Waits for some given communications to complete
MPI_Status array_of_statuses )
|incount ||length of array_of_requests (integer)
|array_of_requests ||array of requests (array of handles)
|outcount ||number of completed requests (integer)
|array_of_indices ||array of indices of operations that
completed (array of integers)
|array_of_statuses ||array of status objects for
operations that completed (array of Status). May be MPI_STATUSES_NULL.
The array of indicies are in the range 0 to incount - 1 for C and
in the range 1 to incount for Fortran.
Null requests are ignored; if all requests are null, then the routine
returns with outcount set to MPI_UNDEFINED.
Note on status for send operations
For send operations, the only use of status is for MPI_Test_cancelled or
in the case that there is an error, in which case the MPI_ERROR field of
status will be set.
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
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER
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_Errhandler_set; 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
- No error; MPI routine completed successfully.
- Invalid MPI_Request. Either null or, in the case of a
MPI_Start or MPI_Startall, not a persistent request.
- Invalid argument. Some argument is invalid and is not
identified by a specific error class (e.g., MPI_ERR_RANK).
The MPI Standard does not specify what the result of the multiple
completion routines is when an error occurs. For example, in an
MPI_WAITALL, does the routine wait for all requests to either fail or
complete, or does it return immediately (with the MPI definition of
immediately, which means independent of actions of other MPI processes)?
MPICH has chosen to make the return immediate (alternately, local in MPI
terms), and to use the error class MPI_ERR_PENDING (introduced in MPI 1.1)
to indicate which requests have not completed. In most cases, only
one request with an error will be detected in each call to an MPI routine
that tests multiple requests. The requests that have not been processed
(because an error occured in one of the requests) will have their
MPI_ERROR field marked with MPI_ERR_PENDING.
- The actual error value is in the MPI_Status argument.
This error class is returned only from the multiple-completion routines
(MPI_Testall, MPI_Testany, MPI_Testsome, MPI_Waitall, MPI_Waitany,
and MPI_Waitsome). The field MPI_ERROR in the status argument
contains the error value or MPI_SUCCESS (no error and complete) or
MPI_ERR_PENDING to indicate that the request has not completed.