DOKK / manpages / debian 13 / openmpi-doc / MPI_Query_thread.openmpi.3.en
MPI_QUERY_THREAD(3) Open MPI MPI_QUERY_THREAD(3)

MPI_Query_thread — Returns the current level of thread support

#include <mpi.h>
int MPI_Query_thread(int *provided)



USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_QUERY_THREAD(PROVIDED, IERROR)


     INTEGER PROVIDED, IERROR



USE mpi_f08
MPI_Query_thread(provided, ierror)


     INTEGER, INTENT(OUT) :: provided


     INTEGER, OPTIONAL, INTENT(OUT) :: ierror


  • provided: C/Fortran only: Level of thread support (integer).
  • ierror: Fortran only: Error status (integer).

This routine returns in provided the current level of thread support. If MPI was initialized by a call to MPI_Init_thread, provided will have the same value as was returned by that function.

The possible values of provided are as follows:

Only one thread may execute.
If the process is multithreaded, only the thread that called MPI_Init[_thread] may make MPI calls.
If the process is multithreaded, only one thread may make MPI library calls at one time.
If the process is multithreaded, multiple threads may call MPI at once with no restrictions.

In Open MPI, provided is always MPI_THREAD_SINGLE, unless the program has been linked with the multithreaded library, in which case provided is MPI_THREAD_MULTIPLE.

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

  • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.
  • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.
  • MPI_ERRORS_RETURN Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

  • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
  • MPI_File_create_errhandler then MPI_File_set_errhandler
  • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
  • MPI_Win_create_errhandler then MPI_Win_set_errhandler

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3.1 standard for more information.

SEE ALSO:

  • MPI_Init
  • MPI_Init_thread



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February 17, 2025