5f96a74e33
implementation was not thread safe). See lengthy comment in ompi/mpi/cxx/intercepts.cc::ompi_mpi_cxx_op_intercept() for a full explanation. This commit was SVN r8606.
288 строки
10 KiB
C++
288 строки
10 KiB
C++
// -*- c++ -*-
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//
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// Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
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// University Research and Technology
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// Corporation. All rights reserved.
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// Copyright (c) 2004-2005 The University of Tennessee and The University
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// of Tennessee Research Foundation. All rights
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// reserved.
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// Copyright (c) 2004-2005 High Performance Computing Center Stuttgart,
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// University of Stuttgart. All rights reserved.
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// Copyright (c) 2004-2005 The Regents of the University of California.
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// All rights reserved.
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// $COPYRIGHT$
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//
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// Additional copyrights may follow
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//
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// $HEADER$
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//
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#include "mpicxx.h"
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#include <stdio.h>
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extern "C"
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void ompi_mpi_cxx_throw_excptn_fctn(MPI_Comm *, int *errcode, ...)
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{
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/* Portland compiler raises a warning if va_start is not used in a
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* variable argument function */
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va_list ap;
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va_start(ap, errcode);
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va_end(ap);
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#if OMPI_HAVE_CXX_EXCEPTION_SUPPORT
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throw(MPI::Exception(*errcode));
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#else
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// Ick. This is really ugly, but necesary if someone uses a C compiler
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// and -lmpi++ (which can legally happen in the LAM MPI implementation,
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// and probably in MPICH and others who include -lmpi++ by default in their
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// wrapper compilers)
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fprintf(stderr, "MPI 2 C++ exception throwing is disabled, MPI::mpi_errno has the error code\n");
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MPI::mpi_errno = *errcode;
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#endif
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}
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MPI::Comm::mpi_comm_map_t MPI::Comm::mpi_comm_map;
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MPI::Comm::mpi_err_map_t MPI::Comm::mpi_err_map;
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MPI::Comm::key_fn_map_t MPI::Comm::key_fn_map;
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opal_mutex_t *MPI::Comm::mpi_comm_map_mutex = NULL;
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opal_mutex_t *MPI::Comm::mpi_err_map_mutex = NULL;
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opal_mutex_t *MPI::Comm::key_fn_map_mutex = NULL;
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extern "C"
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void ompi_mpi_cxx_errhandler_intercept(MPI_Comm *mpi_comm, int *err, ...)
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{
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MPI::Comm* comm = MPI::Comm::mpi_err_map[*mpi_comm];
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if (comm && comm->my_errhandler) {
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va_list ap;
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va_start(ap, err);
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comm->my_errhandler->handler_fn(*comm, err, ap);
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va_end(ap);
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}
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}
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// This is a bit weird; bear with me. The user-supplied function for
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// MPI::Op contains a C++ object reference. So it must be called from
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// a C++-compiled function. However, libmpi does not contain any C++
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// code because there are portability and bootstrapping issues
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// involved if someone tries to make a 100% C application link against
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// a libmpi that contains C++ code. At a minimum, the user will have
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// to use the C++ compiler to link. LA-MPI has shown that users don't
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// want to do this (there are other problems, but this one is easy to
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// cite).
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//
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// Hence, there are two problems when trying to invoke the user's
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// callback funcion from an MPI::Op:
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//
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// 1. The MPI_Datatype that the C library has must be converted to an
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// (MPI::Datatype)
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// 2. The C++ callback function must then be called with a
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// (MPI::Datatype&)
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//
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// Some relevant facts for the discussion:
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//
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// - The main engine for invoking Op callback functions is in libmpi
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// (i.e., in C code).
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//
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// - The C++ bindings are a thin layer on top of the C bindings.
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//
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// - The C++ bindings are a separate library from the C bindings
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// (libmpi_cxx.la).
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//
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// - As a direct result, the mpiCC wrapper compiler must generate a
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// link order thus: "... -lmpi_cxx -lmpi ...", meaning that we cannot
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// have a direct function call from the libmpi to libmpi_cxx. We can
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// only do it by function pointer.
