# Name

`MPI_Finalize`  - Terminates MPI execution environment.

# Syntax

## C Syntax

```c
#include <mpi.h>

int MPI_Finalize()
```

## Fortran Syntax

```fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_FINALIZE(IERROR)
    INTEGER	IERROR
```

## Fortran 2008 Syntax

```fortran
USE mpi_f08

MPI_Finalize(ierror)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# Output Parameter

* `IERROR` : Fortran only: Error status (integer).

# Description

This routine cleans up all MPI states. Once this routine is called, no
MPI routine (not even `MPI_Init`) may be called, except for
`MPI_Get_version`, `MPI_Initialized`, and `MPI_Finalized`. Unless there has
been a call to `MPI_Abort`, you must ensure that all pending
communications involving a process are complete before the process calls
`MPI_Finalize`. If the call returns, each process may either continue
local computations or exit without participating in further
communication with other processes. At the moment when the last process
calls `MPI_Finalize`, all pending sends must be matched by a receive, and
all pending receives must be matched by a send.

`MPI_Finalize` is collective over all connected processes. If no processes
were spawned, accepted, or connected, then this means it is collective
over `MPI_COMM_WORLD`. Otherwise, it is collective over the union of all
processes that have been and continue to be connected.

# Notes

All processes must call this routine before exiting. All processes will
still exist but may not make any further MPI calls. `MPI_Finalize`
guarantees that all local actions required by communications the user
has completed will, in fact, occur before it returns. However,
`MPI_Finalize` guarantees nothing about pending communications that have
not been completed; completion is ensured only by `MPI_Wait`, `MPI_Test,`
or `MPI_Request_free` combined with some other verification of completion.

For example, a successful return from a blocking communication operation
or from `MPI_Wait` or `MPI_Test` means that the communication is completed
by the user and the buffer can be reused, but does not guarantee that
the local process has no more work to do. Similarly, a successful return
from `MPI_Request_free` with a request handle generated by an `MPI_Isend`
nullifies the handle but does not guarantee that the operation has
completed. The `MPI_Isend` is complete only when a matching receive has
completed.

If you would like to cause actions to happen when a process finishes,
attach an attribute to `MPI_COMM_SELF` with a callback function. Then,
when `MPI_Finalize` is called, it will first execute the equivalent of an
`MPI_Comm_free` on `MPI_COMM_SELF`. This will cause the delete callback
function to be executed on all keys associated with `MPI_COMM_SELF` in an
arbitrary order. If no key has been attached to `MPI_COMM_SELF`, then no
callback is invoked. This freeing of `MPI_COMM_SELF` happens before any
other parts of MPI are affected. Calling `MPI_Finalized` will thus return
"false" in any of these callback functions. Once you have done this
with `MPI_COMM_SELF`, the results of `MPI_Finalize` are not specified.

# Errors

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

Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
`MPI_Comm_set_errhandler`; 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.

# See Also

[`MPI_Init`(3)](MPI_Init.html)
[`MPI_Init_thread`(3)](MPI_Init_thread.html)
[`MPI_Initialized`(3)](MPI_Initialized.html)
[`MPI_Finalized`(3)](MPI_Finalized.html)