1 :mod:`asyncore` --- Asynchronous socket handler
2 ===============================================
5 :synopsis: A base class for developing asynchronous socket handling
7 .. moduleauthor:: Sam Rushing <rushing@nightmare.com>
8 .. sectionauthor:: Christopher Petrilli <petrilli@amber.org>
9 .. sectionauthor:: Steve Holden <sholden@holdenweb.com>
10 .. heavily adapted from original documentation by Sam Rushing
12 **Source code:** :source:`Lib/asyncore.py`
16 This module provides the basic infrastructure for writing asynchronous socket
17 service clients and servers.
19 There are only two ways to have a program on a single processor do "more than
20 one thing at a time." Multi-threaded programming is the simplest and most
21 popular way to do it, but there is another very different technique, that lets
22 you have nearly all the advantages of multi-threading, without actually using
23 multiple threads. It's really only practical if your program is largely I/O
24 bound. If your program is processor bound, then pre-emptive scheduled threads
25 are probably what you really need. Network servers are rarely processor
28 If your operating system supports the :c:func:`select` system call in its I/O
29 library (and nearly all do), then you can use it to juggle multiple
30 communication channels at once; doing other work while your I/O is taking
31 place in the "background." Although this strategy can seem strange and
32 complex, especially at first, it is in many ways easier to understand and
33 control than multi-threaded programming. The :mod:`asyncore` module solves
34 many of the difficult problems for you, making the task of building
35 sophisticated high-performance network servers and clients a snap. For
36 "conversational" applications and protocols the companion :mod:`asynchat`
39 The basic idea behind both modules is to create one or more network
40 *channels*, instances of class :class:`asyncore.dispatcher` and
41 :class:`asynchat.async_chat`. Creating the channels adds them to a global
42 map, used by the :func:`loop` function if you do not provide it with your own
45 Once the initial channel(s) is(are) created, calling the :func:`loop` function
46 activates channel service, which continues until the last channel (including
47 any that have been added to the map during asynchronous service) is closed.
50 .. function:: loop([timeout[, use_poll[, map[,count]]]])
52 Enter a polling loop that terminates after count passes or all open
53 channels have been closed. All arguments are optional. The *count*
54 parameter defaults to None, resulting in the loop terminating only when all
55 channels have been closed. The *timeout* argument sets the timeout
56 parameter for the appropriate :func:`select` or :func:`poll` call, measured
57 in seconds; the default is 30 seconds. The *use_poll* parameter, if true,
58 indicates that :func:`poll` should be used in preference to :func:`select`
59 (the default is ``False``).
61 The *map* parameter is a dictionary whose items are the channels to watch.
62 As channels are closed they are deleted from their map. If *map* is
63 omitted, a global map is used. Channels (instances of
64 :class:`asyncore.dispatcher`, :class:`asynchat.async_chat` and subclasses
65 thereof) can freely be mixed in the map.
68 .. class:: dispatcher()
70 The :class:`dispatcher` class is a thin wrapper around a low-level socket
71 object. To make it more useful, it has a few methods for event-handling
72 which are called from the asynchronous loop. Otherwise, it can be treated
73 as a normal non-blocking socket object.
75 The firing of low-level events at certain times or in certain connection
76 states tells the asynchronous loop that certain higher-level events have
77 taken place. For example, if we have asked for a socket to connect to
78 another host, we know that the connection has been made when the socket
79 becomes writable for the first time (at this point you know that you may
80 write to it with the expectation of success). The implied higher-level
83 +----------------------+----------------------------------------+
84 | Event | Description |
85 +======================+========================================+
86 | ``handle_connect()`` | Implied by the first read or write |
88 +----------------------+----------------------------------------+
89 | ``handle_close()`` | Implied by a read event with no data |
91 +----------------------+----------------------------------------+
92 | ``handle_accept()`` | Implied by a read event on a listening |
94 +----------------------+----------------------------------------+
96 During asynchronous processing, each mapped channel's :meth:`readable` and
97 :meth:`writable` methods are used to determine whether the channel's socket
98 should be added to the list of channels :c:func:`select`\ ed or
99 :c:func:`poll`\ ed for read and write events.
101 Thus, the set of channel events is larger than the basic socket events. The
102 full set of methods that can be overridden in your subclass follows:
105 .. method:: handle_read()
107 Called when the asynchronous loop detects that a :meth:`read` call on the
108 channel's socket will succeed.
111 .. method:: handle_write()
113 Called when the asynchronous loop detects that a writable socket can be
114 written. Often this method will implement the necessary buffering for
115 performance. For example::
117 def handle_write(self):
118 sent = self.send(self.buffer)
119 self.buffer = self.buffer[sent:]
122 .. method:: handle_expt()
124 Called when there is out of band (OOB) data for a socket connection. This
125 will almost never happen, as OOB is tenuously supported and rarely used.
128 .. method:: handle_connect()
130 Called when the active opener's socket actually makes a connection. Might
131 send a "welcome" banner, or initiate a protocol negotiation with the
132 remote endpoint, for example.
