下面是针对如何编写C# Guid长度的雪花简单生成器的攻略。
1. 为何选择C# Guid
C# Guid(全称为全球唯一标识符)是一个128位的数字,由字母和数字构成,它具备全局唯一性,即全球内任意两个Guid的相同概率是非常低的。因此,我们可以利用Guid生成唯一字符串,例如用户ID、订单编号等。
2. 如何生成雪花ID
雪花ID是一种Twitter开源的生成分布式唯一ID的算法,可以在分布式系统中生成全局唯一ID,其算法是基于时间戳实现。每次生成ID时,将当前时间戳拼接其它固定的信息(如机器IP、PID等),再通过Hash等算法进行混淆,最终生成一个64位长整数。
将雪花ID生成的64位长整数转化为字符串,再以Guid的方式进行排版,即可生成所需的雪花ID。
下面是示例代码:
using System;
using System.Security.Cryptography;
using System.Text;
namespace Snowflake
{
class Program
{
static void Main(string[] args)
{
Snowflake snowflake = new Snowflake(0, 0);
Console.WriteLine(GuidFromSnowflake(snowflake.NextId()));
}
public static Guid GuidFromSnowflake(long id)
{
return new Guid(
BitConverter.GetBytes(id >> 48 & 0xFFFF),
BitConverter.GetBytes(id >> 32 & 0xFFFF),
BitConverter.GetBytes(id >> 16 & 0xFFFF),
BitConverter.GetBytes(id & 0xFFFF));
}
}
public class Snowflake
{
private long workerId;
private long datacenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;
private static long twepoch = 1288834974657L;
public Snowflake(long workerId, long datacenterId)
{
if (workerId > maxWorkerId || workerId < 0)
{
throw new Exception("worker Id can't be greater than " + maxWorkerId + " or less than 0");
}
if (datacenterId > maxDatacenterId || datacenterId < 0)
{
throw new Exception("datacenter Id can't be greater than " + maxDatacenterId + " or less than 0");
}
this.workerId = workerId;
this.datacenterId = datacenterId;
}
private static long workerIdBits = 5L;
private static long datacenterIdBits = 5L;
private static long maxWorkerId = -1L ^ -1L << (int)workerIdBits;
private static long maxDatacenterId = -1L ^ -1L << (int)datacenterIdBits;
private static long sequenceBits = 12L;
private static long workerIdShift = sequenceBits;
private static long datacenterIdShift = sequenceBits + workerIdBits;
private static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
private static long sequenceMask = -1L ^ -1L << (int)sequenceBits;
private static long GetTimestamp()
{
return (long)(DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds;
}
public long NextId()
{
lock (this)
{
long timestamp = GetTimestamp();
if (timestamp < lastTimestamp)
{
throw new Exception("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");
}
if (lastTimestamp == timestamp)
{
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0)
{
timestamp = TilNextMillis(lastTimestamp);
}
}
else
{
sequence = 0L;
}
lastTimestamp = timestamp;
return (timestamp - twepoch) << (int)timestampLeftShift |
datacenterId << (int)datacenterIdShift |
workerId << (int)workerIdShift |
sequence;
}
}
private long TilNextMillis(long lastTimestamp)
{
long timestamp = GetTimestamp();
while (timestamp <= lastTimestamp)
{
timestamp = GetTimestamp();
}
return timestamp;
}
}
}
上述代码通过 Snowflake 算法实现了雪花ID的生成。我们创建了一个 Snowflake 的类,构造函数接收两个参数:workerId,datacenterId。在 NextId() 方法内部,我们通过 lock 机制对 ID 进行互斥操作,确保在多线程环境下不会生成重复的ID。
3. 示例说明
示例 1:
我们可以根据上述代码编写一个控制台应用程序,用于生成雪花ID,并输出其所对应的Guid。
在控制台中输入以下命令:
Snowflake snowflake = new Snowflake(0, 0);
Console.WriteLine(GuidFromSnowflake(snowflake.NextId()));
运行控制台应用程序,可看到所生成的雪花ID的Guid。
示例 2:
将上述代码封装成一个简单的 Web API,通过 HTTP 请求访问,返回所生成的雪花ID的Guid。
使用 Visual Studio 创建一个 ASP.NET Core Web API 应用程序,并在控制器类中接收 HTTP 请求。示例如下:
using System;
using Microsoft.AspNetCore.Mvc;
namespace SnowflakeWebAPI.Controllers
{
[ApiController]
[Route("[controller]")]
public class SnowflakeController : ControllerBase
{
private Snowflake snowflake = new Snowflake(0, 0);
[HttpGet]
public IActionResult Get()
{
return Ok(new {
guid = GuidFromSnowflake(snowflake.NextId())
});
}
private static Guid GuidFromSnowflake(long id)
{
return new Guid(
BitConverter.GetBytes(id >> 48 & 0xFFFF),
BitConverter.GetBytes(id >> 32 & 0xFFFF),
BitConverter.GetBytes(id >> 16 & 0xFFFF),
BitConverter.GetBytes(id & 0xFFFF));
}
class Snowflake
{
// ...
}
}
}
在浏览器或任意 HTTP 客户端工具中输入 URL:http://localhost:5000/snowflake,即可看到所生成的雪花ID的Guid。
总结
在本篇攻略中,我们详细讲解了如何使用 C# Guid 实现雪花ID的生成器,并提供了两条示例说明。这个生成器是在分布式系统中生成全局唯一ID的理想选择。
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