Implementation of true asynchronous signaling between processes

Communication between Erlang processes has conceptually always been
performed through asynchronous signaling. The runtime system
implementation has however previously preformed most operation
synchronously. In a system with only one true thread of execution, this
is not problematic (often the opposite). In a system with multiple threads
of execution (as current runtime system implementation with SMP support)
it becomes problematic. This since it often involves locking of structures
when updating them which in turn cause resource contention. Utilizing
true asynchronous communication often avoids these resource contention
issues.

The case that triggered this change was contention on the link lock due
to frequent updates of the monitor trees during communication with a
frequently used server. The signal order delivery guarantees of the
language makes it hard to change the implementation of only some signals
to use true asynchronous signaling. Therefore the implementations
of (almost) all signals have been changed.

Currently the following signals have been implemented as true
asynchronous signals:
- Message signals
- Exit signals
- Monitor signals
- Demonitor signals
- Monitor triggered signals (DOWN, CHANGE, etc)
- Link signals
- Unlink signals
- Group leader signals

All of the above already defined as asynchronous signals in the
language. The implementation of messages signals was quite
asynchronous to begin with, but had quite strict delivery constraints
due to the ordering guarantees of signals between a pair of processes.

The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts
that service all kinds of signals. More details regarding the signal
queue can be found in comments in the erl_proc_sig_queue.h file.

The monitor and link implementations have also been completely replaced
in order to fit the new asynchronous signaling implementation as good
as possible. More details regarding the new monitor and link
implementations can be found in the erl_monitor_link.h file.

1 files changed, 4 insertions, 408 deletions

diff --git a/erts/emulator/test/signal_SUITE.erl b/erts/emulator/test/signal_SUITE.erl
index 61a8617165..fab2f45f28 100644
--- a/erts/emulator/test/signal_SUITE.erl
+++ b/erts/emulator/test/signal_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2006-2017. All Rights Reserved.
+%% Copyright Ericsson AB 2006-2018. 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.
@@ -34,23 +34,9 @@
 -export([init_per_testcase/2, end_per_testcase/2]).
 
 % Test cases
--export([xm_sig_order/1,
-	 pending_exit_unlink_process/1,
-	 pending_exit_unlink_dist_process/1,
-	 pending_exit_unlink_port/1,
-	 pending_exit_trap_exit/1,
-	 pending_exit_receive/1,
-	 pending_exit_exit/1,
-	 pending_exit_gc/1,
-	 pending_exit_is_process_alive/1,
-	 pending_exit_process_display/1,
-	 pending_exit_process_info_1/1,
-	 pending_exit_process_info_2/1,
-	 pending_exit_group_leader/1,
-	 exit_before_pending_exit/1]).
+-export([xm_sig_order/1]).
 
 init_per_testcase(Func, Config) when is_atom(Func), is_list(Config) ->
-    available_internal_state(true),
     [{testcase, Func}|Config].
 
 end_per_testcase(_Func, _Config) ->
@@ -60,24 +46,14 @@ init_per_suite(Config) ->
     Config.
 
 end_per_suite(_Config) ->
-    available_internal_state(true),
-    catch erts_debug:set_internal_state(not_running_optimization, true),
-    available_internal_state(false).
+    ok.
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
      {timetrap, {minutes, 2}}].
 
 all() -> 
-    [xm_sig_order, pending_exit_unlink_process,
-     pending_exit_unlink_dist_process,
-     pending_exit_unlink_port, pending_exit_trap_exit,
-     pending_exit_receive, pending_exit_trap_exit,
-     pending_exit_gc, pending_exit_is_process_alive,
-     pending_exit_process_display,
-     pending_exit_process_info_1,
-     pending_exit_process_info_2, pending_exit_group_leader,
-     exit_before_pending_exit].
+    [xm_sig_order].
 
 
 %% Test that exit signals and messages are received in correct order
@@ -113,362 +89,9 @@ xm_sig_order_proc() ->
     end,
     xm_sig_order_proc().
 
