Config static initialization (#2743)

* Change static map/set to functions that return static variables

* Fixed newline

* testing CI

* removed commented-out code fixed formatting

* return const references to parameter_set and alias_table

* fixup whitespace

* Too many requests error when running CI on docs. Triggering a rebuild.

helpers/parameter_generator.py

@@ -269,15 +269,24 @@ def gen_parameter_code(config_hpp, config_out_cpp):
 """
     str_to_write += "#include<LightGBM/config.h>\nnamespace LightGBM {\n"
     # alias table
-    str_to_write += "std::unordered_map<std::string, std::string> Config::alias_table({\n"
+    str_to_write += "const std::unordered_map<std::string, std::string>& Config::alias_table() {\n"
+    str_to_write += "  static std::unordered_map<std::string, std::string> aliases({\n"
+
     for pair in alias:
         str_to_write += "  {\"%s\", \"%s\"},\n" % (pair[0], pair[1])
-    str_to_write += "});\n\n"
+    str_to_write += "  });\n"
+    str_to_write += "  return aliases;\n"
+    str_to_write += "}\n\n"
+
     # names
-    str_to_write += "std::unordered_set<std::string> Config::parameter_set({\n"
+    str_to_write += "const std::unordered_set<std::string>& Config::parameter_set() {\n"
+    str_to_write += "  static std::unordered_set<std::string> params({\n"
+
     for name in names:
         str_to_write += "  \"%s\",\n" % (name)
-    str_to_write += "});\n\n"
+    str_to_write += "  });\n"
+    str_to_write += "  return params;\n"
+    str_to_write += "}\n\n"
     # from strings
     str_to_write += "void Config::GetMembersFromString(const std::unordered_map<std::string, std::string>& params) {\n"
     str_to_write += "  std::string tmp_str = \"\";\n"

include/LightGBM/config.h

@@ -890,8 +890,8 @@ struct Config {
   bool is_parallel = false;
   bool is_parallel_find_bin = false;
   LIGHTGBM_EXPORT void Set(const std::unordered_map<std::string, std::string>& params);
-  static std::unordered_map<std::string, std::string> alias_table;
-  static std::unordered_set<std::string> parameter_set;
+  static const std::unordered_map<std::string, std::string>& alias_table();
+  static const std::unordered_set<std::string>& parameter_set();
   std::vector<std::vector<double>> auc_mu_weights_matrix;
 
  private:
@@ -960,8 +960,8 @@ struct ParameterAlias {
   static void KeyAliasTransform(std::unordered_map<std::string, std::string>* params) {
     std::unordered_map<std::string, std::string> tmp_map;
     for (const auto& pair : *params) {
-      auto alias = Config::alias_table.find(pair.first);
-      if (alias != Config::alias_table.end()) {  // found alias
+      auto alias = Config::alias_table().find(pair.first);
+      if (alias != Config::alias_table().end()) {  // found alias
         auto alias_set = tmp_map.find(alias->second);
         if (alias_set != tmp_map.end()) {  // alias already set
                                            // set priority by length & alphabetically to ensure reproducible behavior
@@ -979,7 +979,7 @@ struct ParameterAlias {
         } else {  // alias not set
           tmp_map.emplace(alias->second, pair.first);
         }
-      } else if (Config::parameter_set.find(pair.first) == Config::parameter_set.end()) {
+      } else if (Config::parameter_set().find(pair.first) == Config::parameter_set().end()) {
         Log::Warning("Unknown parameter: %s", pair.first.c_str());
       }
     }

src/io/config_auto.cpp

@@ -7,7 +7,8 @@
  */
 #include<LightGBM/config.h>
 namespace LightGBM {
-std::unordered_map<std::string, std::string> Config::alias_table({
+const std::unordered_map<std::string, std::string>& Config::alias_table() {
+  static std::unordered_map<std::string, std::string> aliases({
   {"config_file", "config"},
   {"task_type", "task"},
   {"objective_type", "objective"},
@@ -165,9 +166,12 @@ std::unordered_map<std::string, std::string> Config::alias_table({
   {"mlist", "machine_list_filename"},
   {"workers", "machines"},
   {"nodes", "machines"},
-});
+  });
+  return aliases;
+}
 
-std::unordered_set<std::string> Config::parameter_set({
+const std::unordered_set<std::string>& Config::parameter_set() {
+  static std::unordered_set<std::string> params({
   "config",
   "task",
   "objective",
@@ -287,7 +291,9 @@ std::unordered_set<std::string> Config::parameter_set({
   "gpu_platform_id",
   "gpu_device_id",
   "gpu_use_dp",
-});
+  });
+  return params;
+}
 
 void Config::GetMembersFromString(const std::unordered_map<std::string, std::string>& params) {
   std::string tmp_str = "";