Unregister only this module's type registration

src/extended_type_info_typeid.cpp

@@ -102,14 +102,16 @@ extended_type_info_typeid_0::type_unregister()
         // BOOST_ASSERT(! singleton<tkmap>::is_destroyed());
         if(! singleton<tkmap>::is_destroyed()){
             tkmap & x = singleton<tkmap>::get_mutable_instance();
-
-            // remove all entries in map which corresponds to this type
-            // make sure that we don't use any invalidated iterators
-            while(true){
-                const tkmap::iterator & it = x.find(this);
-                if(it == x.end())
+            tkmap::iterator start = x.lower_bound(this);
+            const tkmap::iterator end = x.upper_bound(this);
+            // Entries compare equal when they describe the same type, and
+            // another module may well have registered that same type.  Erase
+            // this entry alone, as key_unregister does.
+            for(; start != end; ++start){
+                if(this == *start){
+                    x.erase(start);
                     break;
-                x.erase(it);
+                }
             }
         }
     }

test/Jamfile.v2

@@ -155,6 +155,7 @@ if ! $(BOOST_ARCHIVE_LIST) {
         [ test-bsl-run test_dll_base_pointer : : dll_polymorphic_base dll_polymorphic_derived2 : <link>static:<build>no ]
         # [ test-bsl-run test_dll_plugin : : dll_derived2 : <link>static:<build>no <target-os>linux:<linkflags>-ldl ]
 
+        [ test-bsl-run test_duplicate_type_registration ]
         [ test-bsl-run test_private_ctor ]
         [ test-bsl-run test_reset_object_address : A ]
         [ test-bsl-run test_void_cast ]

test/test_duplicate_type_registration.cpp

@@ -0,0 +1,64 @@
+/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
+// test_duplicate_type_registration.cpp
+
+// Copyright 2026 Gennaro Prota.
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+// Every module linked against the library registers the types it serializes,
+// so the type registry holds one entry per module per type.  A module going
+// away has to take its own entry with it and leave the others alone, or
+// serialization stops working in the modules still running.
+
+// Reported by gast128 in
+// https://github.com/boostorg/serialization/issues/325, from two COM
+// components in separate DLLs registering the same type: unloading one of
+// them made the other throw unregistered_class.  Both the diagnosis and the
+// remedy in the report were right.  Thanks for the careful write up!
+
+// singleton<T> explicitly allows a class derived from it to be instantiated
+// more than once, which is what stands in for the second module below.
+
+#include <cstddef>
+
+// The lightweight test of Boost.Core is used here in place of
+// test_tools.hpp, whose main locks the singleton module while the test runs,
+// so that the type registry cannot change.  Loading and unloading a module
+// changes it while the program runs, which is the very thing under test.
+#include <boost/core/lightweight_test.hpp>
+
+#include <boost/serialization/extended_type_info_typeid.hpp>
+#include <boost/serialization/singleton.hpp>
+
+struct base {
+    virtual ~base(){}
+};
+
+struct derived : base {
+};
+
+typedef boost::serialization::extended_type_info_typeid<derived> eti_derived;
+
+int
+main(){
+    const eti_derived & first =
+        boost::serialization::singleton<eti_derived>::get_const_instance();
+
+    const derived d;
+    BOOST_TEST(NULL != first.get_derived_extended_type_info(d));
+
+    {
+        // A second module registers the same type.
+        const eti_derived second;
+        BOOST_TEST(NULL != first.get_derived_extended_type_info(d));
+        BOOST_TEST(NULL != second.get_derived_extended_type_info(d));
+    }
+    // The second module is unloaded here.
+
+    BOOST_TEST(NULL != first.get_derived_extended_type_info(d));
+
+    return boost::report_errors();
+}