From 2fe03e832adb11c50bcfc62679cf17779b284124 Mon Sep 17 00:00:00 2001
From: Rickard Green <rickard@erlang.org>
Date: Wed, 27 Jul 2016 19:45:41 +0200
Subject: Reclaim literal area after purge has completed

---
 erts/preloaded/src/erts_literal_area_collector.erl | 113 +++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 erts/preloaded/src/erts_literal_area_collector.erl

(limited to 'erts/preloaded/src/erts_literal_area_collector.erl')

diff --git a/erts/preloaded/src/erts_literal_area_collector.erl b/erts/preloaded/src/erts_literal_area_collector.erl
new file mode 100644
index 0000000000..3befad8dfb
--- /dev/null
+++ b/erts/preloaded/src/erts_literal_area_collector.erl
@@ -0,0 +1,113 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2016. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(erts_literal_area_collector).
+
+-export([start/0]).
+
+%% Currently we only allow two outstanding literal
+%% copying jobs that garbage collect in order to
+%% copy the literals. Maybe we could allow more
+%% than two outstanding processes, but for now we
+%% play it safe...
+-define(MAX_GC_OUTSTND, 2).
+
+%%
+%% The erts_literal_area_collector is started at
+%% VM boot by the VM. It is a spawned as a system
+%% process, i.e, the whole VM will terminate if
+%% this process terminates.
+%%
+start() ->
+    process_flag(trap_exit, true),
+    msg_loop(undefined, 0, 0, []).
+
+%%
+%% The VM will send us a 'copy_literals' message
+%% when it has a new literal area that needs to
+%% be handled is added. We will also be informed
+%% about more areas when we call
+%% erts_internal:release_literal_area_switch().
+%%
+msg_loop(Area, Outstnd, GcOutstnd, NeedGC) ->
+    receive
+
+	%% A new area to handle has arrived...
+	copy_literals when Outstnd == 0 ->
+	    switch_area();
+
+	%% Process (_Pid) has completed the request...
+	{copy_literals, {Area, _GcAllowed, _Pid}, ok} when Outstnd == 1 ->
+	    switch_area(); %% Last process completed...
+	{copy_literals, {Area, false, _Pid}, ok} ->
+	    msg_loop(Area, Outstnd-1, GcOutstnd, NeedGC);
+	{copy_literals, {Area, true, _Pid}, ok} when NeedGC == [] ->
+	    msg_loop(Area, Outstnd-1, GcOutstnd-1, []);
+	{copy_literals, {Area, true, _Pid}, ok} ->
+	    send_copy_req(hd(NeedGC), Area, true),
+	    msg_loop(Area, Outstnd-1, GcOutstnd, tl(NeedGC));
+
+	%% Process (Pid) failed to complete the request
+	%% since it needs to garbage collect in order to
+	%% complete the request...
+	{copy_literals, {Area, false, Pid}, need_gc} when GcOutstnd < ?MAX_GC_OUTSTND ->
+	    send_copy_req(Pid, Area, true),
+	    msg_loop(Area, Outstnd, GcOutstnd+1, NeedGC);
+	{copy_literals, {Area, false, Pid}, need_gc} ->
+	    msg_loop(Area, Outstnd, GcOutstnd, [Pid|NeedGC]);
+
+	%% Not handled message regarding the area that we
+	%% currently are working with. Crash the VM so
+	%% we notice this bug...
+	{copy_literals, {Area, _, _}, _} = Msg when erlang:is_reference(Area) ->
+	    exit({not_handled_message, Msg});
+
+	%% Unexpected garbage message. Get rid of it...
+	_Ignore ->
+	    msg_loop(Area, Outstnd, GcOutstnd, NeedGC)
+
+    end.
+
+switch_area() ->
+    Res = erts_internal:release_literal_area_switch(),
+    erlang:garbage_collect(), %% Almost no live data now...
+    case Res of
+	false ->
+	    %% No more areas to handle...
+	    msg_loop(undefined, 0, 0, []);
+	true ->
+	    %% Send requests to all processes to copy
+	    %% all live data they have referring to the
+	    %% literal area that is to be released...
+	    Area = make_ref(),
+	    Outstnd = send_copy_reqs(erlang:processes(), Area, false),
+	    msg_loop(Area, Outstnd, 0, [])
+    end.
+
+send_copy_reqs(Ps, Area, GC) ->
+    send_copy_reqs(Ps, Area, GC, 0).
+
+send_copy_reqs([], _Area, _GC, N) ->
+    N;
+send_copy_reqs([P|Ps], Area, GC, N) ->
+    send_copy_req(P, Area, GC),
+    send_copy_reqs(Ps, Area, GC, N+1).
+
+send_copy_req(P, Area, GC) ->
+    erts_internal:request_system_task(P, normal, {copy_literals, {Area, GC, P}, GC}).
-- 
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