From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 69010 invoked by alias); 19 Jun 2017 14:26:25 -0000 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 Received: (qmail 68954 invoked by uid 89); 19 Jun 2017 14:26:24 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_HELO_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 19 Jun 2017 14:26:23 +0000 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A9A8880460; Mon, 19 Jun 2017 14:26:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A9A8880460 Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=palves@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com A9A8880460 Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DD00174AD; Mon, 19 Jun 2017 14:26:23 +0000 (UTC) Subject: Re: [PATCH v6] C++ify gdb/common/environ.c To: Simon Marchi , Sergio Durigan Junior References: <20170413040455.23996-1-sergiodj@redhat.com> <20170619043531.32394-1-sergiodj@redhat.com> <87k248y3zp.fsf@redhat.com> <8aabc6fabb04f4e3e8b08e6fa1b0eacc@polymtl.ca> Cc: GDB Patches From: Pedro Alves Message-ID: <816a5744-b3b4-855c-5f2e-4c9f0d255512@redhat.com> Date: Mon, 19 Jun 2017 14:26:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <8aabc6fabb04f4e3e8b08e6fa1b0eacc@polymtl.ca> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2017-06/txt/msg00516.txt.bz2 On 06/19/2017 08:18 AM, Simon Marchi wrote: > On 2017-06-19 06:51, Sergio Durigan Junior wrote: >> On Monday, June 19 2017, I wrote: >> >>> [...] >>> -struct gdb_environ * >>> -make_environ (void) >>> +gdb_environ & >>> +gdb_environ::operator= (gdb_environ &&e) >>> { >>> - struct gdb_environ *e; >>> - >>> - e = XNEW (struct gdb_environ); >>> - >>> - e->allocated = 10; >>> - e->vector = (char **) xmalloc ((e->allocated + 1) * sizeof (char *)); >>> - e->vector[0] = 0; >>> - return e; >>> -} >>> - >>> -/* Free an environment and all the strings in it. */ >>> - >>> -void >>> -free_environ (struct gdb_environ *e) >>> -{ >>> - char **vector = e->vector; >>> - >>> - while (*vector) >>> - xfree (*vector++); >>> - >>> - xfree (e->vector); >>> - xfree (e); >>> + clear (); >>> + m_environ_vector = std::move (e.m_environ_vector); >>> + return *this; >>> } >> >> I should probably do an m_environ_vector.clear () before doing the >> std::move, because the vector will contain the NULL element. I'll make >> sure to do this before I push the patch. > > From what I saw stepping in the STL code, the previous content of the > moved-to vector is cleared, as if you called .clear(). In > _M_move_assign, it moves the old content to a temporary, stack allocated > vector, which gets cleared when exiting that function. So I think it's > not necessary. Right, m_environ_vector.clear() is not necessary. Note that this move assignment (and likewise the move ctor) leaves the source vector empty, which violates the "there's always a NULL entry at the end" invariant. That's OK if the only thing we want to support of moved-from gdb_environ objects is destroying them, but please do document that. Otherwise, people assuming the standard library's rule, may be confused/surprised, into thinking that this, e.g., should work: gdb_environ env1; env1.set ("VAR1", "value1"); gdb_environ env2; env2 = std::move (env1); // env1 has no NULL terminator after this. env1.set ("VAR1", "value2); // whoops. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 17.6.5.15 Moved-from state of library types [lib.types.movedfrom] Objects of types defined in the C++ standard library may be moved from (12.8). Move operations may be explicitly specified or implicitly generated. Unless otherwise specified, such moved-from objects shall be placed in a valid but unspecified state. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Thanks, Pedro Alves