2a1fbb6e88
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1104 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
166 lines
7.2 KiB
HTML
166 lines
7.2 KiB
HTML
<?xml version="1.0" encoding="iso-8859-1"?>
|
|
<?xml-stylesheet type="text/css" href="../styles.css" ?>
|
|
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
|
|
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
|
|
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
|
|
|
|
<head>
|
|
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
|
|
<title>Logtalk tutorial: profiling programs</title>
|
|
<link rel="stylesheet" href="../styles.css" type="text/css" />
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<div class="navtop">
|
|
<a href="../index.html">contents</a> > <a href="index.html">tutorial</a>
|
|
</div>
|
|
|
|
<h1>Profiling programs</h1>
|
|
|
|
<p>
|
|
In this example, we will illustrate the use of:
|
|
</p>
|
|
<ul>
|
|
<li>events</li>
|
|
<li>monitors</li>
|
|
</ul>
|
|
<p>
|
|
by defining a simple profiler that prints the starting and ending time for processing a message sent to an object.
|
|
</p>
|
|
|
|
<h2>Messages as events<a name="events"></a></h2>
|
|
|
|
<p>
|
|
In a pure object-oriented system, all computations start by sending messages to objects. We can thus define an <em>event</em> as the sending of a message to an object. An event can then be specified by the tuple <code>(Object, Message, Sender)</code>. This definition can be refined by interpreting the sending of a message and the return of the control to the object that has sent the message as two distinct events. We call these events respectively <code>before</code> and <code>after</code>. Therefore, we end up by representing an event by the tuple <code>(Event, Object, Message, Sender)</code>. For instance, if we send the message:
|
|
</p>
|
|
<pre>
|
|
| ?- foo::bar(X).
|
|
|
|
X = 1
|
|
yes
|
|
</pre>
|
|
<p>
|
|
the two corresponding events will be:
|
|
</p>
|
|
<pre>
|
|
(before, foo, bar(X), user)
|
|
(after, foo, bar(1), user)
|
|
</pre>
|
|
<p>
|
|
Note that the second event is only generated if the message succeeds. If the message as a goal have multiple solutions, then one <code>after</code> event will be generated for each solution.
|
|
</p>
|
|
<p>
|
|
Events are automatically generated by the message sending mechanisms for each public message sent using the <a title="Consult reference manual" href="../refman/control/to_object2.html"><code>::/2</code></a> operator.
|
|
</p>
|
|
|
|
<h2>Profilers as monitors<a name="monitors"></a></h2>
|
|
|
|
<p>
|
|
A monitor is an object that reacts whenever a spied event occurs. The monitor actions are defined by two event handlers: <a title="Consult reference manual" href="../refman/methods/before3.html"><code>before/3</code></a> for <code>before</code> events and <a title="Consult reference manual" href="../refman/methods/after3.html"><code>after/3</code></a> for <code>after</code> events. These predicates are automatically called by the message sending mechanisms when an event registered for the monitor occurs.
|
|
</p>
|
|
<p>
|
|
In our example, we need a way to get the current time before and after we process a message. We will assume that we have a <code>time</code> object implementing a <code>cpu_time/1</code> predicate that returns the current CPU time for the Prolog session:
|
|
</p>
|
|
<pre>
|
|
:- object(time).
|
|
|
|
:- public(cpu_time/1).
|
|
:- mode(cpu_time(-number), one).
|
|
|
|
...
|
|
|
|
:- end_object.
|
|
</pre>
|
|
<p>
|
|
Our profiler will be named <code>stop_watch</code>. It must define event handlers for the <code>before</code> and <code>after</code> events that will print the event description (object, message, and sender) and the current time:
|
|
</p>
|
|
<pre>
|
|
:- object(stop_watch).
|
|
|
|
:- uses(time).
|
|
|
|
before(Object, Message, Sender) :-
|
|
write(Object), write(' <-- '), writeq(Message),
|
|
write(' from '), write(Sender), nl, write('STARTING at '),
|
|
time::cpu_time(Seconds), write(Seconds), write(' seconds'), nl.
