# MPIX_Comm_agree

Performs agreement operation on comm

## Synopsis

    int MPIX_Comm_agree(MPI_Comm comm, int *flag)

## Input Parameters

comm
  communicator (handle)

## Output Parameters

flag
  new communicator (logical)

## Notes

The purpose of this collective communication is to agree on the integer value flag and on the group of failed processes in comm.

On completion, all non-failed MPI processes have agreed to set the output integer value of flag to the result of a bitwise AND operation over the contributed input values of flag. If comm is an intercommunicator, the value of flagis a bitwise AND operation over the values contributed by the remote group.

When an MPI process fails before contributing to the operation, the flag is computed ignoring its contribution, and MPIX_Comm_agree raises an error of class MPI_ERR_PROC_FAILED. However, if all MPI processes have acknowledged this failure priorto the call to MPIX_Comm_agree, using MPIX_Comm_failure_ack, the error related to this failure is not raised. When an error of class MPI_ERR_PROC_FAILED is raised, it is consistently raised at allMPI processes, in both the local and remote groups (if applicable).

After MPIX_Comm_agree raised an error of class MPI_ERR_PROC_FAILED, a subse-quent call to MPIX_Comm_failure_ack on comm acknowledges the failure of every MPI process that didn`t contribute to the computation offlag.`

## 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_COMM
  Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank`).`

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