RUBY-2771 Allow awaited hello to fail with EOF when client is shutting down (#2328)

Co-authored-by: Oleg Pudeyev <code@olegp.name>

Author: p-mongo

lib/mongo/server/push_monitor.rb

@@ -111,6 +111,12 @@ def do_work
           @topology_version = new_description.topology_version
         end
       rescue Mongo::Error => exc
+        stop_requested = @lock.synchronize { @stop_requested }
+        if stop_requested
+          # Ignore the exception, see RUBY-2771.
+          return
+        end
+
         msg = "Error running awaited hello on #{server.address}"
         Utils.warn_bg_exception(msg, exc,
           logger: options[:logger],

spec/stress/push_monitor_close_spec.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+# encoding: utf-8
+
+require 'spec_helper'
+
+# This test repeatedly creates and closes clients across several threads.
+# Its goal is to ensure that the push monitor connections specifically get
+# closed without any errors or warnings being reported to applications.
+#
+# Although the test is specifically meant to test 4.4+ servers (that utilize
+# the push monitor) in non-LB connections, run it everywhere for good measure.
+describe 'Push monitor close test' do
+  require_stress
+
+  let(:options) do
+    SpecConfig.instance.all_test_options
+  end
+
+  before(:all) do
+    # load if necessary
+    ClusterConfig.instance.primary_address
+    ClientRegistry.instance.close_all_clients
+  end
+
+  it 'does not warn/error on cleanup' do
+    Mongo::Logger.logger.should_not receive(:warn)
+
+    threads = 10.times.map do
+      Thread.new do
+        10.times do
+          client = new_local_client([ClusterConfig.instance.primary_address.seed], options)
+          if rand > 0.33
+            client.command(ping: 1)
+            sleep(rand * 3)
+          end
+          client.close
+          STDOUT << '.'
+        end
+      end
+    end
+    threads.each(&:join)
+    puts
+  end
+end