Concurrency

Spin Then Block

Difficulty

Asked at Hudson River Trading, XTX Markets

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xxx xxxx xx xxxx xxx x xxxx, xxxx xxxxx xx xxxxx xxx.

xxxx xxxxxxxx xxxxx x xxxx. xxxxx, xx xx xxxxxxxxxxxx xxxx xxx xxxxxx xxxx xxxxxxxxxxx: xxx xxxxxxx xxxxxxxx x xxxx xxxxx xxxxxxx xxxxx xxx xxxxxx xx xx xxxxxxx xxx xxxxxx xx xxxxxxxxx xx xxxxxxx. xx x xxxxxxx xxxx xxxx xxxxxxx xxxx xxxxx xxxx xx xxx x xxxx xxxx.

xxxx xxxxxxxx xxxx x xxxxxxx xxx xxx xxxxxxx xxxxxxxx xxxx xxxx xxx xxxx xxx xxxxx xx xx xxxx xx xxxxx xxxxxxxxxxx.

xxxxx xxxxxxxxxx xxxxx, xxxxx'x xxxxxxxx, xxxx xxxx: xxxx xxxxxxx, xxxx xxxx xx xxx xxxxx. xxxxxxxxx xxxxxxxxxxxxx.

xxxx(xxxxxx) — xxxx xx xxxx xxxxxx xxxxx; xx xxxx xxxxx, xxxxx
xxxxxx(), xxxx()
xxxxx(), xxxxxx() — xx xxx xxxxx xxx xxx xxxxx xxxx xxx xxxxx

xxxxxxxx

xxxxxxxxxxxxx x;
xxx (xxx x = x; x < xxxx; ++x) { x.xxxx(xx); x.xxxxxx(); }
x.xxxxx();    // x
x.xxxxxx();   // x

xx xxxxxxxxxxx xxxxxxxxxxx xxxx xxxx xxxxxxx xxx xxxxxx xxxxxxxx. xxxx xxxxxxxxxxxx xxx xxxxxxxxxxx, xxx xx xxxxxxxxxxxxxx xxxx xxxxxx xxx xxxx xxxx xxxxxxxxxxxxxxx xxxx xxx xxxxxxxxxx xx xxxx xxx xxxx.

xxxxxxxxxxx

xxx xxx xxxxx'x xxxxxxxxxx xxxx xxxxx xxxxx xxxxxxxxxxxx: xxx xxxxxxx xx xxxxx, xxx xxxx xx xxxxx xxxx xx xxx xxxxxxx xx xxxx, xxxxx() xxxxx xxxxxxx xxxxxx xxxxx xxx xxxxxxxxxxxx, xxx xxxx() xxxx xxxxx.
x xxxxxx xx x xxxx xxxxx xxxx, xx xxxxx xxxxxxxx xx xxxxxxxx.
xxxxxxx xxx xxxx xxxxxx xx xxx xxx xxxx xxxxxxxxx, xxx xxxxxx xxx xxxxxxx. x xxxxxx xxxx xxxxxxx xx xxxxx xx xxxx xxxxx xxxxxxxxxxx xxxxxx xxxxxxx xxx xxxxxx xx xxx xxxxxxx xxx. xxxxxxx xxxx xxxxxx xxxxx xxxx xxxxx: xxx xxxxxx xxxxx xxx xxxxxxxxx xxxxx xxxxxxx xxx xxxxx (xxx xxxxxxxxx xxxx xx xx_.xxxx xxxx xxxx), xxx xxx xxxxxxxx xxxxxx xxx xxxx xxxxx xxx xxxx xxxxx xxxxxx xxxxxxxxx. xxxxxx xxxx xxxxx xxxxxx xxx xxxx xxxx.

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Language: C++SpinThenBlock

#include <atomic>
#include <condition_variable>
#include <cstddef>
#include <mutex>
#include <thread>
#include <vector>

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class SpinThenBlock {
public:
    void lock(long long budget) {
        // ...
        (void)budget;
    }

    void unlock() {
        // ...
    }

    bool held() const { return held_.load(); }
    long long spins() const { return spins_.load(); }
    long long blocks() const { return blocks_.load(); }

private:
    std::atomic<bool> held_{false};
    std::atomic<long long> spins_{0};
    std::atomic<long long> blocks_{0};
    std::mutex mutex_;
    std::condition_variable cv_;
};

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