1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>when_any, a dubious alternative</title> 5<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../index.html" title="Chapter 1. Fiber"> 8<link rel="up" href="../when_any.html" title="when_any"> 9<link rel="prev" href="when_any__heterogeneous_types.html" title="when_any, heterogeneous types"> 10<link rel="next" href="../when_all_functionality.html" title="when_all functionality"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="when_any__heterogeneous_types.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../when_any.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../when_all_functionality.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="fiber.when_any.when_any.when_any__a_dubious_alternative"></a><a class="link" href="when_any__a_dubious_alternative.html" title="when_any, a dubious alternative">when_any, 28 a dubious alternative</a> 29</h4></div></div></div> 30<p> 31 Certain topics in C++ can arouse strong passions, and exceptions are no 32 exception. We cannot resist mentioning — for purely informational purposes 33 — that when you need only the <span class="emphasis"><em>first</em></span> result from some 34 number of concurrently-running fibers, it would be possible to pass a 35 <code class="literal">shared_ptr<<a class="link" href="../../synchronization/futures/promise.html#class_promise"><code class="computeroutput">promise<></code></a>></code> to the 36 participating fibers, then cause the initiating fiber to call <a class="link" href="../../synchronization/futures/future.html#future_get"><code class="computeroutput">future::get()</code></a> on 37 its <a class="link" href="../../synchronization/futures/future.html#class_future"><code class="computeroutput">future<></code></a>. The first fiber to call <a class="link" href="../../synchronization/futures/promise.html#promise_set_value"><code class="computeroutput">promise::set_value()</code></a> on 38 that shared <code class="computeroutput"><span class="identifier">promise</span></code> will 39 succeed; subsequent <code class="computeroutput"><span class="identifier">set_value</span><span class="special">()</span></code> calls on the same <code class="computeroutput"><span class="identifier">promise</span></code> 40 instance will throw <code class="computeroutput"><span class="identifier">future_error</span></code>. 41 </p> 42<p> 43 Use this information at your own discretion. Beware the dark side. 44 </p> 45</div> 46<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 47<td align="left"></td> 48<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> 49 Distributed under the Boost Software License, Version 1.0. (See accompanying 50 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 51 </p> 52</div></td> 53</tr></table> 54<hr> 55<div class="spirit-nav"> 56<a accesskey="p" href="when_any__heterogeneous_types.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../when_any.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../when_all_functionality.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 57</div> 58</body> 59</html> 60
