[Info-vax] Timeout in a write using QUIW.

[Dave Froble]

On 6/21/2023 7:38 PM, Dave Froble wrote:
> On 6/21/2023 5:36 PM, Jan-Erik Söderholm wrote:
>> Den 2023-06-21 kl. 23:25, skrev Stephen Hoffman:
>>> On 2023-06-21 20:45:12 +0000, Jan-Erik Sderholm said:
>>>
>>>> Now, here is a technical one...
>>>>
>>>> When doing a *read* from a terminal device using QIOW, one
>>>> can use IO$M_TIMED and supply a timeout value in P3. That
>>>> works perfectly and we use that a lot...
>>>
>>> I've never had great success...
>>
>>
>> I'm sorry about that. As I wrote, it works perfectly. In the
>> case of reads, of course, where it is supported.
>>
>> My question was about writes, and it has been confirmed that
>> timeout paramaters are not supported there. Thanks Arne.
>>
>> Now we need to weight the coding work against getting
>> network cables installed to the printers. Wired printers
>> will also "solve" the issue with the current code. We have
>> 15-20 older similar Zebra label printers, all wired, and
>> we do not see these error scenarios with those.
>> All using the same C routine for the QIOW calls.
>>
>>
>> Jan-Erik.
>
>
> Well, if you have an AST routine such as:
>
> 1       !************************************************
>         !     Timer AST Timeout Handler to Cancel I/O
>         !************************************************
>
>         SUB TCP_TIMER(  LONG CH% , &
>                         LONG Z2% , &
>                         LONG Z3% , &
>                         LONG Z4% , &
>                         LONG Z5% )
>
>         CALL SYS$CANCEL( Loc(CH%) By Value )
>
>         SubEnd
>
> And then in you program define the routine as external:
>
>         EXTERNAL LONG FUNCTION TCP_TIMER                !  Timer AST routine
>
> And then queue the timer routine:
>
>         !***************** Set timer AST *****************
>         Stat% = SYS$SETIMR( ,   WAIT.PRD ,              !  Delta time &
>                                 LOC(TCP_TIMER) By Value , &
>                                 CH% By Value , )        !  AST rtn and channel

This code has been working well for years, and I hadn't looked at it until 
recently.  I find the lack of testing the completion status of the system 
service to be sloppy.  One might ask, "what can go wrong?", and probably will 
not, but it is possible, I think.  So, a better practice would be to at least 
test Stat% AND SS$_NORMAL.  Just saying ...


>         Stat% = SYS$QIOW(       ,                       !  Event flag &
>                                 CH% By Value,           !  VMS channel &
>                                 IO$_ACCESS By Value,    !  Operation &
>                                 IOSB::Stat%,            !  I/O status block &
>                                 ,                       !  AST routine &
>                                 ,                       !  AST parameter &
>                                 ,                       !  P1 &
>                                 ,                       !  P2 &
>                                 SERVER.ITEMLST::LEN%,   !  P3 - remote socket n^
>                                 ,                       !  P4 - &
>                                 ,                       !  P5 &
>                                 )                       !  P6
>
>         If      ( Stat% And SS$_NORMAL ) = 0%
>         Then    Call VMSERR( Stat% , E$ )
>                 E$ = "Unable to queue connect to host - " + E$
>                 E% = -1%
>                 SaveStat% = Stat%
>                 GoTo Close_Socket
>         End If
>
>         If      ( IOSB::Stat% And SS$_NORMAL ) = 0%
>         Then    If      IOSB::Stat% = SS$_ABORT &
>                 OR      IOSB::Stat% = SS$_CANCEL
>                 Then    E$ = "Timeout"
>                 Else    Call VMSERR( IOSB::Stat% , E$ )
>                 End If
>                 E$ = "Unable to connect to host - " + E$
>                 E% = -1%
>                 SaveStat% = IOSB::Stat%
>                 GoTo Close_Socket
>         End If
>
> Note, if the QIOW exits with the IOSB status of ABORT or CANCEL then you can
> assume it was the cancel in the AST routine.  However, I feel that some other
> reason might set that status.  Never bothered to look into it further.
>
> My planning is that if this happens, then the QIOW failed, and it's time to move
> on, regardless of why it failed.
>
> Note, the wait period can be set up with:
>
>         WW% = W%                                        !  Set delta time
>         Stat% = LIB$CVT_TO_INTERNAL_TIME( LIB$K_DELTA_SECONDS , WW% , WAIT.PRD )
>
> Should be easy to figure out by reading the docs on the various system services
> and LIB$ routines.
>


-- 
David Froble                       Tel: 724-529-0450
Dave Froble Enterprises, Inc.      E-Mail: davef at tsoft-inc.com
DFE Ultralights, Inc.
170 Grimplin Road
Vanderbilt, PA  15486