Update comments and assertion messages

Author: XuehaiPan

include/pybind11/detail/internals.h

@@ -698,7 +698,7 @@ class internals_pp_manager {
             if (!tstate || tstate->interp == last_istate_tls()) {
                 auto tpp = internals_p_tls();
                 {
-                    std::lock_guard<std::mutex> lock(pps_creation_mutex_);
+                    std::lock_guard<std::mutex> lock(pp_set_mutex_);
                     pps_have_created_content_.erase(tpp);
                     delete tpp;
                 }
@@ -708,32 +708,29 @@ class internals_pp_manager {
         }
 #endif
         {
-            std::lock_guard<std::mutex> lock(pps_creation_mutex_);
+            std::lock_guard<std::mutex> lock(pp_set_mutex_);
             pps_have_created_content_.erase(internals_singleton_pp_);
             delete internals_singleton_pp_;
         }
         unref();
     }
 
     void create_pp_content_once(std::unique_ptr<InternalsType> *pp) {
-        // Assume the GIL is held
-        {
-            std::lock_guard<std::mutex> lock(pps_creation_mutex_);
-
-            // Prevent re-creation of internals after destruction during interpreter shutdown.
-            // If pybind11 code (e.g., tp_traverse/tp_clear calling py::cast) runs after internals
-            // have been destroyed, a new empty internals would be created, causing type lookup
-            // failures. See https://github.com/pybind/pybind11/pull/5958#discussion_r2717645230.
-            if (pps_have_created_content_.find(pp) != pps_have_created_content_.end()) {
-                pybind11_fail(
-                    "pybind11::detail::internals_pp_manager::create_pp_content_once() FAILED: "
-                    "reentrant call detected while fetching pybind11 internals!");
-            }
-            // Each pp can only create its internals once.
-            pps_have_created_content_.insert(pp);
+        std::lock_guard<std::mutex> lock(pp_set_mutex_);
+
+        // Prevent re-creation of internals after destruction during interpreter shutdown.
+        // If pybind11 code (e.g., tp_traverse/tp_clear calling py::cast) runs after internals
+        // have been destroyed, a new empty internals would be created, causing type lookup
+        // failures. See https://github.com/pybind/pybind11/pull/5958#discussion_r2717645230.
+        if (pps_have_created_content_.find(pp) != pps_have_created_content_.end()) {
+            pybind11_fail("pybind11::detail::internals_pp_manager::create_pp_content_once() "
+                          "FAILED: reentrant call detected while fetching pybind11 internals!");
         }
+        // Each pp can only create its internals once.
+        pps_have_created_content_.insert(pp);
 
-        // Create the internals content. May call back into Python.
+        // Assume the GIL is held here. May call back into Python.
+        // Create the internals content.
         pp->reset(new InternalsType());
     }
 
@@ -781,7 +778,7 @@ class internals_pp_manager {
     // Tracks pointer-to-pointers whose internals have been created, to detect re-entrancy.
     // Use instance member over static due to singleton pattern of this class.
     std::unordered_set<std::unique_ptr<InternalsType> *> pps_have_created_content_;
-    std::mutex pps_creation_mutex_;
+    std::mutex pp_set_mutex_;
 };
 
 // If We loaded the internals through `state_dict`, our `error_already_set`