Question

我尝试编写一个可以进行多线程读写的程序。它可以在一次读取和一次写入时正常工作，但当我使用两次读取和一次写入时，它以死锁结束。

任何人都可以帮忙检查一下吗？

const int BUF_SIZE = 10;
const int ITERS = 100;

boost::mutex io_mutex;

class buffer
{
public:

    typedef boost::mutex::scoped_lock scoped_lock;

    buffer() : p(0), c(0), full(0)
    {}

    void put(int m)
    {
        scoped_lock lock(mutex);
        if (full == BUF_SIZE)
        {
            {
                boost::mutex::scoped_lock lock(io_mutex);
                std::cout << "Buffer is full. Waiting..." << std::endl;
            }
            while (full == BUF_SIZE)
                cond.wait(lock);
        }

        buf[p] = m;

        p = (p+1) % BUF_SIZE;

        ++full;

        cond.notify_all();
    }

    int get()
    {
        scoped_lock lk(mutex);

        if (full == 0)
        {
            {
                boost::mutex::scoped_lock lock(io_mutex);
                std::cout << "Buffer is empty. Waiting..." << std::endl;
            }

            while (full == 0)
                cond.wait(lk);
        }

        int i = buf[c];

        c = (c+1) % BUF_SIZE;

        --full;

        cond.notify_one();

        return i;
    }

private:
    boost::mutex mutex;

    boost::condition cond;

    unsigned int p, c, full;

    int buf[BUF_SIZE];
};

buffer buf;

void writer()
{
    for (int n = 0; n < ITERS; ++n)
    {
        {
            boost::mutex::scoped_lock lock(io_mutex);
            std::cout << "sending: " << n << std::endl;
        }
        buf.put(n);
    }
}

void reader()
{
    for (int x = 0; x < ITERS; ++x)
    {
        int n = buf.get();
        {
            boost::mutex::scoped_lock lock(io_mutex);
            std::cout << "reader1: received: " << n <<  std::endl;
        }
    }
}

int main(int argc, char* argv[])
{
    boost::thread thrd1(&reader);
    boost::thread thrd2(&writer);
    boost::thread thrd3(&reader);

    std::string str;

    thrd1.join();
    thrd2.join();
    thrd3.join();

    std::getline(std::cin,str);
}

Answer 1

你可能在这里失去了树林。您的代码写入ITERS值但尝试读取2 * ITERS值，因为您有两个读取器。那不行。

您至少必须编写2 * ITERS值才能完成程序。

提升线程死锁，任何人都可以检查为什么？

1 个答案: