Logging Within A Resource

Every resource capable of hosting custom logging (component, device, service) includes the class member _baseLog. The _baseLog member is a logger instance that has the same logging name as the resource instance. For example, the first instance of comp in a waveform is comp_1. For logging within a REDHAWK resource, _baseLog is the resource’s “root” logger. The log4j root logger still exists and is the parent for the resource’s “root” logger. The log4j root logger is referred to as the empty string.

Each logger object has a member function, getChildLogger(), that takes 1 required argument and a second optional argument. The first argument is the name for the child logger and the second argument is an optional namespace for this logger. If _baseLog belongs to component comp_1, calling getChildLogger() with the first argument set to mylog and no second argument, the logger name comp_1.user.mylog is created. Calling getChildLogger() with the first argument set to mylog and the second argument set to some.namespace creates the logger name comp_1.some.namespace.mylog.

C++ Use

All the following logging statements work with _baseLog. However, to declare a new logger, use the following code in the header:

rh_logger::LoggerPtr my_logger;

To instantiate the new logger, use the following code:

my_logger = this->_baseLog->getChildLogger("my_logger");

To add logging messages within your resource’s code, the following macros are available. These macros use the predefined class logger as the input parameter.

• RH_FATAL(<logger>, message text )
• RH_ERROR(<logger>, message text )
• RH_WARN(<logger>, message text )
• RH_INFO(<logger>, message text )
• RH_DEBUG(<logger>, message text )
• RH_TRACE(<logger>, message text )

where <logger> is the logger instance that should publish the message.

The following example adds DEBUG-level logging messages to the logger my_logger.

RH_DEBUG(this->my_logger, "example log message");

The message text can be combined with stream operations, so the variable my_variable can be added to the logging message:

RH_DEBUG(this->my_logger, "The variable my_variable has the value: "<<my_variable);

Java Use

All of the following logging statements work with _baseLog. However, to declare a new logger, use the following code:

private RHLogger my_logger;

To instantiate the new logger, use the following code:

my_logger = this._baseLog.getChildLogger("my_logger");

The following example adds DEBUG-level logging messages to the logger my_logger.

void someMethod() {
  this.my_logger.debug("example log message");
}

Log4j supports the following severity levels for logging.

_baseLog.fatal(...)
_baseLog.warn(...)
_baseLog.error(...)
_baseLog.info(...)
_baseLog.debug(...)
_baseLog.trace(...)

It also supports programmatically changing the severity level of the logger object.

_baseLog.setLevel(Level.WARN)

Python Use

All the following logging statements work with _baseLog. However, to create a new logger, use the following code:

self.my_logger = self._baseLog.getChildLogger("my_logger")

The following example adds DEBUG-level logging messages to the logger my_logger.

self.my_logger.debug("example log message")

REDHAWK has extended the Python logging support to include the trace method functionality.

self._baseLog.fatal(...)
self._baseLog.warn(...)
self._baseLog.error(...)
self._baseLog.info(...)
self._baseLog.debug(...)
self._baseLog.trace(...)

As with the other logging capabilities, you can programatically change the logging level.

self._baseLog.setLevel(logging.WARN)