Fix to wakeup threads to quit loop in threads

lib/fluent/plugin/output.rb

@@ -181,6 +181,7 @@ def initialize
         @secondary = nil
         @retry = nil
         @dequeued_chunks = nil
+        @output_enqueue_thread = nil
         @output_flush_threads = nil
 
         @simple_chunking = nil
@@ -359,6 +360,9 @@ def start
 
           @buffer.start
 
+          @output_enqueue_thread = nil
+          @output_enqueue_thread_running = true
+
           @output_flush_threads = []
           @output_flush_threads_mutex = Mutex.new
           @output_flush_threads_running = true
@@ -389,7 +393,7 @@ def start
 
           unless @in_tests
             if @flush_mode == :interval || @chunk_key_time
-              thread_create(:enqueue_thread, &method(:enqueue_thread_run))
+              @output_enqueue_thread = thread_create(:enqueue_thread, &method(:enqueue_thread_run))
             end
           end
         end
@@ -416,6 +420,12 @@ def before_shutdown
             force_flush
           end
           @buffer.before_shutdown
+          # Need to ensure to stop enqueueing ... after #shutdown, we cannot write any data
+          @output_enqueue_thread_running = false
+          if @output_enqueue_thread && @output_enqueue_thread.alive?
+            @output_enqueue_thread.wakeup
+            @output_enqueue_thread.join
+          end
         end
 
         super
@@ -1107,7 +1117,7 @@ def enqueue_thread_run
         log.debug "enqueue_thread actually running"
 
         begin
-          while @output_flush_threads_running
+          while @output_enqueue_thread_running
             now_int = Time.now.to_i
             if @output_flush_interrupted
               sleep interval
@@ -1132,16 +1142,17 @@ def enqueue_thread_run
               end
             rescue => e
               raise if @under_plugin_development
-              log.error "unexpected error while checking flushed chunks. ignored.", plugin_id: plugin_id, error_class: e.class, error: e
+              log.error "unexpected error while checking flushed chunks. ignored.", plugin_id: plugin_id, error: e
               log.error_backtrace
+            ensure
+              @output_enqueue_thread_waiting = false
+              @output_enqueue_thread_mutex.unlock
             end
-            @output_enqueue_thread_waiting = false
-            @output_enqueue_thread_mutex.unlock
             sleep interval
           end
         rescue => e
           # normal errors are rescued by inner begin-rescue clause.
-          log.error "error on enqueue thread", plugin_id: plugin_id, error_class: e.class, error: e
+          log.error "error on enqueue thread", plugin_id: plugin_id, error: e
           log.error_backtrace
           raise
         end

lib/fluent/plugin_helper/thread.rb

@@ -70,7 +70,7 @@ def thread_create(title)
             thread_exit = true
             raise
           ensure
-            unless thread_exit
+            if ::Thread.current.alive? && !thread_exit
               log.warn "thread doesn't exit correctly (killed or other reason)", plugin: self.class, title: title, thread: ::Thread.current, error: $!
             end
             @_threads_mutex.synchronize do
@@ -110,11 +110,31 @@ def initialize
 
       def stop
         super
+        wakeup_threads = []
         @_threads_mutex.synchronize do
-          @_threads.each_pair do |obj_id, thread|
+          @_threads.values.each do |thread|
             thread[:_fluentd_plugin_helper_thread_running] = false
+            wakeup_threads << thread if thread.alive? && thread.status == "sleep"
           end
         end
+        wakeup_threads.each do |thread|
+          if thread.alive?
+            thread.wakeup
+          end
+        end
+      end
+
+      def after_shutdown
+        super
+        wakeup_threads = []
+        @_threads_mutex.synchronize do
+          @_threads.values.each do |thread|
+            wakeup_threads << thread if thread.alive? && thread.status == "sleep"
+          end
+        end
+        wakeup_threads.each do |thread|
+          thread.wakeup if thread.alive?
+        end
       end
 
       def close