Feature pass MPI comm from Python script to AMReX during initialization (#2034)

* Added functionality to pass mpi comm from python script to amrex during initialization

* Fixed missing _ in MPI._sizeof()

* Added functions to get the current processor's rank and total number of processors

* Renamed MPI_Comm to _MPI_Comm_type and defined _MPI_Comm_type in except statement

* Updated comment to explain why mpi4py needs to be imported before loading libwarpx

* Removed ifdef flags that prevent amrex_init_with_inited_mpi from being declared when MPI is off

* Changed amrex_init_with_inited_mpi to be declared even when not using mpi, but will be defined to be functionally the same as amrex_init

* Defined MPI = None to signify whether MPI is used, to add another check when initializing amrex

* Changed ifdef blocks in WarpXWrappers.cpp/h to fix compile errors.
Added ifdef block to conditionally declare amrex_init_with_inited_mpi in WarpXWrappers.h to prevent compile error when not using MPI. Removed ifdef block to declare/define same function in WarpXWrappers.cpp since function needs to be declared even when MPI is not used, but will never be called in that case.

* Changed BL_USE_MPI to AMREX_USE_MPI and removed incorrect MPI=None statement

* Changed BL_USE_MPI to AMREX_USE_MPI

* Added test to verify correct passing of MPI communicator to amrex

* Added ability to pass mpi_comm to sim.step

* Change test to check for differeing outputs when passed different inputs

* Removed obsolete comments refactored program to use more shared code

* Refactored comments

* Updated description to match test

* Removed unecessary imports and updated comments

1 files changed, 6 insertions, 2 deletions

diff --git a/Source/Python/WarpXWrappers.h b/Source/Python/WarpXWrappers.h
index a720f0f59..30fa81968 100644
--- a/Source/Python/WarpXWrappers.h
+++ b/Source/Python/WarpXWrappers.h
@@ -11,7 +11,7 @@
 #include <AMReX_Config.H>
 #include <AMReX_REAL.H>
 
-#ifdef BL_USE_MPI
+#ifdef AMREX_USE_MPI
 #   include <mpi.h>
 #endif
 
@@ -34,7 +34,7 @@ extern "C" {
 
     void amrex_init (int argc, char* argv[]);
 
-#ifdef BL_USE_MPI
+#ifdef AMREX_USE_MPI
     void amrex_init_with_inited_mpi (int argc, char* argv[], MPI_Comm mpicomm);
 #endif
 
@@ -113,6 +113,10 @@ extern "C" {
 
   int warpx_finestLevel ();
 
+  int warpx_getMyProc ();
+  int warpx_getNProcs ();
+
+
   void mypc_Redistribute ();
 
 #ifdef __cplusplus