{"id":25847,"url":"https://patchwork.libcamera.org/api/patches/25847/?format=json","web_url":"https://patchwork.libcamera.org/patch/25847/","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":"<20260119113104.3560802-3-barnabas.pocze@ideasonboard.com>","date":"2026-01-19T11:31:00","name":"[v2,2/5] libcamera: base: log: Do not instantiate disabled `LogMessage`s","commit_ref":null,"pull_url":null,"state":"accepted","archived":false,"hash":"644e5c764e219694ff7e812cc7811e9b151d3707","submitter":{"id":216,"url":"https://patchwork.libcamera.org/api/people/216/?format=json","name":"Barnabás Pőcze","email":"barnabas.pocze@ideasonboard.com"},"delegate":null,"mbox":"https://patchwork.libcamera.org/patch/25847/mbox/","series":[{"id":5716,"url":"https://patchwork.libcamera.org/api/series/5716/?format=json","web_url":"https://patchwork.libcamera.org/project/libcamera/list/?series=5716","date":"2026-01-19T11:30:58","name":"libcamera: base: log: Do not instantiate disabled `LogMessage`s","version":2,"mbox":"https://patchwork.libcamera.org/series/5716/mbox/"}],"comments":"https://patchwork.libcamera.org/api/patches/25847/comments/","check":"pending","checks":"https://patchwork.libcamera.org/api/patches/25847/checks/","tags":{},"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 D4EFEC327D\n\tfor ;\n\tMon, 19 Jan 2026 11:31:14 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id B39F861FC6;\n\tMon, 19 Jan 2026 12:31:10 +0100 (CET)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 3787961FB9\n\tfor ;\n\tMon, 19 Jan 2026 12:31:08 +0100 (CET)","from pb-laptop.local (185.221.143.114.nat.pool.zt.hu\n\t[185.221.143.114])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id B6728C79\n\tfor ;\n\tMon, 19 Jan 2026 12:30:37 +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=\"aGG5poCg\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1768822237;\n\tbh=emvrmnnI4/cToii6BSjuUIOwHrDklh9jfJ5ZFeVMMdo=;\n\th=From:To:Subject:Date:In-Reply-To:References:From;\n\tb=aGG5poCgpTCFE2f9YITw3QM6OmsrlA8a7sbsYpEh7oPHTGl3zhibvdWMx6AR7lPKA\n\t+XvCJOjkLKF6CbIBPWwq/Cq2DP0r6DxH+FMKAzhfDsYCRShRyo51NFvGRa9H8qMGk+\n\t1odfw46yQMBnLBLFiart0CTgxPu0zmPzhwi/qi/k=","From":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","To":"libcamera-devel@lists.libcamera.org","Subject":"[PATCH v2 2/5] libcamera: base: log: Do not instantiate disabled\n\t`LogMessage`s","Date":"Mon, 19 Jan 2026 12:31:00 +0100","Message-ID":"<20260119113104.3560802-3-barnabas.pocze@ideasonboard.com>","X-Mailer":"git-send-email 2.52.0","In-Reply-To":"<20260119113104.3560802-1-barnabas.pocze@ideasonboard.com>","References":"<20260119113104.3560802-1-barnabas.pocze@ideasonboard.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","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\" "},"content":"At the moment every `LOG()` macro invocation results in a `LogMessage` being\ncreated, the message serialized into an `std::stringstream`. Only in the\ndestructor is it actually checked whether the given `LogCategory` enables\nthe given log level.\n\nThis is not too efficient, it would be better to skip the log message\nconstruction and all the `operator<<()` invocations if the message will\njust be discarded.\n\nThis could be easily done if the `LOG()` macro accepted its arguments like a\ntraditional function as in that case an appropriate `if` statement can be\ninjected in a do-while loop. However, that is not the case, the `LOG()` macro\nshould effectively \"return\" a stream.\n\nIt is not possible inject an `if` statement directly as that would\nlead to issues:\n\n if (...)\n LOG(...)\n else\n ...\n\nThe `else` would bind the to the `if` in the `LOG()` macro. This is\ndiagnosed by `-Wdangling-else`.\n\nAn alternative approach would be to use a `for` loop and force a single\niteration using a boolean flag or similar. This is entirely doable but\nI think the implemented approach is easier to understand.\n\nThis change implements the early log level checking using a `switch` statement\nas this avoids the dangling else related issues. One small issue arises\nbecause having a boolean controlling expression is diagnosed by clang\n(`-Wswitch-bool`); the result is cast to `int` to avoid the warning.\n\nSigned-off-by: Barnabás Pőcze \n---\n include/libcamera/base/log.h | 9 +++++++--\n 1 file changed, 7 insertions(+), 2 deletions(-)","diff":"diff --git a/include/libcamera/base/log.h b/include/libcamera/base/log.h\nindex d8338d8df..dbd14951c 100644\n--- a/include/libcamera/base/log.h\n+++ b/include/libcamera/base/log.h\n@@ -108,10 +108,15 @@ LogMessage _log(const LogCategory &category, LogSeverity severity,\n #ifndef __DOXYGEN__\n #define _LOG_CATEGORY(name) logCategory##name\n \n+#define _LOG(cat, sev) \\\n+\tswitch (const auto &_logCategory = (cat); int(_logCategory.severity() <= Log##sev)) \\\n+\tcase 1: \\\n+\t\t_log(_logCategory, Log##sev).stream()\n+\n #define _LOG1(severity) \\\n-\t_log(LogCategory::defaultCategory(), Log##severity).stream()\n+\t_LOG(LogCategory::defaultCategory(), severity)\n #define _LOG2(category, severity) \\\n-\t_log(_LOG_CATEGORY(category)(), Log##severity).stream()\n+\t_LOG(_LOG_CATEGORY(category)(), severity)\n \n /*\n * Expand the LOG() macro to _LOG1() or _LOG2() based on the number of\n","prefixes":["v2","2/5"]}