Create NEW_OPERATOR_CN.md

doc/NEW_OPERATOR_CN.md

+# 如何开发一个新的General Op?
+
+在本文档中，我们主要集中于如何为Paddle Serving开发新的服务器端运算符。 在开始编写新运算符之前，让我们看一些示例代码以获得为服务器编写新运算符的基本思想。 我们假设您已经知道Paddle Serving服务器端的基本计算逻辑。 下面的代码您可以在 Serving代码库下的 `core/general-server/op` 目录查阅。
+
+
+``` c++
+// Copyright (c) 2019 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.
+
+#pragma once
+#include <string>
+#include <vector>
+#ifdef BCLOUD
+#ifdef WITH_GPU
+#include "paddle/paddle_inference_api.h"
+#else
+#include "paddle/fluid/inference/api/paddle_inference_api.h"
+#endif
+#else
+#include "paddle_inference_api.h"  // NOLINT
+#endif
+#include "core/general-server/general_model_service.pb.h"
+#include "core/general-server/op/general_infer_helper.h"
+
+namespace baidu {
+namespace paddle_serving {
+namespace serving {
+
+class GeneralInferOp
+    : public baidu::paddle_serving::predictor::OpWithChannel<GeneralBlob> {
+ public:
+  typedef std::vector<paddle::PaddleTensor> TensorVector;
+
+  DECLARE_OP(GeneralInferOp);
+
+  int inference();
+
+};
+
+}  // namespace serving
+}  // namespace paddle_serving
+}  // namespace baidu
+```
+
+## 定义一个Op
+
+上面的头文件声明了一个名为`GeneralInferOp`的PaddleServing运算符。 在运行时，将调用函数 `int inference（)`。 通常，我们将服务器端运算符定义为baidu::paddle_serving::predictor::OpWithChannel的子类，并使用 `GeneralBlob` 数据结构。
+
+## 在Op之间使用 `GeneralBlob` 
+
+`GeneralBlob` 是一种可以在服务器端运算符之间使用的数据结构。 `tensor_vector`是`GeneralBlob`中最重要的数据结构。 服务器端的操作员可以将多个`paddle::PaddleTensor`作为输入，并可以将多个`paddle::PaddleTensor`作为输出。 特别是，`tensor_vector`可以在没有内存拷贝的操作下输入到Paddle推理引擎中。
+
+``` c++
+struct GeneralBlob {
+  std::vector<paddle::PaddleTensor> tensor_vector;
+  int64_t time_stamp[20];
+  int p_size = 0;
+
+  int _batch_size;
+
+  void Clear() {
+    size_t tensor_count = tensor_vector.size();
+    for (size_t ti = 0; ti < tensor_count; ++ti) {
+      tensor_vector[ti].shape.clear();
+    }
+    tensor_vector.clear();
+  }
+
+  int SetBatchSize(int batch_size) { _batch_size = batch_size; }
+
+  int GetBatchSize() const { return _batch_size; }
+  std::string ShortDebugString() const { return "Not implemented!"; }
+};
+```
+
+### 实现 `int Inference()`
+
+``` c++
+int GeneralInferOp::inference() {
+  VLOG(2) << "Going to run inference";
+  const GeneralBlob *input_blob = get_depend_argument<GeneralBlob>(pre_name());
+  VLOG(2) << "Get precedent op name: " << pre_name();
+  GeneralBlob *output_blob = mutable_data<GeneralBlob>();
+
+  if (!input_blob) {
+    LOG(ERROR) << "Failed mutable depended argument, op:" << pre_name();
+    return -1;
+  }
+
+  const TensorVector *in = &input_blob->tensor_vector;
+  TensorVector *out = &output_blob->tensor_vector;
+  int batch_size = input_blob->GetBatchSize();
+  VLOG(2) << "input batch size: " << batch_size;
+
+  output_blob->SetBatchSize(batch_size);
+
+  VLOG(2) << "infer batch size: " << batch_size;
+
+  Timer timeline;
+  int64_t start = timeline.TimeStampUS();
+  timeline.Start();
+
+  if (InferManager::instance().infer(GENERAL_MODEL_NAME, in, out, batch_size)) {
+    LOG(ERROR) << "Failed do infer in fluid model: " << GENERAL_MODEL_NAME;
+    return -1;
+  }
+
+  int64_t end = timeline.TimeStampUS();
+  CopyBlobInfo(input_blob, output_blob);
+  AddBlobInfo(output_blob, start);
+  AddBlobInfo(output_blob, end);
+  return 0;
+}
+DEFINE_OP(GeneralInferOp);
+```
+
+`input_blob` 和 `output_blob` 都有很多的 `paddle::PaddleTensor`, 且Paddle预测库会被 `InferManager::instance().infer(GENERAL_MODEL_NAME, in, out, batch_size)`调用。此函数中的其他大多数代码都与性能分析有关，将来我们也可能会删除多余的代码。
+
+
+基本上，以上代码可以实现一个新的运算符。如果您想访问字典资源，可以参考`core/predictor/framework/resource.cpp`来添加全局可见资源。资源的初始化在启动服务器的运行时执行。
+
+## 定义 Python API
+
+在服务器端为Paddle Serving定义C++运算符后，最后一步是在Python API中为Paddle Serving服务器API添加注册， `python/paddle_serving_server/__init__.py`文件里有关于API注册的代码如下
+
+``` python
+self.op_dict = {
+            "general_infer": "GeneralInferOp",
+            "general_reader": "GeneralReaderOp",
+            "general_response": "GeneralResponseOp",
+            "general_text_reader": "GeneralTextReaderOp",
+            "general_text_response": "GeneralTextResponseOp",
+            "general_single_kv": "GeneralSingleKVOp",
+            "general_dist_kv": "GeneralDistKVOp"
+        }
+```