-pending_exit_unlink_process(Config) when is_list(Config) ->
-    pending_exit_test(self(), unlink).
-
-pending_exit_unlink_dist_process(Config) when is_list(Config) ->
-    {ok, Node} = start_node(Config),
-    From = spawn(Node, fun () -> receive after infinity -> ok end end),
-    Res = pending_exit_test(From, unlink),
-    stop_node(Node),
-    Res.
-
-pending_exit_unlink_port(Config) when is_list(Config) ->
-    pending_exit_test(hd(erlang:ports()), unlink).
-
-pending_exit_trap_exit(Config) when is_list(Config) ->
-    pending_exit_test(self(), trap_exit).
-
-pending_exit_receive(Config) when is_list(Config) ->
-    pending_exit_test(self(), 'receive').
-
-pending_exit_exit(Config) when is_list(Config) ->
-    pending_exit_test(self(), exit).
-
-pending_exit_gc(Config) when is_list(Config) ->
-    pending_exit_test(self(), gc).
-
-pending_exit_test(From, Type) ->
-    OTE = process_flag(trap_exit, true),
-    Ref = make_ref(),
-    Master = self(),
-    ExitBySignal = case Type of
-                       gc ->
-                           lists:duplicate(10000,
-                                           exit_by_signal);
-                       _ ->
-                           exit_by_signal
-                   end,
-    Pid = spawn_link(
-            fun () ->
-                    receive go -> ok end,
-                    false = have_pending_exit(),
-                    exit = fake_exit(From,
-                                     self(),
-                                     ExitBySignal),
-                    true = have_pending_exit(),
-                    Master ! {self(), Ref, Type},
-                    case Type of
-                        gc ->
-                            force_gc(),
-                            erlang:yield();
-                        unlink ->
-                            unlink(From);
-                        trap_exit ->
-                            process_flag(trap_exit, true);
-                        'receive' ->
-                            receive _ -> ok
-                            after 0 -> ok
-                            end;
-                        exit ->
-                            ok
-                    end,
-                    exit(exit_by_myself)
-            end),
-    Mon = erlang:monitor(process, Pid),
-    Pid ! go,
-    Reason = receive
-                 {'DOWN', Mon, process, Pid, R} ->
-                     receive
-                         {Pid, Ref, Type} ->
-                             ok
-                     after 0 ->
-                             ct:fail(premature_exit)
-                     end,
-                     case Type of
-                         exit ->
-                             exit_by_myself = R;
-                         _ ->
-                             ExitBySignal = R
-                     end
-             end,
-    receive
-        {'EXIT', Pid, R2} ->
-            Reason = R2
-    end,
-    process_flag(trap_exit, OTE),
-    ok,
-    {comment, "Test only valid with current SMP emulator."}.
-
-
-
-exit_before_pending_exit(Config) when is_list(Config) ->
-    %% This is a testcase testcase very specific to the smp
-    %% implementation as it is of the time of writing.
-    %%
-    %% The testcase tries to check that a process can
-    %% exit by itself even though it has a pending exit.
-    OTE = process_flag(trap_exit, true),
-    Master = self(),
-    Tester = spawn_link(
-               fun () ->
-                       Opts = case {erlang:system_info(run_queues),
-                                    erlang:system_info(schedulers_online)} of
-                                  {RQ, SO} when RQ =:= 1; SO =:= 1 -> [];
-                                  _ ->
-                                      process_flag(scheduler, 1),
-                                      [{scheduler, 2}]
-                              end,
-                       P = self(),
-                       Exiter = spawn_opt(fun () ->
-                                                  receive
-                                                      {exit_me, P, R} ->
-                                                          exit(P, R)
-                                                  end
-                                          end, Opts),
