From 0408116fa27b5891513d5e8b90e462ecbeff200b Mon Sep 17 00:00:00 2001
From: zmstone <zmstone@gmail.com>
Date: Fri, 19 Jul 2024 09:14:43 +0200
Subject: [PATCH] refactor: remove roundrobin partitioner

roudrobin was never used, and it was implemented wrong (process dict)
if needed, it should be re-implemented using an atomic
---
 README.md               |  2 --
 src/wolff_producers.erl | 32 +++++++++++---------------------
 test/wolff_tests.erl    |  1 -
 3 files changed, 11 insertions(+), 24 deletions(-)

diff --git a/README.md b/README.md
index 2aea154..54698b9 100644
--- a/README.md
+++ b/README.md
@@ -167,8 +167,6 @@ wolff:send(Producers, [Msg], AckFun).
 * `compression`: `no_compression` (default) `snappy` or `gzip`.
 
 * `partitioner`: default `random`. other possible values are:
-   `roundrobin`: Starts from partition `0`, next partition to use is saved in caller's
-   process dictionary.
    `first_key_dispatch`: `erlang:phash2(Key) rem PartitionCount` where Key is the `key`
    field of the first message in the batch to produce.
    `fun((PartitionCount, [msg()]) -> partition())`: Caller defined callback.
diff --git a/src/wolff_producers.erl b/src/wolff_producers.erl
index 4fb6ec7..feb4613 100644
--- a/src/wolff_producers.erl
+++ b/src/wolff_producers.erl
@@ -49,7 +49,6 @@
                       wolff_producer:config_key().
 -type config() :: #{config_key() => term()}.
 -type partitioner() :: random %% default
-                     | roundrobin
                      | first_key_dispatch
                      | fun((PartitionCount :: pos_integer(), [wolff:msg()]) -> partition())
                      | partition().
@@ -183,21 +182,20 @@ pick_producer(#{partitioner := Partitioner,
                 topic := TopicOrAlias
                }, Batch) ->
   Count = get_partition_cnt(ClientId, TopicOrAlias),
-  Partition = pick_partition(Count, Partitioner, Batch),
   LookupFn = fun(P) ->
     {ok, Pid} = find_producer_by_partition(ClientId, TopicOrAlias, P),
     Pid
   end,
   try
+    Partition = pick_partition(Count, Partitioner, Batch),
     do_pick_producer(Partitioner, Partition, Count, LookupFn)
   catch
     throw:Reason ->
-      erlang:throw(#{reason => Reason,
+      erlang:throw(Reason#{
                      topic => get_topic(TopicOrAlias),
                      alias => get_alias(TopicOrAlias),
-                     partition => Partition,
                      client => ClientId
-                    })
+                   })
   end.
 
 do_pick_producer(Partitioner, Partition0, Count, LookupFn) ->
@@ -206,19 +204,15 @@ do_pick_producer(Partitioner, Partition0, Count, LookupFn) ->
     true -> {Partition0, Pid0};
     false when Partitioner =:= random ->
       pick_next_alive(LookupFn, Partition0, Count);
-    false when Partitioner =:= roundrobin ->
-      R = {Partition1, _Pid1} = pick_next_alive(LookupFn, Partition0, Count),
-      _ = put(wolff_roundrobin, (Partition1 + 1) rem Count),
-      R;
     false ->
-      throw(producer_down)
+      throw(#{cause => producer_down, partition => Partition0})
   end.
 
 pick_next_alive(LookupFn, Partition, Count) ->
   pick_next_alive(LookupFn, (Partition + 1) rem Count, Count, _Tried = 1).
 
 pick_next_alive(_LookupFn, _Partition, Count, Count) ->
-  throw(all_producers_down);
+  throw(#{cause => all_producers_down});
 pick_next_alive(LookupFn, Partition, Count, Tried) ->
   Pid = LookupFn(Partition),
   case is_alive(Pid) of
@@ -228,22 +222,18 @@ pick_next_alive(LookupFn, Partition, Count, Tried) ->
 
 is_alive(Pid) -> is_pid(Pid) andalso is_process_alive(Pid).
 
+pick_partition(Count, Partitioner, _) when not is_integer(Count);
+                                           Count =< 0 ->
+  throw(#{cause => invalid_partition_count,
+          count => Count,
+          partitioner => Partitioner
+         });
 pick_partition(_Count, Partition, _) when is_integer(Partition) ->
   Partition;
 pick_partition(Count, F, Batch) when is_function(F) ->
   F(Count, Batch);
-pick_partition(Count, Partitioner, _) when not is_integer(Count);
-                                           Count =< 0 ->
-  error({invalid_partition_count, Count, Partitioner});
 pick_partition(Count, random, _) ->
   rand:uniform(Count) - 1;
-pick_partition(Count, roundrobin, _) ->
-  Partition = case get(wolff_roundrobin) of
-                undefined -> 0;
-                Number    -> Number
-              end,
-  _ = put(wolff_roundrobin, (Partition + 1) rem Count),
-  Partition;
 pick_partition(Count, first_key_dispatch, [#{key := Key} | _]) ->
   erlang:phash2(Key) rem Count.
 
diff --git a/test/wolff_tests.erl b/test/wolff_tests.erl
index 758c107..235d2a7 100644
--- a/test/wolff_tests.erl
+++ b/test/wolff_tests.erl
@@ -227,7 +227,6 @@ test_connection_restart() ->
   ProducerCfg0 = producer_config(),
   %% allow message linger, so we have time to kill the connection
   ProducerCfg = ProducerCfg0#{max_linger_ms => 200,
-                              partitioner => roundrobin,
                               reconnect_delay_ms => 0
                              },
   {ok, Producers} = wolff:start_producers(Client, <<"test-topic">>, ProducerCfg),