🎨 雪花算法变种

alis-rpc/alis-rpc-common/src/main/java/org/alis/rpc/common/util/IdWorker.java

@@ -0,0 +1,171 @@
+package org.alis.rpc.common.util;
+
+import java.net.NetworkInterface;
+import java.util.Enumeration;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * @author lc
+ * @date 2023/9/15 14:55
+ */
+public class IdWorker {
+    /**
+     * Start time cut (2020-05-03)
+     */
+    private final long twepoch = 1588435200000L;
+
+    /**
+     * The number of bits occupied by workerId
+     */
+    private final int workerIdBits = 10;
+
+    /**
+     * The number of bits occupied by timestamp
+     */
+    private final int timestampBits = 41;
+
+    /**
+     * The number of bits occupied by sequence
+     */
+    private final int sequenceBits = 12;
+
+    /**
+     * Maximum supported machine id, the result is 1023
+     */
+    private final int maxWorkerId = ~(-1 << workerIdBits);
+
+    /**
+     * 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 final long timestampAndSequenceMask = ~(-1L << (timestampBits + sequenceBits));
+
+    /**
+     * instantiate an IdWorker using given workerId
+     * @param workerId if null, then will auto assign one
+     */
+    public IdWorker(Long workerId) {
+        initTimestampAndSequence();
+        initWorkerId(workerId);
+    }
+
+    /**
+     * init first timestamp and sequence immediately
+     */
+    private void initTimestampAndSequence() {
+        long timestamp = getNewestTimestamp();
+        long timestampWithSequence = timestamp << sequenceBits;
+        this.timestampAndSequence = new AtomicLong(timestampWithSequence);
+    }
+
+    /**
+     * init workerId
+     * @param workerId if null, then auto generate one
+     */
+    private void initWorkerId(Long workerId) {
+        if (workerId == null) {
+            workerId = generateWorkerId();
+        }
+        if (workerId > maxWorkerId || workerId < 0) {
+            String message = String.format("worker Id can't be greater than %d or less than 0", maxWorkerId);
+            throw new IllegalArgumentException(message);
+        }
+        this.workerId = workerId << (timestampBits + sequenceBits);
+    }
+
+    /**
+     * 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 & timestampAndSequenceMask;
+        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 >>> sequenceBits;
+        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;
+    }
+
+    /**
+     * auto generate workerId, try using mac first, if failed, then randomly generate one
+     * @return workerId
+     */
+    private long generateWorkerId() {
+        try {
+            return generateWorkerIdBaseOnMac();
+        } catch (Exception e) {
+            return generateRandomWorkerId();
+        }
+    }
+
+    /**
+     * use lowest 10 bit of available MAC as workerId
+     * @return workerId
+     * @throws Exception when there is no available mac found
+     */
+    private long generateWorkerIdBaseOnMac() throws Exception {
+        Enumeration<NetworkInterface> all = NetworkInterface.getNetworkInterfaces();
+        while (all.hasMoreElements()) {
+            NetworkInterface networkInterface = all.nextElement();
+            boolean isLoopback = networkInterface.isLoopback();
+            boolean isVirtual = networkInterface.isVirtual();
+            if (isLoopback || isVirtual) {
+                continue;
+            }
+            byte[] mac = networkInterface.getHardwareAddress();
+            return ((mac[4] & 0B11) << 8) | (mac[5] & 0xFF);
+        }
+        throw new RuntimeException("no available mac found");
+    }
+
+    /**
+     * randomly generate one as workerId
+     * @return workerId
+     */
+    private long generateRandomWorkerId() {
+        return ThreadLocalRandom.current().nextInt(maxWorkerId + 1);
+    }
+}