mpi::mpi -- Command ensemble for MPI under tcl.


mpirun -np nprocesses /usr/opt/mpitcl/bin/mpitcl script

mpi::mpi subcommand ...


mpitcl is an enhanced Tcl interpreter that provides simple Tcl-ish extensions to support massively parallel programming with Tcl under the Message Passing Interface (MPI).

In mpitcl, the rank 0 process runs a Tcl interpreter that takes commands from stdin just as a normal interpreter does. All other ranks run a loop that accepts MPI messages that request data transfer, or command execution. Thus the rank 0 process is the driver of the computation, passing out work, in the form of commands and data to the other processes. Processes other than rank 0, can run scripts that communicate with other processes in the same manner, requesting script execution or data transfer.

A notifier thread in the rank 0 process can be used to queue MPI communication events to the interpreter running in the rank 0 process. These events will be seen when that interpreter enters the event loop via e.g. vwait or, if the cluster on which the application runs supports it, by loading the Tk package.

The extension to the interpreter is a single command ensemble: mpi::mpi. This command is defined in the interpreters that run in all ranks. This command has the following subcommands:


Returns the number of processes in the application. This is legal in all ranks.


Returns the rank of the process. More precisely this is the rank within the MPI_COMM_WORLD predefined communicator.

execute rank script

Executes the script in the processes designated by rank. The rank parameter can either be a numeric rank, or it can be one of two special keywords.

If the rank is the keyword others the execution is requested in all other processes but not the requesting process. If the rank is the keyword all the execution is requested first via MPI messaging to all other ranks and then performed directly in the requestor's interpreter.

Note that if other processes request execution of scripts in the rank 0 process, this will be deferred until that process next enteres its event loop with e.g. vwait.

Note that a request like mpi::mpi execute [mpi::mpi rank] ... will use MPI message passing to request this process execute the script. Only in the special all rank is script execution performed directly in the current process's interpreter.

send rank data

Sends the data to the process(es) determined by rank. Note that once more, the special ranks others and all described above in the execute subcommand are recognized.

In order to receive data, the receiving process must have established a data handler via the handle subcommand. Furthermore, messages sent to the rank 0 process require that process to enter the event loop (e.g. via vwait) before they are received.

The data are sent via the the MPI data type MPI_CHAR, this is suitable for arbitrary Tcl data since everything in Tcl has a string representation.

handle script-prefix

Establishes a data receiver handling script. When data are received from a process (sent via mpi::mpi send), the rank of the sender and the data are lappended to the script-prefix which is then executed.

The script-prefix can be a multiword prefix, and normally is a proc invocation, though it need not be.


Stops the notifier thread. This must be done prior to application exit as otherwise the thread might signal an event to an interpreter that no longer exists which can cause segfaults.

stopnotifier might also be used prior to turning over control to a command extension that wants complete control over communication (e.g compiled code distributing data to compiled code).

This subcommand is only legal in the rank 0 process as other ranks don't run a notifier thread.


Starts the notifier after it has been stoppped. This is only legal for rank 0.

Note that mpirun wants to see all processes in the application exit prior to exiting itself. Therefore the proper way to terminate an mpitcl application is with the following script fragment.

Example A-1. Terminating an MPITcl application

mpi::mpi execute all exit