Merge pull request devinus#60 from JYZR/fifo-support

Adds support for FIFO strategy

README.md

@@ -155,6 +155,8 @@ code_change(_OldVsn, State, _Extra) ->
 - `worker_module`: the module that represents the workers
 - `size`: maximum pool size
 - `max_overflow`: maximum number of workers created if pool is empty
+- `strategy`: `lifo` or `fifo`, determines whether checked in workers should be
+  placed first or last in the line of available workers. Default is `lifo`.
 
 ## Authors
 

src/poolboy.erl

@@ -34,7 +34,8 @@
     monitors :: ets:tid(),
     size = 5 :: non_neg_integer(),
     overflow = 0 :: non_neg_integer(),
-    max_overflow = 10 :: non_neg_integer()
+    max_overflow = 10 :: non_neg_integer(),
+    strategy = lifo :: lifo | fifo
 }).
 
 -spec checkout(Pool :: pool()) -> pid().
@@ -132,6 +133,10 @@ init([{size, Size} | Rest], WorkerArgs, State) when is_integer(Size) ->
     init(Rest, WorkerArgs, State#state{size = Size});
 init([{max_overflow, MaxOverflow} | Rest], WorkerArgs, State) when is_integer(MaxOverflow) ->
     init(Rest, WorkerArgs, State#state{max_overflow = MaxOverflow});
+init([{strategy, lifo} | Rest], WorkerArgs, State) ->
+    init(Rest, WorkerArgs, State#state{strategy = lifo});
+init([{strategy, fifo} | Rest], WorkerArgs, State) ->
+    init(Rest, WorkerArgs, State#state{strategy = fifo});
 init([_ | Rest], WorkerArgs, State) ->
     init(Rest, WorkerArgs, State);
 init([], _WorkerArgs, #state{size = Size, supervisor = Sup} = State) ->
@@ -279,7 +284,8 @@ handle_checkin(Pid, State) ->
     #state{supervisor = Sup,
            waiting = Waiting,
            monitors = Monitors,
-           overflow = Overflow} = State,
+           overflow = Overflow,
+           strategy = Strategy} = State,
     case queue:out(Waiting) of
         {{value, {From, Ref}}, Left} ->
             true = ets:insert(Monitors, {Pid, Ref}),
@@ -289,7 +295,10 @@ handle_checkin(Pid, State) ->
             ok = dismiss_worker(Sup, Pid),
             State#state{waiting = Empty, overflow = Overflow - 1};
         {empty, Empty} ->
-            Workers = [Pid | State#state.workers],
+            Workers = case Strategy of
+                lifo -> [Pid | State#state.workers];
+                fifo -> State#state.workers ++ [Pid]
+            end,
             State#state{workers = Workers, waiting = Empty, overflow = 0}
     end.
 

test/poolboy_tests.erl

@@ -56,6 +56,15 @@ pool_test_() ->
             },
             {<<"Pool demonitors when a checkout is cancelled">>,
                 fun demonitors_when_checkout_cancelled/0
+            },
+            {<<"Check that LIFO is the default strategy">>,
+                fun default_strategy_lifo/0
+            },
+            {<<"Check LIFO strategy">>,
+                fun lifo_strategy/0
+            },
+            {<<"Check FIFO strategy">>,
+                fun fifo_strategy/0
             }
         ]
     }.
@@ -432,6 +441,30 @@ demonitors_when_checkout_cancelled() ->
     Pid ! ok,
     ok = pool_call(Pool, stop).
 
+default_strategy_lifo() ->
+    %% Default strategy is LIFO
+    {ok, Pid} = new_pool(2, 0),
+    Worker1 = poolboy:checkout(Pid),
+    ok = poolboy:checkin(Pid, Worker1),
+    Worker1 = poolboy:checkout(Pid),
+    poolboy:stop(Pid).
+
+lifo_strategy() ->
+    {ok, Pid} = new_pool(2, 0, lifo),
+    Worker1 = poolboy:checkout(Pid),
+    ok = poolboy:checkin(Pid, Worker1),
+    Worker1 = poolboy:checkout(Pid),
+    poolboy:stop(Pid).
+
+fifo_strategy() ->
+    {ok, Pid} = new_pool(2, 0, fifo),
+    Worker1 = poolboy:checkout(Pid),
+    ok = poolboy:checkin(Pid, Worker1),
+    Worker2 = poolboy:checkout(Pid),
+    ?assert(Worker1 =/= Worker2),
+    Worker1 = poolboy:checkout(Pid),
+    poolboy:stop(Pid).
+
 get_monitors(Pid) ->
     [{monitors, Monitors}] = erlang:process_info(Pid, [monitors]),
     Monitors.
@@ -441,5 +474,11 @@ new_pool(Size, MaxOverflow) ->
                         {worker_module, poolboy_test_worker},
                         {size, Size}, {max_overflow, MaxOverflow}]).
 
+new_pool(Size, MaxOverflow, Strategy) ->
+    poolboy:start_link([{name, {local, poolboy_test}},
+                        {worker_module, poolboy_test_worker},
+                        {size, Size}, {max_overflow, MaxOverflow},
+                        {strategy, Strategy}]).
+
 pool_call(ServerRef, Request) ->
     gen_server:call(ServerRef, Request).