Hey
I am working on a little tool for myself recentl and had a bug that
was bothering me for ages. Kinda of a basic producer consumer problem.
The consumer was running in a thread:
self.__semaInvoke = threading.Semaphore (1)
self.__semaHandle = threading.Semaphore (0)
def run (self):
self.__running = True
while (self.__running):
print "waiting"
self.__semaHandle.acquire ()
self.info ("Invoking %s" % self.__invoke)
if self.__invoke == 'STOP':
self.__running = False
elif (self.__invoke in self.__steps) and \
hasattr (self, self.__invoke):
self.__steps[self.__invoke] (self)
self.__invoke = None
else:
self.info ("ERROR %s not valid command!" % \
self.__invoke)
self.__running = False
self.__invoke = None
self.__semaInvoke.release ()
print "released"
self.close ()
Then i have a method to invoke which is the producer:
def invoke (self, cmd):
if self.__running:
self.__semaInvoke.acquire ()
print "setting..."
self.__invoke = cmd
self.__semaHandle.release ()
print "set + release!"
So the invoke method isnt in a thread as such just called from the
main thread since its embeded in a C program i call this method. But
the __semaHandle.release was never being released properly and the
consumer thread would hang untill i would invoke again. Then i simply
added time.sleep (1) at the end of the invoke thread and everything
worked perfectly. I reckon the ideal solution was to have the invoke
running in a thread or something but tried to keep it all simple as i
could. Just seemed to be some kind of race where the release would be
called but not fully released if it just returned after that method. I
bet it something to do with GIL in python where the request to release
is in a que since the consumer is trying to read it or something at
the same time.maybe a mutex might help but not sure. Just what i
noticed anyway.
I think if i had the producer in its own thread as well i think this
would solve the problem. But the whole idea was to have my C program
calling bla.invoke (). But this seems to not produce the results i
wanted. Seems just time.sleep fixes everything just making sure things
are set but its not a concrete solution wonder has anyone else seen
this.
--Phil
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