#include 
    
     #define WORKTAG 1#define DIETAG 2/* Local functions */static void master(void);static void slave(void);static unit_of_work_t get_next_work_item(void);static void process_results(unit_result_t result);static unit_result_t do_work(unit_of_work_t work);intmain(int argc, char **argv){  int myrank;  /* Initialize MPI */  MPI_Init(&argc, &argv);  /* Find out my identity in the default communicator */  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);  if (myrank == 0) {    master();  } else {    slave();  }  /* Shut down MPI */  MPI_Finalize();  return 0;}static voidmaster(void){  int ntasks, rank;  unit_of_work_t work;  unit_result_t result;  MPI_Status status;  /* Find out how many processes there are in the default     communicator */  MPI_Comm_size(MPI_COMM_WORLD, &ntasks);  /* Seed the slaves; send one unit of work to each slave. */  for (rank = 1; rank < ntasks; ++rank) {    /* Find the next item of work to do */    work = get_next_work_item();    /* Send it to each rank */    MPI_Send(&work,             /* message buffer */             1,                 /* one data item */             MPI_INT,           /* data item is an integer */             rank,              /* destination process rank */             WORKTAG,           /* user chosen message tag */             MPI_COMM_WORLD);   /* default communicator */  }  /* Loop over getting new work requests until there is no more work     to be done */  work = get_next_work_item();  while (work != NULL) {    /* Receive results from a slave */    MPI_Recv(&result,           /* message buffer */             1,                 /* one data item */             MPI_DOUBLE,        /* of type double real */             MPI_ANY_SOURCE,    /* receive from any sender */             MPI_ANY_TAG,       /* any type of message */             MPI_COMM_WORLD,    /* default communicator */             &status);          /* info about the received message */    /* Send the slave a new work unit */    MPI_Send(&work,             /* message buffer */             1,                 /* one data item */             MPI_INT,           /* data item is an integer */             status.MPI_SOURCE, /* to who we just received from */             WORKTAG,           /* user chosen message tag */             MPI_COMM_WORLD);   /* default communicator */    /* Get the next unit of work to be done */    work = get_next_work_item();  }  /* There's no more work to be done, so receive all the outstanding     results from the slaves. */  for (rank = 1; rank < ntasks; ++rank) {    MPI_Recv(&result, 1, MPI_DOUBLE, MPI_ANY_SOURCE,             MPI_ANY_TAG, MPI_COMM_WORLD, &status);  }  /* Tell all the slaves to exit by sending an empty message with the     DIETAG. */  for (rank = 1; rank < ntasks; ++rank) {    MPI_Send(0, 0, MPI_INT, rank, DIETAG, MPI_COMM_WORLD);  }}static void slave(void){  unit_of_work_t work;  unit_result_t results;  MPI_Status status;  while (1) {    /* Receive a message from the master */    MPI_Recv(&work, 1, MPI_INT, 0, MPI_ANY_TAG,             MPI_COMM_WORLD, &status);    /* Check the tag of the received message. */    if (status.MPI_TAG == DIETAG) {      return;    }    /* Do the work */    result = do_work(work);    /* Send the result back */    MPI_Send(&result, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);  }}static unit_of_work_t get_next_work_item(void){  /* Fill in with whatever is relevant to obtain a new unit of work     suitable to be given to a slave. */}static void process_results(unit_result_t result){  /* Fill in with whatever is relevant to process the results returned     by the slave */}static unit_result_tdo_work(unit_of_work_t work){  /* Fill in with whatever is necessary to process the work and     generate a result */}