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{ "id": 9706, "url": "https://patchwork.libcamera.org/api/patches/9706/?format=api", "web_url": "https://patchwork.libcamera.org/patch/9706/", "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": "<20200922133537.258098-2-paul.elder@ideasonboard.com>", "date": "2020-09-22T13:35:00", "name": "[libcamera-devel,01/38] Documentation: coding-style: Document global variable guidelines", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": false, "hash": "d27927d996e61b66e0d46786049ca9064837e2b4", "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/9706/mbox/", "series": [ { "id": 1309, "url": "https://patchwork.libcamera.org/api/series/1309/?format=api", "web_url": "https://patchwork.libcamera.org/project/libcamera/list/?series=1309", "date": "2020-09-22T13:34:59", "name": "IPA isolation implementation", "version": 1, "mbox": "https://patchwork.libcamera.org/series/1309/mbox/" } ], "comments": "https://patchwork.libcamera.org/api/patches/9706/comments/", "check": "pending", "checks": "https://patchwork.libcamera.org/api/patches/9706/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 B110EC3B5B\n\tfor <parsemail@patchwork.libcamera.org>;\n\tTue, 22 Sep 2020 13:36:00 +0000 (UTC)", "from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 7B04662FDF;\n\tTue, 22 Sep 2020 15:36:00 +0200 (CEST)", "from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id B8A5F6036A\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tTue, 22 Sep 2020 15:35:59 +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 0C981555;\n\tTue, 22 Sep 2020 15:35:52 +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=\"vm5yfgT1\"; dkim-atps=neutral", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1600781754;\n\tbh=8uBsm2yGBXpzYPeq+AyKaw7ypGh+S7GYWG6E+RMnhrk=;\n\th=From:To:Cc:Subject:Date:In-Reply-To:References:From;\n\tb=vm5yfgT1a78qiqWOeKSRSe1Ea9xKi8bXJxKy1CizNd0PnXi5dx5pujTxAnXBXL/U1\n\t93GyxH1i3Us5VppwOkiB2RzVsC6mk8IwvKBSzjzG2kP3yk7KTzD4b328QhJ90/BHnq\n\t1a+h+8FiCZB9Tppbr1D5kRCWQsPun2fwI3oi8fkM=", "From": "Paul Elder <paul.elder@ideasonboard.com>", "To": "libcamera-devel@lists.libcamera.org", "Date": "Tue, 22 Sep 2020 22:35:00 +0900", "Message-Id": "<20200922133537.258098-2-paul.elder@ideasonboard.com>", "X-Mailer": "git-send-email 2.27.0", "In-Reply-To": "<20200922133537.258098-1-paul.elder@ideasonboard.com>", "References": "<20200922133537.258098-1-paul.elder@ideasonboard.com>", "MIME-Version": "1.0", "Subject": "[libcamera-devel] [PATCH 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>\n\n---\nNew in v2\n---\n Documentation/coding-style.rst | 15 +++++++++++++++\n 1 file changed, 15 insertions(+)", "diff": "diff --git a/Documentation/coding-style.rst b/Documentation/coding-style.rst\nindex 8af06d6a..967506db 100644\n--- a/Documentation/coding-style.rst\n+++ b/Documentation/coding-style.rst\n@@ -187,6 +187,21 @@ 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 initialization and destructions of global variables cannot be\n+reasonably controlled. This can cause problems (segfaults) when global\n+variables depend on each other, or when non-globals depend on globals.\n+For example, if the declaration of a global variable calls a constructor,\n+which calls into another global variable that has yet to be initialized, that\n+is likely to segfault.\n+\n+The best solution is to avoid global variables when possible. If required,\n+such as for implementing factories with auto-registration, avoid dependencies\n+by running the minimum amount of code in the constructor and destructor,\n+and move code that contains dependencies to a later point of time.\n+\n C Compatibility Headers\n ~~~~~~~~~~~~~~~~~~~~~~~\n \n", "prefixes": [ "libcamera-devel", "01/38" ] }