根据《linux网络编程》p117的例子改编的,因为书上的例子有一些错误,这里进行了改正,并增加了利用信号中断程序,回收资源的功能。
#include
#include
#include
#include
#include
#include
/***********************
该文可以任意转载,修改,但需保留出处
修改者:rainfish
出处:http://blog.csdn.net/bat603/
版权归《linux网络编程》所有
*****************/
#define SHMKEY1 (key_t)0x10
#define SHMKEY2 (key_t)0x15
#define SEMKEY (key_t)0x20
#define SIZ 5*BUFSIZ
#define IFLAGS (IPC_CREAT|IPC_EXCL)
#define ERR ((struct databuf*)-1)
struct sembuf p1 = {0, -1, 0};
struct sembuf v1 = {0, 1, 0};
struct sembuf p2 = {1, -1, 0};
struct sembuf v2 = {1, 1, 0};
static int shmid1, shmid2, semid;
struct databuf
{
int d_nread;
char d_buf[SIZ];
};
void
fatal(char *mes)
{
perror(mes);
exit (1);
}
void
getshm (struct databuf **p1, struct databuf **p2)
{//创建共享内存
if ((shmid1=shmget(SHMKEY1, sizeof(struct databuf), 0600|IFLAGS)) < 0)
{
fatal ("shmget");
}
if ((shmid2=shmget(SHMKEY2, sizeof(struct databuf), 0600|IFLAGS)) < 0)
{
fatal ("shmget");
}
//映射
if ((*p1=(struct databuf*)(shmat(shmid1, 0, 0))) == ERR)
{
fatal("shmat");
}
if ((*p2=(struct databuf*)(shmat(shmid2, 0, 0))) == ERR)
{
fatal("shmat");
}
}
int
getsem()
{
//int semid;
if ((semid=semget(SEMKEY, 2, 0600|IFLAGS)) < 0)
{
fatal("segmet");
}
//初始化信号量,假定第一个信号灯没有资源
if (semctl(semid, 0, SETVAL, 0) < 0)
{
fatal ("semctl");
}
//第二个有信息,如果两个信号都没有资源,将会出现死锁
//书上该处有问题
if (semctl(semid, 1, SETVAL, 1) < 0)
{
fatal ("semctl");
}
return (semid);
}
void
myremove()
{
if (shmctl(shmid1, IPC_RMID, NULL) < 0)
{
fatal("shmctl");
}
if (shmctl(shmid2, IPC_RMID, NULL) < 0)
{
fatal("shmctl");
}
if (semctl(semid, 0, IPC_RMID, NULL) < 0)
fatal("semctl");
exit(0);
}
void
reader(int semid, struct databuf *buf1, struct databuf *buf2)
{
for(;;)
{
//从键盘读入数据,放在buf1->d_buf,
//read第一个参数是文件描述符,其中0表示从终端输入:如键盘
buf1->d_nread = read(0, buf1->d_buf, SIZ);
//v操作,释放第一个信号灯资源
semop(semid, &v1, 1);
//p操作,申请第二个信号灯资源,若没有资源,则阻塞进程直到有资源.
semop(semid, &p2, 1);
buf2->d_nread = read(0, buf2->d_buf, SIZ);
semop(semid, &v2, 1);
semop(semid, &p1, 1);
}
}
void
writer(int semid, struct databuf *buf1, struct databuf *buf2)
{
for(;;)
{
//p操作,等待第一个信号的资源
semop(semid, &p1, 1);
//1代表输出到屏幕
write(1, buf1->d_buf, buf1->d_nread);
semop(semid, &v1, 1);
semop(semid, &p2, 1);
write(1, buf2->d_buf, buf2->d_nread);
semop(semid, &v2, 1);
}
}
int
main()
{
int semid, pid;
struct databuf *buf1, *buf2;
semid = getsem();
getshm (&buf1, &buf2);
switch(pid=fork())
{
case -1:
fatal("fork");
break;
case 0:
writer(semid, buf1, buf2);
break;
default:
//在主进程中把中断程序的ctrl+c和myremove函数建立联系,来回收系统资源:共享内存区,信号量.
signal (SIGINT, myremove);
reader(semid, buf1, buf2);
break;
}
exit(0);
}
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