Add support for gen_server:start_monitor/3,4

Similar to start_link but with `monitor` option.
Code for all start with name functions has been refactored to avoid
duplication.

Signed-off-by: Davide Bettio <davide@uninstall.it>

Author: bettio

CHANGELOG.md

@@ -23,6 +23,7 @@ also non string parameters (e.g. `Enum.join([1, 2], ",")`
 - Add support to Elixir for `Process.send/2` `Process.send_after/3/4` and `Process.cancel_timer/1`
 - Add support for `handle_continue` callback in `gen_server`
 - Support for Elixir `List.Chars` protocol
+- Support for `gen_server:start_monitor/3,4`
 
 ### Changed
 

libs/estdlib/src/gen_server.erl

@@ -43,6 +43,7 @@
 -export([
     start/3, start/4,
     start_link/3, start_link/4,
+    start_monitor/3, start_monitor/4,
     stop/1, stop/3,
     call/2, call/3,
     cast/2,
@@ -109,9 +110,9 @@
 
 %% @private
 do_spawn(Module, Args, Options, SpawnOpts) ->
-    Pid = spawn_opt(?MODULE, init_it, [self(), Module, Args, Options], SpawnOpts),
-    case wait_ack(Pid) of
-        ok -> {ok, Pid};
+    PidOrMonRet = spawn_opt(?MODULE, init_it, [self(), Module, Args, Options], SpawnOpts),
+    case wait_ack(PidOrMonRet) of
+        ok -> {ok, PidOrMonRet};
         {error, Reason} -> {error, Reason}
     end.
 
@@ -123,6 +124,15 @@ do_spawn(Name, Module, Args, Options, SpawnOpts) ->
         {error, Reason} -> {error, Reason}
     end.
 
+%% @private
+spawn_if_not_registered(Name, Module, Args, Options, SpawnOpts) ->
+    case erlang:whereis(Name) of
+        undefined ->
+            do_spawn(Name, Module, Args, [{name, Name} | Options], SpawnOpts);
+        Pid ->
+            {error, {already_started, Pid}}
+    end.
+
 init_it(Starter, Name, Module, Args, Options) ->
     try erlang:register(Name, self()) of
         true ->
@@ -209,7 +219,11 @@ init_ack(Parent, Return) ->
     Parent ! {ack, self(), Return},
     ok.
 
-wait_ack(Pid) ->
+wait_ack(Pid) when is_pid(Pid) ->
+    receive
+        {ack, Pid, Return} -> Return
+    end;
+wait_ack({Pid, _MonRef}) when is_pid(Pid) ->
     receive
         {ack, Pid, Return} -> Return
     end.
@@ -246,12 +260,7 @@ crash_report(ErrStr, Parent, E, S) ->
     Options :: options()
 ) -> {ok, pid()} | {error, Reason :: term()}.
 start({local, Name}, Module, Args, Options) when is_atom(Name) ->
-    case erlang:whereis(Name) of
-        undefined ->
-            do_spawn(Name, Module, Args, [{name, Name} | Options], []);
-        Pid ->
-            {error, {already_started, Pid}}
-    end.
+    spawn_if_not_registered(Name, Module, Args, Options, []).
 
 %%-----------------------------------------------------------------------------
 %% @param   Module the module in which the gen_server callbacks are defined
@@ -292,12 +301,7 @@ start(Module, Args, Options) ->
     Options :: options()
 ) -> {ok, pid()} | {error, Reason :: term()}.
 start_link({local, Name}, Module, Args, Options) when is_atom(Name) ->
-    case erlang:whereis(Name) of
-        undefined ->
-            do_spawn(Name, Module, Args, [{name, Name} | Options], [link]);
-        Pid ->
-            {error, {already_started, Pid}}
-    end.
+    spawn_if_not_registered(Name, Module, Args, Options, [link]).
 
 %%-----------------------------------------------------------------------------
 %% @param   Module the module in which the gen_server callbacks are defined
@@ -316,6 +320,49 @@ start_link({local, Name}, Module, Args, Options) when is_atom(Name) ->
 start_link(Module, Args, Options) ->
     do_spawn(Module, Args, Options, [link]).
 
