[Swift-devel] Re: scheduler foo

[Ben Clifford]

poking more at this. the approach used in the code at the moment seems to 
have a few problems:

The frist, in situations like the below code fragment the first 
overloadedCount adjustment 
takes away the overloadedness of the host in question, then adds the new 
overloadedness back. However, it relies on the first checkOverloaded 
returning the (negative of the) same as what has been added previously - 
either by a previous checkOverloaded call or by a timer thread.

This seems to not always happen.



                overloadedCount += checkOverloaded(wh, -1);
                wh.setScore(newScore);
                weightedHosts.put(wh.getHost(), wh);
                scores.add(wh);
                sum += wh.getTScore();
                overloadedCount += checkOverloaded(wh, 1);

Secondly timer tasks are not killed, so a large number of timer tasks get 
started up for overloaded sites. This appears to cause some weird 
behaviour.

I've put commits in that tidy up a few apparent bugs a bit but the 
abovementioned behaviour remains. It seems difficult to deal with the 
above in an o(1) fashion - if moving away from that, an explicit check of 
each site's overload status (as implemented in the previous patches on 
this thread) appears to work.

--