├── .gitignore
├── docs
    ├── perf.png
    └── snowflake-64bit.jpg
├── src
    ├── test
    │   └── java
    │   │   └── cn
    │   │       └── izern
    │   │           ├── sequence
    │   │               ├── RepeatedTest.java
    │   │               ├── SequenceTest1.java
    │   │               ├── ContiPerfTest.java
    │   │               └── SequenceTest.java
    │   │           └── hibernate
    │   │               └── id
    │   │                   └── Demo.java
    └── main
    │   └── java
    │       └── cn
    │           ├── izern
    │               ├── hibernate
    │               │   └── id
    │               │   │   └── IDSequenceGenerator.java
    │               └── sequence
    │               │   └── Sequence.java
    │           └── ms
    │               └── sequence
    │                   └── SystemClock.java
├── README.md
├── pom.xml
└── LICENSE


/.gitignore:
--------------------------------------------------------------------------------
1 | .git/
2 | .project
3 | .classpath
4 | .settings/
5 | /target/
6 | 


--------------------------------------------------------------------------------
/docs/perf.png:
--------------------------------------------------------------------------------
https://raw.githubusercontent.com/izern/sequence/HEAD/docs/perf.png


--------------------------------------------------------------------------------
/docs/snowflake-64bit.jpg:
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https://raw.githubusercontent.com/izern/sequence/HEAD/docs/snowflake-64bit.jpg


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/src/test/java/cn/izern/sequence/RepeatedTest.java:
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 1 | package cn.izern.sequence;
 2 | 
 3 | import java.util.HashSet;
 4 | import java.util.Set;
 5 | 
 6 | import org.junit.Test;
 7 | 
 8 | import cn.izern.sequence.Sequence;
 9 | 
10 | public class RepeatedTest {
11 | 
12 | 	/**
13 | 	 * 重复性测试
14 | 	 */
15 | 	@Test
16 | 	public void testRepeated() {
17 | 		Set<Long> set = new HashSet<Long>();
18 | 		int maxTimes = 1000000 * 10;
19 | 		Sequence sequence = new Sequence(0, 0);
20 | 		for (int i = 0; i < maxTimes; i++) {
21 | 			set.add(sequence.nextId());
22 | 		}
23 | 		System.out.println(maxTimes == set.size());
24 | //		Assert.assertEquals(maxTimes, set.size());
25 | 	}
26 | 
27 | }
28 | 


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/src/test/java/cn/izern/sequence/SequenceTest1.java:
--------------------------------------------------------------------------------
 1 | package cn.izern.sequence;
 2 | 
 3 | import org.junit.Test;
 4 | 
 5 | import cn.izern.sequence.Sequence;
 6 | 
 7 | public class SequenceTest1 {
 8 | 
 9 | 	@Test
10 | 	public void name() {
11 | 		try {
12 | 			int times = 0, maxTimes = 1000;
13 | 			Sequence sequence = new Sequence(0, 0);
14 | 			for (int i = 0; i < maxTimes; i++) {
15 | 				long id = sequence.nextId();
16 | 				if(id%2==0){
17 | 					times++;
18 | 				}
19 | 				Thread.sleep(5);
20 | 			}
21 | 			System.out.println("偶数:" + times + ",奇数:" + (maxTimes - times) + "!");
22 | 		} catch (Exception e) {
23 | 			e.printStackTrace();
24 | 		}
25 | 	}
26 | 
27 | }
28 | 


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/src/test/java/cn/izern/sequence/ContiPerfTest.java:
--------------------------------------------------------------------------------
 1 | package cn.izern.sequence;
 2 | 
 3 | import org.databene.contiperf.PerfTest;
 4 | import org.databene.contiperf.junit.ContiPerfRule;
 5 | import org.junit.Rule;
 6 | import org.junit.Test;
 7 | 
 8 | import cn.izern.sequence.Sequence;
 9 | 
10 | /**
11 |  * 性能测试
12 |  * 
13 |  * @author lry
14 |  */
15 | public class ContiPerfTest {
16 | 	
17 | 	@Rule
18 | 	public ContiPerfRule i = new ContiPerfRule();
19 | 
20 | 	Sequence sequence = new Sequence(0, 0);
21 | 	
22 | 	@Test
23 | 	@PerfTest(invocations = 200000000, threads = 16)
24 | 	public void test1() throws Exception {
25 | 		sequence.nextId();
26 | 	}
27 | 
28 | }


