From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Shawn O. Pearce" Subject: Re: [JGIT PATCH v2] FindBugs: don't use new String(String) in RefDatabase Date: Tue, 21 Jul 2009 08:03:37 -0700 Message-ID: <20090721150337.GP11191@spearce.org> References: <49C20D4E.5020203@gmail.com> <551f769b0907130107j51d32e4er54e125f9dc61dd80@mail.gmail.com> <20090713145308.GI11191@spearce.org> <200907211650.36831.robin.rosenberg.lists@dewire.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Yann Simon , git To: Robin Rosenberg X-From: git-owner@vger.kernel.org Tue Jul 21 17:04:01 2009 Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1MTGsq-00084m-Vk for gcvg-git-2@gmane.org; Tue, 21 Jul 2009 17:04:01 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753161AbZGUPDh (ORCPT ); Tue, 21 Jul 2009 11:03:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753038AbZGUPDh (ORCPT ); Tue, 21 Jul 2009 11:03:37 -0400 Received: from george.spearce.org ([209.20.77.23]:52855 "EHLO george.spearce.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753017AbZGUPDh (ORCPT ); Tue, 21 Jul 2009 11:03:37 -0400 Received: by george.spearce.org (Postfix, from userid 1001) id 34682381FD; Tue, 21 Jul 2009 15:03:37 +0000 (UTC) Content-Disposition: inline In-Reply-To: <200907211650.36831.robin.rosenberg.lists@dewire.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: Robin Rosenberg wrote: > Shawn, any references for the ability of JIT's abilities to stack allocate in this context? For > me learning, will commit anyway. See [1] for example. I read a presentation from a HotSpot engineer at Sun a year or two ago that talked about it as a feature in the Sun Java 6 runtime, but I can't track that down now. Its a pretty simple concept. Folks realized that some types, e.g. StringBuilder, are often used only within a single stack frame, and that escape analysis can be used to prove that the StringBuilder instance is only visible within that stack frame. Doing a stack allocation instead of a heap allocation would allow the JVM to avoid creating unnecessary garbage. Ah, according to [2] the feature is only in 6u14 and later, and is an option you still need to enable on the command line. But its the direction the Sun JVM is going. I imagine it would be on by default in the future, various performance tests seem to indicate its a worthwhile optimization. [1] http://www.ibm.com/developerworks/java/library/j-jtp09275.html?ca=dgr-lnxw01JavaUrbanLegends [2] http://java.sun.com/javase/6/webnotes/6u14.html -- Shawn.