Fix race during process detach

[labath]

Summary

The code which was preventing the usage of the OS plugin while detach is in
progress also prevented us to update the thread list correctly. This resulted
in an empty thread list, which confused the detaching logic. Change the
condition do only do what it says (disable the usage of the OS plugin).

lldb/trunk/packages/Python/lldbsuite/test/functionalities/attach_resume/TestAttachResume.py

 
 class AttachResumeTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     @skipIfRemote
     @expectedFailureFreeBSD('llvm.org/pr19310')
     @expectedFailureWindows("llvm.org/pr24778")
-    @expectedFlakeyLinux('llvm.org/pr19310')
     def test_attach_continue_interrupt_detach(self):
         """Test attach/continue/interrupt/detach"""
         self.build()
         self.process_attach_continue_interrupt_detach()
 
     def process_attach_continue_interrupt_detach(self):
         """Test attach/continue/interrupt/detach"""
 

lldb/trunk/source/Target/Process.cpp

if (m_thread_list.GetSize(false) == 0 || stop_id != m_thread_list.GetStopID())
             ThreadList new_thread_list(this);
             // Always update the thread list with the protocol specific
             // thread list, but only update if "true" is returned
             if (UpdateThreadList (m_thread_list_real, real_thread_list))
             {
                 // Don't call into the OperatingSystem to update the thread list if we are shutting down, since
                 // that may call back into the SBAPI's, requiring the API lock which is already held by whoever is
                 // shutting us down, causing a deadlock.
-                if (!m_destroy_in_process)
-                {
-                    OperatingSystem *os = GetOperatingSystem ();
-                    if (os)
-                    {
-                        // Clear any old backing threads where memory threads might have been
-                        // backed by actual threads from the lldb_private::Process subclass
-                        size_t num_old_threads = old_thread_list.GetSize(false);
-                        for (size_t i=0; i<num_old_threads; ++i)
-                            old_thread_list.GetThreadAtIndex(i, false)->ClearBackingThread();
+                if (os && !m_destroy_in_process)
 
-                        // Turn off dynamic types to ensure we don't run any expressions. Objective C
-                        // can run an expression to determine if a SBValue is a dynamic type or not
-                        // and we need to avoid this. OperatingSystem plug-ins can't run expressions
-                        // that require running code...
 
-                        Target &target = GetTarget();
-                        const lldb::DynamicValueType saved_prefer_dynamic = target.GetPreferDynamicValue ();
-                        if (saved_prefer_dynamic != lldb::eNoDynamicValues)
-                            target.SetPreferDynamicValue(lldb::eNoDynamicValues);
 
-                        // Now let the OperatingSystem plug-in update the thread list
 
-                        os->UpdateThreadList (old_thread_list,  // Old list full of threads created by OS plug-in
-                                              real_thread_list, // The actual thread list full of threads created by each lldb_private::Process subclass
-                                              new_thread_list); // The new thread list that we will show to the user that gets filled in
 
-                        if (saved_prefer_dynamic != lldb::eNoDynamicValues)
-                            target.SetPreferDynamicValue(saved_prefer_dynamic);
-                    }
-                    else
-                    {
-                        // No OS plug-in, the new thread list is the same as the real thread list
-                        new_thread_list = real_thread_list;
-                    }
-                }
                 
                 m_thread_list_real.Update(real_thread_list);
                 m_thread_list.Update (new_thread_list);
                 m_thread_list.SetStopID (stop_id);
 
                 if (GetLastNaturalStopID () != m_extended_thread_stop_id)
                 {
                     // Clear any extended threads that we may have accumulated previously