| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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| 2 | <HTML> |
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| 3 | <HEAD> |
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| 4 | <TITLE>Blocking</TITLE> |
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| 5 | <LINK REL="stylesheet" HREF="../../../../boost.css"> |
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| 6 | <LINK REL="stylesheet" HREF="../theme/iostreams.css"> |
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| 7 | </HEAD> |
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| 8 | <BODY> |
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| 9 | |
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| 10 | <!-- Begin Banner --> |
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| 11 | |
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| 12 | <H1 CLASS="title">Blocking</H1> |
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| 13 | <HR CLASS="banner"> |
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| 14 | |
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| 15 | <!-- End Banner --> |
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| 16 | |
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| 17 | <H2>Description</H2> |
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| 18 | |
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| 19 | <P> |
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| 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>. |
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| 21 | </P> |
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| 22 | |
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| 23 | <P> |
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| 24 | The Blocking concept does not apply to filters. Instead, filters are required to be <SPAN CLASS='term'>blocking-preserving</SPAN>, which means that |
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| 25 | </P> |
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| 26 | <UL> |
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| 27 | <LI> |
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| 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 |
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| 29 | </LI> |
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| 30 | <LI> |
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| 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. |
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| 32 | </LI> |
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| 33 | </UL> |
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| 34 | |
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| 35 | <P> |
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| 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. |
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| 37 | </P> |
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| 38 | |
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| 39 | <H2>Refinement of</H2> |
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| 40 | |
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| 41 | <P><A HREF="device.html">Device</A>.</P> |
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| 42 | |
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| 43 | <A NAME="types"></A> |
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| 44 | <H2>Associated Types</H2> |
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| 45 | |
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| 46 | <P>Same as <A HREF="device.html">Device</A>.</P> |
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| 47 | |
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| 48 | <A NAME="expressions"></A> |
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| 49 | <H2>Valid Expressions / Semantics</H2> |
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| 50 | |
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| 51 | <P>Valid expressions are the same as <A HREF="device.html">Device</A>. The additional semantic requirements are described informally above.</P> |
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| 52 | |
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| 53 | <!-- Begin Footer --> |
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| 54 | |
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| 55 | <HR> |
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| 56 | <P CLASS="copyright">Revised |
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| 57 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 58 | 20 May, 2004 |
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| 59 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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| 60 | </P> |
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| 61 | |
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| 62 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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| 63 | <P CLASS="copyright"> |
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| 64 | 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>) |
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| 65 | </P> |
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| 66 | |
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| 67 | <!-- End Footer --> |
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| 68 | |
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| 69 | </BODY> |
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