On Fri, Jun 12, 2015 at 1:00 AM, Thierry Goubier <thierry.goubier@gmail.com> wrote:
Hi all,
anybody knows if, when doing something like:
(Delay forMilliseconds: n) wait
It is possible for the Delay to return immediately if n is small enough or do we have a guaranteed behavior of at least a 'yield' equivalent?
For sufficiently small values of 'n', there will be no yield behaviour. To follow the logic (assuming timingPriority > pollingPriority > userPriority)... 1. Delay>>#wait calls DelayMicrosecondScheduler>>#schedule: (your pollingPriority process) 2. where "timingSemaphore signal" 3. passes control to #runTimerEventLoop and #handleEventTimer: (running in the timingPriority process) 4. which invokes #scheduleDelay: to add your delay to /suspendedDelays/ 5. back in #handleEventTimer: "Signal any expired delays" cycles through /suspendedDelays/ such that if 'n' time has passed your delay's delaySemaphore is immediately signalled, then 6. control returns to #schedule: (your pollingPriority process) 7. and thence to #wait: which does "delaySemaphore wait" -- but this has already been signalled, so it zooms straight without any chance to yield. If you want to ensure yield behaviour I would add the obvious... Delay>>waitWithYield self wait. Processor yield. However for other sufficiently low values 'n2' (n2>n), not enough lines of the userPriority process will be executed before your pollingPriority process takes of, so the UI will effectively be locked again. Perhaps what is needed is for your polling process to observe the /lastCycleTime/ ivar set by WorldState>>interCyclePause: and dynamically adjust your polling interval to keep lastCycleTime at a reasonable value. cheers -ben
I'm looking into active polling for parallel stuff and I noticed that a busy loop with Processor yield may result in more or less locking the vm since it only gives scheduling to processes which have a higher or equal priority, so this is why I'm looking into using Delay wait instead. But I'd like the delay to be as short as possible for performance reason while allowing lower priority processes a chance to run.
Thanks,
Thierry