MPI_Grequest_start(3) Open MPI MPI_Grequest_start(3)
NAME
MPI_Grequest_start - Starts a generalized request and returns a handle
to it in request.
SYNTAX
C Syntax
#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)
Fortran Syntax (see FORTRAN 77 NOTES)
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
Fortran 2008 Syntax
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
C++ Syntax
#include <mpi.h>
static MPI::Grequest
MPI::Grequest::Start(const MPI::Grequest::Query_function
query_fn, const MPI::Grequest::Free_function free_fn,
const MPI::Grequest::Cancel_function cancel_fn,
void *extra_state)
INPUT PARAMETERS
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 (func-
tion).
extra_state
Extra state.
OUTPUT PARAMETERS
request Generalized request (handle).
IERROR Fortran only: Error status (integer).
DESCRIPTION
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 associ-
ated 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
and in C++, it is
typedef int MPI::Grequest::Query_function(void* extra_state,
MPI::Status& status);
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 re-
turned 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 call-
back. The callback function is also invoked by calls to MPI_Re-
quest_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 pro-
vided 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 call-
back function. Note that query_fn is invoked only after MPI_Gre-
quest_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);
In Fortran, it is
SUBROUTINE GREQUEST_FREE_FUNCTION(EXTRA_STATE, IERROR)
INTEGER IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
And in C++, it is
typedef int MPI::Grequest::Free_function(void* extra_state);
The free_fn callback function is invoked to clean up user-allocated re-
sources 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 call-
back. free_fn is invoked after the call to query_fn for the same re-
quest. However, if the MPI call completed multiple generalized re-
quests, 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(re-
quest), 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
In C++, the cancel function is
typedef in MPI::Grequest::Cancel_function(void* extra_state,
bool complete);
The cancel_fn function is invoked to start the cancellation of a gener-
alized request. It is called by MPI_Request_cancel(request). MPI passes
to the callback function complete=true if MPI_Grequest_complete has al-
ready been called on the request, and complete=false otherwise.
FORTRAN 77 NOTES
The MPI standard prescribes portable Fortran syntax for the EXTRA_STATE
argument only for Fortran 90. FORTRAN 77 users may use the non-porta-
ble syntax
INTEGER*MPI_ADDRESS_KIND EXTRA_STATE
where MPI_ADDRESS_KIND is a constant defined in mpif.h and gives the
length of the declared integer in bytes.
ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument. C++ func-
tions do not return errors. If the default error handler is set to
MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
will be used to throw an MPI::Exception object.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does
not guarantee that an MPI program can continue past an error.
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 re-
turned, 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 requests 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 corre-
spond 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.
See the MPI man page for a full list of MPI error codes.
4.1.2 Nov 24, 2021 MPI_Grequest_start(3)
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