[OpenSPARC-T2-SAM] / sam-t2 / devtools / v8plus / html / python / lib / module-asyncore.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="module-asynchat.html" />
<link rel="prev" href="module-DocXMLRPCServer.html" />
<link rel="parent" href="internet.html" />
<link rel="next" href="asyncore-example.html" />
<meta name='aesop' content='information' />
<title>11.25 asyncore -- Asynchronous socket handler</title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="11.24.2 DocCGIXMLRPCRequestHandler"
  href="node567.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="11. Internet Protocols and"
  href="internet.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="11.25.1 asyncore Example basic"
  href="asyncore-example.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="node567.html">11.24.2 DocCGIXMLRPCRequestHandler</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="internet.html">11. Internet Protocols and</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="asyncore-example.html">11.25.1 asyncore Example basic</A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H1><A NAME="SECTION00132500000000000000000">
11.25 <tt class="module">asyncore</tt> --
         Asynchronous socket handler</A>
</H1>

<P>
<A NAME="module-asyncore"></A>

<P>
This module provides the basic infrastructure for writing asynchronous 
socket service clients and servers.

<P>
There are only two ways to have a program on a single processor do 
``more than one thing at a time.'' Multi-threaded programming is the 
simplest and most popular way to do it, but there is another very 
different technique, that lets you have nearly all the advantages of 
multi-threading, without actually using multiple threads.  It's really 
only practical if your program is largely I/O bound.  If your program 
is processor bound, then pre-emptive scheduled threads are probably what 
you really need. Network servers are rarely processor bound, however.

<P>
If your operating system supports the <tt class="cfunction">select()</tt> system call 
in its I/O library (and nearly all do), then you can use it to juggle 
multiple communication channels at once; doing other work while your 
I/O is taking place in the ``background.''  Although this strategy can 
seem strange and complex, especially at first, it is in many ways 
easier to understand and control than multi-threaded programming.  
The <tt class="module">asyncore</tt> module solves many of the difficult problems for 
you, making the task of building sophisticated high-performance 
network servers and clients a snap. For ``conversational'' applications
and protocols the companion  <tt class="module"><a href="module-asynchat.html">asynchat</a></tt> module is invaluable.

<P>
The basic idea behind both modules is to create one or more network
<em>channels</em>, instances of class <tt class="class">asyncore.dispatcher</tt> and
<tt class="class">asynchat.async_chat</tt>. Creating the channels adds them to a global
map, used by the <tt class="function">loop()</tt> function if you do not provide it
with your own <var>map</var>.

<P>
Once the initial channel(s) is(are) created, calling the <tt class="function">loop()</tt>
function activates channel service, which continues until the last
channel (including any that have been added to the map during asynchronous
service) is closed.

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3743' xml:id='l2h-3743' class="function">loop</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>timeout</var><big>[</big><var>, use_poll</var><big>[</big><var>,
                       map</var><big>[</big><var>,count</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Enter a polling loop that terminates after count passes or all open
  channels have been closed.  All arguments are optional.  The <var>(</var>count)
  parameter defaults to None, resulting in the loop terminating only
  when all channels have been closed.  The <var>timeout</var> argument sets the
  timeout parameter for the appropriate <tt class="function">select()</tt> or
  <tt class="function">poll()</tt> call, measured in seconds; the default is 30 seconds.
  The <var>use_poll</var> parameter, if true, indicates that <tt class="function">poll()</tt>
  should be used in preference to <tt class="function">select()</tt> (the default is
  <code>False</code>).  The <var>map</var> parameter is a dictionary whose items are
  the channels to watch.  As channels are closed they are deleted from their
  map.  If <var>map</var> is omitted, a global map is used (this map is updated
  by the default class <tt class="method">__init__()</tt> - make sure you extend, rather
  than override, <tt class="method">__init__()</tt> if you want to retain this behavior).

<P>
Channels (instances of <tt class="class">asyncore.dispatcher</tt>, <tt class="class">asynchat.async_chat</tt>
  and subclasses thereof) can freely be mixed in the map.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-3744' xml:id='l2h-3744' class="class">dispatcher</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  The <tt class="class">dispatcher</tt> class is a thin wrapper around a low-level socket object.
  To make it more useful, it has a few methods for event-handling  which are called
  from the asynchronous loop.  
  Otherwise, it can be treated as a normal non-blocking socket object.

<P>
Two class attributes can be modified, to improve performance,
  or possibly even to conserve memory.