|
|
|
|
after(Object, Message, Sender) :-
|
|
write(Object), write(' <-- '), writeq(Message),
|
|
write(' from '), write(Sender), nl, write('ENDING at '),
|
|
time::cpu_time(Seconds), write(Seconds), write(' seconds'), nl.
|
|
|
|
:- end_object.
|
|
</pre>
|
|
<p>
|
|
After compiling and loading the <code>stop_watch</code> object (and the objects that we want to profile), we can use the <a title="Consult reference manual" href="../refman/builtins/define_events5.html"><code>define_events/5</code></a> built-in predicate to set up our profiler. For example, to profile all messages that are sent to the object <code>foo</code>, we need to call the goal:
|
|
</p>
|
|
<pre>
|
|
| ?- define_events(_, foo, _, _, stop_watch).
|
|
|
|
yes
|
|
</pre>
|
|
<p>
|
|
This call will register <code>stop_watch</code> as a monitor to all messages sent to object <code>foo</code>, for both <code>before</code> and <code>after</code> events. Note that we say "as a monitor", not "the monitor": we can have any number of monitors over the same events.
|
|
</p>
|
|
<p>
|
|
From now on, every time we sent a message to <code>foo</code>, the <code>stop_watch</code> monitor will print the starting and ending times for the message execution. For instance:
|
|
</p>
|
|
<pre>
|
|
| ?- foo::bar(X).
|
|
|
|
foo <-- bar(X) from user
|
|
STARTING at 12.87415 seconds
|
|
foo <-- bar(1) from user
|
|
ENDING at 12.87419 seconds
|
|
|
|
X = 1
|
|
yes
|
|
</pre>
|
|
<p>
|
|
To stop profiling the messages sent to <code>foo</code> we use the <a title="Consult reference manual" href="../refman/builtins/abolish_events5.html"><code>abolish_events/5</code></a>
|
|
built-in predicate:
|
|
</p>
|
|
<pre>
|
|
| ?- abolish_events(_, foo, _, _, stop_watch).
|
|
|
|
yes
|
|
</pre>
|
|
<p>
|
|
This call will abolish all events defined over the object <code>foo</code> assigned to the <code>stop_watch</code> monitor.
|
|
</p>
|
|
|
|
<h2>Summary<a name="summary"></a></h2>
|
|
|
|
<ul>
|
|
<li>An event is defined as the sending of a (public) message to an object.</li>
|
|
</ul>
|
|
<ul>
|
|
<li>There are two kinds of events: <code>before</code> events, generated before a message is processed, and <code>after</code> events, generated after the message processing completed successfully.</li>
|
|
</ul>
|
|
<ul>
|
|
<li>Any object can be declared as a monitor to any event.</li>
|
|
</ul>
|
|
<ul>
|
|
<li>A monitor defines event handlers, the predicates <a title="Consult reference manual" href="../refman/methods/before3.html"><code>before/3</code></a> and <a title="Consult reference manual" href="../refman/methods/after3.html"><code>after/3</code></a>, that are automatically called by the runtime engine when a spied event occurs.</li>
|
|
</ul>
|
|
<ul>
|
|
<li>Three built-in predicates, <a title="Consult reference manual" href="../refman/builtins/define_events5.html"><code>define_events/5</code></a>, <a title="Consult reference manual" href="../refman/builtins/current_event5.html"><code>current_event/5</code></a>, and <a title="Consult reference manual" href="../refman/builtins/abolish_events5.html"><code>abolish_events/5</code></a>, enables us define, query, and abolish both events and monitors.</li>
|
|
</ul>
|
|
|
|
<div class="navbottom">
|
|
<a href="reflection.html">previous</a> | <a href="../glossary.html">glossary</a> | <a href="index.html">next</a>
|
|
</div>
|
|
|
|
<div class="copyright">
|
|
Copyright © <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> — <a href="http://www.logtalk.org">Logtalk.org</a>
|
|
</div>
|
|
|
|
<div class="footer">
|
|
<p><span class="bleft"><a href="http://validator.w3.org/check/referer">XHTML</a> + <a href="http://jigsaw.w3.org/css-validator/check/referer">CSS</a></span><span class="bright">Last updated on: July 22, 2004</span></p>
|
|
</div>
|
|
</body>
|
|
</html>
|