[{"id":3541,"web_url":"https://patchwork.libcamera.org/comment/3541/","msgid":"<20200120141844.lvgry2c2h5cui5ju@uno.localdomain>","date":"2020-01-20T14:18:44","subject":"Re: [libcamera-devel] [PATCH 10/19] libcamera: Define the threading\n\tmodel","submitter":{"id":3,"url":"https://patchwork.libcamera.org/api/people/3/","name":"Jacopo Mondi","email":"jacopo@jmondi.org"},"content":"Hi Laurent,\n\nOn Mon, Jan 20, 2020 at 02:24:28AM +0200, Laurent Pinchart wrote:\n> Document the design of libcamera's threading support, and prepare to\n> document thread-safety of classes and functions with a doxygen alias\n> command.\n>\n> Signed-off-by: Laurent Pinchart \n> ---\n> Documentation/Doxyfile.in | 4 +-\n> src/libcamera/thread.cpp | 82 +++++++++++++++++++++++++++++++++++++++\n> 2 files changed, 85 insertions(+), 1 deletion(-)\n>\n> diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile.in\n> index 8e6fbdbb92b6..734672ed15dc 100644\n> --- a/Documentation/Doxyfile.in\n> +++ b/Documentation/Doxyfile.in\n> @@ -239,7 +239,9 @@ TAB_SIZE = 4\n> # newlines (in the resulting output). You can put ^^ in the value part of an\n> # alias to insert a newline as if a physical newline was in the original file.\n>\n> -ALIASES =\n> +ALIASES = \"context=\\xrefitem context \\\"Thread Safety\\\" \\\"Thread Safety\\\"\"\n> +ALIASES += \"threadbound=\\ref thread-bound \\\"thread-bound\\\"\"\n> +ALIASES += \"threadsafe=\\ref thread-safe \\\"thread-safe\\\"\"\n>\n> # This tag can be used to specify a number of word-keyword mappings (TCL only).\n> # A mapping has the form \"name=value\". For example adding \"class=itcl::class\"\n> diff --git a/src/libcamera/thread.cpp b/src/libcamera/thread.cpp\n> index fe32cd677596..c1698d469a6c 100644\n> --- a/src/libcamera/thread.cpp\n> +++ b/src/libcamera/thread.cpp\n> @@ -19,6 +19,88 @@\n> #include \"log.h\"\n> #include \"message.h\"\n>\n> +/**\n> + * \\page thread Thread Support\n> + *\n> + * libcamera supports multi-threaded applications through a threading model that\n> + * sets precise rules to guarantee thread-safe usage of the API. Additionally,\n> + * libcamera makes internal use of threads, and offers APIs that simplify\n> + * interactions with application threads. Careful compliance with the threading\n> + * model will ensure avoidance of race conditions.\n> + *\n> + * \\section thread-reentrancy Reentrancy and Thread-Safety\n> + *\n> + * Through the documentation, several terms are used to define how classes and\n> + * their member functions can be used from multiple threads.\n> + *\n> + * - A **reentrant** function may be called simultaneously from multiple\n> + * threads if and only if each invocation uses a different instance of the\n> + * class. This is the default for all member functions not explictly marked\n> + * otherwise.\n> + *\n> + * - \\anchor thread-safe A **thread-safe** function may be called\n> + * simultaneously from multiple threads on the same instance of a class. A\n> + * thread-safe function is thus reentrant.\n> + *\n> + * - \\anchor thread-bound A **thread-bound** function may be called only from\n> + * the thread that the class instances lives in (see section \\ref\n> + * thread-objects). For instances of classes that do not derive from the\n> + * Object class, this is the thread in which the instance was created. A\n> + * thread-bound function is not thread-safe, and may or may not be reentrant.\n> + *\n> + * Neither reentrancy nor thread-safety, in this context, mean that a function\n> + * may be called simultaneously from the same thread, for instance from a\n> + * callback invoked by the the function. This may deadlock and isn't allowed\n\ns/the the/the\n\n> + * unless separately documented.\n> + *\n> + * A class is defined as reentrant, thread-safe or thread-bound if all its\n> + * member functions are reentrant, thread-safe or thread-bound respectively.\n> + * Some member functions may additionally be documented as having additional\n> + * thread-related attributes.\n> + *\n> + * Most classes are reentrant but not thread-safe, as making them fully\n> + * thread-safe would incur locking costs considered prohibitive for the\n> + * expected use cases.\n> + *\n> + * \\section thread-objects Threads and Objects\n> + *\n> + * Instances of the Object class and all its derived classes are thread-aware\n> + * and are bound to the thread they are created in. They are said to *live* in\n> + * a thread, and they interact with the event loop of their thread for the\n> + * purpose of message passing and signal delivery. Messages posted to the\n> + * object with Object::postMessage() will be delivered from the event loop of\n> + * the thread that the object lives in. Signals delivered to the object, unless\n> + * explicitly connected with ConnectionTypeDirect, will also be delivered from\n> + * the object thread's event loop.