编程范式16 笔记 信号量

void SellTickets(int i,int TicketsToSell,int numTickets,Samephore lock)
{
    while(True){
       /*临界区开始*/
        SamephoreWait(lock);
        (*numTickets)--;
        SamephoreSignal(lock);
        /*临界区结束*/
        printf("all done\n");
    }

}

信号量要大于0
假设有两个线程都卖出票，那么写回会出问题

http 并行化

char buffer[8];

int main()
{
    ITP(false);//init thread package
    ThreadNew("writer",writer,0);
    ThreadNew("Reader",Reader,0);
    RunAllThread();
}

void writer()
{
    for(int i=0;i<40;i++){
        char=PrepareRondomChar();
        buffer[i%8]=c;
    }
}

void Reader()
{
    for(int i=0;i<40;i++){
        char c=buffer[i%8];
        ProcessChar(c);
    }
}

要保证reader比writer慢
但是buffer有限
writer又不能快太多

char buffer[8];
Samphore emptyBuffers 8;
//Samphore emptyBuffers 4 自由度降低 正确性不影响
//Samphore emptyBuffers 0 死锁
Samphore fullBuffers 0;
//Samphore fullBuffers 1;出错 Reader可能领先
int main()
{
    ITP(false);//init thread package
    ThreadNew("writer",writer,0);
    ThreadNew("Reader",Reader,0);
    RunAllThread();
}

void writer()
{
    for(int i=0;i<40;i++){
        SamphoreWait(emptyBuffers); 
        char=PrepareRondomChar();
        SamphoreSignal(fullBuffers);
        buffer[i%8]=c;
    }
}

void Reader()
{
    for(int i=0;i<40;i++){
        SamphoreWait(fullBuffers); 
        char c=buffer[i%8];
        SamphoreSignal(emptyBuffers);
        ProcessChar(c);
    }
}

哲学家吃饭

Samaphore forks[]={1,1,1,1,1}
Semaphore numOfForkToEat(4);
Semaphore 
void philosopter（int id）
{
    for(int i=0;i<3;i++){
        sw(forks[i]);
        sw(forks[(i+1)%5];
        Eat;
        ss(forks[i]);
        ss(forks[(i+1)%5]);