使用sem_post信号量进行线程同步

写了一小段程序，测试一下线程同步的问题，如下：

#include <stdio.h>
#include <string.h>
#include <semaphore.h>
#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>
 
sem_t sp; 
 
int val = -;
int semPost(sem_t * pSem, int nMaxCount)
{
    int nRet, nSemCount;
 
    sem_getvalue(pSem, &nSemCount);
    if (nSemCount>=nMaxCount)
    {
        return ;
    }
    else
    {
        nRet=sem_post(pSem);
        return nRet;
    }
}
 
int semWait(sem_t * pSem)
{
    int nRet;
    nRet=sem_wait(pSem);
 
    while (sem_trywait(pSem)==) {}
    return nRet;
}
 
void xxx()
{
    while()
    {
        semWait(&sp);
        printf("xxx  val  %d\n",val);
    }
 
}
 
void yyy()
{
    int i = ;
    while()
    {
    //    semPost(&sp,3);
        printf("yyy :  %d\n",i);
        sleep();
        if(i++ >= )
        {
            i = ;
            semPost(&sp,);
            val = ;
            printf("now xxx can run !!!\n");
        }
    }
 
}
 
int main(int argc,char **argv)
{
    pthread_t x;
    pthread_t y;
 
    sem_init(&sp,,);
 
    pthread_create(&x,NULL,(void *)xxx,NULL);
    pthread_create(&y,NULL,(void *)yyy,NULL);
 
    while()
    {
        sleep();
    }
 
    return ;
}