MPI_Grequest_start
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 isqueried (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).
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 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.