How to pop a tkMessageBox in a twisted powered server

Question

I have a server based on twisted reactor, and I need the following scenario: the server can receive two types of request

• ADD(x,y) and returns a sum
• HUMAN_PERMISSION which returns true only if the human user approved the ip of the client

I am using tkMessageBox to ask the human user, but the problem is that it blocks the whole reactor and the server becomes unresponsive to other requests

I understand that I have to use twisted's deferred here in some way, just dont know how this: doesnt seem to work, it still blocks the whole reactor

d = deferLater(reactor, 1,tkMessageBox.showinfo, "is he ok?", clientIp)
d.addCallback(confirmUser)

Answer 1

Deferreds can't do anything to make your code non-blocking. All they can do is manage a callback chain based on an existing non-blocking event. That's what lets you translate low-level events like "some bytes were received" or "a connection was lost" or "a user clicked on a button" into high level events like "the HTTP request was responded to" or "the user answered your question". deferLater, for example, simply fires its Deferred when some time has passed.

You don't need a reactor to use a Deferred, even. For example:

>>> from twisted.internet.defer import Deferred
>>> d = Deferred()
>>> def transformResult(result):
...     return result + 5
... 
>>> d.addCallback(transformResult)
<Deferred at 0x100521200>
>>> def itsDone(result):
...     print("It's done: " + str(result))
... 
>>> d.addCallback(itsDone)
<Deferred at 0x100521200>
>>> d.callback(3)
It's done: 8
>>> 

You can call callback() from anywhere; it's just usually called from a reactor event. In your case, you probably want to call callback from a Tk event instead.

All that said, you need a way to get Tk events into the main reactor thread, which you do by using a reactor that knows about Tk's mainloop. A commenter already mentioned that there is an existing API for this: twisted.internet.tksupport. Given that Tk is not the most popular GUI these days, you may find some issues, so please report them if you find any.