[libcamera-devel] [PATCH] libcamera: log: Destroy LogCategory instances in a controlled way

[Laurent Pinchart]

The LogCategory instances are constructed on first use as static
variables in accessor functions, following the Meyers singleton pattern.
As a result, their destruction order is not guaranteed. This can cause
issues as the global Logger object, constructed in a similar fashion, is
accessed from the LogCategory destructor and may be destroyed first.

To fix this, keep the same singleton pattern, but allocate the
LogCategory instances dynamically. As they get registered with the
global Logger instance, we can destroy them in the Logger destructor.

This only avoids destruction order issues between LogCategory and
Logger, and doesn't address yet the fact that LOG() calls from
destructors of global objects may access an already destroyed Logger.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 include/libcamera/internal/log.h |  5 ++---
 src/libcamera/log.cpp            | 32 +++++++++++---------------------
 2 files changed, 13 insertions(+), 24 deletions(-)

diff --git a/include/libcamera/internal/log.h b/include/libcamera/internal/log.h
index b66bf55bc57d..1032bdd93e7c 100644
--- a/include/libcamera/internal/log.h
+++ b/include/libcamera/internal/log.h
@@ -29,7 +29,6 @@ class LogCategory
 {
 public:
 	explicit LogCategory(const char *name);
-	~LogCategory();
 
 	const char *name() const { return name_; }
 	LogSeverity severity() const { return severity_; }
@@ -48,8 +47,8 @@ extern const LogCategory &_LOG_CATEGORY(name)();
 #define LOG_DEFINE_CATEGORY(name)					\
 const LogCategory &_LOG_CATEGORY(name)()				\
 {									\
-	static LogCategory category(#name);				\
-	return category;						\
+	static LogCategory *category = new LogCategory(#name);		\
+	return *category;						\
 }
 
 class LogMessage
diff --git a/src/libcamera/log.cpp b/src/libcamera/log.cpp
index dd991647b9bc..74829a56916e 100644
--- a/src/libcamera/log.cpp
+++ b/src/libcamera/log.cpp
@@ -248,6 +248,8 @@ void LogOutput::writeStream(const std::string &str)
 class Logger
 {
 public:
+	~Logger();
+
 	static Logger *instance();
 
 	void write(const LogMessage &msg);
@@ -267,7 +269,6 @@ private:
 
 	friend LogCategory;
 	void registerCategory(LogCategory *category);
-	void unregisterCategory(LogCategory *category);
 
 	std::unordered_set<LogCategory *> categories_;
 	std::list<std::pair<std::string, LogSeverity>> levels_;
@@ -369,6 +370,12 @@ void logSetLevel(const char *category, const char *level)
 	Logger::instance()->logSetLevel(category, level);
 }
 
+Logger::~Logger()
+{
+	for (LogCategory *category : categories_)
+		delete category;
+}
+
 /**
  * \brief Retrieve the logger instance
  *
@@ -665,18 +672,6 @@ void Logger::registerCategory(LogCategory *category)
 	}
 }
 
-/**
- * \brief Unregister a log category from the logger
- * \param[in] category The log category
- *
- * If the \a category hasn't been registered with the logger this function
- * performs no operation.
- */
-void Logger::unregisterCategory(LogCategory *category)
-{
-	categories_.erase(category);
-}
-
 /**
  * \enum LogSeverity
  * Log message severity
@@ -711,11 +706,6 @@ LogCategory::LogCategory(const char *name)
 	Logger::instance()->registerCategory(this);
 }
 
-LogCategory::~LogCategory()
-{
-	Logger::instance()->unregisterCategory(this);
-}
-
 /**
  * \fn LogCategory::name()
  * \brief Retrieve the log category name
@@ -746,12 +736,12 @@ void LogCategory::setSeverity(LogSeverity severity)
  * The default log category is named "default" and is used by the LOG() macro
  * when no log category is specified.
  *
- * \return A pointer to the default log category
+ * \return A reference to the default log category
  */
 const LogCategory &LogCategory::defaultCategory()
 {
-	static const LogCategory category("default");
-	return category;
+	static const LogCategory *category = new LogCategory("default");
+	return *category;
 }
 
 /**
-- 
Regards,

Laurent Pinchart