[logger] Move common handler code to logger_h_common

There was a lot of duplicated code in logger_std_h and
logger_disk_log_h. Most of this is now moved to logger_h_common, which
now also serves as the gen_server callback.

3 files changed, 796 insertions, 1164 deletions

diff --git a/lib/kernel/src/logger_disk_log_h.erl b/lib/kernel/src/logger_disk_log_h.erl
index 2a81458ec8..8c09dd071f 100644
--- a/lib/kernel/src/logger_disk_log_h.erl
+++ b/lib/kernel/src/logger_disk_log_h.erl
@@ -19,59 +19,35 @@
 %%
 -module(logger_disk_log_h).
 
--behaviour(gen_server).
-
 -include("logger.hrl").
 -include("logger_internal.hrl").
 -include("logger_h_common.hrl").
 
 %%% API
--export([start_link/3, info/1, filesync/1, reset/1]).
+-export([info/1, filesync/1, reset/1]).
 
-%% gen_server callbacks
--export([init/1, handle_call/3, handle_cast/2, handle_info/2,
-         terminate/2, code_change/3]).
+%% logger_h_common callbacks
+-export([init/2, check_config/4, reset_state/1,
+         async_filesync/2, sync_filesync/2,
+         async_write/3, sync_write/3,
+         handle_info/2, terminate/3]).
 
 %% logger callbacks
 -export([log/2, adding_handler/1, removing_handler/1, changing_config/3,
          filter_config/1]).
 
-%% handler internal
--export([log_handler_info/4]).
-
 %%%===================================================================
 %%% API
 %%%===================================================================
 
 %%%-----------------------------------------------------------------
-%%% Start a disk_log handler process and link to caller.
-%%% This function is called by the kernel supervisor when this
-%%% handler process gets added (as a result of calling add/3).
--spec start_link(Name, Config, HandlerState) -> {ok,Pid} | {error,Reason} when
-      Name :: atom(),
-      Config :: logger:handler_config(),
-      HandlerState :: map(),
-      Pid :: pid(),
-      Reason :: term().
-
-start_link(Name, Config, HandlerState) ->
-    proc_lib:start_link(?MODULE,init,[[Name,Config,HandlerState]]).
-
-%%%-----------------------------------------------------------------
 %%%
 -spec filesync(Name) -> ok | {error,Reason} when
       Name :: atom(),
       Reason :: handler_busy | {badarg,term()}.
 
-filesync(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        disk_log_sync, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;
 filesync(Name) ->
-    {error,{badarg,{filesync,[Name]}}}.
+    logger_h_common:filesync(?MODULE,Name).
 
 %%%-----------------------------------------------------------------
 %%%
@@ -80,15 +56,8 @@ filesync(Name) ->
       Info :: term(),
       Reason :: handler_busy | {badarg,term()}.
 
-info(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        info, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;
 info(Name) ->
-    {error,{badarg,{info,[Name]}}}.
+    logger_h_common:info(?MODULE,Name).
 
 %%%-----------------------------------------------------------------
 %%%
@@ -96,16 +65,8 @@ info(Name) ->
       Name :: atom(),
       Reason :: handler_busy | {badarg,term()}.
 
-reset(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        reset, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;      
 reset(Name) ->
-    {error,{badarg,{reset,[Name]}}}.
-
+    logger_h_common:reset(?MODULE,Name).
 
 %%%===================================================================
 %%% logger callbacks
@@ -113,30 +74,55 @@ reset(Name) ->
 
 %%%-----------------------------------------------------------------
 %%% Handler being added
-adding_handler(#{id:=Name}=Config) ->
-    case check_config(adding, Config) of
-        {ok, #{config:=HConfig}=Config1} ->
-            %% create initial handler state by merging defaults with config
-            HState = maps:merge(get_init_state(), HConfig),
-            case logger_h_common:overload_levels_ok(HState) of
-                true ->
-                    start(Name, Config1, HState);
-                false ->
-                    #{sync_mode_qlen := SMQL,
-                      drop_mode_qlen := DMQL,
-                      flush_qlen     := FQL} = HState, 
-                    {error,{invalid_levels,{SMQL,DMQL,FQL}}}
-            end;
+adding_handler(Config) ->
+    logger_h_common:adding_handler(Config).
+
+%%%-----------------------------------------------------------------
+%%% Updating handler config
+changing_config(SetOrUpdate, OldConfig, NewConfig) ->
+    logger_h_common:changing_config(SetOrUpdate, OldConfig, NewConfig).
+
+%%%-----------------------------------------------------------------
+%%% Handler being removed
+removing_handler(Config) ->
+    logger_h_common:removing_handler(Config).
+
+%%%-----------------------------------------------------------------
+%%% Log a string or report
+-spec log(LogEvent, Config) -> ok when
+      LogEvent :: logger:log_event(),
+      Config :: logger:handler_config().
+
+log(LogEvent, Config) ->
+    logger_h_common:log(LogEvent, Config).
+
+%%%-----------------------------------------------------------------
+%%% Remove internal fields from configuration
+filter_config(Config) ->
+    logger_h_common:filter_config(Config).
+
+%%%===================================================================
+%%% logger_h_common callbacks
+%%%===================================================================
+init(Name, #{file:=File,type:=Type,max_no_bytes:=MNB,max_no_files:=MNF}) ->
+    case open_disk_log(Name, File, Type, MNB, MNF) of
+        ok ->
+            {ok,#{log_opts => #{file => File,
+                                type => Type,
+                                max_no_bytes => MNB,
+                                max_no_files => MNF},
+                  prev_log_result => ok,
+                  prev_sync_result => ok,
+                  prev_disk_log_info => undefined}};
         Error ->
             Error
     end.
 
-%%%-----------------------------------------------------------------
-%%% Updating handler config
-changing_config(SetOrUpdate,OldConfig=#{config:=OldHConfig},NewConfig) ->
+check_config(Name,set,undefined,HConfig0) ->
+    HConfig=merge_default_logopts(Name,maps:merge(get_default_config(),HConfig0)),
+    check_config(HConfig);
+check_config(_Name,SetOrUpdate,OldHConfig,NewHConfig0) ->
     WriteOnce = maps:with([type,file,max_no_files,max_no_bytes],OldHConfig),
-    ReadOnly = maps:with([handler_pid,mode_tab],OldHConfig),
-    NewHConfig0 = maps:get(config, NewConfig, #{}),
     Default =
         case SetOrUpdate of
             set ->
@@ -146,66 +132,25 @@ changing_config(SetOrUpdate,OldConfig=#{config:=OldHConfig},NewConfig) ->
                 OldHConfig
         end,
 
-    %% Allow (accidentially) included read-only fields - just overwrite them
-    NewHConfig = maps:merge(maps:merge(Default,NewHConfig0),ReadOnly),
+    NewHConfig = maps:merge(Default,NewHConfig0),
 
-    %% But fail if write-once fields are changed
+    %% Fail if write-once fields are changed
     case maps:with([type,file,max_no_files,max_no_bytes],NewHConfig) of
         WriteOnce ->
-            changing_config1(maps:get(handler_pid,OldHConfig),
-                             OldConfig,
-                             NewConfig#{config=>NewHConfig});
+            check_config(NewHConfig);
         Other ->
             {Old,New} = logger_server:diff_maps(WriteOnce,Other),
-            {error,{illegal_config_change,#{config=>Old},#{config=>New}}}
+            {error,{illegal_config_change,?MODULE,Old,New}}
     end.
 
-changing_config1(HPid, OldConfig, NewConfig) ->
-    case check_config(changing, NewConfig) of
-        Result = {ok,NewConfig1} ->
-            try gen_server:call(HPid, {change_config,OldConfig,NewConfig1},
-                                ?DEFAULT_CALL_TIMEOUT) of
-                ok      -> Result;
-                Error  -> Error
-            catch
-                _:{timeout,_} -> {error,handler_busy}
-            end;
-        Error ->
-            Error
-    end.
-
-check_config(adding, #{id:=Name}=Config) ->
-    %% merge handler specific config data
-    HConfig1 = maps:get(config, Config, #{}),
-    HConfig2 = maps:merge(get_default_config(), HConfig1),
-    HConfig3 = merge_default_logopts(Name, HConfig2),
-    case check_h_config(maps:to_list(HConfig3)) of
-        ok ->
-            {ok,Config#{config=>HConfig3}};
-        Error ->
-            Error
-    end;
-check_config(changing, Config) ->
-    HConfig = maps:get(config, Config, #{}),
+check_config(HConfig) ->
     case check_h_config(maps:to_list(HConfig)) of
-        ok    -> {ok,Config};
-        Error -> Error
+        ok ->
+            {ok,HConfig};
+        {error,{Key,Value}} ->
+            {error,{invalid_config,?MODULE,#{Key=>Value}}}
     end.
 
-merge_default_logopts(Name, HConfig) ->
-    Type = maps:get(type, HConfig, wrap),
-    {DefaultNoFiles,DefaultNoBytes} =
-        case Type of
-            halt -> {undefined,infinity};
-            _wrap -> {10,1048576}
-        end,
-    {ok,Dir} = file:get_cwd(),
-    Defaults = #{file => filename:join(Dir,Name),
-                 max_no_files => DefaultNoFiles,
-                 max_no_bytes => DefaultNoBytes,
-                 type => Type},
-    maps:merge(Defaults, HConfig).
-
 check_h_config([{file,File}|Config]) when is_list(File) ->
     check_h_config(Config);
 check_h_config([{max_no_files,undefined}|Config]) ->
@@ -218,454 +163,75 @@ check_h_config([{max_no_bytes,N}|Config]) when is_integer(N), N>0 ->
     check_h_config(Config);
 check_h_config([{type,Type}|Config]) when Type==wrap; Type==halt ->
     check_h_config(Config);
-check_h_config([Other | Config]) ->
-    case logger_h_common:check_common_config(Other) of
-        valid ->
-            check_h_config(Config);
-        invalid ->
-            {error,{invalid_config,?MODULE,Other}}
-    end;
+check_h_config([Other | _]) ->
+    {error,Other};
 check_h_config([]) ->
     ok.
 
-%%%-----------------------------------------------------------------
-%%% Handler being removed
-removing_handler(#{id:=Name}) ->
-    stop(Name).
+get_default_config() ->
+     #{}.
 
-%%%-----------------------------------------------------------------
-%%% Log a string or report
--spec log(LogEvent, Config) -> ok when
-      LogEvent :: logger:log_event(),
-      Config :: logger:handler_config().
+merge_default_logopts(Name, HConfig) ->
+    Type = maps:get(type, HConfig, wrap),
+    {DefaultNoFiles,DefaultNoBytes} =
+        case Type of
+            halt -> {undefined,infinity};
+            _wrap -> {10,1048576}
+        end,
+    {ok,Dir} = file:get_cwd(),
+    Defaults = #{file => filename:join(Dir,Name),
+                 max_no_files => DefaultNoFiles,
+                 max_no_bytes => DefaultNoBytes,
+                 type => Type},
+    maps:merge(Defaults, HConfig).
 
