field(LNK2,  "GET_PROP.PROC CA")

                field(WAIT2, "Wait")

                field(FLNK, “PRINT_SET_AND_GET”)

}

 

record(aSub, “PRINT_SET_AND_GET")

{

                field(SCAN,  "Passive")

                field(SNAM, “print_set_and_get”)

                field(INPA, “SET_PROP”)

                field(INPB, “GET_PROP”)

}

 

Thanks,

Andy

From: Mark Rivers <rivers at cars.uchicago.edu>
Sent: Tuesday, March 28, 2023 5:11 AM
To: EPICS tech-talk <tech-talk at aps.anl.gov>; Wang, Andrew <wang126 at llnl.gov>
Subject: Re: SSEQ record does not "appear" to be demanding callback completion from an asynchronous record forward-linked to another asynchronous record

 

Hi Andy,

 

I think your problem is with the WRITE_INST record in the second IOC.  It looks like perhaps you think that WRITE_INST will only write to the VAL field of SET_PROP, but not actually process the SET_PROP record.  Then you have PROCESS_INST that will process the SET_PROP record and wait for completion.

 

I think that would work if all of the records were in the same IOC.  However, the WRITE_INST link to SET_PROP is a CA link, and that will always cause the SET_PROP record to process if the field you are writing to has the PP attribute, which the VAL field does.  That is explained here:

https://epics.anl.gov/base/R3-16/2-docs/AppDevGuide/DatabaseLockingScanningAndProcessing.html#x6-2020005.12

 

which says:

 

The options for process passive are:

• It is not possible to honor PP or NPP options; the put operation completes immediately but whether the destination record will process depends on the process passive attribute of the destination field.
• CA - Force the link to be a channel access link.

So when WRITE_INST processes it forces SET_PROP to process, and then immediately links to PROCESS_INST.  PROCESS_INST will do a CA put, but SET_PROP will probably still be processing (PACT=TRUE).

 

If you combine WRITE_INST and PROCESS_INST into a single sseq record with WAIT1=Wait then I think it will do what you want.

 

I have not tested this, so I could be wrong.

 

Mark

 

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Wang, Andrew via Tech-talk <tech-talk at aps.anl.gov>
Sent: Monday, March 27, 2023 10:58 PM
To: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: SSEQ record does not "appear" to be demanding callback completion from an asynchronous record forward-linked to another asynchronous record

 

Hi all,

 

Today I encountered something kind of interesting and would like to get some outside opinions.

 

To begin with, I have an IOC for an instrument that I shall call DemoInstr. I have a “setter” and “getter” record for one of its properties. The two records are shown below.

 

record(ao, “SET_PROP”)

{

                field(SCAN, “Passive”)

                field(DTYP, “stream”)

field(PRIO, "HIGH")

                field(OUT,  "@DemoInstr.proto setProp $(PORT)")

                field(FLNK, “GET_PROP”)

}

 

record(ai, “GET_PROP”)

{

                field(SCAN, “Passive”)

                field(DTYP, “stream”)

                field(INP,  "@DemoInstr.proto getProp $(PORT)")

}

 

In a separate IOC that I shall call Setup, I declared a SEQ record called “WRITE_INST” that should write a value into “setProp” when it is processed. Then, “PROCESS_INST”, a SSEQ record, will process because it is forward-linked to “WRITE_INST”. “PROCESS_INST” should wait for a completion callback with the way it is written. However, when “PRINT_SET_AND_GET” processes, it reports that GET_PROP still contains the previous value. Shouldn’t GET_PROP have been updated because of the completion callback? I feel like I am missing something in my understanding of completion callbacks.

 

record(ao, “VAL”)

{

                field(SCAN, “Passive”)

}

 

record(seq, "WRITE_INST")

{

                field(SCAN, "Passive")

                field(SELM, "All")

                field(DOL1, “VAL")

                field(LNK1, "SET_PROP")

                field(FLNK, “PROCESS_INST ")

}

 

record(sseq, “PROCESS_INST")

{

                field(SCAN,  "Passive")

                field(SELM,  "All")

                field(LNK1,  "SET_PROP.PROC CA")

                field(WAIT1, "Wait")

                field(FLNK, “PRINT_SET_AND_GET”)

}

 

record(aSub, “PRINT_SET_AND_GET")

{

                field(SCAN,  "Passive")

                field(SNAM, “print_set_and_get”)

                field(INPA, “SET_PROP”)

                field(INPB, “GET_PROP”)

}

 

Thank you,

Andy

 

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