# 18.2.424. MPI_Waitall

MPI_Waitall — Waits for all given communications to complete.

## 18.2.424.1. SYNTAX

### 18.2.424.1.1. C Syntax

    #include <mpi.h>

    int MPI_Waitall(int count, MPI_Request array_of_requests[],
         MPI_Status *array_of_statuses)

### 18.2.424.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_WAITALL(COUNT, ARRAY_OF_REQUESTS, ARRAY_OF_STATUSES, IERROR)
         INTEGER COUNT, ARRAY_OF_REQUESTS(*)
         INTEGER ARRAY_OF_STATUSES(MPI_STATUS_SIZE,*), IERROR

### 18.2.424.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Waitall(count, array_of_requests, array_of_statuses, ierror)
         INTEGER, INTENT(IN) :: count
         TYPE(MPI_Request), INTENT(INOUT) :: array_of_requests(count)
         TYPE(MPI_Status) :: array_of_statuses(*)
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 18.2.424.2. INPUT PARAMETERS

- `count`: Lists length (integer).

- `array_of_requests`: Array of requests (array of handles).

## 18.2.424.3. OUTPUT PARAMETERS

- `array_of_statuses`: Array of status objects (array of status).

- `ierror`: Fortran only: Error status (integer).

## 18.2.424.4. DESCRIPTION

Blocks until all communication operations associated with active handles in the list complete, and returns the status of all these operations (this includes the case where no handle in the list is active). Both arrays have the same number of valid entries. The ith entry in array_of_statuses is set to the return status of the ith operation. Requests that were created by nonblocking communication operations are deallocated, and the corresponding handles in the array are set to MPI_REQUEST_NULL. The list may contain null or inactive handles. The call sets to empty the status of each such entry.

The error-free execution of MPI_Waitall(count, array_of_requests, array_of_statuses) has the same effect as the execution of MPI_Wait(&array_of_request[i], &array_of_statuses[i]), for i=0,…,count-1, in some arbitrary order. MPI_Waitall with an array of length 1 is equivalent to MPI_Wait.

When one or more of the communications completed by a call to MPI_Waitall fail, it is desirable to return specific information on each communication. The function MPI_Waitall will return in such case the error code MPI_ERR_IN_STATUS and will set the error field of each status to a specific error code. This code will be MPI_SUCCESS if the specific communication completed; it will be another specific error code if it failed; or it can be MPI_ERR_PENDING if it has neither failed nor completed. The function MPI_Waitall will return MPI_SUCCESS if no request had an error, or will return another error code if it failed for other reasons (such as invalid arguments). In such cases, it will not update the error fields of the statuses.

If your application does not need to examine the array_of_statuses field, you can save resources by using the predefined constant MPI_STATUSES_IGNORE can be used as a special value for the array_of_statuses argument.

## 18.2.424.5. 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.

For each invocation of MPI_Waitall, if one or more requests generate an MPI error, only the first MPI request that caused an error will be passed to its corresponding error handler. No other error handlers will be invoked (even if multiple requests generated errors). However, all requests that generate an error will have a relevant error code set in the corresponding `status.MPI_ERROR` field (unless `MPI_STATUSES_IGNORE` was used).

If the invoked error handler allows MPI_Waitall to return to the caller, the value `MPI_ERR_IN_STATUS` will be returned in the C and Fortran bindings.

See also

- MPI_Comm_set_errhandler

- MPI_File_set_errhandler

- MPI_Test

- MPI_Testall

- MPI_Testany

- MPI_Testsome

- MPI_Wait

- MPI_Waitany

- MPI_Waitsome

- MPI_Win_set_errhandler