-log(LogEvent, Config = #{id := Name,
-                         config := #{handler_pid := HPid,
-                                     mode_tab := ModeTab}}) ->
-    %% if the handler has crashed, we must drop this event
-    %% and hope the handler restarts so we can try again
-    true = is_process_alive(HPid),
-    Bin = logger_h_common:log_to_binary(LogEvent, Config),
-    logger_h_common:call_cast_or_drop(Name, HPid, ModeTab, Bin).
+async_filesync(Name,State) ->
+    {_,State1} = disk_log_sync(Name,State),
+    State1.
 
-%%%-----------------------------------------------------------------
-%%% Remove internal fields from configuration
-filter_config(#{config:=HConfig}=Config) ->
-    Config#{config=>maps:without([handler_pid,mode_tab],HConfig)}.
+sync_filesync(Name,State) ->
+    disk_log_sync(Name,State).
 
-%%%===================================================================
-%%% gen_server callbacks
-%%%===================================================================
+async_write(Name, Bin, State) ->
+    {_,State1} = disk_log_write(Name, Bin, State),
+    State1.
 
-init([Name,
-      Config = #{config := HConfig = #{file:=File,
-                                       type:=Type,
-                                       max_no_bytes:=MNB,
-                                       max_no_files:=MNF}},
-      State = #{dl_sync_int := DLSyncInt}]) ->
-
-    RegName = ?name_to_reg_name(?MODULE,Name),
-    register(RegName, self()),
-    process_flag(trap_exit, true),
-    process_flag(message_queue_data, off_heap),
-
-    ?init_test_hooks(),
-    ?start_observation(Name),
-    
-    LogOpts = #{file=>File, type=>Type, max_no_bytes=>MNB, max_no_files=>MNF},
-    case open_disk_log(Name, File, Type, MNB, MNF) of
-        ok ->
-            try ets:new(Name, [public]) of
-                ModeTab ->
-                    ?set_mode(ModeTab, async),
-                    T0 = ?timestamp(),
-                    State1 =
-                        ?merge_with_stats(State#{
-                                            id => Name,
-                                            mode_tab => ModeTab,
-                                            mode => async,
-                                            dl_sync => DLSyncInt,
-                                            log_opts => LogOpts,
-                                            last_qlen => 0,
-                                            last_log_ts => T0,
-                                            burst_win_ts => T0,
-                                            burst_msg_count => 0,
-                                            last_op => sync,
-                                            prev_log_result => ok,
-                                            prev_sync_result => ok,
-                                            prev_disk_log_info => undefined}),
-                    Config1 =
-                        Config#{config => HConfig#{handler_pid => self(),
-                                                   mode_tab => ModeTab}},
-                    proc_lib:init_ack({ok,self(),Config1}),
-                    gen_server:cast(self(), repeated_disk_log_sync),
-                    case logger_h_common:unset_restart_flag(Name, ?MODULE) of
-                        true ->
-                            %% inform about restart
-                            gen_server:cast(self(), {log_handler_info,
-                                                     "Handler ~p restarted",
-                                                     [Name]});
-                        false ->
-                            %% initial start
-                            ok
-                    end,
-                    gen_server:enter_loop(?MODULE, [], State1)
-            catch
-                _:Error ->
-                    unregister(RegName),
-                    logger_h_common:error_notify({open_disk_log,Name,Error}),
-                    proc_lib:init_ack(Error)
-            end;
-        Error ->
-            unregister(RegName),
-            logger_h_common:error_notify({open_disk_log,Name,Error}),
-            proc_lib:init_ack(Error)
-    end.
+sync_write(Name, Bin, State) ->
+    disk_log_write(Name, Bin, State).
 
-%% This is the synchronous log event.
-handle_call({log, Bin}, _From, State) ->
-    {Result,State1} = do_log(Bin, call, State),
-    %% Result == ok | dropped
-    {reply, Result, State1};
-
-handle_call(disk_log_sync, _From, State = #{id := Name}) ->
-    State1 = #{prev_sync_result := Result} = disk_log_sync(Name, State),
-    {reply, Result, State1};
-
-handle_call({change_config,_OldConfig,NewConfig}, _From,
-            State = #{filesync_repeat_interval := FSyncInt0}) ->
-    HConfig = maps:get(config, NewConfig, #{}),
-    State1 = #{sync_mode_qlen := SMQL,
-               drop_mode_qlen := DMQL,
-               flush_qlen     := FQL} = maps:merge(State, HConfig),
-    case logger_h_common:overload_levels_ok(State1) of
-        true ->
-            _ = 
-                case maps:get(filesync_repeat_interval, HConfig, undefined) of
-                    undefined ->
-                        ok;
-                    no_repeat ->
-                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
-                                                                  State,
-                                                                  undefined));
-                    FSyncInt0 ->
-                        ok;
-                    _FSyncInt1 ->
-                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
-                                                                  State,
-                                                                  undefined)),
-                        _ = gen_server:cast(self(), repeated_disk_log_sync)
-                end,
-            {reply, ok, State1};
-        false ->
-            {reply, {error,{invalid_levels,{SMQL,DMQL,FQL}}}, State}
-    end;
-
-handle_call(info, _From, State) ->
-    {reply, State, State};
-
-handle_call(reset, _From, State) ->
-    State1 = ?merge_with_stats(State),
-    {reply, ok, State1#{last_qlen => 0,
-                        last_log_ts => ?timestamp(),
-                        prev_log_result => ok,
-                        prev_sync_result => ok,
-                        prev_disk_log_info => undefined}};
-
-handle_call(stop, _From, State) ->
-    {stop, {shutdown,stopped}, ok, State}.
-
-
-%% This is the asynchronous log event.
-handle_cast({log, Bin}, State) ->
-    {_,State1} = do_log(Bin, cast, State),
-    {noreply, State1};
-
-handle_cast({log_handler_info, Format, Args}, State = #{id:=Name}) ->
-    log_handler_info(Name, Format, Args, State),
-    {noreply, State};
-
-%% If FILESYNC_REPEAT_INTERVAL is set to a millisec value, this
-%% clause gets called repeatedly by the handler. In order to
-%% guarantee that a filesync *always* happens after the last log
-%% event, the repeat operation must be active!
-handle_cast(repeated_disk_log_sync,
-            State = #{id := Name,
-                      filesync_repeat_interval := FSyncInt,
-                      last_op := LastOp}) ->
-    State1 =
-        if is_integer(FSyncInt) ->
-                %% only do filesync if something has been
-                %% written since last time we checked
-                NewState = if LastOp == sync ->
-                                   State;
-                              true ->
-                                   disk_log_sync(Name, State)
-                           end,
-                {ok,TRef} =
-                    timer:apply_after(FSyncInt, gen_server,cast,
-                                      [self(),repeated_disk_log_sync]),
-                NewState#{rep_sync_tref => TRef, last_op => sync};
-           true ->
-                State
-        end,
-    {noreply,State1}.
+reset_state(State) ->
+    State#{prev_log_result => ok,
+           prev_sync_result => ok,
+           prev_disk_log_info => undefined}.
 
 %% The disk log owner must handle status messages from disk_log.
 handle_info({disk_log, _Node, _Log, {wrap,_NoLostItems}}, State) ->
-    {noreply, State};
+    State;
 handle_info({disk_log, _Node, Log, Info = {truncated,_NoLostItems}},
             State = #{id := Name, prev_disk_log_info := PrevInfo}) ->
     error_notify_new(Info, PrevInfo, {disk_log,Name,Log,Info}),
-    {noreply, State#{prev_disk_log_info => Info}};
+    State#{prev_disk_log_info => Info};
 handle_info({disk_log, _Node, Log, Info = {blocked_log,_Items}},
             State = #{id := Name, prev_disk_log_info := PrevInfo}) ->
     error_notify_new(Info, PrevInfo, {disk_log,Name,Log,Info}),
-    {noreply, State#{prev_disk_log_info => Info}};
+    State#{prev_disk_log_info => Info};
 handle_info({disk_log, _Node, Log, full},
             State = #{id := Name, prev_disk_log_info := PrevInfo}) ->
     error_notify_new(full, PrevInfo, {disk_log,Name,Log,full}),
-    {noreply, State#{prev_disk_log_info => full}};
+    State#{prev_disk_log_info => full};
 handle_info({disk_log, _Node, Log, Info = {error_status,_Status}},
             State = #{id := Name, prev_disk_log_info := PrevInfo}) ->
     error_notify_new(Info, PrevInfo, {disk_log,Name,Log,Info}),
-    {noreply, State#{prev_disk_log_info => Info}};
-
-handle_info({'EXIT',_Pid,_Why}, State = #{id := _Name}) ->
-    {noreply, State};
-
+    State#{prev_disk_log_info => Info};
 handle_info(_, State) ->
-    {noreply, State}.
+    State.
 
-terminate(Reason, State = #{id := Name}) ->
-    _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref, State,
-                                              undefined)),
+terminate(Name, _Reason, _State) ->
     _ = close_disk_log(Name, normal),
-    ok = logger_h_common:stop_or_restart(Name, Reason, State),
-    unregister(?name_to_reg_name(?MODULE, Name)),
     ok.
 
