多重广播BIGNUM

int MPIbcastBigNum(BIGNUM *num, int rank, char* purpoce){
    int size = BN_num_bytes(num);
    unsigned char *message = OPENSSL_malloc(size);

    if(!BN_bn2bin(num, message)) {
     fprintf(stderr, "RANK %d: Fail to allocate an array for key bytes \"%s\" \n", rank, purpoce);
     fflush(stderr);
     OPENSSL_free(message);
     return -1;    
    }

    //Do the actual Broadcast && Debug
    printf("RANK %d: Broaccasting bignum for purpoce \"%s\" \n", rank, purpoce);
    fflush(stdout);
    int value = MPI_Bcast(message, size, MPI_BYTE, rank, MPI_COMM_WORLD);
    switch(value) {
        case MPI_ERR_COMM:
         fprintf(stderr, "RANK %d: COMMUNICATIPN ERROR on BIGNUM sending for purpoce \"%s\" \n", rank, purpoce);
         fflush(stderr);
         OPENSSL_free(message);
         return -1;

        case MPI_ERR_COUNT:
         fprintf(stderr, "RANK %d: Invalid Size Count on BIGNUM sending for purpoce \"%s\" \n", rank, purpoce);
         fflush(stderr);
         OPENSSL_free(message);
         return -1;

        case MPI_ERR_TYPE:
         fprintf(stderr, "RANK %d: Invalid Data Type on BIGNUM sending for purpoce \"%s\" \n", rank, purpoce);
         fflush(stderr);
         OPENSSL_free(message);
         return -1;

        case MPI_ERR_BUFFER:
         fprintf(stderr, "RANK %d: Invalid Buffer on BIGNUM sending for purpoce \"%s\" \n", rank, purpoce);
         fflush(stderr);
         OPENSSL_free(message);
         return -1;

        default:
          printf("RANK %d: ALL OK on BIGNUM sending on purpoce \"%s\" \n", rank, purpoce);
          fflush(stdout);
    }

    //Cleanups
    OPENSSL_free(message);
    return 0;
}

我试图做的是通过MPI发送一个OpenSSL BIGNUM。但我的问题是,每个BIGNUM可能没有相同的大小。所以我想知道如何通知接收进程我的数据长度。

到目前为止,我认为是广播的大小首先作为 MPI_INT MPI_BYTE 大堆但是,当我尝试接收大小和BigNum时,这些如何不会出问题呢?