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NAME

       cprof  -  A  simple  Call  Count  Profiling  Tool  using  breakpoints  for minimal runtime
       performance impact.

DESCRIPTION

       The cprof module is used to profile a  program  to  find  out  how  many  times  different
       functions  are  called. Breakpoints similar to local call trace, but containing a counter,
       are used to minimise runtime performance impact.

       Since breakpoints are used there is no need for special compilation of any  module  to  be
       profiled. For now these breakpoints can only be set on BEAM code so s cannot be call count
       traced.

       The size of the call counters is the host machine word size. One bit is used when  pausing
       the counter, so the maximum counter value for a 32-bit host is 2147483647.

       The  profiling  result is delivered as a term containing a sorted list of entries, one per
       module. Each module entry contains a sorted list of functions. The sorting order  in  both
       cases is of decreasing call count.

       Call  count  tracing is very lightweight compared to other forms of tracing since no trace
       message has to be generated. Some measurements indicates performance  degradation  in  the
       vicinity of 10 percent.

EXPORTS

       analyse() -> {AllCallCount, ModAnalysisList}
       analyse(Limit) -> {AllCallCount, ModAnalysisList}
       analyse(Mod) -> ModAnlysis
       analyse(Mod, Limit) -> ModAnalysis

              Types:

                 Limit = integer()
                 Mod = atom()
                 AllCallCount = integer()
                 ModAnalysisList = [ModAnalysis]
                 ModAnalysis = {Mod, ModCallCount, FuncAnalysisList}
                 ModCallCount = integer()
                 FuncAnalysisList = [{{Mod, Func, Arity}, FuncCallCount}]
                 Func = atom()
                 Arity = integer()
                 FuncCallCount = integer()

              Collects  and  analyses  the  call counters presently in the node for either module
              Mod, or for all modules (except cprof itself), and returns:

                FuncAnalysisList:
                  A  list  of  tuples,  one  for  each  function  in  a  module,  in   decreasing
                  FuncCallCount order.

                ModCallCount:
                  The sum of FuncCallCount values for all functions in module Mod.

                AllCallCount:
                  The sum of ModCallCount values for all modules concerned in ModAnalysisList.

                ModAnalysisList:
                  A  list of tuples, one for each module except cprof, in decreasing ModCallCount
                  order.

              If call counters are still running while analyse/0..2 is executing, you  might  get
              an  inconsistent  result.  This  happens if the process executing analyse/0..2 gets
              scheduled out so some other process can  increment  the  counters  that  are  being
              analysed, Calling pause() before analysing takes care of the problem.

              If  the  Mod  argument is given, the result contains a ModAnalysis tuple for module
              Mod only, otherwise the result contains  one  ModAnalysis  tuple  for  all  modules
              returned from code:all_loaded() except cprof itself.

              All   functions   with   a   FuncCallCount  lower  than  Limit  are  excluded  from
              FuncAnalysisList. They are still included  in  ModCallCount,  though.  The  default
              value for Limit is 1.

       pause() -> integer()

              Pause  call  count  tracing  for  all  functions in all modules and stop it for all
              functions   in    modules    to    be    loaded.    This    is    the    same    as
              (pause({'_','_','_'})+stop({on_load})).

              See also pause/1..3 below.

       pause(FuncSpec) -> integer()
       pause(Mod, Func) -> integer()
       pause(Mod, Func, Arity) -> integer()

              Types:

                 FuncSpec = Mod | {Mod,Func,Arity}, {FS}
                 Mod = atom()
                 Func = atom()
                 Arity = integer()
                 FS = term()

              Pause call counters for matching functions in matching modules. The FS argument can
              be used to specify the first argument to erlang:trace_pattern/3. See erlang(3erl).

              The call counters for all matching functions that has got  call  count  breakpoints
              are paused at their current count.

              Return  the  number of matching functions that can have call count breakpoints, the
              same as start/0..3 with the same arguments would have returned.

       restart() -> integer()
       restart(FuncSpec) -> integer()
       restart(Mod, Func) -> integer()
       restart(Mod, Func, Arity) -> integer()

              Types:

                 FuncSpec = Mod | {Mod,Func,Arity}, {FS}
                 Mod = atom()
                 Func = atom()
                 Arity = integer()
                 FS = term()

              Restart call counters for the matching functions in matching modules that are  call
              count  traced.  The  FS  argument  can  be  used  to  specify the first argument to
              erlang:trace_pattern/3. See erlang(3erl).

              The call counters for all matching functions that has got  call  count  breakpoints
              are set to zero and running.

              Return  the  number of matching functions that can have call count breakpoints, the
              same as start/0..3 with the same arguments would have returned.

       start() -> integer()

              Start call count tracing for all  functions  in  all  modules,  and  also  for  all
              functions    in    modules    to    be    loaded.    This    is    the    same   as
              (start({'_','_','_'})+start({on_load})).

              See also start/1..3 below.

       start(FuncSpec) -> integer()
       start(Mod, Func) -> integer()
       start(Mod, Func, Arity) -> integer()

              Types:

                 FuncSpec = Mod | {Mod,Func,Arity}, {FS}
                 Mod = atom()
                 Func = atom()
                 Arity = integer()
                 FS = term()

              Start call count tracing  for  matching  functions  in  matching  modules.  The  FS
              argument  can  be used to specify the first argument to erlang:trace_pattern/3, for
              example on_load. See erlang(3erl).

              Set call count breakpoints on  the  matching  functions  that  has  no  call  count
              breakpoints. Call counters are set to zero and running for all matching functions.

              Return the number of matching functions that has got call count breakpoints.

       stop() -> integer()

              Stop  call  count  tracing  for  all  functions  in  all  modules, and also for all
              functions   in    modules    to    be    loaded.    This    is    the    same    as
              (stop({'_','_','_'})+stop({on_load})).

              See also stop/1..3 below.

       stop(FuncSpec) -> integer()
       stop(Mod, Func) -> integer()
       stop(Mod, Func, Arity) -> integer()

              Types:

                 FuncSpec = Mod | {Mod,Func,Arity}, {FS}
                 Mod = atom()
                 Func = atom()
                 Arity = integer()
                 FS = term()

              Stop call count tracing for matching functions in matching modules. The FS argument
              can be used to specify the first argument to  erlang:trace_pattern/3,  for  example
              on_load. See erlang(3erl).

              Remove  call  count  breakpoints  from  the  matching functions that has call count
              breakpoints.

              Return the number of matching functions that can have call count  breakpoints,  the
              same as start/0..3 with the same arguments would have returned.

SEE ALSO

       eprof(3erl), fprof(3erl), erlang(3erl), User's Guide