diff --git a/lib/fluent/plugin/out_secondary_file.rb b/lib/fluent/plugin/out_secondary_file.rb
index 08f027b8de..85d9b000e7 100644
--- a/lib/fluent/plugin/out_secondary_file.rb
+++ b/lib/fluent/plugin/out_secondary_file.rb
@@ -61,20 +61,12 @@ def configure(conf)
 
       @dir_perm = system_config.dir_permission || Fluent::DEFAULT_DIR_PERMISSION
       @file_perm = system_config.file_permission || Fluent::DEFAULT_FILE_PERMISSION
-      @need_worker_lock = system_config.workers > 1
-      @need_thread_lock = @primary_instance.buffer_config.flush_thread_count > 1
     end
 
     def multi_workers_ready?
       true
     end
 
-    def start
-      super
-      extend WriteLocker
-      @write_mutex = Mutex.new
-    end
-
     def write(chunk)
       path_without_suffix = extract_placeholders(@path_without_suffix, chunk)
       generate_path(path_without_suffix) do |path|
@@ -152,35 +144,5 @@ def generate_path(path_without_suffix)
 
     class FileAlreadyExist < StandardError
     end
-
-    module WriteLocker
-      def lock_if_need(path)
-        get_worker_lock_if_need(path) do
-          get_thread_lock_if_need do
-            yield
-          end
-        end
-      end
-
-      def get_worker_lock_if_need(path)
-        unless @need_worker_lock
-          yield
-          return
-        end
-        acquire_worker_lock(path) do
-          yield
-        end
-      end
-
-      def get_thread_lock_if_need
-        unless @need_thread_lock
-          yield
-          return
-        end
-        @write_mutex.synchronize do
-          yield
-        end
-      end
-    end
   end
 end
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 5dd5255652..8e821388f5 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -198,6 +198,7 @@ def rollback_count
       def initialize
         super
         @counter_mutex = Mutex.new
+        @flush_thread_mutex = Mutex.new
         @buffering = false
         @delayed_commit = false
         @as_secondary = false
@@ -597,6 +598,47 @@ def terminate
         super
       end
 
+      def actual_flush_thread_count
+        return 0 unless @buffering
+        return @buffer_config.flush_thread_count unless @as_secondary
+        @primary_instance.buffer_config.flush_thread_count
+      end
+
+      # Run the passed block in the appropriate lock condition for multiple threads and workers.
+      # The lock between workers is made for every `worker_lock_name`.
+      # (For multiple workers, the lock is shared if `worker_lock_name` is the same value).
+      # For multiple threads, `worker_lock_name` is not used, and the lock is shared by all
+      # threads in the same process.
+      def lock_if_need(worker_lock_name)
+        get_worker_lock_if_need(worker_lock_name) do
+          get_flush_thread_lock_if_need do
+            yield
+          end
+        end
+      end
+
+      def get_worker_lock_if_need(name)
+        need_worker_lock = system_config.workers > 1
+        unless need_worker_lock
+          yield
+          return
+        end
+        acquire_worker_lock(name) do
+          yield
+        end
+      end
+
+      def get_flush_thread_lock_if_need
+        need_thread_lock = actual_flush_thread_count > 1
+        unless need_thread_lock
+          yield
+          return
+        end
+        @flush_thread_mutex.synchronize do
+          yield
+        end
+      end
+
       def support_in_v12_style?(feature)
         # for plugins written in v0.12 styles
         case feature