On Tue, Aug 19, 2008 at 6:29 PM, Alex Karasulu <email@example.com>
I have an interesting situation to deal with while trying to find a way to implement search time limits. I'm a bit perplexed on how best to implement this and so any suggestions are great. Here's a quick breakdown of the problem.
Search requests must adhere to search time limits. The request is used to build a system of nested Cursors and evaluators similar in structure to the search filter. The final Cursor produced will return candidates accepted by the filter expression. Cursors can be advanced using first(), last(), next(), and previous() methods. While advancing a loop performs evaluations to find the first, last, next or previous candidate matching the filter. Those entries not matching the filter a not returned. It's a bit more complex than this but this trivial view is sufficient to discuss the problem.
So we have to stop searching after some time limit. Previously before the bigbang we used to just check the time limits high up in the code (in the search handler) after getting each candidate. This did not always work so well because sometimes with very large directories and poor search filters it would take a while to find the next candidate to return so we would overshoot the time limit. The problem is primarily due to these evaluation loops in the Cursor while trying to advance to a candidate. While in this loop, going over entries that do not match, there is no way for the Cursor to detect that time is up.
There are a few ways I thought we can solve this problem. First these loops will have to check if the time is up between iterations either directly or indirectly through some parameter. It would be nice if the Cursor can detect this on it's own but tunnelling the size limits deep down through this system of nested Cursors during construction is a real PITA. I was thinking of using the closed/open state of the Cursor to naturally halt these loops. This should happen anyway. The only problem is another thread is needed in the SearchHandler to close the Cursor when time limits are exceeded.
I talked to Emmanuel about this on IM and he preferred the approach where a Cursor is passed the time limits and handles timing out on it's own. I'm not too keen on this idea because a Cursor by it's nature is not and may not be time limited. However it does need to respond to being closed appropriately even while one thread is advancing it. I think Emmanuel rightfully so dislikes the idea of having a timer thread (really a schedulable executor of tasks for closing search Cursors) in the search handler. Don't know if others see a better option here or if one way is more preferrable than the other.
Microsoft gives you Windows, Linux gives you the whole house ...