philosopher.c

哲学家进餐经典算法的pthread多线程实现代码

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define N 5
#define BusyEating 1
#define BusyThinking 1
#define Left(p) (p)
#define Right(p) (((p)+1)%N)

typedef int *semaphore;
semaphore chopstick[N];

semaphore init_semaphore()
{
     int *s = malloc(2*sizeof(int));
     pipe(s);
     return s;
}
void wait(semaphore s)
{
     int junk;
     read(s[0], &junk, 1);
}
void signal(semaphore s)
{
     write(s[1], "x", 1);
}

void pick_up(int me)
{
     if (me==0) {
	  wait(chopstick[Right(me)]);
	  printf("philosopher %d picks up right chopstick\n", me);
	  sleep(1);
	  wait(chopstick[Left(me)]);
	  printf("philosopher %d picks up left chopstick\n", me);
     } else {
	  wait(chopstick[Left(me)]);
	  printf("philosopher %d picks up left chopstick\n", me);
	  sleep(1);
	  wait(chopstick[Right(me)]);
	  printf("philosopher %d picks up right chopstick\n", me);
     }
}
void put_down(int me)
{
     signal(chopstick[Left(me)]);
     signal(chopstick[Right(me)]);
}

void philosopher(int me)
{
     int i;
     for (i=1; ; i++) {
	  pick_up(me);
	  printf("philosopher %d eating [%d]\n", me, i);
	  sleep(BusyEating);
	  put_down(me);
	  printf("philosopher %d thinking\n", me);
	  sleep(BusyThinking);
     }
}

int main()
{
     int i;
     for (i=0; i<N; i++) {
	  chopstick[i] = init_semaphore();
	  signal(chopstick[i]);
     }
     for (i=0; i<N-1; i++) if (fork()==0) break;
     philosopher(i);
	
     return 0;
}