135 .. method:: handle_close()
137 Called when the socket is closed.
140 .. method:: handle_error()
142 Called when an exception is raised and not otherwise handled. The default
143 version prints a condensed traceback.
146 .. method:: handle_accept()
148 Called on listening channels (passive openers) when a connection can be
149 established with a new remote endpoint that has issued a :meth:`connect`
150 call for the local endpoint.
153 .. method:: readable()
155 Called each time around the asynchronous loop to determine whether a
156 channel's socket should be added to the list on which read events can
157 occur. The default method simply returns ``True``, indicating that by
158 default, all channels will be interested in read events.
161 .. method:: writable()
163 Called each time around the asynchronous loop to determine whether a
164 channel's socket should be added to the list on which write events can
165 occur. The default method simply returns ``True``, indicating that by
166 default, all channels will be interested in write events.
169 In addition, each channel delegates or extends many of the socket methods.
170 Most of these are nearly identical to their socket partners.
173 .. method:: create_socket(family, type)
175 This is identical to the creation of a normal socket, and will use the
176 same options for creation. Refer to the :mod:`socket` documentation for
177 information on creating sockets.
180 .. method:: connect(address)
182 As with the normal socket object, *address* is a tuple with the first
183 element the host to connect to, and the second the port number.
186 .. method:: send(data)
188 Send *data* to the remote end-point of the socket.
191 .. method:: recv(buffer_size)
193 Read at most *buffer_size* bytes from the socket's remote end-point. An
194 empty string implies that the channel has been closed from the other end.
197 .. method:: listen(backlog)
199 Listen for connections made to the socket. The *backlog* argument
200 specifies the maximum number of queued connections and should be at least
201 1; the maximum value is system-dependent (usually 5).
204 .. method:: bind(address)
206 Bind the socket to *address*. The socket must not already be bound. (The
207 format of *address* depends on the address family --- refer to the
208 :mod:`socket` documentation for more information.) To mark
209 the socket as re-usable (setting the :const:`SO_REUSEADDR` option), call
210 the :class:`dispatcher` object's :meth:`set_reuse_addr` method.
215 Accept a connection. The socket must be bound to an address and listening
216 for connections. The return value can be either ``None`` or a pair
217 ``(conn, address)`` where *conn* is a *new* socket object usable to send
218 and receive data on the connection, and *address* is the address bound to
219 the socket on the other end of the connection.
220 When ``None`` is returned it means the connection didn't take place, in
221 which case the server should just ignore this event and keep listening
222 for further incoming connections.
227 Close the socket. All future operations on the socket object will fail.
228 The remote end-point will receive no more data (after queued data is
229 flushed). Sockets are automatically closed when they are
232 .. class:: dispatcher_with_send()
234 A :class:`dispatcher` subclass which adds simple buffered output capability,
235 useful for simple clients. For more sophisticated usage use
236 :class:`asynchat.async_chat`.
238 .. class:: file_dispatcher()
240 A file_dispatcher takes a file descriptor or file object along with an
241 optional map argument and wraps it for use with the :c:func:`poll` or
242 :c:func:`loop` functions. If provided a file object or anything with a
243 :c:func:`fileno` method, that method will be called and passed to the
244 :class:`file_wrapper` constructor. Availability: UNIX.
246 .. class:: file_wrapper()
248 A file_wrapper takes an integer file descriptor and calls :func:`os.dup` to
249 duplicate the handle so that the original handle may be closed independently
250 of the file_wrapper. This class implements sufficient methods to emulate a
251 socket for use by the :class:`file_dispatcher` class. Availability: UNIX.
254 .. _asyncore-example-1:
256 asyncore Example basic HTTP client
257 ----------------------------------
259 Here is a very basic HTTP client that uses the :class:`dispatcher` class to
260 implement its socket handling::
262 import asyncore, socket
264 class HTTPClient(asyncore.dispatcher):
266 def __init__(self, host, path):
267 asyncore.dispatcher.__init__(self)
268 self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
269 self.connect( (host, 80) )
270 self.buffer = 'GET %s HTTP/1.0\r\n\r\n' % path
272 def handle_connect(self):
275 def handle_close(self):
278 def handle_read(self):
279 print self.recv(8192)
282 return (len(self.buffer) > 0)
284 def handle_write(self):
285 sent = self.send(self.buffer)
286 self.buffer = self.buffer[sent:]
289 client = HTTPClient('www.python.org', '/')
292 .. _asyncore-example-2:
294 asyncore Example basic echo server
295 ----------------------------------
297 Here is a basic echo server that uses the :class:`dispatcher` class to accept
298 connections and dispatches the incoming connections to a handler::
303 class EchoHandler(asyncore.dispatcher_with_send):
305 def handle_read(self):
306 data = self.recv(8192)
310 class EchoServer(asyncore.dispatcher):
312 def __init__(self, host, port):
313 asyncore.dispatcher.__init__(self)
314 self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
315 self.set_reuse_addr()
316 self.bind((host, port))
319 def handle_accept(self):
325 print 'Incoming connection from %s' % repr(addr)
326 handler = EchoHandler(sock)
328 server = EchoServer('localhost', 8080)