使用MPI程序，所有进程都可以从用户输入中获取数据吗？

Question

What I'm asking is if I have something like this:

int main(int argc, char *argv[]) //<---input from command line
{

Do I need to use MPI_Bcast in order to send that data to all of the processes, or do all of the processes get the command line input data anyway?

Answer 1

If you use MPI_Init(&argc,&argv) this solves you problem :)

No need to BCast anything ;)

Answer 2

Passing the full command line to all MPI processes is part of the initial launch mechanism. This is intentionally omitted from the MPI standard, but most MPI implementations do the Right Thing (tm) and actually pass all command line arguments to all processes in the MPI job. It is even possible to have different command line arguments passed to different ranks and even several different executables started in a single MPI job.

For example, the following command will start 10 copies of the same executable program and pass each of them the same command line arguments arg1 and arg2 :

$ mpiexec -n 10 program arg1 arg2

The following command will start 10 copies of program and pass arg1 to the first five processes (ranks 0 to 4) and arg2 to the next five processes (ranks 5 to 9):

$ mpiexec -n 5 program arg1 : -n 5 program arg2

The following command will start 5 copies of program1 with arguments arg1 and 5 copies of program2 with arguments arg2 :

$ mpiexec -n 5 program1 arg1 : -n 5 program2 arg2

Calling MPI_Init() has nothing to do with the mechanism by which the MPI processes are started. Passing argc and argv to MPI_Init was required in the very old MPI-1 specification since many MPI implementations used additional command line arguments in order to bootstrap the MPI job. Yet this requirement was somehow artificial since the Fortran bindings didn't have that arguments (in Fortran 77 there is no standard way to obtain the command line arguments) and somehow they were properly implemented. Therefore MPI-2 removed this requirement and allows for NULL s to be passed instead so that it is possible to write parallel libraries that in general have no access to the command line arguments. Therefore most MPI implementations switched to providing all the necessary bootstrap information through environment variables or other OS-specific mechanisms.