<P>
<dl><dt><b><tt id='l2h-3745' xml:id='l2h-3745'>ac_in_buffer_size</tt></b></dt>
<dd>
  The asynchronous input buffer size (default <code>4096</code>).
  </dd></dl>

<P>
<dl><dt><b><tt id='l2h-3746' xml:id='l2h-3746'>ac_out_buffer_size</tt></b></dt>
<dd>
  The asynchronous output buffer size (default <code>4096</code>).
  </dd></dl>

<P>
The firing of low-level events at certain times or in certain connection
  states tells the asynchronous loop that certain higher-level events have
  taken place. For example, if we have asked for a socket to connect to
  another host, we know that the connection has been made when the socket
  becomes writable for the first time (at this point you know that you may
  write to it with the expectation of success). The implied higher-level
  events are:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="left"  >Event</th>
      <th class="left"  >Description</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="left"   valign="baseline"><code>handle_connect()</code></td>
        <td class="left"  >Implied by the first write event</td></tr>
    <tr><td class="left"   valign="baseline"><code>handle_close()</code></td>
        <td class="left"  >Implied by a read event with no data available</td></tr>
    <tr><td class="left"   valign="baseline"><code>handle_accept()</code></td>
        <td class="left"  >Implied by a read event on a listening socket</td></tr></tbody>
</table></div>

<P>
During asynchronous processing, each mapped channel's <tt class="method">readable()</tt>
  and <tt class="method">writable()</tt> methods are used to determine whether the channel's
  socket should be added to the list of channels <tt class="cfunction">select()</tt>ed or
  <tt class="cfunction">poll()</tt>ed for read and write events.

<P>
</dl>

<P>
Thus, the set of channel events is larger than the basic socket events.
The full set of methods that can be overridden in your subclass follows:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3747' xml:id='l2h-3747' class="method">handle_read</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when the asynchronous loop detects that a <tt class="method">read()</tt>
  call on the channel's socket will succeed.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3748' xml:id='l2h-3748' class="method">handle_write</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when the asynchronous loop detects that a writable socket
  can be written.  
  Often this method will implement the necessary buffering for 
  performance.  For example:

<P>
<div class="verbatim"><pre>
def handle_write(self):
    sent = self.send(self.buffer)
    self.buffer = self.buffer[sent:]
</pre></div>
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3749' xml:id='l2h-3749' class="method">handle_expt</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when there is out of band (OOB) data for a socket 
  connection.  This will almost never happen, as OOB is 
  tenuously supported and rarely used.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3750' xml:id='l2h-3750' class="method">handle_connect</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when the active opener's socket actually makes a connection.
  Might send a ``welcome'' banner, or initiate a protocol
  negotiation with the remote endpoint, for example.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3751' xml:id='l2h-3751' class="method">handle_close</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when the socket is closed.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3752' xml:id='l2h-3752' class="method">handle_error</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called when an exception is raised and not otherwise handled.  The default
  version prints a condensed traceback.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3753' xml:id='l2h-3753' class="method">handle_accept</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called on listening channels (passive openers) when a  
  connection can be established with a new remote endpoint that
  has issued a <tt class="method">connect()</tt> call for the local endpoint.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3754' xml:id='l2h-3754' class="method">readable</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called each time around the asynchronous loop to determine whether a
  channel's socket should be added to the list on which read events can
  occur.  The default method simply returns <code>True</code>, 
  indicating that by default, all channels will be interested in
  read events.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3755' xml:id='l2h-3755' class="method">writable</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Called each time around the asynchronous loop to determine whether a
  channel's socket should be added to the list on which write events can
  occur.  The default method simply returns <code>True</code>, 
  indicating that by default, all channels will be interested in
  write events.
</dl>

<P>
In addition, each channel delegates or extends many of the socket methods.
Most of these are nearly identical to their socket partners.

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3756' xml:id='l2h-3756' class="method">create_socket</tt></b>(</nobr></td>
  <td><var>family, type</var>)</td></tr></table></dt>
<dd>
  This is identical to the creation of a normal socket, and 
  will use the same options for creation.  Refer to the
  <tt class="module"><a href="module-socket.html">socket</a></tt> documentation for information on creating
  sockets.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3757' xml:id='l2h-3757' class="method">connect</tt></b>(</nobr></td>
  <td><var>address</var>)</td></tr></table></dt>
<dd>
  As with the normal socket object, <var>address</var> is a 
  tuple with the first element the host to connect to, and the 
  second the port number.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3758' xml:id='l2h-3758' class="method">send</tt></b>(</nobr></td>
  <td><var>data</var>)</td></tr></table></dt>
<dd>
  Send <var>data</var> to the remote end-point of the socket.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3759' xml:id='l2h-3759' class="method">recv</tt></b>(</nobr></td>
  <td><var>buffer_size</var>)</td></tr></table></dt>
<dd>
  Read at most <var>buffer_size</var> bytes from the socket's remote end-point.
  An empty string implies that the channel has been closed from the other
  end.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3760' xml:id='l2h-3760' class="method">listen</tt></b>(</nobr></td>
  <td><var>backlog</var>)</td></tr></table></dt>
<dd>
  Listen for connections made to the socket.  The <var>backlog</var>
  argument specifies the maximum number of queued connections
  and should be at least 1; the maximum value is
  system-dependent (usually 5).
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3761' xml:id='l2h-3761' class="method">bind</tt></b>(</nobr></td>
  <td><var>address</var>)</td></tr></table></dt>
<dd>
  Bind the socket to <var>address</var>.  The socket must not already
  be bound.  (The format of <var>address</var> depends on the address
  family -- see above.)
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3762' xml:id='l2h-3762' class="method">accept</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Accept a connection.  The socket must be bound to an address
  and listening for connections.  The return value is a pair
  <code>(<var>conn</var>, <var>address</var>)</code> where <var>conn</var> is a
  <em>new</em> socket object usable to send and receive data on
  the connection, and <var>address</var> is the address bound to the
  socket on the other end of the connection.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3763' xml:id='l2h-3763' class="method">close</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Close the socket.  All future operations on the socket object
  will fail.  The remote end-point will receive no more data (after
  queued data is flushed).  Sockets are automatically closed
  when they are garbage-collected.
</dl>

<P>

<p><br /></p><hr class='online-navigation' />
<div class='online-navigation'>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>

<UL CLASS="ChildLinks">
<LI><A href="asyncore-example.html">11.25.1 asyncore Example basic HTTP client</a>
</ul>
<!--End of Table of Child-Links-->
</div>

