#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#define FTOK_PATH            "/dev/zero"
#define FTOK_PROJID          0x22

union semun 
{
    int val;
    struct semid_ds *buf;
    unsigned short *arry;
};

int semaphore_init(void);
int semaphore_p(int semid);
int semaphore_v(int semid);
void semaphore_term(int semid);

int main(int argc, char **argv)
{
    int            semid;
    pid_t          pid;
    int            i;

    if( (semid=semaphore_init()) < 0)
    {
	printf("semaphore initial failure: %s\n", strerror(errno)); 
        return -1;
    }

    if( (pid=fork()) < 0)
    {
        printf("fork() failure: %s\n", strerror(errno));
        return -2;
    }
    else if( 0 == pid)  /* child process */
    {
        printf("Child process start running and do something now...\n");
        sleep(3);
        printf("Child process do something over...\n");
        semaphore_v(semid);

        sleep(1);

        printf("Child process exit now\n");
        exit(0);
    }

    printf("Parent process P operator wait child process over\n");
    semaphore_p(semid);
    printf("Parent start do something now...\n");
    sleep(2);
    printf("Child process exit and ");


    semaphore_term(semid);
    return 0;
}

int semaphore_init(void)
{
    key_t          key;
    int            semid;
    union semun    sem_union;
		    
    if( (key=ftok(FTOK_PATH, FTOK_PROJID)) < 0 ) 
    {   
	printf("ftok() get IPC token failure: %s\n", strerror(errno)); 
	return -1;
    } 
    
    semid = semget(key, 1, IPC_CREAT|0644);
    if( semid < 0)
    {
	printf("semget() get semid failure: %s\n", strerror(errno)); 
	return -2;
    }

    sem_union.val = 0;
    if( semctl(semid, 0, SETVAL, sem_union)<0 )
    {
	printf("semctl() set initial value failure: %s\n", strerror(errno)); 
	return -3;
    }

    printf("Semaphore get key_t[0x%x] and semid[%d]\n", key, semid);

    return semid;
}

void semaphore_term(int semid)
{
    union semun    sem_union;
		    
    if( semctl(semid, 0, IPC_RMID, sem_union)<0 )
    {
	printf("semctl() delete semaphore ID failure: %s\n", strerror(errno)); 
    }

    return ;
}



int semaphore_p(int semid)
{
    struct sembuf _sembuf;

    _sembuf.sem_num = 0;
    _sembuf.sem_op = -1;
    _sembuf.sem_flg = SEM_UNDO; //  IPC_NOWAIT  SEM_UNDO


    if( semop(semid, &_sembuf, 1) < 0 )
    { 
        printf("semop P operator failure: %s\n", strerror(errno));
        return -1;
    }

    return 0;
}

int semaphore_v(int semid)
{
    struct sembuf _sembuf;

    _sembuf.sem_num = 0;
    _sembuf.sem_op = 1;
    _sembuf.sem_flg = SEM_UNDO; //  IPC_NOWAIT  SEM_UNDO

    if( semop(semid, &_sembuf, 1) < 0 )
    { 
        printf("semop V operator failure: %s\n", strerror(errno));
        return -1;
    }

    return 0;
}