# MPI_Request_free

Frees a communication request object

## Synopsis

    int MPI_Request_free(MPI_Request *request)

## Input Parameter

request
  communication request (handle)

## Notes

This routine is normally used to free inactive persistent requests created with either `MPI_Recv_init` or `MPI_Send_init` and friends. It is also permissible to free an active request. However, once freed, the request can no longer be used in a wait or test routine (e.g., `MPI_Wait`) to determine completion.

This routine may also be used to free a non-persistent requests such as those created with `MPI_Irecv` or `MPI_Isend` and friends. Like active persistent requests, once freed, the request can no longer be used with test/wait routines to determine completion.

## 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 guarentee 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_REQUEST
  Invalid `MPI_Request`. Either null or, in the case of a `MPI_Start` or `MPI_Startall`, not a persistent request.

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

## See Also

also: MPI_Isend, MPI_Irecv, MPI_Issend, MPI_Ibsend, MPI_Irsend,
MPI_Recv_init, MPI_Send_init, MPI_Ssend_init, MPI_Rsend_init, MPI_Wait, MPI_Test, MPI_Waitall, MPI_Waitany, MPI_Waitsome, MPI_Testall, MPI_Testany, MPI_Testsome

Location:request_free.c