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MPIL_Trace_off(3)			     LAM/MPI				MPIL_Trace_off(3)

       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 cer-
       tain 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 execu-
       tion, 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  func-
       tions  are  never used and tracing is enabled with the -ton option of mpirun (1), a single
       trace segment is produced.

       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 func-
       tion 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  dis-
       carded  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 argu-
       ment 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 Fortran.

       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 excep-
       tions 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


LAM/MPI 6.5.8				    11/10/2002				MPIL_Trace_off(3)
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