[PEAK] trellis activity does not save/restore Contextual context between task switches

[Andrew Svetlov]

>> I made patch for TaskCell._stepper to support this feature. Main
>> change is: STACK now contains not only current generators for tasks
>> but also last context.State for every generator and updates states
>> when need.
>
> Is that really necessary?  It seems to me that you should only need one
> saved state for the entire task, and simply swap it in and out around the
> send/throw/next call.
>
You true, really I need to save only 'current' state for task, switch
to this state at start of _step and restore state at function exit.

---------------
    def _stepper(self, func):
        VALUE = self._result = []
        ERROR = self._error  = []
        STACK = [func()]
        CALL = STACK.append
        RETURN = STACK.pop
        ctrl = trellis.ctrl
        STATE = [context.State.child()]
        def _step():
            outer = STATE[0].swap()
            while STACK:
                try:
                    it = STACK[-1]
                    if VALUE and hasattr(it, 'send'):
                        rv = it.send(VALUE[0])
                    elif ERROR and hasattr(it, 'throw'):
                        rv = it.throw(*ERROR.pop())
                    else:
                        rv = it.next()
                except:
                    del VALUE[:]
                    ERROR.append(sys.exc_info())
                    if ERROR[-1][0] is StopIteration:
                        ERROR.pop() # not really an error
                    RETURN()
                else:
                    del VALUE[:]
                    if rv is Pause:
                        break
                    elif hasattr(rv, 'next'):
                        CALL(rv); continue
                    elif isinstance(rv, Return):
                        rv = rv.value
                    VALUE.append(rv)
                    if len(STACK)==1:
                        break
                    RETURN()
            if STACK and not ERROR and not ctrl.reads:
                ctrl.current_listener.dirty() # re-run if still running
            STATE[0] = outer.swap()
            return resume()

        return _step

---------------

>
>> Please review and if this patch is clean - put it into current trellis
>> trunk.
>> If not - please point where I'm wrong.
>
> It doesn't appear that you've actually provided a patch, and it does
> something involving some "fds_main.utilities.trellis" module in any event.
>  Tests should be either a doctest or a patch to the test_trellis module.
>
I can send you svn diff for activity.py and test_trellis,py modules. Is it ok?

Thank you for feedback.