Always catch StandardError in Threads and release connection

lib/prometheus/controller.rb

@@ -19,6 +19,8 @@ module Prometheus
             initialize_rfc_metrics
           rescue StandardError => e
             Sentry.capture_exception(e)
+          ensure
+            ActiveRecord::Base.connection_pool.release_connection
           end
         end
       end

lib/runner/event_loop.rb

@@ -32,6 +32,8 @@ class Runner::EventLoop
       queue = Queue.new
       Thread.new do
         EventMachine.run { queue.push nil }
+      rescue StandardError => e
+        Sentry.capture_exception(e)
       ensure
         ActiveRecord::Base.connection_pool.release_connection
       end