C++ “雪花算法“原理

#include <iostream>  
#include <chrono>  
#include <thread>  
#include <random>  
  
// 雪花算法生成的ID的位数  
const int64_t kEpoch = 1609459200000; // 起始时间戳（毫秒级），这里假设为2021-01-01 00:00:00 UTC  
const int64_t kWorkerIdBits = 5;      // 机器ID所占的位数  
const int64_t kDatacenterIdBits = 5;  // 数据中心ID所占的位数  
const int64_t kSequenceBits = 12;    // 序列号所占的位数  
  
// 机器ID和数据中心ID，这些值需要根据实际情况进行配置  
const int64_t kWorkerId = 1;  
const int64_t kDatacenterId = 1;  
  
// 用于生成序列号的随机数生成器  
std::mt19937 gen(static_cast<unsigned int>(time(0)));  
std::uniform_int_distribution<> dis(0, (1 << kSequenceBits) - 1);  
  
// 生成雪花算法ID  
int64_t generateSnowflakeId() {  
    int64_t timestamp = std::chrono::duration_cast<std::chrono::milliseconds>(  
        std::chrono::system_clock::now().time_since_epoch()).count() - kEpoch;  
  
    // 如果当前时间小于上一次生成ID的时间戳，说明系统时钟回退过，应当抛出异常  
    static int64_t lastTimestamp = -1;  
    if (timestamp < lastTimestamp) {  
        throw std::runtime_error("Clock moved backwards. Refusing to generate id for "  
                                 + std::to_string(lastTimestamp - timestamp) + " milliseconds");  
    }  
  
    // 如果是同一时间戳，则进行序列号自增  
    if (lastTimestamp == timestamp) {  
        timestamp = lastTimestamp;  
    } else {  
        // 不同时间戳，序列号置为0  
        sequence = 0;  
    }  
  
    // 上次生成ID的时间截  
    lastTimestamp = timestamp;  
  
    // 移位并通过或运算拼到一起组成64位的ID  
    return ((timestamp << (kWorkerIdBits + kDatacenterIdBits + kSequenceBits)) |  
            (kDatacenterId << (kWorkerIdBits + kSequenceBits)) |  
            (kWorkerId << kSequenceBits) |  
            sequence);  
}  
  
int main() {  
    try {  
        for (int i = 0; i < 10; ++i) {  
            int64_t id = generateSnowflakeId();  
            std::cout << "Generated ID: " << id << std::endl;  
        }  
    } catch (const std::exception& e) {  
        std::cerr << "Exception: " << e.what() << std::endl;  
    }  
  
    return 0;  
}