add CComm type for interoperability with the C API (see also #59)

Author: stevengj

deps/CMakeLists.txt

@@ -135,6 +135,16 @@ endif(MPI_Fortran_LINK_FLAGS)
 
 target_link_libraries(juliampi ${MPI_Fortran_LIBRARIES})
 
+include(CheckFunctionExists)
+set(CMAKE_REQUIRED_LIBRARIES ${MPI_C_LIBRARIES})
+check_function_exists(MPI_Comm_c2f HAVE_MPI_COMM_C2F)
+unset(CMAKE_REQUIRED_LIBRARIES)
+if(${HAVE_MPI_COMM_C2F})
+  set(HAVE_MPI_COMM_C2F_BOOL "true")
+else()
+  set(HAVE_MPI_COMM_C2F_BOOL "false")
+endif()
+
 add_executable(gen_functions gen_functions.c)
 add_dependencies(gen_functions version)
 
@@ -150,6 +160,7 @@ file(APPEND \${DST} \${FTWOC})
 file(APPEND \${DST} \"\n\")
 file(APPEND \${DST} \${FCONS})
 file(APPEND \${DST} \"\n\")
+file(APPEND \${DST} \"const HAVE_MPI_COMM_C2F = ${HAVE_MPI_COMM_C2F_BOOL}\n\")
 ")
 
 add_custom_command(OUTPUT ${CMAKE_BINARY_DIR}/compile-time.jl

deps/gen_functions.c

@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include "jlmpi_f2c.h"
+#include "mpi.h"
 #include "version.h"
 
 #define STRING1(s) #s
@@ -58,5 +59,6 @@ int main(int argc, char *argv[])
   printf("const MPI_WAITANY            = Libdl.dlsym(libmpi, \"%s\")\n", STRING(MPI_WAITANY));
   printf("const MPI_WTIME              = Libdl.dlsym(libmpi, \"%s\")\n", STRING(MPI_WTIME));
 
+  printf("bitstype %lu CComm\n", sizeof(MPI_Comm) * 8);
   return 0;
 }

src/mpi-base.jl

@@ -44,6 +44,7 @@ const datatypes = Dict{DataType, Cint}(
 
 type Comm
     val::Cint
+    Comm(val::Integer) = new(val)
 end
 const COMM_NULL  = Comm(MPI_COMM_NULL)
 const COMM_SELF  = Comm(MPI_COMM_SELF)
@@ -526,3 +527,20 @@ function ExScan{T<:MPIDatatype}(object::T, op::Op, comm::Comm)
     sendbuf = T[object]
     ExScan(sendbuf,1,op,comm)
 end
+
+# Conversion between C and Fortran Comm handles:
+
+if HAVE_MPI_COMM_C2F
+    # use MPI_Comm_f2c and MPI_Comm_c2f
+    const MPI_COMM_F2C = Libdl.dlsym(libmpi, "MPI_Comm_f2c")
+    const MPI_COMM_C2F = Libdl.dlsym(libmpi, "MPI_Comm_c2f")
+    Base.convert(::Type{CComm}, comm::Comm) = ccall(MPI_COMM_F2C, CComm, (Cint,), comm.val)
+    Base.convert(::Type{Comm}, ccomm::CComm) = Comm(ccall(MPI_COMM_C2F, Cint, (CComm,), ccomm))
+elseif sizeof(CComm) == sizeof(Cint)
+    # in MPICH, both C and Fortran use identical Cint comm handles
+    # and MPI_Comm_c2f is not provided.
+    Base.convert(::Type{CComm}, comm::Comm) = reinterpret(CComm, comm.val)
+    Base.convert(::Type{Comm}, ccomm::CComm) = Comm(reinterpret(Cint, ccomm))
+else
+    warn("No MPI_Comm_c2f found - conversion to/from MPI.CComm will not work")
+end

test/test_basic.jl

@@ -5,6 +5,8 @@ using MPI
 MPI.Init()
 @test MPI.Initialized()
 
+@test MPI.Comm(MPI.CComm(MPI.COMM_WORLD)).val == MPI.COMM_WORLD.val
+
 @test !MPI.Finalized()
 MPI.Finalize()
 @test MPI.Finalized()