[Python-Dev] Problem with signals in a single threaded application

[Greg Ewing]

Martin v. Löwis wrote:
> Greg Ewing schrieb:
> 
>>>Please
>>>try to come up with a patch (e.g. by putting a while(is_tripped) loop
>>>around the for loop).
>>
>>That isn't going to fix it. 
> 
> Why not?

Correct me if I'm wrong, but what I got from the OP
was that the current method does

   if (is_tripped) {
     for each signal {
       if the signal has occurred, call its handler
     }
     is_tripped = 0;
   }

and the problem is that any setting of is_tripped that
occurs in the midst of calling the handlers gets
wiped out at the end.

Changing this to

   while (is_tripped) {
     for each signal {
       if the signal has occurred, call its handler
     }
     is_tripped = 0;
   }

doesn't solve that, because is_tripped still gets
set to 0 before it's tested again.

> Also, why does it need to clear is_tripped atomically?

Thinking about it more, probably it doesn't. What's
important is to clear it *before* testing whether any
handlers need to be called, i.e.

   if (is_tripped) {
    is_tripped = 0;
    for each signal {
       if the signal has occurred, call its handler
     }
   }

If you really care, you can make that a while instead
of an if so that you don't have to wait until the next
CheckSignals. But if the signal had arrived a few
microseconds later you'd have to do that anyway, so
I don't see it as a big deal.

--
Greg