erts: Create forker process for spawn driver

Instead of forking from the beam process, we create a separate
process in which all forks are done. This has several advantages:

1) performance:
  * don't have to close all fd's in the world
  * fork only has to copy stuff from a small process
  * work is done in a completely seperate process
  * a 3x performance increase has been measured,
    can be made even greater (10x) if we cache the
    environment in child setup

2) stability
  * the exec is done in another process than beam, which means that
    if the file that we exec to is on an nfs that is not available
    right now we will not block a scheduler until the nfs returns.

3) simplicity
  * don't have to deal with SIGCHLD in the erts

Unfortunately, this solution also implies some badness.

1) There will always be a seperate process running together with
   beam on unix. This could be confusing and undesirable.
2) We have to transfer the entire environment to child_setup
   for each command.

OTP-13088

1 files changed, 18 insertions, 12 deletions

diff --git a/erts/emulator/test/port_SUITE.erl b/erts/emulator/test/port_SUITE.erl
index 3d0509a28c..f2a7ddef2c 100644
--- a/erts/emulator/test/port_SUITE.erl
+++ b/erts/emulator/test/port_SUITE.erl
@@ -385,27 +385,33 @@ input_only(Config) when is_list(Config) ->
 output_only(Config) when is_list(Config) ->
     Dog = test_server:timetrap(test_server:seconds(100)),
     Dir = ?config(priv_dir, Config),
+
+    %% First we test that the port program gets the data
     Filename = filename:join(Dir, "output_only_stream"),
-    output_and_verify(Config, Filename, "-h0",
-          	    random_packet(35777, "echo")),
+    Data = random_packet(35777, "echo"),
+    output_and_verify(Config, ["-h0 -o", Filename], Data),
+    Wait_time = 500,
+    test_server:sleep(Wait_time),
+    {ok, Written} = file:read_file(Filename),
+    Data = binary_to_list(Written),
+
+    %% Then we test that any writes to stdout from
+    %% the port program is not sent to erlang
+    output_and_verify(Config, ["-h0"], Data),
+
     test_server:timetrap_cancel(Dog),
     ok.
 
-output_and_verify(Config, Filename, Options, Data) ->
+output_and_verify(Config, Options, Data) ->
     PortTest = port_test(Config),
-    Command = lists:concat([PortTest, " ",
-          		  Options, " -o", Filename]),
+    Command = lists:concat([PortTest, " " | Options]),
     Port = open_port({spawn, Command}, [out]),
     Port ! {self(), {command, Data}},
     Port ! {self(), close},
     receive
-        {Port, closed} -> ok
-    end,
-    Wait_time = 500,
-    test_server:sleep(Wait_time),
-    {ok, Written} = file:read_file(Filename),
-    Data = binary_to_list(Written),
-    ok.
+        {Port, closed} -> ok;
+        Msg -> ct:fail({received_unexpected_message, Msg})
+    end.
 
 %% Test that receiving several packages written in the same
 %% write operation works.