[ceph.git] / ceph / src / boost / libs / iostreams / doc / concepts / blocking.html

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<HEAD>
    <TITLE>Blocking</TITLE>
    <LINK REL="stylesheet" HREF="../../../../boost.css">
    <LINK REL="stylesheet" HREF="../theme/iostreams.css">
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<BODY>

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    <H1 CLASS="title">Blocking</H1>
    <HR CLASS="banner">

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<H2>Description</H2>

<P>
    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>.
</P>

<P>
    The Blocking concept does not apply to filters. Instead, filters are required to be <SPAN CLASS='term'>blocking-preserving</SPAN>, which means that
</P>
<UL>
    <LI>
        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
    </LI>
    <LI>
        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.
    </LI>
</UL>

<P>
    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.
</P>

<H2>Refinement of</H2>

<P><A HREF="device.html">Device</A>.</P>

<A NAME="types"></A>
<H2>Associated Types</H2>

<P>Same as <A HREF="device.html">Device</A>.</P>

<A NAME="expressions"></A>
<H2>Valid Expressions / Semantics</H2>

<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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<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>
<P CLASS="copyright"> 
    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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Commit	Line	Data
7c673cae FG	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">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© 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>