Correct a spurious slot release (#220)

The slot release was incorrect and was run outside of the
manager.predict function meaning we effectively had more slots than
expected.

This change eliminates the added .releaseSlot() call in the wrong
method.

Author: tempusfrangit

internal/runner/manager.go

@@ -136,17 +136,20 @@ func (m *Manager) Start(ctx context.Context) error {
 func (m *Manager) claimSlot() error {
 	select {
 	case <-m.capacity:
+		m.logger.Trace("claiming slot")
 		return nil
 	default:
+		m.logger.Trace("attempted claim slot but no slot available")
 		return ErrNoCapacity
 	}
 }
 
 func (m *Manager) releaseSlot() {
 	select {
 	case m.capacity <- struct{}{}:
+		m.logger.Trace("releasing slot")
 	default:
-		m.logger.Warn("attempted to release slot but channel is full")
+		m.logger.Error("attempted to release slot but channel is full")
 	}
 }
 
@@ -172,8 +175,7 @@ func (m *Manager) PredictAsync(ctx context.Context, req PredictionRequest) (*Pre
 
 	// Release slot when prediction completes in background
 	go func() {
-		defer m.releaseSlot() // Release slot after prediction completes
-		<-respChan            // Wait for prediction to complete
+		<-respChan // Wait for prediction to complete
 		log.Tracew("async prediction completed", "prediction_id", req.ID)
 	}()