New PingPong test for testing channels / concurrency (#9132)

* New test for testing channels / concurrency

* Formatting fix

Author: Varun Arora

python/paddle/fluid/tests/test_concurrency.py

@@ -217,6 +217,57 @@ def fibonacci(channel, quit_channel):
             exe_result = exe.run(fetch_list=[result])
             self.assertEqual(exe_result[0][0], 34)
 
+    def test_ping_pong(self):
+        """
+        Mimics Ping Pong example: https://gobyexample.com/channel-directions
+        """
+        with framework.program_guard(framework.Program()):
+            result = self._create_tensor('return_value',
+                                         core.VarDesc.VarType.LOD_TENSOR,
+                                         core.VarDesc.VarType.FP64)
+
+            ping_result = self._create_tensor('ping_return_value',
+                                              core.VarDesc.VarType.LOD_TENSOR,
+                                              core.VarDesc.VarType.FP64)
+
+            pong_result = self._create_tensor('pong_return_value',
+                                              core.VarDesc.VarType.LOD_TENSOR,
+                                              core.VarDesc.VarType.FP64)
+
+            def ping(ch, message):
+                message_to_send_tmp = fill_constant(
+                    shape=[1], dtype=core.VarDesc.VarType.FP64, value=0)
+
+                assign(input=message, output=message_to_send_tmp)
+                fluid.channel_send(ch, message_to_send_tmp)
+
+            def pong(ch1, ch2):
+                fluid.channel_recv(ch1, ping_result)
+                assign(input=ping_result, output=pong_result)
+                fluid.channel_send(ch2, pong_result)
+
+            pings = fluid.make_channel(
+                dtype=core.VarDesc.VarType.LOD_TENSOR, capacity=1)
+            pongs = fluid.make_channel(
+                dtype=core.VarDesc.VarType.LOD_TENSOR, capacity=1)
+
+            msg = fill_constant(
+                shape=[1], dtype=core.VarDesc.VarType.FP64, value=9)
+
+            ping(pings, msg)
+            pong(pings, pongs)
+
+            fluid.channel_recv(pongs, result)
+
+            fluid.channel_close(pings)
+            fluid.channel_close(pongs)
+
+            cpu = core.CPUPlace()
+            exe = Executor(cpu)
+
+            exe_result = exe.run(fetch_list=[result])
+            self.assertEqual(exe_result[0][0], 9)
+
 
 if __name__ == '__main__':
     unittest.main()