source: CIVL/examples/concurrency/mp_proc2.cvh

#include <civlc.cvh>

int sizeofDatatype(MPI_Datatype datatype) {
  switch (datatype) {
  case MPI_INT:
    return sizeof(int);
  case MPI_FLOAT:
    return sizeof(float);
  case MPI_DOUBLE:
    return sizeof(double);
  case MPI_CHAR:
    return sizeof(char);
  default:
    $assert(0, "Unreachable");
  }
}

int MPI_Comm_size(MPI_Comm comm, int *size) {
  *size = $comm_size(comm);
  return 0;
}

int MPI_Comm_rank(MPI_Comm comm, int* rank) {
  // this only works for MPI_COMM_WORLD.
  // for multiple communicators, you will need 
  // a map (array) from PID to rank for each comm
  *rank = $comm_place(comm);
  return 0;
}

int MPI_Send(void *buf, int count, MPI_Datatype datatype,
             int dest, int tag, MPI_Comm comm) {
  //$atomic {
    int size;
    
    size = sizeofDatatype(datatype);
    $message out = $message_pack(__rank, dest, tag, buf, size);
    $comm_enqueue(comm, out);
  //}
  return 0;
}

int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
             int source, int tag, MPI_Comm comm, MPI_Status *status) {
  $message in = $comm_dequeue(comm, source, tag);
  //$atomic {
    int size;
    
    size = sizeofDatatype(datatype);
    $message_unpack(in, buf, size);
    if (status != MPI_STATUS_IGNORE) {
      status->MPI_SOURCE = in.source;
      status->MPI_TAG = in.tag;
      status->size = in.size;
    }
  //}
  return 0;
}

int MPI_Sendrecv(void *sendbuf, int sendcount, MPI_Datatype sendtype,
             int dest, int sendtag, void *recvbuf, int recvcount, MPI_Datatype recvtype,
             int source, int recvtag, MPI_Comm comm, MPI_Status *status){
  int sendsize, recvsize;
  $message out , in;
  _Bool probe;

  sendsize = sendcount * sizeofDatatype(sendtype);  
  recvsize = recvcount * sizeofDatatype(recvtype);
  out = $message_pack(__rank, dest, sendtag, sendbuf, sendsize);
  probe = $comm_probe(comm, source, recvtag);
  $choose {
    $when (1){ 
      $comm_enqueue(comm, out);
      in = $comm_dequeue(comm, source, recvtag);
    }
    $when (probe){
      in = $comm_dequeue(comm, source, recvtag);
      $comm_enqueue(comm, out);
    }
  }
  $message_unpack(in, recvbuf, recvsize);
  if (status != MPI_STATUS_IGNORE) {
    status->MPI_SOURCE = in.source;
    status->MPI_TAG = in.tag;
    status->size = in.size;
  }
}

$when (__start);