[concurrency-interest] ThreadPoolExecutor implement question!

yangjs yangjs at alibaba-inc.com
Thu Sep 21 04:48:21 EDT 2006


  I think if it does as David said, the optimization should happend  at compile time or  VM  runtime.
  it is a lower level skill for application developer. is right?

  ----- Original Message ----- 
  From: Hanson Char 
  To: dholmes at ieee.org 
  Cc: yangjs ; concurrency-interest at cs.oswego.edu 
  Sent: Thursday, September 21, 2006 4:03 PM
  Subject: Re: [concurrency-interest] ThreadPoolExecutor implement question!

  Is such optimization only applicable to final fields, but not instance member fields in general ?  Does this mean if a final field is accessed more than once in a method, it's always faster to assign it first to a local variable ? 


  On 9/21/06, David Holmes <dcholmes at optusnet.com.au> wrote:
    This was an optimization to work around a VM "glitch" which where the final field is loaded on each access (as a normal field would be) rather than loading it once. To avoid this it is copied to a local variable.

    David Holmes
      -----Original Message-----
      From: concurrency-interest-bounces at cs.oswego.edu [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of yangjs
      Sent: Thursday, 21 September 2006 4:30 PM
      To: concurrency-interest at cs.oswego.edu
      Subject: [concurrency-interest] ThreadPoolExecutor implement question!


      when I read ThreadPoolExecutor code ,I found it's declare the mainLock use "final" ,

        private final ReentrantLock mainLock = new ReentrantLock();

      many method use the lock  guarding state, use case as follow:

           final ReentrantLock mainLock = this.mainLock;
              try {
                  // some code 
              } finally {

      My question is the instance field already use "final" to mainLock, 
      why every method need copy mainLock reference to final  local var.

      this puzzle me,who can tell me why ? thanks.

      Best regards,

    Concurrency-interest mailing list
    Concurrency-interest at altair.cs.oswego.edu 

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