: That is not my understanding. My understanding is that volatile just ensures : the JIT always accesses the var in order - prevents some compiler : optimizations - where as synchronized needs to acquire the lock. (There were : discussions regarding having volatile create synchronized accessors behind : the scenes - but I don't think that semantic was ever agreed upon). : : That coupled with using primitives (to avoid the early memory alloc - since : primitives are allocated on the stack), allows the double-locked : synchronization to work (at least that is my understanding).
perhaps, I'm not expert i was just going based on what i've read, and aparently i forgot to paste the URL in my last email... http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#dcl : -----Original Message----- : From: Chris Hostetter [mailto:[EMAIL PROTECTED] : Sent: Wednesday, May 10, 2006 12:51 AM : To: Lucene Dev : Subject: RE: Multiple threads searching in Lucene and the synchronized : issue. -- solution attached. : : : : : I think you could use a volatile primitive boolean to control whether or : not : : the index needs to be read, and also mark the index data volatile and it : : SHOULD PROBABLY work. : : : : But as stated, I don't think the performance difference is worth it. : : My understanding is: : 1) volatile will only help as of java 1.5 ... lucene targets 1.4 : compatibility. : 2) in 1.5, volatile is basically just as expensive as synchronized. : : : I met these problem before indeed.The compiler did something optimized for : : me that was bad for me when I see the byte-codes. : : When I'm using a function local variable, m_indexTerms and in JDK1.5.06, : it : : seems ok. : : Whether it will break in other environments, I still don't know about it. : : The dangerous thing is that even if the byte code looks okay, and if it : works okay today, your app could run for a while and then all of the : sudden it could stop working because of the order the threads are run, or : becuase of an optimization the JVM applies on the fly. -Hoss --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
