From:	CSBVAX::CSBVAX::MRGATE::"SMTP::CRVAX.SRI.COM::RELAY-INFO-VAX" 10-DEC-1988 22:59
To:	MRGATE::"ARISIA::EVERHART"
Subj:	Re: VMS FORTRAN and WRITE FILE sharing


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Date:     Sat, 10 Dec 88 11:54:14 PST
From:     carl@CitHex.Caltech.Edu (Carl J Lydick)
Message-Id: <881210115414.148@CitHex.Caltech.Edu>
Subject:  Re: VMS FORTRAN and WRITE FILE sharing
In-Reply-To: Your message <8812091722.aa12014@accuvax.nwu.edu> dated  9-Dec-1988
To:       CHOJNACKI@vaxmfg.tech.nwu.edu, info-vax@CitHex.Caltech.Edu

 > Has anyone ever tried to write to shared files in fortran, then  read  from
 > them  whilst  they  are  still  open.   I do a OPEN(UNIT=10, FILE="MYFILE",
 > STATUS="NEW", SHARED), that compiles ok, and every once in a while a do the
 > recommended  UNLOCK  10 as the manual states (even though it claims this is
 > for read unlocks).  Anyway, after the program has run, written to this file
 > and  has already done an UNLOCK, and I do a $ TYPE filename from DCL, I get
 > nothing.  (If I do not  open  the  file  in  SHARED  mode,  VMS  of  course
 > complaines  that  the file is open by another user, but in this case, since
 > it is shared, VMS says nothing.)

The problem is that the FORTRAN run-time I/O routines don't ask RMS  to  flush
its  output  buffers;  the reason a TYPE command doesn't produce any output is
that the data hasn't made it to disk yet.  You can force a flush of the output
to a file open on logical unit number L with the FORTRAN statement:
        CALL SYS$FLUSH(%VAL(FOR$RAB(L)))
where both L and FOR$RAB are declared  to  be  integers  variables  (actually,
since in this case you're never assigning the result of the call to FOR$RAB to
anything, the compiler won't apply a CVTFL to it even if you don't declare it.