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/src/test/java/cn/izern/hibernate/id/Demo.java:
--------------------------------------------------------------------------------
 1 | package cn.izern.hibernate.id;
 2 | 
 3 | import java.io.Serializable;
 4 | 
 5 | import javax.persistence.Entity;
 6 | import javax.persistence.GeneratedValue;
 7 | import javax.persistence.Id;
 8 | import javax.persistence.Table;
 9 | 
10 | import org.hibernate.annotations.GenericGenerator;
11 | 
12 | @Entity
13 | @Table(name = "demo")
14 | public class Demo implements Serializable{
15 | 
16 | 	/**
17 | 	 * 
18 | 	 */
19 | 	private static final long serialVersionUID = -2765770852213608028L;
20 | 
21 | 	private Long id;
22 | 	
23 | 	// other 
24 | 
25 | 	@Id
26 | 	@GeneratedValue(generator = "idGenerator")
27 | 	@GenericGenerator(name = "idGenerator", strategy = "cn.izern.hibernate.id.IDWorkerGenerator")
28 | 	public Long getId() {
29 | 		return id;
30 | 	}
31 | 
32 | 	public void setId(Long id) {
33 | 		this.id = id;
34 | 	}
35 | 	
36 | 	
37 | }
38 | 


--------------------------------------------------------------------------------
/src/main/java/cn/izern/hibernate/id/IDSequenceGenerator.java:
--------------------------------------------------------------------------------
 1 | package cn.izern.hibernate.id;
 2 | 
 3 | import java.io.Serializable;
 4 | import java.util.Properties;
 5 | 
 6 | import org.hibernate.HibernateException;
 7 | import org.hibernate.MappingException;
 8 | import org.hibernate.engine.spi.SessionImplementor;
 9 | import org.hibernate.id.Configurable;
10 | import org.hibernate.id.IdentifierGenerator;
11 | import org.hibernate.service.ServiceRegistry;
12 | import org.hibernate.type.Type;
13 | 
14 | import cn.izern.sequence.Sequence;
15 | 
16 | /**
17 |  * ID生成器,分布式Long型唯一ID,大小序列
18 |  * @author zern
19 |  * create on 2017年8月18日
20 |  */
21 | public class IDSequenceGenerator implements Configurable, IdentifierGenerator{
22 | 
23 | 	private Sequence sequence = new Sequence();
24 | 	
25 | 	@Override
26 | 	public Serializable generate(SessionImplementor arg0, Object arg1) throws HibernateException {
27 | 		return sequence.nextId();
28 | 	}
29 | 
30 | 	@Override
31 | 	public void configure(Type arg0, Properties arg1, ServiceRegistry arg2) throws MappingException {
32 | 		// TODO Auto-generated method stub
33 | 		
34 | 	}
35 | 
36 | }
37 | 


--------------------------------------------------------------------------------
/src/test/java/cn/izern/sequence/SequenceTest.java:
--------------------------------------------------------------------------------
 1 | package cn.izern.sequence;
 2 | 
 3 | import java.util.HashSet;
 4 | import java.util.Set;
 5 | 
 6 | import cn.izern.sequence.Sequence;
 7 | 
 8 | public class SequenceTest {
 9 | 	
10 | 	public static void main(String[] args) {
11 | 		Set<Long> set = new HashSet<Long>();
12 | 		final Sequence idWorker1 = new Sequence(0, 0);
13 | 		final Sequence idWorker2 = new Sequence(1, 0);
14 | 		Thread t1 = new Thread(new IdWorkThread(set, idWorker1));
15 | 		Thread t2 = new Thread(new IdWorkThread(set, idWorker2));
16 | 		t1.setDaemon(true);
17 | 		t2.setDaemon(true);
18 | 		t1.start();
19 | 		t2.start();
20 | 		try {
21 | 			Thread.sleep(30000);
22 | 		} catch (InterruptedException e) {
23 | 			e.printStackTrace();
24 | 		}
25 | 	}
26 | 	
27 | 	static class IdWorkThread implements Runnable {
28 | 		private Set<Long> set;
29 | 		private Sequence idWorker;
30 | 
31 | 		public IdWorkThread(Set<Long> set, Sequence idWorker) {
32 | 			this.set = set;
33 | 			this.idWorker = idWorker;
34 | 		}
35 | 
36 | 		@Override
37 | 		public void run() {
38 | 			while (true) {
39 | 				long id = idWorker.nextId();
40 | 				if (!set.add(id)) {
41 | 					System.out.println("duplicate:" + id);
42 | 				}
43 | 			}
44 | 		}
45 | 	}
46 | 	
47 | }
48 | 


