From 52f9c6df95cae035fda3771e96f1296b880e3370 Mon Sep 17 00:00:00 2001
From: Dmytro Vyazelenko <696855+vyazelenko@users.noreply.github.com>
Date: Wed, 15 May 2024 14:01:14 +0200
Subject: [PATCH] [Java] Increment sequence if the clock is not advancing or
 going backwards.

---
 .../agrona/concurrent/SnowflakeIdGenerator.java  |  7 +------
 .../concurrent/SnowflakeIdGeneratorTest.java     | 16 ++++++++++++----
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/agrona/src/main/java/org/agrona/concurrent/SnowflakeIdGenerator.java b/agrona/src/main/java/org/agrona/concurrent/SnowflakeIdGenerator.java
index c72cc4294..883815cfc 100644
--- a/agrona/src/main/java/org/agrona/concurrent/SnowflakeIdGenerator.java
+++ b/agrona/src/main/java/org/agrona/concurrent/SnowflakeIdGenerator.java
@@ -225,7 +225,7 @@ public long nextId()
                     return newTimestampSequence | nodeBits;
                 }
             }
-            else if (timestampMs == oldTimestampMs)
+            else
             {
                 final long oldSequence = oldTimestampSequence & maxSequence;
                 if (oldSequence < maxSequence)
@@ -237,11 +237,6 @@ else if (timestampMs == oldTimestampMs)
                     }
                 }
             }
-            else
-            {
-                throw new IllegalStateException(
-                    "clock has gone backwards: timestampMs=" + timestampMs + " < oldTimestampMs=" + oldTimestampMs);
-            }
 
             if (Thread.currentThread().isInterrupted())
             {
diff --git a/agrona/src/test/java/org/agrona/concurrent/SnowflakeIdGeneratorTest.java b/agrona/src/test/java/org/agrona/concurrent/SnowflakeIdGeneratorTest.java
index fd8cd3ede..f95c63900 100644
--- a/agrona/src/test/java/org/agrona/concurrent/SnowflakeIdGeneratorTest.java
+++ b/agrona/src/test/java/org/agrona/concurrent/SnowflakeIdGeneratorTest.java
@@ -205,7 +205,7 @@ void shouldAdvanceTimestamp()
     }
 
     @Test
-    void shouldDetectClockGoingBackwards()
+    void shouldAdvanceSequenceWhenClockIsGoingBackwards()
     {
         final long nodeId = 7;
         final long timestampOffset = 0;
@@ -215,10 +215,18 @@ void shouldDetectClockGoingBackwards()
             NODE_ID_BITS_DEFAULT, SEQUENCE_BITS_DEFAULT, nodeId, timestampOffset, clock);
         clock.update(7);
 
-        idGenerator.nextId();
+        final long firstId = idGenerator.nextId();
+        final long firstTimestamp = clock.time();
+        assertEquals(firstTimestamp, idGenerator.extractTimestamp(firstId));
+        assertEquals(nodeId, idGenerator.extractNodeId(firstId));
+        assertEquals(0L, idGenerator.extractSequence(firstId));
 
-        clock.update(3);
-        assertThrows(IllegalStateException.class, idGenerator::nextId);
+        clock.update(4);
+
+        final long secondId = idGenerator.nextId();
+        assertEquals(firstTimestamp, idGenerator.extractTimestamp(secondId));
+        assertEquals(nodeId, idGenerator.extractNodeId(secondId));
+        assertEquals(1L, idGenerator.extractSequence(secondId));
     }
 
     @Test