Make error messages in net_dag more clear

Author: Kutta Srinivasan

caffe2/core/net_dag.cc

@@ -193,12 +193,12 @@ void DAGNetBase::HandleException(
       operator_nodes_[operator_idx].operator_->debug_def().name();
   const std::string& operator_type =
       operator_nodes_[operator_idx].operator_->debug_def().type();
-  const char* prefix = "Exception from operator '";
+  const char* prefix = "Exception from operator chain starting at '";
 #ifdef CAFFE2_USE_EXCEPTION_PTR
   if (!caught_exception_yet_.exchange(true)) {
     caught_exception_ = std::current_exception();
   } else {
-    prefix = "Secondary exception from operator '";
+    prefix = "Secondary exception from operator chain starting at '";
   }
 #endif // CAFFE2_USE_EXCEPTION_PTR
   LOG(ERROR) << prefix << operator_name << "' (type '" << operator_type
@@ -228,7 +228,7 @@ void DAGNetBase::WorkerFunction() {
           task_timers_[idx]->MicroSeconds());
     }
 
-    VLOG(1) << "Running operator #" << idx << " "
+    VLOG(1) << "Running chain starting at operator #" << idx << " "
             << operator_nodes_[idx].operator_->debug_def().name() << "("
             << operator_nodes_[idx].operator_->debug_def().type() << ").";
     CAFFE_ENFORCE(
@@ -244,7 +244,7 @@ void DAGNetBase::WorkerFunction() {
       if (!this_success) {
         // If an exception was thrown, the operator def will get printed
         // by Operator::Run[Async], but if no exception occurs we print it here.
-        LOG(ERROR) << "Operator chain failed: "
+        LOG(ERROR) << "Operator chain failed starting at: "
                    << ProtoDebugString(
                           operator_nodes_[idx].operator_->debug_def());
       }