Merge pull request #1283 from bettio/gen_server-start_monitor

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.

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

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
 %%