Add block when channel empty, successfully transfer when there is a send

paddle/framework/channel_test.cc

@@ -125,3 +125,27 @@ TEST(Channel, UnbufferedLessReceiveMoreSendTest) {
  t.join();
  delete ch;
 }
+
+TEST(Channel, UnbufferedEmptyReceiveSendReceiveTest) {
+ auto ch = MakeChannel<int>(0);
+ unsigned sum_recv = 0;
+ int i = 10;
+ // Receive should block initially since channel is
+ // empty. Once the main thread sends something, it
+ // should successfully receive and update the sum
+ std::thread t([&]() {
+ int recv;
+ ch->Receive(&recv); //should block the first time
+ EXPECT_EQ(recv, i);
+ sum_recv += recv;
+ });
+ std::this_thread::sleep_for(std::chrono::milliseconds(100)); // wait 0.5 sec
+ EXPECT_EQ(sum_recv, 0U);
+
+ ch->Send(&i);
+
+ CloseChannel(ch);
+ t.join();
+ EXPECT_EQ(sum_recv, 10U);
+ delete ch;
+}