Add test checking that we do not create TClass at tear down

Author: pcanal

root/meta/tclass/CMakeLists.txt

@@ -111,4 +111,9 @@ ROOTTEST_ADD_TEST(tclassStl
 		  OUTREF tclassStl.ref
 		  RUN_SERIAL)
 
+ROOTTEST_ADD_TEST(TClassAtTearDown
+                  MACRO execTClassAtTearDown.C
+		  COPY_TO_BUILDDIR empty.root
+		  OUTREF execTClassAtTearDown.ref)
+
 ROOTTEST_ADD_TESTDIRS()

root/meta/tclass/empty.root

@@ -0,0 +1,25 @@
+#include "TFile.h"
+
+void execTClassAtTearDown()
+{
+   TFile f("empty.root", "READ");
+
+   // Because of this call to exit, even-though the TFile is
+   // on the stack, it will not be destructed.
+   // Furthermore, TROOT::CloseFile will not destructed either
+   // since it is on the stack.
+   // Subsequently the TFile object will still be on the list of
+   // files when it is being deleted and thus will need to
+   // interogate the object *AND* its TClass.
+   // We setup this exmaple so that at the time `exit` is called
+   // the `TClass` for `TFile` has not been created yet.
+   // Consequently, its creation will be asked for during
+   // the deletion of the list of files ... which is in the
+   // middle of the tear down ... if a TClass object is created
+   // at that time, it will use some resources (static tables)
+   // that have already been tear down, resulting in crashes.
+   // The new behavior is to sort-of ignore this late request
+   // and build only a dummy TClass object (which does not
+   // do any registrations).
+   exit(0);
+}

root/meta/tclass/execTClassAtTearDown.C

@@ -0,0 +1 @@
+