#include<sys/ipc.h>#include<stdio.h>#include<stdlib.h>#include<sys/types.h>#include<sys/sem.h>#include<signal.h>#include<unistd.h>int semid;              /*五個信號量的共同ID*/ void (*old_handler)(int);     void ctrl_c(int dump)                   /*按ctrl_c退出程序*/ {if(semctl(semid,0,IPC_RMID)<0){perror("semctl IPC_RMID");exit(EXIT_FAILURE);}signal(SIGINT,old_handler);exit(0);}int main(){int phi,i;int ran;pid_t val;int nsems=5;int flags=0666;struct sembuf buf[2];semid=semget(IPC_PRIVATE,nsems,flags);                  /*創建5個信號量 */if(semid<0){perror("semget");exit(EXIT_FAILURE);}/*剛創建的信號量為0，將其設為1才能用*/for(i=0;i<5;i++){buf[0].sem_num=i;buf[0].sem_op=1;buf[0].sem_flg=IPC_NOWAIT;semop(semid,buf,1);}val=fork();if(val!=0){phi=1;val=fork();        /*創建5個子進程*/ 	if(val!=0){val=fork();		if(val!=0){val=fork();			if(val==0)phi=5;}		else phi=4;}	else phi=3;}else phi=2;if(val!=0)old_handler=signal(SIGINT,ctrl_c);     /*為父進程重新設置退出信號*/ while(1){	ran=rand()%5;	if(phi==ran){printf("			%d is hungry,%d want to eat!\n",phi,phi);sleep(1);		buf[0].sem_num=phi;buf[0].sem_op=-1;buf[0].sem_flg=0;           /*設置第一個信號量*/ 		buf[1].sem_num=(phi+1)%5;buf[1].sem_op=-1;buf[1].sem_flg=0;      /*設置第二個信號量*/ 		semop(semid,buf,2);         /*根據剛才的設置同時對兩個信號量進行p操作*/ 		printf("							%d has eaten!\n",phi);sleep(1);		buf[0].sem_num=phi;buf[0].sem_op=1;buf[0].sem_flg=0;             /*設置第一個信號量*/		buf[1].sem_num=(phi+1)%5;buf[1].sem_op=1;buf[1].sem_flg=0;       /*設置第二個信號量*/		semop(semid,buf,2);}        /*根據剛才的設置同時對兩個信號量進行p操作*/	else {printf("%d is thinking!\n",phi);sleep(1);}	}}