---
name: "MPI_File_read_at_all_begin"
section: "3"
platform: "linux"
package: "openmpi"
version: "5.0.11-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_File_read_at_all_begin"
---

# MPI\_File\_read\_at\_all\_begin(3)

*MPI\_File\_read\_at\_all\_begin* — Reads a file at explicitly specified offsets; beginning part of a split collective routine (nonblocking).

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_File_read_at_all_begin(MPI_File fh, MPI_Offset
     offset, void *buf, int count, MPI_Datatype
     datatype)
```

### Fortran Syntax

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_READ_AT_ALL_BEGIN(FH, OFFSET, BUF,
     COUNT, DATATYPE, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, IERROR
     INTEGER(KIND=MPI_OFFSET_KIND)   OFFSET
```

### Fortran 2008 Syntax

```
USE mpi_f08
MPI_File_read_at_all_begin(fh, offset, buf, count, datatype, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: offset
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

## INPUT PARAMETERS

- •

  **fh**: File handle (handle).

- •

  **offset**: File offset (integer).

- •

  **count**: Number of elements in buffer (integer).

- •

  **datatype**: Data type of each buffer element.

## OUTPUT PARAMETERS

- •

  **buf**: Initial address of buffer (choice).

- •

  **ierror**: Fortran only: Error status (integer).

## DESCRIPTION

*MPI\_File\_read\_at\_all\_begin* is the beginning part of a split collective routine that attempts to read from the file associated with *fh* (at the *offset* position) a total number of *count* data items having *datatype* type into the user’s buffer *buf.* The *offset* is in etype units relative to the current view. That is, holes are not counted when locating an offset. The data is taken out of those parts of the file specified by the current view.

## NOTES

All the nonblocking collective routines for data access are “split” into two routines, each with **\_begin** or **\_end** as a suffix. These split collective routines are subject to the semantic rules described in Section 9.4.5 of the MPI-2 standard.

## ERRORS

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.

## COPYRIGHT

2003-2026, The Open MPI Community