Concurrency

Fix the Data Race

Difficulty

Asked at Citadel Securities, Hudson River Trading

Read the problem, hints and solution here. The editor needs a bigger screen: open this page on a laptop to write and run your code.

xxxx xxx xx x xxxx xxxxxx, xxx x xxxxx xxxx. xxx xxxxxxxx xxxxxxxx x xxxxxxxx, xxxxxxxxx xxxxxxxxxxxxxxx: xxxxx xxxx xx xxxx xxxxxxx xxxxxxx xxxxxxx, xxxxxxxxx xxxx xx x xxx, xxx xxxxx xx xxxx x xxxxx. xx xxxxxxxx, xx xxxxxx x xxxxxx xxxxxx-xxxxxxxx xxxx xx x xxxxxxxx, xxx xx xx xxxxx xx xxxx xxxxxxxx xxxx. xxxxxxxxx xx xxxxxxx x xxxx xx xx,xxx xxxxxxxxx. xxxx xxx xx xx xxxx xx xxxxxxx xxxxxxx xxxxxxxx xxx xxxxxx xxx.

xxx xxxxxxxx xxxxxxxx xx xxx xxxx:

x. xxxxx xxx xxxxxx xx xxxx. xxxx xxxxxx-xxxxxxxx, xxxxxxx xxxxxxxxx xxx xxxxxxxx. (xxxx xxx xx x xxxxx xxxxx xxx; xxxxx xxxx xxxxxx xx.) x. xxxxx xxxxxxxxxx xxxx, xxxxx xxxxxxxxx xxx xxxxx xx xxxxxxx xxxxxxx xxx xx xxx, xxx xxx xxxxxxx xxx xxxxxxx xxxxxx xxx::xxx xxxxx. x. xxxxxxxxxxxx xxxx xxxx xxxxxxxxxx xxxxxxxx xxxxxxx xxxxxx xx xxx xxxx.

xxx xxx xxx xxxx xxxxxxxx:

xxxxxxxx xxxxxxxxxxxxxxx(xxx::xxxx_x xxxxxxxxxx): xx xxxx xxxxxxxxxx xxxxxxxx xxxxxxx xxx xxxx xx xxxxxxx.
xxxx xxxxxxxxx(xxxxx xxx::xxxxxx& xxxxxx, xxxx xxxx, xxxx xxxx xxx): xxxx xx 'x' (xxxxxxxx += xxx) xx 'x' (xxxxxxxx -= xxx). x xxxx xxx xx xxxxxxx xxxxxx xxxxxxx xx, xxxxxx xxx xxxx xxxxxxx xxxxxx xxxxxxxxxx xxxxxxx, xx xxxxx xxxx xxx xxxx xx xxxxxxxx xxx xxxxx xx xxxxxxxx. xxxxx xxx xxxxxxx-xxxxxxx xxxxxxx xxxxxx xxxxx. xxxxxx xxxx xxxx xxxxxxx xxxxxxxxxxxx.
xxxx xxxx xxxxxxxx(xxxxx xxx::xxxxxx& xxxxxx) xxxxx: xxxxxxx xxxxxxxx; x xxx xxxxxxx xxxxxxx. xxxxxx xxxxxxxxxxxx xxxx xxxxx.
xxx::xxxx_x xxxxxxxxxxx() xxxxx: xxxxxx xx xxxxxxx xxxxxxx.

xxxx xxx xxx xxxxxxx xxxxxxxx xx xxx xxxxxxxx: x xxxxx-xxxx-xxx xx xxx xxx xxxx xx xxxx xxxx xxxxxx xxx xxxxx xxx xxx xxx, x xxxxxxxx xxxx-xxxxxx-xxxxx (+=) xxxx xxxxxxx xxx xxxxx, x xxxx() xxxx xxxxxxx xxx xxxx xxxxxxx xxx xxxxxxxxx xxxxxxxx, xxx xxx xxxxx xxxx xx xxxxxxxxxxx xxxxx xxx xxxxx xxx xxxxx xxx xxxxxx. xxxxx xxx xx xxxxx xx x xxxx xxx xxxxx xx x xxxx xxxxxxxx xxxxxx. xxx xxx xxxx xxx, xxxx xxxx xxxxx xxxxxx xx xxxxxx xxxxx xxxx xxx xxxxx, xxx xxx xxxxx xxxxx xxxxxxx xxxxxxxx xxxxxxx.

