From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id 2D7923A19830 for ; Fri, 13 Nov 2020 08:14:22 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 2D7923A19830 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EB9F7142F for ; Fri, 13 Nov 2020 00:14:21 -0800 (PST) Received: from localhost (e121540-lin.manchester.arm.com [10.32.98.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 93FA83F718 for ; Fri, 13 Nov 2020 00:14:21 -0800 (PST) From: Richard Sandiford To: gcc-patches@gcc.gnu.org Mail-Followup-To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com Subject: [06/23] Add an RAII class for managing obstacks References: Date: Fri, 13 Nov 2020 08:14:19 +0000 In-Reply-To: (Richard Sandiford's message of "Fri, 13 Nov 2020 08:10:54 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-12.6 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, KAM_SHORT, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Nov 2020 08:14:23 -0000 This patch adds an RAII class for managing the lifetimes of objects on an obstack. See the comments in the patch for more details and example usage. gcc/ * obstack-utils.h: New file. --- gcc/obstack-utils.h | 86 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 gcc/obstack-utils.h diff --git a/gcc/obstack-utils.h b/gcc/obstack-utils.h new file mode 100644 index 00000000000..ee389f89923 --- /dev/null +++ b/gcc/obstack-utils.h @@ -0,0 +1,86 @@ +// Obstack-related utilities. +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of GCC. +// +// GCC is free software; you can redistribute it and/or modify it under +// the terms of the GNU General Public License as published by the Free +// Software Foundation; either version 3, or (at your option) any later +// version. +// +// GCC is distributed in the hope that it will be useful, but WITHOUT ANY +// WARRANTY; without even the implied warranty of MERCHANTABILITY or +// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +// for more details. +// +// You should have received a copy of the GNU General Public License +// along with GCC; see the file COPYING3. If not see +// . + +#ifndef GCC_OBSTACK_UTILS_H +#define GCC_OBSTACK_UTILS_H + +// This RAII class automatically frees memory allocated on an obstack, +// unless told not to via keep (). It automatically converts to an +// obstack, so it can (optionally) be used in place of the obstack +// to make the scoping clearer. For example: +// +// obstack_watermark watermark (ob); +// auto *ptr1 = XOBNEW (watermark, struct1); +// if (...) +// // Frees ptr1. +// return false; +// +// auto *ptr2 = XOBNEW (watermark, struct2); +// if (...) +// // Frees ptr1 and ptr2. +// return false; +// +// // Retains ptr1 and ptr2. +// watermark.keep (); +// +// auto *ptr3 = XOBNEW (watermark, struct3); +// if (...) +// // Frees ptr3. +// return false; +// +// // Retains ptr3 (in addition to ptr1 and ptr2 above). +// watermark.keep (); +// return true; +// +// The move constructor makes it possible to transfer ownership to a caller: +// +// obstack_watermark +// foo () +// { +// obstack_watermark watermark (ob); +// ... +// return watermark; +// } +// +// void +// bar () +// { +// // Inherit ownership of everything that foo allocated. +// obstack_watermark watermark = foo (); +// ... +// } +class obstack_watermark +{ +public: + obstack_watermark (obstack *ob) : m_obstack (ob) { keep (); } + constexpr obstack_watermark (obstack_watermark &&) = default; + ~obstack_watermark () { obstack_free (m_obstack, m_start); } + + operator obstack *() const { return m_obstack; } + void keep () { m_start = XOBNEWVAR (m_obstack, char, 0); } + +private: + DISABLE_COPY_AND_ASSIGN (obstack_watermark); + +protected: + obstack *m_obstack; + char *m_start; +}; + +#endif -- 2.17.1