[{"id":29385,"web_url":"https://patchwork.libcamera.org/comment/29385/","msgid":"","date":"2024-05-02T10:27:09","subject":"Re: [PATCH v3] treewide: Query list of cameras just once","submitter":{"id":143,"url":"https://patchwork.libcamera.org/api/people/143/","name":"Jacopo Mondi","email":"jacopo.mondi@ideasonboard.com"},"content":"Hi Barnabás\n\nOn Mon, Apr 29, 2024 at 02:24:09PM GMT, Barnabás Pőcze wrote:\n> This is more efficient since only a single vector will be constructed,\n> and furthermore, it prevents the TOCTOU issue that might arise when\n> the list of cameras changes between the two queries.\n>\n> Signed-off-by: Barnabás Pőcze \n> ---\n>\n> changes in v3\n> * drop std::move() from this change\n> * extend note in documentation\n> * limit scope of `cameras` in `CameraSession::CameraSession()`\n>\n> changes in v2\n> * fix code block in documentation\n> * add comment noting that the camera may disappear\n>\n> ---\n> Documentation/guides/application-developer.rst | 12 +++++++-----\n> src/apps/cam/camera_session.cpp | 11 ++++++++---\n> src/gstreamer/gstlibcamerasrc.cpp | 5 +++--\n> 3 files changed, 18 insertions(+), 10 deletions(-)\n>\n> diff --git a/Documentation/guides/application-developer.rst b/Documentation/guides/application-developer.rst\n> index 9a9905b1..92e2a373 100644\n> --- a/Documentation/guides/application-developer.rst\n> +++ b/Documentation/guides/application-developer.rst\n> @@ -116,19 +116,21 @@ available.\n>\n> .. code:: cpp\n>\n> - if (cm->cameras().empty()) {\n> + auto cameras = cm->cameras();\n> + if (cameras.empty()) {\n> std::cout << \"No cameras were identified on the system.\"\n> << std::endl;\n> cm->stop();\n> return EXIT_FAILURE;\n> }\n>\n> - std::string cameraId = cm->cameras()[0]->id();\n> - camera = cm->get(cameraId);\n> + std::string cameraId = cameras[0]->id();\n>\n> + auto camera = cm->get(cameraId);\n> /*\n> - * Note that is equivalent to:\n> - * camera = cm->cameras()[0];\n> + * Note that `camera` may not compare equal to `cameras[0]`.\n> + * In fact, it might simply be a `nullptr`, as the particular\n> + * device might have disappeared (and reappeared) in the meantime.\n> */\n>\n> Once a camera has been selected an application needs to acquire an exclusive\n> diff --git a/src/apps/cam/camera_session.cpp b/src/apps/cam/camera_session.cpp\n> index 8447f932..334d2ed8 100644\n> --- a/src/apps/cam/camera_session.cpp\n> +++ b/src/apps/cam/camera_session.cpp\n> @@ -39,9 +39,14 @@ CameraSession::CameraSession(CameraManager *cm,\n> {\n> \tchar *endptr;\n> \tunsigned long index = strtoul(cameraId.c_str(), &endptr, 10);\n> -\tif (*endptr == '\\0' && index > 0 && index <= cm->cameras().size())\n> -\t\tcamera_ = cm->cameras()[index - 1];\n> -\telse\n> +\n> +\tif (*endptr == '\\0' && index > 0) {\n> +\t\tauto cameras = cm->cameras();\n> +\t\tif (index <= cameras.size())\n> +\t\t\tcamera_ = cameras[index - 1];\n> +\t}\n> +\n> +\tif (!camera_)\n> \t\tcamera_ = cm->get(cameraId);\n\nI guess this is ok even if the window between the two accesses to\ncameras() is really tiny and the optimization is relatively minor\n\n>\n> \tif (!camera_) {\n> diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp\n> index f015c6d2..4eddfa3e 100644\n> --- a/src/gstreamer/gstlibcamerasrc.cpp\n> +++ b/src/gstreamer/gstlibcamerasrc.cpp\n> @@ -385,13 +385,14 @@ gst_libcamera_src_open(GstLibcameraSrc *self)\n> \t\t\treturn false;\n> \t\t}\n> \t} else {\n> -\t\tif (cm->cameras().empty()) {\n> +\t\tauto cameras = cm->cameras();\n> +\t\tif (cameras.empty()) {\n> \t\t\tGST_ELEMENT_ERROR(self, RESOURCE, NOT_FOUND,\n> \t\t\t\t\t (\"Could not find any supported camera on this system.\"),\n> \t\t\t\t\t (\"libcamera::CameraMananger::cameras() is empty\"));\n> \t\t\treturn false;\n> \t\t}\n> -\t\tcam = cm->cameras()[0];\n> +\t\tcam = cameras[0];\n\nack!\n\nReviewed-by: Jacopo Mondi \n\n> \t}\n>\n> \tGST_INFO_OBJECT(self, \"Using camera '%s'\", cam->id().c_str());\n>\n> base-commit: fb74bb7df66b96dbe28702155cddfc96a1b30f78\n> --\n> 2.44.0\n>","headers":{"Return-Path":"","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 34CD3C3220\n\tfor ;\n\tThu, 2 May 2024 10:27:14 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 4B2FE63419;\n\tThu, 2 May 2024 12:27:13 +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 50A7F6340B\n\tfor ;\n\tThu, 2 May 2024 12:27:12 +0200 (CEST)","from ideasonboard.com (93-61-96-190.ip145.fastwebnet.it\n\t[93.61.96.190])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id B2D6D3A3;\n\tThu, 2 May 2024 12:26:14 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"JwCoh89q\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1714645574;\n\tbh=+Rm/Z9Chz+/bn7Cb03NdMOluOErjxPsz0x/Z8rIHuBk=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=JwCoh89q/vr02oehBvKLTD7HNL/29Kk3HEAGNvD3c/7AJGQgB/D6Q5wWLi5zTv72F\n\tEsHdbaBy/rIktidx1Jd4vkpF+X/nlv5n7iybTW/GCcUS+XrTJomIREhAgU/m1/9CGu\n\tKPCR4tsRlbgLIFF0jHYhr90I86TxYu1MNozoOstE=","Date":"Thu, 2 May 2024 12:27:09 +0200","From":"Jacopo Mondi ","To":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","Cc":"libcamera-devel@lists.libcamera.org","Subject":"Re: [PATCH v3] treewide: Query list of cameras just once","Message-ID":"","References":"<20240429142406.59765-1-pobrn@protonmail.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"<20240429142406.59765-1-pobrn@protonmail.com>","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":29434,"web_url":"https://patchwork.libcamera.org/comment/29434/","msgid":"<171509796175.1857112.2635291919652405354@ping.linuxembedded.co.uk>","date":"2024-05-07T16:06:01","subject":"Re: [PATCH v3] treewide: Query list of cameras just once","submitter":{"id":4,"url":"https://patchwork.libcamera.org/api/people/4/","name":"Kieran Bingham","email":"kieran.bingham@ideasonboard.com"},"content":"Quoting Barnabás Pőcze (2024-04-29 15:24:09)\n> This is more efficient since only a single vector will be constructed,\n> and furthermore, it prevents the TOCTOU issue that might arise when\n> the list of cameras changes between the two queries.\n> \n> Signed-off-by: Barnabás Pőcze \n> ---\n> \n> changes in v3\n> * drop std::move() from this change\n> * extend note in documentation\n> * limit scope of `cameras` in `CameraSession::CameraSession()`\n> \n> changes in v2\n> * fix code block in documentation\n> * add comment noting that the camera may disappear\n> \n> ---\n> Documentation/guides/application-developer.rst | 12 +++++++-----\n> src/apps/cam/camera_session.cpp | 11 ++++++++---\n> src/gstreamer/gstlibcamerasrc.cpp | 5 +++--\n> 3 files changed, 18 insertions(+), 10 deletions(-)\n> \n> diff --git a/Documentation/guides/application-developer.rst b/Documentation/guides/application-developer.rst\n> index 9a9905b1..92e2a373 100644\n> --- a/Documentation/guides/application-developer.rst\n> +++ b/Documentation/guides/application-developer.rst\n> @@ -116,19 +116,21 @@ available.\n> \n> .. code:: cpp\n> \n> - if (cm->cameras().empty()) {\n> + auto cameras = cm->cameras();\n> + if (cameras.empty()) {\n> std::cout << \"No cameras were identified on the system.\"\n> << std::endl;\n> cm->stop();\n> return EXIT_FAILURE;\n> }\n> \n> - std::string cameraId = cm->cameras()[0]->id();\n> - camera = cm->get(cameraId);\n> + std::string cameraId = cameras[0]->id();\n> \n> + auto camera = cm->get(cameraId);\n> /*\n> - * Note that is equivalent to:\n> - * camera = cm->cameras()[0];\n> + * Note that `camera` may not compare equal to `cameras[0]`.\n> + * In fact, it might simply be a `nullptr`, as the particular\n> + * device might have disappeared (and reappeared) in the meantime.\n> */\n\nWe should probably do the same corresponding change to simple-cam which\n'implements' this application-developer guide too when this is merged.\n\nBut as that's a separate repository - it's definitely a separate patch.\n\n> Once a camera has been selected an application needs to acquire an exclusive\n> diff --git a/src/apps/cam/camera_session.cpp b/src/apps/cam/camera_session.cpp\n> index 8447f932..334d2ed8 100644\n> --- a/src/apps/cam/camera_session.cpp\n> +++ b/src/apps/cam/camera_session.cpp\n> @@ -39,9 +39,14 @@ CameraSession::CameraSession(CameraManager *cm,\n> {\n> char *endptr;\n> unsigned long index = strtoul(cameraId.c_str(), &endptr, 10);\n> - if (*endptr == '\\0' && index > 0 && index <= cm->cameras().size())\n> - camera_ = cm->cameras()[index - 1];\n> - else\n> +\n> + if (*endptr == '\\0' && index > 0) {\n> + auto cameras = cm->cameras();\n> + if (index <= cameras.size())\n> + camera_ = cameras[index - 1];\n> + }\n> +\n> + if (!camera_)\n\nIs camera_ already initialised to false/0/null by default? Checking...