Add missing cowboy_children module

My bad! Still new at this.

src/cowboy_children.erl

@@ -0,0 +1,160 @@
+%% Copyright (c) 2017, Loïc Hoguin <essen@ninenines.eu>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+-module(cowboy_children).
+
+-export([init/0]).
+-export([up/4]).
+-export([down/2]).
+-export([shutdown/2]).
+-export([shutdown_timeout/3]).
+-export([terminate/1]).
+-export([which_children/2]).
+-export([count_children/1]).
+
+-record(child, {
+	pid :: pid(),
+	streamid :: cowboy_stream:streamid() | undefined,
+	shutdown :: timeout(),
+	timer = undefined :: undefined | reference()
+}).
+
+-type children() :: [#child{}].
+-export_type([children/0]).
+
+-spec init() -> [].
+init() ->
+	[].
+
+-spec up(Children, pid(), cowboy_stream:streamid(), timeout())
+	-> Children when Children::children().
+up(Children, Pid, StreamID, Shutdown) ->
+	[#child{
+		pid=Pid,
+		streamid=StreamID,
+		shutdown=Shutdown
+	}|Children].
+
+-spec down(Children, pid())
+	-> {ok, cowboy_stream:streamid() | undefined, Children} | error
+	when Children::children().
+down(Children0, Pid) ->
+	case lists:keytake(Pid, #child.pid, Children0) of
+		{value, #child{streamid=StreamID, timer=Ref}, Children} ->
+			_ = case Ref of
+				undefined -> ok;
+				_ -> erlang:cancel_timer(Ref, [{async, true}, {info, false}])
+			end,
+			{ok, StreamID, Children};
+		false ->
+			error
+	end.
+
+%% We ask the processes to shutdown first. This gives
+%% a chance to processes that are trapping exits to
+%% shut down gracefully. Others will exit immediately.
+%%
+%% @todo We currently fire one timer per process being
+%% shut down. This is probably not the most efficient.
+%% A more efficient solution could be to maintain a
+%% single timer and decrease the shutdown time of all
+%% processes when it fires. This is however much more
+%% complex, and there aren't that many processes that
+%% will need to be shutdown through this function, so
+%% this is left for later.
+-spec shutdown(Children, cowboy_stream:streamid())
+	-> Children when Children::children().
+shutdown(Children0, StreamID) ->
+	[
+		case Child of
+			#child{pid=Pid, streamid=StreamID, shutdown=Shutdown} ->
+				exit(Pid, shutdown),
+				Ref = erlang:start_timer(Shutdown, self(), {shutdown, Pid}),
+				Child#child{streamid=undefined, timer=Ref};
+			_ ->
+				Child
+		end
+	|| Child <- Children0].
+
+-spec shutdown_timeout(children(), reference(), pid()) -> ok.
+shutdown_timeout(Children, Ref, Pid) ->
+	case lists:keyfind(Pid, #child.pid, Children) of
+		#child{timer=Ref} ->
+			exit(Pid, kill),
+			ok;
+		_ ->
+			ok
+	end.
+
+-spec terminate(children()) -> ok.
+terminate(Children) ->
+	%% Ask all children to shutdown first.
+	_ = [exit(Pid, shutdown) || #child{pid=Pid} <- Children],
+	%% Loop until that time or until all children are dead.
+	before_terminate_loop(Children).
+
+before_terminate_loop([]) ->
+	ok;
+before_terminate_loop(Children) ->
+	%% Find the longest shutdown time.
+	Time = longest_shutdown_time(Children, 0),
+	%% We delay the creation of the timer if one of the
+	%% processes has an infinity shutdown value.
+	TRef = case Time of
+		infinity -> undefined;
+		_ -> erlang:start_timer(Time, self(), terminate)
+	end,
+	terminate_loop(Children, TRef).
+
+terminate_loop([], _) ->
+	ok;
+terminate_loop(Children, TRef) ->
+	receive
+		{'EXIT', Pid, _} when TRef =:= undefined ->
+			{value, #child{shutdown=Shutdown}, Children1}
+				= lists:keytake(Pid, #child.pid, Children),
+			%% We delayed the creation of the timer. If a process with
+			%% infinity shutdown just ended, we might have to start that timer.
+			case Shutdown of
+				infinity -> before_terminate_loop(Children1);
+				_ -> terminate_loop(Children1, TRef)
+			end;
+		{'EXIT', Pid, _} ->
+			terminate_loop(lists:keydelete(Pid, #child.pid, Children), TRef);
+		{timeout, TRef, terminate} ->
+			%% Brutally kill any remaining children.
+			_ = [exit(Pid, kill) || #child{pid=Pid} <- Children],
+			ok
+	end.
+
+longest_shutdown_time([], Time) ->
+	Time;
+longest_shutdown_time([#child{shutdown=ChildTime}|Tail], Time) when ChildTime > Time ->
+	longest_shutdown_time(Tail, ChildTime);
+longest_shutdown_time([_|Tail], Time) ->
+	longest_shutdown_time(Tail, Time).
+
+-spec which_children(children(), module()) -> [{module(), pid(), worker, [module()]}].
+which_children(Children, Module) ->
+	[{Module, Pid, worker, [Module]} || #child{pid=Pid} <- Children].
+
+-spec count_children(children()) -> [{atom(), non_neg_integer()}].
+count_children(Children) ->
+	Count = length(Children),
+	[
+		{specs, 1},
+		{active, Count},
+		{supervisors, 0},
+		{workers, Count}
+	].