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//
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// So the problem remains -- how to invoke a C++ MPI::Op callback
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// function (which only occurrs for user-defined datatypes, BTW) from
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// within the C Op callback engine in libmpi?
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//
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// It is easy to cache a function pointer to the
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// ompi_mpi_cxx_op_intercept() function on the MPI_Op (that is located
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// in the libmpi_cxx library, and is therefore compiled with a C++
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// compiler). But the normal C callback MPI_User_function type
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// signature is (void*, void*, int*, MPI_Datatype*) -- so if
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// ompi_mpi_cxx_op_intercept() is invoked with these arguments, it has
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// no way to deduce what the user-specified callback function is that
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// is associated with the MPI::Op.
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//
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// One can easily imagine a scenario of caching the callback pointer
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// of the current MPI::Op in a global variable somewhere, and when
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// ompi_mpi_cxx_op_intercept() is invoked, simply use that global
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// variable. This is unfortunately not thread safe.
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//
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// So what we do is as follows:
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//
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// 1. The C++ dispatch function ompi_mpi_cxx_op_intercept() is *not*
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// of type (MPI_User_function*). More specifically, it takes an
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// additional argument: a function pointer. its signature is (void*,
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// void*, int*, MPI_Datatype*, MPI_Op*, MPI::User_function*). This
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// last argument is the function pointer of the user callback function
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// to be invoked.
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//
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// The careful reader will notice that it is impossible for the C Op
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// dispatch code in libmpi to call this function properly because the
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// last argument is of a type that is not defined in libmpi (i.e.,
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// it's only in libmpi_cxx). Keep reading -- this is explained below.
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//
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// 2. When the MPI::Op is created (in MPI::Op::Init()), we call the
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// back-end C MPI_Op_create() function as normal (just like the F77
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// bindings, in fact), and pass it the ompi_mpi_cxx_op_intercept()
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// function (casting it to (MPI_User_function*) -- it's a function
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// pointer, so its size is guaranteed to be the same, even if the
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// signature of the real function is different).
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//
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// 3. The function pointer to ompi_mpi_cxx_op_intercept() will be
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// cached in the MPI_Op in op->o_func[0].cxx_intercept_fn.
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//
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// Recall that MPI_Op is implemented to have an array of function
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// pointers so that optimized versions of reduction operations can be
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// invoked based on the corresponding datatype. But when an MPI_Op
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// represents a user-defined function operation, there is only one
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// function, so it is always stored in function pointer array index 0.
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//
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// 4. When MPI_Op_create() returns, the C++ MPI::Op::Init function
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// manually sets OMPI_OP_FLAGS_CXX_FUNC flag on the resulting MPI_Op
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// (again, very similar to the F77 MPI_OP_CREATE wrapper). It also
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// caches the user's C++ callback function in op->o_func[1].c_fn
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// (recall that the array of function pointers is actually a union of
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// multiple different function pointer types -- it doesn't matter
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// which type the user's callback function pointer is stored in; since
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// all the types in the union are function pointers, it's guaranteed
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// to be large enough to hold what we need.
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//
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// Note that we don't have a member of the union for the C++ callback
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// function because its signature includes a (MPI::Datatype&), which
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// we can't put in the C library libmpi.
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//
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// 5. When the user invokes an function that uses the MPI::Op (or,
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// more specifically, when the Op dispatch engine in ompi/op/op.c [in
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// libmpi] tries to dispatch off to it), it will see the
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// OMPI_OP_FLAGS_CXX_FUNC flag and know to use the
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// op->o_func[0].cxx_intercept_fn and also pass as the 4th argument,
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// op->o_func[1].c_fn.
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//
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// 6. ompi_mpi_cxx_op_intercept() is therefore invoked and receives
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// both the (MPI_Datatype*) (which is easy to convert to
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// (MPI::Datatype&)) and a pointer to the user's C++ callback function
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// (albiet cast as the wrong type). So it casts the callback function
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// pointer to (MPI::User_function*) and invokes it.
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//
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// Wasn't that simple?
