To:         J3 Members                                       J3/16-120r3
From:       Van Snyder & Steve Lionel
Subject:    Several units for one file, nonadvancing, asynchronous, etc.
Reference:  15-226, 14-174r1 (UK-12), 16-007
Date: 2016 February 11

1. Introduction
===============

[211:24-25 9.5.4p4 and 212:31 9.5.6.1p8 in 15-007r2] 9.5.4p4 says it is
processor dependent whether a file can be connected to more than one
unit at the same time.  9.5.6.1p8 prevents it.  Which one is it?  Since
the permission was added by work item UK-12 (14-174r1) we can presume it
is intended to be allowed.

Once you open a can of worms, you need a bigger can to put them back.

Connecting several units to a file is not mentioned in the introduction.

If a file is connected to more than one unit, how do asynchronous output
and nonadvancing output work?  Are their behaviors processor dependent,
or should these actions be prohibited?

/JOR's position is that wording is needed to say that any I/O where
multiple units are connected to the same external file is
processor dependent.

8.1.6.5p5 says that if records are written to a file connected for
sequential access during more than one iteration of a DO CONCURRENT
construct, the ordering between records is processor dependent.  This is
posed by reference to a file, not a unit, so if a file is connected to
more than one unit, there is no new problem.  The subclause is silent
concerning the relationship between DO CONCURRENT and asynchronous
output.  Asynchronous is probably OK because 9.6.2.5p3 says asynchronous
transfers are "read, written, and processed as they would have been if
the data transfers were synchronous.

/JOR's position is that no edits are needed here.

The description of the NUMBER= specifier says it assigns the unit number
of the connected file.  It doesn't say which unit number is assigned if
more than one is connected.  The simplest answer is that it is processor
dependent.  A complicated additional feature is to allow (but not
require) a rank-one allocatable array, which is thereby allocated with a
size equal to the number of units attached to the file (zero if there
are none), and each element is assigned the external unit number for one
of those units.

/JOR prefers saying that the number returned in such cases is processor-
dependent. The alternative would be a new feature and out-of-scope.

2. Edits
========

[211:35+ 9.5.4p5+] Insert a paragraph:

"If input/output operations are performed on more than one
unit while they are connected to the same external file,
the results are processor dependent."

[212:31 9.5.6.1p8] Delete the paragraph that begins "If a file is
already connected...."

{Restriction is no longer valid - case covered by 9.5.4}

[243:14 9.10.2.18p1] Insert a sentence before the one that begins "If
there is no unit...": "If more than one unit on an image is connected
to the file, which of the connected external unit numbers is assigned
to the <scalar-int-variable> is processor dependent."

[509:8+] Insert a list item:

"o the effect of performing input/output operations on multiple
   units while they are connected to the same external file (9.5.4);"

[510:10+] Insert a list item:

" o which of the connected external unit numbers is assigned to the
    <scalar-int-variable> in the NUMBER= specifier in an INQUIRE by file
    statement if more than one unit on an image is connected to the
    file (9.10.2.18);"