--------------------------------------------------------------------------------
/README.md:
--------------------------------------------------------------------------------
 1 | # 分布式高效唯一ID生成器(sequence)
 2 | 
 3 | 
 4 | 基于开源项目[sequence](https://git.oschina.net/yu120/sequence)
 5 | 
 6 | 
 7 | ## 简介
 8 | 高效GUID产生算法(sequence),基于Snowflake实现64位自增ID算法。
 9 | 
10 | Twitter-Snowflake算法产生的背景相当简单，为了满足Twitter每秒上万条消息的请求，每条消息都必须分配一条唯一的id，这些id还需要一些大致的顺序（方便客户端排序），并且在分布式系统中不同机器产生的id必须不同。
11 | 
12 | 性能测试数据：
13 | 
14 | ![性能测试结果](docs/perf.png)
15 | 
16 | ## Snowflake算法核心
17 | 把时间戳，工作机器id，序列号组合在一起。
18 | 
19 | ![Snowflake算法核心](docs/snowflake-64bit.jpg)
20 | 
21 | 除了最高位bit标记为不可用以外，其余三组bit占位均可浮动，看具体的业务需求而定。默认情况下41bit的时间戳可以支持该算法使用到2082年，10bit的工作机器id可以支持1023台机器，序列号支持1毫秒产生4095个自增序列id。下文会具体分析。
22 | 
23 | ## Snowflake – 时间戳
24 | 这里时间戳的细度是毫秒级，具体代码如下，建议使用64位linux系统机器，因为有vdso，gettimeofday()在用户态就可以完成操作，减少了进入内核态的损耗。
25 | 
26 | ## Snowflake – 工作机器id
27 | 严格意义上来说这个bit段的使用可以是进程级，机器级的话你可以使用MAC地址来唯一标示工作机器，工作进程级可以使用IP+Path来区分工作进程。如果工作机器比较少，可以使用配置文件来设置这个id是一个不错的选择，如果机器过多配置文件的维护是一个灾难性的事情。
28 | 
29 | ## Snowflake – 序列号
30 | 序列号就是一系列的自增id（多线程建议使用atomic），为了处理在同一毫秒内需要给多条消息分配id，若同一毫秒把序列号用完了，则“等待至下一毫秒”。
31 | 
32 | # 获取
33 | ```xml
34 | <dependency>
35 | 	<groupId>cn.izern</groupId>
36 | 	<artifactId>sequence</artifactId>
37 | 	<version>${version}</version>
38 | </dependency>
39 | ```
40 | ## 使用
41 | ```java
42 | import cn.izern.sequence.Sequence;
43 | 
44 | Sequence sequence = new Sequence();
45 | sequence.nextId();
46 | ```
47 | 线程安全,生成唯一序列ID
48 | 
49 | ## hibernate/jpa 使用Sequence作为ID生成方式
50 | 
51 | ```java
52 | private Long id;
53 | 	
54 | // other 
55 | 
56 | @Id
57 | @GeneratedValue(generator = "idGenerator")
58 | @GenericGenerator(name = "idGenerator", strategy = "cn.izern.hibernate.id.IDSequenceGenerator")
59 | public Long getId() {
60 | 	return id;
61 | }
62 | 
63 | public void setId(Long id) {
64 | 	this.id = id;
65 | }
66 | ```


