<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Handler Tracking</title> <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../../../boost_asio.html" title="Boost.Asio"> <link rel="up" href="../core.html" title="Core Concepts and Functionality"> <link rel="prev" href="allocation.html" title="Custom Memory Allocation"> <link rel="next" href="coroutine.html" title="Stackless Coroutines"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="allocation.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="coroutine.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="boost_asio.overview.core.handler_tracking"></a><a class="link" href="handler_tracking.html" title="Handler Tracking">Handler Tracking</a> </h4></div></div></div> <p> To aid in debugging asynchronous programs, Boost.Asio provides support for handler tracking. When enabled by defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_HANDLER_TRACKING</span></code>, Boost.Asio writes debugging output to the standard error stream. The output records asynchronous operations and the relationships between their handlers. </p> <p> This feature is useful when debugging and you need to know how your asynchronous operations are chained together, or what the pending asynchronous operations are. As an illustration, here is the output when you run the HTTP Server example, handle a single request, then shut down via Ctrl+C: </p> <pre class="programlisting">@asio|1298160085.070638|0*1|signal_set@0x7fff50528f40.async_wait @asio|1298160085.070888|0*2|socket@0x7fff50528f60.async_accept @asio|1298160085.070913|0|resolver@0x7fff50528e28.cancel @asio|1298160118.075438|>2|ec=asio.system:0 @asio|1298160118.075472|2*3|socket@0xb39048.async_receive @asio|1298160118.075507|2*4|socket@0x7fff50528f60.async_accept @asio|1298160118.075527|<2| @asio|1298160118.075540|>3|ec=asio.system:0,bytes_transferred=122 @asio|1298160118.075731|3*5|socket@0xb39048.async_send @asio|1298160118.075778|<3| @asio|1298160118.075793|>5|ec=asio.system:0,bytes_transferred=156 @asio|1298160118.075831|5|socket@0xb39048.close @asio|1298160118.075855|<5| @asio|1298160122.827317|>1|ec=asio.system:0,signal_number=2 @asio|1298160122.827333|1|socket@0x7fff50528f60.close @asio|1298160122.827359|<1| @asio|1298160122.827370|>4|ec=asio.system:125 @asio|1298160122.827378|<4| @asio|1298160122.827394|0|signal_set@0x7fff50528f40.cancel </pre> <p> Each line is of the form: </p> <pre class="programlisting"><tag>|<timestamp>|<action>|<description> </pre> <p> The <code class="computeroutput"><tag></code> is always <code class="computeroutput">@asio</code>, and is used to identify and extract the handler tracking messages from the program output. </p> <p> The <code class="computeroutput"><timestamp></code> is seconds and microseconds from 1 Jan 1970 UTC. </p> <p> The <code class="computeroutput"><action></code> takes one of the following forms: </p> <div class="variablelist"> <p class="title"><b></b></p> <dl class="variablelist"> <dt><span class="term">>n</span></dt> <dd><p> The program entered the handler number <code class="computeroutput">n</code>. The <code class="computeroutput"><description></code> shows the arguments to the handler. </p></dd> <dt><span class="term"><n</span></dt> <dd><p> The program left handler number <code class="computeroutput">n</code>. </p></dd> <dt><span class="term">!n</span></dt> <dd><p> The program left handler number n due to an exception. </p></dd> <dt><span class="term">~n</span></dt> <dd><p> The handler number <code class="computeroutput">n</code> was destroyed without having been invoked. This is usually the case for any unfinished asynchronous operations when the <code class="computeroutput">io_service</code> is destroyed. </p></dd> <dt><span class="term">n*m</span></dt> <dd><p> The handler number <code class="computeroutput">n</code> created a new asynchronous operation with completion handler number <code class="computeroutput">m</code>. The <code class="computeroutput"><description></code> shows what asynchronous operation was started. </p></dd> <dt><span class="term">n</span></dt> <dd><p> The handler number n performed some other operation. The <code class="computeroutput"><description></code> shows what function was called. Currently only <code class="computeroutput">close()</code> and <code class="computeroutput">cancel()</code> operations are logged, as these may affect the state of pending asynchronous operations. </p></dd> </dl> </div> <p> Where the <code class="computeroutput"><description></code> shows a synchronous or asynchronous operation, the format is <code class="computeroutput"><object-type>@<pointer>.<operation></code>. For handler entry, it shows a comma-separated list of arguments and their values. </p> <p> As shown above, Each handler is assigned a numeric identifier. Where the handler tracking output shows a handler number of 0, it means that the action was performed outside of any handler. </p> <h6> <a name="boost_asio.overview.core.handler_tracking.h0"></a> <span class="phrase"><a name="boost_asio.overview.core.handler_tracking.visual_representations"></a></span><a class="link" href="handler_tracking.html#boost_asio.overview.core.handler_tracking.visual_representations">Visual Representations</a> </h6> <p> The handler tracking output may be post-processed using the included <code class="literal">handlerviz.pl</code> tool to create a visual representation of the handlers (requires the GraphViz tool <code class="literal">dot</code>). </p> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2003-2015 Christopher M. Kohlhoff<p> 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" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="allocation.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="coroutine.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>