Experimental Physics and
Industrial Control System

I think PUTF is for EPICS to keep track of whether a record was processed
by a CA client, or by a PP link.  EPICS uses this to decide whether break
a loop in a lockset (a PP link trying to process a record that's already
executing as the result of a PP link) or allow two independent actors to
process a record at overlapping times (accidental collision between a PP
link and a CA put).  I'm not sure about your item 4, but I don't think a
database link should ever result in PUTF being set.  Also, I think
recGblFwdLink should clear PUTF always.  If RPRO and PUTF are both set,
it means a record was processing because of a CA put, and a PP link tried
to process it, so the processing motivated by RPRO must be PP-link processing.

Tim


Andrew Johnson wrote:

Hi Bob,

On Friday 24 April 2009 14:55:25 Bob Dalesio wrote:

Do you know what the PUTF record processed by dbPutfield, and RPRO
reprocess fields are used to accomplish?

I'm cross-posting this message to core-talk because while replying to Bob's question I think I've found a couple of bugs associated with those fields, and I'd like some more eyes on the issue.

I believe PUTF was provided as a way of telling a record that it's being processed because someone changed one of its fields, so it can distinguish between that and processing resulting from a forward link or other scan mechanism. I don't know of any record types that actually look at PUTF, but there could be some. However there are occasions where PUTF lies, which makes it less useful (see below).

RPRO is needed to ensure that a pending asynchronous operation doesn't cause the processing resulting from a put operation to be missed. It is less relevent to the record type, being mostly for internal use but is related to the PUTF field.

Here's what I get from reading the source, which uses these two fields in four places:

1. If something [usually CA but it could be a dbpf command] calls dbPutField() to set a field which is marked as PP, the routine will try to process the record immediately. If PACT is true however it can't, so it sets RPRO to request reprocessing later; if PACT is false it sets PUTF and calls dbProcess() to do the actual processing.

2. Inside dbProcess(), if a record is found to be disabled because DISA==DISV, both PUTF and RPRO are cleared immediately.

3. When a record finishes processing, usually the last thing its process() routine does is to call recGblFwdLink(). This checks and clears the RPRO field and if set it sticks this record on the scanOnce() queue to be run again as soon as possible. recGblFwdLink() always clears PUTF.

4. In dbPutLinkValue() when a DB link from another record has the PP flag set or points to the PROC field, if the destination record has its PUTF field set it just sets RPRO. If PUTF is not set, it calls dbScanLink() to process the destination record. This code really doesn't make any sense to me.

I think there are two bugs in the above code, which make the PUTF field less useful than it could/should be.

A) I suspect that in item 4 above, the dbPutLinkValue() code really should be testing PACT not PUTF, and it should actually set PUTF before the call to dbScanLink(). I have some vestigial memories that before PACT was introduced the PUTF field was involved in asynchronous processing, but I wasn't involved at the time so I may be confused about that.

B) I also think that recGblFwdLink() should not clear PUTF if RPRO was set, because the *next* time the record processes is the one that is due to a call to dbPutField() or dbPutLink(). Instead it should be setting PUTF if RPRO was set, and clearing it otherwise.

I propose to apply the attached change in src/db and would appreciate comments from other core developers in case I've missed or misunderstood something about how this is supposed to work.

Without this patch, PUTF is actually an almost useless field; the only place where its value gets looked at is in the dbPutLinkValue() routine as described above, unless there are some non-core record types that use it.

- Andrew

--
Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab.

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Re: some field definitions Andrew Johnson

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