diff --git a/python/pipeline/dag.py b/python/pipeline/dag.py
new file mode 100644
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+++ b/python/pipeline/dag.py
@@ -0,0 +1,398 @@
+#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# pylint: disable=doc-string-missing
+import threading
+import multiprocessing
+import sys
+if sys.version_info.major == 2:
+    import Queue
+elif sys.version_info.major == 3:
+    import queue as Queue
+else:
+    raise Exception("Error Python version")
+import os
+import logging
+
+from .operator import Op, RequestOp, ResponseOp, VirtualOp
+from .channel import ThreadChannel, ProcessChannel, ChannelData, ChannelDataEcode, ChannelDataType
+from .util import NameGenerator
+
+_LOGGER = logging.getLogger()
+
+
+class DAGExecutor(object):
+    def __init__(self, response_op, profiler, use_multithread, retry,
+                 client_type, channel_size):
+        self.name = "#G"
+        self._retry = min(retry, 1)
+        self._profiler = profiler
+        self._dag = DAG(response_op, profiler, use_multithread, client_type,
+                        channel_size)
+        in_channel, out_channel, pack_rpc_func, unpack_rpc_func = self._dag.build(
+        )
+        self._dag.start()
+
+        self._set_in_channel(in_channel)
+        self.set_out_channel(out_channel)
+        self._pack_rpc_func = pack_rpc_func
+        self._unpack_rpc_func = unpack_rpc_func
+
+        _LOGGER.debug(self._log(in_channel.debug()))
+        _LOGGER.debug(self._log(out_channel.debug()))
+
+        self._id_lock = threading.Lock()
+        self._cv = threading.Condition()
+        self._globel_resp_dict = {}
+        self._id_counter = 0
+        self._reset_max_id = 1000000000000000000
+        self._is_run = True
+        self._recive_func = threading.Thread(
+            target=DAGExecutor._recive_out_channel_func, args=(self, ))
+        self._recive_func.start()
+
+    def stop(self):
+        self._is_run = False
+        self._dag.stop()
+        self._dag.join()
+
+    def _get_next_data_id(self):
+        with self._id_lock:
+            if self._id_counter >= self._reset_max_id:
+                self._id_counter -= self._reset_max_id
+            self._id_counter += 1
+            return self._id_counter - 1
+
+    def _set_in_channel(self, in_channel):
+        if not isinstance(in_channel, (ThreadChannel, ProcessChannel)):
+            raise TypeError(
+                self._log('in_channel must be Channel type, but get {}'.format(
+                    type(in_channel))))
+        in_channel.add_producer(self.name)
+        self._in_channel = in_channel
+
+    def _set_out_channel(self, out_channel):
+        if not isinstance(out_channel, (ThreadChannel, ProcessChannel)):
+            raise TypeError(
+                self._log('out_channel must be Channel type, but get {}'.format(
+                    type(out_channel))))
+        out_channel.add_consumer(self.name)
+        self._out_channel = out_channel
+
+    def _recive_out_channel_func(self):
+        while self._is_run:
+            channeldata_dict = self._out_channel.front(self.name)
+            if len(channeldata_dict) != 1:
+                _LOGGER.error("out_channel cannot have multiple input ops")
+                os._exit(-1)
+            (_, channeldata), = channeldata_dict.items()
+            if not isinstance(channeldata, ChannelData):
+                raise TypeError(
+                    self._log('data must be ChannelData type, but get {}'.
