Use picked port instead of assigned port

src/python/grpcio_tests/tests_aio/benchmark/BUILD.bazel

@@ -60,6 +60,7 @@ py_library(
         "//src/python/grpcio/grpc:grpcio",
         "//src/python/grpcio_tests/tests/qps:histogram",
         "//src/python/grpcio_tests/tests/unit:resources",
+        "//src/python/grpcio_tests/tests/unit/framework/common",
     ],
 )
 

src/python/grpcio_tests/tests_aio/benchmark/worker_servicer.py

@@ -29,6 +29,7 @@ from src.proto.grpc.testing import (benchmark_service_pb2_grpc, control_pb2,
 from tests.qps import histogram
 from tests.unit import resources
 from tests_aio.benchmark import benchmark_client, benchmark_servicer
+from tests.unit.framework.common import get_socket
 
 _NUM_CORES = multiprocessing.cpu_count()
 _NUM_CORE_PYTHON_CAN_USE = 1
@@ -124,14 +125,17 @@ WORKER_ENTRY_FILE = os.path.split(os.path.abspath(__file__))[0] + '/worker.py'
 SubWorker = collections.namedtuple('SubWorker', ['process', 'port', 'channel', 'stub'])
 
 
-async def _create_sub_worker(port: int) -> SubWorker:
+async def _create_sub_worker() -> SubWorker:
+    address, port, sock = get_socket()
+    sock.close()
+    _LOGGER.info('Creating sub worker at port [%d]...', port)
     process = await asyncio.create_subprocess_exec(
         sys.executable,
         WORKER_ENTRY_FILE,
         '--driver_port', str(port)
     )
     _LOGGER.info('Created sub worker process for port [%d] at pid [%d]', port, process.pid)
-    channel = aio.insecure_channel(f'localhost:{port}')
+    channel = aio.insecure_channel(f'{address}:{port}')
     _LOGGER.info('Waiting for sub worker at port [%d]', port)
     await aio.channel_ready(channel)
     stub = worker_service_pb2_grpc.WorkerServiceStub(channel)
@@ -210,9 +214,7 @@ class WorkerServicer(worker_service_pb2_grpc.WorkerServiceServicer):
         else:
             sub_workers = []
             for i in range(config.async_client_threads):
-                port = 40000+i
-                _LOGGER.info('Creating sub worker at port [%d]...', port)
-                sub_workers.append(await _create_sub_worker(port))
+                sub_workers.append(await _create_sub_worker())
 
             calls = [worker.stub.RunClient() for worker in sub_workers]
 
@@ -237,7 +239,8 @@ class WorkerServicer(worker_service_pb2_grpc.WorkerServiceServicer):
                     await call.write(request)
                     sub_status = await call.read()
                     result.merge(sub_status.stats.latencies)
-                    _LOGGER.debug('Update from sub worker count=[%d]', sub_status.stats.latencies.count)
+                    _LOGGER.debug('Update from sub worker count=[%d]',
+                                  sub_status.stats.latencies.count)
 
                 status = _get_client_status(start_time, end_time, result)
                 if request.mark.reset: