J3/04-254

To:         J3
From:       Craig Dedo
Date:       February 16, 2004
Subject:    File Sharing Modes

Number:

Title:                File Sharing Modes

Submitted By:    Craig Dedo

Status:            For Consideration

References:

Basic Functionality:
    The new standard should allow for the specification of file sharing
modes.  The file sharing specifier should allow the programmer to
specify any of the four sharing modes:
* Exclusive use by this unit
* Reading by others, but not writing
* Writing by others but not reading
* Permit full access by others

Rationale:
    Currently, there is no facility for file sharing in the Fortran
standard.  Some processors already provide this capability but there are
widely varying implementations.  Some implementations do not allow
specification of all four sharing modes.  The ability to specify file
sharing modes would allow Fortran developers to support frequently
accessed multi-user data bases on time-sharing systems or local area
networks.  With the growing complexity of software and the growing
numbers of networked desktop PCs, there will be a large demand for
simultaneous access to complex data bases.

Estimated Impact:
    There should be no impact on exiting codes.  Processors which
already provide this capability in a non-standard manner will have to
develop the support for the standard syntax.

Detailed Specification:
    The best method would be to allow for a second specification in the
character expression that follows the ACTION= keyword, in the same
manner that Lahey Fortran does.  In the character expression, the access
mode specifier and sharing mode specifier would be separated by a
comma.  Either one could come first.

    Alternatively, there could be a separate keyword, such as SHARE or
something similar.

    The sharing mode specifier could have one of these four values, with
the indicated actions:

Sharing Mode Keywords    Action

NONE        For exclusive use by this unit in this process
READONLY    Allows reading by others, but not writing
WRITEONLY   Allows writing by others, but not reading
READWRITE   Allows others to open the file for both reading or writing

History: