layers get a pointer back to their owning Net

This allows layers to do things that depend, e.g., on net topology.

include/caffe/layer.hpp

@@ -15,6 +15,8 @@
 
 namespace caffe {
 
+template <typename Dtype> class Net;
+
 /**
  * @brief An interface for the units of computation which can be composed into a
  *        Net.
@@ -301,6 +303,10 @@ class Layer {
     return DiagonalAffineMap<Dtype>(vector<pair<Dtype, Dtype> >());
   }
 
+  /**
+   * @brief Used by Net to give layers a pointer to their owning net.
+   */
+  void set_net(Net<Dtype>* net) { net_ = net; }
 
  protected:
   /** The protobuf that stores the layer parameters */
@@ -314,6 +320,9 @@ class Layer {
    *  the objective function. */
   vector<Dtype> loss_;
 
+  /** The net to which this layer belongs. */
+  Net<Dtype>* net_;
+
   /** @brief Using the CPU device, compute the layer output. */
   virtual void Forward_cpu(const vector<Blob<Dtype>*>& bottom,
       const vector<Blob<Dtype>*>& top) = 0;

src/caffe/net.cpp

@@ -64,6 +64,7 @@ void Net<Dtype>::Init(const NetParameter& in_param) {
     const LayerParameter& layer_param = param.layers(layer_id);
     layers_.push_back(shared_ptr<Layer<Dtype> >(
           LayerRegistry<Dtype>::CreateLayer(layer_param)));
+    layers_[layer_id]->set_net(this);
     layer_names_.push_back(layer_param.name());
     LOG(INFO) << "Creating Layer " << layer_param.name();
     bool need_backward = false;