2 :mod:`asyncore` --- Asynchronous socket handler
3 ===============================================
6 :synopsis: A base class for developing asynchronous socket handling
8 .. moduleauthor:: Sam Rushing <rushing@nightmare.com>
9 .. sectionauthor:: Christopher Petrilli <petrilli@amber.org>
10 .. sectionauthor:: Steve Holden <sholden@holdenweb.com>
11 .. heavily adapted from original documentation by Sam Rushing
14 This module provides the basic infrastructure for writing asynchronous socket
15 service clients and servers.
17 There are only two ways to have a program on a single processor do "more than
18 one thing at a time." Multi-threaded programming is the simplest and most
19 popular way to do it, but there is another very different technique, that lets
20 you have nearly all the advantages of multi-threading, without actually using
21 multiple threads. It's really only practical if your program is largely I/O
22 bound. If your program is processor bound, then pre-emptive scheduled threads
23 are probably what you really need. Network servers are rarely processor
26 If your operating system supports the :cfunc:`select` system call in its I/O
27 library (and nearly all do), then you can use it to juggle multiple
28 communication channels at once; doing other work while your I/O is taking
29 place in the "background." Although this strategy can seem strange and
30 complex, especially at first, it is in many ways easier to understand and
31 control than multi-threaded programming. The :mod:`asyncore` module solves
32 many of the difficult problems for you, making the task of building
33 sophisticated high-performance network servers and clients a snap. For
34 "conversational" applications and protocols the companion :mod:`asynchat`
37 The basic idea behind both modules is to create one or more network
38 *channels*, instances of class :class:`asyncore.dispatcher` and
39 :class:`asynchat.async_chat`. Creating the channels adds them to a global
40 map, used by the :func:`loop` function if you do not provide it with your own
43 Once the initial channel(s) is(are) created, calling the :func:`loop` function
44 activates channel service, which continues until the last channel (including
45 any that have been added to the map during asynchronous service) is closed.
48 .. function:: loop([timeout[, use_poll[, map[,count]]]])
50 Enter a polling loop that terminates after count passes or all open
51 channels have been closed. All arguments are optional. The *count*
52 parameter defaults to None, resulting in the loop terminating only when all
53 channels have been closed. The *timeout* argument sets the timeout
54 parameter for the appropriate :func:`select` or :func:`poll` call, measured
55 in seconds; the default is 30 seconds. The *use_poll* parameter, if true,
56 indicates that :func:`poll` should be used in preference to :func:`select`
57 (the default is ``False``).
59 The *map* parameter is a dictionary whose items are the channels to watch.
60 As channels are closed they are deleted from their map. If *map* is
61 omitted, a global map is used. Channels (instances of
62 :class:`asyncore.dispatcher`, :class:`asynchat.async_chat` and subclasses
63 thereof) can freely be mixed in the map.
66 .. class:: dispatcher()
68 The :class:`dispatcher` class is a thin wrapper around a low-level socket
69 object. To make it more useful, it has a few methods for event-handling
70 which are called from the asynchronous loop. Otherwise, it can be treated
71 as a normal non-blocking socket object.
73 The firing of low-level events at certain times or in certain connection
74 states tells the asynchronous loop that certain higher-level events have
75 taken place. For example, if we have asked for a socket to connect to
76 another host, we know that the connection has been made when the socket
77 becomes writable for the first time (at this point you know that you may
78 write to it with the expectation of success). The implied higher-level
81 +----------------------+----------------------------------------+
82 | Event | Description |
83 +======================+========================================+
84 | ``handle_connect()`` | Implied by the first read or write |
86 +----------------------+----------------------------------------+
87 | ``handle_close()`` | Implied by a read event with no data |
89 +----------------------+----------------------------------------+
90 | ``handle_accept()`` | Implied by a read event on a listening |
92 +----------------------+----------------------------------------+
94 During asynchronous processing, each mapped channel's :meth:`readable` and
95 :meth:`writable` methods are used to determine whether the channel's socket
96 should be added to the list of channels :cfunc:`select`\ ed or
97 :cfunc:`poll`\ ed for read and write events.
99 Thus, the set of channel events is larger than the basic socket events. The
100 full set of methods that can be overridden in your subclass follows:
103 .. method:: handle_read()
105 Called when the asynchronous loop detects that a :meth:`read` call on the
106 channel's socket will succeed.
