Merge branch 'nybek/speed_up_supervisor_count_children' into maint

* nybek/speed_up_supervisor_count_children:
  Speed up supervisor:count_children/1; simple_one_for_one
  Add supervisor:get_callback_module/1

OTP-13290

4 files changed, 103 insertions, 31 deletions

diff --git a/lib/stdlib/doc/src/supervisor.xml b/lib/stdlib/doc/src/supervisor.xml
index 24ff251ce3..815bf4a489 100644
--- a/lib/stdlib/doc/src/supervisor.xml
+++ b/lib/stdlib/doc/src/supervisor.xml
@@ -543,7 +543,10 @@
           </item>
           <item>
             <p><c>active</c> - the count of all actively running child processes
-              managed by this supervisor.</p>
+              managed by this supervisor. In the case of <c>simple_one_for_one</c>
+              supervisors, no check is carried out to ensure that each child process
+              is still alive, though the result provided here is likely to be very
+              accurate unless the supervisor is heavily overloaded.</p>
           </item>
           <item>
             <p><c>supervisors</c> - the count of all children marked as
diff --git a/lib/stdlib/src/supervisor.erl b/lib/stdlib/src/supervisor.erl
index 92a0c29011..cecdebd0c8 100644
--- a/lib/stdlib/src/supervisor.erl
+++ b/lib/stdlib/src/supervisor.erl
@@ -33,6 +33,9 @@
 	 terminate/2, code_change/3]).
 -export([try_again_restart/2]).
 
+%% For release_handler only
+-export([get_callback_module/1]).
+
 %%--------------------------------------------------------------------------
 
 -export_type([sup_flags/0, child_spec/0, startchild_ret/0, strategy/0]).
@@ -113,6 +116,7 @@
 		intensity              :: non_neg_integer(),
 		period                 :: pos_integer(),
 		restarts = [],
+		dynamic_restarts = 0   :: non_neg_integer(),
 	        module,
 	        args}).
 -type state() :: #state{}.
@@ -250,6 +254,17 @@ try_again_restart(Supervisor, Child) ->
 cast(Supervisor, Req) ->
     gen_server:cast(Supervisor, Req).
 
+%%%-----------------------------------------------------------------
+%%% Called by release_handler during upgrade
+-spec get_callback_module(Pid) -> Module when
+      Pid :: pid(),
+      Module :: atom().
+get_callback_module(Pid) ->
+    {status, _Pid, {module, _Mod},
+     [_PDict, _SysState, _Parent, _Dbg, Misc]} = sys:get_status(Pid),
+    [_Header, _Data, {data, [{"State", State}]}] = Misc,
+    State#state.module.
+
 %%% ---------------------------------------------------
 %%% 
 %%% Initialize the supervisor.
@@ -504,39 +519,26 @@ handle_call(which_children, _From, State) ->
 handle_call(count_children, _From, #state{children = [#child{restart_type = temporary,
 							     child_type = CT}]} = State)
   when ?is_simple(State) ->
-    {Active, Count} =
-	?SETS:fold(fun(Pid, {Alive, Tot}) ->
-			   case is_pid(Pid) andalso is_process_alive(Pid) of
-			       true ->{Alive+1, Tot +1};
-			       false ->
-				   {Alive, Tot + 1}
-			   end
-		   end, {0, 0}, dynamics_db(temporary, State#state.dynamics)),
+    Sz = ?SETS:size(dynamics_db(temporary, State#state.dynamics)),
     Reply = case CT of
-		supervisor -> [{specs, 1}, {active, Active},
-			       {supervisors, Count}, {workers, 0}];
-		worker -> [{specs, 1}, {active, Active},
-			   {supervisors, 0}, {workers, Count}]
+		supervisor -> [{specs, 1}, {active, Sz},
+			       {supervisors, Sz}, {workers, 0}];
+		worker -> [{specs, 1}, {active, Sz},
+			   {supervisors, 0}, {workers, Sz}]
 	    end,
     {reply, Reply, State};
 
