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Re: java thread question

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Eric Sosman於 2014年4月3日星期四UTC+8下午11時43分54秒寫道：
> On 4/3/2014 10:51 AM, mcheung63@gmail.com wrote:
> 
> > Hi All
> 
> >      I have write a little program to keep running some threads, i got questions:
> 
> > 1) All threads are running within one process (ps command show me this), but it will eat up all cpu cores, how to explain this?
> 
> 
> 
>      What needs explanation?  That is, what puzzles you?  The *purpose*
> 
> of threads is to break up a large task into smaller pieces and let them
> 
> execute in parallel; you *want* those smaller pieces to use whatever
> 
> machine resources they can get.
> 
> 
> 
> > 2) If thread will eat multiple cpu core, why wee need fork/join in java?
> 
> 
> 
>      (I assume you're referring to java.util.concurrent.ForkJoinTask.)
> 
> If your large task subdivides into a million smaller pieces, you don't
> 
> want to try running each piece in a separate thread.  A thread is
> 
> "lighter-weight" than a full-scale process, but its weight is non-zero:
> 
> There's a stack, there's other CPU context, there's management overhead
> 
> like schedulers and garbage collectors, ...  When you multiply this by
> 
> a million, or even by several thousand, your system will collapse under
> 
> the load, most probably by throwing an OutOfMemoryException.
> 
> 
> 
>      That's where ForkJoinPool and ForkJoinTask come in.  The pool runs
> 
> a manageable number of long-lived threads, and each thread executes many
> 
> ForkJoinTasks in succession.  (There are additional intricacies, but
> 
> that's the essence.)  You don't have to create, start, shut down, and
> 
> garbage-collect a million threads to get the million sub-tasks done.
> 
> 
> 
> -- 
> 
> Eric Sosman
> 
> esosman@comcast-dot-net.invalid

Thanks, that mean the advantage of fork/join is : I don't need to manage a thread pool by myself.

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Thread

java thread question mcheung63@gmail.com - 2014-04-03 07:51 -0700
  Re: java thread question Nigel Wade <nmw@ion.le.ac.uk> - 2014-04-03 16:17 +0100
  Re: java thread question Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-04-03 11:43 -0400
    Re: java thread question mcheung63@gmail.com - 2014-04-03 15:10 -0700
      Re: java thread question Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-04-03 19:00 -0400
        Re: java thread question mcheung63@gmail.com - 2014-04-04 09:29 -0700
  Re: java thread question Roedy Green <see_website@mindprod.com.invalid> - 2014-04-03 17:52 -0700
    Re: java thread question mcheung63@gmail.com - 2014-04-04 09:31 -0700
    Re: java thread question Roedy Green <see_website@mindprod.com.invalid> - 2014-04-04 09:49 -0700
      Re: java thread question mcheung63@gmail.com - 2014-04-05 09:41 -0700

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