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wrap lines to <80 characters before fixing errors
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Fred Drake
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2 changed files with 189 additions and 177 deletions
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@ -3,7 +3,8 @@
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===============================================
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.. module:: asyncore
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:synopsis: A base class for developing asynchronous socket handling services.
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:synopsis: A base class for developing asynchronous socket handling
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services.
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.. moduleauthor:: Sam Rushing <rushing@nightmare.com>
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.. sectionauthor:: Christopher Petrilli <petrilli@amber.org>
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.. sectionauthor:: Steve Holden <sholden@holdenweb.com>
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@ -16,59 +17,62 @@ service clients and servers.
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There are only two ways to have a program on a single processor do "more than
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one thing at a time." Multi-threaded programming is the simplest and most
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popular way to do it, but there is another very different technique, that lets
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popular way to do it, but there is another very different technique, that lets
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you have nearly all the advantages of multi-threading, without actually using
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multiple threads. It's really only practical if your program is largely I/O
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bound. If your program is processor bound, then pre-emptive scheduled threads
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are probably what you really need. Network servers are rarely processor bound,
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however.
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bound. If your program is processor bound, then pre-emptive scheduled threads
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are probably what you really need. Network servers are rarely processor
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bound, however.
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If your operating system supports the :cfunc:`select` system call in its I/O
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library (and nearly all do), then you can use it to juggle multiple
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communication channels at once; doing other work while your I/O is taking place
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in the "background." Although this strategy can seem strange and complex,
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especially at first, it is in many ways easier to understand and control than
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multi-threaded programming. The :mod:`asyncore` module solves many of the
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difficult problems for you, making the task of building sophisticated
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high-performance network servers and clients a snap. For "conversational"
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applications and protocols the companion :mod:`asynchat` module is invaluable.
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communication channels at once; doing other work while your I/O is taking
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place in the "background." Although this strategy can seem strange and
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complex, especially at first, it is in many ways easier to understand and
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control than multi-threaded programming. The :mod:`asyncore` module solves
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many of the difficult problems for you, making the task of building
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sophisticated high-performance network servers and clients a snap. For
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"conversational" applications and protocols the companion :mod:`asynchat`
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module is invaluable.
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The basic idea behind both modules is to create one or more network *channels*,
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instances of class :class:`asyncore.dispatcher` and
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:class:`asynchat.async_chat`. Creating the channels adds them to a global map,
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used by the :func:`loop` function if you do not provide it with your own *map*.
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The basic idea behind both modules is to create one or more network
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*channels*, instances of class :class:`asyncore.dispatcher` and
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:class:`asynchat.async_chat`. Creating the channels adds them to a global
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map, used by the :func:`loop` function if you do not provide it with your own
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*map*.
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Once the initial channel(s) is(are) created, calling the :func:`loop` function
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activates channel service, which continues until the last channel (including any
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that have been added to the map during asynchronous service) is closed.
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activates channel service, which continues until the last channel (including
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any that have been added to the map during asynchronous service) is closed.
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.. function:: loop([timeout[, use_poll[, map[,count]]]])
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Enter a polling loop that terminates after count passes or all open channels
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have been closed. All arguments are optional. The *count* parameter defaults
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to None, resulting in the loop terminating only when all channels have been
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closed. The *timeout* argument sets the timeout parameter for the appropriate
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:func:`select` or :func:`poll` call, measured in seconds; the default is 30
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seconds. The *use_poll* parameter, if true, indicates that :func:`poll` should
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be used in preference to :func:`select` (the default is ``False``).
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Enter a polling loop that terminates after count passes or all open
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channels have been closed. All arguments are optional. The *count*
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parameter defaults to None, resulting in the loop terminating only when all
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channels have been closed. The *timeout* argument sets the timeout
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parameter for the appropriate :func:`select` or :func:`poll` call, measured
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in seconds; the default is 30 seconds. The *use_poll* parameter, if true,
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indicates that :func:`poll` should be used in preference to :func:`select`
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(the default is ``False``).
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The *map* parameter is a dictionary whose items are the channels to watch. As
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channels are closed they are deleted from their map. If *map* is omitted, a
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global map is used. Channels (instances of :class:`asyncore.dispatcher`,
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:class:`asynchat.async_chat` and subclasses thereof) can freely be mixed in the
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map.
