[concurrency-interest] ThreadPoolExecutor implement question!

[yangjs]

 thx, 

  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 ? 

  Hanson


  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.

    Cheers,
    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!


      hi,all

      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;
              mainLock.lock();
              try {
                  // some code 
              } finally {
                  mainLock.unlock();
              }

      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,

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