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/src/main/java/cn/ms/sequence/SystemClock.java:
--------------------------------------------------------------------------------
 1 | package cn.ms.sequence;
 2 | 
 3 | import java.sql.Timestamp;
 4 | import java.util.concurrent.Executors;
 5 | import java.util.concurrent.ScheduledExecutorService;
 6 | import java.util.concurrent.ThreadFactory;
 7 | import java.util.concurrent.TimeUnit;
 8 | import java.util.concurrent.atomic.AtomicLong;
 9 | 
10 | /**
11 |  * 高并发场景下System.currentTimeMillis()的性能问题的优化
12 |  * System.currentTimeMillis()的调用比new一个普通对象要耗时的多（具体耗时高出多少我还没测试过，有人说是100倍左右）<p>
13 |  * System.currentTimeMillis()之所以慢是因为去跟系统打了一次交道<p>
14 |  * 后台定时更新时钟，JVM退出时，线程自动回收<p>
15 |  * 10亿：43410,206,210.72815533980582%<p>
16 |  * 1亿：4699,29,162.0344827586207%<p>
17 |  * 1000万：480,12,40.0%<p>
18 |  * 100万：50,10,5.0%<p>
19 |  * @author lry
20 |  */
21 | public class SystemClock {
22 | 
23 |     private final long period;
24 |     private final AtomicLong now;
25 | 
26 |     private SystemClock(long period) {
27 |         this.period = period;
28 |         this.now = new AtomicLong(System.currentTimeMillis());
29 |         scheduleClockUpdating();
30 |     }
31 | 
32 |     private static class InstanceHolder {
33 |         public static final SystemClock INSTANCE = new SystemClock(1);
34 |     }
35 | 
36 |     private static SystemClock instance() {
37 |         return InstanceHolder.INSTANCE;
38 |     }
39 | 
40 |     private void scheduleClockUpdating() {
41 |         ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
42 |             public Thread newThread(Runnable runnable) {
43 |                 Thread thread = new Thread(runnable, "System Clock");
44 |                 thread.setDaemon(true);
45 |                 return thread;
46 |             }
47 |         });
48 |         scheduler.scheduleAtFixedRate(new Runnable() {
49 |             public void run() {
50 |                 now.set(System.currentTimeMillis());
51 |             }
52 |         }, period, period, TimeUnit.MILLISECONDS);
53 |     }
54 | 
55 |     private long currentTimeMillis() {
56 |         return now.get();
57 |     }
58 | 
59 |     public static long now() {
60 |         return instance().currentTimeMillis();
61 |     }
62 |     
63 | 	public static String nowDate() {
64 | 		return new Timestamp(instance().currentTimeMillis()).toString();
65 | 	}
66 | 
67 | }
68 | 


