philosopher_th.c

五个哲学家的就餐问题

#include "apue.h"
#include <semaphore.h>

static sem_t *forks;
static int time,N;
void thinking(int i,int nsecs){
	printf("philosopher %d is thinking\n",i);
	sleep(nsecs);
}
void eating(int i,int nsecs){
	printf("philosopher %d is eating\n",i);
	sleep(nsecs);
}
void takefork(int i){
	if(i==N-1){
		sem_wait(&forks[0]);
		sem_wait(&forks[i]);
	}
	else{
		sem_wait(&forks[i]);
		sem_wait(&forks[i+1]);
	}
}
void putfork(int i){
	if(i==N-1){
		sem_post(&forks[0]);
		sem_post(&forks[i]);
	}
	else{
		sem_post(&forks[i]);
		sem_post(&forks[i+1]);
	}
}
void * philosopher(void *n){
	int i;
	i=(int)n;
	while(1){
		thinking(i,time);
		takefork(i);
		eating(i,time);
		putfork(i);
	}
}
int main(int argc,char *argv[]){
	int i,status;
	pthread_t tpid;
	if(argc==2)	time=2;
	else if(argc==4 && !strcmp(argv[2],"-t"))
		time=atoi(argv[3]);
	else
		err_sys("usage:philosopher_th <N> [-t <time>]\n");
	N=atoi(argv[1]);
	forks=(sem_t*)malloc(N*sizeof(sem_t));
	for(i=0;i<N;i++)
		sem_init(forks+i,0,1);
	for(i=0;i<N;i++){
		status=pthread_create(&tpid,NULL,philosopher,(void *)i);
		if(status!=0)
			err_quit("can't creat thread:%s\n",strerror(status));
	}
	pthread_join(tpid,NULL);
	return 0;
}