引入 Seata 的修改版雪花算法

src/main/java/xyz/zhouxy/plusone/commons/util/IdGenerator.java

@@ -1,10 +1,10 @@
 package xyz.zhouxy.plusone.commons.util;
 
+import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
 
 import com.google.common.annotations.Beta;
-import com.google.common.collect.HashBasedTable;
-import com.google.common.collect.Table;
 
 @Beta
 public class IdGenerator {
@@ -39,26 +39,15 @@ public class IdGenerator {
 
     // ===== SnowflakeId =====
 
-    private static final Table<Long, Long, SnowflakeIdGenerator> snowflakePool = HashBasedTable.create();
+    private static final Map<Long, IdWorker> snowflakePool = new ConcurrentHashMap<>();
 
-    public static long nextSnowflakeId(long workerId, long datacenterId) {
-        SnowflakeIdGenerator generator = getSnowflakeIdGenerator(workerId, datacenterId);
+    public static long nextSnowflakeId(long workerId) {
+        IdWorker generator = getSnowflakeIdGenerator(workerId);
         return generator.nextId();
     }
 
-    public static SnowflakeIdGenerator getSnowflakeIdGenerator(long workerId, long datacenterId) {
-        SnowflakeIdGenerator generator = snowflakePool.get(workerId, datacenterId);
-        if (generator == null) {
-            // 其它地方需注意，对 snowflakePool 的操作，也都锁 snowflakePool 对象。
-            synchronized (snowflakePool) {
-                generator = snowflakePool.get(workerId, datacenterId);
-                if (generator == null) {
-                    generator = new SnowflakeIdGenerator(workerId, datacenterId);
-                    snowflakePool.put(workerId, datacenterId, generator);
-                }
-            }
-        }
-        return generator;
+    public static IdWorker getSnowflakeIdGenerator(long workerId) {
+        return snowflakePool.computeIfAbsent(workerId, wid -> new IdWorker(workerId));
     }
 
     private IdGenerator() {

src/main/java/xyz/zhouxy/plusone/commons/util/IdWorker.java

@@ -0,0 +1,142 @@
+/*
+ *  Copyright 1999-2019 Seata.io Group.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package xyz.zhouxy.plusone.commons.util;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * IdWorker from Seata.
+ *
+ * @author funkye
+ * @author selfishlover
+ */
+public class IdWorker {
+
+    /**
+     * Start time cut (2020-05-03)
+     */
+    private static final long TWEPOCH = 1588435200000L;
+
+    /**
+     * The number of bits occupied by workerId
+     */
+    private static final int WORKER_ID_BITS = 10;
+
+    /**
+     * The number of bits occupied by timestamp
+     */
+    private static final int TIMESTAMP_BITS = 41;
+
+    /**
+     * The number of bits occupied by sequence
+     */
+    private static final int SEQUENCE_BITS = 12;
+
+    /**
+     * Maximum supported machine id, the result is 1023
+     */
+    private static final int MAX_WORKER_ID = ~(-1 << WORKER_ID_BITS);
+
+    /**
+     * business meaning: machine ID (0 ~ 1023)
+     * actual layout in memory:
+     * highest 1 bit: 0
+     * middle 10 bit: workerId
+     * lowest 53 bit: all 0
+     */
+    private long workerId;
+
+    /**
+     * timestamp and sequence mix in one Long
+     * highest 11 bit: not used
+     * middle  41 bit: timestamp
+     * lowest  12 bit: sequence
+     */
+    private AtomicLong timestampAndSequence;
+
+    /**
+     * mask that help to extract timestamp and sequence from a long
+     */
+    private static final long TIMESTAMP_AND_SEQUENCE_MASK = ~(-1L << (TIMESTAMP_BITS + SEQUENCE_BITS));
+
+    /**
+     * instantiate an IdWorker using given workerId
+     */
+    public IdWorker(long workerId) {
+        initTimestampAndSequence();
+        initWorkerId(workerId);
+    }
+
+    /**
+     * init first timestamp and sequence immediately
+     */
+    private void initTimestampAndSequence() {
+        long timestamp = getNewestTimestamp();
+        long timestampWithSequence = timestamp << SEQUENCE_BITS;
+        this.timestampAndSequence = new AtomicLong(timestampWithSequence);
+    }
+
+    /**
+     * init workerId
+     * @param workerId if null, then auto generate one
+     */
+    private void initWorkerId(long workerId) {
+        if (workerId > MAX_WORKER_ID || workerId < 0) {
+            String message = String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID);
+            throw new IllegalArgumentException(message);
+        }
+        this.workerId = workerId << (TIMESTAMP_BITS + SEQUENCE_BITS);
+    }
+
+    /**
+     * get next UUID(base on snowflake algorithm), which look like:
+     * highest 1 bit: always 0
+     * next   10 bit: workerId
+     * next   41 bit: timestamp
+     * lowest 12 bit: sequence
+     * @return UUID
+     */
+    public long nextId() {
+        waitIfNecessary();
+        long next = timestampAndSequence.incrementAndGet();
+        long timestampWithSequence = next & TIMESTAMP_AND_SEQUENCE_MASK;
+        return workerId | timestampWithSequence;
+    }
+
+    /**
+     * block current thread if the QPS of acquiring UUID is too high
+     * that current sequence space is exhausted
+     */
+    private void waitIfNecessary() {
+        long currentWithSequence = timestampAndSequence.get();
+        long current = currentWithSequence >>> SEQUENCE_BITS;
+        long newest = getNewestTimestamp();
+        if (current >= newest) {
+            try {
+                Thread.sleep(5);
+            } catch (InterruptedException ignore) {
+                // don't care
+            }
+        }
+    }
+
+    /**
+     * get newest timestamp relative to twepoch
+     */
+    private long getNewestTimestamp() {
+        return System.currentTimeMillis() - TWEPOCH;
+    }
+}