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The *map* parameter is a dictionary whose items are the channels to watch.
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As channels are closed they are deleted from their map. If *map* is
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omitted, a global map is used. Channels (instances of
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:class:`asyncore.dispatcher`, :class:`asynchat.async_chat` and subclasses
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thereof) can freely be mixed in the map.
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.. class:: dispatcher()
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The :class:`dispatcher` class is a thin wrapper around a low-level socket
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object. To make it more useful, it has a few methods for event-handling which
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are called from the asynchronous loop. Otherwise, it can be treated as a
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normal non-blocking socket object.
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object. To make it more useful, it has a few methods for event-handling
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which are called from the asynchronous loop. Otherwise, it can be treated
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as a normal non-blocking socket object.
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Two class attributes can be modified, to improve performance, or possibly even
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to conserve memory.
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Two class attributes can be modified, to improve performance, or possibly
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even to conserve memory.
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.. data:: ac_in_buffer_size
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@ -80,12 +84,13 @@ that have been added to the map during asynchronous service) is closed.
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The asynchronous output buffer size (default ``4096``).
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The firing of low-level events at certain times or in certain connection states
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tells the asynchronous loop that certain higher-level events have taken place.
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For example, if we have asked for a socket to connect to another host, we know
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that the connection has been made when the socket becomes writable for the first
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time (at this point you know that you may write to it with the expectation of
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success). The implied higher-level events are:
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The firing of low-level events at certain times or in certain connection
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states tells the asynchronous loop that certain higher-level events have
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taken place. For example, if we have asked for a socket to connect to
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another host, we know that the connection has been made when the socket
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becomes writable for the first time (at this point you know that you may
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write to it with the expectation of success). The implied higher-level
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events are:
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+----------------------+----------------------------------------+
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| Event | Description |
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@ -101,11 +106,11 @@ that have been added to the map during asynchronous service) is closed.
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During asynchronous processing, each mapped channel's :meth:`readable` and
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:meth:`writable` methods are used to determine whether the channel's socket
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should be added to the list of channels :cfunc:`select`\ ed or :cfunc:`poll`\ ed
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for read and write events.
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should be added to the list of channels :cfunc:`select`\ ed or
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:cfunc:`poll`\ ed for read and write events.
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Thus, the set of channel events is larger than the basic socket events. The full
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set of methods that can be overridden in your subclass follows:
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Thus, the set of channel events is larger than the basic socket events. The
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full set of methods that can be overridden in your subclass follows:
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.. method:: dispatcher.handle_read()
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@ -116,9 +121,9 @@ set of methods that can be overridden in your subclass follows:
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.. method:: dispatcher.handle_write()
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Called when the asynchronous loop detects that a writable socket can be written.
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Often this method will implement the necessary buffering for performance. For
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example::
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Called when the asynchronous loop detects that a writable socket can be
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written. Often this method will implement the necessary buffering for
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performance. For example::
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def handle_write(self):
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sent = self.send(self.buffer)
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@ -127,15 +132,15 @@ set of methods that can be overridden in your subclass follows:
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.. method:: dispatcher.handle_expt()
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Called when there is out of band (OOB) data for a socket connection. This will
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almost never happen, as OOB is tenuously supported and rarely used.
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Called when there is out of band (OOB) data for a socket connection. This
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will almost never happen, as OOB is tenuously supported and rarely used.
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.. method:: dispatcher.handle_connect()
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Called when the active opener's socket actually makes a connection. Might send a
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"welcome" banner, or initiate a protocol negotiation with the remote endpoint,
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for example.
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Called when the active opener's socket actually makes a connection. Might
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send a "welcome" banner, or initiate a protocol negotiation with the remote
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endpoint, for example.
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.. method:: dispatcher.handle_close()
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@ -152,40 +157,40 @@ set of methods that can be overridden in your subclass follows:
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.. method:: dispatcher.handle_accept()
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Called on listening channels (passive openers) when a connection can be
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established with a new remote endpoint that has issued a :meth:`connect` call
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for the local endpoint.
