[ace-users] ACE_OS::sendv() behavior question concerning
Douglas C. Schmidt
schmidt at dre.vanderbilt.edu
Fri Aug 24 10:18:31 CDT 2007
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> By looking at the ACE::sendv_n_i() code, I have found out that
> writev() can perform partial writes. I am surprised of that behavior
> because in the book Unix network programming vol. 1, second edition,
> it is written that writev() is an atomic operation.
I don't think that's correct. Please see the official documentation for
and look at this statement:
"Upon successful completion, writev() shall return the number of bytes
actually written. Otherwise, it shall return a value of -1, the
file-pointer shall remain unchanged, and errno shall be set to indicate
> My understanding of what an atomic operation is, is that it either
> writes all the data or it does not write anything but obviously in the
> writev() context, atomic operation means something else.
Can you please provide the quote from the UNPv1 book that you're
> So I would like to ask this group what atomic operation means for
> writev() and besides if ACE_IOV_MAX is defined what are the conditions
> with a non blocking stream socket that could result in a writev()
> partial write?
I suspect it's the usual suspects, e.g, a flow controlled connection
that leads to "short writes". Please see
for a summary of why short writes can occur.
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