caffe源码解析：insertSplits对 top输出到多个 Layer的情况进行分割

作用：对 top输出到多个 Layer的情况进行分割，建立完整的网络结构

重要的参数说明举例：

• layer_idx_to_layer_name[i]
  记录各层的名称，如 [0x00000000] "input"
• blob_name_to_last_top_idx[“conv1”]=(1,0)
  这个例子相当于说”conv1” 这层是第1层的第0个top，
• bottom_idx_to_source_top_idx[bottom_idx=(2,0)] = (1,0); 
  相当于说：第2层，第0个bottom，对应着第1层，第0个top
  即： [(0x00000001, 0x00000000)] (0x00000000, 0x00000000)
• top_idx_to_bottom_count[(1,0)]=2
  表示第1个layer的第0个top有2个top(blob?)，要分叉，程序会对此建立新的分叉层

 

理解：整个函数分为两个部分

1. 遍历整个网络，记录每一个Layer的top的使用情况，记录结构放在 top_idx_to_bottom_count中。

2. 遍历整个网络，对 top_idx_to_bottom_count > 1 的情况进行处理: 分两步走

第一步. 首先是对有多个top层的Layer进行分割，主要的做法是在该层的后面新建一个Layer ，这个新的Layer的会按照 top_idx_to_bottom_count 的个数和约定的分割名称（SplitBlobName）去新建top，参考void ConfigureSplitLayer…

第二步，是对使用同一个top的后续层的bottom的blob进行改名（使用与上一步相同的命名规则）。

下面是源码

void InsertSplits(const NetParameter& param, NetParameter* param_split) {
  // Initialize by copying from the input NetParameter.
  param_split->CopyFrom(param);
  param_split->clear_layer();
  map<string, pair<int, int> > blob_name_to_last_top_idx;
  map<pair<int, int>, pair<int, int> > bottom_idx_to_source_top_idx;
  map<pair<int, int>, int> top_idx_to_bottom_count;
  map<pair<int, int>, float> top_idx_to_loss_weight;
  map<pair<int, int>, int> top_idx_to_bottom_split_idx;
  map<int, string> layer_idx_to_layer_name; // 每层网络的名称
  for (int i = 0; i < param.layer_size(); ++i) {
    const LayerParameter& layer_param = param.layer(i);
    layer_idx_to_layer_name[i] = layer_param.name();
    for (int j = 0; j < layer_param.bottom_size(); ++j) {
      const string& blob_name = layer_param.bottom(j);
      if (blob_name_to_last_top_idx.find(blob_name) ==
          blob_name_to_last_top_idx.end()) {
        LOG(FATAL) << "Unknown bottom blob '" << blob_name << "' (layer '"
                   << layer_param.name() << "', bottom index " << j << ")";
      }
      const pair<int, int>& bottom_idx = make_pair(i, j);
      const pair<int, int>& top_idx = blob_name_to_last_top_idx[blob_name];
      bottom_idx_to_source_top_idx[bottom_idx] = top_idx;
      ++top_idx_to_bottom_count[top_idx];
    }
    for (int j = 0; j < layer_param.top_size(); ++j) {
      const string& blob_name = layer_param.top(j);
      blob_name_to_last_top_idx[blob_name] = make_pair(i, j);
    }
    // A use of a top blob as a loss should be handled similarly to the use of
    // a top blob as a bottom blob to another layer.
    const int last_loss =
        std::min(layer_param.loss_weight_size(), layer_param.top_size());
    for (int j = 0; j < last_loss; ++j) {
      const string& blob_name = layer_param.top(j);
      const pair<int, int>& top_idx = blob_name_to_last_top_idx[blob_name];
      top_idx_to_loss_weight[top_idx] = layer_param.loss_weight(j);
      if (top_idx_to_loss_weight[top_idx]) {
        ++top_idx_to_bottom_count[top_idx];
      }
    }
  }
  for (int i = 0; i < param.layer_size(); ++i) {
    LayerParameter* layer_param = param_split->add_layer();
    layer_param->CopyFrom(param.layer(i));
    // Replace any shared bottom blobs with split layer outputs.
    for (int j = 0; j < layer_param->bottom_size(); ++j) {
      const pair<int, int>& top_idx =
          bottom_idx_to_source_top_idx[make_pair(i, j)];
      //表示第i层的第j个bottom, 是第top_idx0层的第top_idx1个top, 
      //   有split_count个bottom
      const int split_count = top_idx_to_bottom_count[top_idx];
      if (split_count > 1) {
        const string& layer_name = layer_idx_to_layer_name[top_idx.first];
        const string& blob_name = layer_param→bottom(j);
        // 只是改个名称,这个名称由 SplitBlobName创建
        layer_param->set_bottom(j, SplitBlobName(layer_name,
            blob_name, top_idx.second, top_idx_to_bottom_split_idx[top_idx]++));
      }
    }
    // Create split layer for any top blobs used by other layer as bottom
    // blobs more than once.
    for (int j = 0; j < layer_param->top_size(); ++j) {
      const pair<int, int>& top_idx = make_pair(i, j);
      //表示第i层的第j个top有split_count个blob
      const int split_count = top_idx_to_bottom_count[top_idx];
      if (split_count > 1) {
         // 如果要分叉（对应多个top）
        const string& layer_name = layer_idx_to_layer_name[i]; //第i层的名称
        const string& blob_name = layer_param->top(j);  // 第j个top的blob名称
        LayerParameter* split_layer_param = param_split->add_layer(); // 新建一层
        const float loss_weight = top_idx_to_loss_weight[top_idx];
        // 第i层的第j个top有的loss_weight
        ConfigureSplitLayer(layer_name, blob_name, j, split_count,
            loss_weight, split_layer_param);
        if (loss_weight) {
          layer_param->clear_loss_weight();
          top_idx_to_bottom_split_idx[top_idx]++;
        }
      }
    }
  }
}