Terminate Riemann::Tools::HttpCheck threads between tests

Gemfile

@@ -4,3 +4,14 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in riemann-tools.gemspec
 gemspec
+
+if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.7.0')
+  # XXX: Needed for Ruby 2.6 compatibility
+  #
+  # With Ruby 2.6 an older version of rakup is installed that cause other gems
+  # to be installed with a legacy version.
+  #
+  # Because rakup is only needed when using rack 3, we can just ignore this
+  # with Ruby 2.6.
+  gem 'rackup'
+end

lib/riemann/tools/http_check.rb

@@ -37,10 +37,15 @@ def initialize
         @resolve_queue = Queue.new
         @work_queue = Queue.new
 
+        @resolvers = []
+        @workers = []
+
         opts[:resolvers].times do
-          Thread.new do
+          @resolvers << Thread.new do
             loop do
               uri = @resolve_queue.pop
+              Thread.exit unless uri
+
               host = uri.host
 
               addresses = Resolv::DNS.new.getaddresses(host)
@@ -59,9 +64,11 @@ def initialize
         end
 
         opts[:workers].times do
-          Thread.new do
+          @workers << Thread.new do
             loop do
               uri, addresses = @work_queue.pop
+              Thread.exit unless uri
+
               test_uri_addresses(uri, addresses)
             end
           end
@@ -70,6 +77,23 @@ def initialize
         super
       end
 
+      # Under normal operation, we have a single instance of this class for the
+      # lifetime of the process.  But when testing, we create a new instance
+      # for each test, each with its resolvers and worker threads.  The test
+      # process may end-up with a lot of running threads, hitting the OS limit
+      # of max threads by process and being unable to create more thread:
+      #
+      # ThreadError: can't create Thread: Resource temporarily unavailable
+      #
+      # To avoid this situation, we provide this method.
+      def shutdown
+        @resolve_queue.close
+        @resolvers.map(&:join)
+
+        @work_queue.close
+        @workers.map(&:join)
+      end
+
       def tick
         report(
           service: 'riemann http-check resolvers utilization',

spec/riemann/tools/http_check_spec.rb

@@ -1,7 +1,13 @@
 # frozen_string_literal: true
 
 require 'openssl'
-require 'rack/handler/webrick'
+begin
+  require 'rackup/handler/webrick'
+rescue LoadError
+  # XXX: Needed for Ruby 2.6 compatibility
+  # Moved to the rackup gem in recent versions
+  require 'rack/handler/webrick'
+end
 require 'sinatra/base'
 require 'webrick'
 require 'webrick/https'
@@ -110,6 +116,10 @@ def protected!
         @server&.shutdown
       end
 
+      after(:each) do
+        subject.shutdown
+      end
+
       let(:test_webserver_port) { @server.config[:Port] }
 
       let(:reported_uri) { uri }