Thanks! On Wed, May 9, 2012 at 9:52 AM, Ralph Castain <r...@open-mpi.org> wrote: > Sure! See attached the original note to the libevent folks > > > Hi folks > > I'm working with priorities in events using libevent 2.0.13. Since I'm not > using the most current release, I thought I'd ask about a behavior we are > seeing that might be a potential bug. > > I have attached a simple reproducer of the problem. In short, suppose I have > setup 8 priorities for my event base. I then execute an event at priority 4. > In that callback, I setup and activate two new events - first one at priority > 4, and then another at priority 0. We then cycle back through the event loop. > > Given the prioritized event base, I would expect the event at priority 0 to > be called back first. However, this isn't what happens. Instead, the first > event to be defined (in this case, the one at priority 4) is called back > first. > > Is this the expected behavior? Can someone point me to the error in this > reproducer that might be causing the problem? > > FWIW: I found that if I adjust the initial event's priority to something > different than 4 (i.e., the level of the next event to be defined), then I > get the expected behavior. So it appears that the problem is that when we > return to the loop, we trigger any pending event of the same priority as the > one we were in, instead of looping around to check the highest priority first. > > Thanks > Ralph > > > > > > > On May 9, 2012, at 7:45 AM, Josh Hursey wrote: > >> Ralph, >> > >> Can you point me to the small reproducer for the libevent bug that was >> fixed? I'm just curious. >> >> Thanks, >> Josh >> >> On Fri, May 4, 2012 at 4:09 PM, Ralph Castain <r...@open-mpi.org> wrote: >>> FYI: 2.0.19-stable was released yesterday. I have a Mercurial repo all set >>> to go: >>> >>> https://bitbucket.org/rhc/ompi-libevent2019 >>> >>> Please check it out - timeout is now set for May 11th. >>> >>> Thanks >>> Ralph >>> >>> On May 1, 2012, at 8:38 AM, Ralph Castain wrote: >>> >>>> WHAT: Update libevent to 2.0.19 release >>>> >>>> WHEN: As soon as it is released, expected around May 11 >>>> >>>> WHY: The 2.0.19 release contains a critical fix to a bug I recently >>>> discovered in the libevent 2.0.x series >>>> >>>> >>>> Details: >>>> I discovered a bug in libevent over the last few days that causes it to >>>> unexpectedly "invert" event priorities. It is a slightly subtle bug, but >>>> we were able to provide a simple reproducer and so the libevent folks were >>>> able to quickly implement a fix. >>>> >>>> Stated simply, if you were in an event of a given priority and activated >>>> an event of higher priority, that new event would not get serviced if any >>>> event of the current priority were to become active prior to leaving the >>>> current event. In other words, libevent would service all active events of >>>> the current priority before even looking to see if a higher priority event >>>> was active. >>>> >>>> The patch adds the following logic to event_active: >>>> >>>>> IF <I am in an event> AND >>>>> IF <ev->base> EQ <current-base> AND >>>>> IF <pri> LT <current-pri> THEN >>>>> <rescan queues on next loop> >>>> >>>> >>>> Thus, a rescan only occurs if a higher priority event becomes active >>>> during an event of lower priority. Unfortunately, ORTE relies on this >>>> behavior to handle errors - without the change, an error reported in a >>>> message from a daemon (for example) cannot be serviced until ALL messages >>>> that arrive during the processing of the message have been handled. In the >>>> case of a large cluster that is receiving a long list of messages, this >>>> prevents the error from being handled for quite some time. >>>> >>>> >>> >>> >>> _______________________________________________ >>> devel mailing list >>> de...@open-mpi.org >>> http://www.open-mpi.org/mailman/listinfo.cgi/devel >> >> >> >> -- >> Joshua Hursey >> Postdoctoral Research Associate >> Oak Ridge National Laboratory >> http://users.nccs.gov/~jjhursey >> >> _______________________________________________ >> devel mailing list >> de...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
-- Joshua Hursey Postdoctoral Research Associate Oak Ridge National Laboratory http://users.nccs.gov/~jjhursey
