共享内存

#include
#include
#include
#include
#include
#include
#include
#include
#include
#if defined(_GNU_LIBRARY_) && ! defined(_SEM_SEMUN_UNDEFINED)
#else
union semun
{
 int val;
 struct semid_ds *buf;
 unsigned short int *array;
 struct seminfo *_buf;
};
#endif
#define SHMDATASIZE 1000
#define BUFFERSIZE (SHMDATASIZE - sizeof(int))
#define SN_EMPTY 0
#define SN_FULL 1
int DeleteSemid=0;

void server(void);
void client(int shmid);
void delete(void);
void sigdelete(int sginum);
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;
 semid=semget(IPC_PRIVATE,2,SHM_R|SHM_W);
 DeleteSemid=semid;

 /*删除信号量*/
 atexit(&delete);
 signal(SIGINT,&sigdelete);

 /*初始化信号量*/
 sunion.val=1;
 semctl(semid,SN_EMPTY,SETVAL,sunion);
 sunion.val=0;
 semctl(semid,SN_FULL,SETVAL,sunion);

 /*分配共享内存段*/
 shmid=shmget(IPC_PRIVATE,SHMDATASIZE,IPC_CREAT|SHM_R|SHM_W);
 
 /*影射到内存空间*/
 shmdata=shmat(shmid,0,0);

 /*结束进程后自动删除共享内存*/
 shmctl(shmid,IPC_RMID,NULL);
 *(int *)shdata=semid;
 buffer=shmdata+sizeof(int);
 printf("server is running with id  %d\n",shmid);

 while(1)
 {
  printf("waiting untill full...");
  fflush(stdout);
  locksem(semid,SN_FULL);
  printf("done.\n");
  printf("message received:%s\n",buffer);
  unlocksem(semid,SN_EMPTY);

 }
}
void client(int shmid)
{
 int semid;
 char *buffer;
 void *shmdata;
 shmdata=shmat(shmid,0,0);
 semid=*(int *)shmdata;
 buffer=shmdata+sizeof(int);
 printf("client operational:shm id is %d\n",shmid);
 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 delete(void)
{
 printf("master exiting:deleting semaphore.\n");
 if(semctl(DeleteSemid,0,IPC_RMID,0)==-1)
  printf("error releasing semaphore.\n");
}
void sigdelete(int signum)
{
 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); 
}
void clientwrite(int shmid,int semid,char *buffer)
{
 printf("waiting until empty...");
 fflush(stdout);
 locksem(semid,SN_EMPTY);
 printf("done.\n");
 printf("enter message:");
 fgets(buffer,BUFFERSIZE,stdin);
 unlocksem(semid,SN_FULL);
}