[kernel] Add some utility functions (prep for observer).

Add a couple of utility functions, soch as listing monitors
for a socket och which processes has monitored a socket.
Also add utility function to convert a socket to a string (to_list/1)
comparable to erlang:port_to_list/1.

OTP-17155

4 files changed, 207 insertions, 26 deletions

diff --git a/lib/kernel/src/gen_tcp_socket.erl b/lib/kernel/src/gen_tcp_socket.erl
index 743c64cfe5..1d49c1c666 100644
--- a/lib/kernel/src/gen_tcp_socket.erl
+++ b/lib/kernel/src/gen_tcp_socket.erl
@@ -37,7 +37,7 @@
         ]).
 
 %% Utility
--export([info/1]).
+-export([info/1, socket_to_list/1]).
 
 -ifdef(undefined).
 -export([unrecv/2]).
@@ -511,8 +511,10 @@ monitor(?module_socket(_Server, ESock) = Socket) ->
 monitor(Socket) ->
     erlang:error(badarg, [Socket]).
 
+cancel_monitor(MRef) when is_reference(MRef) ->
+    socket:cancel_monitor(MRef);
 cancel_monitor(MRef) ->
-    socket:cancel_monitor(MRef).
+    erlang:error(badarg, [MRef]).
 
 
 %% -------------------------------------------------------------------------
@@ -554,6 +556,15 @@ info(?MODULE_socket(Server, _Socket)) ->
     call(Server, info).
 
 
+%% -------------------------------------------------------------------------
+
+socket_to_list(?module_socket(_Server, Socket)) ->
+    "#Socket" ++ Id = socket:to_list(Socket),
+    "#InetSocket" ++ Id;
+socket_to_list(Socket) ->
+    erlang:error(badarg, [Socket]).
+
+
 %%% ========================================================================
 %%% Socket glue code
 %%%
diff --git a/lib/kernel/src/inet.erl b/lib/kernel/src/inet.erl
index 219876bac2..17c278923f 100644
--- a/lib/kernel/src/inet.erl
+++ b/lib/kernel/src/inet.erl
@@ -31,7 +31,7 @@
 	 getif/1, getif/0, getiflist/0, getiflist/1,
 	 ifget/3, ifget/2, ifset/3, ifset/2,
 	 getstat/1, getstat/2,
-         info/1,
+         info/1, socket_to_list/1,
 	 ip/1, stats/0, options/0, 
 	 pushf/3, popf/1, close/1, gethostname/0, gethostname/1, 
 	 parse_ipv4_address/1, parse_ipv6_address/1, parse_ipv4strict_address/1,
@@ -655,6 +655,17 @@ gethostbyaddr_tm(Address,Timer) ->
     gethostbyaddr_tm(Address, Timer, inet_db:res_option(lookup)).
 
 
+-spec socket_to_list(Socket) -> list() when
+      Socket :: socket().
+
+socket_to_list({'$inet', GenSocketMod, _} = Socket)
+  when is_atom(GenSocketMod) ->
+    GenSocketMod:to_list(Socket);
+socket_to_list(Socket) when is_port(Socket) ->
+    erlang:port_to_list(Socket).
+
+
+
 -spec info(Socket) -> Info when
       Socket :: socket(),
       Info :: term().
diff --git a/lib/kernel/src/socket.erl b/lib/kernel/src/socket.erl
index d63d80bfe8..cc973d81c2 100644
--- a/lib/kernel/src/socket.erl
+++ b/lib/kernel/src/socket.erl
@@ -31,12 +31,15 @@
 	 %% (registry) Socket monitor functions
          number_of_monitors/0, number_of_monitors/1,
          which_monitors/1,
+	 monitored_by/1,
 
          debug/1, socket_debug/1, use_registry/1,
 	 info/0, info/1,
          monitor/1, cancel_monitor/1,
          supports/0, supports/1, supports/2,
-         is_supported/1, is_supported/2, is_supported/3
+         is_supported/1, is_supported/2, is_supported/3,
+
+	 to_list/1
         ]).
 
