logger - System to control logging of events.

package require Tcl 8.2 package require logger ?0.5? logger::init service logger::import ?-all? ?-force? ?-prefix prefix? ?-namespace namespace? service logger::services logger::enable level logger::disable level logger::setlevel level logger::levels logger::servicecmd service ${log}::debug message ${log}::info message ${log}::notice message ${log}::warn message ${log}::error message ${log}::critical message ${log}::setlevel level ${log}::enable level ${log}::disable level ${log}::logproc level ${log}::logproc level command ${log}::logproc level argname body ${log}::services ${log}::servicename ${log}::currentloglevel ${log}::delproc command ${log}::delproc ${log}::delete

The logger package provides a flexible system for logging messages from different services, at priority levels, with different commands.

To begin using the logger package, we do the following:

    package require logger
    set log [logger::init myservice]
    ${log}::notice "Initialized myservice logging"

... code ...

${log}::notice "Ending myservice logging" ${log}::delete

In the above code, after the package is loaded, the following things happen:

logger::init service

Initializes the service service for logging. The service names are actually Tcl namespace names, so they are seperated with '::'. When a logger service is initialized, it "inherits" properties from its parents. For instance, if there were a service foo, and we did a logger::init foo::bar (to create a bar service underneath foo), bar would copy the current configuration of the foo service, although it would of course, also be possible to then seperately configure bar. If a logger service is initialized and the parent does not yet exist, the parent is also created.

logger::import ?-all? ?-force? ?-prefix prefix? ?-namespace namespace? service

Import the logger service commands into the current namespace. Without the -all option only the commands corresponding to the log levels are imported. If -all is given, all the ${log}::cmd style commands are imported. If the import would overwrite a command an error is returned and no command is imported. Use the -force option to force the import and overwrite existing commands without complaining. If the -prefix option is given, the commands are imported with the given prefix prepended to their names. If the -namespace option is given, the commands are imported into the given namespace. If the namespace does not exist, it is created. If a namespace without a leading :: is given, it is interpreted as a child namespace to the current namespace.

logger::services

Returns a list of all the available services.

logger::enable level

Globally enables logging at and "above" the given level. Levels are debug, info, notice, warn, error, critical.

logger::disable level

Globally disables logging at and "below" the given level. Levels are those listed above.

logger::setlevel level

Globally enable logging at and "above" the given level. Levels are those listed above.

logger::levels

Returns a list of the available log levels (also listed above under enable).

logger::servicecmd service

Returns the ${log} token created by logger::init for this service.

${log}::debug message

${log}::info message

${log}::notice message

${log}::warn message

${log}::error message

${log}::critical message

These are the commands called to actually log a message about an event. ${log} is the variable obtained from logger::init.

${log}::setlevel level

Enable logging, in the service referenced by ${log}, and its children, at and above the level specified, and disable logging below it.

${log}::enable level

Enable logging, in the service referenced by ${log}, and its children, at and above the level specified. Note that this does not disable logging below this level, so you should probably use setlevel instead.

${log}::disable level

Disable logging, in the service referenced by ${log}, and its children, at and below the level specified. Note that this does not enable logging above this level, so you should probably use setlevel instead. Disabling the loglevel critical switches logging off for the service and its children.

${log}::logproc level

${log}::logproc level command

${log}::logproc level argname body

This command comes in three forms - the third, older one is deprecated and may be removed from future versions of the logger package. The current set version takes one argument, a command to be executed when the level is called. The callback command takes on argument, the text to be logged. If called only with a valid level logproc returns the name of the command currently registered as callback command. logproc specifies which command will perform the actual logging for a given level. The logger package ships with default commands for all log levels, but with logproc it is possible to replace them with custom code. This would let you send your logs over the network, to a database, or anything else. For example:

    proc logtoserver {txt} {
        variable socket
        puts $socket "Notice: $txt"
    }

${log}::logproc notice logtoserver

${log}::services

Returns a list of the registered logging services which are children of this service.

${log}::servicename

Returns the name of this service.

${log}::currentloglevel

Returns the currently enabled log level for this service. If no logging is enabled returns none.

${log}::delproc command

${log}::delproc

Set the script to call when the log instance in question is deleted. If called without a command it returns the currently registered command. For example:

    ${log}::delproc [list closesock $logsock]

${log}::delete

This command deletes a particular logging service, and its children. You must call this to clean up the resources used by a service.

The logger package is implemented in such a way as to optimize (for Tcl 8.4 and newer) log procedures which are disabled. They are aliased to a proc which has no body, which is compiled to a no op in bytecode. This should make the peformance hit minimal. If you really want to pull out all the stops, you can replace the ${log} token in your code with the actual namespace and command (${log}::warn becomes ::logger::tree::myservice::warn), so that no variable lookup is done. This puts the performance of disabled logger commands very close to no logging at all.

The "object orientation" is done through a hierarchy of namespaces. Using an actual object oriented system would probably be a better way of doing things, or at least provide for a cleaner implementation.

The service "object orientation" is done with namespaces.

log, log level, logger, service