有关条件变量的使用

[5G菜鸟成长日记]

pthread_mutex_t count_lock;
pthread_cond_t count_nonzero;
unsigned count;
decrement_count　() {
　pthread_mutex_lock (&count_lock);
　while(count==0)
　　pthread_cond_wait( &count_nonzero, &count_lock);
　　count=count -1;
　pthread_mutex_unlock (&count_lock);
}

increment_count(){
　pthread_mutex_lock(&count_lock);
　if(count==0)
　　pthread_cond_signal(&count_nonzero);
　　count=count+1;
　pthread_mutex_unlock(&count_lock);
}

哪位大侠能详细地告诉我这个例子的执行过程?