Merge pull request #51 from Cysharp/codex/fix-round-robin-overflow

Fix round-robin index overflow

Author: mayuki

src/LogicLooper/RoundRobinLogicLooperPoolBalancer.cs

@@ -11,6 +11,7 @@ internal RoundRobinLogicLooperPoolBalancer()
 
     public ILogicLooper GetPooledLooper(ILogicLooper[] pooledLoopers)
     {
-        return pooledLoopers[Interlocked.Increment(ref _index) % pooledLoopers.Length];
+        var index = unchecked((uint)Interlocked.Increment(ref _index));
+        return pooledLoopers[(int)(index % (uint)pooledLoopers.Length)];
     }
 }

test/LogicLooper.Test/RoundRobinLogicLooperPoolBalancerTest.cs

@@ -19,4 +19,24 @@ public void GetPooledLooper_ReturnsLoopersInRoundRobinOrder()
         Assert.Equal(loopers[2], balancer.GetPooledLooper(loopers));
         Assert.Equal(loopers[0], balancer.GetPooledLooper(loopers));
     }
+
+    [Fact]
+    public void GetPooledLooper_ReturnsLoopersInRoundRobinOrder_WhenIndexOverflows()
+    {
+        var balancer = new RoundRobinLogicLooperPoolBalancer();
+        var indexField = typeof(RoundRobinLogicLooperPoolBalancer).GetField("_index", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
+        Assert.NotNull(indexField);
+        indexField.SetValue(balancer, int.MaxValue - 1);
+
+        var loopers = new ILogicLooper[]
+        {
+            new ManualLogicLooper(1),
+            new ManualLogicLooper(2),
+            new ManualLogicLooper(3)
+        };
+
+        Assert.Equal(loopers[1], balancer.GetPooledLooper(loopers));
+        Assert.Equal(loopers[2], balancer.GetPooledLooper(loopers));
+        Assert.Equal(loopers[0], balancer.GetPooledLooper(loopers));
+    }
 }