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//
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extern "C" void
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ompi_mpi_cxx_op_intercept(void *invec, void *outvec, int *len,
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MPI_Datatype *datatype, MPI_User_function *c_fn)
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{
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MPI::Datatype cxx_datatype = *datatype;
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MPI::User_function *cxx_callback = (MPI::User_function*) c_fn;
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cxx_callback(invec, outvec, *len, cxx_datatype);
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}
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extern "C" int
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ompi_mpi_cxx_copy_attr_intercept(MPI_Comm oldcomm, int keyval,
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void *extra_state, void *attribute_val_in,
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void *attribute_val_out, int *flag)
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{
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int ret = 0;
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MPI::Comm::key_pair_t* copy_and_delete =
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MPI::Comm::key_fn_map[keyval];
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MPI::Comm::Copy_attr_function* copy_fn;
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copy_fn = copy_and_delete->first;
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MPI::Comm::comm_pair_t *comm_type =
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MPI::Comm::mpi_comm_map[oldcomm];
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// Just in case...
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if (comm_type == 0)
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return MPI::ERR_OTHER;
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MPI::Intracomm intracomm;
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MPI::Intercomm intercomm;
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MPI::Graphcomm graphcomm;
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MPI::Cartcomm cartcomm;
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int thetype = (int)comm_type->second;
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bool bflag = (bool)*flag;
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switch (thetype) {
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case eIntracomm:
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intracomm = MPI::Intracomm(*comm_type->first);
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ret = copy_fn(intracomm, keyval, extra_state,
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attribute_val_in, attribute_val_out, bflag);
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break;
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case eIntercomm:
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intercomm = MPI::Intercomm(*comm_type->first);
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ret = copy_fn(intercomm, keyval, extra_state,
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attribute_val_in, attribute_val_out, bflag);
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break;
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case eGraphcomm:
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graphcomm = MPI::Graphcomm(*comm_type->first);
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ret = copy_fn(graphcomm, keyval, extra_state,
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attribute_val_in, attribute_val_out, bflag);
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break;
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case eCartcomm:
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cartcomm = MPI::Cartcomm(*comm_type->first);
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ret = copy_fn(cartcomm, keyval, extra_state,
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attribute_val_in, attribute_val_out, bflag);
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break;
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}
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*flag = (int)bflag;
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return ret;
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}
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extern "C" int
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ompi_mpi_cxx_delete_attr_intercept(MPI_Comm comm, int keyval,
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void *attribute_val, void *extra_state)
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{
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int ret = 0;
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MPI::Comm::key_pair_t *copy_and_delete =
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MPI::Comm::key_fn_map[keyval];
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MPI::Comm::Delete_attr_function* delete_fn;
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delete_fn = copy_and_delete->second;
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MPI::Comm::comm_pair_t *comm_type =
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MPI::Comm::mpi_comm_map[comm];
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// Just in case...
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if (comm_type == 0)
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return MPI::ERR_OTHER;
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MPI::Intracomm intracomm;
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MPI::Intercomm intercomm;
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MPI::Graphcomm graphcomm;
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MPI::Cartcomm cartcomm;
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int thetype = (long)(comm_type->second);
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if (delete_fn > (MPI::Comm::Delete_attr_function*) 100) {
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switch (thetype) {
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case eIntracomm:
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intracomm = MPI::Intracomm(*comm_type->first);
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ret = delete_fn(intracomm, keyval, attribute_val, extra_state);
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break;
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case eIntercomm:
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intercomm = MPI::Intercomm(*comm_type->first);
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ret = delete_fn(intercomm, keyval, attribute_val, extra_state);
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break;
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case eGraphcomm:
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graphcomm = MPI::Graphcomm(*comm_type->first);
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ret = delete_fn(graphcomm, keyval, attribute_val, extra_state);
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break;
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case eCartcomm:
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cartcomm = MPI::Cartcomm(*comm_type->first);
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ret = delete_fn(cartcomm, keyval, attribute_val, extra_state);
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break;
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}
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} else
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ret = MPI::ERR_OTHER;
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return ret;
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}
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