[Stackless] Suggestions: getscheduledcount() and Deadlock Exceptions

Andrew Francis andrewfr_ice at yahoo.com
Fri Jan 13 15:32:00 CET 2006


Hello Colleagues:

Let me start by thanking everyone for their help in
2005. I wish everyone a happy 2006.

I am slowing getting the hang of Stackless Python, and
perhaps someday I will understand the Tao of Stackless
:-)

In my coding, I notice that deadlock is my biggest
problem. In the near future, I will summarise the help
I have received on the mailing list and post an
article on the Wiki. That said, I notice that one of
my gotchas is being thrown by getruncount(). Some
suggestions.

1. Perhaps it would be feasible to create a new
scheduler property: getScheduledCount(). "scheduled" I
believe is a property of a task - that is the task is
blocked or on the runnable list. 

So instead of an idiom like:

while stackless.getruncount() > 1:
   stackless.schedule()

one would have

while stackless.getScheduledCount() > 1
    stackless.schedule()

Deadlock Detection:

I believe database applications like Berkeley DB have
deadlock detection. I have been reviewing deadlock
detection algorithms seeing if it is possible to use
one with the stackless scheduler. Yes these algorithms
tend to be o(n^2) and perhaps not feasible if there
are too many channels and tasklets. However I would
see a deadlock detector being activated in a debugger
mode, or manually as follows:

# if only the main taskless is running and one knows
there
# are N tasklets
if getruncount() == 1 and getScheduledCount() < n:
   try:
       stackless.cycleDetect()
   except CycleDetectedException:
       # print offensive cycle
    
Perhaps to partition the problem, a TaskletGroup
(similar to a thread group) method could be added. I
find that in my own work, a tasklet spawns other
tasklets and I am interested in them as a group.

Comments?

Cheers,
Andrew

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