philosopher.c

五个哲学家的就餐问题

#include "apue.h"
#include "lock.c"
#define	 N	5

static char *forks[5]={"fork0","fork1","fork2","fork3","fork4"};
static int  time;
void thinking(int k,int nsecs){
	printf("philosopher %d is thinking\n",k);
	sleep(nsecs);
}

void eating(int k,int nsecs){
	printf("philosopher %d is eating\n",k);
	sleep(nsecs);
}

void takefork(int k){
	if(k==N-1){
		lock(forks[0]);
		lock(forks[k]);
	}
	else{
		lock(forks[k]);
		lock(forks[k+1]);
	}
}
void putfork(int k){
	if(k==N-1){
		unlock(forks[0]);
		unlock(forks[k]);
	}
	else{
		unlock(forks[k]);
		unlock(forks[k+1]);
	}
}
void philosopher(int i){
	while(1){
		thinking(i,time);
		takefork(i);
		eating(i,time);
		putfork(i);
	}
}


int main(int argc,char *argv[]){
	int 	i;
	pid_t	pid;
	if(argc==3 && !strcmp(argv[1],"-t"))	time=atoi(argv[2]);
	else if(argc==1)	time=2;
	else	err_sys("usage:philosopher [-t <time>]\n");
	for(i=0;i<N;i++)	initlock(forks[i]);
	for(i=0;i<N;i++){
		if((pid=fork())<0)
			err_sys("fork error!");
		else if(!pid)
			philosopher(i);
	}
	wait(NULL);
	return 0;
}