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       MPIL_Trace_off -  LAM/MPI-specific function to disable run-time tracing


       #include <mpi.h>
       int MPIL_Trace_off(void)


       These functions give the application the flexibility to generate traces
       only  during certain interesting phases of the application's execution.
       This technique can considerably reduce the size of the trace files  and
       burden of displaying them.

       Both functions are collective over the MPI_COMM_WORLD communicator.  In
       typical usage, the -toff option of mpirun (1) would be used  to  enable
       tracing, but start with the runtime switch in the off position.  At the
       beginning of an interesting phase of program  execution,  MPIL_Trace_on
       would  be called.  MPIL_Trace_off would be called after the interesting
       phase.  Tracing can be turned on and off many times.   Each  period  of
       tracing eventually forms a trace segment in the trace file extracted by
       lamtrace (1).  If the on/off functions are never used  and  tracing  is
       enabled  with  the -ton option of mpirun (1), a single trace segment is

       The on/off functions have no effect if tracing is not enabled by mpirun
       (1)  with  either the -ton or -toff switches.  Thus, an application can
       be littered with these functions but run without trace  collection  and
       very little additional overhead due to the no-operation function calls.

       This  is  a  LAM/MPI-specific  function  and  is  intended  mainly  for
       debugging.   If this function is used, it should be used in conjunction
       with the LAM_MPI C preprocessor macro

       #if LAM_MPI


       After the volume of generated traces exceeds a preset limit, the oldest
       traces  are  discarded  in  favour  of  new traces.  Avoiding discarded
       traces is further incentive to use MPIL_Trace_on and MPIL_Trace_off .


       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK )  have
       an  additional  argument ierr at the end of the argument list.  ierr is
       an integer and has the same meaning as the return value of the  routine
       in  C.   In Fortran, MPI routines are subroutines, and are invoked with
       the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in


       If an error occurs in an MPI function, the current MPI error handler is
       called to handle it.  By default, this error  handler  aborts  the  MPI
       job.   The  error  handler may be changed with MPI_Errhandler_set ; the
       predefined error handler MPI_ERRORS_RETURN may be used to  cause  error
       values  to  be  returned  (in C and Fortran; this error handler is less
       useful in with the C++ MPI  bindings.   The  predefined  error  handler
       MPI::ERRORS_THROW_EXCEPTIONS  should  be used in C++ if the error value
       needs to be recovered).  Note that MPI does not guarantee that  an  MPI
       program can continue past an error.

       All  MPI  routines  (except  MPI_Wtime  and MPI_Wtick ) return an error
       value; C routines as the value of the function and Fortran routines  in
       the  last  argument.   The  C++  bindings  for  MPI do not return error
       values; instead, error values are communicated by  throwing  exceptions
       of  type  MPI::Exception  (but  not  by  default).  Exceptions are only
       thrown if the error value is not MPI::SUCCESS .

       Note that if the MPI::ERRORS_RETURN handler is set in  C++,  while  MPI
       functions  will  return  upon an error, there will be no way to recover
       what the actual error value was.
              - No error; MPI routine completed successfully.
              - Other error; use  MPI_Error_string  to  get  more  information
              about this error code.


       MPI_Trace_on, mpirun