MPIL_Trace_on(3) LAM/MPI MPIL_Trace_on(3)
MPIL_Trace_on - LAM/MPI-specific function to enable run-time tracing
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
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
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
NOTES FOR FORTRAN
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.
LAM/MPI 6.5.8 11/10/2002 MPIL_Trace_on(3)