-                       erlang:yield(),
-                       Exiter ! {exit_me, self(), exited_by_exiter},
-                       %% We want to get a pending exit
-                       %% before we exit ourselves. We
-                       %% don't want to be scheduled out
-                       %% since we will then see the
-                       %% pending exit.
-                       %%
-                       %% Do something that takes
-                       %% relatively long time but
-                       %% consumes few reductions...
-                       repeat(fun() -> erlang:system_info(procs) end,10),
-                       %% ... then exit.
-                       Master ! {self(),
-                                 pending_exit,
-                                 have_pending_exit()},
-                       exit(exited_by_myself)
-               end),
-    PendingExit = receive {Tester, pending_exit, PE} -> PE end,
-    receive
-	      {'EXIT', Tester, exited_by_myself} ->
-		  process_flag(trap_exit, OTE),
-		  ok;
-	      Msg ->
-		  ct:fail({unexpected_message, Msg})
-	  end,
-    NoScheds = integer_to_list(erlang:system_info(schedulers_online)),
-    {comment,
-     "Was "
-     ++ case PendingExit of
-	    true -> "";
-	    false ->"*not*"
-	end ++ " able to trigger a pending exit. "
-     ++ "Running on " ++ NoScheds ++ " scheduler(s). "
-     ++ "This test is only interesting with at least two schedulers."}.
-
--define(PE_INFO_REPEAT, 100).
-
-pending_exit_is_process_alive(Config) when is_list(Config) ->
-    S = exit_op_test_init(),
-    TestFun = fun (P) -> false = is_process_alive(P) end,
-    repeated_exit_op_test(TestFun, ?PE_INFO_REPEAT),
-    verify_pending_exit_success(S),
-    comment().
-
-pending_exit_process_info_1(Config) when is_list(Config) ->
-    S = exit_op_test_init(),
-    TestFun = fun (P) ->
-			    undefined = process_info(P)
-		    end,
-    repeated_exit_op_test(TestFun, ?PE_INFO_REPEAT),
-    verify_pending_exit_success(S),
-    comment().
-
-pending_exit_process_info_2(Config) when is_list(Config) ->
-    S0 = exit_op_test_init(),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, messages)
-				end, ?PE_INFO_REPEAT),
-    S1 = verify_pending_exit_success(S0),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, status)
-				end, ?PE_INFO_REPEAT),
-    S2 = verify_pending_exit_success(S1),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, links)
-				end, ?PE_INFO_REPEAT),
-    S3 = verify_pending_exit_success(S2),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [messages])
-				end, ?PE_INFO_REPEAT),
-    S4 = verify_pending_exit_success(S3),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [status])
-				end, ?PE_INFO_REPEAT),
-    S5 = verify_pending_exit_success(S4),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [links])
-				end, ?PE_INFO_REPEAT),
-    S6 = verify_pending_exit_success(S5),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [status,
-								     links])
-				end, ?PE_INFO_REPEAT),
-    S7 = verify_pending_exit_success(S6),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [messages,
-								     status])
-				end, ?PE_INFO_REPEAT),
-    S8 = verify_pending_exit_success(S7),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [messages,
-								     links])
-				end, ?PE_INFO_REPEAT),
-    S9 = verify_pending_exit_success(S8),
-    repeated_exit_op_test(
-	    fun (P) ->
-		    undefined = process_info(P, [message_queue_len,
-						 status])
-	    end, ?PE_INFO_REPEAT),
-    S10 = verify_pending_exit_success(S9),
-    repeated_exit_op_test(fun (P) ->
-					undefined = process_info(P, [messages,
-								     links,
-								     status])
-				end, ?PE_INFO_REPEAT),
-    verify_pending_exit_success(S10),
-    comment().
-
-pending_exit_process_display(Config) when is_list(Config) ->
-    S = exit_op_test_init(),
-    TestFun = fun (P) ->
-			    badarg = try
-					 erlang:process_display(P, backtrace)
-				     catch
-					 error:badarg -> badarg
-				     end
-		    end,
-    repeated_exit_op_test(TestFun, ?PE_INFO_REPEAT),
-    verify_pending_exit_success(S),
-    comment().
-
-pending_exit_group_leader(Config) when is_list(Config) ->
-    S = exit_op_test_init(),
-    TestFun = fun (P) ->