<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="11.24.2 DocCGIXMLRPCRequestHandler"
  href="node567.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="11. Internet Protocols and"
  href="internet.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="11.25.1 asyncore Example basic"
  href="asyncore-example.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="node567.html">11.24.2 DocCGIXMLRPCRequestHandler</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="internet.html">11. Internet Protocols and</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="asyncore-example.html">11.25.1 asyncore Example basic</A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>
Commit	Line	Data
920dae64 AT	1	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	2	<html>
	3	<head>
	4	<link rel="STYLESHEET" href="lib.css" type='text/css' />
	5	<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
	6	<link rel='start' href='../index.html' title='Python Documentation Index' />
	7	<link rel="first" href="lib.html" title='Python Library Reference' />
	8	<link rel='contents' href='contents.html' title="Contents" />
	9	<link rel='index' href='genindex.html' title='Index' />
	10	<link rel='last' href='about.html' title='About this document...' />
	11	<link rel='help' href='about.html' title='About this document...' />
	12	<link rel="next" href="module-asynchat.html" />
	13	<link rel="prev" href="module-DocXMLRPCServer.html" />
	14	<link rel="parent" href="internet.html" />
	15	<link rel="next" href="asyncore-example.html" />
	16	<meta name='aesop' content='information' />
	17	<title>11.25 asyncore -- Asynchronous socket handler</title>
	18	</head>
	19	<body>
	20	<DIV CLASS="navigation">
	21	<div id='top-navigation-panel' xml:id='top-navigation-panel'>
	22	<table align="center" width="100%" cellpadding="0" cellspacing="2">
	23	<tr>
	24	<td class='online-navigation'><a rel="prev" title="11.24.2 DocCGIXMLRPCRequestHandler"
	25	href="node567.html"><img src='../icons/previous.png'
	26	border='0' height='32' alt='Previous Page' width='32' /></A></td>
	27	<td class='online-navigation'><a rel="parent" title="11. Internet Protocols and"
	28	href="internet.html"><img src='../icons/up.png'
	29	border='0' height='32' alt='Up One Level' width='32' /></A></td>
	30	<td class='online-navigation'><a rel="next" title="11.25.1 asyncore Example basic"
	31	href="asyncore-example.html"><img src='../icons/next.png'
	32	border='0' height='32' alt='Next Page' width='32' /></A></td>
	33	<td align="center" width="100%">Python Library Reference</td>
	34	<td class='online-navigation'><a rel="contents" title="Table of Contents"
	35	href="contents.html"><img src='../icons/contents.png'
	36	border='0' height='32' alt='Contents' width='32' /></A></td>
	37	<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
	38	border='0' height='32' alt='Module Index' width='32' /></a></td>
	39	<td class='online-navigation'><a rel="index" title="Index"
	40	href="genindex.html"><img src='../icons/index.png'
	41	border='0' height='32' alt='Index' width='32' /></A></td>
	42	</tr></table>
	43	<div class='online-navigation'>
	44	<b class="navlabel">Previous:</b>
	45	<a class="sectref" rel="prev" href="node567.html">11.24.2 DocCGIXMLRPCRequestHandler</A>
	46	<b class="navlabel">Up:</b>
	47	<a class="sectref" rel="parent" href="internet.html">11. Internet Protocols and</A>
	48	<b class="navlabel">Next:</b>
	49	<a class="sectref" rel="next" href="asyncore-example.html">11.25.1 asyncore Example basic</A>
	50	</div>
	51	<hr /></div>
	52	</DIV>
	53	<!--End of Navigation Panel-->
	54
	55	<H1><A NAME="SECTION00132500000000000000000">
	56	11.25 <tt class="module">asyncore</tt> --
	57	Asynchronous socket handler</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-asyncore"></A>
	62
	63	<P>
	64	This module provides the basic infrastructure for writing asynchronous
65	socket service clients and servers.
66
67	<P>
68	There are only two ways to have a program on a single processor do
69	``more than one thing at a time.'' Multi-threaded programming is the
70	simplest and most popular way to do it, but there is another very
71	different technique, that lets you have nearly all the advantages of
72	multi-threading, without actually using multiple threads. It's really
73	only practical if your program is largely I/O bound. If your program
74	is processor bound, then pre-emptive scheduled threads are probably what
75	you really need. Network servers are rarely processor bound, however.
76
77	<P>
78	If your operating system supports the <tt class="cfunction">select()</tt> system call
79	in its I/O library (and nearly all do), then you can use it to juggle
80	multiple communication channels at once; doing other work while your
81	I/O is taking place in the ``background.'' Although this strategy can
82	seem strange and complex, especially at first, it is in many ways
83	easier to understand and control than multi-threaded programming.
84	The <tt class="module">asyncore</tt> module solves many of the difficult problems for
85	you, making the task of building sophisticated high-performance
