{"id":267,"url":"https://patchwork.libcamera.org/api/patches/267/?format=json","web_url":"https://patchwork.libcamera.org/patch/267/","project":{"id":1,"url":"https://patchwork.libcamera.org/api/projects/1/?format=json","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Documentation: coding_style: Add object ownership rules","commit_ref":null,"pull_url":null,"state":"superseded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=json","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=json","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":"","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 ;\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 ;\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 ","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":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","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 \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"]}