-code_change(_OldVsn, State, _Extra) ->
-    {ok, State}.
-
 %%%-----------------------------------------------------------------
 %%% Internal functions
-
-%%%-----------------------------------------------------------------
-%%%
-get_default_config() ->
-     #{sync_mode_qlen              => ?SYNC_MODE_QLEN,
-       drop_mode_qlen              => ?DROP_MODE_QLEN,
-       flush_qlen                  => ?FLUSH_QLEN,
-       burst_limit_enable          => ?BURST_LIMIT_ENABLE,
-       burst_limit_max_count       => ?BURST_LIMIT_MAX_COUNT,
-       burst_limit_window_time     => ?BURST_LIMIT_WINDOW_TIME,
-       overload_kill_enable        => ?OVERLOAD_KILL_ENABLE,
-       overload_kill_qlen          => ?OVERLOAD_KILL_QLEN,
-       overload_kill_mem_size      => ?OVERLOAD_KILL_MEM_SIZE,
-       overload_kill_restart_after => ?OVERLOAD_KILL_RESTART_AFTER,
-       filesync_repeat_interval    => ?FILESYNC_REPEAT_INTERVAL}.
-
-get_init_state() ->
-     #{dl_sync_int                 => ?CONTROLLER_SYNC_INTERVAL,
-       filesync_ok_qlen            => ?FILESYNC_OK_QLEN}.
-
-%%%-----------------------------------------------------------------
-%%% Add a disk_log handler to the logger.
-%%% This starts a dedicated handler process which should always
-%%% exist if the handler is registered with logger (and should not
-%%% exist if the handler is not registered).
-%%%
-%%% Config is the logger:handler_config() map. Handler specific parameters
-%%% should be provided with a sub map associated with a key named
-%%% 'config', e.g:
-%%%
-%%% Config = #{config => #{sync_mode_qlen => 50}
-%%%
-%%% The 'config' sub map will also contain parameters for configuring
-%%% the disk_log:
-%%%
-%%% Config = #{config => #{file          => file:filename(),
-%%%                        max_no_bytes  => integer(),
-%%%                        max_no_files  => integer(),
-%%%                        type          => wrap | halt}}.
-%%%
-%%% If type == halt, then max_no_files is ignored.
-%%%
-%%% The disk_log handler process is linked to logger_sup, which is
-%%% part of the kernel application's supervision tree.
-start(Name, Config, HandlerState) ->
-    LoggerDLH =
-        #{id       => Name,
-          start    => {?MODULE, start_link, [Name,Config,HandlerState]},
-          restart  => temporary,
-          shutdown => 2000,
-          type     => worker,
-          modules  => [?MODULE]},
-    case supervisor:start_child(logger_sup, LoggerDLH) of
-        {ok,Pid,Config1} ->
-            ok = logger_handler_watcher:register_handler(Name,Pid),
-            {ok,Config1};
-        Error ->
-            Error
-    end.
-
-%%%-----------------------------------------------------------------
-%%% Stop and remove the handler.
-stop(Name) ->
-    case whereis(?name_to_reg_name(?MODULE,Name)) of
-        undefined ->
-            ok;
-        Pid ->
-            %% We don't want to do supervisor:terminate_child here
-            %% since we need to distinguish this explicit stop from a
-            %% system termination in order to avoid circular attempts
-            %% at removing the handler (implying deadlocks and
-            %% timeouts).
-            %% And we don't need to do supervisor:delete_child, since
-            %% the restart type is temporary, which means that the
-            %% child specification is automatically removed from the
-            %% supervisor when the process dies.
-            _ = gen_server:call(Pid, stop),
-            ok
-    end.
-
-%%%-----------------------------------------------------------------
-%%% Logging and overload control.
--define(update_dl_sync(C, Interval),
-        if C == 0 -> Interval;
-           true -> C-1 end).
-
-%% check for overload between every event (and set Mode to async,
-%% sync or drop accordingly), but never flush the whole mailbox
-%% before LogWindowSize events have been handled
-do_log(Bin, CallOrCast, State = #{id:=Name, mode := Mode0}) ->
-    T1 = ?timestamp(),
-
-    %% check if the handler is getting overloaded, or if it's
-    %% recovering from overload (the check must be done for each
-    %% event to react quickly to large bursts of events and
-    %% to ensure that the handler can never end up in drop mode
-    %% with an empty mailbox, which would stop operation)
-    {Mode1,QLen,Mem,State1} = logger_h_common:check_load(State),
-
-    if (Mode1 == drop) andalso (Mode0 =/= drop) ->
-            log_handler_info(Name, "Handler ~p switched to drop mode",
-                              [Name], State);
-       (Mode0 == drop) andalso ((Mode1 == async) orelse (Mode1 == sync)) ->
-            log_handler_info(Name, "Handler ~p switched to ~w mode",
-                             [Name,Mode1], State);
-       true ->
-            ok
-    end,    
-
-    %% kill the handler if it can't keep up with the load
-    logger_h_common:kill_if_choked(Name, QLen, Mem, ?MODULE, State),
-
-    if Mode1 == flush ->            
-            flush(Name, QLen, T1, State1);
-       true ->
-            write(Name, Mode1, T1, Bin, CallOrCast, State1)
-    end.
-
-%% this function is called by do_log/3 after an overload check
-%% has been performed, where QLen > FlushQLen
-flush(Name, _QLen0, T1, State=#{last_log_ts := _T0, mode_tab := ModeTab}) ->
-    %% flush messages in the mailbox (a limited number in
-    %% order to not cause long delays)
-    NewFlushed = logger_h_common:flush_log_events(?FLUSH_MAX_N),
-
-    %% write info in log about flushed messages
-    log_handler_info(Name, "Handler ~p flushed ~w log events",
-                      [Name,NewFlushed], State),
-
-    %% because of the receive loop when flushing messages, the
-    %% handler will be scheduled out often and the mailbox could
-    %% grow very large, so we'd better check the queue again here
-    {_,_QLen1} = process_info(self(), message_queue_len),
-    ?observe(Name,{max_qlen,_QLen1}),
-
-    %% Add 1 for the current log event
-    ?observe(Name,{flushed,NewFlushed+1}),
-
-    State1 = ?update_max_time(?diff_time(T1,_T0),State),
-    {dropped,?update_other(flushed,FLUSHED,NewFlushed,
-                           State1#{mode => ?set_mode(ModeTab,async),
-                                   last_qlen => 0,
-                                   last_log_ts => T1})}.
-
-%% this function is called to write to disk_log
-write(Name, Mode, T1, Bin, _CallOrCast,
-      State = #{mode_tab := ModeTab,
-                dl_sync := DLSync,
-                dl_sync_int := DLSyncInt,
-                last_qlen := LastQLen,
-                last_log_ts := T0}) ->
-    %% check if we need to limit the number of writes
-    %% during a burst of log events
-    {DoWrite,BurstWinT,BurstMsgCount} = logger_h_common:limit_burst(State),
-
-    %% only send a synhrounous event to the disk_log process
-    %% every DLSyncInt time, to give the handler time between
-    %% writes so it can keep up with incoming messages
-    {Status,LastQLen1,State1} =
-        if DoWrite, DLSync == 0 ->
-                ?observe(Name,{_CallOrCast,1}),
-                NewState = disk_log_write(Name, Bin, State),
-                {ok, element(2,process_info(self(),message_queue_len)),
-                 NewState};
-           DoWrite ->
-                ?observe(Name,{_CallOrCast,1}),
-                NewState = disk_log_write(Name, Bin, State),
-                {ok, LastQLen, NewState};
-           not DoWrite ->
-                ?observe(Name,{flushed,1}),
-                {dropped, LastQLen, State}
-        end,
-
-    %% Check if the time since the previous log event is long enough -
-    %% and the queue length small enough - to assume the mailbox has
-    %% been emptied, and if so, do filesync operation and reset mode to
-    %% async. Note that this is the best we can do to detect an idle
-    %% handler without setting a timer after each log call/cast. If the
-    %% time between two consecutive log events is fast and no new
-    %% event comes in after the last one, idle state won't be detected!
-    Time = ?diff_time(T1,T0),
-    {Mode1,BurstMsgCount1,State2} =
-        if (LastQLen1 < ?FILESYNC_OK_QLEN) andalso
-           (Time > ?IDLE_DETECT_TIME_USEC) ->
-                {?change_mode(ModeTab,Mode,async), 0, disk_log_sync(Name,State1)};
-           true ->
-                {Mode, BurstMsgCount,State1}
-        end,
-    
-    State3 =
-        ?update_calls_or_casts(_CallOrCast,1,State2),
-    State4 =
-        ?update_max_time(Time,
-                         State3#{mode => Mode1,
-                                 last_qlen := LastQLen1,
-                                 last_log_ts => T1,
-                                 burst_win_ts => BurstWinT,
-                                 burst_msg_count => BurstMsgCount1,
-                                 dl_sync => ?update_dl_sync(DLSync,DLSyncInt)}),
-    {Status,State4}.
-
-
-log_handler_info(Name, Format, Args, State) ->
-    Config =
-        case logger:get_handler_config(Name) of
-            {ok,Conf} -> Conf;
-            _ -> #{formatter=>{?DEFAULT_FORMATTER,?DEFAULT_FORMAT_CONFIG}}
-        end,
-    Meta = #{time=>erlang:system_time(microsecond)},
-    Bin = logger_h_common:log_to_binary(#{level => notice,
-                                          msg => {Format,Args},
-                                          meta => Meta}, Config),
-    _ = disk_log_write(Name, Bin, State),
-    ok.
-
-
 open_disk_log(Name, File, Type, MaxNoBytes, MaxNoFiles) ->
     case filelib:ensure_dir(File) of
         ok ->
@@ -701,7 +267,7 @@ close_disk_log(Name, _) ->
 disk_log_write(Name, Bin, State) ->
         case ?disk_log_blog(Name, Bin) of
             ok ->
-                State#{prev_log_result => ok, last_op => write};
+                {ok,State#{prev_log_result => ok, last_op => write}};
             LogError ->
                 _ = case maps:get(prev_log_result, State) of
                         LogError ->
@@ -713,13 +279,13 @@ disk_log_write(Name, Bin, State) ->
                                                           LogOpts,
                                                           LogError})
                     end,
-                State#{prev_log_result => LogError}
+                {LogError,State#{prev_log_result => LogError}}
         end.
 
 disk_log_sync(Name, State) ->
     case ?disk_log_sync(Name) of
         ok ->
-            State#{prev_sync_result => ok, last_op => sync};
+            {ok,State#{prev_sync_result => ok, last_op => sync}};
         SyncError ->
             _ = case maps:get(prev_sync_result, State) of
                     SyncError ->
@@ -731,7 +297,7 @@ disk_log_sync(Name, State) ->
                                                       LogOpts,
                                                       SyncError})
                 end,
-            State#{prev_sync_result => SyncError}
+            {SyncError,State#{prev_sync_result => SyncError}}
     end.
 
 error_notify_new(Info,Info, _Term) ->
diff --git a/lib/kernel/src/logger_h_common.erl b/lib/kernel/src/logger_h_common.erl
index 94c640cb92..d01851b2b1 100644
--- a/lib/kernel/src/logger_h_common.erl
+++ b/lib/kernel/src/logger_h_common.erl
@@ -18,26 +18,541 @@
 %% %CopyrightEnd%
 %%
 -module(logger_h_common).
+-behaviour(gen_server).
 
 -include("logger_h_common.hrl").
 -include("logger_internal.hrl").
 
