Provided by: tcllib_1.14-dfsg-1_all bug

NAME

       logger - System to control logging of events.

SYNOPSIS

       package require Tcl  8.2

       package require logger  ?0.9?

       logger::init service

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

       logger::initNamespace ns ?level?

       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}::alert message

       ${log}::emergency message

       ${log}::setlevel level

       ${log}::enable level

       ${log}::disable level

       ${log}::lvlchangeproc command

       ${log}::lvlchangeproc

       ${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

       ${log}::trace command

       ${log}::trace on

       ${log}::trace off

       ${log}::trace status ?procName? ?...?

       ${log}::trace add procName ?...?

       ${log}::trace add ?-ns? nsName ?...?

       ${log}::trace remove procName ?...?

       ${log}::trace remove ?-ns? nsName ?...?

_________________________________________________________________

DESCRIPTION

       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  separated  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 separately configure bar.  If
              a logger service is initialized and the parent does not yet exist,  the  parent  is
              also  created.  The new logger service is initialized with the default loglevel set
              with logger::setlevel.

       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::initNamespace ns ?level?
              Convenience  command  for  setting  up  a  namespace  for logging. Creates a logger
              service named after the namespace ns (a :: prefix is stripped), imports all the log
              commands  into  the  namespace,  and  sets the default logging level, either to the
              specified level, or the default level, "warn".

       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, alert, emergency.

       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.  This  command  changes  the  default  loglevel for new loggers created with
              logger::init.

       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

       ${log}::alert message

       ${log}::emergency 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  emergency
              switches logging off for the service and its children.

       ${log}::lvlchangeproc command

       ${log}::lvlchangeproc
              Set the script to call when the log instance in question changes its log level.  If
              called without a command it returns the currently registered command.  The  command
              gets  two arguments appended, the old and the new loglevel. The callback is invoked
              after all changes have been done.  If child loggers are affected,  their  callbacks
              are called before their parents callback.

                proc lvlcallback {old new} {
                    puts "Loglevel changed from $old to $new"
                }
                ${log}::lvlchangeproc lvlcallback

       ${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

              Trace  logs  are slightly different: instead of a plain text argument, the argument
              provided to the logproc is a dictionary consisting of the enter  or  leave  keyword
              along with another dictionary of details about the trace.  These include:

              ·      proc - Name of the procedure being traced.

              ·      level - The stack level for the procedure invocation (from info level).

              ·      script - The name of the file in which the procedure is defined, or an empty
                     string if defined in interactive mode.

              ·      caller - The name of the procedure calling the procedure being traced, or an
                     empty  string if the procedure was called from the global scope (stack level
                     0).

              ·      procargs - A  dictionary  consisting  of  the  names  of  arguments  to  the
                     procedure paired with values given for those arguments (enter traces only).

              ·      status - The Tcl return code (e.g. ok, continue, etc.) (leave traces only).

              ·      result - The value returned by the procedure (leave traces only).

       ${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.

       ${log}::trace command
              This  command  controls logging of enter/leave traces for specified procedures.  It
              is used to enable and disable tracing, query tracing status, and specify procedures
              are  to be traced.  Trace handlers are unregistered when tracing is disabled.  As a
              result, there is not performance impact to a library when tracing is disabled, just
              as with other log level commands.

                proc tracecmd { dict } {
                    puts $dict
                }

                set log [::logger::init example]
                ${log}::logproc trace tracecmd

                proc foo { args } {
                    puts "In foo"
                    bar 1
                    return "foo_result"
                }

                proc bar { x } {
                    puts "In bar"
                    return "bar_result"
                }

                ${log}::trace add foo bar
                ${log}::trace on

                foo

              # Output:
              enter {proc ::foo level 1 script {} caller {} procargs {args {}}}
              In foo
              enter {proc ::bar level 2 script {} caller ::foo procargs {x 1}}
              In bar
              leave {proc ::bar level 2 script {} caller ::foo status ok result bar_result}
              leave {proc ::foo level 1 script {} caller {} status ok result foo_result}

       ${log}::trace on
              Turns  on  trace  logging  for procedures registered through the trace add command.
              This is similar to the enable command for other logging levels,  but  allows  trace
              logging to take place at any level.  The trace logging mechanism takes advantage of
              the execution trace feature of Tcl 8.4 and later.  The trace on command will return
              an error if called from earlier versions of Tcl.

       ${log}::trace off
              Turns  off  trace  logging  for procedures registered for trace logging through the
              trace add command.  This is similar  to  the  disable  command  for  other  logging
              levels,  but  allows  trace logging to take place at any level.  Procedures are not
              unregistered, so logging for them can be turned back on with the trace on  command.
              There is no overhead imposed by trace registration when trace logging is disabled.

       ${log}::trace status ?procName? ?...?
              This  command  returns  a  list  of  the  procedures currently registered for trace
              logging, or a flag indicating whether or not a trace is registered for one or  more
              specified procedures.

       ${log}::trace add procName ?...?

       ${log}::trace add ?-ns? nsName ?...?
              This  command  registers  one  or more procedures for logging of entry/exit traces.
              Procedures can be specified via a list of procedure names or  namespace  names  (in
              which  case  all procedure within the namespace are targeted by the operation).  By
              default, each name is first interpreted as a procedure name  or  glob-style  search
              pattern,  and if not found its interpreted as a namespace name.  The -ns option can
              be used to force interpretation of  all  provided  arguments  as  namespace  names.
              Procedures  must be defined prior to registering them for tracing through the trace
              add command.  Any procedure  or  namespace  names/patterns  that  don't  match  any
              existing procedures will be silently ignored.

       ${log}::trace remove procName ?...?

       ${log}::trace remove ?-ns? nsName ?...?
              This  command  unregisters  one or more procedures so that they will no longer have
              trace logging performed, with the same matching rules as  that  of  the  trace  add
              command.

IMPLEMENTATION

       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.

LOGPROCS AND CALLSTACK

       The  logger  package  takes  extra  care  to keep the logproc out of the call stack.  This
       enables logprocs to execute code in the callers scope by using uplevel or linking to local
       variables by using upvar. This may fire traces with all usual side effects.

                   # Print caller and current vars in the calling proc
                   proc log_local_var {txt} {
                        set caller [info level -1]
                        set vars [uplevel 1 info vars]
                        foreach var [lsort $vars] {
                           if {[uplevel 1 [list array exists $var]] == 1} {
                           lappend val $var <Array>
                           } else {
                           lappend val $var [uplevel 1 [list set $var]]
                           }
                        }
                        puts "$txt"
                        puts "Caller: $caller"
                        puts "Variables in callers scope:"
                        foreach {var value} $val {
                        puts "$var = $value"
                        }
                   }

                   # install as logproc
                   ${log}::logproc debug log_local_var

BUGS, IDEAS, FEEDBACK

       This  document,  and  the  package  it  describes, will undoubtedly contain bugs and other
       problems.   Please  report  such  in  the  category  logger  of  the  Tcllib  SF  Trackers
       [http://sourceforge.net/tracker/?group_id=12883].    Please  also  report  any  ideas  for
       enhancements you may have for either package and/or documentation.

KEYWORDS

       log, log level, logger, service

CATEGORY

       Programming tools