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)
- 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.