--------------------------------------------------------------------------------
/pom.xml:
--------------------------------------------------------------------------------
  1 | <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  2 | 	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  3 | 	<modelVersion>4.0.0</modelVersion>
  4 | 	<groupId>cn.izern</groupId>
  5 | 	<artifactId>sequence</artifactId>
  6 | 	<version>1.0.0</version>
  7 | 	<packaging>jar</packaging>
  8 | 	
  9 | 	<name>sequence</name>
 10 | 	<url>https://github.com/izern/sequence</url>
 11 |   	<inceptionYear>2017</inceptionYear>
 12 |   	<description>高效GUID产生算法(sequence),基于Snowflake实现64位自增ID算法。</description>
 13 | 	<scm>
 14 | 		<url>https://github.com/izern/sequence</url>
 15 | 		<connection>scm:https://github.com/izern/sequence.git</connection>
 16 |   	</scm>
 17 | 	<developers>
 18 |         <developer>
 19 |             <name>zern</name>
 20 |             <email>jiaozi362330@gmail.com</email>
 21 |         </developer>
 22 |   	</developers>
 23 |   	<distributionManagement>
 24 | 		<snapshotRepository>
 25 | 			<id>oss</id>
 26 | 			<url>https://oss.sonatype.org/content/repositories/snapshots/</url>
 27 | 		</snapshotRepository>
 28 | 		<repository>
 29 | 			<id>oss</id>
 30 | 			<url>https://oss.sonatype.org/service/local/staging/deploy/maven2/</url>
 31 | 		</repository>
 32 | 	</distributionManagement>
 33 |   	<licenses>
 34 | 		<license>
 35 | 			<name>Apache 2</name>
 36 | 			<url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
 37 | 			<distribution>repo</distribution>
 38 | 			<comments>A business-friendly OSS license</comments>
 39 | 		</license>
 40 | 	</licenses>
 41 | 	
 42 | 	<properties>
 43 | 		<junit>4.7</junit>
 44 | 		<hibernate.version>5.0.12.Final</hibernate.version>
 45 | 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 46 | 		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 47 | 		<java.version>1.8</java.version>
 48 | 	</properties>
 49 | 	<dependencies>
 50 | 		<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
 51 | 		<dependency>
 52 | 		    <groupId>org.hibernate</groupId>
 53 | 		    <artifactId>hibernate-core</artifactId>
 54 | 		    <version>${hibernate.version}</version>
 55 | 		    <scope>provided</scope>
 56 | 		</dependency>
 57 | 	
 58 | 		<!-- 单元测试 -->
 59 | 		<dependency>
 60 | 			<groupId>junit</groupId>
 61 | 			<artifactId>junit</artifactId>
 62 | 			<version>4.7</version>
 63 | 			<scope>test</scope>
 64 | 		</dependency>
 65 | 		<!-- 性能测试 -->
 66 | 		<dependency>
 67 | 			<groupId>org.databene</groupId>
 68 | 			<artifactId>contiperf</artifactId>
 69 | 			<version>2.1.0</version>
 70 | 			<scope>test</scope>
 71 | 		</dependency>
 72 | 	</dependencies>
 73 | 	<build>
 74 | 		<plugins>
 75 | 			<plugin>
 76 | 				<groupId>org.apache.maven.plugins</groupId>
 77 | 				<artifactId>maven-compiler-plugin</artifactId>
 78 | 				<version>2.3.2</version>
 79 | 				<configuration>
 80 | 					<source>${java.version}</source>
 81 | 					<target>${java.version}</target>
 82 | 					<encoding>${project.build.sourceEncoding}</encoding>
 83 | 					<skip>true</skip>
 84 | 				</configuration>
 85 | 			</plugin>
 86 | 			<plugin>    
 87 | 			    <groupId>org.apache.maven.plugins</groupId>    
 88 | 			    <artifactId>maven-surefire-plugin</artifactId>    
 89 | 			    <version>2.5</version>    
 90 | 			    <configuration>    
 91 | 			        <skip>true</skip>    
 92 | 			    </configuration>    
 93 | 			</plugin>  
 94 | 		</plugins>
 95 | 	</build>
 96 | 	<profiles>
 97 | 		<profile>
 98 | 			<id>release</id>
 99 | 			<build>
100 | 				<plugins>
101 | 				<!-- Source -->
102 | 				<plugin>
103 | 					<groupId>org.apache.maven.plugins</groupId>
104 | 					<artifactId>maven-source-plugin</artifactId>
105 | 					<version>2.2.1</version>
106 | 					<executions>
107 | 						<execution>
108 | 						<phase>package</phase>
109 | 						<goals>
110 | 						<goal>jar-no-fork</goal>
111 | 						</goals>
112 | 						</execution>
113 | 					</executions>
114 | 					</plugin>
115 | 					<!-- Javadoc -->
116 | 					<plugin>
117 | 						<groupId>org.apache.maven.plugins</groupId>
118 | 						<artifactId>maven-javadoc-plugin</artifactId>
119 | 						<version>2.9.1</version>
120 | 						<executions>
121 | 						<execution>
122 | 						<phase>package</phase>
123 | 						<goals>
124 | 						<goal>jar</goal>
125 | 						</goals>
126 | 						</execution>
127 | 						</executions>
128 | 					</plugin>
129 | 					<!-- GPG -->
130 | 					<plugin>
131 | 						<groupId>org.apache.maven.plugins</groupId>
132 | 						<artifactId>maven-gpg-plugin</artifactId>
133 | 						<version>1.5</version>
134 | 						<executions>
135 | 						<execution>
136 | 						<phase>verify</phase>
137 | 						<goals>
138 | 						<goal>sign</goal>
139 | 						</goals>
140 | 						</execution>
141 | 						</executions>
142 | 					</plugin>
143 | 				</plugins>
144 | 			</build>
145 | 			<distributionManagement>
146 | 				<snapshotRepository>
147 | 					<id>oss</id>
148 | 					<url>https://oss.sonatype.org/content/repositories/snapshots/</url>
149 | 				</snapshotRepository>
150 | 				<repository>
151 | 					<id>oss</id>
152 | 					<url>https://oss.sonatype.org/service/local/staging/deploy/maven2/</url>
153 | 				</repository>
154 | 			</distributionManagement>
155 | 		</profile>
156 | 	</profiles>
157 | </project>


