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{ "id": 9910, "url": "https://patchwork.libcamera.org/api/patches/9910/?format=api", "web_url": "https://patchwork.libcamera.org/patch/9910/", "project": { "id": 1, "url": "https://patchwork.libcamera.org/api/projects/1/?format=api", "name": "libcamera", "link_name": "libcamera", "list_id": "libcamera_core", "list_email": "libcamera-devel@lists.libcamera.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20201002143154.468162-2-paul.elder@ideasonboard.com>", "date": "2020-10-02T14:31:17", "name": "[libcamera-devel,v3,01/38] Documentation: coding-style: Document global variable guidelines", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": false, "hash": "dedff91ce860d1de7790d8120d4fa9c451c48b2b", "submitter": { "id": 17, "url": "https://patchwork.libcamera.org/api/people/17/?format=api", "name": "Paul Elder", "email": "paul.elder@ideasonboard.com" }, "delegate": null, "mbox": "https://patchwork.libcamera.org/patch/9910/mbox/", "series": [ { "id": 1348, "url": "https://patchwork.libcamera.org/api/series/1348/?format=api", "web_url": "https://patchwork.libcamera.org/project/libcamera/list/?series=1348", "date": "2020-10-02T14:31:16", "name": "IPA isolation implementation", "version": 3, "mbox": "https://patchwork.libcamera.org/series/1348/mbox/" } ], "comments": "https://patchwork.libcamera.org/api/patches/9910/comments/", "check": "pending", "checks": "https://patchwork.libcamera.org/api/patches/9910/checks/", "tags": {}, "headers": { "Return-Path": "<libcamera-devel-bounces@lists.libcamera.org>", "X-Original-To": "parsemail@patchwork.libcamera.org", "Delivered-To": "parsemail@patchwork.libcamera.org", "Received": [ "from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id CA811C3B5C\n\tfor <parsemail@patchwork.libcamera.org>;\n\tFri, 2 Oct 2020 14:32:09 +0000 (UTC)", "from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 864E663B6A;\n\tFri, 2 Oct 2020 16:32:09 +0200 (CEST)", "from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id D954763B59\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tFri, 2 Oct 2020 16:32:07 +0200 (CEST)", "from pyrite.rasen.tech (unknown\n\t[IPv6:2400:4051:61:600:2c71:1b79:d06d:5032])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id ABF36528;\n\tFri, 2 Oct 2020 16:32:05 +0200 (CEST)" ], "Authentication-Results": "lancelot.ideasonboard.com;\n\tdkim=fail reason=\"signature verification failed\" (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"OklxCzZ6\"; dkim-atps=neutral", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1601649127;\n\tbh=u2gyxacPihn9ZLzANFT9dxHtFdESh1oXWYz2HI8cvTg=;\n\th=From:To:Cc:Subject:Date:In-Reply-To:References:From;\n\tb=OklxCzZ6Z2k6+yDqawnnKD+UHf6iF1Si0gZXwUx2bxVOscY5yqQHlPKj81lVIiz7F\n\t2Fa6qI19h9t9vN6he7qgfPnSFl5vaXNzMptlsGG6qwL7PmrEsZciGwbzSZi8r6ZG1v\n\tBBtXLQOSvObSjA1mj/FgI/KcvAPivcE/vKr6P5/I=", "From": "Paul Elder <paul.elder@ideasonboard.com>", "To": "libcamera-devel@lists.libcamera.org", "Date": "Fri, 2 Oct 2020 23:31:17 +0900", "Message-Id": "<20201002143154.468162-2-paul.elder@ideasonboard.com>", "X-Mailer": "git-send-email 2.27.0", "In-Reply-To": "<20201002143154.468162-1-paul.elder@ideasonboard.com>", "References": "<20201002143154.468162-1-paul.elder@ideasonboard.com>", "MIME-Version": "1.0", "Subject": "[libcamera-devel] [PATCH v3 01/38] Documentation: coding-style:\n\tDocument global variable guidelines", "X-BeenThere": "libcamera-devel@lists.libcamera.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<libcamera-devel.lists.libcamera.org>", "List-Unsubscribe": "<https://lists.libcamera.org/options/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=unsubscribe>", "List-Archive": "<https://lists.libcamera.org/pipermail/libcamera-devel/>", "List-Post": "<mailto:libcamera-devel@lists.libcamera.org>", "List-Help": "<mailto:libcamera-devel-request@lists.libcamera.org?subject=help>", "List-Subscribe": "<https://lists.libcamera.org/listinfo/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=subscribe>", "Content-Type": "text/plain; charset=\"us-ascii\"", "Content-Transfer-Encoding": "7bit", "Errors-To": "libcamera-devel-bounces@lists.libcamera.org", "Sender": "\"libcamera-devel\" <libcamera-devel-bounces@lists.libcamera.org>" }, "content": "Document the issue related to global variable dependencies and how to\navoid them.\n\nSigned-off-by: Paul Elder <paul.elder@ideasonboard.com>\nReviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>\n\n---\nChanges in v3:\n- add more detail\n\nNew in v2\n---\n Documentation/coding-style.rst | 19 +++++++++++++++++++\n 1 file changed, 19 insertions(+)", "diff": "diff --git a/Documentation/coding-style.rst b/Documentation/coding-style.rst\nindex 8af06d6a..71d5c0b2 100644\n--- a/Documentation/coding-style.rst\n+++ b/Documentation/coding-style.rst\n@@ -187,6 +187,25 @@ These rules match the `object ownership rules from the Chromium C++ Style Guide`\n long term borrowing isn't marked through language constructs, it shall be\n documented explicitly in details in the API.\n \n+Global Variables\n+~~~~~~~~~~~~~~~~\n+\n+The order of initializations and destructions of global variables cannot be\n+reasonably controlled. This can cause problems (including segfaults) when global\n+variables depend on each other, directly or indirectly. For example, if the\n+declaration of a global variable calls a constructor which uses another global\n+variable that hasn't been initialized yet, incorrect behavior is likely.\n+Similar issues may occur when the library is unloaded and global variables are\n+destroyed.\n+\n+Global variables that are statically initialized and have trivial destructors\n+(such as an integer constant) do not cause any issue. Other global variables\n+shall be avoided when possible, but are allowed when required (for instance to\n+implement factories with auto-registration). They shall not depend on any other\n+global variable, should run a minimal amount of code in the constructor and\n+destructor, and code that contains dependencies should be moved to a later\n+point in time. \n+\n C Compatibility Headers\n ~~~~~~~~~~~~~~~~~~~~~~~\n \n", "prefixes": [ "libcamera-devel", "v3", "01/38" ] }