From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5635 invoked by alias); 4 Oct 2011 15:45:20 -0000 Received: (qmail 5624 invoked by uid 22791); 4 Oct 2011 15:45:18 -0000 X-SWARE-Spam-Status: No, hits=-7.2 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 04 Oct 2011 15:44:58 +0000 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p94FiuEP025732 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Tue, 4 Oct 2011 11:44:56 -0400 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id p94Fiux5012435; Tue, 4 Oct 2011 11:44:56 -0400 Received: from barimba (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id p94Fit27015273; Tue, 4 Oct 2011 11:44:55 -0400 From: Tom Tromey To: Paul Koning Cc: gdb-patches@sourceware.org Subject: Re: Python: fetch value when building gdb.Value object References: <36B29E9D-F2B3-446F-AF8A-97254A3AAEE2@comcast.net> Date: Tue, 04 Oct 2011 15:45:00 -0000 In-Reply-To: <36B29E9D-F2B3-446F-AF8A-97254A3AAEE2@comcast.net> (Paul Koning's message of "Wed, 21 Sep 2011 11:54:01 -0400") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2011-10/txt/msg00087.txt.bz2 >>>>> "Paul" == Paul Koning writes: Paul> GDB sometimes lazily evaluates operations on values, and Paul> py-value.c wasn't taking that into account. The result was that Paul> assigning a Value object to a Python variable could assign a lazy Paul> value, so that any errors in accessing the data would occur at a Paul> later time, and sometimes would not be handled right. (For Paul> example, the "nonzero" operation would fail without a Python Paul> traceback.) The attached patch cures this by fetching any lazy Paul> values when the gdb.Value object is built, and adds a test in the Paul> testcases to verify this. Paul> Ok to submit? I am not convinced that this is the right approach. I think it would probably be better to expose the laziness to the Python programmer -- via a new attribute and a new method to un-lazy the object. The reason is that eager fetching can be very expensive. E.g., you may construct an intermediate value that is a very large array, but intend only to reference a few elements. This can be done efficiently by gdb, but eager fetching will defeat that. Tom