Enable ROOT thread safety during FORM initialization

form/root_storage/CMakeLists.txt

@@ -7,6 +7,7 @@ set(FORM_ROOT_STORAGE_SOURCES)
 list(
   APPEND FORM_ROOT_STORAGE_SOURCES
   root_tfile.cpp
+  root_thread_safety.cpp
   root_ttree_write_container.cpp
   root_tbranch_read_container.cpp
   root_tbranch_write_container.cpp

form/root_storage/root_thread_safety.cpp

@@ -0,0 +1,11 @@
+// Copyright (C) 2025 ...
+
+#include "root_thread_safety.hpp"
+
+#include <TROOT.h>
+
+namespace form::detail::experimental {
+
+  void ensure_root_thread_safety() { ROOT::EnableThreadSafety(); }
+
+} // namespace form::detail::experimental

form/root_storage/root_thread_safety.hpp

@@ -0,0 +1,13 @@
+// Copyright (C) 2025 ...
+
+#ifndef FORM_ROOT_STORAGE_ROOT_THREAD_SAFETY_HPP
+#define FORM_ROOT_STORAGE_ROOT_THREAD_SAFETY_HPP
+
+namespace form::detail::experimental {
+
+  /// Enable ROOT thread safety.
+  void ensure_root_thread_safety();
+
+} // namespace form::detail::experimental
+
+#endif // FORM_ROOT_STORAGE_ROOT_THREAD_SAFETY_HPP

form/storage/factories.cpp

@@ -16,6 +16,7 @@
 #include "root_storage/root_tbranch_read_container.hpp"
 #include "root_storage/root_tbranch_write_container.hpp"
 #include "root_storage/root_tfile.hpp"
+#include "root_storage/root_thread_safety.hpp"
 #include "root_storage/root_ttree_write_container.hpp"
 #endif
 
@@ -31,6 +32,13 @@ namespace form::detail::experimental {
 
   using major = form::technology::major;
 
+  void ensure_backend_thread_safety()
+  {
+#ifdef USE_ROOT_STORAGE
+    ensure_root_thread_safety();
+#endif
+  }
+
   std::shared_ptr<i_storage_file> create_file(form::technology::id tech,
                                               std::string const& name,
                                               char mode)

form/storage/factories.hpp

@@ -11,6 +11,8 @@
 
 namespace form::detail::experimental {
 
+  void ensure_backend_thread_safety();
+
   std::shared_ptr<i_storage_file> create_file(form::technology::id tech,
                                               std::string const& name,
                                               char mode);

form/storage/storage_reader.cpp

@@ -190,6 +190,7 @@ namespace {
 namespace form::detail::experimental {
   std::unique_ptr<i_storage_reader> create_storage_reader()
   {
+    ensure_backend_thread_safety();
     return std::unique_ptr<i_storage_reader>(new storage_reader());
   }
 }

form/storage/storage_writer.cpp

@@ -58,6 +58,7 @@ namespace {
 namespace form::detail::experimental {
   std::unique_ptr<i_storage_writer> create_storage_writer()
   {
+    ensure_backend_thread_safety();
     return std::unique_ptr<i_storage_writer>(new storage_writer());
   }
 }