跳转至

雪花算法计算唯一的UUID

利用现成的算法https://github.com/sniper00/snowflake-cpp github开源算法

A CPP port of Twitter's Snowflake id generation algorithm

Use

C++
1
2
3
4
5
6
7
8
9
    using snowflake_t = snowflake<1534832906275L>;
    snowflake_t uuid;
    uuid.init(1, 1);

    for (int64_t i = 0; i < 10000; ++i)
    {
        auto id = uuid.nextid();
        std::cout << id << "\n";
    }

CPP

Use with lock

C++
1
2
3
4
5
6
7
8
9
    using snowflake_t = snowflake<1534832906275L,std::mutex>;
    snowflake_t uuid;
    uuid.init(1, 1);

    for (int64_t i = 0; i < 10000; ++i)
    {
        auto id = uuid.nextid();
        std::cout << id << "\n";
    }

CPP

snowflake-cpp

C++
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
#pragma once
#include <cstdint>
#include <chrono>
#include <stdexcept>
#include <mutex>

class snowflake_nonlock
{
public:
    void lock()
    {
    }
    void unlock()
    {
    }
};

template<int64_t Twepoch, typename Lock = snowflake_nonlock>
class snowflake
{
    using lock_type = Lock;
    static constexpr int64_t TWEPOCH = Twepoch;
    static constexpr int64_t WORKER_ID_BITS = 5L;
    static constexpr int64_t DATACENTER_ID_BITS = 5L;
    static constexpr int64_t MAX_WORKER_ID = (1 << WORKER_ID_BITS) - 1;
    static constexpr int64_t MAX_DATACENTER_ID = (1 << DATACENTER_ID_BITS) - 1;
    static constexpr int64_t SEQUENCE_BITS = 12L;
    static constexpr int64_t WORKER_ID_SHIFT = SEQUENCE_BITS;
    static constexpr int64_t DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    static constexpr int64_t TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    static constexpr int64_t SEQUENCE_MASK = (1 << SEQUENCE_BITS) - 1;

    using time_point = std::chrono::time_point<std::chrono::steady_clock>;

    time_point start_time_point_ = std::chrono::steady_clock::now();
    int64_t start_millsecond_ = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count();

    int64_t last_timestamp_ = -1;
    int64_t workerid_ = 0;
    int64_t datacenterid_ = 0;
    int64_t sequence_ = 0;
    lock_type lock_;
public:
    snowflake() = default;

    snowflake(const snowflake&) = delete;

    snowflake& operator=(const snowflake&) = delete;

    void init(int64_t workerid, int64_t datacenterid)
    {
        if (workerid > MAX_WORKER_ID || workerid < 0) {
            throw std::runtime_error("worker Id can't be greater than 31 or less than 0");
        }

        if (datacenterid > MAX_DATACENTER_ID || datacenterid < 0) {
            throw std::runtime_error("datacenter Id can't be greater than 31 or less than 0");
        }

        workerid_ = workerid;
        datacenterid_ = datacenterid;
    }

    int64_t nextid()
    {
        std::lock_guard<lock_type> lock(lock_);
        //std::chrono::steady_clock  cannot decrease as physical time moves forward
        auto timestamp = millsecond();
        if (last_timestamp_ == timestamp)
        {
            sequence_ = (sequence_ + 1)&SEQUENCE_MASK;
            if (sequence_ == 0)
            {
                timestamp = wait_next_millis(last_timestamp_);
            }
        }
        else
        {
            sequence_ = 0;
        }

        last_timestamp_ = timestamp;

        return ((timestamp - TWEPOCH) << TIMESTAMP_LEFT_SHIFT)
            | (datacenterid_ << DATACENTER_ID_SHIFT)
            | (workerid_ << WORKER_ID_SHIFT)
            | sequence_;
    }

private:
    int64_t millsecond() const noexcept
    {
        auto diff = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - start_time_point_);
        return start_millsecond_ + diff.count();
    }

    int64_t wait_next_millis(int64_t last) const noexcept
    {
        auto timestamp = millsecond();
        while (timestamp <= last)
        {
            timestamp = millsecond();
        }
        return timestamp;
    }
};