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established with a new remote endpoint that has issued a :meth:`connect`
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call for the local endpoint.
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.. method:: dispatcher.readable()
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Called each time around the asynchronous loop to determine whether a channel's
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socket should be added to the list on which read events can occur. The default
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method simply returns ``True``, indicating that by default, all channels will
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be interested in read events.
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Called each time around the asynchronous loop to determine whether a
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channel's socket should be added to the list on which read events can
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occur. The default method simply returns ``True``, indicating that by
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default, all channels will be interested in read events.
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.. method:: dispatcher.writable()
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Called each time around the asynchronous loop to determine whether a channel's
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socket should be added to the list on which write events can occur. The default
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method simply returns ``True``, indicating that by default, all channels will
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be interested in write events.
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Called each time around the asynchronous loop to determine whether a
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channel's socket should be added to the list on which write events can
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occur. The default method simply returns ``True``, indicating that by
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default, all channels will be interested in write events.
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In addition, each channel delegates or extends many of the socket methods. Most
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of these are nearly identical to their socket partners.
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In addition, each channel delegates or extends many of the socket methods.
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Most of these are nearly identical to their socket partners.
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.. method:: dispatcher.create_socket(family, type)
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This is identical to the creation of a normal socket, and will use the same
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options for creation. Refer to the :mod:`socket` documentation for information
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on creating sockets.
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This is identical to the creation of a normal socket, and will use the same
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options for creation. Refer to the :mod:`socket` documentation for
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information on creating sockets.
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.. method:: dispatcher.connect(address)
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As with the normal socket object, *address* is a tuple with the first element
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the host to connect to, and the second the port number.
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As with the normal socket object, *address* is a tuple with the first
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element the host to connect to, and the second the port number.
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.. method:: dispatcher.send(data)
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@ -195,38 +200,41 @@ of these are nearly identical to their socket partners.
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.. method:: dispatcher.recv(buffer_size)
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Read at most *buffer_size* bytes from the socket's remote end-point. An empty
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string implies that the channel has been closed from the other end.
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Read at most *buffer_size* bytes from the socket's remote end-point.
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An empty string implies that the channel has been closed from the other
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end.
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.. method:: dispatcher.listen(backlog)
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Listen for connections made to the socket. The *backlog* argument specifies the
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maximum number of queued connections and should be at least 1; the maximum value
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is system-dependent (usually 5).
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Listen for connections made to the socket. The *backlog* argument
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specifies the maximum number of queued connections and should be at least
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1; the maximum value is system-dependent (usually 5).
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.. method:: dispatcher.bind(address)
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Bind the socket to *address*. The socket must not already be bound. (The
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format of *address* depends on the address family --- see above.) To mark the
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socket as re-usable (setting the :const:`SO_REUSEADDR` option), call the
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:class:`dispatcher` object's :meth:`set_reuse_addr` method.
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format of *address* depends on the address family --- see above.) To mark
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the socket as re-usable (setting the :const:`SO_REUSEADDR` option), call
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the :class:`dispatcher` object's :meth:`set_reuse_addr` method.
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.. method:: dispatcher.accept()
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Accept a connection. The socket must be bound to an address and listening for
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connections. The return value is a pair ``(conn, address)`` where *conn* is a
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*new* socket object usable to send and receive data on the connection, and
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*address* is the address bound to the socket on the other end of the connection.
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Accept a connection. The socket must be bound to an address and listening
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for connections. The return value is a pair ``(conn, address)`` where
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*conn* is a *new* socket object usable to send and receive data on the
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connection, and *address* is the address bound to the socket on the other
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end of the connection.
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.. method:: dispatcher.close()
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Close the socket. All future operations on the socket object will fail. The
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remote end-point will receive no more data (after queued data is flushed).
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Sockets are automatically closed when they are garbage-collected.
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Close the socket. All future operations on the socket object will fail.
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The remote end-point will receive no more data (after queued data is
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flushed). Sockets are automatically closed when they are
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garbage-collected.
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.. _asyncore-example:
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@ -266,4 +274,3 @@ implement its socket handling::
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c = http_client('www.python.org', '/')
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asyncore.loop()
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