J3/04-105

Date:    7 Dec 03
To:      J3
From:    Dan Nagle
Subject: DEFER= specifier on CLOSE


Named scratch files would have provided some functionality
if a way could have been found to avoid the unsatisfactory
lack of a way to specify the desired interaction between
the name specified and existing names in the file syatem.

Adding a defer= specifier to close gives a superset
of the functionality of named scratch files.

Number:

Title: DEFER= on the CLOSE statement

Submitted By: J3

Status: For Consideration

References: Section 9.4.6, page 185

Basic Functionality: A CLOSE with DEFER='YES' sets the parameters
      (primarily STATUS=) of the CLOSE, the connection
      is actually closed when a subsequent CLOSE or
      at program termination.  A CLOSE with DEFER='NO' or DEFER= absent
      is effective immediately (as the present CLOSE statement).

Rationale:  A program may write a logfile of its actions which is desired
            to be kept only if the program terminates abnormally
            (this may be especially true of library writers).  This
            functionality was one supporting reason for the proposed
            named scratch files feature.  Other files may be desired
            to be kept only if the program terminates normally
            (a very large output file).  Adding DEFER=['YES'|'NO']
            to CLOSE gives both.

            An alternative is to add a CLOSE='<close-status>'
            to the OPEN statement.  However, it seems to me
            to be desirable to have close specifiers on the close statement,
            and open specifiers on the open statement, rather
            than mixing the two.  The alternative does allow
            one statement to do the work of two.

            An example of the expected use:

            OPEN( i, 'my_log_file', STATUS='replace')
            CLOSE( i, STATUS='keep', DEFER='yes')
            ...
            ! normal termination
            CLOSE( i, STATUS='delete')

            If the program terminates abnormally, the lof file is
            available for inspection.  Otherwise, it is deleted.

Estimated Impact: No other statement is affected.  The affect
                  on compilers is low, as the compiler must "package"
                  the close parameters for the system close routine
                  anyway.  This feature simply requires the processor
                  to keep the user-specified parameters for later use.

Detailed Specification: Add DEFER=['YES'|'NO'] to the CLOSE statement.
         The IOSTAT= variable, if present, should reflect whether
         legal values are passed to CLOSE only.  The IOSTAT= variable
         on the subsequent close statement, if any, may reflect
         the status of the actual close.

         Given DEFER=<scalar-default-character-expression>, if the s-d-c-e
         with trailing blanks removed, evaluates to 'YES',
         the close action is deferred until the file
         is otherwise closed.  If the s-d-c-e evaluates to 'NO'
         with trailing blanks removed, or DEFER= is absent,
         the close is effective immediately.

         It may be desirable to add a specifier to the INQUIRE statement
         to detect when a deferred close has been specified, but
         this paper does not propose to do so.

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