xAODRootAccess: Work around root 6.20.02 destructor issue.

~TMethodCall dereferences gCling. But if it is being run as part of global destructors, then gCling may have already been destroyed by the time the TMethodCall destructor runs.

Change TAuxVectorFactory to hold the TMethodCall instance by pointer to guard against this.

Needed to fix test failure in xAODDataSource.

See !31633 (merged).

Control/xAODRootAccess/Root/TAuxVectorFactory.cxx

@@ -5,6 +5,7 @@
 #include <TError.h>
 #include <TString.h>
 #include <TVirtualCollectionProxy.h>
+#include <TInterpreter.h>
 
 // Local include(s):
 #include "xAODRootAccess/tools/TAuxVectorFactory.h"
@@ -15,7 +16,7 @@ namespace xAOD {
 
    TAuxVectorFactory::TAuxVectorFactory( ::TClass* cl )
       : m_class( cl ), m_proxy( cl->GetCollectionProxy() ),
-        m_assign(), m_defElt( 0 ) {
+        m_defElt( 0 ) {
 
       // A little sanity check:
       if( ! m_proxy ) {
@@ -31,8 +32,9 @@ namespace xAOD {
          ::TString proto = "const ";
          proto += eltClass->GetName();
          proto += "&";
-         m_assign.InitWithPrototype( eltClass, "operator=", proto );
-         if( ! m_assign.IsValid() ) {
+         m_assign = new TMethodCall;
+         m_assign->InitWithPrototype( eltClass, "operator=", proto );
+         if( ! m_assign->IsValid() ) {
             ::Warning( "xAOD::TAuxVectorFactory::TAuxVectorFactory",
                        XAOD_MESSAGE( "Can't get assignment operator for "
                                      "class %s" ),
@@ -48,6 +50,12 @@ namespace xAOD {
       if( m_defElt ) {
          m_proxy->GetValueClass()->Destructor( m_defElt );
       }
+
+      // The TMethodCall destructor will fail if TCling has already
+      // been destroyed...
+      if( gCling ) {
+        delete m_assign;
+      }
    }
 
    std::unique_ptr< SG::IAuxTypeVector >
@@ -78,10 +86,10 @@ namespace xAOD {
 
       // Do the copy either using the assignment operator of the type, or using
       // simple memory copying:
-      if( m_assign.IsValid() ) {
-         m_assign.ResetParam();
-         m_assign.SetParam( ( Long_t ) src );
-         m_assign.Execute( dst );
+      if( m_assign && m_assign->IsValid() ) {
+         m_assign->ResetParam();
+         m_assign->SetParam( ( Long_t ) src );
+         m_assign->Execute( dst );
       } else {
          memcpy( dst, src, eltsz );
       }
@@ -113,24 +121,24 @@ namespace xAOD {
       b = reinterpret_cast< void* >( reinterpret_cast< unsigned long >( b ) +
                                      eltsz * bindex );
 
-      if( m_assign.IsValid() ) {
+      if( m_assign && m_assign->IsValid() ) {
 
          // Create a temporary object in memory:
          TClass* eltClass = m_proxy->GetValueClass();
          void* tmp = eltClass->New();
 
          // tmp = a
-         m_assign.ResetParam();
-         m_assign.SetParam( ( Long_t ) a );
-         m_assign.Execute( tmp );
+         m_assign->ResetParam();
+         m_assign->SetParam( ( Long_t ) a );
+         m_assign->Execute( tmp );
          // a = b
-         m_assign.ResetParam();
-         m_assign.SetParam( ( Long_t ) b );
-         m_assign.Execute( a );
+         m_assign->ResetParam();
+         m_assign->SetParam( ( Long_t ) b );
+         m_assign->Execute( a );
          // b = tmp
-         m_assign.ResetParam();
-         m_assign.SetParam( ( Long_t ) tmp );
-         m_assign.Execute( b );
+         m_assign->ResetParam();
+         m_assign->SetParam( ( Long_t ) tmp );
+         m_assign->Execute( b );
 
          // Delete the temporary object:
          eltClass->Destructor( tmp );
@@ -159,11 +167,11 @@ namespace xAOD {
       dst = reinterpret_cast< void* >( reinterpret_cast< unsigned long >( dst ) +
                                        eltsz * dst_index );
 
-      if( m_assign.IsValid() ) {
+      if( m_assign && m_assign->IsValid() ) {
          // Assign the default element's contents to this object:
-         m_assign.ResetParam();
-         m_assign.SetParam( ( Long_t ) m_defElt );
-         m_assign.Execute( dst );
+         m_assign->ResetParam();
+         m_assign->SetParam( ( Long_t ) m_defElt );
+         m_assign->Execute( dst );
       } else {
          // Set the memory to zero:
          memset( dst, 0, eltsz );