Refine code according to reviewer's advices

paddle/framework/op_registry.h

@@ -309,6 +309,14 @@ class OpRegistry {
 
 class Registrar {
  public:
+  // In our design, various kinds of classes, e.g., operators and kernels, have
+  // their corresponding registry and registrar. The action of registration is
+  // in the constructor of a global registrar variable, which, however, are not
+  // used in the code that calls package framework, and would be removed from
+  // the generated binary file by the linker. To avoid such removal, we add
+  // Touch to all registrar classes and make USE_OP macros to call this
+  // method. So, as long as the callee code calls USE_OP, the global
+  // registrar variable won't be removed by the linker.
   void Touch() {}
 };
 
@@ -332,10 +340,9 @@ template <typename PlaceType, typename KernelType>
 class OpKernelRegistrar : public Registrar {
  public:
   explicit OpKernelRegistrar(const char* op_type) {
-    ::paddle::framework::OperatorWithKernel::OpKernelKey key;
+    OperatorWithKernel::OpKernelKey key;
     key.place_ = PlaceType();
-    ::paddle::framework::OperatorWithKernel::AllOpKernels()[op_type][key].reset(
-        new KernelType);
+    OperatorWithKernel::AllOpKernels()[op_type][key].reset(new KernelType);
   }
 };
 
@@ -349,7 +356,7 @@ class OpKernelRegistrar : public Registrar {
                 msg)
 
 /**
- * Macro to Register Operator.
+ * Macro to register Operator.
  */
 #define REGISTER_OP(op_type, op_class, op_maker_class)                        \
   STATIC_ASSERT_GLOBAL_NAMESPACE(                                             \
@@ -362,7 +369,7 @@ class OpKernelRegistrar : public Registrar {
   }
 
 /**
- * Macro to Register Gradient Operator.
+ * Macro to register Gradient Operator.
  */
 #define REGISTER_GRADIENT_OP(op_type, grad_op_type, grad_op_class)           \
   STATIC_ASSERT_GLOBAL_NAMESPACE(                                            \
@@ -377,7 +384,7 @@ class OpKernelRegistrar : public Registrar {
   }
 
 /**
- * Macro to Register OperatorKernel.
+ * Macro to register OperatorKernel.
  */
 #define REGISTER_OP_KERNEL(op_type, DEVICE_TYPE, place_class, ...)        \
   STATIC_ASSERT_GLOBAL_NAMESPACE(                                         \