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| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Overview</title> | |
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| 7 | <link rel="home" href="../../index.html" title="Chapter 1. Fiber"> | |
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| 13 | <table cellpadding="2" width="100%"><tr> | |
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| 22 | <div class="spirit-nav"> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="fiber.callbacks.overview"></a><a class="link" href="overview.html" title="Overview">Overview</a> | |
| 28 | </h3></div></div></div> | |
| 29 | <p> | |
| 30 | One of the primary benefits of <span class="bold"><strong>Boost.Fiber</strong></span> | |
| 31 | is the ability to use asynchronous operations for efficiency, while at the | |
| 32 | same time structuring the calling code <span class="emphasis"><em>as if</em></span> the operations | |
| 33 | were synchronous. Asynchronous operations provide completion notification | |
| 34 | in a variety of ways, but most involve a callback function of some kind. | |
| 35 | This section discusses tactics for interfacing <span class="bold"><strong>Boost.Fiber</strong></span> | |
| 36 | with an arbitrary async operation. | |
| 37 | </p> | |
| 38 | <p> | |
| 39 | For purposes of illustration, consider the following hypothetical API: | |
| 40 | </p> | |
| 41 | <p> | |
| 42 | </p> | |
| 43 | <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">AsyncAPI</span> <span class="special">{</span> | |
| 44 | <span class="keyword">public</span><span class="special">:</span> | |
| 45 | <span class="comment">// constructor acquires some resource that can be read and written</span> | |
| 46 | <span class="identifier">AsyncAPI</span><span class="special">();</span> | |
| 47 | ||
| 48 | <span class="comment">// callbacks accept an int error code; 0 == success</span> | |
| 49 | <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">errorcode</span><span class="special">;</span> | |
| 50 | ||
| 51 | <span class="comment">// write callback only needs to indicate success or failure</span> | |
| 52 | <span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">></span> | |
| 53 | <span class="keyword">void</span> <span class="identifier">init_write</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">data</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&&</span> <span class="identifier">callback</span><span class="special">);</span> | |
| 54 | ||
| 55 | <span class="comment">// read callback needs to accept both errorcode and data</span> | |
| 56 | <span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">></span> | |
| 57 | <span class="keyword">void</span> <span class="identifier">init_read</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&&</span> <span class="identifier">callback</span><span class="special">);</span> | |
| 58 | ||
| 59 | <span class="comment">// ... other operations ...</span> | |
| 60 | <span class="special">};</span> | |
| 61 | </pre> | |
| 62 | <p> | |
| 63 | </p> | |
| 64 | <p> | |
| 65 | The significant points about each of <code class="computeroutput"><span class="identifier">init_write</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">init_read</span><span class="special">()</span></code> are: | |
| 66 | </p> | |
| 67 | <div class="itemizedlist"><ul class="itemizedlist" type="disc"> | |
| 68 | <li class="listitem"> | |
| 69 | The <code class="computeroutput"><span class="identifier">AsyncAPI</span></code> method only | |
| 70 | initiates the operation. It returns immediately, while the requested | |
| 71 | operation is still pending. | |
| 72 | </li> | |
| 73 | <li class="listitem"> | |
| 74 | The method accepts a callback. When the operation completes, the callback | |
| 75 | is called with relevant parameters (error code, data if applicable). | |
| 76 | </li> | |
| 77 | </ul></div> | |
| 78 | <p> | |
| 79 | We would like to wrap these asynchronous methods in functions that appear | |
| 80 | synchronous by blocking the calling fiber until the operation completes. | |
| 81 | This lets us use the wrapper function’s return value to deliver relevant data. | |
| 82 | </p> | |
| 83 | <div class="tip"><table border="0" summary="Tip"> | |
| 84 | <tr> | |
| 85 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td> | |
| 86 | <th align="left">Tip</th> | |
| 87 | </tr> | |
| 88 | <tr><td align="left" valign="top"><p> | |
| 89 | <a class="link" href="../synchronization/futures/promise.html#class_promise"><code class="computeroutput">promise<></code></a> and <a class="link" href="../synchronization/futures/future.html#class_future"><code class="computeroutput">future<></code></a> are your friends | |
| 90 | here. | |
| 91 | </p></td></tr> | |
| 92 | </table></div> | |
| 93 | </div> | |
| 94 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 95 | <td align="left"></td> | |
| 96 | <td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> | |
| 97 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 98 | 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>) | |
| 99 | </p> | |
| 100 | </div></td> | |
| 101 | </tr></table> | |
| 102 | <hr> | |
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| 105 | </div> | |
| 106 | </body> | |
| 107 | </html> |