ceph/src/boost/libs/iostreams/doc/concepts/blocking.html

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
   2 <HTML>
   3 <HEAD>
   4     <TITLE>Blocking</TITLE>
   5     <LINK REL="stylesheet" HREF="../../../../boost.css">
   6     <LINK REL="stylesheet" HREF="../theme/iostreams.css">
   7 </HEAD>
   8 <BODY>
   9
  10 <!-- Begin Banner -->
  11
  12     <H1 CLASS="title">Blocking</H1>
  13     <HR CLASS="banner">
  14
  15 <!-- End Banner -->
  16
  17 <H2>Description</H2>
  18
  19 <P>
  20     A <A HREF="device.html">Device</A> is Blocking if a <CODE>read</CODE> request never produces fewer characters than requested except at end-of-stream, and if a <CODE>write</CODE> 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 <A HREF='../guide/asynchronous.html'>asynchronous and non-blocking i/o</A>.
  21 </P>
  22
  23 <P>
  24     The Blocking concept does not apply to filters. Instead, filters are required to be <SPAN CLASS='term'>blocking-preserving</SPAN>, which means that
  25 </P>
  26 <UL>
  27     <LI>
  28         a <CODE>read</CODE> request never produces fewer characters than requested unless end-of-stream has been reached or unless a <CODE>read</CODE> request to a downsteam Source produces fewer characters than requested, and
  29     </LI>
  30     <LI>
  31         a <CODE>write</CODE> request never consumes fewer characters than requested unless a <CODE>write</CODE> request to a downsteam Sink consumes fewer characters than requested.
  32     </LI>
  33 </UL>
  34
  35 <P>
  36     Unlike other Iostreams library concepts, Blocking is not associated with any <A HREF='../guide/traits.html#category_tags'>category tag</A>. In the future, a <CODE>non_blocking_tag</CODE> may be introduced.
  37 </P>
  38
  39 <H2>Refinement of</H2>
  40
  41 <P><A HREF="device.html">Device</A>.</P>
  42
  43 <A NAME="types"></A>
  44 <H2>Associated Types</H2>
  45
  46 <P>Same as <A HREF="device.html">Device</A>.</P>
  47
  48 <A NAME="expressions"></A>
  49 <H2>Valid Expressions / Semantics</H2>
  50
  51 <P>Valid expressions are the same as <A HREF="device.html">Device</A>. The additional semantic requirements are described informally above.</P>
  52
  53 <!-- Begin Footer -->
  54
  55 <HR>
  56
  57 <P CLASS="copyright">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P>
  58 <P CLASS="copyright">
  59     Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
  60 </P>
  61
  62 <!-- End Footer -->
  63
  64 </BODY>