+                              format(type(channeldata))))
+            with self._cv:
+                data_id = channeldata.id
+                self._globel_resp_dict[data_id] = channeldata
+                self._cv.notify_all()
+
+    def _get_channeldata_from_fetch_buffer(self, data_id):
+        resp = None
+        with self._cv:
+            while data_id not in self._globel_resp_dict:
+                self._cv.wait()
+            resp = self._globel_resp_dict.pop(data_id)
+            self._cv.notify_all()
+        return resp
+
+    def _pack_channeldata(self, rpc_request):
+        _LOGGER.debug(self._log('start inferce'))
+        data_id = self._get_next_data_id()
+        dictdata = None
+        try:
+            dictdata = self._unpack_rpc_func(rpc_request)
+        except Exception as e:
+            return ChannelData(
+                ecode=ChannelDataEcode.RPC_PACKAGE_ERROR.value,
+                error_info="rpc package error: {}".format(e),
+                data_id=data_id), data_id
+        else:
+            return ChannelData(
+                datatype=ChannelDataType.DICT.value,
+                dictdata=dictdata,
+                data_id=data_id), data_id
+
+    def call(self, rpc_request):
+        self._profiler.record("{}-prepack_0".format(self.name))
+        req_channeldata, data_id = self._pack_channeldata(rpc_request)
+        self._profiler.record("{}-prepack_1".format(self.name))
+
+        resp_channeldata = None
+        for i in range(self._retry):
+            _LOGGER.debug(self._log('push data'))
+            #self._profiler.record("{}-push_0".format(self.name))
+            self._in_channel.push(req_channeldata, self.name)
+            #self._profiler.record("{}-push_1".format(self.name))
+
+            _LOGGER.debug(self._log('wait for infer'))
+            #self._profiler.record("{}-fetch_0".format(self.name))
+            resp_channeldata = self._get_channeldata_from_fetch_buffer(data_id)
+            #self._profiler.record("{}-fetch_1".format(self.name))
+
+            if resp_channeldata.ecode == ChannelDataEcode.OK.value:
+                break
+            if i + 1 < self._retry:
+                _LOGGER.warn("retry({}): {}".format(
+                    i + 1, resp_channeldata.error_info))
+
+        self._profiler.record("{}-postpack_0".format(self.name))
+        rpc_resp = self._pack_for_rpc_resp(resp_channeldata)
+        self._profiler.record("{}-postpack_1".format(self.name))
+        self._profiler.print_profile()
+        return rpc_resp
+
+    def _pack_for_rpc_resp(self, channeldata):
+        _LOGGER.debug(self._log('get channeldata'))
+        return self._pack_rpc_func(channeldata)
+
+    def _log(self, info_str):
+        return "[{}] {}".format(self.name, info_str)
+
+
+class DAG(object):
+    def __init__(slef, response_op, profiler, use_multithread, client_type,
+                 channel_size):
+        self._response_op = response_op
+        self._use_multithread = use_multithread
+        self._channel_size = channel_size
+        self._client_type = client_type
+        if not self._use_multithread:
+            self._manager = multiprocessing.Manager()
+        self._profiler = profiler
+
+    def get_use_ops(self, response_op):
+        unique_names = set()
+        use_ops = set()
+        succ_ops_of_use_op = {}  # {op_name: succ_ops}
+        que = Queue.Queue()
+        que.put(response_op)
+        while que.qsize() != 0:
+            op = que.get()
+            for pred_op in op.get_input_ops():
+                if pred_op.name not in succ_ops_of_use_op:
+                    succ_ops_of_use_op[pred_op.name] = []
+                if op != response_op:
+                    succ_ops_of_use_op[pred_op.name].append(op)
+                if pred_op not in use_ops:
+                    que.put(pred_op)
+                    use_ops.add(pred_op)
+                    # check the name of op is globally unique
+                    if pred_op.name in unique_names:
+                        raise Exception("the name of Op must be unique: {}".
+                                        format(pred_op.name))
+                    unique_names.add(pred_op.name)
+        return use_ops, succ_ops_of_use_op
+
+    def _gen_channel(self, name_gen):
+        channel = None
+        if self._use_multithread:
+            channel = ThreadChannel(
+                name=name_gen.next(), maxsize=self._channel_size)
+        else:
+            channel = ProcessChannel(
+                self._manager, name=name_gen.next(), maxsize=self._channel_size)
+        return channel
+
+    def _gen_virtual_op(self, name_gen):
+        return VirtualOp(name=name_gen.next())
+
+    def _topo_sort(self, used_ops, response_op, out_degree_ops):
+        out_degree_num = {
+            name: len(ops)
+            for name, ops in out_degree_ops.items()
+        }
+        que_idx = 0  # scroll queue 
+        ques = [Queue.Queue() for _ in range(2)]
+        zero_indegree_num = 0
+        for op in use_ops:
+            if len(op.get_input_ops()) == 0:
+                zero_indegree_num += 1
+        if zero_indegree_num != 1:
+            raise Exception("DAG contains multiple input Ops")
+        last_op = response_op.get_input_ops()[0]
+        ques[que_idx].put(last_op)
+
+        # topo sort to get dag_views
+        dag_views = []
+        sorted_op_num = 0
+        while True:
+            que = ques[que_idx]
+            next_que = ques[(que_idx + 1) % 2]
+            dag_view = []
+            while que.qsize() != 0:
+                op = que.get()
+                dag_view.append(op)
+                sorted_op_num += 1
+                for pred_op in op.get_input_ops():
+                    out_degree_num[pred_op.name] -= 1
+                    if out_degree_num[pred_op.name] == 0:
+                        next_que.put(pred_op)
+            dag_views.append(dag_view)
+            if next_que.qsize() == 0:
+                break
+            que_idx = (que_idx + 1) % 2
+        if sorted_op_num < len(use_ops):
+            raise Exception("not legal DAG")
+
+        return dag_views, last_op
+
+    def build(slef, response_op):
+        if response_op is None:
+            raise Exception("response_op has not been set.")
+        use_ops, out_degree_ops = self.get_use_ops(response_op)
+        _LOGGER.info("================= use op ==================")
+        for op in use_ops:
+            _LOGGER.info(op.name)
+        _LOGGER.info("===========================================")
+        if len(use_ops) <= 1:
+            raise Exception(
+                "Besides RequestOp and ResponseOp, there should be at least one Op in DAG."
