Provided by: openmpi-doc_2.1.1-8_all 
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)
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
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 (function).
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 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
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 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);
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 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
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 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.
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-portable 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++ functions 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 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 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 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.
See the MPI man page for a full list of MPI error codes.