make MPI STUBS a C++ library so its symbols won't collide when loading a real MPI library

cmake/CMakeLists.txt

@@ -156,8 +156,7 @@ if(BUILD_MPI)
     endif()
   endif()
 else()
-  enable_language(C)
-  file(GLOB MPI_SOURCES ${LAMMPS_SOURCE_DIR}/STUBS/mpi.c)
+  file(GLOB MPI_SOURCES ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs STATIC ${MPI_SOURCES})
   set_target_properties(mpi_stubs PROPERTIES OUTPUT_NAME lammps_mpi_stubs${LAMMPS_MACHINE})
   target_include_directories(mpi_stubs PUBLIC $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)

cmake/Modules/Packages/MESSAGE.cmake

@@ -2,8 +2,7 @@ if(LAMMPS_SIZES STREQUAL BIGBIG)
   message(FATAL_ERROR "The MESSAGE Package is not compatible with -DLAMMPS_BIGBIG")
 endif()
 option(MESSAGE_ZMQ "Use ZeroMQ in MESSAGE package" OFF)
-file(GLOB_RECURSE cslib_SOURCES ${LAMMPS_LIB_SOURCE_DIR}/message/cslib/[^.]*.F
-    ${LAMMPS_LIB_SOURCE_DIR}/message/cslib/[^.]*.c
+file(GLOB_RECURSE cslib_SOURCES
         ${LAMMPS_LIB_SOURCE_DIR}/message/cslib/[^.]*.cpp)
 
 add_library(cslib STATIC ${cslib_SOURCES})

src/STUBS/Makefile

@@ -11,13 +11,13 @@ SHELL = /bin/sh
 
 # Files
 
-SRC =		mpi.c
+SRC =		mpi.cpp
 INC =		mpi.h
 
 # Definitions
 
 EXE =		libmpi_stubs.a
-OBJ = 		$(SRC:.c=.o)
+OBJ = 		$(SRC:.cpp=.o)
 
 # System-specific settings
 
@@ -36,7 +36,7 @@ clean:
 
 # Compilation rules
 
-.c.o:
+.cpp.o:
 	$(CC) $(CCFLAGS) -c $<
 
 # Individual dependencies

src/STUBS/Makefile.mingw32-cross

@@ -5,17 +5,17 @@ SHELL = /bin/sh
 
 # Files
 
-SRC =		mpi.c
+SRC =		mpi.cpp
 INC =		mpi.h
 
 # Definitions
 
 EXE =		libmpi_mingw32.a
-OBJ = 		$(SRC:%.c=%_mingw32.o)
+OBJ = 		$(SRC:%.cpp=%_mingw32.o)
 
 # System-specific settings
 
-CC =	        i686-w64-mingw32-gcc
+CC =	        i686-w64-mingw32-g++
 CCFLAGS =	-O2 -Wall -march=i686 -mtune=generic -mfpmath=387 -mpc64 -I.
 ARCHIVE =	i686-w64-mingw32-ar
 ARCHFLAG =	rs

src/STUBS/Makefile.mingw64-cross

@@ -5,17 +5,17 @@ SHELL = /bin/sh
 
 # Files
 
-SRC =		mpi.c
+SRC =		mpi.cpp
 INC =		mpi.h
 
 # Definitions
 
 EXE =		libmpi_mingw64.a
-OBJ = 		$(SRC:%.c=%_mingw64.o)
+OBJ = 		$(SRC:%.cpp=%_mingw64.o)
 
 # System-specific settings
 
-CC =	        x86_64-w64-mingw32-gcc
+CC =	        x86_64-w64-mingw32-g++
 CCFLAGS =	-O2 -Wall -march=core2 -mtune=core2 -msse2 -mpc64 -I.
 ARCHIVE =	x86_64-w64-mingw32-ar
 ARCHFLAG =	rs

src/STUBS/mpi.h

@@ -16,12 +16,17 @@
 
 #include <stdlib.h>
 
-/* use C bindings for MPI interface */
+/* We compile STUBS with C++ so the symbols embedded
+ * the serial shared library will not collide with any
+ * corresponding symbols from a real MPI library (which
+ * uses C bindings). As a consequence the header *must*
+ * enforce compiling with C++ only. */
 
-#ifdef __cplusplus
-extern "C" {
+#ifndef __cplusplus
+#error "MPI STUBS must be compiled with a C++ compiler"
 #endif
 
+
 /* Dummy defs for MPI stubs */
 
 #define MPI_COMM_WORLD 0
@@ -176,8 +181,4 @@ int MPI_Alltoallv(void *sendbuf, int *sendcounts, int *sdispls,
                   MPI_Datatype recvtype, MPI_Comm comm);
 /* ---------------------------------------------------------------------- */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif