IPC之读者-写者问题

 1 typedef int semaphore;
 2 semaphore mutex = 1;
 3 semaphore db = 1;
 4 int rc = 0;
 5 void reader(void)
 6 {
 7     while(TRUE)
 8     {
 9          down(&mutex);
10          rc += 1;
11          if(rc == 1)down(&db);
12          up(&mutex);
13          read_date();
14          down(&mutex);
15          rc -= 1;
16          if(rc == 0)up(&db);
17          up(&mutex);
18     }
19 }
20 void writer(void)
21 {
22     while(TRUE)
23     {
24         think_up_data();
25         down(&mutex);
26         write_data();
27         up(&mutex);
28     }
29 }