├── .classpath
├── .project
├── README.md
├── lib
    ├── commons-codec-1.6.jar
    └── uuid-3.2.1-SNAPSHOT.jar
└── src
    └── uniq
        └── UniqueId.java


/.classpath:
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1 | <?xml version="1.0" encoding="UTF-8"?>
2 | <classpath>
3 | 	<classpathentry kind="src" path="src"/>
4 | 	<classpathentry kind="lib" path="lib/commons-codec-1.6.jar"/>
5 | 	<classpathentry kind="lib" path="lib/uuid-3.2.1-SNAPSHOT.jar"/>
6 | 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
7 | 	<classpathentry kind="output" path="bin"/>
8 | </classpath>
9 | 


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/.project:
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 1 | <?xml version="1.0" encoding="UTF-8"?>
 2 | <projectDescription>
 3 | 	<name>flake-java</name>
 4 | 	<comment></comment>
 5 | 	<projects>
 6 | 	</projects>
 7 | 	<buildSpec>
 8 | 		<buildCommand>
 9 | 			<name>org.eclipse.jdt.core.javabuilder</name>
10 | 			<arguments>
11 | 			</arguments>
12 | 		</buildCommand>
13 | 	</buildSpec>
14 | 	<natures>
15 | 		<nature>org.eclipse.jdt.core.javanature</nature>
16 | 	</natures>
17 | </projectDescription>
18 | 


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/README.md:
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 1 | # Unique Id generator
 2 | 
 3 | Based on http://blog.boundary.com/2012/01/12/Flake-A-decentralized-k-ordered-id-generation-service-in-Erlang.html
 4 | which is in turn based on Twitter's Snowflake project: http://engineering.twitter.com/2010/06/announcing-snowflake.html
 5 | 
 6 | Generates unique ids based on the current epoch time, current machine identity,
 7 | and a counter. The result are mostly ordered unique ids that require no
 8 | synchronization between machines.
 9 | 
10 | 
11 | # Compile and run
12 | 
13 |     javac -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar src/uniq/UniqueId.java
14 |     java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId
15 | 
16 | # Performance
17 | 
18 | 2011 MacBook Pro, 2.8Ghz i7
19 | 
20 | ## Cat to file
21 | 
22 |     $ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > out
23 |     
24 |     real    0m18.498s
25 |     user    0m5.662s
26 |     sys     0m12.973s
27 | 
28 |     $ ls -lh out
29 |     -rw-r--r--  1 mumrah  staff   153M May 22 10:52 out
30 | 
31 | 540 id/ms
32 | 
33 | Since each id is 128 bits, the I/O rate comes out to 8640000 bytes per second, or 8.24 MB/s.
34 | Compare this to 66.59 MB/s which is the speed that the same system can "yes > omgyes". I guess that order of
35 | magnitude difference is the price of safety/synchronization.
36 | 
37 | ## Pipe to /dev/null
38 | 
39 |     $ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > /dev/null
40 | 
41 |     real    0m7.794s
42 |     user    0m4.688s
43 |     sys     0m3.253s
44 | 
45 | 1280 id/ms
46 | 
47 | ## Pipe to fifo, fifo to /dev/null
48 | 
49 |     $ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > foo
50 | 
51 |     real    0m18.051s
52 |     user    0m5.594s
53 |     sys     0m12.594s
54 | 
55 | 554 id/ms
56 | 
57 | 
58 | 


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/lib/commons-codec-1.6.jar:
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https://raw.githubusercontent.com/mumrah/flake-java/59515e66db968dd473e30c7427c28386aefa5d73/lib/commons-codec-1.6.jar


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/lib/uuid-3.2.1-SNAPSHOT.jar:
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https://raw.githubusercontent.com/mumrah/flake-java/59515e66db968dd473e30c7427c28386aefa5d73/lib/uuid-3.2.1-SNAPSHOT.jar


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/src/uniq/UniqueId.java:
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 1 | package uniq;
 2 | 
 3 | import java.io.IOException;
 4 | import java.nio.ByteBuffer;
 5 | 
 6 | import com.eaio.uuid.UUIDGen;
 7 | 
 8 | public class UniqueId {
 9 |   
10 |     // Get the MAC address (i.e., the "node" from a UUID1)
11 |     private final long clockSeqAndNode = UUIDGen.getClockSeqAndNode();
12 |     private final byte[] node = new byte[]{
13 |         (byte)((clockSeqAndNode >> 40) & 0xff),
14 |         (byte)((clockSeqAndNode >> 32) & 0xff),
15 |         (byte)((clockSeqAndNode >> 24) & 0xff),
16 |         (byte)((clockSeqAndNode >> 16) & 0xff),
17 |         (byte)((clockSeqAndNode >> 8) & 0xff),
18 |         (byte)((clockSeqAndNode >> 0) & 0xff),
19 |     };
20 |     private final ThreadLocal<ByteBuffer> tlbb = new ThreadLocal<ByteBuffer>() {
21 |         @Override
22 |         public ByteBuffer initialValue() {
23 |             return ByteBuffer.allocate(16);
24 |         }       
25 |     };
26 | 
27 |     private volatile int seq;
28 |     private volatile long lastTimestamp;
29 |     private final Object lock = new Object();
30 | 
31 |     private final int maxShort = (int)0xffff;
32 |         
33 |     public byte[] getId() {
34 |         if(seq == maxShort) {
35 |             throw new RuntimeException("Too fast");
36 |         }
37 |         
38 |         long time;
39 |         synchronized(lock) {
40 |             time = System.currentTimeMillis();
41 |             if(time != lastTimestamp) {
42 |                 lastTimestamp = time;
43 |                 seq = 0;
44 |             }
45 |             seq++;
46 |             ByteBuffer bb = tlbb.get();
47 |             bb.rewind();
48 |             bb.putLong(time);
49 |             bb.put(node);
50 |             bb.putShort((short)seq);
51 |             return bb.array();    			
52 |         }
53 |     }
54 | 
55 |     public String getStringId() {
56 |       byte[] ba = getId();
57 |       ByteBuffer bb = ByteBuffer.wrap(ba);
58 |       long ts = bb.getLong();
59 |       int node_0 = bb.getInt();
60 |       short node_1 = bb.getShort();
61 |       short seq = bb.getShort();
62 |       return String.format("%016d-%s%s-%04d", ts, Integer.toHexString(node_0), Integer.toHexString(node_1), seq);
63 |     }
64 | 
65 |     public static void main(String[] args) throws IOException {
66 |         UniqueId uid = new UniqueId();
67 |         int n = Integer.parseInt(args[0]);
68 |         
69 |         for(int i=0; i<n; i++) {
70 |             System.out.write(uid.getId());
71 |             //System.out.println(uid.getStringId());
72 |         }
73 |     }
74 | }
75 | 


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