86	network servers and clients a snap. For ``conversational'' applications
87	and protocols the companion <tt class="module"><a href="module-asynchat.html">asynchat</a></tt> module is invaluable.
88
89	<P>
90	The basic idea behind both modules is to create one or more network
91	<em>channels</em>, instances of class <tt class="class">asyncore.dispatcher</tt> and
92	<tt class="class">asynchat.async_chat</tt>. Creating the channels adds them to a global
93	map, used by the <tt class="function">loop()</tt> function if you do not provide it
94	with your own <var>map</var>.
95
96	<P>
97	Once the initial channel(s) is(are) created, calling the <tt class="function">loop()</tt>
98	function activates channel service, which continues until the last
99	channel (including any that have been added to the map during asynchronous
100	service) is closed.
101
102	<P>
103	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
104	<td><nobr><b><tt id='l2h-3743' xml:id='l2h-3743' class="function">loop</tt></b>(</nobr></td>
105	<td><var></var><big>[</big><var>timeout</var><big>[</big><var>, use_poll</var><big>[</big><var>,
106	map</var><big>[</big><var>,count</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
107	<dd>
108	Enter a polling loop that terminates after count passes or all open
109	channels have been closed. All arguments are optional. The <var>(</var>count)
110	parameter defaults to None, resulting in the loop terminating only
111	when all channels have been closed. The <var>timeout</var> argument sets the
112	timeout parameter for the appropriate <tt class="function">select()</tt> or
113	<tt class="function">poll()</tt> call, measured in seconds; the default is 30 seconds.
114	The <var>use_poll</var> parameter, if true, indicates that <tt class="function">poll()</tt>
115	should be used in preference to <tt class="function">select()</tt> (the default is
116	<code>False</code>). The <var>map</var> parameter is a dictionary whose items are
117	the channels to watch. As channels are closed they are deleted from their
118	map. If <var>map</var> is omitted, a global map is used (this map is updated
119	by the default class <tt class="method">__init__()</tt> - make sure you extend, rather
120	than override, <tt class="method">__init__()</tt> if you want to retain this behavior).
121
122	<P>
123	Channels (instances of <tt class="class">asyncore.dispatcher</tt>, <tt class="class">asynchat.async_chat</tt>
124	and subclasses thereof) can freely be mixed in the map.
125	</dl>
126
127	<P>
128	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
129	<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-3744' xml:id='l2h-3744' class="class">dispatcher</tt></b>(</nobr></td>
130	<td><var></var>)</td></tr></table></dt>
131	<dd>
132	The <tt class="class">dispatcher</tt> class is a thin wrapper around a low-level socket object.
133	To make it more useful, it has a few methods for event-handling which are called
134	from the asynchronous loop.
135	Otherwise, it can be treated as a normal non-blocking socket object.
136
137	<P>
138	Two class attributes can be modified, to improve performance,
139	or possibly even to conserve memory.
140
141	<P>
142	<dl><dt><b><tt id='l2h-3745' xml:id='l2h-3745'>ac_in_buffer_size</tt></b></dt>
143	<dd>
144	The asynchronous input buffer size (default <code>4096</code>).
145	</dd></dl>
146
147	<P>
148	<dl><dt><b><tt id='l2h-3746' xml:id='l2h-3746'>ac_out_buffer_size</tt></b></dt>
149	<dd>
150	The asynchronous output buffer size (default <code>4096</code>).
151	</dd></dl>
152
153	<P>
154	The firing of low-level events at certain times or in certain connection
155	states tells the asynchronous loop that certain higher-level events have
156	taken place. For example, if we have asked for a socket to connect to
157	another host, we know that the connection has been made when the socket
158	becomes writable for the first time (at this point you know that you may
159	write to it with the expectation of success). The implied higher-level
160	events are:
161
162	<P>
163	<div class="center"><table class="realtable">
164	<thead>
165	<tr>
166	<th class="left" >Event</th>
167	<th class="left" >Description</th>
168	</tr>
169	</thead>
170	<tbody>
171	<tr><td class="left" valign="baseline"><code>handle_connect()</code></td>
172	<td class="left" >Implied by the first write event</td></tr>
173	<tr><td class="left" valign="baseline"><code>handle_close()</code></td>
174	<td class="left" >Implied by a read event with no data available</td></tr>
175	<tr><td class="left" valign="baseline"><code>handle_accept()</code></td>
176	<td class="left" >Implied by a read event on a listening socket</td></tr></tbody>
177	</table></div>
178
179	<P>
180	During asynchronous processing, each mapped channel's <tt class="method">readable()</tt>
181	and <tt class="method">writable()</tt> methods are used to determine whether the channel's
182	socket should be added to the list of channels <tt class="cfunction">select()</tt>ed or
183	<tt class="cfunction">poll()</tt>ed for read and write events.
184
185	<P>
186	</dl>