\n\nIt's a shared_ptr, so I think we're good here.\n\nReviewed-by: Kieran Bingham \n\n> camera_ = cm->get(cameraId);\n> \n> if (!camera_) {\n> diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp\n> index f015c6d2..4eddfa3e 100644\n> --- a/src/gstreamer/gstlibcamerasrc.cpp\n> +++ b/src/gstreamer/gstlibcamerasrc.cpp\n> @@ -385,13 +385,14 @@ gst_libcamera_src_open(GstLibcameraSrc *self)\n> return false;\n> }\n> } else {\n> - if (cm->cameras().empty()) {\n> + auto cameras = cm->cameras();\n> + if (cameras.empty()) {\n> GST_ELEMENT_ERROR(self, RESOURCE, NOT_FOUND,\n> (\"Could not find any supported camera on this system.\"),\n> (\"libcamera::CameraMananger::cameras() is empty\"));\n> return false;\n> }\n> - cam = cm->cameras()[0];\n> + cam = cameras[0];\n> }\n> \n> GST_INFO_OBJECT(self, \"Using camera '%s'\", cam->id().c_str());\n> \n> base-commit: fb74bb7df66b96dbe28702155cddfc96a1b30f78\n> --\n> 2.44.0\n>","headers":{"Return-Path":"","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 C6370C3226\n\tfor ;\n\tTue, 7 May 2024 16:06:06 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id BC4DA6342D;\n\tTue, 7 May 2024 18:06:05 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id C8C80633E4\n\tfor ;\n\tTue, 7 May 2024 18:06:04 +0200 (CEST)","from pendragon.ideasonboard.com\n\t(cpc89244-aztw30-2-0-cust6594.18-1.cable.virginm.net [86.31.185.195])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 5A8FB3D5;\n\tTue, 7 May 2024 18:06:02 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"KP2XbdEk\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1715097962;\n\tbh=sTwQ8XDwb8f8XJiO6YLUCQyNKL1qwG5nDKa1TVwV+tY=;\n\th=In-Reply-To:References:Subject:From:To:Date:From;\n\tb=KP2XbdEkE+gRjLF7XUik+A4R1uAV1WA8JGhE0tIZtUiz8YT2FHe9EWVsI8s2do7oa\n\tLE6XCWaB3RpgT+UebD0ALDoS0XWvK5i6gsAUaoi+uWXL12z1Kdna9VITZ4/ZGaVq+f\n\tLV34oCQyzcUBzK9u3U6fNsxZsiTCywPgN4A7m3iU=","Content-Type":"text/plain; charset=\"utf-8\"","MIME-Version":"1.0","Content-Transfer-Encoding":"quoted-printable","In-Reply-To":"<20240429142406.59765-1-pobrn@protonmail.com>","References":"<20240429142406.59765-1-pobrn@protonmail.com>","Subject":"Re: [PATCH v3] treewide: Query list of cameras just once","From":"Kieran Bingham ","To":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ,\n\tlibcamera-devel@lists.libcamera.org","Date":"Tue, 07 May 2024 17:06:01 +0100","Message-ID":"<171509796175.1857112.2635291919652405354@ping.linuxembedded.co.uk>","User-Agent":"alot/0.10","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":29538,"web_url":"https://patchwork.libcamera.org/comment/29538/","msgid":"<-K0V4eL1IHMBdwMXHE_12thVBKf1B_j5eScJEYh8RkYdpN8XrbeztNbAMToFYHZhlg2rQn272QhBh3mGF74aPHh83sEOHf1CObYZUeoZhPU=@protonmail.com>","date":"2024-05-14T21:57:19","subject":"Re: [PATCH v3] treewide: Query list of cameras just once","submitter":{"id":133,"url":"https://patchwork.libcamera.org/api/people/133/","name":"Pőcze Barnabás","email":"pobrn@protonmail.com"},"content":"Hi\n\n\n2024. április 29., hétfő 16:24 keltezéssel, Barnabás Pőcze írta:\n\n> This is more efficient since only a single vector will be constructed,\n> and furthermore, it prevents the TOCTOU issue that might arise when\n> the list of cameras changes between the two queries.\n> \n> [...]\n\n\nAre there any additional changes I should make?\n\n\nRegards,\nBarnabás Pőcze","headers":{"Return-Path":"","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 234C7BDE6B\n\tfor ;\n\tTue, 14 May 2024 21:57:26 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 2DDFC63480;\n\tTue, 14 May 2024 23:57:25 +0200 (CEST)","from mail-4316.protonmail.ch (mail-4316.protonmail.ch\n\t[185.70.43.16])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 1F6EE63469\n\tfor ;\n\tTue, 14 May 2024 23:57:24 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; 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