Reinitialize averagers when saved sync file was reloaded. (#629)

dlib/dnn/trainer.h

@@ -713,7 +713,7 @@ namespace dlib
                     // We can't do this outside the loop because the tensors that get
                     // averaged need to be allocated to their devices before we call set()
                     // so that the averagers can determine how best to average them.
-                    if (averagers.size() == 0)
+                    if (averagers.size() == 0 || sync_file_reloaded)
                     {
                         averagers = std::vector<tt::multi_device_tensor_averager>(net_type::num_computational_layers);
                         // setup the averagers to point to the tensors in the networks.
@@ -736,6 +736,8 @@ namespace dlib
                             if (temp[0]->size() != 0)
                                 averagers[i].set(temp);
                         }
+
+                        sync_file_reloaded = false;
                     }
 
 
@@ -855,6 +857,7 @@ namespace dlib
             prob_loss_increasing_thresh_max_value = 0.99999;
             prob_loss_increasing_thresh = prob_loss_increasing_thresh_default_value;
             updated_net_since_last_sync = false;
+            sync_file_reloaded = false;
             start();
         }
 
@@ -979,6 +982,7 @@ namespace dlib
                 {
                     std::ifstream fin(sync_filename, std::ios::binary);
                     deserialize(*this, fin);
+                    sync_file_reloaded = true;
                     if (verbose)
                         std::cout << "Loss has been increasing, reloading saved state from " << sync_filename << std::endl;
                 }
@@ -1230,6 +1234,7 @@ namespace dlib
         double prob_loss_increasing_thresh;
         std::atomic<bool> updated_net_since_last_sync;
 
+        bool sync_file_reloaded;
     };
 
 // ----------------------------------------------------------------------------------------