--export([log_to_binary/2,
-         check_common_config/1,
-         call_cast_or_drop/4,
-         check_load/1,
-         limit_burst/1,
-         kill_if_choked/5,
-         flush_log_events/0,
-         flush_log_events/1,
-         handler_exit/2,
-         set_restart_flag/2,
-         unset_restart_flag/2,
-         cancel_timer/1,
-         stop_or_restart/3,
-         overload_levels_ok/1,
-         error_notify/1,
-         info_notify/1]).
+%% API
+-export([start_link/3, info/2, filesync/2, reset/2]).
+
+%% gen_server and proc_lib callbacks
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
+         terminate/2, code_change/3]).
+
+%% logger callbacks
+-export([log/2, adding_handler/1, removing_handler/1, changing_config/3,
+         filter_config/1]).
+
+%% Library functions for handlers
+-export([error_notify/1]).
+
+%%%-----------------------------------------------------------------
+-define(CONFIG_KEYS,[sync_mode_qlen,
+                     drop_mode_qlen,
+                     flush_qlen,
+                     burst_limit_enable,
+                     burst_limit_max_count,
+                     burst_limit_window_time,
+                     overload_kill_enable,
+                     overload_kill_qlen,
+                     overload_kill_mem_size,
+                     overload_kill_restart_after,
+                     filesync_repeat_interval]).
+-define(READ_ONLY_KEYS,[handler_pid,mode_tab]).
+
+%%%-----------------------------------------------------------------
+%%%
+filesync(Module, Name) when is_atom(Name) ->
+    try
+        gen_server:call(?name_to_reg_name(Module,Name),
+                        filesync, ?DEFAULT_CALL_TIMEOUT)
+    catch
+        _:{timeout,_} -> {error,handler_busy}
+    end;
+filesync(_, Name) ->
+    {error,{badarg,{filesync,[Name]}}}.
+
+info(Module, Name) when is_atom(Name) ->
+    try
+        gen_server:call(?name_to_reg_name(Module,Name),
+                        info, ?DEFAULT_CALL_TIMEOUT)
+    catch
+        _:{timeout,_} -> {error,handler_busy}
+    end;
+info(_, Name) ->
+    {error,{badarg,{info,[Name]}}}.
+
+reset(Module, Name) when is_atom(Name) ->
+    try
+        gen_server:call(?name_to_reg_name(Module,Name),
+                        reset, ?DEFAULT_CALL_TIMEOUT)
+    catch
+        _:{timeout,_} -> {error,handler_busy}
+    end;
+reset(_, Name) ->
+    {error,{badarg,{reset,[Name]}}}.
+
+
+
+%%%-----------------------------------------------------------------
+%%% Handler being added
+adding_handler(#{id:=Name,module:=Module}=Config) ->
+    HConfig = maps:get(config, Config, #{}),
+    HandlerConfig0 = maps:without(?CONFIG_KEYS,HConfig),
+    case Module:check_config(Name,set,undefined,HandlerConfig0) of
+        {ok,HandlerConfig} ->
+            ModifiedCommon = maps:with(?CONFIG_KEYS,HandlerConfig),
+            CommonConfig0 = maps:with(?CONFIG_KEYS,HConfig),
+            CommonConfig = maps:merge(
+                             maps:merge(get_default_config(), CommonConfig0),
+                             ModifiedCommon),
+            case check_config(CommonConfig) of
+                ok ->
+                    State = maps:merge(get_init_state(), CommonConfig),
+                    HConfig1 = maps:merge(CommonConfig,HandlerConfig),
+                    Config1 = Config#{config=>HConfig1},
+                    case overload_levels_ok(State) of
+                        true ->
+                            start(Name, Config1, State);
+                        false ->
+                            #{sync_mode_qlen := SMQL,
+                              drop_mode_qlen := DMQL,
+                              flush_qlen     := FQL} = State,
+                            {error,{invalid_levels,{SMQL,DMQL,FQL}}}
+                    end;
+                {error,Faulty} ->
+                    {error,{invalid_config,Module,Faulty}}
+            end;
+        Error ->
+            Error
+    end.
+
+%%%-----------------------------------------------------------------
+%%% Handler being removed
+removing_handler(#{id:=Name, module:=Module}) ->
+    case whereis(?name_to_reg_name(Module,Name)) of
+        undefined ->
+            ok;
+        Pid ->
+            %% We don't want to do supervisor:terminate_child here
+            %% since we need to distinguish this explicit stop from a
+            %% system termination in order to avoid circular attempts
+            %% at removing the handler (implying deadlocks and
+            %% timeouts).
+            %% And we don't need to do supervisor:delete_child, since
+            %% the restart type is temporary, which means that the
+            %% child specification is automatically removed from the
+            %% supervisor when the process dies.
+            _ = gen_server:call(Pid, stop),
+            ok
+    end.
+
+%%%-----------------------------------------------------------------
+%%% Updating handler config
+changing_config(SetOrUpdate,
+                OldConfig=#{id:=Name,config:=OldHConfig,module:=Module},
+                NewConfig0) ->
+    NewHConfig0 = maps:get(config, NewConfig0, #{}),
+    OldHandlerConfig = maps:without(?CONFIG_KEYS++?READ_ONLY_KEYS,OldHConfig),
+    NewHandlerConfig0 = maps:without(?CONFIG_KEYS++?READ_ONLY_KEYS,NewHConfig0),
+    case Module:check_config(Name, SetOrUpdate,
+                             OldHandlerConfig,NewHandlerConfig0) of
+        {ok, NewHandlerConfig} ->
+            ModifiedCommon = maps:with(?CONFIG_KEYS,NewHandlerConfig),
+            NewCommonConfig0 = maps:with(?CONFIG_KEYS,NewHConfig0),
+            CommonDefault =
+                case SetOrUpdate of
+                    set ->
+                        get_default_config();
+                    update ->
+                        maps:with(?CONFIG_KEYS,OldHConfig)
+                end,
+            NewCommonConfig = maps:merge(
+                                maps:merge(CommonDefault,NewCommonConfig0),
+                                ModifiedCommon),
+            case check_config(NewCommonConfig) of
+                ok ->
+                    ReadOnly = maps:with(?READ_ONLY_KEYS,OldHConfig),
+                    NewHConfig = maps:merge(
+                                   maps:merge(NewCommonConfig,NewHandlerConfig),
+                                   ReadOnly),
+                    NewConfig = NewConfig0#{config=>NewHConfig},
+                    HPid = maps:get(handler_pid,OldHConfig),
+                    try gen_server:call(HPid, {change_config,OldConfig,NewConfig},
+                                        ?DEFAULT_CALL_TIMEOUT) of
+                        ok      -> {ok,NewConfig};
+                        Error  -> Error
+                    catch
+                        _:{timeout,_} -> {error,handler_busy}
+                    end;
+                {error,Faulty} ->
+                    {error,{invalid_config,Module,Faulty}}
+            end;
+        Error ->
+            Error
+    end.
+
+%%%-----------------------------------------------------------------
+%%% Log a string or report
+-spec log(LogEvent, Config) -> ok when
+      LogEvent :: logger:log_event(),
+      Config :: logger:handler_config().
+
+log(LogEvent, Config = #{id := Name,
+                         config := #{handler_pid := HPid,
+                                     mode_tab := ModeTab}}) ->
+    %% if the handler has crashed, we must drop this event
+    %% and hope the handler restarts so we can try again
+    true = is_process_alive(HPid),
+    Bin = log_to_binary(LogEvent, Config),
+    call_cast_or_drop(Name, HPid, ModeTab, Bin).
+
+%%%-----------------------------------------------------------------
+%%% Remove internal fields from configuration
+filter_config(#{config:=HConfig}=Config) ->
+    Config#{config=>maps:without(?READ_ONLY_KEYS,HConfig)}.
+
+%%%-----------------------------------------------------------------
+%%% Add a standard handler to the logger.
+%%% This starts a dedicated handler process which should always
+%%% exist if the handler is registered with logger (and should not
+%%% exist if the handler is not registered).
+%%%
+%%% Handler specific config should be provided with a sub map associated
+%%% with a key named 'config', e.g:
+%%%
+%%% Config = #{config => #{sync_mode_qlen => 50}
+%%%
+%%% The standard handler process is linked to logger_sup, which is
+%%% part of the kernel application's supervision tree.
+start(Name, Config, HandlerState) ->
+    ChildSpec =
+        #{id       => Name,
+          start    => {?MODULE, start_link, [Name,Config,HandlerState]},
+          restart  => temporary,
+          shutdown => 2000,
+          type     => worker,
+          modules  => [?MODULE]},
+    case supervisor:start_child(logger_sup, ChildSpec) of
+        {ok,Pid,Config1} ->
+            ok = logger_handler_watcher:register_handler(Name,Pid),
+            {ok,Config1};
+        Error ->
+            Error
+    end.
+
+%%%-----------------------------------------------------------------
+%%% Start a standard handler process and link to caller.
+%%% This function is called by the kernel supervisor when this
+%%% handler process gets added
+-spec start_link(Name, Config, HandlerState) -> {ok,Pid} | {error,Reason} when
+      Name :: atom(),
+      Config :: logger:handler_config(),
+      HandlerState :: map(),
+      Pid :: pid(),
+      Reason :: term().
+
+start_link(Name, Config, HandlerState) ->
+    proc_lib:start_link(?MODULE,init,[[Name,Config,HandlerState]]).
+
+%%%-----------------------------------------------------------------
+%%%
+get_init_state() ->
+     #{ctrl_sync_int               => ?CONTROLLER_SYNC_INTERVAL,
+       filesync_ok_qlen            => ?FILESYNC_OK_QLEN}.
+
+%%%===================================================================
+%%% gen_server callbacks
+%%%===================================================================
+
+init([Name, Config = #{config := HConfig, module := Module},
+      State = #{filesync_repeat_interval := FSyncInt,
+                ctrl_sync_int := CtrlSyncInt}]) ->
+    RegName = ?name_to_reg_name(Module,Name),
+    register(RegName, self()),
+    process_flag(trap_exit, true),
+    process_flag(message_queue_data, off_heap),
+
+    ?init_test_hooks(),
+    ?start_observation(Name),
+
+    case Module:init(Name, HConfig) of
+        {ok,HState} ->
+            try ets:new(Name, [public]) of
+                ModeTab ->
+                    ?set_mode(ModeTab, async),
+                    T0 = ?timestamp(),
+                    State1 =
+                        ?merge_with_stats(State#{id => Name,
+                                                 module => Module,
+                                                 mode_tab => ModeTab,
+                                                 mode => async,
+                                                 ctrl_sync_count => CtrlSyncInt,
+                                                 last_qlen => 0,
+                                                 last_log_ts => T0,
+                                                 last_op => sync,
+                                                 burst_win_ts => T0,
+                                                 burst_msg_count => 0,
+                                                 handler_state => HState}),
+                    Config1 =
+                        Config#{config => HConfig#{handler_pid => self(),
+                                                   mode_tab => ModeTab}},
+                    proc_lib:init_ack({ok,self(),Config1}),
+                    if is_integer(FSyncInt) ->
+                            gen_server:cast(self(), repeated_filesync);
+                       true ->
+                            ok
+                    end,
+                    case unset_restart_flag(Name, Module) of
+                        true ->
+                            %% inform about restart
+                            gen_server:cast(self(), {log_handler_info,
+                                                     "Handler ~p restarted",
+                                                     [Name]});
+                        false ->
+                            %% initial start
+                            ok
+                    end,
+                    gen_server:enter_loop(?MODULE, [], State1)
+            catch
+                _:Error ->
+                    unregister(RegName),
+                    error_notify({init_handler,Name,Error}),
+                    proc_lib:init_ack(Error)
+            end;
+        Error ->
+            unregister(RegName),
+            error_notify({init_handler,Name,Error}),
+            proc_lib:init_ack(Error)
+    end.
+
+%% This is the synchronous log event.
+handle_call({log, Bin}, _From, State) ->
+    {Result,State1} = do_log(Bin, call, State),
+    %% Result == ok | dropped
+    {reply,Result, State1};
+
+handle_call(filesync, _From, State = #{id := Name,
+                                       module := Module,
+                                       handler_state := HandlerState}) ->
+    {Result,HandlerState1} = Module:sync_filesync(Name,HandlerState),
+    {reply, Result, State#{handler_state=>HandlerState1, last_op=>sync}};
+
+handle_call({change_config,_OldConfig,NewConfig}, _From,
+            State = #{filesync_repeat_interval := FSyncInt0}) ->
+    HConfig = maps:get(config, NewConfig, #{}),
+    State1 = maps:merge(State, HConfig),
+    case overload_levels_ok(State1) of
+        true ->
+            _ =
+                case maps:get(filesync_repeat_interval, HConfig, undefined) of
+                    undefined ->
+                        ok;
+                    no_repeat ->
+                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
+                                                                  State,
+                                                                  undefined));
+                    FSyncInt0 ->
+                        ok;
+                    _FSyncInt1 ->
+                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
+                                                                  State,
+                                                                  undefined)),
+                        gen_server:cast(self(), repeated_filesync)
+                end,
+            {reply, ok, State1};
+        false ->
+            #{sync_mode_qlen := SMQL,
+              drop_mode_qlen := DMQL,
+              flush_qlen     := FQL} = State1,
+            {reply, {error,{invalid_levels,{SMQL,DMQL,FQL}}}, State}
+    end;
+
+handle_call(info, _From, State) ->
+    {reply, State, State};
+
+handle_call(reset, _From, #{module:=Module,handler_state:=HandlerState}=State) ->
+    State1 = ?merge_with_stats(State),
+    {reply, ok, State1#{last_qlen => 0,
+                        last_log_ts => ?timestamp(),
+                        handler_state => Module:reset_state(HandlerState)}};
+
+handle_call(stop, _From, State) ->
+    {stop, {shutdown,stopped}, ok, State}.
+
+%% This is the asynchronous log event.
+handle_cast({log, Bin}, State) ->
+    {_,State1} = do_log(Bin, cast, State),
+    {noreply, State1};
+
+handle_cast({log_handler_info, Format, Args}, State = #{id:=Name}) ->
+    log_handler_info(Name, Format, Args, State),
+    {noreply, State};
+
+%% If FILESYNC_REPEAT_INTERVAL is set to a millisec value, this
+%% clause gets called repeatedly by the handler. In order to
+%% guarantee that a filesync *always* happens after the last log
+%% event, the repeat operation must be active!
+handle_cast(repeated_filesync,State = #{filesync_repeat_interval := no_repeat}) ->
+    {noreply,State};
+handle_cast(repeated_filesync,
+            State = #{id := Name,
+                      module := Module,
+                      handler_state := HandlerState,
+                      filesync_repeat_interval := FSyncInt,
+                      last_op := LastOp}) ->
+    HandlerState1 =
+        if LastOp == sync ->
+                HandlerState;
+           true ->
+                Module:async_filesync(Name,HandlerState)
+        end,
+    {ok,TRef} = timer:apply_after(FSyncInt, gen_server,cast,
+                                  [self(),repeated_filesync]),
+    {noreply,State#{handler_state=>HandlerState1,
+                    rep_sync_tref => TRef,
+                    last_op => sync}}.
+
+handle_info(Info, #{module := Module, handler_state := HandlerState} = State) ->
+    {noreply,State#{handler_state => Module:handle_info(Info,HandlerState)}}.
+
+terminate(Reason, State = #{id := Name,
+                            module := Module,
+                            handler_state := HandlerState}) ->
+    _ = cancel_timer(maps:get(rep_sync_tref, State, undefined)),
+    _ = Module:terminate(Name, Reason, HandlerState),
+    ok = stop_or_restart(Name, Reason, State),
+    unregister(?name_to_reg_name(Module, Name)),
+    ok.
+
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.
+
+
+%% check for overload between every event (and set Mode to async,
+%% sync or drop accordingly), but never flush the whole mailbox
+%% before LogWindowSize events have been handled
+do_log(Bin, CallOrCast, State = #{id:=Name, module:=Module, mode:=Mode0}) ->
+    T1 = ?timestamp(),
+
+    %% check if the handler is getting overloaded, or if it's
+    %% recovering from overload (the check must be done for each
+    %% event to react quickly to large bursts of events and
+    %% to ensure that the handler can never end up in drop mode
+    %% with an empty mailbox, which would stop operation)
+    {Mode1,QLen,Mem,State1} = check_load(State),
+
+    if (Mode1 == drop) andalso (Mode0 =/= drop) ->
+            log_handler_info(Name, "Handler ~p switched to drop mode",
+                             [Name], State);
+       (Mode0 == drop) andalso ((Mode1 == async) orelse (Mode1 == sync)) ->
+            log_handler_info(Name, "Handler ~p switched to ~w mode",
+                             [Name,Mode1], State);
+       true ->
+            ok
+    end,
+
+    %% kill the handler if it can't keep up with the load
+    kill_if_choked(Name, Module, QLen, Mem, State),
+
+    if Mode1 == flush ->
+            flush(Name, QLen, T1, State1);
+       true ->
+            write(Name, Mode1, T1, Bin, CallOrCast, State1)
+    end.
+
+%% this clause is called by do_log/3 after an overload check
+%% has been performed, where QLen > FlushQLen
+flush(Name, _QLen0, T1, State=#{last_log_ts := _T0, mode_tab := ModeTab}) ->
+    %% flush messages in the mailbox (a limited number in
+    %% order to not cause long delays)
+    NewFlushed = flush_log_events(?FLUSH_MAX_N),
+
+    %% write info in log about flushed messages
+    log_handler_info(Name, "Handler ~p flushed ~w log events",
+                     [Name,NewFlushed], State),
+
+    %% because of the receive loop when flushing messages, the
+    %% handler will be scheduled out often and the mailbox could
+    %% grow very large, so we'd better check the queue again here
+    {_,_QLen1} = process_info(self(), message_queue_len),
+    ?observe(Name,{max_qlen,_QLen1}),
+
+    %% Add 1 for the current log event
+    ?observe(Name,{flushed,NewFlushed+1}),
+
+    State1 = ?update_max_time(?diff_time(T1,_T0),State),
+    {dropped,?update_other(flushed,FLUSHED,NewFlushed,
+                           State1#{mode => ?set_mode(ModeTab,async),
+                                   last_qlen => 0,
+                                   last_log_ts => T1})}.
+
+%% this clause is called to write to file
+write(Name, Mode, T1, Bin, _CallOrCast,
+      State = #{module := Module,
+                handler_state := HandlerState,
+                mode_tab := ModeTab,
+                ctrl_sync_count := CtrlSync,
+                ctrl_sync_int := CtrlSyncInt,
+                last_qlen := LastQLen,
+                last_log_ts := T0}) ->
+    %% check if we need to limit the number of writes
+    %% during a burst of log events
+    {DoWrite,BurstWinT,BurstMsgCount} = limit_burst(State),
+
+    %% only log synhrounously every CtrlSyncInt time, to give the
+    %% handler time between writes so it can keep up with incoming
+    %% messages
+    {Result,LastQLen1,HandlerState1} =
+        if DoWrite, CtrlSync == 0 ->
+                ?observe(Name,{_CallOrCast,1}),
+                {_,HS1} = Module:sync_write(Name, Bin, HandlerState),
+                {ok,element(2, process_info(self(), message_queue_len)),HS1};
+           DoWrite ->
+                ?observe(Name,{_CallOrCast,1}),
+                HS1 = Module:async_write(Name, Bin, HandlerState),
+                {ok,LastQLen,HS1};
+           not DoWrite ->
+                ?observe(Name,{flushed,1}),
+                {dropped,LastQLen,HandlerState}
+        end,
+
+    %% Check if the time since the previous log event is long enough -
+    %% and the queue length small enough - to assume the mailbox has
+    %% been emptied, and if so, do filesync operation and reset mode to
+    %% async. Note that this is the best we can do to detect an idle
+    %% handler without setting a timer after each log call/cast. If the
+    %% time between two consecutive log events is fast and no new
+    %% event comes in after the last one, idle state won't be detected!
+    Time = ?diff_time(T1,T0),
+    {Mode1,BurstMsgCount1,HandlerState2} =
+        if (LastQLen1 < ?FILESYNC_OK_QLEN) andalso
+           (Time > ?IDLE_DETECT_TIME_USEC) ->
+                HS2 = Module:async_filesync(Name,HandlerState),
+                {?change_mode(ModeTab, Mode, async),0,HS2};
+           true ->
+                {Mode,BurstMsgCount,HandlerState1}
+        end,
+    State1 =
+        ?update_calls_or_casts(_CallOrCast,1,State),
+    State2 =
+        ?update_max_time(Time,
+                         State1#{mode => Mode1,
+                                 last_qlen := LastQLen1,
+                                 last_log_ts => T1,
+                                 last_op => write,
+                                 burst_win_ts => BurstWinT,
+                                 burst_msg_count => BurstMsgCount1,
+                                 ctrl_sync_count => if CtrlSync==0 -> CtrlSyncInt;
+                                                       true -> CtrlSync-1
+                                                    end,
+                                 handler_state => HandlerState2}),
+    {Result,State2}.
+
+log_handler_info(Name, Format, Args, #{module:=Module,
+                                       handler_state:=HandlerState}) ->
+    Config =
+        case logger:get_handler_config(Name) of
+            {ok,Conf} -> Conf;
+            _ -> #{formatter=>{?DEFAULT_FORMATTER,?DEFAULT_FORMAT_CONFIG}}
+        end,
+    Meta = #{time=>erlang:system_time(microsecond)},
+    Bin = log_to_binary(#{level => notice,
+                          msg => {Format,Args},
+                          meta => Meta}, Config),
+    _ = Module:async_write(Name, Bin, HandlerState),
+    ok.
 
