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Revise asyncore documentation and document asynchat for the first time.

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Steve Holden 2002-07-03 18:36:39 +00:00
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Doc/lib/libasyncore.tex
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@ -6,6 +6,7 @@
handling services.}
\moduleauthor{Sam Rushing}{rushing@nightmare.com}
\sectionauthor{Christopher Petrilli}{petrilli@amber.org}
\sectionauthor{Steve Holden}{sholden@holdenweb.com}
% Heavily adapted from original documentation by Sam Rushing.
This module provides the basic infrastructure for writing asynchronous
@ -26,35 +27,21 @@ 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 module documented here solves many of the difficult problems for
The \module{asyncore} module solves many of the difficult problems for
you, making the task of building sophisticated high-performance
network servers and clients a snap.
network servers and clients a snap. For ``conversational'' applications
and protocols the companion \refmodule{asynchat} module is invaluable.
\begin{classdesc}{dispatcher}{}
The first class we will introduce is the \class{dispatcher} class.
This is a thin wrapper around a low-level socket object. To make
it more useful, it has a few methods for event-handling on it.
Otherwise, it can be treated as a normal non-blocking socket object.
The basic idea behind both modules is to create one or more network
\emph{channels}, instances of class \class{asyncore.dispatcher} and
\class{asynchat.async_chat}. Creating the channels adds them to a global
map, used by the \function{loop()} function if you do not provide it
with your own \var{map}.
The direct interface between the select loop and the socket object
are the \method{handle_read_event()} and
\method{handle_write_event()} methods. These are called whenever an
object `fires' that event.
The firing of these low-level events can tell us whether certain
higher-level events have taken place, depending on the timing and
the state of the connection. 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 fires a write event (at this point you
know that you may write to it with the expectation of success).
The implied higher-level events are:
\begin{tableii}{l|l}{code}{Event}{Description}
\lineii{handle_connect()}{Implied by a write event}
\lineii{handle_close()}{Implied by a read event with no data available}
\lineii{handle_accept()}{Implied by a read event on a listening socket}
\end{tableii}
\end{classdesc}
Once the initial channel(s) is(are) created, calling the \function{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.
\begin{funcdesc}{loop}{\optional{timeout\optional{, use_poll\optional{,
map}}}}
@ -64,21 +51,67 @@ network servers and clients a snap.
\function{select()} or \function{poll()} call, measured in seconds;
the default is 30 seconds. The \var{use_poll} parameter, if true,
indicates that \function{poll()} should be used in preference to
\function{select()} (the default is false). The \var{map} parameter
is a dictionary that gives a list of channels to watch. As channels
\function{select()} (the default is \code{False}). The \var{map} parameter
is a dictionary whose items are the channels to watch. As channels
are closed they are deleted from their map. If \var{map} is
omitted, a global map is used.
omitted, a global map is used (this map is updated by the default
class \method{__init__()}
-- make sure you extend, rather than override, \method{__init__()}
if you want to retain this behavior).
Channels (instances of \class{asyncore.despatcher}, \class{asynchat.async_chat}
and subclasses thereof) can freely be mixed in the map.
\end{funcdesc}
This set of user-level events is larger than the basics. The
full set of methods that can be overridden in your subclass are:
\begin{classdesc}{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.
\begin{datadesc}{ac_in_buffer_size}
The asynchronous input buffer size (default \code{4096}).
\end{datadesc}
\begin{datadesc}{ac_out_buffer_size}
The asynchronous output buffer size (default \code{4096}).
\end{datadesc}
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:
\begin{tableii}{l|l}{code}{Event}{Description}
\lineii{handle_connect()}{Implied by the first write event}
\lineii{handle_close()}{Implied by a read event with no data available}
\lineii{handle_accept()}{Implied by a read event on a listening socket}
\end{tableii}
During asynchronous processing, each mapped channel's \method{readable()}
and \method{writable()} methods are used to determine whether the channel's
socket should be added to the list of channels \cfunction{select()}ed or
\cfunction{poll()}ed for read and write events.
\end{classdesc}
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:
\begin{methoddesc}{handle_read}{}
Called when there is new data to be read from a socket.
Called when the asynchronous loop detects that a \method{read()}
call on the channel's socket will succeed.
\end{methoddesc}
\begin{methoddesc}{handle_write}{}
Called when there is an attempt to write data to the object.
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:
@ -96,9 +129,9 @@ def handle_write(self):
\end{methoddesc}
\begin{methoddesc}{handle_connect}{}
Called when the socket actually makes a connection. This
might be used to send a ``welcome'' banner, or something
similar.
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.
\end{methoddesc}
\begin{methoddesc}{handle_close}{}
@ -111,28 +144,29 @@ def handle_write(self):
\end{methoddesc}
\begin{methoddesc}{handle_accept}{}
Called on listening sockets when they actually accept a new
connection.
Called on listening channels (passive openers) when a
connection can be established with a new remote endpoint that
has issued a \method{connect()} call for the local endpoint.
\end{methoddesc}
\begin{methoddesc}{readable}{}
Each time through the \method{select()} loop, the set of sockets
is scanned, and this method is called to see if there is any
interest in reading. The default method simply returns \code{True},
indicating that by default, all channels will be interested.
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 \code{True},
indicating that by default, all channels will be interested in
read events.
\end{methoddesc}
\begin{methoddesc}{writable}{}
Each time through the \method{select()} loop, the set of sockets
is scanned, and this method is called to see if there is any
interest in writing. The default method simply returns \code{True},
indicating that by default, all channels will be interested.
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 \code{True},
indicating that by default, all channels will be interested in
write events.
\end{methoddesc}
In addition, there are the basic methods needed to construct and
manipulate ``channels,'' which are what we will call the socket
connections in this context. Note that most of these are nearly
identical to their socket partners.
In addition, each channel delegates or extends many of the socket methods.
Most of these are nearly identical to their socket partners.
\begin{methoddesc}{create_socket}{family, type}
This is identical to the creation of a normal socket, and
@ -144,15 +178,17 @@ identical to their socket partners.
\begin{methoddesc}{connect}{address}
As with the normal socket object, \var{address} is a
tuple with the first element the host to connect to, and the
second the port.
second the port number.
\end{methoddesc}
\begin{methoddesc}{send}{data}
Send \var{data} out the socket.
Send \var{data} to the remote end-point of the socket.
\end{methoddesc}
\begin{methoddesc}{recv}{buffer_size}
Read at most \var{buffer_size} bytes from the socket.
Read at most \var{buffer_size} bytes from the socket's remote end-point.
An empty string implies that the channel has been closed from the other
end.
\end{methoddesc}
\begin{methoddesc}{listen}{backlog}
@ -179,13 +215,13 @@ identical to their socket partners.
\begin{methoddesc}{close}{}
Close the socket. All future operations on the socket object
will fail. The remote end will receive no more data (after
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.
\end{methoddesc}
\subsection{Example basic HTTP client \label{asyncore-example}}
\subsection{asyncore Example basic HTTP client \label{asyncore-example}}
As a basic example, below is a very basic HTTP client that uses the
\class{dispatcher} class to implement its socket handling: