semaphore empty = N;	//缓冲区可用单元数量
semaphore odd = 0, even = 0; 	//奇数和偶数的数量 
semaphore mutex = 1;	//互斥信号量
p1(){
    int x = product();
    p(empty);
    p(mutex);
    if(x % 2 == 1) v(odd);
    else v(even)
    put(x);
    v(mutex);
}
p2(){
    p(odd);
    p(mutex);
    getodd();
    v(mutex);
    v(empty);
    countodd();
}
p3(){
    p(even);
    p(mutex);
    geteven();
    v(mutex);
    v(empty);
    counteven();
}