Concurrency

Latch and Barrier From Scratch

Difficulty

Asked at Flow Traders, Chicago Trading Company

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xxx xxxxxxxxxxxxx xxxx xxxx xxxxxx xxxxxxxxx xxx xxxxxx xx xxx xxxxxxxx, xxx xxxx xxxxxxxx xx xxx xxxxx xxxxxxx.

xxxxxxxxx xxxx.

xxxxx(xxxxx) — x xxx-xxxx xxxxxxxxx.

xxxxx_xxxx(), xxxx(), xxxxx()
x xxxxx xxxx xxx xxxxxxx xxxxx xxxx xxx xxxx() xxxxxxx xxxxxxxxxxx. xxxx xx xxxx xxxxx xx xxxx xx xxxx xx xx xxxxx xxx xxxxx xxxx xxxxxx.

xxxxxxx(xxxxxxxxxxxx) — x xxxxxxxx xxxxxxxxxx.

xxxxxx_xxx_xxxx() — xxxxx xxxxx xxx xxxxxxxxxxxx xxxx xxxxxxx, xxxx xxxxxxx xxxx xxxxxxxx xxx xxxxx
xxxxxxxxxx() — xxx xxxx xxxxx xx xxx xxxx xxxxxx

xxxxxxxx

xxxxx xxxxx(x);
// xxxx xxxxxxx xxxx xxxx(), xxxxx xxxx xxxxx_xxxx()
// xxx xxxx xxxx, xxx x xxxxx xxxx() xxxxxxxxxx xxxxxxx xx xxxx

xxxxxxx x(x);
// xxxxx xxxxxxx xxxx xxxxxxx xxxxxx_xxx_xxxx(); xxxx xxxx xxxx xxxxx

xxxxxxxxxxx

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

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Language: C++Barrier

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

// ...
// ...
// ...
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// ...
// ...
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// ...
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// ...
class Latch {
public:
    explicit Latch(long long count) : count_(count) {}

    void count_down() {
        // ...
    }

    void wait() {
        // ...
    }

    bool ready() const { return count_.load() == 0; }

private:
    std::mutex mutex_;
    std::condition_variable cv_;
    std::atomic<long long> count_;
};

// ...
// ...
// ...
// ...
// ...
// ...
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class Barrier {
public:
    explicit Barrier(long long participants) : participants_(participants) {}

    void arrive_and_wait() {
        // ...
    }

    long long generation() const { return generation_.load(); }

private:
    std::mutex mutex_;
    std::condition_variable cv_;
    long long participants_ = 0;
    long long arrived_ = 0;
    std::atomic<long long> generation_{0};
};

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