MPI_Init(3) LAM/MPI MPI_Init(3)
MPI_Init - Initialize the MPI execution environment
int MPI_Init(int *pargc, char ***pargv)
pargc - Pointer to the number of arguments
pargv - Pointer to the argument vector
MPI specifies no command-line arguments but does allow an MPI implementation to make use
of them. LAM/MPI neither uses nor adds any values to the argc and argv parameters. As
such, it is legal to pass NULL for both argc and argv in LAM/MPI.
Instead, LAM/MPI relies upon the mpirun command to pass meta-information between nodes in
order to start MPI programs (of course, the LAM daemons must have previously been launched
with the lamboot command). As such, every rank in MPI_COMM_WORLD will receive the argc
and argv that was specified with the mpirun command (either via the mpirun command line or
an app schema) as soon as main begins. See the mpirun (1) man page for more information.
If mpirun is not used to start MPI programs, the resulting process will be rank 0 in
MPI_COMM_WORLD , and MPI_COMM_WORLD will have a size of 1. This is known as a "singleton"
MPI. It should be noted that LAM daemons are still used for singleton MPI programs - lam-
boot must still have been successfully executed before running a singleton process.
LAM/MPI takes care to ensure that the normal Unix process model of execution is preserved:
no extra threads or processes are forked from the user's process. Instead, the LAM dae-
mons are used for all process management and meta-environment information. Consequently,
LAM/MPI places no restriction on what may be invoked before MPI_Init* or after MPI_Final-
ize ; this is not a safe assumption for those attempting to write portable MPI programs -
see "Portability Concerns", below.
MPI mandates that the same thread must call MPI_Init or MPI_Init_thread and MPI_Finalize
Note that the Fortran binding for this routine has only the error return argument (
Because the Fortran and C versions of MPI_Init are different, there is a restriction on
who can call MPI_Init
. The version (Fortran or C) must match the main program. That is, if the main program
is in C, then the C version of MPI_Init must be called. If the main program is in For-
tran, the Fortran version must be called.
On exit from this routine, all processes will have a copy of the argument list. This is
not required by the MPI standard, and truely portable codes should not rely on it. This
is provided as a service by this implementation (an MPI implementation is allowed to dis-
tribute the command line arguments but is not required to).
The LAM implementation of MPI uses, by default, SIGUSR2
. This may be changed when LAM is compiled, however, with the --with-signal command line
switch to LAM's configure script. Consult your system administrator to see if they speci-
fied a different signal when LAM was installed.
LAM/MPI catches several signals for the purpose of printing error messages before invoking
the next signal handler. That is, LAM "chains" its signal handler to be executed before
the signal handler that was already set. This scheme prevents nodes (remote nodes, espe-
cially) from silently dying and hanging the remaining MPI ranks because of unfinished com-
munications - a very confusing situation when debugging parallel programs.
Therefore, it is safe for users to set their own signal handlers. If they wish the LAM
signal handlers to be executed as well, users should set their handlers before MPI_Init*
is invoked. If users do not wish to have LAM catch signals (a bad idea!), they should set
their handlers after MPI_Init* is invoked.
LAM/MPI catches the following signals
SIGSEGV , SIGBUS , SIGFPE , SIGILL
All other signals are unused by LAM/MPI, and will be passed to their respective signal
Portable MPI programs cannot assume the same process model that LAM uses (i.e., essen-
tially the same as POSIX). MPI does not mandate anything before MPI_Init (or
MPI_Init_thread ), nor anything after MPI_Finalize executes. Different MPI implementa-
tions make different assumptions; some fork auxillary threads and/or processes to "help"
with the MPI run-time environment (this may interfere with the constructors and destruc-
tors of global C++ objects, particularly in the case where using atexit() or onexit(), for
example). As such, if you are writing a portable MPI program, you cannot make the same
assumptions that LAM/MPI does.
In general, it is safest to call MPI_Init (or MPI_Init_thread ) as soon as possible after
main begins, and call MPI_Finalize immediately before the program is supposed to end.
Consult the documentation for each MPI implementation for their intialize and finalize
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.
- This error class is associated with an error code that indicates that an attempt
was made to call MPI_INIT a second time. MPI_INIT may only be called once in a
- Other error; use MPI_Error_string to get more information about this error code.
MPI_Init_thread, MPI_Finalize, lamboot, mpirun, lamhalt
For more information, please see the official MPI Forum web site, which contains the text
of both the MPI-1 and MPI-2 standards. These documents contain detailed information about
each MPI function (most of which is not duplicated in these man pages).
The LAM Team would like the thank the MPICH Team for the handy program to generate man
pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial for-
matting, and some initial text for most of the MPI-1 man pages.
LAM/MPI 6.5.8 11/10/2002 MPI_Init(3)