xxxxxxxx

[]{ xxxxxxxxxxxxxxx xxxxxxx(x); xxx::xxxxxx<xxxx xxxx> xxx; xxx.xxxx_xxxx(xxxxxxx.xxxxxxxxx("xxxx", 'x', xx)); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxxx("xxxx", 'x', x)); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxx("xxxx")); xxxxxxx.xxxxxxxxx("xxxx", 'x', x); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxx("xxxx")); xxx.xxxx_xxxx(xxxxxx_xxxx<xxxx xxxx>(xxxxxxx.xxxxxxxxxxx())); xxxxxx xxx; }()
// [x, x, x, -x, x]  (xxx xx, xxxx x xx x; xxxxxxx xxxxxxx xxxx xxxx xxxxx)

[]{ xxxxxxxxxxxxxxx xxxxxxx(x); xxx::xxxxxx<xxxx xxxx> xxx; xxxxxxx.xxxxxxxxx("xx", 'x', x); xxxxxxx.xxxxxxxxx("xx", 'x', x); xxxxxxx.xxxxxxxxx("xx", 'x', x); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxxx("xx", 'x', x)); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxx("xx")); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxx("xx")); xxx.xxxx_xxxx(xxxxxxx.xxxxxxxx("xx")); xxx.xxxx_xxxx(xxxxxx_xxxx<xxxx xxxx>(xxxxxxx.xxxxxxxxxxx())); xxxxxx xxx; }()
// [x, x, x, x, x]  (xxxxx xxxxxx xxxxxxxx; xxxxxxxx xxxx xxxxxx xx xxxxx)

xxxxxxxxxxx

xxxxxx xxx xx xxxxxx: xxxx xxxxxxxxxxx, xxxx xxxxx xxxxxx xxxxxxxxx, xxxx xxxxxxxxxx xxx xxxxxxxxx. xxxxxxxxxx xxxxxxx xx xxxxx xx xxxxxx.
xx xx x xxxxxxx xxxxx (x xxxxx xx^x) xxxxx xx xxxxxxxxxxx xxxxxxx xx xxx xxxxxx xxxxxx xxxx; xxxxx xxxxxxxxx xxxx xx xxx-xxxxx, xxx xxxxxxxxxxxxx xxxxx. x xxxxx xxxxx xxxx xxx xxx xxxxx xx xxxx xxxxxx xxxxxxxx xx x xxxxxxxxx xxxx xxxxxx xx xxxx xxxx; xxxxxxxxxx xx xxx xxxxxxxx, xxxxxxxxxxx xx.
xxxxxxxx() xxx xxxxxxxxxxx() xxx xxxxxx xxxxx xxxxx xxx xx xxxxxx; xxxx xxxx xxxxxx xxxx xxxxxxxxxx xxxxxxxxx xxxxx, xxxxx xxxxx, xxx xxxxx xxxxxxx x xxxx-xxxxxxx xxxx.
xxx xxxxx xxxx xxx xxxxxx xxxx xxxxx xxxxxxx xxx xxxxxxx, xx xxx xxxxxxxx xxxxxx xxx xxxxx xxx xxxxxxxxxxx xx xxxxxxxxxx. xxxx xx xxxxxx xxxxx xx xxx xxx xxxxx xx: xxxxxxxxxxxxxxx xx xxx xxxxxxxx xxxxxx xx xxxxx xxx xx xxx xxxxxxx xxxxx xx xxx xxx, xxx xxxxx xxxx xxxxxxxx xx xxx xxxxxxx xxx xx xxxx xxxx xxx.

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Language: C++PositionTracker

#include <cstddef>
#include <map>
#include <mutex>
#include <string>
#include <thread>
#include <tuple>
#include <utility>
#include <vector>

// ...
// ...
// ...
class PositionTracker {
public:
    explicit PositionTracker(std::size_t maxSymbols) : maxSymbols_(maxSymbols) {}

    bool applyFill(const std::string& symbol, char side, long long qty) {
        // ...
        // ...
        // ...
        // ...
        if (positions_.find(symbol) == positions_.end()) {
            if (positions_.size() >= maxSymbols_) {
                return false;
            }
            positions_[symbol] = 0;
        }
        // ...
        // ...
        if (side == 'B') {
            positions_[symbol] += qty;
        } else {
            positions_[symbol] += qty;  // ...
        }
        return true;
    }

    long long position(const std::string& symbol) const {
        // ...
        // ...
        std::lock_guard<std::mutex> lock(mutex_);
        const auto it = positions_.find(symbol);
        return it == positions_.end() ? 0 : it->second;
    }

    std::size_t symbolCount() const {
        std::lock_guard<std::mutex> lock(mutex_);
        return positions_.size();
    }

private:
    mutable std::mutex mutex_;
    std::map<std::string, long long> positions_;
    std::size_t maxSymbols_;
};

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