]>
Commit | Line | Data |
---|---|---|
7c673cae FG |
1 | <html> |
2 | <head> | |
3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
4 | <title>Overview</title> | |
5 | <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> | |
6 | <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> | |
7 | <link rel="home" href="../../index.html" title="Chapter 1. Fiber"> | |
8 | <link rel="up" href="../callbacks.html" title="Integrating Fibers with Asynchronous Callbacks"> | |
9 | <link rel="prev" href="../callbacks.html" title="Integrating Fibers with Asynchronous Callbacks"> | |
10 | <link rel="next" href="return_errorcode.html" title="Return Errorcode"> | |
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="../callbacks.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../callbacks.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="return_errorcode.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
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> | |
103 | <div class="spirit-nav"> | |
104 | <a accesskey="p" href="../callbacks.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../callbacks.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="return_errorcode.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
105 | </div> | |
106 | </body> | |
107 | </html> |