Handle race condition when calling ActivityStream#assets (fixes #2066)

lib/sessions/backend/activity_stream.rb

@@ -31,8 +31,13 @@ class Sessions::Backend::ActivityStream
     assets = {}
     item_ids = []
     activity_stream.each do |item|
+      begin
+        assets = item.assets(assets)
+      rescue ActiveRecord::RecordNotFound
+        next
+      end
+
       item_ids.push item.id
-      assets = item.assets(assets)
     end
 
     {

spec/lib/sessions/backend/activity_stream_spec.rb

@@ -0,0 +1,24 @@
+require 'rails_helper'
+
+RSpec.describe Sessions::Backend::ActivityStream do
+  context 'when async processes affect associated objects / DB records (#2066)' do
+    let(:subject)            { described_class.new(user, {}) }
+    let(:user)               { create(:agent_user, groups: [group]) }
+    let(:group)              { Group.find_by(name: 'Users') }
+    let(:associated_tickets) { create_list(:ticket, ticket_count, group: group) }
+    let(:ticket_count)       { 20 }
+
+    before do
+      Setting.set('system_init_done', true)
+
+      # these records must be created before the example begins
+      # (same as `let!`, but harder to miss)
+      associated_tickets
+    end
+
+    it 'manages race condition' do
+      Thread.new { associated_tickets.each(&:destroy) }
+      expect { subject.load }.not_to raise_error
+    end
+  end
+end