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{ "id": 267, "url": "https://patchwork.libcamera.org/api/patches/267/?format=api", "web_url": "https://patchwork.libcamera.org/patch/267/", "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": "<20190117235916.1906-2-laurent.pinchart@ideasonboard.com>", "date": "2019-01-17T23:59:13", "name": "[libcamera-devel,1/4] Documentation: coding_style: Add object ownership rules", "commit_ref": null, "pull_url": null, "state": "superseded", "archived": false, "hash": "0b42f126f181b9cff439fd4b85da718bc1377588", "submitter": { "id": 2, "url": "https://patchwork.libcamera.org/api/people/2/?format=api", "name": "Laurent Pinchart", "email": "laurent.pinchart@ideasonboard.com" }, "delegate": null, "mbox": "https://patchwork.libcamera.org/patch/267/mbox/", "series": [ { "id": 90, "url": "https://patchwork.libcamera.org/api/series/90/?format=api", "web_url": "https://patchwork.libcamera.org/project/libcamera/list/?series=90", "date": "2019-01-17T23:59:12", "name": "Object lifetime management", "version": 1, "mbox": "https://patchwork.libcamera.org/series/90/mbox/" } ], "comments": "https://patchwork.libcamera.org/api/patches/267/comments/", "check": "pending", "checks": "https://patchwork.libcamera.org/api/patches/267/checks/", "tags": {}, "headers": { "Return-Path": "<laurent.pinchart@ideasonboard.com>", "Received": [ "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 8E04260C98\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tFri, 18 Jan 2019 00:59:20 +0100 (CET)", "from pendragon.bb.dnainternet.fi\n\t(dfj612yhrgyx302h3jwwy-3.rev.dnainternet.fi\n\t[IPv6:2001:14ba:21f5:5b00:ce28:277f:58d7:3ca4])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 213CAD4B\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tFri, 18 Jan 2019 00:59:20 +0100 (CET)" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1547769560;\n\tbh=do84Lty8iKl/q6ouiHDarTfhWNEcG7ZNcrkdQ8kkUj8=;\n\th=From:To:Subject:Date:In-Reply-To:References:From;\n\tb=Ka7AAMjdVc14NeJvHGGuDkaj8nni/X7P1YbcvRBLwsIxvstAR9jHvy5QQ1bAmlQGz\n\tntvh9ljR+5egxAf7qlWJzSi8JqgxsRrK1rIHgTlW3Grmcy+55YuD6yeqwF5TJEYPT5\n\txujcKYDekGDYPHcX9ykg5qeFfa4SQwCwH9nm9Yrc=", "From": "Laurent Pinchart <laurent.pinchart@ideasonboard.com>", "To": "libcamera-devel@lists.libcamera.org", "Date": "Fri, 18 Jan 2019 01:59:13 +0200", "Message-Id": "<20190117235916.1906-2-laurent.pinchart@ideasonboard.com>", "X-Mailer": "git-send-email 2.19.2", "In-Reply-To": "<20190117235916.1906-1-laurent.pinchart@ideasonboard.com>", "References": "<20190117235916.1906-1-laurent.pinchart@ideasonboard.com>", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "Subject": "[libcamera-devel] [PATCH 1/4] Documentation: coding_style: Add\n\tobject ownership rules", "X-BeenThere": "libcamera-devel@lists.libcamera.org", "X-Mailman-Version": "2.1.23", "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>", "X-List-Received-Date": "Thu, 17 Jan 2019 23:59:20 -0000" }, "content": "Object ownership is a complex topic that can lead to many issues, from\nmemory leak to crashes. Document the rules that libcamera enforces to\nmake object ownership tracking explicit.\n\nThis is a first version of the rules and is expected to be expanded as\nthe library is developed.\n\nSigned-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>\n---\n Documentation/coding-style.rst | 62 ++++++++++++++++++++++++++++++++++\n 1 file changed, 62 insertions(+)", "diff": "diff --git a/Documentation/coding-style.rst b/Documentation/coding-style.rst\nindex f8d2fdfeda8e..f77325239bfa 100644\n--- a/Documentation/coding-style.rst\n+++ b/Documentation/coding-style.rst\n@@ -81,6 +81,68 @@ C++-11-specific features:\n overused.\n * Variadic class and function templates\n \n+Object Ownership\n+~~~~~~~~~~~~~~~~\n+\n+libcamera creates and destroys many objects at runtime, for both objects\n+internal to the library and objects exposed to the user. To guarantee proper\n+operation without use after free, double free or memory leaks, knowing who owns\n+each object at any time is crucial. The project has enacted a set of rules to\n+make object ownership tracking as explicit and fool-proof as possible.\n+\n+In the context of this section, the terms object and instance are used\n+interchangeably and both refer to an instance of a class. The term reference\n+refers to both C++ references and C++ pointers in their capacity to refer to an\n+object. Passing a reference means offering a way to a callee to obtain a\n+reference to an object that the caller has a valid reference to. Borrowing a\n+reference means using a reference passed by a caller without ownership transfer\n+based on the assumption that the caller guarantees the validate of the\n+reference for the duration of the operation that borrows the reference.\n+\n+#. Single Owner Objects\n+\n+ * By default an object has a single owner at any time.\n+ * References to a single owner object can be borrowed by passing them from\n+ the owner to the borrower, providing that\n+\n+ * the owner guarantees the validity of the reference for the whole duration\n+ of borrowing, and\n+ * the borrower doesn't access the reference after the end of the borrowing.\n+\n+ When borrowing from caller to callee for the duration of a function call,\n+ this implies that the callee shall not keep any stored reference after it\n+ returns. These rules applies to the callee and all the functions it calls,\n+ directly or indirectly.\n+ * When the object doesn't need to be modified and may not be null, borrowed\n+ references are passed as 'const &'.\n+ * When the object may be modified or can be null, borrowed references are\n+ passed as pointers. Unless otherwise specified, pointers passed to\n+ functions are considered as borrowed references valid for the duration of\n+ the function only.\n+ * Single ownership is emphasized as much as possible by storing the unique\n+ reference as a std::unique_ptr<>.\n+ * Ownership is transfered by passing the reference as a std::unique_ptr<>.\n+\n+#. Shared Objects\n+\n+ * Objects that may have multiple owners at a given time are called shared\n+ objects. They are reference-counted and live as long as any references to\n+ the object exist.\n+ * Shared objects are created with std::make_shared<> or\n+ std::allocate_shared<> an stored in an std::shared_ptr<>.\n+ * Borrowed references to shared objects are passed with the same rules as for\n+ single owner objects.\n+ * Ownership is shared by creating and passing copies of any valid\n+ std::shared_ptr<> reference. Ownership is released by destroying the\n+ corresponding std::shared_ptr<>.\n+\n+.. attention:: Long term borrowing of single owner objects is allowed. Example\n+ use cases are implementation of the singleton pattern (where the singleton\n+ guarantees the validity of the reference forever), or returning references\n+ to global objects whose lifetime matches the lifetime of the application. As\n+ long term borrowing isn't marked through language constructs, it shall be\n+ documented explicitly in details in the API.\n+\n \n Tools\n -----\n", "prefixes": [ "libcamera-devel", "1/4" ] }