IPC(shm+sem)

/*一个例子程序，来自《linux环境下C编程指南》，有小改动：

*简单的服务器和客户端程序,启动不带参数运行服务器,带参数则是客户端

*服务器启动后,创建信号量和共享内存,并将共享内存的引用ID显示出来,

* 将信号量的引用ID放在共享内存中,利用服务器端提供的共享内存引用ID

*将共享内存附加到地址段,读取信号量以实现两个进程之间的同步,之后,这两个进程就可 *利用共享内存进行进程间通信,客户端输入的信息将在服务器端显示出来

*/

#include
<sys/sem.h>

#include
<sys/shm.h>

#include
<sys/ipc.h>

#include
<stdio.h>

#include
<string.h>

#include
<signal.h>

#include
<stdlib.h>

#define SHMDATASZ 1000

#define BUFSZ
(SHMDATASZ-sizeof(int))

#define SN_EMPTY 0

#define SN_FULL 1

int delete_semid = 0;

union semun

{

int val;

struct semid_ds
*buf;

ushort array;

};

void server(void);

void client(int shmid);

void delete(void);

void sigdelete(int signum);

void locksem(int semid,
int semnum);

void unlocksem(int semid,
int semnum);

void clientwrite(int shmid,
int semid,
char *buffer);

int main(int argc,
char *argv[])

{

if(argc
< 2)

server();

else

client(atoi(argv[1]));

return 0;

}

void server(void)

{

union semun sunion;

int semid, shmid;

void *shmdata;

char *buffer;

//创建2个信号量

semid = semget(IPC_PRIVATE, 2, SHM_R|SHM_W);

if(semid
== -1)

perror("semget");

delete_semid = semid;

// 当接收到SIGINT信号时删除信号量并终止程序

atexit(&delete);

signal(SIGINT,
&sigdelete);

//设EN_EMPYT的信号值为1

sunion.val = 1;

if(semctl(semid, SN_EMPTY, SETVAL, sunion)
==
-1)

perror("semctl");

sunion.val = 0;

//设EN_FULL的信号值为0,说明没有一个资源可用

if(semctl(semid, SN_FULL, SETVAL, sunion)
==
-1)

perror("semctl");

//创建一块共享内存

shmid = shmget(IPC_PRIVATE, SHMDATASZ, IPC_CREAT|SHM_R|SHM_W);

if(shmid
== -1)

perror("shmget");

//附加到shmdata

shmdata = shmat(shmid, 0, 0);

if(shmdata
==
(void*)-1)

perror("shmat");

//删除共享内存，刚刚创建还没用呢，就删了，不明白

// if(shmctl(shmid, IPC_RMID, NULL) == -1)

// perror("shmctl");

//把信号标识符放在首地址

*(int*)shmdata
= semid;

buffer = shmdata
+ sizeof(int);  //后面是缓冲区

printf("Server is running with SHM id ** %d **\n", shmid);

while(1)

{

printf("waiting until full...");

fflush(stdout);

//申请一个资源

locksem(semid, SN_FULL);

printf("done\n");

printf("message received :%s\n", buffer);

//释放用完的资源

unlocksem(semid, SN_EMPTY);

}

}

void client(int shmid)

{

int semid;

void *shmdata;

char *buffer;

//把server创建的共享内存附加到shmdata

shmdata = shmat(shmid, 0, 0);

//取出信号标识符

semid = *(int*)shmdata;

//再找到缓冲区

buffer = shmdata+sizeof(int);

printf("client operational: shm id is %d, sem id is %d\n", shmid, semid);

while(1)

{

char input[3];

printf("\n\nMenu\n1.Send a message\n");

printf("2.Exit\n");

fgets(input,
sizeof(input),
stdin);

switch(input[0])

{

case ‘1‘:clientwrite(shmid, semid, buffer);

break;

case ‘2‘:exit(0);

break;

}

}

}

void clientwrite(int shmid,
int semid,
char *buffer)

{

printf("waiting until empty..");

fflush(stdout);

//申请EMPTY资源

locksem(semid, SN_EMPTY);

printf("Enter Message:");

fgets(buffer, BUFSZ,
stdin);

//释放资源

unlocksem(semid, SN_FULL);

}

void delete()

{

printf("\nMaster exiting; deleting semaphore %d\n", delete_semid);

if(semctl(delete_semid, IPC_RMID, 0)
==
-1)

perror("release semaphore");

}

void sigdelete(int num)

{

exit(0);

}

void locksem(int semid,
int semnum)

{

struct sembuf sb;

sb.sem_num = semnum;

sb.sem_op =
-1;

sb.sem_flg = SEM_UNDO;

semop(semid,
&sb, 1);

}

void unlocksem(int semid,
int semnum)

{

struct sembuf sb;

sb.sem_num = semnum;

sb.sem_op = 1;

sb.sem_flg = SEM_UNDO;

semop(semid,
&sb, 1);

}