Repository: cassandra Updated Branches: refs/heads/trunk 8a5a82b8a -> 1c4768a88
ninja fix comments in SharedExecutorPool Project: http://git-wip-us.apache.org/repos/asf/cassandra/repo Commit: http://git-wip-us.apache.org/repos/asf/cassandra/commit/ca431888 Tree: http://git-wip-us.apache.org/repos/asf/cassandra/tree/ca431888 Diff: http://git-wip-us.apache.org/repos/asf/cassandra/diff/ca431888 Branch: refs/heads/trunk Commit: ca431888efd91bb8a7900c0219bd821744153686 Parents: 0401761 Author: Benedict Elliott Smith <bened...@apache.org> Authored: Tue Jul 15 18:20:48 2014 +0100 Committer: Benedict Elliott Smith <bened...@apache.org> Committed: Tue Jul 15 18:20:48 2014 +0100 ---------------------------------------------------------------------- .../cassandra/concurrent/SharedExecutorPool.java | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/cassandra/blob/ca431888/src/java/org/apache/cassandra/concurrent/SharedExecutorPool.java ---------------------------------------------------------------------- diff --git a/src/java/org/apache/cassandra/concurrent/SharedExecutorPool.java b/src/java/org/apache/cassandra/concurrent/SharedExecutorPool.java index e03ec57..161b326 100644 --- a/src/java/org/apache/cassandra/concurrent/SharedExecutorPool.java +++ b/src/java/org/apache/cassandra/concurrent/SharedExecutorPool.java @@ -35,17 +35,22 @@ import static org.apache.cassandra.concurrent.SEPWorker.Work; * To keep producers from incurring unnecessary delays, once an executor is "spun up" (i.e. is processing tasks at a steady * rate), adding tasks to the executor often involves only placing the task on the work queue and updating the * task permits (which imposes our max queue length constraints). Only when it cannot be guaranteed the task will be serviced - * promptly does the producer have to signal a thread itself to perform the work. + * promptly, and the maximum concurrency has not been reached, does the producer have to schedule a thread itself to perform + * the work ('promptly' in this context means we already have a worker spinning for work, as described next). * - * We do this by scheduling only if - * - * The worker threads schedule themselves as far as possible: when they are assigned a task, they will attempt to spawn + * Otherwise the worker threads schedule themselves: when they are assigned a task, they will attempt to spawn * a partner worker to service any other work outstanding on the queue (if any); once they have finished the task they * will either take another (if any remaining) and repeat this, or they will attempt to assign themselves to another executor * that does have tasks remaining. If both fail, it will enter a non-busy-spinning phase, where it will sleep for a short * random interval (based upon the number of threads in this mode, so that the total amount of non-sleeping time remains - * approximately fixed regardless of the number of spinning threads), and upon waking up will again try to assign themselves - * an executor with outstanding tasks to perform. + * approximately fixed regardless of the number of spinning threads), and upon waking will again try to assign itself to + * an executor with outstanding tasks to perform. As a result of always scheduling a partner before committing to performing + * any work, with a steady state of task arrival we should generally have either one spinning worker ready to promptly respond + * to incoming work, or all possible workers actively committed to tasks. + * + * In order to prevent this executor pool acting like a noisy neighbour to other processes on the system, workers also deschedule + * themselves when it is detected that there are too many for the current rate of operation arrival. This is decided as a function + * of the total time spent spinning by all workers in an interval; as more workers spin, workers are descheduled more rapidly. */ public class SharedExecutorPool { @@ -96,4 +101,4 @@ public class SharedExecutorPool if (current == 0 && spinningCount.compareAndSet(0, 1)) schedule(Work.SPINNING); } -} \ No newline at end of file +}
