读者-写者问题

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