Question

I’m building an XML-RPC server using Twisted which periodically checks if the timestamps of its source files have changed and reloads them using rebuild.

from twisted.python.rebuild import rebuild

rebuild(mymodule)

The functions the server exposes get reloaded fine, but there in another protocol class active which calls callback functions on the same class of mymodule but they don’t use the reloaded version of the functions. This protocol simply has a dict with normal functions as values.

I found this mixin class which is intended to deal with limitations of rebuild.

http://twistedmatrix.com/documents/current/api/twisted.python.rebuild.Sensitive.html

How do I make sure my callbacks use up to date code?

Answer 1

You’re correct; this is a limitation of twisted.python.rebuild. It’s on updating the __class__ attribute of existing instances, and imported functions and classes.

One way to deal with this would be to simply submit a patch to Twisted that fixes rebuild for this case.

However, if you want to use Sensitive for its intended purpose, you can also implement your callback-holding class to work with rebuild on current versions of Twisted. The following examples demonstrates how to use all three methods of the relevant class to update a dictionary of callbacks pointing at functions. Note that even without the if needRebuildUpdate... test, calling x() directly will always get the most up-to-date version.

from twisted.python.rebuild import rebuild, Sensitive
from twisted.python.filepath import FilePath

p = FilePath("mymodule.py")
def clearcache():
    bytecode = p.sibling("mymodule.pyc")
    if bytecode.exists():
        bytecode.remove()
clearcache()
p.setContent("def x(): return 1")
import mymodule
from mymodule import x
p.setContent("def x(): return 2")

class Something(Sensitive, object):
    def __init__(self):
        self.stuff = {"something": x}
    def invoke(self):
        if self.needRebuildUpdate():
            for key in list(self.stuff):
                self.stuff[key] = self.latestVersionOf(self.stuff[key])
            self.rebuildUpToDate()
        return self.stuff["something"]()

def test():
    print s.invoke()
    print x()

s = Something()
test()

clearcache()
rebuild(mymodule)

test()