信息量编程

1.#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

   //int semget(key_t key, int nsems, int semflg);
    //int semctl(int semid, int semnum, int cmd, ...);
     union semun {
           int              val;    /* Value for SETVAL */
           struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
           unsigned short  *array;  /* Array for GETALL, SETALL */
           struct seminfo  *__buf;  /* Buffer for IPC_INFO
                                       (Linux-specific) */
       };

int main()
{
key_t key;
int semid;

    key = ftok(".",1);
    semid = semget(key,1,IPC_CREAT|0666);
    union semun initsem;
    initsem.val = 1;
    semctl(semid,0,SETVAL,initsem);//

    int pid = fork();
    if(pid>0) {
            printf("this is father\n");
    } else if(pid == 0) {
            printf("this is child\n");
    } else {
            printf("fork error\n");
    }
    return 0;

}
2.终极信号量编程
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

   //int semget(key_t key, int nsems, int semflg);
   //int semop(int semid, struct sembuf *sops, size_t nsops);

    //int semctl(int semid, int semnum, int cmd, ...);
     union semun {
           int              val;    /* Value for SETVAL */
           struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
           unsigned short  *array;  /* Array for GETALL, SETALL */
           struct seminfo  *__buf;  /* Buffer for IPC_INFO
                                       (Linux-specific) */
       };

void pGetkey(int id)
{
struct sembuf set;
set.sem_num = 0;
set.sem_op = -1;
set.sem_flg = SEM_UNDO;
semop(id,&set,1);
printf(“getkey\n”);
}

void vPutBackkey(int id)
{
struct sembuf set;
set.sem_num = 0;
set.sem_op = 1;
set.sem_flg = SEM_UNDO;
semop(id,&set,1);
printf(“putbackkey\n”);
}
int main()
{
key_t key;
int semid;

    key = ftok(".",1);
    semid = semget(key,1,IPC_CREAT|0666);
    union semun initsem;
    initsem.val = 0;
    semctl(semid,0,SETVAL,initsem);//

    int pid = fork();
    if(pid>0) {
            pGetkey(semid);
            printf("this is father\n");
            vPutBackkey(semid);
            semctl(semid,0,IPC_RMID );    //销毁
    } else if(pid == 0) {
            printf("this is child\n");
             vPutBackkey(semid);
    } else {
            printf("fork error\n");

    }
    return 0;

}