fix: if blocked, defer async event insertion to prevent deadlocks

v2/pkg/engine/resolve/resolve.go

@@ -954,6 +954,18 @@ func (r *Resolver) AsyncUnsubscribeSubscription(id SubscriptionIdentifier) error
 		id:   id,
 		kind: subscriptionEventKindRemoveSubscription,
 	}:
+	default:
+		// In the event we cannot insert immediately, defer insertion a goroutine, this should prevent deadlocks, at the cost of goroutine creation.
+		go func() {
+			select {
+			case <-r.ctx.Done():
+				return
+			case r.events <- subscriptionEvent{
+				id:   id,
+				kind: subscriptionEventKindRemoveSubscription,
+			}:
+			}
+		}()
 	}
 	return nil
 }
@@ -968,6 +980,20 @@ func (r *Resolver) AsyncUnsubscribeClient(connectionID int64) error {
 		},
 		kind: subscriptionEventKindRemoveClient,
 	}:
+	default:
+		// In the event we cannot insert immediately, defer insertion a goroutine, this should prevent deadlocks, at the cost of goroutine creation.
+		go func() {
+			select {
+			case <-r.ctx.Done():
+				return
+			case r.events <- subscriptionEvent{
+				id: SubscriptionIdentifier{
+					ConnectionID: connectionID,
+				},
+				kind: subscriptionEventKindRemoveClient,
+			}:
+			}
+		}()
 	}
 	return nil
 }
@@ -1126,7 +1152,14 @@ func (r *Resolver) AsyncResolveGraphQLSubscription(ctx *Context, subscription *G
 		return writeFlushComplete(writer, msg)
 	}
 
-	event := subscriptionEvent{
+	select {
+	case <-r.ctx.Done():
+		// Stop resolving if the resolver is shutting down
+		return r.ctx.Err()
+	case <-ctx.ctx.Done():
+		// Stop resolving if the client is gone
+		return ctx.ctx.Err()
+	case r.events <- subscriptionEvent{
 		triggerID: xxh.Sum64(),
 		kind:      subscriptionEventKindAddSubscription,
 		addSubscription: &addSubscription{
@@ -1137,13 +1170,7 @@ func (r *Resolver) AsyncResolveGraphQLSubscription(ctx *Context, subscription *G
 			id:        id,
 			completed: make(chan struct{}),
 		},
-	}
-
-	select {
-	case <-r.ctx.Done():
-		// Stop resolving if the resolver is shutting down
-		return r.ctx.Err()
-	case r.events <- event:
+	}:
 	}
 	return nil
 }