Add count_children/1 to supervisor.erl

Signed-off-by: Peter M <petermm@gmail.com>

Author: petermm

CHANGELOG.md

@@ -52,7 +52,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `erlang:module_loaded/1`
 - Added `binary:replace/3`, `binary:replace/4`
 - Added `binary:match/2` and `binary:match/3`
-- Added `supervisor:which_children/1`
+- Added `supervisor:which_children/1` and `supervisor:count_children/1`
 - Added `monitored_by` in `process_info/2`
 
 ### Changed

libs/estdlib/src/supervisor.erl

@@ -29,7 +29,8 @@
     terminate_child/2,
     restart_child/2,
     delete_child/2,
-    which_children/1
+    which_children/1,
+    count_children/1
 ]).
 
 -export([
@@ -112,6 +113,9 @@ delete_child(Supervisor, ChildId) ->
 which_children(Supervisor) ->
     gen_server:call(Supervisor, which_children).
 
+count_children(Supervisor) ->
+    gen_server:call(Supervisor, count_children).
+
 init({Mod, Args}) ->
     erlang:process_flag(trap_exit, true),
     case Mod:init(Args) of
@@ -280,7 +284,12 @@ handle_call({delete_child, ID}, _From, #state{children = Children} = State) ->
     end;
 handle_call(which_children, _From, #state{children = Children} = State) ->
     ChildrenInfo = lists:map(fun child_to_info/1, Children),
-    {reply, ChildrenInfo, State}.
+    {reply, ChildrenInfo, State};
+handle_call(count_children, _From, #state{children = Children} = State) ->
+    {Specs, Active, Supers, Workers} =
+        lists:foldl(fun count_child/2, {0, 0, 0, 0}, Children),
+    Reply = [{specs, Specs}, {active, Active}, {supervisors, Supers}, {workers, Workers}],
+    {reply, Reply, State}.
 
 handle_cast(_Msg, State) ->
     {noreply, State}.
@@ -364,6 +373,17 @@ child_to_info(#child{id = Id, pid = Pid, type = Type, modules = Modules}) ->
         end,
     {Id, Child, Type, Modules}.
 
+count_child(#child{pid = Pid, type = worker}, {Specs, Active, Supers, Workers}) ->
+    case is_pid(Pid) andalso is_process_alive(Pid) of
+        true -> {Specs + 1, Active + 1, Supers, Workers + 1};
+        false -> {Specs + 1, Active, Supers, Workers + 1}
+    end;
+count_child(#child{pid = Pid, type = supervisor}, {Specs, Active, Supers, Workers}) ->
+    case is_pid(Pid) andalso is_process_alive(Pid) of
+        true -> {Specs + 1, Active + 1, Supers + 1, Workers};
+        false -> {Specs + 1, Active, Supers + 1, Workers}
+    end.
+
 do_terminate(#child{pid = Pid, shutdown = brutal_kill}) ->
     exit(Pid, kill);
 do_terminate(#child{pid = Pid, shutdown = infinity}) ->

tests/libs/estdlib/test_supervisor.erl

@@ -34,6 +34,7 @@ test() ->
     ok = test_terminate_delete_child(),
     ok = test_terminate_timeout(),
     ok = test_which_children(),
+    ok = test_count_children(),
     ok.
 
 test_basic_supervisor() ->
@@ -88,6 +89,55 @@ test_start_child() ->
     exit(SupPid, shutdown),
     ok.
 
+test_count_children() ->
+    % Test with no children - all counts should be zero
+    {ok, SupPid} = supervisor:start_link(?MODULE, {test_no_child, self()}),
+    [{specs, 0}, {active, 0}, {supervisors, 0}, {workers, 0}] = supervisor:count_children(SupPid),
+
+    % Add a worker child and verify counts
+    {ok, _ChildPid} = supervisor:start_child(SupPid, #{
+        id => test_worker,
+        start => {ping_pong_server, start_link, [self()]},
+        restart => permanent,
+        shutdown => 5000,
+        type => worker
+    }),
+
+    % Check count_children with one active worker
+    [{specs, 1}, {active, 1}, {supervisors, 0}, {workers, 1}] = supervisor:count_children(SupPid),
+
+    % Add a supervisor child and verify counts
+    {ok, _SupervisorPid} = supervisor:start_child(SupPid, #{
+        id => test_supervisor,
+        start => {?MODULE, start_link, [self()]},
+        restart => permanent,
+        shutdown => infinity,
+        type => supervisor
+    }),
+
+    % Check count_children with one worker and one supervisor
+    [{specs, 2}, {active, 2}, {supervisors, 1}, {workers, 1}] = supervisor:count_children(SupPid),
+
+    % Terminate the worker child - spec remains but child becomes inactive
+    ok = supervisor:terminate_child(SupPid, test_worker),
+    [{specs, 2}, {active, 1}, {supervisors, 1}, {workers, 1}] = supervisor:count_children(SupPid),
+
+    % Delete the worker child - removes the spec completely
+    ok = supervisor:delete_child(SupPid, test_worker),
+    [{specs, 1}, {active, 1}, {supervisors, 1}, {workers, 0}] = supervisor:count_children(SupPid),
+
+    % Terminate the supervisor child - spec remains but child becomes inactive
+    ok = supervisor:terminate_child(SupPid, test_supervisor),
+    [{specs, 1}, {active, 0}, {supervisors, 1}, {workers, 0}] = supervisor:count_children(SupPid),
+
+    % Delete the supervisor child - removes the spec completely
+    ok = supervisor:delete_child(SupPid, test_supervisor),
+    [{specs, 0}, {active, 0}, {supervisors, 0}, {workers, 0}] = supervisor:count_children(SupPid),
+
+    unlink(SupPid),
+    exit(SupPid, shutdown),
+    ok.
+
 test_terminate_delete_child() ->
     {ok, SupPid} = supervisor:start_link(?MODULE, {test_no_child, self()}),
     {ok, Pid} = supervisor:start_child(SupPid, #{