Try to prevent a deadlock when a reservation ends and starts within a…

… second and in the wrong order

app/services/reservation_manager.rb

@@ -10,8 +10,13 @@ def initialize(reservation)
   end
 
   def start_reservation
-    reservation.reservation_statuses.create!(status: 'Starting')
-    manage_reservation(:start)
+    if previous_reservation_ended_fully?
+      reservation.reservation_statuses.create!(status: 'Starting')
+      manage_reservation(:start)
+    else
+      reservation.update_attribute(:start_instantly, false)
+      reservation.reservation_statuses.create!(status: 'Waiting for other reservation on server to end fully')
+    end
   end
 
   def end_reservation
@@ -28,4 +33,10 @@ def update_reservation
   def manage_reservation(action)
     ReservationWorker.perform_async(reservation.id, action.to_s)
   end
+
+  private
+
+  def previous_reservation_ended_fully?
+    Reservation.where.not(id: reservation.id).where(server_id: reservation.server_id, ended: false).where('reservations.ends_at > ?', 15.minutes.ago).none?
+  end
 end

spec/models/reservation_spec.rb

@@ -222,6 +222,16 @@
         ReservationWorker.should_receive(:perform_async).with(reservation.id, 'start')
         reservation.start_reservation
       end
+
+      it 'should wait if a previous reservation is not fully ended' do
+        previous_reservation = create(:reservation)
+        previous_reservation.update_attribute(:server_id, reservation.server_id)
+        previous_reservation.update_attribute(:ends_at, 1.minute.ago)
+
+        reservation.start_reservation
+
+        expect(reservation.reservation_statuses.map(&:status)).to include 'Waiting for other reservation on server to end fully'
+      end
     end
 
     describe '#update_reservation' do