Great and Powerful Logger

Great and Powerfull Logger is part of Sweetie Bot project. It is meant as drop in replacment for RTT::Logger.

Native OROCOS logging system suffers a few drawbacks:

1. RTT::Logger does not support categories and individual log levels for components. Also it is not real-time.

2. OCL::logging::Category provides real-time logging service, but suffers from not very convinent syntax for << operator:

    log->getRTStream(log4cpp::ERROR) << 
   

   Moreover it creates temporary ostringstream any getRTStream call.

3. log4cpp::Category is not realtime, deployer does not support log4cpp out of box (recompiling is needed).

4. All logging systems lack ROS integration.

Great and Powerfull Loger is hear to fix thoese deficiencies! It has many tricks under its mantle.

1. log4cpp::RosAppender is log4cpp appender which forward messages to \rosout ROS topic.

2. RosAppenderService (rosout service) is able to forward given log4cpp category to \rosut (use addCategory operation).

3. Log4cppService (log4cpp service) allows to initialize log4cpp using configuration file.

4. OCL::logging::RosAppender component forwards log from OCL::logging category to \rosut (use OCL::logging::LoggerService to setup connection).

5. Logger interface includes:

   • LoggerLog4Cpp logs directly to specified log4cpp category.

   • LoggerOCL logs to OCL category.

   • LoggerRos directry logs to \rosout, for log priority assigment may use OCL or log4cpp categories.

   • LoggerRTT uses RTT::Logger to display messages. Loggers do not rely on dynamic memory allocation and use RTT::Loger style syntax:

     using sweetie_bot::Logger; sweetie_bot::LoggerLog4Cpp log("robot.component");

     log(Logger::INFO) << "I'm GREAT and POWERFULL LOGEER!" << Logger::endl;

   Great and Powerfull Logger creates unexisting categories (despite generosity is clearly not its element). But you should set log levels via log4cpp configuration file or using ocl::logging::LoggerService component. By default log levels are UNSET so no messages are shown.

   Log is flushed by Logger::endl manipulator, RTT::Logger maipulators are also supported. See LoggerTest for example.

Usage

Your should select the logger facility and declare log4cpp categories.

Using LoggerRTT and LoggerRos

Your should configure loglevels using log4cpp configuration file or OCL LoggerService cpf file. See scripts/logger.log4cpp and scripts/logger.cpf for example. This files contains log levels for hierarchical tree of categories see log4cpp documentation for more details.

Then there are three ways to provide deployer with this information:

1. Use --rtt-log4cpp-config-file option of deployer on startup. (Deployer must be compiled with log4cpp support).
2. Use log4cpp service to load .log4cpp file (see scripts/test_logger.ops and scripts/test_logger_log4cpp.lua).
3. Use marshalling service to load .cpf file in OCL::LoggerService component.

Basic deployment code looks like:

loadService("Deployer", "log4cpp");
log4cpp.configure("logger.log4cpp");

or in lua (see scripts/logger.lua helper module and scripts/test_logger_log4cpp.lua for details):

dofile(rttros.find_rospack("sweetie_bot_logger") .. "logger.lua")
logger.init_loglevels_log4cpp("logging.log4cpp")

Using LoggerLog4cpp

Use log4cpp configuration file to declare loglevels and appenders. See log4cpp documentation for details. Example configuration may be found in scripts/logger_log4cpp.log4cpp.

Also you may add RosAppender to any category to redirect messages to /rosout.

log4cpp.addRosAppender("<category_name>", 20);

Using LoggerOCL

Use OCL logging infrastructure deployment procedure as described in OROCOS documentation. See scripts/test_logger_ocl.ops as example.

Redirecting RTT::Logger to /rosout

If deployer is compiled with log4cpp support you can redirect RTT::Logger category org.orocos.rtt to \rosout:

log4cpp.addRosAppender("org.orocos.rtt", 20);

But during shutdown deadlock occurs due to logging attempt using appender being destructed. Currently this bug is fixed by assert. Also you can call log4cpp.shutdown explicitly to prevent deadlock.

Test scripts:

LOGGER_SCRIPTS=`rospack find sweetie_bot_logger`/scripts

deployer -s $LOGGER_SCRIPTS/test_logger.ops
deployer -s $LOGGER_SCRIPTS/test_logger_log4cpp.ops
rttlua -i $LOGGER_SCRIPTS/test_logger_log4cpp.lua
deployer -s $LOGGER_SCRIPTS/test_logger_ocl.ops

Known bugs and limitations

1. LoggerRosut uses Mutex to prevent concurrent write.
2. If output port of log4cpp:::RosAppender is connected during object destruction Ursa Major is being summomed (deadlock happens). It is caused by attempt to log via appender being destructed. Currently bug is amended with assert but also log4cpp.shutdown just before exit.
3. It seems \rosout is unable to process connection requests fast enoughs. First bunch of messages from LoggerTest is missing on \rosout. Just call sleep.