| :mod:`asyncore` --- Asynchronous socket handler |
| =============================================== |
| |
| .. module:: asyncore |
| :synopsis: A base class for developing asynchronous socket handling |
| services. |
| .. moduleauthor:: Sam Rushing <[email protected]> |
| .. sectionauthor:: Christopher Petrilli <[email protected]> |
| .. sectionauthor:: Steve Holden <[email protected]> |
| .. heavily adapted from original documentation by Sam Rushing |
| |
| **Source code:** :source:`Lib/asyncore.py` |
| |
| -------------- |
| |
| This module provides the basic infrastructure for writing asynchronous socket |
| service clients and servers. |
| |
| 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. |
| |
| If your operating system supports the :c:func:`select` 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 :mod:`asyncore` 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 :mod:`asynchat` |
| module is invaluable. |
| |
| The basic idea behind both modules is to create one or more network |
| *channels*, instances of class :class:`asyncore.dispatcher` and |
| :class:`asynchat.async_chat`. Creating the channels adds them to a global |
| map, used by the :func:`loop` function if you do not provide it with your own |
| *map*. |
| |
| Once the initial channel(s) is(are) created, calling the :func:`loop` function |
| activates channel service, which continues until the last channel (including |
| any that have been added to the map during asynchronous service) is closed. |
| |
| |
| .. function:: loop([timeout[, use_poll[, map[,count]]]]) |
| |
| Enter a polling loop that terminates after count passes or all open |
| channels have been closed. All arguments are optional. The *count* |
| parameter defaults to None, resulting in the loop terminating only when all |
| channels have been closed. The *timeout* argument sets the timeout |
| parameter for the appropriate :func:`select` or :func:`poll` call, measured |
| in seconds; the default is 30 seconds. The *use_poll* parameter, if true, |
| indicates that :func:`poll` should be used in preference to :func:`select` |
| (the default is ``False``). |
| |
| The *map* parameter is a dictionary whose items are the channels to watch. |
| As channels are closed they are deleted from their map. If *map* is |
| omitted, a global map is used. Channels (instances of |
| :class:`asyncore.dispatcher`, :class:`asynchat.async_chat` and subclasses |
| thereof) can freely be mixed in the map. |
| |
| |
| .. class:: dispatcher() |
| |
| The :class:`dispatcher` 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. |
| |
| 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: |
| |
| +----------------------+----------------------------------------+ |
| | Event | Description | |
| +======================+========================================+ |
| | ``handle_connect()`` | Implied by the first read or write | |
| | | event | |
| +----------------------+----------------------------------------+ |
| | ``handle_close()`` | Implied by a read event with no data | |
| | | available | |
| +----------------------+----------------------------------------+ |
| | ``handle_accept()`` | Implied by a read event on a listening | |
| | | socket | |
| +----------------------+----------------------------------------+ |
| |
| During asynchronous processing, each mapped channel's :meth:`readable` and |
| :meth:`writable` methods are used to determine whether the channel's socket |
| should be added to the list of channels :c:func:`select`\ ed or |
| :c:func:`poll`\ ed for read and write events. |
| |
| 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: |
| |
| |
| .. method:: handle_read() |
| |
| Called when the asynchronous loop detects that a :meth:`read` call on the |
| channel's socket will succeed. |
| |
| |
| .. method:: handle_write() |
| |
| 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:: |
| |
| def handle_write(self): |
| sent = self.send(self.buffer) |
| self.buffer = self.buffer[sent:] |
| |
| |
| .. method:: handle_expt() |
| |
| 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. |
| |
| |
| .. method:: handle_connect() |
| |
| 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. |
| |
| |
| .. method:: handle_close() |
| |
| Called when the socket is closed. |
| |
| |
| .. method:: handle_error() |
| |
| Called when an exception is raised and not otherwise handled. The default |
| version prints a condensed traceback. |
| |
| |
| .. method:: handle_accept() |
| |
| Called on listening channels (passive openers) when a connection can be |
| established with a new remote endpoint that has issued a :meth:`connect` |
| call for the local endpoint. |
| |
| |
| .. method:: readable() |
| |
| 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 ``True``, indicating that by |
| default, all channels will be interested in read events. |
| |
| |
| .. method:: writable() |
| |
| 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 ``True``, indicating that by |
| default, all channels will be interested in write events. |
| |
| |
| In addition, each channel delegates or extends many of the socket methods. |
| Most of these are nearly identical to their socket partners. |
| |
| |
| .. method:: create_socket(family, type) |
| |
| This is identical to the creation of a normal socket, and will use the |
| same options for creation. Refer to the :mod:`socket` documentation for |
| information on creating sockets. |
| |
| |
| .. method:: connect(address) |
| |
| As with the normal socket object, *address* is a tuple with the first |
| element the host to connect to, and the second the port number. |
| |
| |
| .. method:: send(data) |
| |
| Send *data* to the remote end-point of the socket. |
| |
| |
| .. method:: recv(buffer_size) |
| |
| Read at most *buffer_size* bytes from the socket's remote end-point. An |
| empty string implies that the channel has been closed from the other end. |
| |
| |
| .. method:: listen(backlog) |
| |
| Listen for connections made to the socket. The *backlog* argument |
| specifies the maximum number of queued connections and should be at least |
| 1; the maximum value is system-dependent (usually 5). |
| |
| |
| .. method:: bind(address) |
| |
| Bind the socket to *address*. The socket must not already be bound. (The |
| format of *address* depends on the address family --- refer to the |
| :mod:`socket` documentation for more information.) To mark |
| the socket as re-usable (setting the :const:`SO_REUSEADDR` option), call |
| the :class:`dispatcher` object's :meth:`set_reuse_addr` method. |
| |
| |
| .. method:: accept() |
| |
| Accept a connection. The socket must be bound to an address and listening |
| for connections. The return value can be either ``None`` or a pair |
| ``(conn, address)`` where *conn* is a *new* socket object usable to send |
| and receive data on the connection, and *address* is the address bound to |
| the socket on the other end of the connection. |
| When ``None`` is returned it means the connection didn't take place, in |
| which case the server should just ignore this event and keep listening |
| for further incoming connections. |
| |
| |
| .. method:: close() |
| |
| 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. |
| |
| .. class:: dispatcher_with_send() |
| |
| A :class:`dispatcher` subclass which adds simple buffered output capability, |
| useful for simple clients. For more sophisticated usage use |
| :class:`asynchat.async_chat`. |
| |
| .. class:: file_dispatcher() |
| |
| A file_dispatcher takes a file descriptor or file object along with an |
| optional map argument and wraps it for use with the :c:func:`poll` or |
| :c:func:`loop` functions. If provided a file object or anything with a |
| :c:func:`fileno` method, that method will be called and passed to the |
| :class:`file_wrapper` constructor. Availability: UNIX. |
| |
| .. class:: file_wrapper() |
| |
| A file_wrapper takes an integer file descriptor and calls :func:`os.dup` to |
| duplicate the handle so that the original handle may be closed independently |
| of the file_wrapper. This class implements sufficient methods to emulate a |
| socket for use by the :class:`file_dispatcher` class. Availability: UNIX. |
| |
| |
| .. _asyncore-example-1: |
| |
| asyncore Example basic HTTP client |
| ---------------------------------- |
| |
| Here is a very basic HTTP client that uses the :class:`dispatcher` class to |
| implement its socket handling:: |
| |
| import asyncore, socket |
| |
| class HTTPClient(asyncore.dispatcher): |
| |
| def __init__(self, host, path): |
| asyncore.dispatcher.__init__(self) |
| self.create_socket(socket.AF_INET, socket.SOCK_STREAM) |
| self.connect( (host, 80) ) |
| self.buffer = 'GET %s HTTP/1.0\r\n\r\n' % path |
| |
| def handle_connect(self): |
| pass |
| |
| def handle_close(self): |
| self.close() |
| |
| def handle_read(self): |
| print self.recv(8192) |
| |
| def writable(self): |
| return (len(self.buffer) > 0) |
| |
| def handle_write(self): |
| sent = self.send(self.buffer) |
| self.buffer = self.buffer[sent:] |
| |
| |
| client = HTTPClient('www.python.org', '/') |
| asyncore.loop() |
| |
| .. _asyncore-example-2: |
| |
| asyncore Example basic echo server |
| ---------------------------------- |
| |
| Here is a basic echo server that uses the :class:`dispatcher` class to accept |
| connections and dispatches the incoming connections to a handler:: |
| |
| import asyncore |
| import socket |
| |
| class EchoHandler(asyncore.dispatcher_with_send): |
| |
| def handle_read(self): |
| data = self.recv(8192) |
| if data: |
| self.send(data) |
| |
| class EchoServer(asyncore.dispatcher): |
| |
| def __init__(self, host, port): |
| asyncore.dispatcher.__init__(self) |
| self.create_socket(socket.AF_INET, socket.SOCK_STREAM) |
| self.set_reuse_addr() |
| self.bind((host, port)) |
| self.listen(5) |
| |
| def handle_accept(self): |
| pair = self.accept() |
| if pair is not None: |
| sock, addr = pair |
| print 'Incoming connection from %s' % repr(addr) |
| handler = EchoHandler(sock) |
| |
| server = EchoServer('localhost', 8080) |
| asyncore.loop() |
