(j3.2006) synchronizing I/O

malcolm at nag-j.co.jp malcolm
Tue Feb 10 08:19:19 EST 2009

  John Reid <John.Reid at stfc.ac.uk>

> Robert Corbett wrote:
> > The second paragraph of Section 13 of WG5/N1762 says that
> > Fortran 2008 processors must implement record-level
> > synchronization for OUTPUT_UNIT and ERROE_UNIT.  I have
> > not found language in the draft standard that specifies
> > that requirement.  Have I missed it, or is the language
> > yet to be added?
> We seem to have somehow lost this bullet point that was in of 08-007:
> "Each record shall be read or written by a single image. The processor shall 
> ensure that once an image commences transferring the data of a record to the 
> file, no other image transfers data to the file until the whole record has been 
> transferred."

That must have been me - I seem to have thought this had something to do with team i/o.  I can understand why.

> > I am interested in seeing how record-level synchronization
> > interacts with nonadvancing I/O.
> I don't see a problem here.

Try reading what data transfer statements do - they transfer data to/from the file.  The removed bullet point would mean locking the file from the first item transferred to it (by which we mean executing the data transfer statement and processing the list item) until the record is finished.

John, and the quoted text, seems to be operating under the impression that READ and WRITE do data transfers to an internal buffer until a whole record is built up and then blat the whole thing to the file in one go.  That is not, in fact, how the i/o is described or indeed how some i/o subsystems actually work.

Bob is absolutely right in his concern.  According to John's quoted text,
will lock OUTPUT_UNIT on all other images until the original image does a record-advancing operation.


I'd happily reinstate the text if it were correct... obviously something needs to be done but the wording needs to be much more careful.

..............Malcolm Cohen, J3 meeting, Las Vegas.

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