init

LightlessSync/Services/PairProcessingLimiter.cs

@@ -15,6 +15,7 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
     private readonly SemaphoreSlim _semaphore;
     private int _currentLimit;
     private int _pendingReductions;
+    private int _pendingIncrements;
     private int _waiting;
     private int _inFlight;
 
@@ -70,7 +71,7 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
 
         if (!IsEnabled)
         {
-            _semaphore.Release();
+            TryReleaseSemaphore();
             return NoopReleaser.Instance;
         }
 
@@ -90,18 +91,12 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
                 var releaseAmount = HardLimit - _semaphore.CurrentCount;
                 if (releaseAmount > 0)
                 {
-                    try
-                    {
-                        _semaphore.Release(releaseAmount);
-                    }
-                    catch (SemaphoreFullException)
-                    {
-                        // ignore, already at max
-                    }
+                    TryReleaseSemaphore(releaseAmount);
                 }
 
                 _currentLimit = desiredLimit;
                 _pendingReductions = 0;
+                _pendingIncrements = 0;
                 return;
             }
 
@@ -113,10 +108,13 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
             if (desiredLimit > _currentLimit)
             {
                 var increment = desiredLimit - _currentLimit;
-                var allowed = Math.Min(increment, HardLimit - _semaphore.CurrentCount);
-                if (allowed > 0)
+                _pendingIncrements += increment;
+
+                var available = HardLimit - _semaphore.CurrentCount;
+                var toRelease = Math.Min(_pendingIncrements, available);
+                if (toRelease > 0 && TryReleaseSemaphore(toRelease))
                 {
-                    _semaphore.Release(allowed);
+                    _pendingIncrements -= toRelease;
                 }
             }
             else
@@ -133,6 +131,13 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
                 {
                     _pendingReductions += remaining;
                 }
+
+                if (_pendingIncrements > 0)
+                {
+                    var offset = Math.Min(_pendingIncrements, _pendingReductions);
+                    _pendingIncrements -= offset;
+                    _pendingReductions -= offset;
+                }
             }
 
             _currentLimit = desiredLimit;
@@ -146,6 +151,25 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
         return Math.Clamp(configured, 1, HardLimit);
     }
 
+    private bool TryReleaseSemaphore(int count = 1)
+    {
+        if (count <= 0)
+        {
+            return true;
+        }
+
+        try
+        {
+            _semaphore.Release(count);
+            return true;
+        }
+        catch (SemaphoreFullException ex)
+        {
+            Logger.LogDebug(ex, "Attempted to release {count} pair processing slots but semaphore is already at the hard limit.", count);
+            return false;
+        }
+    }
+
     private void ReleaseOne()
     {
         var inFlight = Interlocked.Decrement(ref _inFlight);
@@ -166,9 +190,20 @@ public sealed class PairProcessingLimiter : DisposableMediatorSubscriberBase
                 _pendingReductions--;
                 return;
             }
+
+            if (_pendingIncrements > 0)
+            {
+                if (!TryReleaseSemaphore())
+                {
+                    return;
+                }
+
+                _pendingIncrements--;
+                return;
+            }
         }
 
-        _semaphore.Release();
+        TryReleaseSemaphore();
     }
 
     protected override void Dispose(bool disposing)