+%%-----------------------------------------------------------------------------
+%% @param   Module the module in which the gen_server callbacks are defined
+%% @param   Args the arguments to pass to the module's init callback
+%% @param   Options the options used to create the gen_server
+%% @returns the gen_server pid and monitor reference tuple if successful;
+%%          {error, Reason}, otherwise.
+%% @doc     Start and monitor an un-named gen_server.
+%%
+%%          This function will start a gen_server instance.
+%%
+%%          <em><b>Note.</b>  The Options argument is currently ignored.</em>
+%% @end
+%%-----------------------------------------------------------------------------
+-spec start_monitor(Module :: module(), Args :: term(), Options :: options()) ->
+    {ok, {Pid :: pid(), MonRef :: reference()}} | {error, Reason :: term()}.
+start_monitor(Module, Args, Options) ->
+    do_spawn(Module, Args, Options, [monitor]).
+
+%%-----------------------------------------------------------------------------
+%% @param   ServerName the name with which to register the gen_server
+%% @param   Module the module in which the gen_server callbacks are defined
+%% @param   Args the arguments to pass to the module's init callback
+%% @param   Options the options used to create the gen_server
+%% @returns the gen_server pid and monitor reference tuple if successful;
+%%          {error, Reason}, otherwise.
+%% @doc     Start and monitor a named gen_server.
+%%
+%%          This function will start a gen_server instance and register the
+%%          newly created process with the process registry.  Subsequent calls
+%%          may use the gen_server name, in lieu of the process id.
+%%
+%%          <em><b>Note.</b>  The Options argument is currently ignored.</em>
+%% @end
+%%-----------------------------------------------------------------------------
+-spec start_monitor(
+    ServerName :: {local, Name :: atom()},
+    Module :: module(),
+    Args :: term(),
+    Options :: options()
+) -> {ok, {Pid :: pid(), MonRef :: reference()}} | {error, Reason :: term()}.
+start_monitor({local, Name}, Module, Args, Options) when is_atom(Name) ->
+    spawn_if_not_registered(Name, Module, Args, Options, [monitor]).
+
 %%-----------------------------------------------------------------------------
 %% @equiv   stop(ServerRef, normal, infinity)
 %% @doc     Stop a previously started gen_server instance.

tests/libs/estdlib/test_gen_server.erl

@@ -36,6 +36,7 @@ test() ->
     ok = test_cast(),
     ok = test_info(),
     ok = test_start_link(),
+    ok = test_start_monitor(),
     ok = test_continue(),
     ok = test_init_exception(),
     ok = test_late_reply(),
@@ -78,6 +79,24 @@ test_start_link() ->
     true = erlang:process_flag(trap_exit, false),
     ok.
 
+test_start_monitor() ->
+    case get_otp_version() of
+        Version when Version =:= atomvm orelse (is_integer(Version) andalso Version >= 23) ->
+            {ok, {Pid, Ref}} = gen_server:start_monitor(?MODULE, [], []),
+
+            pong = gen_server:call(Pid, ping),
+            pong = gen_server:call(Pid, reply_ping),
+            ok = gen_server:cast(Pid, crash),
+            ok =
+                receive
+                    {'DOWN', Ref, process, Pid, _Reason} -> ok
+                after 30000 -> timeout
+                end,
+            ok;
+        _ ->
+            ok
+    end.
+
 test_continue() ->
     {ok, Pid} = gen_server:start_link(?MODULE, {continue, self()}, []),
     [{Pid, continue}, {Pid, after_continue}] = read_replies(Pid),
@@ -392,6 +411,14 @@ test_stop_noproc() ->
             ok
     end.
 
+get_otp_version() ->
+    case erlang:system_info(machine) of
+        "BEAM" ->
+            list_to_integer(erlang:system_info(otp_release));
+        _ ->
+            atomvm
+    end.
+
 %%
 %% callbacks
 %%