LINUX下的生产者消费者模型算法

#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#define NEED_P 2
#define NEED_C 3
#define WORKS_P 6
#define WORKS_C 4
#define BUF_LENGTH (sizeof(struct mybuffer))
#define LETTER_NUM 3
#define SHM_MODE 0600
#define SEM_ALL_KEY 1234
#define SEM_EMPTY 0
#define SEM_FULL 1
//缓冲区结构（循环队列）
struct mybuffer{
  char letter[LETTER_NUM];
  int head;
  int tail;    
  int is_empty;
};
//得到5以内的一个随机数
int get_random(){
  int t;   
  srand((unsigned)(getpid()+time(NULL)));
  t=rand()%5;   
  return t;
}