Allow que to be started and create pid file

lib/que/command_line_interface.rb

@@ -151,6 +151,14 @@ def parse(
             ) do |p|
               options[:wait_period] = p
             end
+
+            opts.on(
+              '--pidfile [PATH]',
+              String,
+              "Write the PID of this process to the specified file.",
+              ) do |p|
+              options[:pidfile] = File.expand_path(p)
+            end
           end
 
         parser.parse!(args)

lib/que/locker.rb

@@ -61,7 +61,8 @@ def initialize(
       wait_period:         DEFAULT_WAIT_PERIOD,
       maximum_buffer_size: DEFAULT_MAXIMUM_BUFFER_SIZE,
       worker_priorities:   DEFAULT_WORKER_PRIORITIES,
-      on_worker_start:     nil
+      on_worker_start:     nil,
+      pidfile:             nil
     )
 
       # Sanity-check all our arguments, since some users may instantiate Locker
@@ -215,10 +216,16 @@ def initialize(
             @connection.wrapped_connection.close
           end
         end
+
+      @pidfile = pidfile
+      at_exit { delete_pid }
+      write_pid
     end
 
     def stop!
-      stop; wait_for_stop
+      stop
+      wait_for_stop
+      delete_pid
     end
 
     def stop
@@ -512,5 +519,19 @@ def mark_id_as_locked(id)
         "Tried to lock a job that was already locked: #{id}"
       end
     end
+
+    def write_pid
+      return unless @pidfile
+
+      File.open(@pidfile, "w+") do |f|
+        f.write(Process.pid.to_s)
+      end
+    end
+
+    def delete_pid
+      return unless @pidfile
+
+      File.delete(@pidfile) if File.exist?(@pidfile)
+    end
   end
 end

spec/que/locker_spec.rb

@@ -185,6 +185,30 @@ def assert_que_locker_insertion(
     locker.stop!
   end
 
+  describe "with pidfile" do
+    it "should create and delete pid file, if not exist" do
+      pidfile = "./spec/temp/pidfile_#{Time.new.to_i}.pid"
+      locker_settings[:pidfile] = pidfile
+      locker
+      assert File.exist?(pidfile)
+
+      locker.stop!
+      refute File.exist?(pidfile)
+    end
+
+    it "should create and delete pid file, if exist" do
+      pidfile = "./spec/temp/pidfile_#{Time.new.to_i}.pid"
+      File.open(pidfile, "w+") { |f| f.write "test" }
+
+      locker_settings[:pidfile] = pidfile
+      locker
+      assert File.exist?(pidfile)
+
+      locker.stop!
+      refute File.exist?(pidfile)
+    end
+  end
+
   describe "on startup" do
     it "should do batch polls for jobs in its specified queue" do
       job1, job2 = BlockJob.enqueue, BlockJob.enqueue