5. astm.asynclib :: Asynchronous socket handler

astm.asynclib.loop(timeout=30.0, map=None, tasks=None, count=None)

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 select() or poll() call, measured in seconds; the default is 30 seconds. The use_poll parameter, if true, indicates that poll() should be used in preference to 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 asyncore.dispatcher, asynchat.async_chat and subclasses thereof) can freely be mixed in the map.

class astm.asynclib.Dispatcher(sock=None, map=None)

The 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 readable() and writable() methods are used to determine whether the channel’s socket should be added to the list of channels select()ed or poll()ed for read and write events.


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.


Bind the socket to address.

The socket must not already be bound. The format of address depends on the address family — refer to the socket documentation for more information. To mark the socket as re-usable (setting the SO_REUSEADDR option), call the Dispatcher object’s set_reuse_addr() method.


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.


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.

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 socket documentation for information on creating sockets.


Called on listening channels (passive openers) when a connection can be established with a new remote endpoint that has issued a connect() call for the local endpoint.


Called when the socket is closed.


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.


Called when an exception is raised and not otherwise handled. The default version prints a condensed traceback.


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:]

Listen for connections made to the socket.

The num argument specifies the maximum number of queued connections and should be at least 1; the maximum value is system-dependent (usually 5).


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.


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.


Send data to the remote end-point of the socket.


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.

class astm.asynclib.AsyncChat(sock=None, map=None)

This class is an abstract subclass of Dispatcher. To make practical use of the code you must subclass AsyncChat, providing meaningful meth:found_terminator method. The Dispatcher methods can be used, although not all make sense in a message/response context.

Like Dispatcher, AsyncChat defines a set of events that are generated by an analysis of socket conditions after a select() call. Once the polling loop has been started the AsyncChat object’s methods are called by the event-processing framework with no action on the part of the programmer.


Automatically close this channel once the outgoing queue is empty.


In emergencies this method will discard any data held in the input and output buffers.


Sends all data from outgoing queue.


Called when the incoming data stream matches the termination condition. The default method, which must be overridden, raises a NotImplementedError exception. The buffered input data should be available via an instance attribute.


Puts data into incoming queue. Also available by alias collect_incoming_data.


Pushes data on to the channel’s fifo to ensure its transmission. This is all you need to do to have the channel write the data out to the network.


Predicate for inclusion in the readable for select()


Predicate for inclusion in the writable for select()