From 7d5321ac52b908f8ec156852a33d867944532625 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Barnab=C3=A1s=20P=C5=91cze?= Date: Mon, 3 Mar 2025 16:28:28 +0100 Subject: [PATCH] libcamera: base: log: Do not instantiate disabled `LogMessage`s MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit At the moment every `LOG()` macro invocation results in a `LogMessage` being created, the message serialized into an `std::stringstream`. Only in the destructor is it actually checked whether the given `LogCategory` enables the given log level. This is not too efficient, it would be better to skip the log message construction and all the `operator<<()` invocations if the message will just be discarded. This could be easily done if the `LOG()` macro accepted its arguments like a traditional function as in that case an appropriate `if` statement can be injected in a do-while loop. However, that is not the case, the `LOG()` macro should effectively "return" a stream. It is not possible inject an `if` statement directly as that would lead to issues: if (...) LOG(...) else ... The `else` would bind the to the `if` in the `LOG()` macro. This is diagnosed by `-Wdangling-else`. An alternative approach would be to use a `for` loop and force a single iteration using a boolean flag or similar. This is entirely doable but I think the implemented approach is easier to understand. This change implements the early log level checking using a `switch` statement as this avoids the dangling else related issues. One small issue arises because having a boolean controlling expression is diagnosed by clang (`-Wswitch-bool`); the result is cast to `int` to avoid the warning. Signed-off-by: Barnabás Pőcze Reviewed-by: Kieran Bingham Reviewed-by: Laurent Pinchart --- include/libcamera/base/log.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/include/libcamera/base/log.h b/include/libcamera/base/log.h index d8338d8d..cc50415e 100644 --- a/include/libcamera/base/log.h +++ b/include/libcamera/base/log.h @@ -108,10 +108,16 @@ LogMessage _log(const LogCategory &category, LogSeverity severity, #ifndef __DOXYGEN__ #define _LOG_CATEGORY(name) logCategory##name +#define _LOG(cat, sev) \ + switch (const auto &_logCategory = (cat); \ + static_cast(_logCategory.severity() <= Log##sev)) \ + case 1: \ + _log(_logCategory, Log##sev).stream() + #define _LOG1(severity) \ - _log(LogCategory::defaultCategory(), Log##severity).stream() + _LOG(LogCategory::defaultCategory(), severity) #define _LOG2(category, severity) \ - _log(_LOG_CATEGORY(category)(), Log##severity).stream() + _LOG(_LOG_CATEGORY(category)(), severity) /* * Expand the LOG() macro to _LOG1() or _LOG2() based on the number of