Merge branch 'john/erts/prim_file-init-restart/OTP-15495/ERL-821' into maint

* john/erts/prim_file-init-restart/OTP-15495/ERL-821:
  Remove an unused variable
  Spawn prim_file helper as a system process

2 files changed, 20 insertions, 12 deletions

diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index 8f29a569f2..305b524438 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -97,6 +97,8 @@
 -export([counters_new/1, counters_get/2, counters_add/3,
          counters_put/3, counters_info/1]).
 
+-export([spawn_system_process/3]).
+
 %%
 %% Await result of send to port
 %%
@@ -726,3 +728,10 @@ counters_put(_Ref, _Ix, _Value) ->
 -spec counters_info(reference()) -> #{}.
 counters_info(_Ref) ->
     erlang:nif_error(undef).
+
+-spec spawn_system_process(Mod, Func, Args) -> pid() when
+    Mod :: atom(),
+    Func :: atom(),
+    Args :: list().
+spawn_system_process(_Mod, _Func, _Args) ->
+    erlang:nif_error(undefined).
diff --git a/erts/preloaded/src/prim_file.erl b/erts/preloaded/src/prim_file.erl
index 5fc22bc582..0994e2a9f4 100644
--- a/erts/preloaded/src/prim_file.erl
+++ b/erts/preloaded/src/prim_file.erl
@@ -46,7 +46,7 @@
 -define(MIN_READLINE_SIZE, 256).
 -define(LARGEFILESIZE, (1 bsl 63)).
 
--export([copy/3]).
+-export([copy/3, start/0]).
 
 -include("file_int.hrl").
 
@@ -85,14 +85,21 @@ is_translatable(_) ->
 
 %% This is a janitor process used to close files whose controlling process has
 %% died. The emulator will be torn down if this is killed.
-delayed_close_loop() ->
+start() ->
+    helper_loop().
+
+helper_loop() ->
     receive
         {close, FRef} when is_reference(FRef) -> delayed_close_nif(FRef);
         _ -> ok
     end,
-    delayed_close_loop().
+    helper_loop().
 
-%%
+on_load() ->
+    %% This is spawned as a system process to prevent init:restart/0 from
+    %% killing it.
+    Pid = erts_internal:spawn_system_process(?MODULE, start, []),
+    ok = erlang:load_nif(atom_to_list(?MODULE), Pid).
 
 %% Returns {error, Reason} | {ok, BytesCopied}
 copy(#file_descriptor{module = ?MODULE} = Source,
@@ -103,14 +110,6 @@ copy(#file_descriptor{module = ?MODULE} = Source,
     %% XXX Should be moved down to the driver for optimization.
     file:copy_opened(Source, Dest, Length).
 
-on_load() ->
-    Pid = spawn(fun() ->
-                    process_flag(trap_exit, true),
-                    delayed_close_loop()
-                end),
-    true = register(erts_prim_file, Pid),
-    ok = erlang:load_nif(atom_to_list(?MODULE), Pid).
-
 open(Name, Modes) ->
     %% The try/catch pattern seen here is used throughout the file to adhere to
     %% the public file interface, which has leaked through for ages because of