32?? ??? 64?? ?? ??? ??

??:

? ????? ??? ???? 64?? ?? ???? ?? ? ??? ????. 32?? ??? ??. ?? ???? ?? ????? ?? ?? ???? ???? ?? ??? ??, ?? ?? ??? ?? ???? ?? ????? ?????.

??? ?? ??:

??? ?? ???? ?? ???? ???? ?? ??? ?? 32?? ?? ?? ???? "SeqLock" ??? ???? ???. ????.

?? ??:

class counter {
    atomic<uint32_t> lo_;
    atomic<uint32_t> hi_;
    atomic<uint32_t> gen_;

    uint64_t read() const {
        auto acquire = memory_order_acquire;
        uint32_t lo, hi, gen1, gen2;
        do {
            gen1 = gen_.load(acquire);
            lo = lo_.load(acquire);
            hi = hi_.load(acquire);
            gen2 = gen_.load(acquire);
        } while (gen1 != gen2 || (gen1 & 1));
        return (uint64_t(hi) << 32) | lo;
    }

    void increment() {
        auto release = memory_order_release;
        gen_.fetch_add(1, release);
        uint32_t newlo = 1 + lo_.fetch_add(1, release);
        if (newlo == 0) {
            hi_.fetch_add(1, release);
        }
        gen_.fetch_add(1, release);
    }
};

?? ??:

1. ???: ? ???? 64?? ?? ???? ??? ??? ???? ?? ??? ???? ?? ???? ??? ?? ?????.
2. ???: 64?? ?? ?? 32?? ??? ???? ?? 64?? ?? ?? ??? ?? ?? ????? ??? ?????.
3. ?? ??: SeqLock ??? ??? ???? ???? ???? ????. ???? ??????.

?? ???:

??? RMW(??-??-??) ??? ???? ?? ?? ??? ?? ???? ?? ?????. ?? ??. ??, ? ???? ?? ??? ??? ??? ??? ?? ?? ?? ? ??? ???? ????.

void increment() {
    auto release = memory_order_release;
    uint64_t count = lo_.load(release) | (uint64_t(hi_.load(release)) << 32);
    count++;
    lo_.store(count & uint32_t(-1), release);
    hi_.store((count >> 32) & uint32_t(-1), release);
}

??:

??? ??? ????? ??? ???? ?????. 32?? ??? ???? 64?? ?? ???? ?????. SeqLock ??? ?? ???? ?? ?? ???? ??? ??? ?? ?? ?? ???? ?? ???? ??? ??? ? ????.

? ??? 32?? ??? ???? 64?? ?? ???? ???? ??? ??????? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!