Introduce interarrival api to amoc throttle

Author: NelsonVides

src/throttle/amoc_throttle.erl

@@ -23,11 +23,17 @@
 %% controlled, which corresponds to the number of processes started
 -type throttle() :: #{rate := rate(),
                       interval := interval()}.
+-type interarrival() :: #{interarrival := non_neg_integer()}.
 %% Throttle unit of measurement
 -type config() :: #{rate := rate(),
                     interval => interval(),
+                    parallelism => non_neg_integer()}
+                | #{interarrival := non_neg_integer(),
                     parallelism => non_neg_integer()}.
-%% Literal throttle configuration
+%% Literal throttle configuration. It can state `interarrival', in milliseconds,
+%% in which case the rate per interval is calculated to allow one event every given milliseconds,
+%% or, literally give the rate per interval.
+
 -type gradual_rate_config() :: #{from_rate := rate(),
                                  to_rate := rate(),
                                  interval => interval(),

src/throttle/amoc_throttle_controller.erl

@@ -70,6 +70,13 @@ start_link() ->
 -spec ensure_throttle_processes_started(name(), amoc_throttle:config()) ->
     {ok, started | already_started} |
     {error, invalid_throttle | wrong_reconfiguration | wrong_no_of_procs}.
+ensure_throttle_processes_started(
+  Name, #{interarrival := EveryMs} = Config)
+  when is_atom(Name), ?NONNEG_INT(EveryMs) ->
+    raise_event_on_slave_node(Name, init),
+    Config1 = #{rate => ?DEFAULT_INTERVAL div EveryMs, interval => ?DEFAULT_INTERVAL},
+    Config2 = Config1#{parallelism => maps:get(parallelism, Config, ?DEFAULT_NO_PROCESSES)},
+    gen_server:call(?MASTER_SERVER, {start_processes, Name, Config2});
 ensure_throttle_processes_started(
   Name, #{rate := Rate, interval := Interval, parallelism := NoOfProcesses} = Config)
   when is_atom(Name), ?POS_INT(Rate), ?NONNEG_INT(Interval), ?POS_INT(NoOfProcesses) ->

test/throttle_SUITE.erl

@@ -19,6 +19,7 @@ groups() ->
       [
        start,
        start_descriptive,
+       start_interarrival,
        rate_zero_is_not_accepted,
        low_rate_gets_remapped,
        low_interval_get_remapped,
@@ -77,6 +78,17 @@ start_descriptive(_) ->
     Description = #{rate => 100, interval => 5000, parallelism => 12},
     ?assertMatch({ok, started}, amoc_throttle:start(?FUNCTION_NAME, Description)).
 
+start_interarrival(_) ->
+    %% Starts successfully
+    Description = #{interarrival => 50, parallelism => 1},
+    ?assertMatch({ok, started}, amoc_throttle:start(?FUNCTION_NAME, Description)),
+    State = get_state_of_one_process(?FUNCTION_NAME),
+    ?assertMatch(#{name := ?FUNCTION_NAME,
+                   interval := 60000,
+                   delay_between_executions := 50,
+                   n := 1200},
+                 State).
+
 rate_zero_is_not_accepted(_) ->
     ?assertMatch({error, invalid_throttle}, amoc_throttle:start(?FUNCTION_NAME, 0, 100, 1)).