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

From: Robert Ramey (ramey_at_[hidden])
Date: 2006-01-31 11:51:46

Actually this does reveal the true issue - and one that can and should
be addressed from withing the serialization library.

text archives output each value preceeded with a space to
separate the tokens. The space is used to delimit the data value.
the last is >> t is waiting for a space to return - it doesn't find it
untl the next archive.

So text archives should be terminated with a space or newline
to prevent this from happening.

I will add this to the text_oarchive destructor.  This should
address the problem.

Good work gentlemen,

Robert Ramey

Maciej Sobczak wrote:
> Robert Ramey wrote:
>
>>> 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).
>>
>> It may look that way, but that's not what's happening.  I recomend
>> you investigate the management (or lack there of, flushing of the
>> underlying stream.
>
> OK, after further investigation it appears that the archive reader is
> in fact sensitive to one of these two:
>
> - end of line
> - end of stream
>
> It is possible to reuse long-lived connection for sending many
> archives (and receiving them without unnecessary waits), provided one
> of these two happens. So, the sender might look like this:
>
> ?ostream outstream(...);
>
> while (...)
> {
>     {
>         boost::archive::text_oarchive ar(outstream);
>
>         ar << myObject;
>     }
>
>     // this:
>     outstream << std::endl;  // or '\n' followed by .flush()
> }
>
> With this additional newline+flush the receiver has no problems with
> de-serializing the data as soon as they arrive.
>
> Thank you for helping solving this.
> Regards,