The Logger is a C++ class that provides a configurable and flexible way to view and save logging data.

  • Class name: Logger
  • Location: $ADOPT_ROOT/lib
  • Files: Logger.h, Logger.cpp (Utils.h)

The public interface of the Logger class is easily understandable: please read the Logger.h file. To have a general overview, please first have a look to the following paragraph.


The Logger class provides a pool of "user-defined" objects, defined by a specific name and logging level ( local settings): for this reason the Logger class will be called Logger pool, and each single logger will be called Logger.

Only a unique Logger pool can exists for each process (singleton): there isn't any way to have more than one pool. The reason is that all the loggers inside the pool can be accessed from everywhere in your code in a static way:

Example: Logger* myLogger = Logger::get(Logger::LOG_LEV_XXX, "LoggerName")

Note that:
If the logger already exists, its current level is always preserved (the given LOG_LEV_XXX doesn' have any effect).
If the name of the logger is not specified, the default logger named "MAIN" is returned.
If the level of the logger is not specified, the default level is used (Logger::LOG_LEV_DEFAULT).

The Logger pool is defined by some global settings, commons to each contained loggers:

  • Parent name: the name of the process using the Logger pool. This should be set ONLY in the program main, and never changed.
  • Log method: STDOUT, FILE, MSGD; the default is FILE (mutually exclusive, except MsgD, see below)
  • Log file: the file, including the full path, where the data are logged (if method is FILE).

For each Logger belonging to the Logger pool the following levels are available: TRACE (6), DEBUG (5), INFO (4), WARNING (3), ERROR (2), FATAL (1).
There are also 2 special levels: ALWAYS (-1), DISABLED (0).

A log level is used to:

  • Set the Logger level: this can be done at the moment of the Logger instantiation (or later), and defines the amount of information logged; the default is ERROR.
  • Log a line: the line will be logged only if: 1) Logger setting is not DISABLED; 2) The given level is less than the Logger setting.

A request with level ERROR or FATAL is logged also to MSGD (NB: if Logger setting is not DISABLED).

Example: myLogger->log(Logger::LOG_LEV_XXX, "This is a logging line")

Consider that the log level is only set when the named logger is created, and is NOT modified by the following get(...). The only way to modify the log level ii using the object's method set(LogLevel).

Example: myLogger->setLevel(Logger::LOG_LEV_YYY)

Log method FILE
Here some details about the global log method FILE.

The Logger pool allow to set both the file name and the file path:

static void setLogFile(string fileName, string filePath, bool renaming = false) throw(LoggerFatalException);

The extension ".log" is always added to the log file name.

Some default values are provided:

  • Logger::LOG_PATH_DEFAULT = "/tmp"; this is used also if the given filePath doesn't exists or is not writable

The Logger pool provides two static methods to setup the log to file:

  • Logger::setLogFile(string fileName, string filePath, bool renaming)
  • Logger:::setMethod(int method)

Please see Logger.h for detailed explaination.

The Logger pool also perform a transparent log file record keeping, renaming a "full" file to an archive file. A log file is considered "full" when the number of logged lines is equal to Logger::MAX_LINES_PER_LOGFILE. This task is transparent because the client (usually an AOApp) can continue to log without taking care of the archives.
Given a log file named PROCESS_NAME.log, the archived file is PROCESS_NAME.secsFrom1Jan1970.log (see Utils::timeAsString() method).


It's important to understand where and why your AOApp is logging.

Each AOApp defines the following config parameters related to the logger: LogLevel and LogMethod. These parameters ar not mandatory, and their default values (see AOApp.h) are:

The path used for the logging is got from $ADOPT_LOG environment variable; if the variable doesn't exists or is set to a wrong directory (not existing or not writable), a default directory is used (see AOApp.h, AOApp::DEFAULT_LOG_PATH) .

The name of the log file is obtained concatenating the config file parameters MyName and ID, just to have an unique filename (in the same way the AOApp register itself in MsgD).

Because all these parameters (name, level and method) are known only AFTER the configuration is loaded, but of course the logging must be provided also BEFORE, a temporary log file name is used ( aopp_[pid].log) and then the file is renamed. This means that the configuration loading is always logged to the file aopp_pid.log with a default logger level statically defined by AOApp (see AOApp.h, AOApp::CONFIG_LOADER_LOG_LEVEL).

NOTE that, if a problem occurs before the log file is renamed (i.e. in configuration reading), the log file will have the temporary name.
Switching to log method STDOUT

Let's see the bahaviour of the Logger when the log method is switched to STDOUT, becuase it could appear a little complicated

As mentioned above, th default logging method is FILE. When an AOApp starts, immediately instantiates a Logger named "MAIN": the Logger pool initialize the log filename to aoapp_pid.log, and this log file is created in $ADOPT_LOG (or, if $ADOPT_LOG not set, in Logger::LOG_PATH_DEFAULT).

As soon as the log method is switched to STDOUT, the file aoapp_pid.log is archived, so you will find the archive ( aoapp_pid.time.log) it in the log path; depending on the log level, it could be empty. Then, when the AOApp load its name from the config file, the new name for the config file is set: it will be used when you set the method FILE again.


The Logger is implemented as a singleton object containing a collection of "named" Logger objects. This collection is a STL map, which maps a "logger name" to a "logger reference".

-- FabioTosetti - 18 Mar 2008
Topic revision: r12 - 22 Oct 2009, LucaFini
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