-			    badarg = try
-					 group_leader(self(), P)
-				     catch
-					 error:badarg -> badarg
-				     end
-		    end,
-    repeated_exit_op_test(TestFun, ?PE_INFO_REPEAT),
-    verify_pending_exit_success(S),
-    comment().
-
 %%
 %% -- Internal utils --------------------------------------------------------
 %%
-exit_op_test_init() ->
-    put(no_pending_exit_success, 0),
-    put(no_pending_exit_tries, 0),
-    {case {erlang:system_info(run_queues),
-	   erlang:system_info(schedulers_online)} of
-	 {RQ, SO} when RQ =:= 1; SO =:= 1 -> false;
-	 _ -> true
-     end, 0, 0}.
-
-verify_pending_exit_success({false, _, _} = S) ->
-    S;
-verify_pending_exit_success({true, S, T}) ->
-    NewS = get(no_pending_exit_success),
-    NewT = get(no_pending_exit_tries),
-    case NewT =:= T of
-	true -> ok;
-	_ -> case NewS > S of
-		 true -> ok;
-		 _ -> exit(no_pending_exits)
-	     end
-    end,
-    {true, NewS, NewT}.
-
-comment() ->
-    {comment,
-     "Pending exit trigger ratio "
-     ++ integer_to_list(get(no_pending_exit_success))
-     ++ "/"
-     ++ integer_to_list(get(no_pending_exit_tries))
-     ++ "."
-     ++ case get(not_running_opt_test) of
-	    true -> " No 'not running optimization' to disable.";
-	    _ -> ""
-	end}.
-
-repeated_exit_op_test(TestFun, N) ->
-    WorkFun0 = fun () ->
-		       lists:sort(lists:reverse(lists:seq(1, 1000)))
-	       end,
-    repeat(fun () -> exit_op_test(TestFun, WorkFun0) end, N),
-    try erts_debug:set_internal_state(not_running_optimization, false) of
-	Bool when Bool == true; Bool == false -> 
-	    WorkFun1 = fun () ->
-			       erts_debug:set_internal_state(sleep, 0),
-			       lists:sort(lists:reverse(lists:seq(1, 1000)))
-			    end,
-	    repeat(fun () ->
-			   exit_op_test(TestFun, WorkFun1)
-		   end, N)
-    catch
-	error:notsup -> put(not_running_opt_test, true)
-    after
-	catch erts_debug:set_internal_state(not_running_optimization, true)
-    end.
-
-exit_op_test(TestFun, WorkFun) ->
-    Opts = case {erlang:system_info(run_queues),
-		 erlang:system_info(schedulers_online)} of
-	       {RQ, SO} when RQ =:= 1; SO =:= 1 -> [];
-	       _ ->
-		   process_flag(scheduler, 1),
-		   [{scheduler, 2}]
-	   end,
-    Master = self(),
-    Going = make_ref(),
-    P = spawn_opt(fun () ->
-			  loop(10, WorkFun),
-			  Master ! Going,
-			  loop(infinity, WorkFun)
-		  end, Opts),
-    receive Going -> ok end,
-    loop(10, WorkFun),
-    erlang:yield(),
-    exit(P, bang),
-    PE0 = have_pending_exit(P),
-    TestFun(P),
-    PE = case PE0 of
-	     true -> true;
-	     _ -> false
-	 end,
-    case {PE, get(no_pending_exit_success), get(no_pending_exit_tries)} of
-	{true, undefined, undefined} ->
-	    put(no_pending_exit_success, 1),
-	    put(no_pending_exit_tries, 1);
-	{false, undefined, undefined} ->
-	    put(no_pending_exit_success, 0),
-	    put(no_pending_exit_tries, 1);
-	{true, S, T} ->
-	    put(no_pending_exit_success, S+1),
-	    put(no_pending_exit_tries, T+1);
-	{false, _S, T} ->
-	    put(no_pending_exit_tries, T+1)
-    end,
-    ok.
-
-loop(infinity, WorkFun) ->
-    do_loop(infinity, WorkFun);
-loop(0, _WorkFun) ->
-    ok;
-loop(N, WorkFun) when is_integer(N) ->
-    do_loop(N-1, WorkFun).
-
-do_loop(N, WorkFun) ->
-    WorkFun(),
-    loop(N, WorkFun).
 
 repeat(_Fun, N) when is_integer(N), N =< 0 ->
     ok;
@@ -486,30 +109,3 @@ start_node(Config) ->
 
 stop_node(Node) ->
     test_server:stop_node(Node).
-
-have_pending_exit() ->
-    have_pending_exit(self()).
-
-have_pending_exit(Pid) ->
-    erts_debug:get_internal_state({have_pending_exit, Pid}).
-
-force_gc() ->
-    erts_debug:set_internal_state(force_gc, self()).
-
-fake_exit(From, To, Reason) ->
-    erts_debug:set_internal_state(send_fake_exit_signal, {From, To, Reason}).
-
-available_internal_state(Bool) when Bool == true; Bool == false ->
-    case {Bool,
-          (catch erts_debug:get_internal_state(available_internal_state))} of
-        {true, true} ->
-            true;
-        {false, true} ->
-            erts_debug:set_internal_state(available_internal_state, false),
-            true;
-        {true, _} ->
-            erts_debug:set_internal_state(available_internal_state, true),
-            false;
-        {false, _} ->
-            false
-    end.