-handle_call(count_children, _From,  #state{children = [#child{restart_type = RType,
+handle_call(count_children, _From,  #state{dynamic_restarts = Restarts,
+					   children = [#child{restart_type = RType,
 							      child_type = CT}]} = State)
   when ?is_simple(State) ->
-    {Active, Count} =
-	?DICTS:fold(fun(Pid, _Val, {Alive, Tot}) ->
-			   case is_pid(Pid) andalso is_process_alive(Pid) of
-			       true ->
-				   {Alive+1, Tot +1};
-			       false ->
-				   {Alive, Tot + 1}
-			   end
-		   end, {0, 0}, dynamics_db(RType, State#state.dynamics)),
+    Sz = ?DICTS:size(dynamics_db(RType, State#state.dynamics)),
+    Active = Sz - Restarts,
     Reply = case CT of
 		supervisor -> [{specs, 1}, {active, Active},
-			       {supervisors, Count}, {workers, 0}];
+			       {supervisors, Sz}, {workers, 0}];
 		worker -> [{specs, 1}, {active, Active},
-			   {supervisors, 0}, {workers, Count}]
+			   {supervisors, 0}, {workers, Sz}]
 	    end,
     {reply, Reply, State};
 
@@ -806,8 +808,15 @@ restart(Child, State) ->
 	    {shutdown, remove_child(Child, NState)}
     end.
 
-restart(simple_one_for_one, Child, State) ->
+restart(simple_one_for_one, Child, State0) ->
     #child{pid = OldPid, mfargs = {M, F, A}} = Child,
+    State = case OldPid of
+		?restarting(_) ->
+		    NRes = State0#state.dynamic_restarts - 1,
+		    State0#state{dynamic_restarts = NRes};
+		_ ->
+		    State0
+	    end,
     Dynamics = ?DICTS:erase(OldPid, dynamics_db(Child#child.restart_type,
 					       State#state.dynamics)),
     case do_start_child_i(M, F, A) of
@@ -818,7 +827,9 @@ restart(simple_one_for_one, Child, State) ->
 	    NState = State#state{dynamics = ?DICTS:store(Pid, A, Dynamics)},
 	    {ok, NState};
 	{error, Error} ->
-	    NState = State#state{dynamics = ?DICTS:store(restarting(OldPid), A,
+	    NRestarts = State#state.dynamic_restarts + 1,
+	    NState = State#state{dynamic_restarts = NRestarts,
+				 dynamics = ?DICTS:store(restarting(OldPid), A,
 							Dynamics)},
 	    report_error(start_error, Error, Child, State#state.name),
 	    {try_again, NState}
diff --git a/lib/stdlib/test/supervisor_SUITE.erl b/lib/stdlib/test/supervisor_SUITE.erl
index 8cb2a5194a..903ca76575 100644
--- a/lib/stdlib/test/supervisor_SUITE.erl
+++ b/lib/stdlib/test/supervisor_SUITE.erl
@@ -67,6 +67,7 @@
 
 %% Misc tests
 -export([child_unlink/1, tree/1, count_children/1,
+	 count_restarting_children/1,
 	 do_not_save_start_parameters_for_temporary_children/1,
 	 do_not_save_child_specs_for_temporary_children/1,
 	 simple_one_for_one_scale_many_temporary_children/1,
@@ -90,7 +91,8 @@ all() ->
      {group, normal_termination},
      {group, shutdown_termination},
      {group, abnormal_termination}, child_unlink, tree,
-     count_children, do_not_save_start_parameters_for_temporary_children,
+     count_children, count_restarting_children,
+     do_not_save_start_parameters_for_temporary_children,
      do_not_save_child_specs_for_temporary_children,
      simple_one_for_one_scale_many_temporary_children, temporary_bystander,
      simple_global_supervisor, hanging_restart_loop, hanging_restart_loop_simple,
@@ -1459,6 +1461,54 @@ count_children(Config) when is_list(Config) ->
     [1,0,0,0] = get_child_counts(sup_test).
 