 -export([
@@ -807,14 +810,50 @@ number_of_monitors(Pid) when is_pid(Pid) ->
 %% *** which_monitors/1 ***
 %%
 %% Interface function to the socket registry
-%% Returns a list of all the monitors of the process.
+%% Returns a list of all the monitors of the process or socket.
 %%
 
 -spec which_monitors(Pid) -> [reference()] when
-	 Pid :: pid().
+      Pid :: pid();
+                    (Socket) -> [reference()] when
+      Socket :: socket().
 
 which_monitors(Pid) when is_pid(Pid) ->
-    ?REGISTRY:which_monitors(Pid).
+    ?REGISTRY:which_monitors(Pid);
+which_monitors(?socket(SockRef) = Socket) when is_reference(SockRef) ->
+    ?REGISTRY:which_monitors(Socket);
+which_monitors(Socket) ->
+    erlang:error(badarg, [Socket]).
+
+
+%% *** monitor_by/1 ***
+%%
+%% Interface function to the socket registry
+%% Returns a list of all the process'es monitoring the socket.
+%%
+
+-spec monitored_by(Socket) -> [reference()] when
+						Socket :: socket().
+
+monitored_by(?socket(SockRef) = Socket) when is_reference(SockRef) ->
+    ?REGISTRY:monitored_by(Socket);
+monitored_by(Socket) ->
+    erlang:error(badarg, [Socket]).
+
+
+%% *** to_list/1 ***
+%%
+%% This is intended to convert a socket() to a printable string.
+%%
+
+-spec to_list(Socket) -> list() when
+      Socket :: socket().
+
+to_list(?socket(SockRef)) when is_reference(SockRef) ->
+    "#Ref" ++ Id = erlang:ref_to_list(SockRef),
+    "#Socket" ++ Id;
+to_list(Socket) ->
+    erlang:error(badarg, [Socket]).
 
 
 %% ===========================================================================
diff --git a/lib/kernel/test/socket_SUITE.erl b/lib/kernel/test/socket_SUITE.erl
index 221e0ea888..efa755fa73 100644
--- a/lib/kernel/test/socket_SUITE.erl
+++ b/lib/kernel/test/socket_SUITE.erl
@@ -25822,20 +25822,60 @@ mon_simple_open_and_close(InitState) ->
 			   0 = socket:number_of_monitors(self()),
 			   ok
                    end},
-         #{desc => "monitor socket",
+         #{desc => "monitor socket - create two",
            cmd  => fun(#{sock := Sock} = State) ->
-                           MRef = socket:monitor(Sock),
-			   ?SEV_IPRINT("Monitor: ~p", [MRef]),
-			   {ok, State#{mon => MRef}}
+                           MRef1 = socket:monitor(Sock),
+                           MRef2 = socket:monitor(Sock),
+			   ?SEV_IPRINT("Monitor(s): "
+				       "~n   1: ~p"
+				       "~n   2: ~p", [MRef1, MRef2]),
+			   {ok, State#{mon1 => MRef1, mon2 => MRef2}}
                    end},
-         #{desc => "verify total number of monitors (=1)",
+         #{desc => "verify total number of monitors (=2)",
            cmd  => fun(_State) ->
-			   1 = socket:number_of_monitors(),
+			   2 = socket:number_of_monitors(),
 			   ok
                    end},
-         #{desc => "verify own number of monitors (=1)",
+         #{desc => "verify own number of monitors (=2)",
            cmd  => fun(_State) ->
-			   1 = socket:number_of_monitors(self()),
+			   2 = socket:number_of_monitors(self()),
+			   ok
+                   end},
+         #{desc => "verify which monitors - (self) two",
+           cmd  => fun(#{mon1 := MRef1,
+			 mon2 := MRef2} = _State) ->
+			   Mons = lists:sort([MRef1, MRef2]),
+			   case lists:sort(socket:which_monitors(self())) of
+			       Mons ->
+				   ok;
+			       SMons ->
+				   ?SEV_EPRINT("Unexpected (self) monitors: "
+					       "~n   Expected: ~p"
+					       "~n   Actual:   ~p",
+					       [Mons, SMons]),
+				   {error, unexpected_monitors}
+			   end
+                   end},
+         #{desc => "verify which monitors - (sock) two",
+           cmd  => fun(#{sock := Sock,
+			 mon1 := MRef1,
+			 mon2 := MRef2} = _State) ->
+			   Mons = lists:sort([MRef1, MRef2]),
+			   case lists:sort(socket:which_monitors(Sock)) of
+			       Mons ->
+				   ok;
+			       SMons ->
+				   ?SEV_EPRINT("Unexpected (sock) monitors: "
+					       "~n   Expected: ~p"
+					       "~n   Actual:   ~p",
+					       [Mons, SMons]),
+				   {error, unexpected_monitors}
+			   end
+                   end},
+         #{desc => "verify monitored by - only us",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   Self   = self(),
+			   [Self] = socket:monitored_by(Sock),
 			   ok
                    end},
 
