:ref:`MPI_Grequest_start` |mdash| Starts a generalized request and returns a
handle to it in request
.
#include <mpi.h>
int MPI_Grequest_start(MPI_Grequest_query_function *query_fn,
MPI_Grequest_free_function *free_fn,
MPI_Grequest_cancel_function *cancel_fn, void *extra_state,
MPI_Request *request)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_GREQUEST_START(QUERY_FN, FREE_FN, CANCEL_FN, EXTRA_STATE,
REQUEST, IERROR)
INTEGER REQUEST, IERROR
EXTERNAL QUERY_FN, FREE_FN, CANCEL_FN
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
USE mpi_f08
MPI_Grequest_start(query_fn, free_fn, cancel_fn, extra_state, request,
ierror)
PROCEDURE(MPI_Grequest_query_function) :: query_fn
PROCEDURE(MPI_Grequest_free_function) :: free_fn
PROCEDURE(MPI_Grequest_cancel_function) :: cancel_fn
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
query_fn
: Callback function invoked when request status is- queried (function).
free_fn
: Callback function invoked when request is freed- (function).
cancel_fn
: Callback function invoked when request is canceled- (function).
extra_state
: Extra state.
request
: Generalized request (handle).ierror
: Fortran only: Error status (integer).
:ref:`MPI_Grequest_start` starts a generalized request
and returns a
handle to it in request
.
The syntax and meaning of the callback functions are listed below. All
callback functions are passed the extra_state
argument that was
associated with the request
by the starting call
:ref:`MPI_Grequest_start`. This can be used to maintain user-defined state
for the request
. In C, the query function is
typedef int MPI_Grequest_query_function(void *extra_state,
MPI_Status *status);
In Fortran, it is
SUBROUTINE GREQUEST_QUERY_FUNCTION(EXTRA_STATE, STATUS, IERROR)
INTEGER STATUS(MPI_STATUS_SIZE), IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
The query_fn
function computes the status that should be returned
for the generalized request. The status also includes information about
successful/unsuccessful cancellation of the request (result to be
returned by MPI_Test_cancelled
).
The query_fn
function is invoked by the
MPI_{Wait|Test}{any|some|all}
call that completed the generalized
request associated with this callback. The callback function is also
invoked by calls to MPI_Request_get_status
if the request is
complete when the call occurs. In both cases, the callback is passed a
reference to the corresponding status variable passed by the user to the
MPI call. If the user provided MPI_STATUS_IGNORE
or
MPI_STATUSES_IGNORE
to the MPI function that causes query_fn
to
be called, then MPI will pass a valid status object to query_fn
, and
this status will be ignored upon return of the callback function. Note
that query_fn
is invoked only after MPI_Grequest_complete
is
called on the request; it may be invoked several times for the same
generalized request. Note also that a call to
MPI_{Wait|Test}{some|all}
may cause multiple invocations of
query_fn
callback functions, one for each generalized request that
is completed by the MPI call. The order of these invocations is not
specified by MPI.
In C, the free function is
typedef int MPI_Grequest_free_function(void *extra_state);
And in Fortran, it is
SUBROUTINE GREQUEST_FREE_FUNCTION(EXTRA_STATE, IERROR)
INTEGER IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
The free_fn
callback function is invoked to clean up user-allocated
resources when the generalized request is freed.
The free_fn
function is invoked by the
MPI_{Wait|Test}{any|some|all}
call that completed the generalized
request associated with this callback. free_fn
is invoked after the
call to query_fn
for the same request. However, if the MPI call
completed multiple generalized requests, the order in which free_fn
callback functions are invoked is not specified by MPI.
The free_fn
callback is also invoked for generalized requests that
are freed by a call to MPI_Request_free
(no call to
MPI_{Wait|Test}{any|some|all}
will occur for such a request). In
this case, the callback function will be called either in the MPI call
MPI_Request_free(request)
or in the MPI call
MPI_Grequest_complete(request)
, whichever happens last. In other
words, in this case the actual freeing code is executed as soon as both
calls (MPI_Request_free
and MPI_Grequest_complete
) have
occurred. The request
is not deallocated until after free_fn
completes. Note that free_fn
will be invoked only once per request
by a correct program.
In C, the cancel function is
typedef int MPI_Grequest_cancel_function(void *extra_state, int complete);
In Fortran, the cancel function is
SUBROUTINE GREQUEST_CANCEL_FUNCTION(EXTRA_STATE, COMPLETE, IERROR)
INTEGER IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
LOGICAL COMPLETE
The cancel_fn
function is invoked to start the cancellation of a
generalized request. It is called by MPI_Request_cancel(request)
.
MPI passes to the callback function complete=true if
MPI_Grequest_complete
has already been called on the request, and
complete=false otherwise.
All callback functions return an error code. The code is passed back and
dealt with as appropriate for the error code by the MPI function that
invoked the callback function. For example, if error codes are returned,
then the error code returned by the callback function will be returned
by the MPI function that invoked the callback function. In the case of a
MPI_{Wait|Test}any
call that invokes both query_fn
and
free_fn
, the MPI call will return the error code returned by the
last callback, namely free_fn
. If one or more of the request``s
in a call to ``MPI_{Wait|Test}{some|all
} has failed, then the MPI call
will return MPI_ERR_IN_STATUS
. In such a case, if the MPI call was
passed an array of statuses, then MPI will return in each of the
statuses that correspond to a completed generalized request
the
error code returned by the corresponding invocation of its free_fn
callback function. However, if the MPI function was passed
MPI_STATUSES_IGNORE
, then the individual error codes returned by
each callback function will be lost.