1/* Copyright 2016 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7    http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#include "tensorflow/core/framework/op_kernel.h"
17#include "tensorflow/core/framework/tensor.h"
18#include "tensorflow/core/platform/mutex.h"
19
20namespace tensorflow {
21
22// This Op takes in a list of strings and a counter (ref). It increments the
23// counter by 1 and returns the element at that position in the list (circling
24// around if need to).
25class ObtainNextOp : public OpKernel {
26 public:
27  explicit ObtainNextOp(OpKernelConstruction* context) : OpKernel(context) {}
28
29  void Compute(OpKernelContext* ctx) override {
30    const Tensor* list;
31    OP_REQUIRES_OK(ctx, ctx->input("list", &list));
32    int64 num_elements = list->NumElements();
33    auto list_flat = list->flat<string>();
34
35    // Allocate output.
36    Tensor* output_tensor = nullptr;
37    OP_REQUIRES_OK(ctx, ctx->allocate_output("out_element", TensorShape({}),
38                                             &output_tensor));
39
40    // Obtain mutex for the "counter" tensor.
41    mutex* mu;
42    OP_REQUIRES_OK(ctx, ctx->input_ref_mutex("counter", &mu));
43    mutex_lock l(*mu);
44    // Increment "counter" tensor by 1.
45    Tensor counter_tensor;
46    OP_REQUIRES_OK(ctx, ctx->mutable_input("counter", &counter_tensor, true));
47    int64* pos = &counter_tensor.scalar<int64>()();
48    *pos = (*pos + 1) % num_elements;
49
50    // Assign value to output.
51    output_tensor->scalar<string>()() = list_flat(*pos);
52  }
53};
54
55REGISTER_KERNEL_BUILDER(Name("ObtainNext").Device(DEVICE_CPU), ObtainNextOp);
56
57}  // namespace tensorflow
58