Concurrency

Work-Stealing Deque

Difficulty

Asked at Jump Trading, Citadel Securities

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x xxxxxx xxxx xxxxx xxxxx xxxxxx xxxxx xxxx xxx xxxxxx xxxxx xxxxxx xxx xxxx xxxxxxxx xxxx xxx xxxxx'x xxxx. xxxx xxxxxxxx xxxxx xxxx xxxxxx xxx xxx xxxxx xxxxxxx: xx xxxxxx xxx xxxx xxx xxx xxxxx xx xxx xxx, xxx xxxx xxxx xx xxxx xxx xxxx xx xxxxx xxxx xxxxxxxx xxxx'x, xx xxx xxxxx xxx.

xxx xxxxxxxxx xx xxx xxxxx xxxxxx. xxx xxxxx'x xxxxxx xxxx xxxxxxx xxxxxxx xxx xxxxx xxxxxx, xx xxx xxxx xxxx xxxx xxxxxxxxxx xxx xx xxxxxxxxxx xx xx.

xxxxxxxxx xxx xxxxx-xxx xxxxx, xxxxxxxxxx xx x xxxxx xxxxxxxx.

xxxx(xxxx) — xxxxx xxxx, xxxxxxx xx xxx xxxxxx, xxxxx xx xxxx
xxx() — xxxxx xxxx, xxxxx xxxx xxx xxxxxx, xxxx
xxxxx() — xxx xxxxxx, xxxxx xxxx xxx xxx, xxxx
xxxx() — xx xxxxxxxx, xxx xxx xxxxx

xxxxxxxx

xxxxxxxxxx<xx> x;
xxx (xxx x = x; x <= x; ++x) x.xxxx(x);
x.xxx();     // x, xxx xxxxxx: xxx xxxx xx xxxxx xx xxxxx
x.xxxxx();   // x, xxx xxxxxx: xx x xxxxxx-xxx-xxxxxxx xxxxxxxx, xxx xxxxxxx

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

xxxxxxxxxxx

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

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Language: C++StealDeque

#include <atomic>
#include <cstddef>
#include <optional>
#include <thread>
#include <vector>

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template <std::size_t Capacity>
class StealDeque {
public:
    bool push(long long task) {
        // ...
        (void)task;
        return false;
    }

    std::optional<long long> pop() {
        // ...
        return std::nullopt;
    }

    std::optional<long long> steal() {
        // ...
        return std::nullopt;
    }

    long long size() const {
        const long long b = bottom_.load(std::memory_order_relaxed);
        const long long t = top_.load(std::memory_order_relaxed);
        return b - t;
    }

private:
    std::atomic<long long> top_{0};
    std::atomic<long long> bottom_{0};
    std::atomic<long long> buffer_[Capacity]{};
};

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