\n> + *\n> + * All Object instances created by libcamera are bound to an internal thread,\n> + * an applications don't need to provide an event loop to support them. Object\n> + * instances created by applications require an event loop. It is the\n> + * responsibility of applications to provide that event loop, either explicitly\n> + * through CameraManager::setEventDispatcher(), or by running the default event\n> + * loop provided by CameraManager::eventDispatcher() in their main thread. The\n> + * main thread of an application is the one that calls CameraManager::start().\n\nThis is all good, but I would move this before the thread-safety\npart..\n\nApart from that\nReviewed-by: Jacopo Mondi \n\nThanks\n j\n\n> + *\n> + * \\section thread-signals Threads and Signals\n> + *\n> + * When sent to a receiver that does not inherit from the Object class, signals\n> + * are delivered synchronously in the thread of the sender. When the receiver\n> + * inherits from the Object class, delivery is by default asynchronous if the\n> + * sender and receiver live in different threads. In that case, the signal is\n> + * posted to the receiver's message queue and will be delivered from the\n> + * receiver's event loop, running in the receiver's thread. This mechanism can\n> + * be overridden by selecting a different connection type when calling\n> + * Signal::connect().\n> + *\n> + * Asynchronous signal delivery is used internally in libcamera, but is also\n> + * available to applications if desired. To use this feature, applications\n> + * shall create receiver classes that inherit from the Object class, and\n> + * provide an event loop to the CameraManager as explained above. Note that\n> + * Object instance created by the application are limited to living in the\n> + * application's main thread. Creating Object instances from another thread of\n> + * an application causes undefined behaviour.\n> + */\n> +\n> /**\n> * \\file thread.h\n> * \\brief Thread support\n> --\n> Regards,\n>\n> Laurent Pinchart\n>\n> _______________________________________________\n> libcamera-devel mailing list\n> libcamera-devel@lists.libcamera.org\n> https://lists.libcamera.org/listinfo/libcamera-devel","headers":{"Return-Path":"","Received":["from relay9-d.mail.gandi.net (relay9-d.mail.gandi.net\n\t[217.70.183.199])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id B91C160804\n\tfor ;\n\tMon, 20 Jan 2020 15:16:13 +0100 (CET)","from uno.localdomain (93-34-114-233.ip49.fastwebnet.it\n\t[93.34.114.233]) (Authenticated sender: jacopo@jmondi.org)\n\tby relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 4D311FF808;\n\tMon, 20 Jan 2020 14:16:13 +0000 (UTC)"],"X-Originating-IP":"93.34.114.233","Date":"Mon, 20 Jan 2020 15:18:44 +0100","From":"Jacopo Mondi ","To":"Laurent Pinchart ","Cc":"libcamera-devel@lists.libcamera.org","Message-ID":"<20200120141844.lvgry2c2h5cui5ju@uno.localdomain>","References":"<20200120002437.6633-1-laurent.pinchart@ideasonboard.com>\n\t<20200120002437.6633-11-laurent.pinchart@ideasonboard.com>","MIME-Version":"1.0","Content-Type":"multipart/signed; micalg=pgp-sha256;\n\tprotocol=\"application/pgp-signature\"; boundary=\"6c5cxh4gh3lmzzqn\"","Content-Disposition":"inline","In-Reply-To":"<20200120002437.6633-11-laurent.pinchart@ideasonboard.com>","Subject":"Re: [libcamera-devel] [PATCH 10/19] libcamera: Define the threading\n\tmodel","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","X-List-Received-Date":"Mon, 20 Jan 2020 14:16:13 -0000"}},{"id":3571,"web_url":"https://patchwork.libcamera.org/comment/3571/","msgid":"<20200122153131.GR1124294@oden.dyn.berto.se>","date":"2020-01-22T15:31:31","subject":"Re: [libcamera-devel] [PATCH 10/19] libcamera: Define the threading\n\tmodel","submitter":{"id":5,"url":"https://patchwork.libcamera.org/api/people/5/","name":"Niklas Söderlund","email":"niklas.soderlund@ragnatech.se"},"content":"Hi Laurent,\n\nThanks for this grate write up.\n\nOn 2020-01-20 02:24:28 +0200, Laurent Pinchart wrote:\n> Document the design of libcamera's threading support, and prepare to\n> document thread-safety of classes and functions with a doxygen alias\n> command.