187
188	<P>
189	Thus, the set of channel events is larger than the basic socket events.
190	The full set of methods that can be overridden in your subclass follows:
191
192	<P>
193	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
194	<td><nobr><b><tt id='l2h-3747' xml:id='l2h-3747' class="method">handle_read</tt></b>(</nobr></td>
195	<td><var></var>)</td></tr></table></dt>
196	<dd>
197	Called when the asynchronous loop detects that a <tt class="method">read()</tt>
198	call on the channel's socket will succeed.
199	</dl>
200
201	<P>
202	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
203	<td><nobr><b><tt id='l2h-3748' xml:id='l2h-3748' class="method">handle_write</tt></b>(</nobr></td>
204	<td><var></var>)</td></tr></table></dt>
205	<dd>
206	Called when the asynchronous loop detects that a writable socket
207	can be written.
208	Often this method will implement the necessary buffering for
209	performance. For example:
210
211	<P>
212	<div class="verbatim"><pre>
213	def handle_write(self):
214	sent = self.send(self.buffer)
215	self.buffer = self.buffer[sent:]
216	</pre></div>
217	</dl>
218
219	<P>
220	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
221	<td><nobr><b><tt id='l2h-3749' xml:id='l2h-3749' class="method">handle_expt</tt></b>(</nobr></td>
222	<td><var></var>)</td></tr></table></dt>
223	<dd>
224	Called when there is out of band (OOB) data for a socket
225	connection. This will almost never happen, as OOB is
226	tenuously supported and rarely used.
227	</dl>
228
229	<P>
230	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
231	<td><nobr><b><tt id='l2h-3750' xml:id='l2h-3750' class="method">handle_connect</tt></b>(</nobr></td>
232	<td><var></var>)</td></tr></table></dt>
233	<dd>
234	Called when the active opener's socket actually makes a connection.
235	Might send a ``welcome'' banner, or initiate a protocol
236	negotiation with the remote endpoint, for example.
237	</dl>
238
239	<P>
240	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
241	<td><nobr><b><tt id='l2h-3751' xml:id='l2h-3751' class="method">handle_close</tt></b>(</nobr></td>
242	<td><var></var>)</td></tr></table></dt>
243	<dd>
244	Called when the socket is closed.
245	</dl>
246
247	<P>
248	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
249	<td><nobr><b><tt id='l2h-3752' xml:id='l2h-3752' class="method">handle_error</tt></b>(</nobr></td>
250	<td><var></var>)</td></tr></table></dt>
251	<dd>
252	Called when an exception is raised and not otherwise handled. The default
253	version prints a condensed traceback.
254	</dl>
255
256	<P>
257	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
258	<td><nobr><b><tt id='l2h-3753' xml:id='l2h-3753' class="method">handle_accept</tt></b>(</nobr></td>
259	<td><var></var>)</td></tr></table></dt>
260	<dd>
261	Called on listening channels (passive openers) when a
262	connection can be established with a new remote endpoint that
263	has issued a <tt class="method">connect()</tt> call for the local endpoint.
264	</dl>
265
266	<P>
267	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
268	<td><nobr><b><tt id='l2h-3754' xml:id='l2h-3754' class="method">readable</tt></b>(</nobr></td>
269	<td><var></var>)</td></tr></table></dt>
270	<dd>
271	Called each time around the asynchronous loop to determine whether a
272	channel's socket should be added to the list on which read events can
273	occur. The default method simply returns <code>True</code>,
274	indicating that by default, all channels will be interested in
275	read events.
276	</dl>
277
278	<P>
279	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
280	<td><nobr><b><tt id='l2h-3755' xml:id='l2h-3755' class="method">writable</tt></b>(</nobr></td>
281	<td><var></var>)</td></tr></table></dt>
282	<dd>
283	Called each time around the asynchronous loop to determine whether a
284	channel's socket should be added to the list on which write events can
285	occur. The default method simply returns <code>True</code>,
286	indicating that by default, all channels will be interested in
287	write events.
288	</dl>
289
290	<P>
291	In addition, each channel delegates or extends many of the socket methods.
292	Most of these are nearly identical to their socket partners.
293
294	<P>
295	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
296	<td><nobr><b><tt id='l2h-3756' xml:id='l2h-3756' class="method">create_socket</tt></b>(</nobr></td>
297	<td><var>family, type</var>)</td></tr></table></dt>
298	<dd>
299	This is identical to the creation of a normal socket, and
300	will use the same options for creation. Refer to the
301	<tt class="module"><a href="module-socket.html">socket</a></tt> documentation for information on creating
302	sockets.
303	</dl>
304
305	<P>
306	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
307	<td><nobr><b><tt id='l2h-3757' xml:id='l2h-3757' class="method">connect</tt></b>(</nobr></td>
308	<td><var>address</var>)</td></tr></table></dt>
309	<dd>
310	As with the normal socket object, <var>address</var> is a
311	tuple with the first element the host to connect to, and the
312	second the port number.
