To Spin or not to Spin!

11:02AM Sep 12, 2015 in category General by Zoltan Farkas

Both spf4j LifoThreadPool and java ForkJoin pool use Spinning to try to improve performance. It seems like FJP decided to stop spinning...

Latest JDK update disabled spinning for the fork-join pool:

http://bugs.java.com/view_bug.do?bug_id=8080623

the latest update also fixes serious bugs with FJP like:

http://bugs.java.com/view_bug.do?bug_id=8078490 

The spf4j thread pool spinning is configurable (on by default) and the decision to employ it is in the hands of the user... By default spf4j will have max nr_processors/2 spinning threads at any  (configurable via system property: lifoTp.maxSpinning). 

There are significant differences between spf4j lifo thread pool and FJP, and these differences make them useful for different use cases...  

FJP lacks the configurability of the spf4j thread pool. It is not possible to configure a FJP to reject tasks before and unrecoverable error like a OOM happens. FJP timeout to retire a thread is hardcoded to 2S, why isn't this at least configurable via a System property is a bit of a mystery to me... I am a big fan of minimalistic configurability, but in case of FJP it is a bit extreme... The cost of creating a thread can be significant if one factors all the thread local caches that are typically created by the average Server software and which are lost when the thread is brought down... so it would be useful if one could specify a minimal number of threads to be kept alive and a custom timeout... I understand that you can fork the FJP code, but if you need only a thread pool you can use spf4j thread pool instead... and you can even choose to spin. 

SPF4J thread pool will schedule the tasks in FIFO order to worker threads who are picked in a LIFO order... 

On the performance side, in some of the tests FJP is faster that spf4j in others it is significantly slower... which means that my tests need improvement...  

  

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