Ensure to close DB connections within threads

app/controllers/concerns/submission_scoring.rb

@@ -53,6 +53,8 @@ module SubmissionScoring
           rfc.full_score_reached = true
           rfc.save
         }
+      ensure
+        ActiveRecord::Base.connection_pool.release_connection
       end
     end
     if @embed_options.present? && @embed_options[:hide_test_results] && outputs.present?

app/controllers/request_for_comments_controller.rb

@@ -99,6 +99,8 @@ class RequestForCommentsController < ApplicationController
         # create thread here and execute tests. A run is triggered from the frontend and does not need to be handled here.
         Thread.new do
           score_submission(@request_for_comment.submission)
+        ensure
+          ActiveRecord::Base.connection_pool.release_connection
         end
         format.json { render :show, status: :created, location: @request_for_comment }
       else
@@ -136,18 +138,18 @@ class RequestForCommentsController < ApplicationController
 
   private
     # Use callbacks to share common setup or constraints between actions.
-    def set_request_for_comment
-      @request_for_comment = RequestForComment.find(params[:id])
-    end
+  def set_request_for_comment
+    @request_for_comment = RequestForComment.find(params[:id])
+  end
 
     # Never trust parameters from the scary internet, only allow the white list through.
-    def request_for_comment_params
-      # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
-      params.require(:request_for_comment).permit(:exercise_id, :file_id, :question, :requested_at, :solved, :submission_id).merge(user_id: current_user.id, user_type: current_user.class.name)
-    end
+  def request_for_comment_params
+    # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
+    params.require(:request_for_comment).permit(:exercise_id, :file_id, :question, :requested_at, :solved, :submission_id).merge(user_id: current_user.id, user_type: current_user.class.name)
+  end
 
-    def comment_params
-      params.permit(:exercise_id, :feedback_text).merge(user_id: current_user.id, user_type: current_user.class.name)
-    end
+  def comment_params
+    params.permit(:exercise_id, :feedback_text).merge(user_id: current_user.id, user_type: current_user.class.name)
+  end
 
 end

app/controllers/submissions_controller.rb

@@ -147,7 +147,13 @@ class SubmissionsController < ApplicationController
       #   #guarantee that the thread is releasing the DB connection after it is done
       #   ApplicationRecord.connectionpool.releaseconnection
       # end
-      Thread.new { EventMachine.run } unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+      unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+        Thread.new do
+          EventMachine.run
+        ensure
+          ActiveRecord::Base.connection_pool.release_connection
+        end
+      end
 
 
       # socket is the socket into the container, tubesock is the socket to the client
@@ -319,19 +325,27 @@ class SubmissionsController < ApplicationController
         return
       end
 
-      Thread.new { EventMachine.run } unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+      unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+        Thread.new do
+          EventMachine.run
+        ensure
+          ActiveRecord::Base.connection_pool.release_connection
+        end
+      end
       # tubesock is the socket to the client
 
       # the score_submission call will end up calling docker exec, which is blocking.
       # to ensure responsiveness, we therefore open a thread here.
-      Thread.new {
+      Thread.new do
         tubesock.send_data JSON.dump(score_submission(@submission))
 
         # To enable hints when scoring a submission, uncomment the next line:
         #send_hints(tubesock, StructuredError.where(submission: @submission))
 
         tubesock.send_data JSON.dump({'cmd' => 'exit'})
-      }
+      ensure
+        ActiveRecord::Base.connection_pool.release_connection
+      end
     end
   end
 
@@ -388,7 +402,13 @@ class SubmissionsController < ApplicationController
 
   def test
     hijack do |tubesock|
-      Thread.new { EventMachine.run } unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+      unless EventMachine.reactor_running? && EventMachine.reactor_thread.alive?
+        Thread.new do
+          EventMachine.run
+        ensure
+          ActiveRecord::Base.connection_pool.release_connection
+        end
+      end
 
       output = @docker_client.execute_test_command(@submission, sanitize_filename)
 

app/helpers/action_cable_helper.rb

@@ -1,17 +1,20 @@
+# frozen_string_literal: true
 module ActionCableHelper
-def trigger_rfc_action_cable
-  Thread.new do
-    # Context: RfC
-    if submission.study_group_id.present?
-      ActionCable.server.broadcast(
-          "la_exercises_#{exercise_id}_channel_study_group_#{submission.study_group_id}",
-          type: :rfc,
-          id: id,
-          html: (ApplicationController.render(partial: 'request_for_comments/list_entry',
-                                              locals: {request_for_comment: self})))
+  def trigger_rfc_action_cable
+    Thread.new do
+      # Context: RfC
+      if submission.study_group_id.present?
+        ActionCable.server.broadcast(
+            "la_exercises_#{exercise_id}_channel_study_group_#{submission.study_group_id}",
+            type: :rfc,
+            id: id,
+            html: ApplicationController.render(partial: 'request_for_comments/list_entry',
+                                               locals: {request_for_comment: self}))
+      end
+    ensure
+      ActiveRecord::Base.connection_pool.release_connection
     end
   end
-end
 
   def trigger_rfc_action_cable_from_comment
     # Context: Comment
@@ -27,6 +30,8 @@ end
             type: :working_times,
             working_time_data: exercise.get_working_times_for_study_group(study_group_id, user))
       end
+    ensure
+      ActiveRecord::Base.connection_pool.release_connection
     end
   end
 end