<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="content-type" content="application/xml+xhtml; charset=utf-8" />
<title>Logtalk built-in predicate: threaded_peek/1-2</title>
<link rel="stylesheet" href="../../screen.css" type="text/css" media="screen"/>
<link rel="stylesheet" href="../../print.css" type="text/css" media="print"/>
</head>
<body>
<div class="top-left">Logtalk reference manual</div>
<div class="top-right">Built-in predicate: threaded_peek/1-2</div>
<div class="bottom-left"><span class="page"/></div>
<div class="bottom-right"><span class="page"/></div>
<div class="navtop"><a href="../../index.html">contents</a> > <a href="../index.html">reference manual</a> > <a href="../index.html#builtins">built-in predicates</a></div>
<h2 id="builtins_threaded_peek1_2" class="codenp">threaded_peek/1-2</h2>
<h4>Description</h4>
<pre>threaded_peek(Goal)
threaded_peek(Goal, Tag)</pre>
<p>
Checks if the result of proving <code>Goal</code> in a new thread is already available. This call succeeds or fails without blocking execution waiting for a reply to be available.
</p>
<p>
The argument of this predicate should be a <em>variant</em> of the argument of the corresponding <a href="threaded_call1_2.html">threaded_call/1</a> call. When the predicate argument is subsumed by the <a href="threaded_call1_2.html">threaded_call/1</a> call argument, the <code>threaded_peek/1</code> call will succeed iff its argument unifies with an already available solution of the (more general) goal.
</p>
<p>
The variant <code>threaded_peek/2</code> accepts a threaded call identifier tag generated by the calls to the <a title="Consult reference manual" href="threaded_call1_2.html"><code>threaded_call/2</code></a> and <a title="Consult reference manual" href="threaded_once1_2.html"><code>threaded_once/2</code></a> predicates. Tags shall be considered as an opaque term; users shall not rely on its type.
</p>
<h4>Template and modes</h4>
<pre>threaded_peek(+callable)
threaded_peek(+callable, +nonvar)</pre>
<h4>Errors</h4>
<dl>
<dt>Goal is a variable:</dt>
<dd><code>instantiation_error</code></dd>
<dt>Goal is neither a variable nor a callable term:</dt>
<dd><code>type_error(callable, Goal)</code></dd>
<dt>Tag is a variable:</dt>
<dd><code>instantiation_error</code></dd>
</dl>
<h4>Examples</h4>
<dl>
<dt>To check for an asynchronous goal proof result:</dt>
<dd><code>threaded_peek(Goal)</code></dd>
<dt>To check for an asynchronous message to <em>self</em> result:</dt>
<dd><code>threaded_peek(::Goal)</code></dd>
<dt>To check for an asynchronous message result:</dt>
<dd><code>threaded_peek(Object::Goal)</code></dd>
</dl>
<div class="footer">
<div class="copyright">
<span>Copyright © <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> — <a href="http://logtalk.org">Logtalk.org</a></span><br/>
<span>Last updated on: September 15, 2007</span>
</div>
<div class="navbottom">
<span><a href="threaded_exit1_2.html">previous</a> | <a href="../../glossary.html">glossary</a> | <a href="threaded_wait1.html">next</a></span><br/>
<span><a href="http://validator.w3.org/check/referer">XHTML</a> + <a href="http://jigsaw.w3.org/css-validator/check/referer">CSS</a></span>
</div>
</div>
</body>
</html>