# MPI_Query_thread

Return the level of thread support provided by the MPI library

## Synopsis

    int MPI_Query_thread(int *provided)

## Output Parameters

provided
  provided level of thread support (integer)

## Notes

The valid values for the level of thread support are:

MPI_THREAD_SINGLE
  Only one thread will execute.
MPI_THREAD_FUNNELED
  The process may be multi-threaded, but only the main thread will make MPI calls (all MPI calls are funneled to the main thread).
MPI_THREAD_SERIALIZED
  The process may be multi-threaded, and multiple threads may make MPI calls, but only one at a time: MPI calls are not made concurrently from two distinct threads (all MPI calls are serialized).
MPI_THREAD_MULTIPLE
  Multiple threads may call MPI, with no restrictions.

If `MPI_Init` was called instead of `MPI_Init_thread`, the level of thread support is defined by the implementation. This routine allows you to find out the provided level. It is also useful for library routines that discover that MPI has already been initialized and wish to determine what level of thread support is available.

## Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as `malloc` or other non-MPICH runtime routines that are themselves not interrupt-safe.

## Notes for Fortran

All MPI routines in Fortran (except for `MPI_WTIME` and `MPI_WTICK`) have an additional argument `ierr` at the end of the argument list. `ierr` is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the `call` statement.

All MPI objects (e.g., `MPI_Datatype`, `MPI_Comm`) are of type `INTEGER` in Fortran.

## Errors

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. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with `MPI_Comm_set_errhandler` (for communicators), `MPI_File_set_errhandler` (for files), and `MPI_Win_set_errhandler` (for RMA windows). The MPI-1 routine `MPI_Errhandler_set` may be used but its use is deprecated. The predefined error handler `MPI_ERRORS_RETURN` may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_ARG
  Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., `MPI_ERR_RANK`).

MPI_ERR_OTHER
  Other error; use `MPI_Error_string` to get more information about this error code.