[Stackless] "Attempt to run a locked frame!"

[Christian Tismer]

Bernd Rinn wrote:
> 
> On Tue, Feb 20, 2001 at 08:35:33AM -0500, Gordon McMillan wrote:
> > Well after modifying Bernd's code so it works with 1.5.2
> > stackless (and an older uthreads that does not have "wait"), I
> > can report that it runs fine. I simply commented out the
> > uthread.wait and used delay as the select timeout.
> 
> Thank you for pointing out that magic methods may cause problems with
> continuations.
> 
> Can that error occur only when I am doing something stupid like
> calling 'uthread.wait()' from within a magic method or can it also
> occur by chance, when the scheduler decides to perform a task switch
> within a magic method like __init__? What can one do against that? I
> assume using atomic() leaves a little chance that the task-switch
> occurs _before_ or _after_ atomic(), so that not even

The above cannot happen, since every recursion blocks by its
uthread_lock variable which defaults to no scheduling.
It can only happen from inside out.

> def __init__(self, ...): atomic(self.myinit(...)
> 
> would be completely safe. Am I right here?

Yep.

> And: Is there a way to detect if  is running in a recursive
> interpreter?

Well, there is an undocumented way to do this:
Frames have a computed "locked" flag.
Something like this works:

>>> co=continuation.caller()
>>> while co:
... 	if co.frame.locked:
... 		print "locked frame"
... 	co = co.caller

ciao - chris

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