313	</dl>
314
315	<P>
316	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
317	<td><nobr><b><tt id='l2h-3758' xml:id='l2h-3758' class="method">send</tt></b>(</nobr></td>
318	<td><var>data</var>)</td></tr></table></dt>
319	<dd>
320	Send <var>data</var> to the remote end-point of the socket.
321	</dl>
322
323	<P>
324	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
325	<td><nobr><b><tt id='l2h-3759' xml:id='l2h-3759' class="method">recv</tt></b>(</nobr></td>
326	<td><var>buffer_size</var>)</td></tr></table></dt>
327	<dd>
328	Read at most <var>buffer_size</var> bytes from the socket's remote end-point.
329	An empty string implies that the channel has been closed from the other
330	end.
331	</dl>
332
333	<P>
334	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
335	<td><nobr><b><tt id='l2h-3760' xml:id='l2h-3760' class="method">listen</tt></b>(</nobr></td>
336	<td><var>backlog</var>)</td></tr></table></dt>
337	<dd>
338	Listen for connections made to the socket. The <var>backlog</var>
339	argument specifies the maximum number of queued connections
340	and should be at least 1; the maximum value is
341	system-dependent (usually 5).
342	</dl>
343
344	<P>
345	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
346	<td><nobr><b><tt id='l2h-3761' xml:id='l2h-3761' class="method">bind</tt></b>(</nobr></td>
347	<td><var>address</var>)</td></tr></table></dt>
348	<dd>
349	Bind the socket to <var>address</var>. The socket must not already
350	be bound. (The format of <var>address</var> depends on the address
351	family -- see above.)
352	</dl>
353
354	<P>
355	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
356	<td><nobr><b><tt id='l2h-3762' xml:id='l2h-3762' class="method">accept</tt></b>(</nobr></td>
357	<td><var></var>)</td></tr></table></dt>
358	<dd>
359	Accept a connection. The socket must be bound to an address
360	and listening for connections. The return value is a pair
361	<code>(<var>conn</var>, <var>address</var>)</code> where <var>conn</var> is a
362	<em>new</em> socket object usable to send and receive data on
363	the connection, and <var>address</var> is the address bound to the
364	socket on the other end of the connection.
365	</dl>
366
367	<P>
368	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
369	<td><nobr><b><tt id='l2h-3763' xml:id='l2h-3763' class="method">close</tt></b>(</nobr></td>
370	<td><var></var>)</td></tr></table></dt>
371	<dd>
372	Close the socket. All future operations on the socket object
373	will fail. The remote end-point will receive no more data (after
374	queued data is flushed). Sockets are automatically closed
375	when they are garbage-collected.
376	</dl>
377
378	<P>
379
380	<p><br /></p><hr class='online-navigation' />
381	<div class='online-navigation'>
382	<!--Table of Child-Links-->
383	<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
384
385	<UL CLASS="ChildLinks">
386	<LI><A href="asyncore-example.html">11.25.1 asyncore Example basic HTTP client</a>
387	</ul>
388	<!--End of Table of Child-Links-->
389	</div>
390
391	<DIV CLASS="navigation">
392	<div class='online-navigation'>
393	<p></p><hr />
394	<table align="center" width="100%" cellpadding="0" cellspacing="2">
395	<tr>
396	<td class='online-navigation'><a rel="prev" title="11.24.2 DocCGIXMLRPCRequestHandler"
397	href="node567.html"><img src='../icons/previous.png'
398	border='0' height='32' alt='Previous Page' width='32' /></A></td>
399	<td class='online-navigation'><a rel="parent" title="11. Internet Protocols and"
400	href="internet.html"><img src='../icons/up.png'
401	border='0' height='32' alt='Up One Level' width='32' /></A></td>
402	<td class='online-navigation'><a rel="next" title="11.25.1 asyncore Example basic"
403	href="asyncore-example.html"><img src='../icons/next.png'
404	border='0' height='32' alt='Next Page' width='32' /></A></td>
405	<td align="center" width="100%">Python Library Reference</td>
406	<td class='online-navigation'><a rel="contents" title="Table of Contents"
407	href="contents.html"><img src='../icons/contents.png'
408	border='0' height='32' alt='Contents' width='32' /></A></td>
409	<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
410	border='0' height='32' alt='Module Index' width='32' /></a></td>
411	<td class='online-navigation'><a rel="index" title="Index"
412	href="genindex.html"><img src='../icons/index.png'
413	border='0' height='32' alt='Index' width='32' /></A></td>
414	</tr></table>
415	<div class='online-navigation'>
416	<b class="navlabel">Previous:</b>
417	<a class="sectref" rel="prev" href="node567.html">11.24.2 DocCGIXMLRPCRequestHandler</A>
418	<b class="navlabel">Up:</b>
419	<a class="sectref" rel="parent" href="internet.html">11. Internet Protocols and</A>
420	<b class="navlabel">Next:</b>
421	<a class="sectref" rel="next" href="asyncore-example.html">11.25.1 asyncore Example basic</A>
422	</div>
423	</div>
424	<hr />
425	<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
426	</DIV>
427	<!--End of Navigation Panel-->
428	<ADDRESS>
429	See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
430	</ADDRESS>
431	</BODY>
432	</HTML>