Provide temporary logging level change support using RAII

src/main/include/log4cxx/levelchange.h

@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef LOG4CXX_LEVEL_CHANGE_HDR_
+#define LOG4CXX_LEVEL_CHANGE_HDR_
+
+#include <log4cxx/logmanager.h>
+#include <log4cxx/logger.h>
+
+namespace LOG4CXX_NS
+{
+
+/**
+ * Changes a verbosity level for the instance variable's lifetime.
+
+ * Create a LevelChange variable on the stack
+ * to temporarily (e.g. for a single method)
+ * increase the quantity of information logged.
+
+ * Typically used to propagate the locally used logger's level (e.g. DEBUG or TRACE)
+ * to another named (e.g. the name of the class of the method invoked next) logger.
+
+ * The LevelChange variable does not need to be removed from the code (e.g. for a release build)
+ * as it has no impact when the local and other logger point to the same level
+ * (e.g. null_ptr, implying their level is inherited).
+ */
+ class LevelChange
+{
+	LoggerPtr m_otherCategory;
+	LevelPtr m_savedLevel;
+public: // ...structors
+	/// Set \c otherCategory to \c level
+	LevelChange(const LoggerPtr& otherCategory, const LevelPtr& level)
+		: m_otherCategory(otherCategory)
+		, m_savedLevel(otherCategory->getLevel())
+	{
+		m_otherCategory->setLevel(level);
+	}
+	/// Set \c otherCategory to the level of \c thisCategory
+	LevelChange(const LoggerPtr& otherCategory, const LoggerPtr& thisCategory)
+		: LevelChange(otherCategory, m_otherCategory->getLevel())
+	{
+	}
+	/// Set the logger named \c otherCategory to \c level
+	template <class StringType>
+	LevelChange(const StringType& otherCategory, const LevelPtr& level)
+		: LevelChange(LogManager::getLogger(otherCategory), level)
+	{
+	}
+	/// Set the logger named \c otherCategory to the level of \c thisCategory
+	template <class StringType>
+	LevelChange(const StringType& otherCategory, const LoggerPtr& thisCategory)
+		: LevelChange(LogManager::getLogger(otherCategory), thisCategory->getLevel())
+	{
+	}
+	/// Restore the verbosity level of the other logger
+	~LevelChange()
+	{
+		m_otherCategory->setLevel(m_savedLevel);
+	}
+private: // Prevent copies and assignment 
+	LevelChange(const LevelChange&) = delete;
+	LevelChange(LevelChange&&) = delete;
+	LevelChange& operator=(const LevelChange&) = delete;
+	LevelChange& operator=(LevelChange&&) = delete;
+};
+
+} // namespace LOG4CXX_NS
+
+#endif // LOG4CXX_LEVEL_CHANGE_HDR_

src/test/cpp/CMakeLists.txt

@@ -50,6 +50,7 @@ set(ALL_LOG4CXX_TESTS
     jsonlayouttest
     l7dtestcase
     leveltestcase
+    levelchangetestcase
     loggertestcase
     mdctestcase
     minimumtestcase

src/test/cpp/levelchangetestcase.cpp

@@ -0,0 +1,143 @@
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <log4cxx/levelchange.h>
+#include <log4cxx/appenderskeleton.h>
+#include <log4cxx/helpers/loglog.h>
+#include "logunit.h"
+
+using namespace log4cxx;
+
+namespace
+{
+
+class CountingAppender : public AppenderSkeleton
+{
+	public:
+		int count;
+
+		CountingAppender() : count(0)
+		{}
+
+		void close() override
+		{}
+
+		void append(const spi::LoggingEventPtr& /*event*/, helpers::Pool& /*p*/) override
+		{
+			count++;
+		}
+
+		bool requiresLayout() const override
+		{
+			return true;
+		}
+
+		LogString getName() const override
+		{
+			return LOG4CXX_STR("counter");
+		}
+};
+
+LoggerPtr getLogger(const std::string& name)
+{
+	static struct initializer {
+		initializer() {
+			// Prevent default configuration
+			LogManager::getLoggerRepository()->ensureIsConfigured([](){});
+			// Install my appender
+			LogManager::getRootLogger()->addAppender( std::make_shared<CountingAppender>() );
+		}
+	} init;
+	return LogManager::getLogger(name);
+}
+
+} // anonymous namespace
+
+// A mocked worker
+class ComplexProcessing
+{
+public:
+	LoggerPtr logger = getLogger("ComplexProcessing");
+	void DoStep1()
+	{
+		LOG4CXX_DEBUG(logger, "Step 1 message");
+	}
+	void DoStep2()
+	{
+		LOG4CXX_DEBUG(logger, "Step 2 message");
+	}
+	void DoStep3()
+	{
+		LOG4CXX_DEBUG(logger, "Step 3 message");
+	}
+};
+static ComplexProcessing processor;
+
+LOGUNIT_CLASS(LevelChangeTestCase)
+{
+	LOGUNIT_TEST_SUITE(LevelChangeTestCase);
+	LOGUNIT_TEST(testLevelChange);
+	LOGUNIT_TEST_SUITE_END();
+
+#ifdef _DEBUG
+	struct Fixture
+	{
+		Fixture() {
+			helpers::LogLog::setInternalDebugging(true);
+		}
+	} suiteFixture;
+#endif
+
+public:
+	void setUp()
+	{
+		// Disable DEBUG output from ComplexProcessing
+		processor.logger->setLevel(Level::getInfo());
+	}
+
+	void testLevelChange()
+	{
+		auto appender = dynamic_cast<CountingAppender*>(LogManager::getRootLogger()->getAppender(LOG4CXX_STR("counter")).get());
+		LOGUNIT_ASSERT(appender);
+
+		auto myLogger = getLogger("Controller");
+		myLogger->setLevel(Level::getDebug());
+
+		// Check this debug request is sent to the appender
+		LOG4CXX_DEBUG(myLogger, "Start test");
+		auto initialCount = appender->count;
+		LOGUNIT_ASSERT_EQUAL(initialCount, 1);
+
+		// Check the ComplexProcessing debug request is not sent to the appender
+		processor.DoStep1();
+		LOGUNIT_ASSERT_EQUAL(appender->count, initialCount);
+		{
+			LevelChange x(LOG4CXX_STR("ComplexProcessing"), myLogger);
+			processor.DoStep2();
+			// Check the ComplexProcessing debug request was sent to the appender
+			LOGUNIT_ASSERT_EQUAL(appender->count, initialCount + 1);
+		}
+
+		// Check the ComplexProcessing debug request is no longer sent to the appender
+		auto finalCount = appender->count;
+		processor.DoStep3();
+		LOGUNIT_ASSERT_EQUAL(appender->count, finalCount);
+	}
+};
+
+LOGUNIT_TEST_SUITE_REGISTRATION(LevelChangeTestCase);