From 17e198d6ee60f7dec9abfed272cf4226aea44535 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Fri, 18 Aug 2017 19:56:02 +0200
Subject: erts: Async auto-connect for monitor/2

---
 erts/emulator/beam/bif.c      | 23 ++++++-----------------
 erts/preloaded/src/erlang.erl | 21 ++++-----------------
 2 files changed, 10 insertions(+), 34 deletions(-)

(limited to 'erts')

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 2583a5f8d6..2af61e6ebc 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -790,31 +790,20 @@ remote_monitor(Process *p, Eterm bifarg1, Eterm bifarg2,
     BIF_RETTYPE ret;
     int code;
 
+    ASSERT(dep);
     erts_proc_lock(p, ERTS_PROC_LOCK_LINK);
     code = erts_dsig_prepare(&dsd, &dep,
 			     p, (ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK),
-			     ERTS_DSP_RLOCK, 0, 0);
+			     ERTS_DSP_RLOCK, 0, 1);
     switch (code) {
-    case ERTS_DSIG_PREP_PENDING:
-	/*
-	 * Must wait for connection to know if node supports monitor.
-	 * Damn these synchronous errors.
-	 */
-	erts_smp_de_runlock(dep);
-	/* fall through */
     case ERTS_DSIG_PREP_NOT_ALIVE:
     case ERTS_DSIG_PREP_NOT_CONNECTED:
 	erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
 	ERTS_BIF_PREP_TRAP2(ret, dmonitor_p_trap, p, bifarg1, bifarg2);
 	break;
+    case ERTS_DSIG_PREP_PENDING:
     case ERTS_DSIG_PREP_CONNECTED:
-	if (!(dep->flags & DFLAG_DIST_MONITOR)
-	    || (byname && !(dep->flags & DFLAG_DIST_MONITOR_NAME))) {
-	    erts_de_runlock(dep);
-	    erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
-	    ERTS_BIF_PREP_ERROR(ret, p, BADARG);
-	}
-	else {
+	{
 	    Eterm p_trgt, p_name, d_name, mon_ref;
 
 	    mon_ref = erts_make_ref(p);
@@ -917,17 +906,17 @@ local_port:
 	if (!erts_is_alive && remote_node != am_Noname) {
             goto badarg; /* Remote monitor from (this) undistributed node */
 	}
-	dep = erts_sysname_to_connected_dist_entry(remote_node);
+	dep = erts_find_or_insert_dist_entry(remote_node);
 	if (dep == erts_this_dist_entry) {
             ret = local_name_monitor(BIF_P, BIF_ARG_1, name);
 	} else {
 	    ret = remote_monitor(BIF_P, BIF_ARG_1, BIF_ARG_2, dep, name, 1);
 	}
+	erts_deref_dist_entry(dep);
     } else {
 badarg:
 	ERTS_BIF_PREP_ERROR(ret, BIF_P, BADARG);
     }
-
     return ret;
 }
 
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index 9630c0c934..d63a413f21 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -3367,23 +3367,10 @@ dsend({Name, Node}, Msg, Opts) ->
 
 -spec erlang:dmonitor_p('process', pid() | {atom(),atom()}) -> reference().
 dmonitor_p(process, ProcSpec) ->
-    %% ProcSpec = pid() | {atom(),atom()}
-    %% ProcSpec CANNOT be an atom because a locally registered process
-    %% is never handled here.
-    Node = case ProcSpec of
-	       {S,N} when erlang:is_atom(S),
-                          erlang:is_atom(N),
-                          N =/= erlang:node() -> N;
-	       _ when erlang:is_pid(ProcSpec) -> erlang:node(ProcSpec)
-	   end,
-    case net_kernel:connect(Node) of
-	true ->
-	    erlang:monitor(process, ProcSpec);
-	false ->
-	    Ref = erlang:make_ref(),
-	    erlang:self() ! {'DOWN', Ref, process, ProcSpec, noconnection},
-	    Ref
-    end.
+    %% Only called when auto-connect attempt failed early in VM
+    Ref = erlang:make_ref(),
+    erlang:self() ! {'DOWN', Ref, process, ProcSpec, noconnection},
+    Ref.
 
 %%
 %% Trap function used when modified timing has been enabled.
-- 
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