[{"id":28559,"web_url":"https://patchwork.libcamera.org/comment/28559/","msgid":"<8734up6rha.fsf@redhat.com>","date":"2024-01-22T20:30:25","subject":"Re: [PATCH 11/12] libcamera: object: Document and ensure Object\n\tdeletion constraints","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"Laurent Pinchart writes:\n\n> Object instances are meant to be deleted from the thread they are bound\n> to, and this requirement is documented. There are however exceptions to\n> the rule, as threads may be stopped and restarted, with objects bound to\n> them not being deleted and recreated for every stop/restart cycle. Bound\n> objects may therefore need to be deleted after the thread has stopped,\n> making it impossible to use Object::deleteLater().\n>\n> Document the lifetime requirements more precisely, and enforce them with\n> an assertion.\n>\n> Signed-off-by: Laurent Pinchart \n\nReviewed-by: Milan Zamazal \n\n> ---\n> src/libcamera/base/object.cpp | 16 ++++++++++++++--\n> 1 file changed, 14 insertions(+), 2 deletions(-)\n>\n> diff --git a/src/libcamera/base/object.cpp b/src/libcamera/base/object.cpp\n> index 1fce5a2af9af..8af0337f5448 100644\n> --- a/src/libcamera/base/object.cpp\n> +++ b/src/libcamera/base/object.cpp\n> @@ -40,8 +40,9 @@ LOG_DEFINE_CATEGORY(Object)\n> * Object class.\n> *\n> * Deleting an object from a thread other than the one the object is bound to is\n> - * unsafe, unless the caller ensures that the object isn't processing any\n> - * message concurrently.\n> + * unsafe, unless the caller ensures that the object's thread is stopped and no\n> + * parent or child of the object gets deleted concurrently. See\n> + * Object::~Object() for more information.\n> *\n> * Object slots connected to signals will also run in the context of the\n> * object's thread, regardless of whether the signal is emitted in the same or\n> @@ -84,9 +85,20 @@ Object::Object(Object *parent)\n> * Object instances shall be destroyed from the thread they are bound to,\n> * otherwise undefined behaviour may occur. If deletion of an Object needs to\n> * be scheduled from a different thread, deleteLater() shall be used.\n> + *\n> + * As an exception to this rule, Object instances may be deleted from a\n> + * different thread if the thread the instance is bound to is stopped through\n> + * the whole duration of the object's destruction, *and* the parent and children\n> + * of the object do not get deleted concurrently. The caller is responsible for\n> + * fulfilling those requirements.\n> + *\n> + * In all cases Object instances shall be deleted before the Thread they are\n> + * bound to.\n> */\n> Object::~Object()\n> {\n> +\tASSERT(Thread::current() == thread_ || !thread_->isRunning());\n> +\n> \t/*\n> \t * Move signals to a private list to avoid concurrent iteration and\n> \t * deletion of items from Signal::disconnect().","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 EBF44BDB1C\n\tfor ;\n\tMon, 22 Jan 2024 20:30:33 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id E78A062936;\n\tMon, 22 Jan 2024 21:30:32 +0100 (CET)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.129.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 2295F61D30\n\tfor ;\n\tMon, 22 Jan 2024 21:30:32 +0100 (CET)","from mail-ed1-f69.google.com (mail-ed1-f69.google.com\n\t[209.85.208.69]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-203-m9G-bBXHMm-77ZoR9uImdw-1; Mon, 22 Jan 2024 15:30:29 -0500","by mail-ed1-f69.google.com with SMTP id\n\t4fb4d7f45d1cf-55c795a8a74so34170a12.0\n\tfor ;\n\tMon, 22 Jan 2024 12:30:29 -0800 (PST)","from nuthatch (ip-77-48-47-2.net.vodafone.cz. 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