supervisor: reduce memory usage of cleanup_lock_dir with huge number of lock files

lib/fluent/supervisor.rb

@@ -100,7 +100,14 @@ def after_run
     end
 
     def cleanup_lock_dir
-      FileUtils.rm(Dir.glob(File.join(@fluentd_lock_dir, "fluentd-*.lock")))
+      begin
+        Dir.each_child(@fluentd_lock_dir) do |name|
+          FileUtils.rm_f(File.join(@fluentd_lock_dir, name)) if File.fnmatch?("fluentd-*.lock", name)
+        end
+      rescue Errno::ENOENT
+        # Directory is already missing. Fall through and let rmdir below
+        # fail in the same way as the current implementation.
+      end
       FileUtils.rmdir(@fluentd_lock_dir)
     end
 

test/test_supervisor.rb

@@ -1003,6 +1003,39 @@ def test_log_result((result, expected_message))
     end
   end
 
+  sub_test_case "cleanup_lock_dir" do
+    def create_server(lock_dir)
+      server = DummyServer.new
+      server.instance_variable_set(:@fluentd_lock_dir, lock_dir)
+      server
+    end
+
+    def test_remove_lock_dir
+      lock_dir = File.join(@tmp_dir, "fluentd-lock")
+      FileUtils.mkdir_p(lock_dir)
+      FileUtils.touch(File.join(lock_dir, "fluentd-0.lock"))
+      FileUtils.touch(File.join(lock_dir, "fluentd-1.lock"))
+
+      create_server(lock_dir).cleanup_lock_dir
+
+      assert_false(File.exist?(lock_dir))
+    end
+
+    def test_keep_unrelated_file
+      lock_dir = File.join(@tmp_dir, "fluentd-lock")
+      FileUtils.mkdir_p(lock_dir)
+      FileUtils.touch(File.join(lock_dir, "fluentd-0.lock"))
+      FileUtils.touch(File.join(lock_dir, "unrelated.txt"))
+
+      assert_raise(Errno::ENOTEMPTY) do
+        create_server(lock_dir).cleanup_lock_dir
+      end
+
+      assert_false(File.exist?(File.join(lock_dir, "fluentd-0.lock")))
+      assert_true(File.exist?(File.join(lock_dir, "unrelated.txt")))
+    end
+  end
+
   sub_test_case "zero_downtime_restart" do
     setup do
       omit "Not supported on Windows" if Fluent.windows?