Speed up supervisor:count_children/1; simple_one_for_one

Speed up supervisor:count_children/1 for simple_one_for_one
supervisors. This is achieved by avoiding looping through all the
child process and verifying that each one is alive.

For a supervisor with 100,000 'temporary' children the count-time will
drop from approx 25ms to about 0.005ms.

For a supervisor with 100,000 'permanent' or 'transient' children the
count-time will drop from approx 30ms to about 0.005ms.

This avoids having the supervisor block for an extended period while
the count takes place. Under normal circumstances the accuracy of the
result should also improve since the duration is too short for many
processes to die during the count.

1 files changed, 11 insertions, 3 deletions

diff --git a/lib/stdlib/test/supervisor_deadlock.erl b/lib/stdlib/test/supervisor_deadlock.erl
index 288547a972..8d3d1c6f30 100644
--- a/lib/stdlib/test/supervisor_deadlock.erl
+++ b/lib/stdlib/test/supervisor_deadlock.erl
@@ -11,9 +11,11 @@ init([child]) ->
             %% terminates immediately
             {ok, []};
         [{fail_start, true}] ->
-	    %% Restart frequency is MaxR=8, MaxT=10, so this will
-	    %% ensure that restart intensity is not reached -> restart
-	    %% loop
+	    %% A restart frequency of MaxR=8, MaxT=10 should ensure
+	    %% that restart intensity is not reached -> restart loop.
+	    %% (Note that if we use simple_one_for_one, and start
+	    %% 'many' child instances, the restart frequency must be
+	    %% ajusted accordingly.)
             timer:sleep(2000), % NOTE: this could be a gen_server call timeout
 
             {stop, error}
@@ -41,5 +43,11 @@ code_change(_OldVsn, State, _Extra) ->
 start_child() ->
     gen_server:start_link({local, ?MODULE}, ?MODULE, [child], []).
 
+start_child_noreg() ->
+    gen_server:start_link(?MODULE, [child], []).
+
 restart_child() ->
     gen_server:cast(supervisor_deadlock, restart).
+
+restart_child(Pid) ->
+    gen_server:cast(Pid, restart).