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 CPU bound, then pre-emptive scheduled threads are probably what you really need. Network servers are rarely CPU-bound, however.
If your operating system supports the 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 module documented here solves many of the difficult problems for you, making the task of building sophisticated high-performance network servers and clients a snap.
The direct interface between the select loop and the socket object are the handle_read_event() and 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:
||Implied by a write event|
||Implied by a read event with no data available|
||Implied by a read event on a listening socket|
This set of user-level events is larger than the basics. The full set of methods that can be overridden in your subclass are:
def handle_write(self): sent = self.send(self.buffer) self.buffer = self.buffer[sent:]
1, indicating that by default, all channels will be interested.
1, indiciating that by default, all channels will be interested.
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.
(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.