[Twisted-Python] Patterns in Twisted
lists at itamarst.org
Sun Sep 16 08:10:39 EDT 2001
I've been reading POSA2, and I see Twisted uses a lot of the patterns there.
You can find more info on each pattern by searching for it in google - most
of the content in the book is also in publically accessable papers that can
be found on the web. I'm including here the one sentence description from
= Reactor =
"* The Reactor architectural pattern allows event-driven applications to
demultiplex and dispatch service requests that are delivered to an
application from one or more clients."
The main event loop in twisted.internt.main is a Reactor - it reacts to
events from select() and Delayed objects and dispatches them.
= Acceptor-Connector =
"* The Acceptor-Connector design pattern decouples the connection and
initialization of cooperating peer services in a networked system from the
processing performed by the peer services after they are connected and
This is how twisted works as well - once a connection has been accepted, a
new Protocol object is created that registers itself with the event loop and
from then on it deals with this connection.
= Active Object =
"* The Active Object design pattern decouples method execution from method
invocation to enhance concurrency and simplify synchronized access to
objects that reside in their own threads of control."
It does this by having a separate thread that runs the methods that. Which
is how internet.main.threadtask works - threads add tasks to it which are
then executed by the event loop's thread.
= Async / Half-Async =
"* The Half-Sync/Half-Async architectural pattern decouples asynchronous and
synchronous service processing in concurrent systems, to simplify
programming without unduly reducing performance. The pattern introduces two
intercommunicating layers, one for asynchronous and one for synchronous
This is how threading protocols can be created (see the echoserv_threaded.py
example). Protocol instances in the async layer add received messages to a
queue that the threads read, and their results are added back to async layer
using an implicit queuing layer, the threadtask Active Object.
Strategized Locking is what threadable.synchronize does, I think, Wrapper
Facade is is used in making the transport level abstract, and Component
Configurator is implicit in twisted's abilities to add/remove/configure
different components at runtime.
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