Linux 信号量 生产者消费者小例题 （嘘，我是菜鸟～）

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

#include <x86_64-linux-gnu/sys/types.h>
#include <x86_64-linux-gnu/sys/ipc.h>
#include <x86_64-linux-gnu/sys/sem.h>

int semInite(int semId, int value);
int semDelete(int semId);
int semP(int semId);
int semV(int semId);

//declare a union to be used
union semun 
{
    int val;                        /* value for SETVAL */ 
    struct semid_ds *buf;                /* buffer for IPC_STAT, IPC_SET */ 
    unsigned short int *array;         /* array for GETALL, SETALL */ 
    struct seminfo *__buf;                /* buffer for IPC_INFO */ 
};


//semaphore declare
static int semFullId;
static int semEmptyId;
static int source = 0;        //source definition    


//new thread as a consumer
void* child_thread(void* arg)
{
    int ttt = 1;
        
    while(1)
    {
        sleep(rand() % 19);
        printf("child No.%d times wants to consume...\n", ttt);
        
        semP(semFullId);    //
        printf("child No.%d times start consuming. source = %d\n", ttt, source);
        source = 0;
        printf("child No.%d times end consuming. source = %d\n\n", ttt++, source);
        semV(semEmptyId);    //
    }
    
    return (void*)0;
}

int main(void)
{    
    //create semaphore
    semFullId = semget((key_t)1235, 1, 0666 | IPC_CREAT);
    semEmptyId = semget((key_t)1236, 1, 0666 | IPC_CREAT);
    semInite(semFullId, 0);
    semInite(semEmptyId, 1);
    
    pthread_t pid;
    pthread_create(&pid, NULL, child_thread, NULL);
    
    int tt = 1;    
    while(1)
    {
        sleep(rand() % 18);
        printf("parent No.%d times wants to produce...\n", tt);
        
        semP(semEmptyId);    //
        printf("parent No.%d times start producing. source = %d\n", tt, source);
        source = rand() % 100;
        printf("parent No.%d times end producing. source = %d\n", tt++, source);
        semV(semFullId);    //
    }
    
    semDelete(semFullId);
    semDelete(semEmptyId);
    return 0;
}


//set semaphore as default value
int semInite(int semId, int value)
{
    union semun semUnion;
    semUnion.val = value;    //set default semaphore
    return semctl(semId, 0, SETVAL, semUnion);
}

//delete semaphore
int semDelete(int semId)
{
    union semun semUnion;
    return semctl(semId, 0, IPC_RMID, semUnion);
}

//semaphore P operation
int semP(int semId)
{
    struct sembuf semBuf;
    semBuf.sem_num = 0;        //indicate it is not semaphore array
    semBuf.sem_op = -1;        //subtract one
    semBuf.sem_flg = SEM_UNDO;
    
    return semop(semId, &semBuf, 1);    //return value
}

//semaphore V operation
int semV(int semId)
{
    struct sembuf semBuf;
    semBuf.sem_num = 0;        //indicate it is not semaphore array
    semBuf.sem_op = 1;        //subtract one
    semBuf.sem_flg = SEM_UNDO;
    
    return semop(semId, &semBuf, 1);    //return value
}