A Device is Blocking if a read request never produces fewer characters than requested except at end-of-stream, and if a write request never consumes fewer characters than requested under any circumstances. All Devices currently provided with the Iostreams library are Blocking. Limited support for non-Blocking Devices has been provided as a foundation for future more comprehensive support of asynchronous and non-blocking i/o.
The Blocking concept does not apply to filters. Instead, filters are required to be blocking-preserving, which means that
read request never produces fewer characters than requested unless end-of-stream has been reached or unless a read request to a downsteam Source produces fewer characters than requested, and
write request never consumes fewer characters than requested unless a write request to a downsteam Sink consumes fewer characters than requested.
Unlike other Iostreams library concepts, Blocking is not associated with any category tag. In the future, a non_blocking_tag may be introduced.
Same as Device.
Valid expressions are the same as Device. The additional semantic requirements are described informally above.
Revised 20 May, 2004
© Copyright Jonathan Turkanis, 2004
Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)