\n> \n> Signed-off-by: Laurent Pinchart \n\nReviewed-by: Niklas Söderlund \n\n> ---\n> Documentation/Doxyfile.in | 4 +-\n> src/libcamera/thread.cpp | 82 +++++++++++++++++++++++++++++++++++++++\n> 2 files changed, 85 insertions(+), 1 deletion(-)\n> \n> diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile.in\n> index 8e6fbdbb92b6..734672ed15dc 100644\n> --- a/Documentation/Doxyfile.in\n> +++ b/Documentation/Doxyfile.in\n> @@ -239,7 +239,9 @@ TAB_SIZE = 4\n> # newlines (in the resulting output). You can put ^^ in the value part of an\n> # alias to insert a newline as if a physical newline was in the original file.\n> \n> -ALIASES =\n> +ALIASES = \"context=\\xrefitem context \\\"Thread Safety\\\" \\\"Thread Safety\\\"\"\n> +ALIASES += \"threadbound=\\ref thread-bound \\\"thread-bound\\\"\"\n> +ALIASES += \"threadsafe=\\ref thread-safe \\\"thread-safe\\\"\"\n> \n> # This tag can be used to specify a number of word-keyword mappings (TCL only).\n> # A mapping has the form \"name=value\". For example adding \"class=itcl::class\"\n> diff --git a/src/libcamera/thread.cpp b/src/libcamera/thread.cpp\n> index fe32cd677596..c1698d469a6c 100644\n> --- a/src/libcamera/thread.cpp\n> +++ b/src/libcamera/thread.cpp\n> @@ -19,6 +19,88 @@\n> #include \"log.h\"\n> #include \"message.h\"\n> \n> +/**\n> + * \\page thread Thread Support\n> + *\n> + * libcamera supports multi-threaded applications through a threading model that\n> + * sets precise rules to guarantee thread-safe usage of the API. Additionally,\n> + * libcamera makes internal use of threads, and offers APIs that simplify\n> + * interactions with application threads. Careful compliance with the threading\n> + * model will ensure avoidance of race conditions.\n> + *\n> + * \\section thread-reentrancy Reentrancy and Thread-Safety\n> + *\n> + * Through the documentation, several terms are used to define how classes and\n> + * their member functions can be used from multiple threads.\n> + *\n> + * - A **reentrant** function may be called simultaneously from multiple\n> + * threads if and only if each invocation uses a different instance of the\n> + * class. This is the default for all member functions not explictly marked\n> + * otherwise.\n> + *\n> + * - \\anchor thread-safe A **thread-safe** function may be called\n> + * simultaneously from multiple threads on the same instance of a class. A\n> + * thread-safe function is thus reentrant.\n> + *\n> + * - \\anchor thread-bound A **thread-bound** function may be called only from\n> + * the thread that the class instances lives in (see section \\ref\n> + * thread-objects). For instances of classes that do not derive from the\n> + * Object class, this is the thread in which the instance was created. A\n> + * thread-bound function is not thread-safe, and may or may not be reentrant.\n> + *\n> + * Neither reentrancy nor thread-safety, in this context, mean that a function\n> + * may be called simultaneously from the same thread, for instance from a\n> + * callback invoked by the the function. This may deadlock and isn't allowed\n> + * unless separately documented.\n> + *\n> + * A class is defined as reentrant, thread-safe or thread-bound if all its\n> + * member functions are reentrant, thread-safe or thread-bound respectively.\n> + * Some member functions may additionally be documented as having additional\n> + * thread-related attributes.\n> + *\n> + * Most classes are reentrant but not thread-safe, as making them fully\n> + * thread-safe would incur locking costs considered prohibitive for the\n> + * expected use cases.\n> + *\n> + * \\section thread-objects Threads and Objects\n> + *\n> + * Instances of the Object class and all its derived classes are thread-aware\n> + * and are bound to the thread they are created in. They are said to *live* in\n> + * a thread, and they interact with the event loop of their thread for the\n> + * purpose of message passing and signal delivery. Messages posted to the\n> + * object with Object::postMessage() will be delivered from the event loop of\n> + * the thread that the object lives in. Signals delivered to the object, unless\n> + * explicitly connected with ConnectionTypeDirect, will also be delivered from\n> + * the object thread's event loop.\n> + *\n> + * All Object instances created by libcamera are bound to an internal thread,\n> + * an applications don't need to provide an event loop to support them. Object\n> + * instances created by applications require an event loop. It is the\n> + * responsibility of applications to provide that event loop, either explicitly\n> + * through CameraManager::setEventDispatcher(), or by running the default event\n> + * loop provided by CameraManager::eventDispatcher() in their main thread. The\n> + * main thread of an application is the one that calls CameraManager::start().