On Tue, 27 Jan 2009 05:46:25 -0800 (PST), koranthala <[email protected]>
wrote:
Twisted, being twisted in its behavior is causing quite a lot of
confusion in design decisions.
I'm not sure I agree with your premise. ;)
I will put forward a comparison of reactor and non-reactor patterns.
The code is not exact - whatever is shown is the gist of it.
For example, a message handler - in a usual scenario:
class messageHandler:
def run():
msg = self.get_next_msg()
if not msg.send():
self.handle_failure()
To handle parallel execution, we will have to use threads, but the
code flow is similar.
How do we do the same in a reactor pattern (Twisted)?
msg.send will cause a deferred to be raised - the failure, if it
happens will happen much later.
i.e. other than sending messageHandler object in msg.send(), I cannot
see any mechanism of running handle_failure.
In Twisted:
class messageHandler:
def run():
msg = self.get_next_msg()
msg.send(self):
class msgClass:
def send(o):
d = deferred.addCallBack(success_handler, o).addErrBack
(failure_handler, o)
def failure_handler(o):
o.handle_failure()
This doesn't look like a correct or faithful translation of the original.
Here are two possibilities. First:
class messageHandler:
def run():
msg = self.get_next_msg()
d = msg.send()
def cbSendFailed(result):
if not result:
self.handle_failure()
d.addErrback(cbSendFailed)
return d
Next:
class messageHandler:
@inlineCallbacks
def run():
msg = self.get_next_msg()
if not (yield msg.send()):
self.handle_failure()
These are both just straight translations from your version so as to
be able to handle a Deferred from `msg.send´.
Basically, what I find is that a lot of functional encapsulation is
now lost by following reactor pattern. handle_failure is
messageHandlers code and makes for pretty viewing if called from
inside messageHandler itself. But, due to the twisted nature of
reactor pattern, the msg Class - who is functionally a lower class to
messageHandler invoking messageHandler's code.
You don't need to lose anything. I don't know what your motivation was
for re-arranging the code when you wrote the Twisted version, but it doesn't
appear to have been necessary.
Is there a way to solve this in a more beautiful way? Am I missing
something here?
Hope this helps,
Jean-Paul
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