Programming lunch philosophers with the MPI C program

Question

I have a problem with my MPI C program. This is the code:

void wantEat(int p, int rank, char *state, char* stateLeft, char* stateRight){ char *s; MPI_Status status ; /* if left or right neighbor is eating */ if(compare(stateLeft, "eat") || compare (stateRight, "eat")){ state = "want_Eat"; printf("%s : I wait for eating\n", nomPhilosophe(rank)); /* the process have to send his new state to his neighbors */ MPI_Send(state, strlen(state)+1, MPI_CHAR, (rank - 1 + p) % p, 0, MPI_COMM_WORLD); MPI_Send(state, strlen(state)+1, MPI_CHAR, (rank + 1) % p, 0, MPI_COMM_WORLD); /* if only left neighbor is eating */ if(compare(stateLeft,"eat") && !compare(stateRight,"eat")){ /* Wait for left neighbor finishes eating */ MPI_Recv(stateLeft, 6, MPI_CHAR, (rank - 1 + p) % p, 0, MPI_COMM_WORLD, &status); /* and eat */ state = "eat"; } /* if only right neighbor is eating */ if(compare(stateRight,"eat") && !compare(stateLeft,"eat")){ /* wait for right neighbor message */ MPI_Recv(stateRight, 6, MPI_CHAR, (rank + 1) % p, 0, MPI_COMM_WORLD, &status); /* and eat */ state = "eat"; } /* if both neighboors are eating */ if(compare(stateRight,"eat") && compare(stateLeft,"eat")){ /* wait for messages of the 2 neighbors */ MPI_Recv(stateLeft, strlen("think")+1, MPI_CHAR, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status); MPI_Recv(stateRight, strlen("think")+1, MPI_CHAR, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status); /* and eat */ state = "eat"; } } /* if neighbors are not eating */ else{ /* eat */ state= "eat"; } /* send the new state to neighbors */ MPI_Send(state, strlen(state)+1, MPI_CHAR, (rank - 1 + p) % p, 0, MPI_COMM_WORLD); MPI_Send(state, strlen(state)+1, MPI_CHAR, (rank + 1) % p, 0, MPI_COMM_WORLD); } int main(int argc, char* argv[]){ int my_rank; /* rank of process */ int p; /* number of processes */ char* state = "think"; /* state of process (think, eat, or want_eat) */ char* stateLeft = "think"; /* state of the left neighbor of the process */ char* etatD = "think"; /* state of the right neighbor of the process */ /* start up MPI */ MPI_Init(&argc, &argv); /* find out process rank */ MPI_Comm_rank(MPI_COMM_WORLD, &my_rank); /* find out number of processes */ MPI_Comm_size(MPI_COMM_WORLD, &p); think(my_rank); /* process "my_rank" is thinking */ wantEat(p, my_rank, state, stateLeft, stateRight); /* process "my_rank" wants to eat */ eat(my_rank); /* process "my_rank" is eating */ /* shut down MPI */ MPI_Finalize(); return 0; } 

The problem is that all processes feed at the same time, without waiting for neighbors. I think that the MPI messages of new states are not accepted by neighbors. Do you have an idea to fix this problem?