📄 poll-objects.html
字号:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>7.3.1 Polling Objects </title>
<META NAME="description" CONTENT="7.3.1 Polling Objects ">
<META NAME="keywords" CONTENT="lib">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="lib.css" tppabs="http://www.python.org/doc/current/lib/lib.css">
<LINK REL="previous" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">
<LINK REL="up" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">
<LINK REL="next" href="module-thread.html" tppabs="http://www.python.org/doc/current/lib/module-thread.html">
</head>
<body>
<DIV CLASS="navigation"><table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html"><img src="previous.gif" tppabs="http://www.python.org/doc/current/icons/previous.gif" border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html"><img src="up.gif" tppabs="http://www.python.org/doc/current/icons/up.gif" border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A href="module-thread.html" tppabs="http://www.python.org/doc/current/lib/module-thread.html"><img src="next.gif" tppabs="http://www.python.org/doc/current/icons/next.gif" border="0" height="32"
alt="Next Page" width="32"></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td><A href="contents.html" tppabs="http://www.python.org/doc/current/lib/contents.html"><img src="contents.gif" tppabs="http://www.python.org/doc/current/icons/contents.gif" border="0" height="32"
alt="Contents" width="32"></A></td>
<td><a href="modindex.html" tppabs="http://www.python.org/doc/current/lib/modindex.html" title="Module Index"><img src="modules.gif" tppabs="http://www.python.org/doc/current/icons/modules.gif" border="0" height="32"
alt="Module Index" width="32"></a></td>
<td><A href="genindex.html" tppabs="http://www.python.org/doc/current/lib/genindex.html"><img src="index.gif" tppabs="http://www.python.org/doc/current/icons/index.gif" border="0" height="32"
alt="Index" width="32"></A></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">7.3 select </A>
<b class="navlabel">Up:</b> <a class="sectref" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">7.3 select </A>
<b class="navlabel">Next:</b> <a class="sectref" href="module-thread.html" tppabs="http://www.python.org/doc/current/lib/module-thread.html">7.4 thread </A>
<br><hr></DIV>
<!--End of Navigation Panel-->
<H2>
<BR>
7.3.1 Polling Objects
</H2>
<P>
The <tt class="cfunction">poll()</tt> system call, supported on most Unix systems,
provides better scalability for network servers that service many,
many clients at the same time.
<tt class="cfunction">poll()</tt> scales better because the system call only
requires listing the file descriptors of interest, while <tt class="cfunction">select()</tt>
builds a bitmap, turns on bits for the fds of interest, and then
afterward the whole bitmap has to be linearly scanned again.
<tt class="cfunction">select()</tt> is O(highest file descriptor), while
<tt class="cfunction">poll()</tt> is O(number of file descriptors).
<P>
<dl><dt><b><a name='l2h-1615'><tt class='method'>register</tt></a></b> (<var>fd</var><big>[</big><var>, eventmask</var><big>]</big>)
<dd>
Register a file descriptor with the polling object. Future calls to
the <tt class="method">poll()</tt> method will then check whether the file descriptor
has any pending I/O events. <var>fd</var> can be either an integer, or an
object with a <tt class="method">fileno()</tt> method that returns an integer. File
objects implement
<tt class="method">fileno()</tt>, so they can also be used as the argument.
<P>
<var>eventmask</var> is an optional bitmask describing the type of events you
want to check for, and can be a combination of the constants
<tt class="constant">POLLIN</tt>, <tt class="constant">POLLPRI</tt>, and <tt class="constant">POLLOUT</tt>,
described in the table below. If not specified, the default value
used will check for all 3 types of events.
<P>
<table border align="center" style="border-collapse: collapse">
<thead>
<tr class="tableheader">
<th align="left"><b>Constant</b> </th>
<th align="left"><b>Meaning</b> </th>
</thead>
<tbody valign='baseline'>
<tr><td align="left" valign="baseline"><code>POLLIN</code></td>
<td align="left">There is data to read</td>
<tr><td align="left" valign="baseline"><code>POLLPRI</code></td>
<td align="left">There is urgent data to read</td>
<tr><td align="left" valign="baseline"><code>POLLOUT</code></td>
<td align="left">Ready for output: writing will not block</td>
<tr><td align="left" valign="baseline"><code>POLLERR</code></td>
<td align="left">Error condition of some sort</td>
<tr><td align="left" valign="baseline"><code>POLLHUP</code></td>
<td align="left">Hung up</td>
<tr><td align="left" valign="baseline"><code>POLLNVAL</code></td>
<td align="left">Invalid request: descriptor not open</td></tbody>
</table>
<P>
Registering a file descriptor that's already registered is not an
error, and has the same effect as registering the descriptor exactly
once.
<P>
</dl>
<P>
<dl><dt><b><a name='l2h-1616'><tt class='method'>unregister</tt></a></b> (<var>fd</var>)
<dd>
Remove a file descriptor being tracked by a polling object. Just like
the <tt class="method">register()</tt> method, <var>fd</var> can be an integer or an
object with a <tt class="method">fileno()</tt> method that returns an integer.
<P>
Attempting to remove a file descriptor that was never registered
causes a <tt class="exception">KeyError</tt> exception to be raised.
</dl>
<P>
<dl><dt><b><a name='l2h-1617'><tt class='method'>poll</tt></a></b> (<big>[</big><var>timeout</var><big>]</big>)
<dd>
Polls the set of registered file descriptors, and returns a
possibly-empty list containing <code>(<var>fd</var>, <var>event</var>)</code> 2-tuples
for the descriptors that have events or errors to report.
<var>fd</var> is the file descriptor, and <var>event</var> is a bitmask
with bits set for the reported events for that descriptor
-- <tt class="constant">POLLIN</tt> for waiting input,
<tt class="constant">POLLOUT</tt> to indicate that the descriptor can be written to, and
so forth.
An empty list indicates that the call timed out and no file
descriptors had any events to report.
</dl>
<P>
<DIV CLASS="navigation"><p><hr><table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html"><img src="previous.gif" tppabs="http://www.python.org/doc/current/icons/previous.gif" border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html"><img src="up.gif" tppabs="http://www.python.org/doc/current/icons/up.gif" border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A href="module-thread.html" tppabs="http://www.python.org/doc/current/lib/module-thread.html"><img src="next.gif" tppabs="http://www.python.org/doc/current/icons/next.gif" border="0" height="32"
alt="Next Page" width="32"></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td><A href="contents.html" tppabs="http://www.python.org/doc/current/lib/contents.html"><img src="contents.gif" tppabs="http://www.python.org/doc/current/icons/contents.gif" border="0" height="32"
alt="Contents" width="32"></A></td>
<td><a href="modindex.html" tppabs="http://www.python.org/doc/current/lib/modindex.html" title="Module Index"><img src="modules.gif" tppabs="http://www.python.org/doc/current/icons/modules.gif" border="0" height="32"
alt="Module Index" width="32"></a></td>
<td><A href="genindex.html" tppabs="http://www.python.org/doc/current/lib/genindex.html"><img src="index.gif" tppabs="http://www.python.org/doc/current/icons/index.gif" border="0" height="32"
alt="Index" width="32"></A></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">7.3 select </A>
<b class="navlabel">Up:</b> <a class="sectref" href="module-select.html" tppabs="http://www.python.org/doc/current/lib/module-select.html">7.3 select </A>
<b class="navlabel">Next:</b> <a class="sectref" href="module-thread.html" tppabs="http://www.python.org/doc/current/lib/module-thread.html">7.4 thread </A>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
<hr>See <i><a href="about.html" tppabs="http://www.python.org/doc/current/lib/about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -