| |
| :mod:`asyncore` --- Asynchronous socket handler |
| =============================================== |
| |
| .. module:: asyncore |
| :synopsis: A base class for developing asynchronous socket handling services. |
| .. moduleauthor:: Sam Rushing <rushing@nightmare.com> |
| .. sectionauthor:: Christopher Petrilli <petrilli@amber.org> |
| .. sectionauthor:: Steve Holden <sholden@holdenweb.com> |
| |
| |
| This module provides the basic infrastructure for writing asynchronous socket |
| service clients and servers. |
| |
| .. % Heavily adapted from original documentation by Sam Rushing. |
| |
| 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 :cfunc:`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. |
| |
| Two class attributes can be modified, to improve performance, or possibly even |
| to conserve memory. |
| |
| |
| .. data:: ac_in_buffer_size |
| |
| The asynchronous input buffer size (default ``4096``). |
| |
| |
| .. data:: ac_out_buffer_size |
| |
| The asynchronous output buffer size (default ``4096``). |
| |
| 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 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 :cfunc:`select`\ ed or :cfunc:`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:: dispatcher.handle_read() |
| |
| Called when the asynchronous loop detects that a :meth:`read` call on the |
| channel's socket will succeed. |
| |
| |
| .. method:: dispatcher.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:: dispatcher.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:: dispatcher.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:: dispatcher.handle_close() |
| |
| Called when the socket is closed. |
| |
| |
| .. method:: dispatcher.handle_error() |
| |
| Called when an exception is raised and not otherwise handled. The default |
| version prints a condensed traceback. |
| |
| |
| .. method:: dispatcher.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:: dispatcher.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:: dispatcher.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:: dispatcher.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:: dispatcher.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:: dispatcher.send(data) |
| |
| Send *data* to the remote end-point of the socket. |
| |
| |
| .. method:: dispatcher.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:: dispatcher.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:: dispatcher.bind(address) |
| |
| Bind the socket to *address*. The socket must not already be bound. (The |
| format of *address* depends on the address family --- see above.) 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:: dispatcher.accept() |
| |
| Accept a connection. The socket must be bound to an address and listening for |
| connections. The return value is 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. |
| |
| |
| .. method:: dispatcher.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. |
| |
| |
| .. _asyncore-example: |
| |
| 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 http_client(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:] |
| |
| c = http_client('www.python.org', '/') |
| |
| asyncore.loop() |
| |