 %%%-----------------------------------------------------------------
 %%% Convert log data on any form to binary
@@ -94,46 +609,52 @@ string_to_binary(String) ->
             throw(Error)
     end.
 
-
 %%%-----------------------------------------------------------------
 %%% Check that the configuration term is valid
-check_common_config({mode_tab,_Tid}) ->
-    valid;
-check_common_config({handler_pid,Pid}) when is_pid(Pid) ->
-    valid;
-
-check_common_config({sync_mode_qlen,N}) when is_integer(N) ->
-    valid;
-check_common_config({drop_mode_qlen,N}) when is_integer(N) ->
-    valid;
-check_common_config({flush_qlen,N}) when is_integer(N) ->
-    valid;
-
-check_common_config({burst_limit_enable,Bool}) when Bool == true;
-                                                    Bool == false ->
-    valid;
-check_common_config({burst_limit_max_count,N}) when is_integer(N) ->
-    valid;
-check_common_config({burst_limit_window_time,N}) when is_integer(N) ->
-    valid;
-
-check_common_config({overload_kill_enable,Bool}) when Bool == true;
-                                                      Bool == false ->
-    valid;
-check_common_config({overload_kill_qlen,N}) when is_integer(N) ->
-    valid;
-check_common_config({overload_kill_mem_size,N}) when is_integer(N) ->
-    valid;
-check_common_config({overload_kill_restart_after,NorA})  when is_integer(NorA);
-                                                              NorA == infinity ->
-    valid;
-
-check_common_config({filesync_repeat_interval,NorA}) when is_integer(NorA);
-                                                          NorA == no_repeat ->
-    valid;
-check_common_config(_) ->
-    invalid.
+check_config(Config) when is_map(Config) ->
+    check_common_config(maps:to_list(Config)).
 
+check_common_config([{sync_mode_qlen,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{drop_mode_qlen,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{flush_qlen,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{burst_limit_enable,Bool}|Config]) when is_boolean(Bool) ->
+    check_common_config(Config);
+check_common_config([{burst_limit_max_count,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{burst_limit_window_time,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{overload_kill_enable,Bool}|Config]) when is_boolean(Bool) ->
+    check_common_config(Config);
+check_common_config([{overload_kill_qlen,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{overload_kill_mem_size,N}|Config]) when is_integer(N) ->
+    check_common_config(Config);
+check_common_config([{overload_kill_restart_after,NorA}|Config])
+  when is_integer(NorA); NorA == infinity ->
+    check_common_config(Config);
+check_common_config([{filesync_repeat_interval,NorA}|Config])
+  when is_integer(NorA); NorA == no_repeat ->
+    check_common_config(Config);
+check_common_config([{Key,Value}|_]) ->
+    {error,#{Key=>Value}};
+check_common_config([]) ->
+    ok.
+
+get_default_config() ->
+    #{sync_mode_qlen              => ?SYNC_MODE_QLEN,
+      drop_mode_qlen              => ?DROP_MODE_QLEN,
+      flush_qlen                  => ?FLUSH_QLEN,
+      burst_limit_enable          => ?BURST_LIMIT_ENABLE,
+      burst_limit_max_count       => ?BURST_LIMIT_MAX_COUNT,
+      burst_limit_window_time     => ?BURST_LIMIT_WINDOW_TIME,
+      overload_kill_enable        => ?OVERLOAD_KILL_ENABLE,
+      overload_kill_qlen          => ?OVERLOAD_KILL_QLEN,
+      overload_kill_mem_size      => ?OVERLOAD_KILL_MEM_SIZE,
+      overload_kill_restart_after => ?OVERLOAD_KILL_RESTART_AFTER,
+      filesync_repeat_interval    => ?FILESYNC_REPEAT_INTERVAL}.
 