 %%-------------------------------------------------------------------------
+%% Test count_children when some children are restarting
+count_restarting_children(Config) when is_list(Config) ->
+    process_flag(trap_exit, true),
+    Child = {child, {supervisor_deadlock, start_child_noreg, []},
+	     permanent, brutal_kill, worker, []},
+    %% 2 sek delay on failing restart (see supervisor_deadlock.erl) ->
+    %% MaxR=20, MaxT=10 should ensure a restart loop when starting and
+    %% restarting 3 instances of the child (as below)
+    {ok, SupPid} = start_link({ok, {{simple_one_for_one, 20, 10}, [Child]}}),
+
+    %% Ets table with state read by supervisor_deadlock.erl
+    ets:new(supervisor_deadlock,[set,named_table,public]),
+    ets:insert(supervisor_deadlock,{fail_start,false}),
+
+    [1,0,0,0] = get_child_counts(SupPid),
+    {ok, Ch1_1} = supervisor:start_child(SupPid, []),
+    [1,1,0,1] = get_child_counts(SupPid),
+    {ok, Ch1_2} = supervisor:start_child(SupPid, []),
+    [1,2,0,2] = get_child_counts(SupPid),
+    {ok, Ch1_3} = supervisor:start_child(SupPid, []),
+    [1,3,0,3] = get_child_counts(SupPid),
+
+    supervisor_deadlock:restart_child(Ch1_1),
+    supervisor_deadlock:restart_child(Ch1_2),
+    supervisor_deadlock:restart_child(Ch1_3),
+    test_server:sleep(400),
+    [1,3,0,3] = get_child_counts(SupPid),
+    [Ch2_1, Ch2_2, Ch2_3] = [C || {_,C,_,_} <- supervisor:which_children(SupPid)],
+
+    ets:insert(supervisor_deadlock,{fail_start,true}),
+    supervisor_deadlock:restart_child(Ch2_1),
+    supervisor_deadlock:restart_child(Ch2_2),
+    test_server:sleep(4000), % allow restart to happen before proceeding
+    [1,1,0,3] = get_child_counts(SupPid),
+
+    ets:insert(supervisor_deadlock,{fail_start,false}),
+    test_server:sleep(4000), % allow restart to happen before proceeding
+    [1,3,0,3] = get_child_counts(SupPid),
+
+    ok = supervisor:terminate_child(SupPid, Ch2_3),
+    [1,2,0,2] = get_child_counts(SupPid),
+    [Ch3_1, Ch3_2] = [C || {_,C,_,_} <- supervisor:which_children(SupPid)],
+    ok = supervisor:terminate_child(SupPid, Ch3_1),
+    [1,1,0,1] = get_child_counts(SupPid),
+    ok = supervisor:terminate_child(SupPid, Ch3_2),
+    [1,0,0,0] = get_child_counts(SupPid).
+
+%%-------------------------------------------------------------------------
 %% Temporary children shall not be restarted so they should not save
 %% start parameters, as it potentially can take up a huge amount of
 %% memory for no purpose.
diff --git a/lib/stdlib/test/supervisor_deadlock.erl b/lib/stdlib/test/supervisor_deadlock.erl
index 288547a972..8d3d1c6f30 100644
--- a/lib/stdlib/test/supervisor_deadlock.erl
+++ b/lib/stdlib/test/supervisor_deadlock.erl
@@ -11,9 +11,11 @@ init([child]) ->
             %% terminates immediately
             {ok, []};
         [{fail_start, true}] ->
-	    %% Restart frequency is MaxR=8, MaxT=10, so this will
-	    %% ensure that restart intensity is not reached -> restart
-	    %% loop
+	    %% A restart frequency of MaxR=8, MaxT=10 should ensure
+	    %% that restart intensity is not reached -> restart loop.
+	    %% (Note that if we use simple_one_for_one, and start
+	    %% 'many' child instances, the restart frequency must be
+	    %% ajusted accordingly.)
             timer:sleep(2000), % NOTE: this could be a gen_server call timeout
 
             {stop, error}
@@ -41,5 +43,11 @@ code_change(_OldVsn, State, _Extra) ->
 start_child() ->
     gen_server:start_link({local, ?MODULE}, ?MODULE, [child], []).
 
+start_child_noreg() ->
+    gen_server:start_link(?MODULE, [child], []).
+
 restart_child() ->
     gen_server:cast(supervisor_deadlock, restart).
+
+restart_child(Pid) ->
+    gen_server:cast(Pid, restart).