\n> + *\n> + * \\section thread-signals Threads and Signals\n> + *\n> + * When sent to a receiver that does not inherit from the Object class, signals\n> + * are delivered synchronously in the thread of the sender. When the receiver\n> + * inherits from the Object class, delivery is by default asynchronous if the\n> + * sender and receiver live in different threads. In that case, the signal is\n> + * posted to the receiver's message queue and will be delivered from the\n> + * receiver's event loop, running in the receiver's thread. This mechanism can\n> + * be overridden by selecting a different connection type when calling\n> + * Signal::connect().\n> + *\n> + * Asynchronous signal delivery is used internally in libcamera, but is also\n> + * available to applications if desired. To use this feature, applications\n> + * shall create receiver classes that inherit from the Object class, and\n> + * provide an event loop to the CameraManager as explained above. Note that\n> + * Object instance created by the application are limited to living in the\n> + * application's main thread. Creating Object instances from another thread of\n> + * an application causes undefined behaviour.\n> + */\n> +\n> /**\n> * \\file thread.h\n> * \\brief Thread support\n> -- \n> Regards,\n> \n> Laurent Pinchart\n> \n> _______________________________________________\n> libcamera-devel mailing list\n> libcamera-devel@lists.libcamera.org\n> https://lists.libcamera.org/listinfo/libcamera-devel","headers":{"Return-Path":"","Received":["from mail-lf1-x141.google.com (mail-lf1-x141.google.com\n\t[IPv6:2a00:1450:4864:20::141])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id D8990607F3\n\tfor ;\n\tWed, 22 Jan 2020 16:31:33 +0100 (CET)","by mail-lf1-x141.google.com with SMTP id 203so5615092lfa.12\n\tfor ;\n\tWed, 22 Jan 2020 07:31:33 -0800 (PST)","from localhost (h-93-159.A463.priv.bahnhof.se. 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You can put ^^ in the value part of an\n> # alias to insert a newline as if a physical newline was in the original file.\n> \n> -ALIASES =\n> +ALIASES = \"context=\\xrefitem context \\\"Thread Safety\\\" \\\"Thread Safety\\\"\"\n> +ALIASES += \"threadbound=\\ref thread-bound \\\"thread-bound\\\"\"\n> +ALIASES += \"threadsafe=\\ref thread-safe \\\"thread-safe\\\"\"\n> \n> # This tag can be used to specify a number of word-keyword mappings (TCL only).\n> # A mapping has the form \"name=value\". For example adding \"class=itcl::class\"\n> diff --git a/src/libcamera/thread.cpp b/src/libcamera/thread.cpp\n> index fe32cd677596..c1698d469a6c 100644\n> --- a/src/libcamera/thread.cpp\n> +++ b/src/libcamera/thread.cpp\n> @@ -19,6 +19,88 @@\n> #include \"log.h\"\n> #include \"message.h\"\n> \n> +/**\n> + * \\page thread Thread Support\n> + *\n> + * libcamera supports multi-threaded applications through a threading model that\n> + * sets precise rules to guarantee thread-safe usage of the API. Additionally,\n> + * libcamera makes internal use of threads, and offers APIs that simplify\n> + * interactions with application threads. Careful compliance with the threading\n> + * model will ensure avoidance of race conditions.\n> + *\n> + * \\section thread-reentrancy Reentrancy and Thread-Safety\n> + *\n> + * Through the documentation, several terms are used to define how classes and\n> + * their member functions can be used from multiple threads.\n> + *\n> + * - A **reentrant** function may be called simultaneously from multiple\n> + * threads if and only if each invocation uses a different instance of the\n> + * class. This is the default for all member functions not explictly marked\n> + * otherwise.\n> + *\n> + * - \\anchor thread-safe A **thread-safe** function may be called\n> + * simultaneously from multiple threads on the same instance of a class. A\n> + * thread-safe function is thus reentrant.\n> + *\n> + * - \\anchor thread-bound A **thread-bound** function may be called only from\n> + * the thread that the class instances lives in (see section \\ref\n> + * thread-objects). For instances of classes that do not derive from the\n> + * Object class, this is the thread in which the instance was created. A\n> + * thread-bound function is not thread-safe, and may or may not be reentrant.\n> + *\n> + * Neither reentrancy nor thread-safety, in this context, mean that a function\n> + * may be called simultaneously from the same thread, for instance from a\n> + * callback invoked by the the function. This may deadlock and isn't allowed\n> + * unless separately documented.