 %%%-----------------------------------------------------------------
 %%% Overload Protection
@@ -243,16 +764,16 @@ limit_burst(#{burst_win_ts := BurstWinT0,
             {true,BurstWinT0,BurstMsgCount+1}
     end.
 
-kill_if_choked(Name, QLen, Mem, HandlerMod,
+kill_if_choked(Name, Module, QLen, Mem,
                State = #{overload_kill_enable   := KillIfOL,
                          overload_kill_qlen     := OLKillQLen,
                          overload_kill_mem_size := OLKillMem}) ->
     if KillIfOL andalso
        ((QLen > OLKillQLen) orelse (Mem > OLKillMem)) ->
-            HandlerMod:log_handler_info(Name,
-                                        "Handler ~p overloaded and stopping",
-                                        [Name], State),
-            set_restart_flag(Name, HandlerMod),
+            log_handler_info(Name,
+                             "Handler ~p overloaded and stopping",
+                             [Name], State),
+            set_restart_flag(Name, Module),
             handler_exit(Name, {shutdown,{overloaded,Name,QLen,Mem}});
        true ->
             ok
@@ -290,9 +811,9 @@ cancel_timer(TRef) -> timer:cancel(TRef).
 stop_or_restart(Name, {shutdown,Reason={overloaded,_Name,_QLen,_Mem}},
                 #{overload_kill_restart_after := RestartAfter}) ->
     %% If we're terminating because of an overload situation (see
-    %% logger_h_common:kill_if_choked/4), we need to remove the handler
-    %% and set a restart timer. A separate process must perform this
-    %% in order to avoid deadlock.
+    %% kill_if_choked/5), we need to remove the handler and set a
+    %% restart timer. A separate process must perform this in order to
+    %% avoid deadlock.
     HandlerPid = self(),
     ConfigResult = logger:get_handler_config(Name),
     RemoveAndRestart =
@@ -334,6 +855,3 @@ overload_levels_ok(HandlerConfig) ->
 
 error_notify(Term) ->
     ?internal_log(error, Term).
-
-info_notify(Term) ->
-    ?internal_log(info, Term).
diff --git a/lib/kernel/src/logger_std_h.erl b/lib/kernel/src/logger_std_h.erl
index 42e0f5caf4..95e7d17c0d 100644
--- a/lib/kernel/src/logger_std_h.erl
+++ b/lib/kernel/src/logger_std_h.erl
@@ -19,8 +19,6 @@
 %%
 -module(logger_std_h).
 
--behaviour(gen_server).
-
 -include("logger.hrl").
 -include("logger_internal.hrl").
 -include("logger_h_common.hrl").
@@ -28,52 +26,30 @@
 -include_lib("kernel/include/file.hrl").
 
 %% API
--export([start_link/3, info/1, filesync/1, reset/1]).
+-export([info/1, filesync/1, reset/1]).
 
-%% gen_server and proc_lib callbacks
--export([init/1, handle_call/3, handle_cast/2, handle_info/2,
-         terminate/2, code_change/3]).
+%% logger_h_common callbacks
+-export([init/2, check_config/4, reset_state/1,
+         async_filesync/2, sync_filesync/2,
+         async_write/3, sync_write/3,
+         handle_info/2, terminate/3]).
 
 %% logger callbacks
 -export([log/2, adding_handler/1, removing_handler/1, changing_config/3,
          filter_config/1]).
 
-%% handler internal
--export([log_handler_info/4]).
-
 %%%===================================================================
 %%% API
 %%%===================================================================
 
 %%%-----------------------------------------------------------------
-%%% Start a standard handler process and link to caller.
-%%% This function is called by the kernel supervisor when this
-%%% handler process gets added
--spec start_link(Name, Config, HandlerState) -> {ok,Pid} | {error,Reason} when
-      Name :: atom(),
-      Config :: logger:handler_config(),
-      HandlerState :: map(),
-      Pid :: pid(),
-      Reason :: term().
-
-start_link(Name, Config, HandlerState) ->
-    proc_lib:start_link(?MODULE,init,[[Name,Config,HandlerState]]).
-
-%%%-----------------------------------------------------------------
 %%%
 -spec filesync(Name) -> ok | {error,Reason} when
       Name :: atom(),
       Reason :: handler_busy | {badarg,term()}.
 
-filesync(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        filesync, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;
 filesync(Name) ->
-    {error,{badarg,{filesync,[Name]}}}.
+    logger_h_common:filesync(?MODULE,Name).
 
 %%%-----------------------------------------------------------------
 %%%
@@ -82,15 +58,8 @@ filesync(Name) ->
       Info :: term(),
       Reason :: handler_busy | {badarg,term()}.
 
-info(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        info, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;
 info(Name) ->
-    {error,{badarg,{info,[Name]}}}.
+    logger_h_common:info(?MODULE,Name).
 
 %%%-----------------------------------------------------------------
 %%%
@@ -98,16 +67,8 @@ info(Name) ->
       Name :: atom(),
       Reason :: handler_busy | {badarg,term()}.
 
-reset(Name) when is_atom(Name) ->
-    try
-        gen_server:call(?name_to_reg_name(?MODULE,Name),
-                        reset, ?DEFAULT_CALL_TIMEOUT)
-    catch
-        _:{timeout,_} -> {error,handler_busy}
-    end;      
 reset(Name) ->
-    {error,{badarg,{reset,[Name]}}}.
-
+    logger_h_common:reset(?MODULE,Name).
 
 %%%===================================================================
 %%% logger callbacks
@@ -115,30 +76,48 @@ reset(Name) ->
 
 %%%-----------------------------------------------------------------
 %%% Handler being added
-adding_handler(#{id:=Name}=Config) ->
-    case check_config(adding, Config) of
-        {ok, #{config:=HConfig}=Config1} ->
-            %% create initial handler state by merging defaults with config
-            HState = maps:merge(get_init_state(), HConfig),
-            case logger_h_common:overload_levels_ok(HState) of
-                true ->
-                    start(Name, Config1, HState);
-                false ->
-                    #{sync_mode_qlen := SMQL,
-                      drop_mode_qlen := DMQL,
-                      flush_qlen     := FQL} = HState, 
-                    {error,{invalid_levels,{SMQL,DMQL,FQL}}}
-            end;
+adding_handler(Config) ->
+    logger_h_common:adding_handler(Config).
+
+%%%-----------------------------------------------------------------
+%%% Updating handler config
+changing_config(SetOrUpdate, OldConfig, NewConfig) ->
+    logger_h_common:changing_config(SetOrUpdate, OldConfig, NewConfig).
+
+%%%-----------------------------------------------------------------
+%%% Handler being removed
+removing_handler(Config) ->
+    logger_h_common:removing_handler(Config).
+
+%%%-----------------------------------------------------------------
+%%% Log a string or report
+-spec log(LogEvent, Config) -> ok when
+      LogEvent :: logger:log_event(),
+      Config :: logger:handler_config().
+
+log(LogEvent, Config) ->
+    logger_h_common:log(LogEvent, Config).
+
+%%%-----------------------------------------------------------------
+%%% Remove internal fields from configuration
+filter_config(Config) ->
+    logger_h_common:filter_config(Config).
+
+%%%===================================================================
+%%% logger_h_common callbacks
+%%%===================================================================
+init(Name, #{type := Type}) ->
+    case open_log_file(Name, Type) of
+        {ok,FileCtrlPid} ->
+            {ok,#{type=>Type,file_ctrl_pid=>FileCtrlPid}};
         Error ->
             Error
     end.
 
-%%%-----------------------------------------------------------------
-%%% Updating handler config
-changing_config(SetOrUpdate,OldConfig=#{config:=OldHConfig},NewConfig) ->
+check_config(_Name,set,undefined,NewHConfig) ->
+    check_config(maps:merge(get_default_config(),NewHConfig));
+check_config(_Name,SetOrUpdate,OldHConfig,NewHConfig0) ->
     WriteOnce = maps:with([type],OldHConfig),
-    ReadOnly = maps:with([handler_pid,mode_tab],OldHConfig),
-    NewHConfig0 = maps:get(config, NewConfig, #{}),
     Default =
         case SetOrUpdate of
             set ->
@@ -148,48 +127,24 @@ changing_config(SetOrUpdate,OldConfig=#{config:=OldHConfig},NewConfig) ->
                 OldHConfig
         end,
 
-    %% Allow (accidentially) included read-only fields - just overwrite them
-    NewHConfig = maps:merge(maps:merge(Default, NewHConfig0),ReadOnly),
+    NewHConfig = maps:merge(Default, NewHConfig0),
 
-    %% But fail if write-once fields are changed
+    %% Fail if write-once fields are changed
     case maps:with([type],NewHConfig) of
         WriteOnce ->
-            changing_config1(maps:get(handler_pid,OldHConfig),
-                             OldConfig,
-                             NewConfig#{config=>NewHConfig});
+            check_config(NewHConfig);
         Other ->
-            {error,{illegal_config_change,#{config=>WriteOnce},#{config=>Other}}}
+            {error,{illegal_config_change,?MODULE,WriteOnce,Other}}
     end.
 
-changing_config1(HPid, OldConfig, NewConfig) ->
-    case check_config(changing, NewConfig) of
-        Result = {ok,NewConfig1} ->
-            try gen_server:call(HPid, {change_config,OldConfig,NewConfig1},
-                                ?DEFAULT_CALL_TIMEOUT) of
-                ok      -> Result;
-                HError  -> HError
-            catch
-                _:{timeout,_} -> {error,handler_busy}
-            end;
-        Error ->
-            Error
-    end.    
-
-check_config(adding, Config) ->
-    %% Merge in defaults on handler level
-    HConfig0 = maps:get(config, Config, #{}),
-    HConfig = maps:merge(get_default_config(),HConfig0),
+check_config(#{type:=Type}=HConfig) ->
     case check_h_config(maps:to_list(HConfig)) of
+        ok when is_atom(Type) ->
+            {ok,HConfig#{filesync_repeat_interval=>no_repeat}};
         ok ->
-            {ok,Config#{config=>HConfig}};
-        Error ->
-            Error
-    end;
-check_config(changing, Config) ->
-    HConfig = maps:get(config, Config, #{}),
-    case check_h_config(maps:to_list(HConfig)) of
-        ok    -> {ok,Config};
-        Error -> Error
+            {ok,HConfig};
+        {error,{Key,Value}} ->
+            {error,{invalid_config,?MODULE,#{Key=>Value}}}
     end.
 
 check_h_config([{type,Type} | Config]) when Type == standard_io;
@@ -200,219 +155,44 @@ check_h_config([{type,{file,File}} | Config]) when is_list(File) ->
 check_h_config([{type,{file,File,Modes}} | Config]) when is_list(File),
                                                          is_list(Modes) ->
     check_h_config(Config);
-check_h_config([Other | Config]) ->
-    case logger_h_common:check_common_config(Other) of
-        valid ->
-            check_h_config(Config);
-        invalid ->
-            {error,{invalid_config,?MODULE,Other}}
-    end;
+check_h_config([Other | _]) ->
+    {error,Other};
 check_h_config([]) ->
     ok.
 
