fix parallel run dist unit test

Author: Yancey0623

python/paddle/fluid/tests/unittests/test_dist_base.py

@@ -55,6 +55,7 @@ def run_pserver(self, args):
         pserver_prog = t.get_pserver_program(args.current_endpoint)
         startup_prog = t.get_startup_program(args.current_endpoint,
                                              pserver_prog)
+
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
         exe.run(startup_prog)
@@ -147,6 +148,8 @@ def runtime_main(test_class):
 
 
 import paddle.compat as cpt
+import socket
+from contextlib import closing
 
 
 class TestDistBase(unittest.TestCase):
@@ -156,13 +159,19 @@ def _setup_config(self):
     def setUp(self):
         self._trainers = 2
         self._pservers = 2
-        self._ps_endpoints = "127.0.0.1:9123,127.0.0.1:9124"
+        self._ps_endpoints = "127.0.0.1:%s,127.0.0.1:%s" % (
+            self._find_free_port(), self._find_free_port())
         self._python_interp = "python"
         self._sync_mode = True
         self._mem_opt = False
         self._use_reduce = False
         self._setup_config()
 
+    def _find_free_port(self):
+        with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
+            s.bind(('', 0))
+            return s.getsockname()[1]
+
     def start_pserver(self, model_file, check_error_log):
         ps0_ep, ps1_ep = self._ps_endpoints.split(",")
         ps_cmd = "%s %s --role pserver --endpoints %s --trainer_id 0 --current_endpoint %s --trainers %d --is_dist"