11-259
To: J3
Subject: COPY_ASYNC using asynchronous I/O
From: Van Snyder
Date: 13 October 2011
References: 11-256

Background
----------

Paper 11-256 included a proposal for asynchronous copying between
images, using a new statement or intrinsic procedure.

Proposal
--------

Rather than multiply concepts, asynchronous I/O could be adapted to
solve this problem, with additional functionality not possible with the
proposal in 11-256.  In particular, WRITE is a gather, and READ is a
scatter.

Method
------

1. Extend "internal file" to arrays of variables of any type,
restricting formatted I/O using internal files to character variables.
For variables of other types, only unformatted I/O is permitted.  In
either case, the internal file can be a coarray.

2. In the unformatted internal file case, the type and kind of every
effective list item shall be the same as the type and kind of the
internal file.  Care is needed here when describing expansion of list
items of derived type:  Expansion stops when components of the type of
the internal file are reached.

3. The internal file is used in array element order.

4. Extend the ID= specifier in a control information list to allow
variables of type(EVENT).  This applies to READ, WRITE and WAIT
statements.  ID= variables of type(EVENT) could equally be used for
external file I/O.

5. Use the WAIT statement rather than a new statement for event-type
based notify/query synchronization.

6. Internal I/O using a coarray internal file does not have to be
asynchronous.  It is then a synchronous gather or scatter.

7. A WAIT statement with an event that appears in a WRITE statement
completes when the data in the I/O list have been transferred to the
internal file.  Existing rules concerning access continue to apply.

8. A WAIT statement with an event that appears in a READ statement
completes when the variables in the I/O list have been transferred from
the internal file.  Existing rules concerning access continue to apply.