topic Re: Fortran program hangs when writing to offline reverse TNA device in Operating System - OpenVMS

Fortran program hangs when writing to offline reverse TNA device

R_B_W — Thu, 11 May 2023 04:29:17 GMT

Hi All,

I've recently inherited our VMS system and I'm running into problems when a fortran program tries to write to a reverse TNA device that is offline at the device end (e.g. powered off, network outage). These still show up as online when using:
>show dev tna
(Which I believe to be property of reverse telnet devices.)

The TNA devices are opened in fortran using the standard Open() function and are written to using the standard write() function.

Ideally the write function, or underlying tcp, would hit a timeout/error condition and return an iostat which can be handled and the program can continue.

I've read through the available documentation on fortran and tcpip but haven't found anything I think is relevant.

Any ideas on how I can prevent the program hanging? Thanks!

Running:
OpenVMS 8.4-2
TCPIP V5.7 - ECO5
VSI Fortran V8.3

Apologies if this is poorly worded/explained, I'm new to both VMS and software management.

Cheers,

RBW

Re: Fortran program hangs when writing to offline reverse TNA device

Volker Halle — Wed, 10 May 2023 09:32:09 GMT

RBW,

AFAIK a write with timeout cannot be done with standard FORTRAN statements.

You have 2 alternatives. both require OpenVMS programming skills and changes to your source code:

- use USEROPEN and set RAB$V_TMO and RAB$B_TMO

see VSI Fortran for OpenVMS User Manual — VMS Software, Inc.

- use QIOs with a timer, ASTs and/or event flags

Volker.

Re: Fortran program hangs when writing to offline reverse TNA device

R_B_W — Mon, 15 May 2023 21:09:01 GMT

Thanks for the leads Volker! I'll accept this as the solution until I get around to testing/confirming useropen.

Cheers,

RBW

Re: Fortran program hangs when writing to offline reverse TNA device

Tom Wade_1 — Tue, 16 May 2023 16:15:36 GMT

Hi,

I did something similar with useropen to set the wait-for-lock bit. I've modified this slightly to use the timeout bit to produce a demo program. Hopefully this will help. It does I/O to the terminal using Fortran Read/Write. If the read times out, it will exit with an error.

Tom Wade

C Program to demonstrate timeout I/O Program Demo_Timeout Implicit None Integer status, unit, length Character *256 line Integer Set_Timeout_IO External Set_Timeout_IO Call Lib$Get_LUN (unit) Open (unit, name='SYS$COMMAND', status='old', useropen=Set_Timeout_IO) C Write and read some data. Write (unit, 21, err=80) 21 Format (' This is some data') Read (unit, 11, err=80) length, line 11 Format (Q, A) Write (unit, 22, err=80) line (1:length) 22 Format (' Read "', A, '"') Close (unit) Call Lib$Free_Lun (unit) Call Exit C Error branch 80 Call Errsns (,status,,,) Call Exit (status) End C+ Integer Function Set_Timeout_IO (fab, rab, unit) C Open the file described by File Access Block 'fab', Record Access Block C 'rab' and logical unit number 'unit'. We open the file so that all I/O C is subject to a timeout. C- Integer unit, status Include '($FABDEF)' Include '($RABDEF)' Include '($SYSSRVNAM)' Record /FABDEF/ fab Record /RABDEF/ rab C Set the required bit for timeout rab.Rab$L_Rop = rab.Rab$L_Rop .or. Rab$M_Tmo C Set the timeout period rab.Rab$B_Tmo = 5 ! seconds C Open the file. status = Sys$Open (fab) If (status) status = Sys$Connect (rab) C Return status Set_Timeout_IO = status End

Re: Fortran program hangs when writing to offline reverse TNA device

R_B_W — Tue, 16 May 2023 23:17:54 GMT

Hi Tom,

Thanks for the code, I have a similar test program based on the info Volker directed me to. It seems to me the timeout only concerns reads and not writes, my program will still hang indefinitely when I write to the device and it's off.

c Program test_useropen c integer iostat,ierr,sysfil external timeout_config c sysfil = 10000 c Print *, 'opening device' OPEN (UNIT=SYSFIL, 1 STATUS='OLD', 1 SHARED, 1 ACCESS='APPEND', 1 FILE='FIL', ! FIL is a system logical = TNA101: 1 IOSTAT=IOSTAT, 1 FORM='FORMATTED', 1 USEROPEN=TIMEOUT_CONFIG) Print *, 'open status: ',iostat c c Print *, 'starting write' write(sysfil,fmt=10,iostat=iostat) 10 format(1x,'testing writing to an offline device') Print *, 'finished or skipped write with status: ',iostat close(sysfil) c END c c Integer Function Timeout_config(FAB,RAB,LUN) c Include '($FABDEF)' Include '($RABDEF)' Include '($SYSSRVNAM)' c Record /FABDEF/ FAB Record /RABDEF/ RAB c RAB.RAB$L_ROP = IBSET(RAB.RAB$L_ROP,RAB$V_TMO) RAB.RAB$B_TMO = 5 c Timeout_config = sys$open(fab) IF (.not. timeout_config) RETURN Timeout_config = sys$connect(rab) c Return END c

Cheers,

RBW

Re: Fortran program hangs when writing to offline reverse TNA device

Volker Halle — Thu, 18 May 2023 05:50:48 GMT

RBW,

as the RAB$V_TMO mechanism does not seem to work on WRITE - see above examples - I checked the DCL READ and WRITE statements. There is a /TIME_OUT=n parameter for READ, but not for WRITE. This might mean, that a timeout for a RMS WRITE operation is not implemented - except for a timeout on a record lock.

So the best approch would be to write a subroutine, which uses QIOs and TIMER ASTs

See previous discussion of a similar questions in

Re: SYS$QIOW doesn't return to caller - Hewlett Packard Enterprise Community (hpe.com)

Volker.