+            )
+
+        dag_views, last_op = self._topo_sort(used_ops, response_op,
+                                             out_degree_ops)
+
+        # create channels and virtual ops
+        virtual_op_name_gen = NameGenerator("vir")
+        channel_name_gen = NameGenerator("chl")
+        virtual_ops = []
+        channels = []
+        input_channel = None
+        actual_view = None
+        dag_views = list(reversed(dag_views))
+        for v_idx, view in enumerate(dag_views):
+            if v_idx + 1 >= len(dag_views):
+                break
+            next_view = dag_views[v_idx + 1]
+            if actual_view is None:
+                actual_view = view
+            actual_next_view = []
+            pred_op_of_next_view_op = {}
+            for op in actual_view:
+                # find actual succ op in next view and create virtual op
+                for succ_op in out_degree_ops[op.name]:
+                    if succ_op in next_view:
+                        if succ_op not in actual_next_view:
+                            actual_next_view.append(succ_op)
+                        if succ_op.name not in pred_op_of_next_view_op:
+                            pred_op_of_next_view_op[succ_op.name] = []
+                        pred_op_of_next_view_op[succ_op.name].append(op)
+                    else:
+                        # create virtual op
+                        virtual_op = self._gen_virtual_op(virtual_op_name_gen)
+                        virtual_ops.append(virtual_op)
+                        out_degree_ops[virtual_op.name] = [succ_op]
+                        actual_next_view.append(virtual_op)
+                        pred_op_of_next_view_op[virtual_op.name] = [op]
+                        virtual_op.add_virtual_pred_op(op)
+            actual_view = actual_next_view
+            # create channel
+            processed_op = set()
+            for o_idx, op in enumerate(actual_next_view):
+                if op.name in processed_op:
+                    continue
+                channel = self._gen_channel(channel_name_gen)
+                channels.append(channel)
+                _LOGGER.debug("{} => {}".format(channel.name, op.name))
+                op.add_input_channel(channel)
+                pred_ops = pred_op_of_next_view_op[op.name]
+                if v_idx == 0:
+                    input_channel = channel
+                else:
+                    # if pred_op is virtual op, it will use ancestors as producers to channel
+                    for pred_op in pred_ops:
+                        _LOGGER.debug("{} => {}".format(pred_op.name,
+                                                        channel.name))
+                        pred_op.add_output_channel(channel)
+                processed_op.add(op.name)
+                # find same input op to combine channel
+                for other_op in actual_next_view[o_idx + 1:]:
+                    if other_op.name in processed_op:
+                        continue
+                    other_pred_ops = pred_op_of_next_view_op[other_op.name]
+                    if len(other_pred_ops) != len(pred_ops):
+                        continue
+                    same_flag = True
+                    for pred_op in pred_ops:
+                        if pred_op not in other_pred_ops:
+                            same_flag = False
+                            break
+                    if same_flag:
+                        _LOGGER.debug("{} => {}".format(channel.name,
+                                                        other_op.name))
+                        other_op.add_input_channel(channel)
+                        processed_op.add(other_op.name)
+        output_channel = self._gen_channel(channel_name_gen)
+        channels.append(output_channel)
+        last_op.add_output_channel(output_channel)
+
+        pack_func, unpack_func = None, None
+        pack_func = response_op.pack_response_package
+
+        actual_ops = virtual_ops
+        for op in use_ops:
+            if len(op.get_input_ops()) == 0:
+                unpack_func = op.unpack_request_package
+                continue
+            actual_ops.append(op)
+
+        for c in channels:
+            _LOGGER.debug(c.debug())
+
+        return (actual_ops, channels, input_channel, output_channel, pack_func,
+                unpack_func)
+
+    def build(self):
+        (actual_ops, channels, input_channel, output_channel, pack_func,
+         unpack_func) = self._topo_sort(self._response_op)
+
+        self._actual_ops = actual_ops
+        self._channels = channels
+        self._input_channel = input_channel
+        self._output_channel = output_channel
+        self._pack_func = pack_func
+        self._unpack_func = unpack_func
+
+        return self._input_channel, self._output_channel, self._pack_func, self._unpack_func
+
+    def start(self):
+        self._threads_or_proces = []
+        for op in self._actual_ops:
+            op.init_profiler(self._profiler)
+            if self._use_multithread:
+                threads_or_proces.extend(
+                    op.start_with_thread(self._client_type))
+            else:
+                threads_or_proces.extend(
+                    op.start_with_process(self._client_type))
+        # not join yet
+        return self._threads_or_proces
+
+    def join(self):
+        for x in self._threads_or_proces:
+            x.join()
+
+    def stop(self):
+        for op in self._actual_ops:
+            op.stop()
+        for chl in self._channels:
+            chl.stop()