--------------------------------------------------------------------------------
/src/main/java/cn/izern/sequence/Sequence.java:
--------------------------------------------------------------------------------
  1 | package cn.izern.sequence;
  2 | 
  3 | import java.lang.management.ManagementFactory;
  4 | import java.net.InetAddress;
  5 | import java.net.NetworkInterface;
  6 | 
  7 | import cn.ms.sequence.SystemClock;
  8 | 
  9 | /**
 10 |  * <p>
 11 |  * 分布式高效有序ID生产黑科技(sequence) <br>
 12 |  * 优化开源项目：http://git.oschina.net/yu120/sequence
 13 |  * </p>
 14 |  * 自定义生成全局唯一ID
 15 |  * @author zern
 16 |  * create on 2017年8月18日
 17 |  */
 18 | public class Sequence {
 19 | 	
 20 | 	/** 开始时间截 */
 21 | 	private final long twepoch = 1288834974657L;
 22 | 	/** 机器id所占的位数 */
 23 | 	private final long workerIdBits = 5L;
 24 | 	/** 数据标识id所占的位数 */
 25 | 	private final long datacenterIdBits = 5L;
 26 | 	/** 支持的最大机器id，结果是31 (这个移位算法可以很快的计算出几位二进制数所能表示的最大十进制数) */
 27 | 	private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
 28 | 	/** 支持的最大数据标识id，结果是31 */
 29 | 	private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
 30 | 	/** 序列在id中占的位数 */
 31 | 	private final long sequenceBits = 12L;
 32 | 	/** 机器ID向左移12位 */
 33 | 	private final long workerIdShift = sequenceBits;
 34 | 	/** 数据标识id向左移17位(12+5) */
 35 | 	private final long datacenterIdShift = sequenceBits + workerIdBits;
 36 | 	/** 时间截向左移22位(5+5+12) */
 37 | 	private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
 38 | 	/** 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095) */
 39 | 	private final long sequenceMask = -1L ^ (-1L << sequenceBits);
 40 | 
 41 | 	/** 工作机器ID(0~31) */
 42 | 	private long workerId;
 43 | 	/** 数据中心ID(0~31) */
 44 | 	private long datacenterId;
 45 | 	/** 毫秒内序列(0~4095) */
 46 | 	private long sequence = 0L;
 47 | 	/** 上次生成ID的时间截 */
 48 | 	private long lastTimestamp = -1L;
 49 | 
 50 | 
 51 | 	public Sequence() {
 52 | 		datacenterId = getDatacenterId(maxDatacenterId);
 53 | 		workerId = getMaxWorkerId(datacenterId, maxWorkerId);
 54 |     }
 55 | 	
 56 | 	public Sequence(long workerId, long datacenterId) {
 57 | 		if (workerId > maxWorkerId || workerId < 0) {
 58 | 			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
 59 | 		}
 60 | 		
 61 | 		if (datacenterId > maxDatacenterId || datacenterId < 0) {
 62 | 			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
 63 | 		}
 64 | 		
 65 | 		this.workerId = workerId;
 66 | 		this.datacenterId = datacenterId;
 67 | 	}
 68 | 	
 69 | 
 70 | 	/**
 71 | 	 * 获取 maxWorkerId
 72 | 	 * @param datacenterId	 数据中心id
 73 | 	 * @param maxWorkerId	 机器id
 74 | 	 * @return	maxWorkerId
 75 | 	 */
 76 | 	protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
 77 | 		StringBuilder mpid = new StringBuilder();
 78 | 		mpid.append(datacenterId);
 79 | 		String name = ManagementFactory.getRuntimeMXBean().getName();
 80 | 		if (name != null && "".equals(name)) {
 81 | 			// GET jvmPid
 82 | 			mpid.append(name.split("@")[0]);
 83 | 		}
 84 | 		//MAC + PID 的 hashcode 获取16个低位
 85 | 		return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
 86 | 	}
 87 | 
 88 | 	/**
 89 | 	 * <p>
 90 |      * 数据标识id部分
 91 |      * </p>
 92 | 	 * @param maxDatacenterId
 93 | 	 * @return 
 94 | 	 */
 95 | 	protected static long getDatacenterId(long maxDatacenterId) {
 96 | 		long id = 0L;
 97 | 		try {
 98 | 			InetAddress ip = InetAddress.getLocalHost();
 99 | 			NetworkInterface network = NetworkInterface.getByInetAddress(ip);
100 | 			if (network == null) {
101 | 				id = 1L;
102 | 			} else {
103 | 				byte[] mac = network.getHardwareAddress();
104 | 				if (null != mac) {
105 | 					id = ((0x000000FF & (long) mac[mac.length - 1]) | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
106 | 					id = id % (maxDatacenterId + 1);
107 | 				}
108 | 			}
109 | 		} catch (Exception e) {
110 | 			System.err.println(" getDatacenterId: " + e.getMessage());
111 | 		}
112 | 		return id;
113 |     }
114 | 	
115 | 	/**
116 | 	 * 获得下一个ID (该方法是线程安全的)
117 | 	 * 
118 | 	 * @return nextId
119 | 	 */
120 | 	public synchronized long nextId() {
121 | 		long timestamp = timeGen();
122 | 
123 | 		// 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
124 | 		if (timestamp < lastTimestamp) {// 闰秒
125 | 			long offset = lastTimestamp - timestamp;
126 | 			if (offset <= 5) {
127 | 				try {
128 | 					wait(offset << 1);
129 | 					timestamp = timeGen();
130 | 					if (timestamp < lastTimestamp) {
131 | 						throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
132 | 					}
133 | 				} catch (Exception e) {
134 | 					throw new RuntimeException(e);
135 | 				}
136 | 			} else {
137 | 				throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
138 | 			}
139 | 		}
140 | 		
141 | 		//$NON-NLS-解决跨毫秒生成ID序列号始终为偶数的缺陷$
142 | 		// 如果是同一时间生成的，则进行毫秒内序列
143 | 		if (lastTimestamp == timestamp) {
144 | 			sequence = (sequence + 1) & sequenceMask;
145 | 			// 毫秒内序列溢出
146 | 			if (sequence == 0) {
147 | 				// 阻塞到下一个毫秒,获得新的时间戳
148 | 				timestamp = tilNextMillis(lastTimestamp);
149 | 			}
150 | 		} else {// 时间戳改变，毫秒内序列重置
151 | 			sequence = 0L;
152 | 		}
153 | 		/**
154 | 		// 如果是同一时间生成的，则进行毫秒内序列
155 | 		if (lastTimestamp == timestamp) {
156 | 		    long old = sequence;
157 | 		    sequence = (sequence + 1) & sequenceMask;
158 | 		    // 毫秒内序列溢出
159 | 		    if (sequence == old) {
160 | 		        // 阻塞到下一个毫秒,获得新的时间戳
161 | 		        timestamp = tilNextMillis(lastTimestamp);
162 | 		    }
163 | 		} else {// 时间戳改变，毫秒内序列重置
164 | 		    sequence = ThreadLocalRandom.current().nextLong(0, 2);
165 | 		}
166 | 		**/
167 | 
168 | 		// 上次生成ID的时间截
169 | 		lastTimestamp = timestamp;
170 | 
171 | 		// 移位并通过或运算拼到一起组成64位的ID
172 | 		return ((timestamp - twepoch) << timestampLeftShift) //
173 | 				| (datacenterId << datacenterIdShift) //
174 | 				| (workerId << workerIdShift) //
175 | 				| sequence;
176 | 	}
177 | 
178 | 	/**
179 | 	 * 阻塞到下一个毫秒，直到获得新的时间戳
180 | 	 * 
181 | 	 * @param lastTimestamp 上次生成ID的时间截
182 | 	 * @return 当前时间戳
183 | 	 */
184 | 	protected long tilNextMillis(long lastTimestamp) {
185 | 		long timestamp = timeGen();
186 | 		while (timestamp <= lastTimestamp) {
187 | 			timestamp = timeGen();
188 | 		}
189 | 		
190 | 		return timestamp;
191 | 	}
192 | 
193 | 	/**
194 | 	 * 返回以毫秒为单位的当前时间
195 | 	 * 
196 | 	 * @return 当前时间(毫秒)
197 | 	 */
198 | 	protected long timeGen() {
199 | 		return SystemClock.now();
200 | 	}
201 | 
202 | }
203 | 


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