-
-%%%-----------------------------------------------------------------
-%%% Handler being removed
-removing_handler(#{id:=Name}) ->
-    stop(Name).
-
-%%%-----------------------------------------------------------------
-%%% Log a string or report
--spec log(LogEvent, Config) -> ok when
-      LogEvent :: logger:log_event(),
-      Config :: logger:handler_config().
-
-log(LogEvent, Config = #{id := Name,
-                         config := #{handler_pid := HPid,
-                                     mode_tab := ModeTab}}) ->
-    %% if the handler has crashed, we must drop this event
-    %% and hope the handler restarts so we can try again
-    true = is_process_alive(HPid),
-    Bin = logger_h_common:log_to_binary(LogEvent, Config),
-    logger_h_common:call_cast_or_drop(Name, HPid, ModeTab, Bin).
-
-%%%-----------------------------------------------------------------
-%%% Remove internal fields from configuration
-filter_config(#{config:=HConfig}=Config) ->
-    Config#{config=>maps:without([handler_pid,mode_tab],HConfig)}.
-
-%%%===================================================================
-%%% gen_server callbacks
-%%%===================================================================
-
-init([Name, Config = #{config := HConfig},
-      State0 = #{type := Type, file_ctrl_sync_int := FileCtrlSyncInt}]) ->    
-    RegName = ?name_to_reg_name(?MODULE,Name),
-    register(RegName, self()),
-    process_flag(trap_exit, true),
-    process_flag(message_queue_data, off_heap),
-
-    ?init_test_hooks(),
-    ?start_observation(Name),
-
-    case do_init(Name, Type) of
-        {ok,InitState} ->
-            try ets:new(Name, [public]) of
-                ModeTab ->
-                    ?set_mode(ModeTab, async),
-                    State = maps:merge(State0, InitState),
-                    T0 = ?timestamp(),
-                    State1 =
-                        ?merge_with_stats(State#{
-                                            mode_tab => ModeTab,
-                                            mode => async,
-                                            file_ctrl_sync => FileCtrlSyncInt,
-                                            last_qlen => 0,
-                                            last_log_ts => T0,
-                                            last_op => sync,
-                                            burst_win_ts => T0,
-                                            burst_msg_count => 0}),
-                    Config1 =
-                        Config#{config => HConfig#{handler_pid => self(),
-                                                   mode_tab => ModeTab}},
-                    proc_lib:init_ack({ok,self(),Config1}),
-                    gen_server:cast(self(), repeated_filesync),
-                    gen_server:enter_loop(?MODULE, [], State1)
-            catch
-                _:Error ->
-                    unregister(RegName),
-                    logger_h_common:error_notify({init_handler,Name,Error}),
-                    proc_lib:init_ack(Error)
-            end;
-        Error ->
-            unregister(RegName),
-            logger_h_common:error_notify({init_handler,Name,Error}),
-            proc_lib:init_ack(Error)
-    end.
-
-do_init(Name, Type) ->
-    case open_log_file(Name, Type) of
-        {ok,FileCtrlPid} ->
-            case logger_h_common:unset_restart_flag(Name, ?MODULE) of
-                true ->
-                    %% inform about restart
-                    gen_server:cast(self(), {log_handler_info,
-                                             "Handler ~p restarted",
-                                             [Name]});
-                false ->
-                    %% initial start
-                    ok
-            end,
-            {ok,#{id=>Name,type=>Type,file_ctrl_pid=>FileCtrlPid}};
-        Error ->
-            Error
-    end.
-
-%% This is the synchronous log event.
-handle_call({log, Bin}, _From, State) ->
-    {Result,State1} = do_log(Bin, call, State),
-    %% Result == ok | dropped
-    {reply,Result, State1};
-
-handle_call(filesync, _From, State = #{type := Type,
-                                       file_ctrl_pid := FileCtrlPid}) ->
-    if is_atom(Type) ->
-            {reply, ok, State};
-       true ->
-            {reply, file_ctrl_filesync_sync(FileCtrlPid), State#{last_op=>sync}}
-    end;
-
-handle_call({change_config,_OldConfig,NewConfig}, _From,
-            State = #{filesync_repeat_interval := FSyncInt0}) ->
-    HConfig = maps:get(config, NewConfig, #{}),
-    State1 = maps:merge(State, HConfig),
-    case logger_h_common:overload_levels_ok(State1) of
-        true ->
-            _ =
-                case maps:get(filesync_repeat_interval, HConfig, undefined) of
-                    undefined ->
-                        ok;
-                    no_repeat ->
-                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
-                                                                  State,
-                                                                  undefined));
-                    FSyncInt0 ->
-                        ok;
-                    _FSyncInt1 ->
-                        _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref,
-                                                                  State,
-                                                                  undefined)),
-                        gen_server:cast(self(), repeated_filesync)
-                end,
-            {reply, ok, State1};
-        false ->
-            #{sync_mode_qlen := SMQL,
-              drop_mode_qlen := DMQL,
-              flush_qlen     := FQL} = State1,
-            {reply, {error,{invalid_levels,{SMQL,DMQL,FQL}}}, State}
-    end;
-
-handle_call(info, _From, State) ->
-    {reply, State, State};
-
-handle_call(reset, _From, State) ->
-    State1 = ?merge_with_stats(State),
-    {reply, ok, State1#{last_qlen => 0,
-                        last_log_ts => ?timestamp()}};
-
-handle_call(stop, _From, State) ->
-    {stop, {shutdown,stopped}, ok, State}.
-
-%% This is the asynchronous log event.
-handle_cast({log, Bin}, State) ->
-    {_,State1} = do_log(Bin, cast, State),
-    {noreply, State1};
-
-handle_cast({log_handler_info, Format, Args}, State = #{id:=Name}) ->
-    log_handler_info(Name, Format, Args, State),
-    {noreply, State};
-
-%% If FILESYNC_REPEAT_INTERVAL is set to a millisec value, this
-%% clause gets called repeatedly by the handler. In order to
-%% guarantee that a filesync *always* happens after the last log
-%% event, the repeat operation must be active!
-handle_cast(repeated_filesync,
-            State = #{type := Type,
-                      file_ctrl_pid := FileCtrlPid,
-                      filesync_repeat_interval := FSyncInt,
-                      last_op := LastOp}) ->
-    State1 =
-        if not is_atom(Type), is_integer(FSyncInt) ->
-                %% only do filesync if something has been
-                %% written since last time we checked
-                if LastOp == sync ->
-                        ok;
-                   true ->
-                        file_ctrl_filesync_async(FileCtrlPid)
-                end,
-                {ok,TRef} =
-                    timer:apply_after(FSyncInt, gen_server,cast,
-                                      [self(),repeated_filesync]),
-                State#{rep_sync_tref => TRef, last_op => sync};
-           true ->
-                State
-        end,
-    {noreply,State1}.
-
-handle_info({'EXIT',Pid,Why}, State = #{id := Name, type := FileInfo}) ->
-    case maps:get(file_ctrl_pid, State, undefined) of
-        Pid ->
-            %% file error, terminate handler
-            logger_h_common:handler_exit(Name,
-                                         {error,{write_failed,FileInfo,Why}});
-        _Other ->
-            %% ignore EXIT
-            ok
-    end,
-    {noreply, State};
-
-handle_info(_Info, State) ->
-    {noreply, State}.
-
-terminate(Reason, State = #{id:=Name, file_ctrl_pid:=FWPid,
-                            type:=_FileInfo}) ->
-    _ = logger_h_common:cancel_timer(maps:get(rep_sync_tref, State,
-                                              undefined)),
+get_default_config() ->
+     #{type => standard_io}.
+
+async_filesync(_Name,#{type := Type}=State) when is_atom(Type) ->
+    State;
+async_filesync(_Name,#{file_ctrl_pid := FileCtrlPid}=State) ->
+    ok = file_ctrl_filesync_async(FileCtrlPid),
+    State.
+
+sync_filesync(_Name,#{type := Type}=State) when is_atom(Type) ->
+    {ok,State};
+sync_filesync(_Name,#{file_ctrl_pid := FileCtrlPid}=State) ->
+    Result = file_ctrl_filesync_sync(FileCtrlPid),
+    {Result,State}.
+
+async_write(_Name, Bin, #{file_ctrl_pid:=FileCtrlPid} = State) ->
+    ok = file_write_async(FileCtrlPid, Bin),
+    State.
+
+sync_write(_Name, Bin, #{file_ctrl_pid:=FileCtrlPid} = State) ->
+    Result = file_write_sync(FileCtrlPid, Bin),
+    {Result,State}.
+
+reset_state(State) ->
+    State.
+
+handle_info({'EXIT',Pid,Why}, #{type := FileInfo, file_ctrl_pid := Pid}) ->
+    %% file_ctrl_pid died, file error, terminate handler
+    exit({error,{write_failed,FileInfo,Why}});
+handle_info(_, State) ->
+    State.
+
+terminate(_Name, _Reason, #{file_ctrl_pid:=FWPid}) ->
     case is_process_alive(FWPid) of
         true ->
             unlink(FWPid),
@@ -427,13 +207,7 @@ terminate(Reason, State = #{id:=Name, file_ctrl_pid:=FWPid,
             end;
         false ->
             ok
-    end,
-    ok = logger_h_common:stop_or_restart(Name, Reason, State),
-    unregister(?name_to_reg_name(?MODULE, Name)),
-    ok.
-                                                  
-code_change(_OldVsn, State, _Extra) ->
-    {ok, State}.
+    end.
 