\n> + *\n> + * A class is defined as reentrant, thread-safe or thread-bound if all its\n> + * member functions are reentrant, thread-safe or thread-bound respectively.\n> + * Some member functions may additionally be documented as having additional\n> + * thread-related attributes.\n> + *\n> + * Most classes are reentrant but not thread-safe, as making them fully\n> + * thread-safe would incur locking costs considered prohibitive for the\n> + * expected use cases.\n> + *\n> + * \\section thread-objects Threads and Objects\n> + *\n> + * Instances of the Object class and all its derived classes are thread-aware\n> + * and are bound to the thread they are created in. They are said to *live* in\n> + * a thread, and they interact with the event loop of their thread for the\n> + * purpose of message passing and signal delivery. Messages posted to the\n> + * object with Object::postMessage() will be delivered from the event loop of\n> + * the thread that the object lives in. Signals delivered to the object, unless\n> + * explicitly connected with ConnectionTypeDirect, will also be delivered from\n> + * the object thread's event loop.\n> + *\n> + * All Object instances created by libcamera are bound to an internal thread,\n> + * an applications don't need to provide an event loop to support them. Object\n\ns/* an applications/* and applications/\n\n\n> + * instances created by applications require an event loop. It is the\n> + * responsibility of applications to provide that event loop, either explicitly\n> + * through CameraManager::setEventDispatcher(), or by running the default event\n> + * loop provided by CameraManager::eventDispatcher() in their main thread. The\n> + * main thread of an application is the one that calls CameraManager::start().\n> + *\n> + * \\section thread-signals Threads and Signals\n> + *\n> + * When sent to a receiver that does not inherit from the Object class, signals\n> + * are delivered synchronously in the thread of the sender. When the receiver\n> + * inherits from the Object class, delivery is by default asynchronous if the\n> + * sender and receiver live in different threads. In that case, the signal is\n> + * posted to the receiver's message queue and will be delivered from the\n> + * receiver's event loop, running in the receiver's thread. This mechanism can\n> + * be overridden by selecting a different connection type when calling\n> + * Signal::connect().\n> + *\n> + * Asynchronous signal delivery is used internally in libcamera, but is also\n> + * available to applications if desired. To use this feature, applications\n> + * shall create receiver classes that inherit from the Object class, and\n> + * provide an event loop to the CameraManager as explained above. Note that\n> + * Object instance created by the application are limited to living in the\n\ns/instance/instances/\n\n> + * application's main thread. Creating Object instances from another thread of\n> + * an application causes undefined behaviour.\n> + */\n> +\n> /**\n> * \\file thread.h\n> * \\brief Thread support\n>","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 945F2607F3\n\tfor ;\n\tWed, 22 Jan 2020 16:43:42 +0100 (CET)","from [192.168.0.20]\n\t(cpc89242-aztw30-2-0-cust488.18-1.cable.virginm.net [86.31.129.233])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id D4B6E2E5;\n\tWed, 22 Jan 2020 16:43:41 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1579707822;\n\tbh=Oi36tMIrN+D5Hx07pvAgCGKdmQl9Y+xef9iBXlHM00Q=;\n\th=Reply-To:Subject:To:References:From:Date:In-Reply-To:From;\n\tb=F3FTO58h3U4eC6w2k0mivjEVlbrsV3DR2ro5o7C+hz/bmLttpJgeKXeoWo+bbz5+r\n\tZTokK7PI9ltwm3rmV9oyBwM/0MdvSPCVfKipBeQIg5EuAvgXHE9PLuNmtQsoxZRgwA\n\tFjbEf8dNPTMrRaKpB7euUHGY7YpiBjxvxixgPCdA=","Reply-To":"kieran.bingham@ideasonboard.com","To":"Laurent Pinchart ,\n\tlibcamera-devel@lists.libcamera.org","References":"<20200120002437.6633-1-laurent.pinchart@ideasonboard.com>\n\t<20200120002437.6633-11-laurent.pinchart@ideasonboard.com>","From":"Kieran Bingham ","Openpgp":"preference=signencrypt","Autocrypt":"addr=kieran.bingham@ideasonboard.com; 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Linux x86_64; rv:60.0) Gecko/20100101\n\tThunderbird/60.9.0","MIME-Version":"1.0","In-Reply-To":"<20200120002437.6633-11-laurent.pinchart@ideasonboard.com>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-GB","Content-Transfer-Encoding":"7bit","Subject":"Re: [libcamera-devel] [PATCH 10/19] libcamera: Define the threading\n\tmodel","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","X-List-Received-Date":"Wed, 22 Jan 2020 15:43:42 -0000"}}]