[{"id":33276,"web_url":"https://patchwork.libcamera.org/comment/33276/","msgid":"<3cmaxazbtlrgyf27o3jjx5b2xuosnfb22qtutdd7yrglf2x3zs@byu7e2wl7lqy>","date":"2025-02-03T19:14:31","subject":"Re: [RFC PATCH v3 01/21] apps: common: event_loop: Take callbacks by\n\trvalue ref","submitter":{"id":143,"url":"https://patchwork.libcamera.org/api/people/143/","name":"Jacopo Mondi","email":"jacopo.mondi@ideasonboard.com"},"content":"Hi Barnabás\n\nOn Thu, Jan 30, 2025 at 11:50:08AM +0000, Barnabás Pőcze wrote:\n> Using a const lvalue reference to `std::function<>` is not ideal\n> because it forces a copy to happen. Use an rvalue reference and\n> `std::move()` to avoid that.\n>\n> Signed-off-by: Barnabás Pőcze \n> Reviewed-by: Jacopo Mondi \n> Reviewed-by: Paul Elder \n> ---\n> src/apps/common/event_loop.cpp | 16 ++++++++--------\n> src/apps/common/event_loop.h | 8 ++++----\n> 2 files changed, 12 insertions(+), 12 deletions(-)\n>\n> diff --git a/src/apps/common/event_loop.cpp b/src/apps/common/event_loop.cpp\n> index f7f9afa0c..bc8cf17ab 100644\n> --- a/src/apps/common/event_loop.cpp\n> +++ b/src/apps/common/event_loop.cpp\n> @@ -50,20 +50,20 @@ void EventLoop::exit(int code)\n> \tevent_base_loopbreak(base_);\n> }\n>\n> -void EventLoop::callLater(const std::function &func)\n> +void EventLoop::callLater(std::function &&func)\n> {\n> \t{\n> \t\tstd::unique_lock locker(lock_);\n> -\t\tcalls_.push_back(func);\n> +\t\tcalls_.push_back(std::move(func));\n> \t}\n>\n> \tevent_base_once(base_, -1, EV_TIMEOUT, dispatchCallback, this, nullptr);\n> }\n>\n> void EventLoop::addFdEvent(int fd, EventType type,\n> -\t\t\t const std::function &callback)\n> +\t\t\t std::function &&callback)\n> {\n> -\tstd::unique_ptr event = std::make_unique(callback);\n> +\tstd::unique_ptr event = std::make_unique(std::move(callback));\n\n // rvalue reference variables are lvalues when used in expressions\n int&& x = 1;\n f(x); // calls f(int& x)\n f(std::move(x)); // calls f(int&& x)\n\nDoes one ever stop being fooled by C++ ? ;)\n\n\n> \tshort events = (type & Read ? EV_READ : 0)\n> \t\t | (type & Write ? EV_WRITE : 0)\n> \t\t | EV_PERSIST;\n> @@ -85,9 +85,9 @@ void EventLoop::addFdEvent(int fd, EventType type,\n> }\n>\n> void EventLoop::addTimerEvent(const std::chrono::microseconds period,\n> -\t\t\t const std::function &callback)\n> +\t\t\t std::function &&callback)\n> {\n> -\tstd::unique_ptr event = std::make_unique(callback);\n> +\tstd::unique_ptr event = std::make_unique(std::move(callback));\n> \tevent->event_ = event_new(base_, -1, EV_PERSIST, &EventLoop::Event::dispatch,\n> \t\t\t\t event.get());\n> \tif (!event->event_) {\n> @@ -131,8 +131,8 @@ void EventLoop::dispatchCall()\n> \tcall();\n> }\n>\n> -EventLoop::Event::Event(const std::function &callback)\n> -\t: callback_(callback), event_(nullptr)\n> +EventLoop::Event::Event(std::function &&callback)\n> +\t: callback_(std::move(callback)), event_(nullptr)\n> {\n> }\n>\n> diff --git a/src/apps/common/event_loop.h b/src/apps/common/event_loop.h\n> index ef129b9aa..d7d012c76 100644\n> --- a/src/apps/common/event_loop.h\n> +++ b/src/apps/common/event_loop.h\n> @@ -33,18 +33,18 @@ public:\n> \tint exec();\n> \tvoid exit(int code = 0);\n>\n> -\tvoid callLater(const std::function &func);\n> +\tvoid callLater(std::function &&func);\n>\n> \tvoid addFdEvent(int fd, EventType type,\n> -\t\t\tconst std::function &handler);\n> +\t\t\tstd::function &&handler);\n>\n> \tusing duration = std::chrono::steady_clock::duration;\n> \tvoid addTimerEvent(const std::chrono::microseconds period,\n> -\t\t\t const std::function &handler);\n> +\t\t\t std::function &&handler);\n>\n> private:\n> \tstruct Event {\n> -\t\tEvent(const std::function &callback);\n> +\t\tEvent(std::function &&callback);\n> \t\t~Event();\n>\n> \t\tstatic void dispatch(int fd, short events, void *arg);\n> --\n> 2.48.1\n>\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 7BD48C3260\n\tfor ;\n\tMon, 3 Feb 2025 19:14:37 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 66C58685A5;\n\tMon, 3 Feb 2025 20:14:36 +0100 (CET)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id D03CE61876\n\tfor ;\n\tMon, 3 Feb 2025 20:14:34 +0100 (CET)","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 126EF514;\n\tMon, 3 Feb 2025 20:13:23 +0100 (CET)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"cVo8Kf2b\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1738610003;\n\tbh=5G0EsIE0oRKzT2ijxiCDEDra3t7agODW9ICA6s2Ca8g=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=cVo8Kf2b2Rd8IhV234yR9A/9E6UMlO7lrETDEz1SnGUEZYQj8YN+Ea5j3R1j+TSid\n\t3cAPZQW7QWFBRgZyO9cq2xMLCbGPhcjpVeIOP/O5uEhF8ZZHBVzLmzaN0mPzOXUtMj\n\tH0ra0dvRPmAvFjFllB+Y5IdS/XXKkPWE48wwoFc4=","Date":"Mon, 3 Feb 2025 20:14:31 +0100","From":"Jacopo Mondi ","To":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","Cc":"libcamera-devel@lists.libcamera.org, \n\tJacopo Mondi ,\n\tPaul Elder ","Subject":"Re: [RFC PATCH v3 01/21] apps: common: event_loop: Take callbacks by\n\trvalue ref","Message-ID":"<3cmaxazbtlrgyf27o3jjx5b2xuosnfb22qtutdd7yrglf2x3zs@byu7e2wl7lqy>","References":"<20250130115001.1129305-1-pobrn@protonmail.com>\n\t<20250130115001.1129305-2-pobrn@protonmail.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"<20250130115001.1129305-2-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\" "}}]