2.2. Knowing the execution evironment

Your commands may need to know if you are running as an MPI application and, if so, the sort of process you are. mpiSpecTcl has three types of functionally distinct processes: The Root process runs the interactive Tcl interpreter (and therefore any GUI), the Event sink pipeline process and workers, which run the event processing pipline you write. The organization of the MPI application is described in greater detail in How mpiSpecTcl works in parallel mode..

There is only one Root and one Event sink pipeline process. There are as many Worker processes as you implicitly specify in the mpirun command. User command extensions generally affect the operation of the event processing pipeline and, therefore when running MPI should onhly actually do something in worker processes.

In MPI processes are grouped together in communicators. Each process is assigned an unsigned integer number called a rank within each communicator to which it belongs. WHen an MPI application starts, an initial communicator called the world communicator is created by the MPI run-time and processes are assigned a rank within the world communicator. It is the world communicator rank that mpiSpecTcl uses to assign roles to each process.

The header Globals.h defines three preprocessor constants:

The header TclPump.h provides a pair of functions:

Here is sample code for a command processor that only executes in worker processes when the SpecTcl is an mpi application but executes as well if SpecTcl is run serially.

#include <TclPump.h>
...
int SomCommandProcessor::operator()(
    CTCLInterpreter& interp, std::vector<CTCLObject>& objv
) {
    if (isMpiApp() && (myRank() < MPI_FIRST_WORKER_RANK)) {
        return TCL_OK;
    }
    // The actual stuff the command does...


}