refactor and add comments

src/replica/replica_stub.cpp

@@ -34,7 +34,6 @@
 #include <algorithm>
 #include <chrono>
 #include <cstdint>
-#include <cstdio>
 #include <cstdlib>
 #include <iterator>
 #include <mutex>
@@ -2228,7 +2227,7 @@ replica *replica_stub::new_replica(gpid gpid,
                                    bool restore_if_necessary,
                                    bool is_duplication_follower)
 {
-    return new_replica(gpid, app, restore_if_necessary, is_duplication_follower, "");
+    return new_replica(gpid, app, restore_if_necessary, is_duplication_follower, {});
 }
 
 /*static*/ std::string replica_stub::get_replica_dir_name(const std::string &dir)
@@ -3017,27 +3016,33 @@ replica_ptr replica_stub::create_child_replica_if_not_found(gpid child_pid,
         });
 
     zauto_write_lock l(_replicas_lock);
-    auto it = _replicas.find(child_pid);
+
+    const auto it = _replicas.find(child_pid);
     if (it != _replicas.end()) {
         return it->second;
-    } else {
-        if (_opening_replicas.find(child_pid) != _opening_replicas.end()) {
-            LOG_WARNING("failed create child replica({}) because it is under open", child_pid);
-            return nullptr;
-        } else if (_closing_replicas.find(child_pid) != _closing_replicas.end()) {
-            LOG_WARNING("failed create child replica({}) because it is under close", child_pid);
-            return nullptr;
-        } else {
-            replica *rep = new_replica(child_pid, *app, false, false, parent_dir);
-            if (rep != nullptr) {
-                auto pr = _replicas.insert(replica_map_by_gpid::value_type(child_pid, rep));
-                CHECK(pr.second, "child replica {} has been existed", rep->name());
-                METRIC_VAR_INCREMENT(total_replicas);
-                _closed_replicas.erase(child_pid);
-            }
-            return rep;
-        }
     }
+
+    if (_opening_replicas.find(child_pid) != _opening_replicas.end()) {
+        LOG_WARNING("failed create child replica({}) because it is under open", child_pid);
+        return nullptr;
+    }
+
+    if (_closing_replicas.find(child_pid) != _closing_replicas.end()) {
+        LOG_WARNING("failed create child replica({}) because it is under close", child_pid);
+        return nullptr;
+    }
+
+    replica *rep = new_replica(child_pid, *app, false, false, parent_dir);
+    if (rep == nullptr) {
+        return nullptr;
+    }
+
+    const auto pr = _replicas.insert(replica_map_by_gpid::value_type(child_pid, rep));
+    CHECK(pr.second, "child replica {} has been existed", rep->name());
+    METRIC_VAR_INCREMENT(total_replicas);
+    _closed_replicas.erase(child_pid);
+
+    return rep;
 }
 
 // ThreadPool: THREAD_POOL_REPLICATION

src/replica/replica_stub.h

@@ -359,19 +359,22 @@ class replica_stub : public serverlet<replica_stub>, public ref_counter
                       gpid id,
                       const std::shared_ptr<group_check_request> &req,
                       const std::shared_ptr<configuration_update_request> &req2);
-    // Create a new replica according to the parameters.
-    // 'parent_dir' is used in partition split for create_child_replica_dir().
+
+    // Create a child replica for partition split, with 'parent_dir' specified as the parent
+    // replica dir used for `create_child_replica_dir()`.
     replica *new_replica(gpid gpid,
                          const app_info &app,
                          bool restore_if_necessary,
                          bool is_duplication_follower,
                          const std::string &parent_dir);
 
+    // Create a new replica, choosing and assigning the best dir for it.
     replica *new_replica(gpid gpid,
                          const app_info &app,
                          bool restore_if_necessary,
                          bool is_duplication_follower);
 
+    // Each disk with its candidate replica dirs, used to load replicas while initializing.
     struct disk_replicas_info
     {
         // `dir_node` for each disk.
@@ -384,11 +387,11 @@ class replica_stub : public serverlet<replica_stub>, public ref_counter
     // Get the absolute dirs of all replicas for all disks.
     std::vector<disk_replicas_info> get_all_disk_dirs() const;
 
-    // Get the dir name for a replica from a potentially longer path (both absolute and
-    // relative paths are possible).
+    // Get the replica dir name from a potentially longer path (`dir` could be an absolute
+    // or relative path).
     static std::string get_replica_dir_name(const std::string &dir);
 
-    // Parse app id, partition id and app type from the dir name of a replica.
+    // Parse app id, partition id and app type from the replica dir name.
     static bool
     parse_replica_dir_name(const std::string &dir_name, gpid &pid, std::string &app_type);
 
@@ -503,7 +506,7 @@ class replica_stub : public serverlet<replica_stub>, public ref_counter
 
     using opening_replica_map_by_gpid = std::unordered_map<gpid, task_ptr>;
 
-    // `task_ptr` is the task being closed.
+    // `task_ptr` is the task closing a replica.
     using closing_replica_map_by_gpid =
         std::unordered_map<gpid, std::tuple<task_ptr, replica_ptr, app_info, replica_info>>;