From 89d80db0450b08dd23f407d8863cfa087fab5871 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pe=CC=81ter=20Go=CC=88mo=CC=88ri?=
 <peter.gomori@erlang-solutions.com>
Date: Thu, 15 May 2014 17:03:10 +0200
Subject: [PATCH] Fix race condition in dynamic pool creation

---
 src/lhttpc_manager.erl        |  4 +++-
 test/lhttpc_manager_tests.erl | 40 ++++++++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/lhttpc_manager.erl b/src/lhttpc_manager.erl
index 80ee047c..9872be21 100644
--- a/src/lhttpc_manager.erl
+++ b/src/lhttpc_manager.erl
@@ -195,7 +195,7 @@ start_link(Options0) ->
 %% @end
 %%------------------------------------------------------------------------------
 -spec ensure_call(pool_id(), pid(), host(), port_num(), boolean(), options()) ->
-                        socket() | 'no_socket'.
+                        socket() | 'undefined'.
 ensure_call(Pool, Pid, Host, Port, Ssl, Options) ->
     SocketRequest = {socket, Pid, Host, Port, Ssl},
     try gen_server:call(Pool, SocketRequest, infinity) of
@@ -224,6 +224,8 @@ ensure_call(Pool, Pid, Host, Port, Ssl, Options) ->
                     case lhttpc:add_pool(Pool, ConnTimeout, PoolMaxSize) of
                         {ok, _Pid} ->
                             ensure_call(Pool, Pid, Host, Port, Ssl, Options);
+                        {error, already_exists} ->
+                            ensure_call(Pool, Pid, Host, Port, Ssl, Options);
                         _ ->
                             %% Failed to create pool, exit as expected
                             exit({noproc, Reason})
diff --git a/test/lhttpc_manager_tests.erl b/test/lhttpc_manager_tests.erl
index 4e24afe0..7183e1cc 100644
--- a/test/lhttpc_manager_tests.erl
+++ b/test/lhttpc_manager_tests.erl
@@ -53,7 +53,8 @@ manager_test_() ->
                 ?_test(one_socket()),
                 {timeout, 60, ?_test(connection_timeout())},
                 {timeout, 60, ?_test(many_sockets())},
-                {timeout, 60, ?_test(closed_race_cond())}
+                {timeout, 60, ?_test(closed_race_cond())},
+                {timeout, 60, ?_test(dyn_pool_race())}
             ]}
     }.
 
@@ -320,6 +321,43 @@ closed_race_cond() ->
     unlink(whereis(lhttpc_manager)),
     ok.
 
+dyn_pool_race() ->
+    ?assertEqual(undefined, whereis(mypool)),
+
+    %% suspend the supervisor so both process reaches
+    %% and gets stuck in lhttpc:add_pool/3
+    erlang:suspend_process(whereis(lhttpc_sup)),
+
+    Parent = self(),
+    Pid1 = spawn_pool_req(Parent),
+    Pid2 = spawn_pool_req(Parent),
+
+    erlang:yield(), % make sure that the spawned processes have run
+    erlang:resume_process(whereis(lhttpc_sup)),
+
+    worker_done([Pid1, Pid2]),
+    ?assertNotEqual(undefined, whereis(mypool)),
+    ok.
+
+spawn_pool_req(Parent) ->
+    spawn_link(
+      fun() ->
+              Opts = [{pool, mypool}, {pool_ensure, true}],
+              undefined = lhttpc_manager:ensure_call(
+                            mypool, self(), ?HOST, get_port(), ?SSL, Opts),
+              Parent ! {self(), done}
+      end).
+
+worker_done([Pid|Pids]) ->
+    receive
+        {Pid, done} -> worker_done(Pids)
+    after
+        1000 -> error({error, worker_timeout})
+    end;
+worker_done([]) ->
+    ok.
+
+
 %%% Helpers functions
 
 spawn_client() ->