@@ -25845,17 +25885,37 @@ mon_simple_open_and_close(InitState) ->
                            ?SEV_ANNOUNCE_CONTINUE(Pid, close),
                            ok
                    end},
-         #{desc => "await socket down",
+         #{desc => "await socket down 1",
            cmd  => fun(#{sock := Sock,
-			 mon  := MRef} = _State) ->
+			 mon1  := MRef} = _State) ->
 			   receive
 			       {'DOWN', MRef, socket, Sock, Info} ->
 				   ?SEV_IPRINT("received expected down: "
 					       "~n      MRef:   ~p"
-					       "~n      Socket: ~p"
+					       "~n      Socket: ~s"
 					       "~n      Info:   ~p",
-					       [MRef, Sock, Info]),
-				   ok
+					       [MRef,
+						socket:to_list(Sock),
+						Info]),
+				   {ok, maps:remove(mon1, State)}
+			   after 5000 ->
+				   ?SEV_EPRINT("socket down timeout"),
+				   {error, timeout}
+			   end
+                   end},
+         #{desc => "await socket down 2",
+           cmd  => fun(#{sock := Sock,
+			 mon2  := MRef} = State) ->
+			   receive
+			       {'DOWN', MRef, socket, Sock, Info} ->
+				   ?SEV_IPRINT("received expected down: "
+					       "~n      MRef:   ~p"
+					       "~n      Socket: ~s"
+					       "~n      Info:   ~p",
+					       [MRef,
+						socket:to_list(Sock),
+						Info]),
+				   {ok, maps:remove(mon2, State)}
 			   after 5000 ->
 				   ?SEV_EPRINT("socket down timeout"),
 				   {error, timeout}
@@ -25871,6 +25931,17 @@ mon_simple_open_and_close(InitState) ->
 			   0 = socket:number_of_monitors(self()),
 			   ok
                    end},
+         #{desc => "verify which monitors - only one",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   [] = socket:which_monitors(self()),
+			   [] = socket:which_monitors(Sock),
+			   ok
+                   end},
+         #{desc => "verify monitored by - none",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   [] = socket:monitored_by(Sock),
+			   ok
+                   end},
 
          %% Cleanup
          #{desc => "order (owner) terminate",
@@ -26016,6 +26087,19 @@ mon_simple_open_and_exit(InitState) ->
 			   1 = socket:number_of_monitors(self()),
 			   ok
                    end},
+         #{desc => "verify which monitors - only one",
+           cmd  => fun(#{sock := Sock,
+			 mon  := MRef} = _State) ->
+			   [MRef] = socket:which_monitors(self()),
+			   [MRef] = socket:which_monitors(Sock),
+			   ok
+                   end},
+         #{desc => "verify monitored by - only us",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   Self   = self(),
+			   [Self] = socket:monitored_by(Sock),
+			   ok
+                   end},
 
