Reuse runners per user and execution environment

Co-authored-by: Jan-Eric Hellenberg <jan-eric.hellenberg@student.hpi.uni-potsdam.de>
Co-authored-by: Maximilian Pass <maximilian.pass@student.hpi.uni-potsdam.de>

app/jobs/application_job.rb

@@ -0,0 +1,3 @@
+class ApplicationJob < ActiveJob::Base
+  queue_as :default
+end

app/jobs/runner_cleanup_job.rb

@@ -0,0 +1,16 @@
+class RunnerCleanupJob < ApplicationJob
+  CLEANUP_INTERVAL = CodeOcean::Config.new(:code_ocean).read[:runner_management][:cleanup_interval].seconds
+
+  after_perform do |job|
+    # re-schedule job
+    self.class.set(wait: CLEANUP_INTERVAL).perform_later
+  end
+
+  def perform
+    Rails.logger.debug(Time.now)
+    Runner.inactive_runners.each do |runner|
+      Rails.logger.debug("Destroying runner #{runner.runner_id}, unused since #{runner.last_used}")
+      runner.destroy
+    end
+  end
+end