 %%%===================================================================
 %%% Internal functions
@@ -441,203 +215,6 @@ code_change(_OldVsn, State, _Extra) ->
 
 %%%-----------------------------------------------------------------
 %%%
-get_default_config() ->
-     #{type                        => standard_io,
-       sync_mode_qlen              => ?SYNC_MODE_QLEN,
-       drop_mode_qlen              => ?DROP_MODE_QLEN,
-       flush_qlen                  => ?FLUSH_QLEN,
-       burst_limit_enable          => ?BURST_LIMIT_ENABLE,
-       burst_limit_max_count       => ?BURST_LIMIT_MAX_COUNT,
-       burst_limit_window_time     => ?BURST_LIMIT_WINDOW_TIME,
-       overload_kill_enable        => ?OVERLOAD_KILL_ENABLE,
-       overload_kill_qlen          => ?OVERLOAD_KILL_QLEN,
-       overload_kill_mem_size      => ?OVERLOAD_KILL_MEM_SIZE,
-       overload_kill_restart_after => ?OVERLOAD_KILL_RESTART_AFTER,
-       filesync_repeat_interval    => ?FILESYNC_REPEAT_INTERVAL}.
-
-get_init_state() ->
-    #{file_ctrl_sync_int          => ?CONTROLLER_SYNC_INTERVAL,
-      filesync_ok_qlen            => ?FILESYNC_OK_QLEN}.
-
-%%%-----------------------------------------------------------------
-%%% Add a standard handler to the logger.
-%%% This starts a dedicated handler process which should always
-%%% exist if the handler is registered with logger (and should not
-%%% exist if the handler is not registered).
-%%%
-%%% Handler specific config should be provided with a sub map associated
-%%% with a key named 'config', e.g:
-%%%
-%%% Config = #{config => #{sync_mode_qlen => 50}
-%%%
-%%% The standard handler process is linked to logger_sup, which is
-%%% part of the kernel application's supervision tree.
-start(Name, Config, HandlerState) ->
-    LoggerStdH =
-        #{id       => Name,
-          start    => {?MODULE, start_link, [Name,Config,HandlerState]},
-          restart  => temporary,
-          shutdown => 2000,
-          type     => worker,
-          modules  => [?MODULE]},
-    case supervisor:start_child(logger_sup, LoggerStdH) of
-        {ok,Pid,Config1} ->
-            ok = logger_handler_watcher:register_handler(Name,Pid),
-            {ok,Config1};
-        Error ->
-            Error
-    end.
-
-%%%-----------------------------------------------------------------
-%%% Stop and remove the handler.
-stop(Name) ->
-    case whereis(?name_to_reg_name(?MODULE,Name)) of
-        undefined ->
-            ok;
-        Pid ->
-            %% We don't want to do supervisor:terminate_child here
-            %% since we need to distinguish this explicit stop from a
-            %% system termination in order to avoid circular attempts
-            %% at removing the handler (implying deadlocks and
-            %% timeouts).
-            %% And we don't need to do supervisor:delete_child, since
-            %% the restart type is temporary, which means that the
-            %% child specification is automatically removed from the
-            %% supervisor when the process dies.
-            _ = gen_server:call(Pid, stop),
-            ok
-    end.
-
-%%%-----------------------------------------------------------------
-%%% Logging and overload control.
--define(update_file_ctrl_sync(C, Interval),
-        if C == 0 -> Interval;
-           true -> C-1 end).
-
-%% check for overload between every event (and set Mode to async,
-%% sync or drop accordingly), but never flush the whole mailbox
-%% before LogWindowSize events have been handled
-do_log(Bin, CallOrCast, State = #{id:=Name, mode:=Mode0}) ->
-    T1 = ?timestamp(),
-
-    %% check if the handler is getting overloaded, or if it's
-    %% recovering from overload (the check must be done for each
-    %% event to react quickly to large bursts of events and
-    %% to ensure that the handler can never end up in drop mode
-    %% with an empty mailbox, which would stop operation)
-    {Mode1,QLen,Mem,State1} = logger_h_common:check_load(State),
-
-    if (Mode1 == drop) andalso (Mode0 =/= drop) ->
-            log_handler_info(Name, "Handler ~p switched to drop mode",
-                             [Name], State);
-       (Mode0 == drop) andalso ((Mode1 == async) orelse (Mode1 == sync)) ->
-            log_handler_info(Name, "Handler ~p switched to ~w mode",
-                             [Name,Mode1], State);
-       true ->
-            ok
-    end,
-
-    %% kill the handler if it can't keep up with the load
-    logger_h_common:kill_if_choked(Name, QLen, Mem, ?MODULE, State),
-
-    if Mode1 == flush ->
-            flush(Name, QLen, T1, State1);
-       true ->
-            write(Name, Mode1, T1, Bin, CallOrCast, State1)
-    end.
-
-%% this clause is called by do_log/3 after an overload check
-%% has been performed, where QLen > FlushQLen
-flush(Name, _QLen0, T1, State=#{last_log_ts := _T0, mode_tab := ModeTab}) ->
-    %% flush messages in the mailbox (a limited number in
-    %% order to not cause long delays)
-    NewFlushed = logger_h_common:flush_log_events(?FLUSH_MAX_N),
-
-    %% write info in log about flushed messages
-    log_handler_info(Name, "Handler ~p flushed ~w log events",
-                     [Name,NewFlushed], State),
-
-    %% because of the receive loop when flushing messages, the
-    %% handler will be scheduled out often and the mailbox could
-    %% grow very large, so we'd better check the queue again here
-    {_,_QLen1} = process_info(self(), message_queue_len),
-    ?observe(Name,{max_qlen,_QLen1}),
-    
-    %% Add 1 for the current log event
-    ?observe(Name,{flushed,NewFlushed+1}),
- 
-    State1 = ?update_max_time(?diff_time(T1,_T0),State),
-    {dropped,?update_other(flushed,FLUSHED,NewFlushed,
-                           State1#{mode => ?set_mode(ModeTab,async),
-                                   last_qlen => 0,
-                                   last_log_ts => T1})}.
-
-%% this clause is called to write to file
-write(_Name, Mode, T1, Bin, _CallOrCast,
-      State = #{mode_tab := ModeTab,
-                file_ctrl_pid := FileCtrlPid,
-                file_ctrl_sync := FileCtrlSync,
-                last_qlen := LastQLen,
-                last_log_ts := T0,
-                file_ctrl_sync_int := FileCtrlSyncInt}) ->
-    %% check if we need to limit the number of writes
-    %% during a burst of log events
-    {DoWrite,BurstWinT,BurstMsgCount} = logger_h_common:limit_burst(State),
-
-    %% only send a synhrounous event to the file controller process
-    %% every FileCtrlSyncInt time, to give the handler time between
-    %% file writes so it can keep up with incoming messages
-    {Result,LastQLen1} =
-        if DoWrite, FileCtrlSync == 0 ->
-                ?observe(_Name,{_CallOrCast,1}),
-                file_write_sync(FileCtrlPid, Bin, false),
-                {ok,element(2, process_info(self(), message_queue_len))};
-           DoWrite ->
-                ?observe(_Name,{_CallOrCast,1}),
-                file_write_async(FileCtrlPid, Bin),
-                {ok,LastQLen};
-           not DoWrite ->
-                ?observe(_Name,{flushed,1}),
-                {dropped,LastQLen}
-        end,
-    
-    %% Check if the time since the previous log event is long enough -
-    %% and the queue length small enough - to assume the mailbox has
-    %% been emptied, and if so, do filesync operation and reset mode to
-    %% async. Note that this is the best we can do to detect an idle
-    %% handler without setting a timer after each log call/cast. If the
-    %% time between two consecutive log events is fast and no new
-    %% event comes in after the last one, idle state won't be detected!
-    Time = ?diff_time(T1,T0),
-    {Mode1,BurstMsgCount1} =
-        if (LastQLen1 < ?FILESYNC_OK_QLEN) andalso
-           (Time > ?IDLE_DETECT_TIME_USEC) ->
-                %% do filesync if necessary
-                case maps:get(type, State) of
-                    Std when is_atom(Std) ->
-                        ok;
-                    _File ->
-                        file_ctrl_filesync_async(FileCtrlPid)
-                end,
-                {?change_mode(ModeTab, Mode, async),0};
-           true ->
-                {Mode,BurstMsgCount}
-        end,
-    State1 =
-        ?update_calls_or_casts(_CallOrCast,1,State),
-    State2 =
-        ?update_max_time(Time,
-                         State1#{mode => Mode1,
-                                 last_qlen := LastQLen1,
-                                 last_log_ts => T1,
-                                 last_op => write,
-                                 burst_win_ts => BurstWinT,
-                                 burst_msg_count => BurstMsgCount1,
-                                 file_ctrl_sync =>
-                                     ?update_file_ctrl_sync(FileCtrlSync,
-                                                            FileCtrlSyncInt)}),
-    {Result,State2}.
-
 open_log_file(HandlerName, FileInfo) ->
     case file_ctrl_start(HandlerName, FileInfo) of
         OK = {ok,_FileCtrlPid} -> OK;
@@ -669,19 +246,6 @@ close_log_file(Fd) ->
     _ = file:close(Fd).
 
 
-log_handler_info(Name, Format, Args, #{file_ctrl_pid := FileCtrlPid}) ->
-    Config =
-        case logger:get_handler_config(Name) of
-            {ok,Conf} -> Conf;
-            _ -> #{formatter=>{?DEFAULT_FORMATTER,?DEFAULT_FORMAT_CONFIG}}
-        end,
-    Meta = #{time=>erlang:system_time(microsecond)},
-    Bin = logger_h_common:log_to_binary(#{level => notice,
-                                          msg => {Format,Args},
-                                          meta => Meta}, Config),
-    _ = file_write_async(FileCtrlPid, Bin),
-    ok.
-
 %%%-----------------------------------------------------------------
 %%% File control process
 
@@ -708,13 +272,8 @@ file_write_async(Pid, Bin) ->
     Pid ! {log,Bin},
     ok.
 
-file_write_sync(Pid, Bin, FileSync) ->
-    case file_ctrl_call(Pid, {log,self(),Bin,FileSync}) of
-        {error,Reason} ->
-            {error,{write_failed,Bin,Reason}};
-        Result ->
-            Result
-    end.
+file_write_sync(Pid, Bin) ->
+    file_ctrl_call(Pid, {log,self(),Bin}).
 
 file_ctrl_filesync_async(Pid) ->
     Pid ! filesync,
@@ -766,33 +325,22 @@ file_ctrl_loop(Fd, Type, DevName, Synced,
                            Result, PrevSyncResult, HandlerName);
 
         %% synchronous event
-        {{log,From,Bin,FileSync},MRef} ->
-            if Type == file ->
-                    %% check that file hasn't been deleted
-                    CheckFile =
-                        fun() -> {ok,_} = file:read_file_info(DevName) end,
-                    spawn_link(CheckFile),
-                    WResult = write_to_dev(Fd, Bin, DevName,
-                                           PrevWriteResult, HandlerName),
-                    {Synced1,SResult} =
-                        if not FileSync ->
-                                {false,PrevSyncResult};
-                           true ->
-                                case sync_dev(Fd, DevName,
-                                              PrevSyncResult, HandlerName) of
-                                    ok     -> {true,ok};
-                                    Error  -> {false,Error}
-                                end
-                        end,
-                    From ! {MRef,ok},
-                    file_ctrl_loop(Fd, Type, DevName, Synced1,
-                                   WResult, SResult, HandlerName);
-               true ->
-                    _ = io:put_chars(Fd, Bin),
-                    From ! {MRef,ok},
-                    file_ctrl_loop(Fd, Type, DevName, false,
-                                   ok, PrevSyncResult, HandlerName)
-            end;
+        {{log,From,Bin},MRef} ->
+            WResult =
+                if Type == file ->
+                        %% check that file hasn't been deleted
+                        CheckFile =
+                            fun() -> {ok,_} = file:read_file_info(DevName) end,
+                        spawn_link(CheckFile),
+                        write_to_dev(Fd, Bin, DevName,
+                                     PrevWriteResult, HandlerName);
+                   true ->
+                        _ = io:put_chars(Fd, Bin),
+                        ok
+                end,
+            From ! {MRef,ok},
+            file_ctrl_loop(Fd, Type, DevName, false,
+                           WResult, PrevSyncResult, HandlerName);
 
         filesync when not Synced ->
             Result = sync_dev(Fd, DevName, PrevSyncResult, HandlerName),