          %% The actual test
          #{desc => "order (owner) terminate",
@@ -26059,6 +26143,17 @@ mon_simple_open_and_exit(InitState) ->
 			   0 = socket:number_of_monitors(self()),
 			   ok
                    end},
+         #{desc => "verify which monitors - only one",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   [] = socket:which_monitors(self()),
+			   [] = socket:which_monitors(Sock),
+			   ok
+                   end},
+         #{desc => "verify monitored by - none",
+           cmd  => fun(#{sock := Sock} = _State) ->
+			   [] = socket:monitored_by(Sock),
+			   ok
+                   end},
 
          %% *** We are done ***
          ?SEV_FINISH_NORMAL
@@ -26519,9 +26614,11 @@ mon_open_and_close_multi_socks(InitState) ->
 			       {'DOWN', MRef, socket, Sock, Info} ->
 				   ?SEV_IPRINT("received expected down: "
 					       "~n      MRef:   ~p"
-					       "~n      Socket: ~p"
+					       "~n      Socket: ~s"
 					       "~n      Info:   ~p",
-					       [MRef, Sock, Info]),
+					       [MRef,
+						socket:to_list(Sock),
+						Info]),
 				   State2 = maps:remove(sock1, State),
 				   State3 = maps:remove(mon1,  State2),
 				   {ok, State3}
@@ -26553,9 +26650,11 @@ mon_open_and_close_multi_socks(InitState) ->
 			       {'DOWN', MRef, socket, Sock, Info} ->
 				   ?SEV_IPRINT("received expected down: "
 					       "~n      MRef:   ~p"
-					       "~n      Socket: ~p"
+					       "~n      Socket: ~s"
 					       "~n      Info:   ~p",
-					       [MRef, Sock, Info]),
+					       [MRef,
+						socket:to_list(Sock),
+						Info]),
 				   State2 = maps:remove(sock2, State),
 				   State3 = maps:remove(mon2,  State2),
 				   {ok, State3}
@@ -26587,9 +26686,11 @@ mon_open_and_close_multi_socks(InitState) ->
 			       {'DOWN', MRef, socket, Sock, Info} ->
 				   ?SEV_IPRINT("received expected down: "
 					       "~n      MRef:   ~p"
-					       "~n      Socket: ~p"
+					       "~n      Socket: ~s"
 					       "~n      Info:   ~p",
-					       [MRef, Sock, Info]),
+					       [MRef,
+						socket:to_list(Sock),
+						Info]),
 				   State2 = maps:remove(sock3, State),
 				   State3 = maps:remove(mon3,  State2),
 				   {ok, State3}
@@ -27792,6 +27893,25 @@ mon_open_and_close_multi_mon(InitState) ->
 			   5 = socket:number_of_monitors(),
 			   ok
                    end},
+         #{desc => "verify monitored by - none",
+           cmd  => fun(#{sock    := Sock,
+			 client1 := Pid1,
+			 client2 := Pid2,
+			 client3 := Pid3,
+			 client4 := Pid4,
+			 client5 := Pid5} = _State) ->
+			   Clients = lists:sort([Pid1, Pid2, Pid3, Pid4, Pid5]),
+			   case lists:sort(socket:monitored_by(Sock)) of
+			       Clients ->
+				   ok;
+			       SClients ->
+				   ?SEV_EPRINT("Unexpected clients: "
+					       "~n   Expected: ~p"
+					       "~n   Actual:   ~p",
+					       [Clients, SClients]),
+				   {error, unexpected_clients}
+			   end
+                   end},
 
          #{desc => "order client 1 to await down",
            cmd  => fun(#{client1 := Pid} = _State) ->