109 .. method:: handle_write()
111 Called when the asynchronous loop detects that a writable socket can be
112 written. Often this method will implement the necessary buffering for
113 performance. For example::
115 def handle_write(self):
116 sent = self.send(self.buffer)
117 self.buffer = self.buffer[sent:]
120 .. method:: handle_expt()
122 Called when there is out of band (OOB) data for a socket connection. This
123 will almost never happen, as OOB is tenuously supported and rarely used.
126 .. method:: handle_connect()
128 Called when the active opener's socket actually makes a connection. Might
129 send a "welcome" banner, or initiate a protocol negotiation with the
130 remote endpoint, for example.
133 .. method:: handle_close()
135 Called when the socket is closed.
138 .. method:: handle_error()
140 Called when an exception is raised and not otherwise handled. The default
141 version prints a condensed traceback.
144 .. method:: handle_accept()
146 Called on listening channels (passive openers) when a connection can be
147 established with a new remote endpoint that has issued a :meth:`connect`
148 call for the local endpoint.
151 .. method:: readable()
153 Called each time around the asynchronous loop to determine whether a
154 channel's socket should be added to the list on which read events can
155 occur. The default method simply returns ``True``, indicating that by
156 default, all channels will be interested in read events.
159 .. method:: writable()
161 Called each time around the asynchronous loop to determine whether a
162 channel's socket should be added to the list on which write events can
163 occur. The default method simply returns ``True``, indicating that by
164 default, all channels will be interested in write events.
167 In addition, each channel delegates or extends many of the socket methods.
168 Most of these are nearly identical to their socket partners.
171 .. method:: create_socket(family, type)
173 This is identical to the creation of a normal socket, and will use the
174 same options for creation. Refer to the :mod:`socket` documentation for
175 information on creating sockets.
178 .. method:: connect(address)
180 As with the normal socket object, *address* is a tuple with the first
181 element the host to connect to, and the second the port number.
184 .. method:: send(data)
186 Send *data* to the remote end-point of the socket.
189 .. method:: recv(buffer_size)
191 Read at most *buffer_size* bytes from the socket's remote end-point. An
192 empty string implies that the channel has been closed from the other end.
195 .. method:: listen(backlog)
197 Listen for connections made to the socket. The *backlog* argument
198 specifies the maximum number of queued connections and should be at least
199 1; the maximum value is system-dependent (usually 5).
202 .. method:: bind(address)
204 Bind the socket to *address*. The socket must not already be bound. (The
205 format of *address* depends on the address family --- see above.) To mark
206 the socket as re-usable (setting the :const:`SO_REUSEADDR` option), call
207 the :class:`dispatcher` object's :meth:`set_reuse_addr` method.
212 Accept a connection. The socket must be bound to an address and listening
213 for connections. The return value is a pair ``(conn, address)`` where
214 *conn* is a *new* socket object usable to send and receive data on the
215 connection, and *address* is the address bound to the socket on the other
216 end of the connection.
221 Close the socket. All future operations on the socket object will fail.
222 The remote end-point will receive no more data (after queued data is
223 flushed). Sockets are automatically closed when they are
226 .. class:: file_dispatcher()
228 A file_dispatcher takes a file descriptor or file object along with an
229 optional map argument and wraps it for use with the :cfunc:`poll` or
230 :cfunc:`loop` functions. If provided a file object or anything with a
231 :cfunc:`fileno` method, that method will be called and passed to the
232 :class:`file_wrapper` constructor. Availability: UNIX.
234 .. class:: file_wrapper()
236 A file_wrapper takes an integer file descriptor and calls :func:`os.dup` to
237 duplicate the handle so that the original handle may be closed independently
238 of the file_wrapper. This class implements sufficient methods to emulate a
239 socket for use by the :class:`file_dispatcher` class. Availability: UNIX.
242 .. _asyncore-example:
244 asyncore Example basic HTTP client
245 ----------------------------------
247 Here is a very basic HTTP client that uses the :class:`dispatcher` class to
248 implement its socket handling::
250 import asyncore, socket
252 class http_client(asyncore.dispatcher):
254 def __init__(self, host, path):
255 asyncore.dispatcher.__init__(self)
256 self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
257 self.connect( (host, 80) )
258 self.buffer = 'GET %s HTTP/1.0\r\n\r\n' % path
260 def handle_connect(self):
263 def handle_close(self):
266 def handle_read(self):
267 print self.recv(8192)
270 return (len(self.buffer) > 0)
272 def handle_write(self):
273 sent = self.send(self.buffer)
274 self.buffer = self.buffer[sent:]
276 c = http_client('www.python.org', '/')