(Wangle) Clean up some data races in tests

Summary: Not 100% about the `ThreadWheelTimekeeper` test. It makes TSAN happy
though.

Reviewed By: @yfeldblum

Differential Revision: D2187901

folly/futures/detail/ThreadWheelTimekeeper.cpp

@@ -76,8 +76,8 @@ ThreadWheelTimekeeper::ThreadWheelTimekeeper() :
 ThreadWheelTimekeeper::~ThreadWheelTimekeeper() {
   eventBase_.runInEventBaseThreadAndWait([this]{
     wheelTimer_->cancelAll();
+    eventBase_.terminateLoopSoon();
   });
-  eventBase_.terminateLoopSoon();
   thread_.join();
 }
 

folly/futures/test/TimekeeperTest.cpp

@@ -52,8 +52,9 @@ TEST_F(TimekeeperFixture, after) {
 
 TEST(Timekeeper, futureGet) {
   Promise<int> p;
-  std::thread([&]{ p.setValue(42); }).detach();
+  auto t = std::thread([&]{ p.setValue(42); });
   EXPECT_EQ(42, p.getFuture().get());
+  t.join();
 }
 
 TEST(Timekeeper, futureGetBeforeTimeout) {

folly/futures/test/ViaTest.cpp

@@ -72,7 +72,7 @@ struct ViaFixture : public testing::Test {
   std::shared_ptr<ManualExecutor> eastExecutor;
   std::shared_ptr<ManualWaiter> waiter;
   InlineExecutor inlineExecutor;
-  bool done;
+  std::atomic<bool> done;
   std::thread t;
 };