Re: [boost] Serialization and disctintion between eof and end of archive

From: Maciej Sobczak (prog_at_[hidden])
Date: 2006-01-30 18:00:21

Hi,

Robert Ramey wrote:

>>The boost.serialization library seems to use eod-of-stream in the
>>underlying istream object to denote the end-of-archive.
> 
> Why does it seem that way? It would certainly be contray to my
> intention.

It seems that way, because this is how it's shown by the example program 
provided by Seweryn on the "users" list:

http://lists.boost.org/boost-users/2006/01/16646.php

I have experimented a bit with this program and I've found that when the 
sender (the server in this case) flushes the stream, it's enough for the 
data to arrive at the destination, and it can be retrieved by regular 
stream read (the data is then identical as if the same archive was 
written to cout in the first place). But when the text_iarchive object 
is used to read it, it blocks. The only way to make it continue is to 
close the stream on the server side. So it looks like the text_iarchive 
is really waiting for eof (or for something else in the stream).

> I don't see that this would be a problem.  What is the matter with
> the following?
> 
> ?ostream os("pipename or whatever");
> 
> // first archive
> {
>     ?_oarchive oa(os);
>     oa << ...;
> } // archive is destroyed here - stream remains open and available
> // second archive
> {
>     ?_oarchive oa(os);
>     oa << ...;
> } // archive is destroyed here - stream remains open and available
> 
> os.close();

The matter is that there might be hours of pause between these two 
blocks above and the receiver might not want to wait that long. The 
archive (the first one) should be succesfully read on the other end of 
the wire as soon as the bytes make their way to the receiver.
It does not seem to be the case.

> I don't believe the conclusion follows.  The archive has to be
> constructed and destroyed - but the stream doesn't have to be.

Yes, but what about the reading part? Is it possible for the reader to 
successfully read the first archive *before* the next archive arrives 
(which can happen hours later)?

I hope to be mistaken, but my initial experiments with the OP's code led 
me to the above considerations.

Regards,

-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/