用信号量解决哲学家就餐问题

#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <unistd.h>

#include <sys/mman.h>#include <string.h>#include <sys/ipc.h>#include <sys/shm.h>#include <string.h>#include <sys/ipc.h>#include <sys/sem.h>#include <sys/wait.h>#define ERR_EXIT(m)\do\{\perror(m);\exit(EXIT_FAILURE);\}while(0)int semid;#define DELAY (rand() % 5 + 1 )union semun {               int   val;    /* Value for SETVAL */struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET 

unsigned short  *array;  /* Array for GETALL, SETALL */ struct seminfo  *__buf;  /* Buffer for IPC_INFO                                           (Linux-specific) */              };}int sem_p(int semid){struct sembuf sb = {0,-1,0};int ret = semop(semid, &sb,1);if (ret == -1)ERR_EXIT("sem_p");return ret;}int sem_v(int semid){struct sembuf sb = {0,1,0};int ret = semop(semid, &sb,1);if (ret == -1)ERR_EXIT("sem_p");return ret;}void wait_for_2fork(int no){int left = no;int right = (no+1)%5;struct sembuf sb[2] = {{left, -1, 0},{right, -1, 0}};semop(semid, sb, 2);}void free_2fork(int no){int left = no;int right = (no+1)%5;struct sembuf sb[2] = {{left, 1, 0},{right, 1, 0}};semop(semid, sb, 2);}void philosophere(int no){srand(getpid());for (;;){printf("%d is thinking!\n", no);sleep(DELAY);printf("%d is hungry!\n", no);wait_for_2fork(no);printf("%d is eating!\n", no);sleep(DELAY);free_2fork(no);}}int main(int argc, char *argv[]){semid = semget(IPC_PRIVATE, 5, IPC_CREAT | 0666);if (semid == -1)ERR_EXIT("semget");union semun su;su.val = 1;int i;for (i = 0; i < 5; i++){semctl(semid,i ,SETVAL,su);}pid_t pid;int no;for (i = 0; i < 5; i++){pid = fork();if (pid == -1)ERR_EXIT("fork");if (pid == 0){no = i;break;}}philosophere(no);return 0;}