I'm trying to figure out how can i make my code more asynchronous using twisted.
deferred_obj.callback
however chained callbacks will not be considered asynchronous because they're chained and the event loop will keep firing each one of them concurrently until there is no more, right?
However, if I have a deferred object, and I attach as its callback the deferred_obj.callback as in d.addCallback(deferred_obj.callback)
then this will be considered asynchronous, because the deferred_obj is waiting for the data, and then the method that will pass the data is waiting on data as well, however once i d.callback 'd' object processes the data then it call deferred_obj.callback however since this object is deferred, unlike the case of chained callbacks, it will execute asynchronously... correct?
Assuming all of my code is non-blocking, this means that chained callbacks are NOT asynchronous while chained deferreds are, correct?
The callbacks are (by default) synchronous. However, as the Twisted doc points out:
If you need one Deferred to wait on another, all you need to do is return a Deferred from a method added to addCallbacks.
So you can use that to do some asynchronous processing in your callback chain. Let's do that:
from twisted.internet import reactor, defer
def callback_func_2(result, previous_data):
# here we pass the result of the deferred down the callback chain
# (done synchronously)
print "calling function 1 on result:%s with previous result:%s" % (result, previous_data)
return result
def callback_func(result):
#let's do some asynchronous stuff in this callback
# simple trick here is to return a deferred from a callback
# instead of the result itself.
#
# so we can do asynchronous stuff here,
# like firing something 1 second later and have
# another method processing the result
print "calling function 1 on result:%s" % result
d = defer.Deferred()
reactor.callLater(1, d.callback, "second callback")
d.addCallback(callback_func_2, result)
return d
def do():
d = defer.Deferred()
reactor.callLater(1, d.callback, "first callback")
d.addCallback(callback_func)
return d
do()
reactor.run()