Index: lldb/trunk/include/lldb/Target/Process.h
===================================================================
--- lldb/trunk/include/lldb/Target/Process.h
+++ lldb/trunk/include/lldb/Target/Process.h
@@ -3309,9 +3309,13 @@
     bool
     PrivateStateThreadIsValid () const
     {
-        return m_private_state_thread.IsJoinable();
+        lldb::StateType state = m_private_state.GetValue();
+        return state != lldb::eStateInvalid &&
+               state != lldb::eStateDetached &&
+               state != lldb::eStateExited &&
+               m_private_state_thread.IsJoinable();
     }
-    
+
     void
     ForceNextEventDelivery()
     {
Index: lldb/trunk/source/Target/Process.cpp
===================================================================
--- lldb/trunk/source/Target/Process.cpp
+++ lldb/trunk/source/Target/Process.cpp
@@ -4088,7 +4088,7 @@
 void
 Process::StopPrivateStateThread ()
 {
-    if (PrivateStateThreadIsValid ())
+    if (m_private_state_thread.IsJoinable ())
         ControlPrivateStateThread (eBroadcastInternalStateControlStop);
     else
     {
@@ -4110,21 +4110,23 @@
     if (log)
         log->Printf ("Process::%s (signal = %d)", __FUNCTION__, signal);
 
-    // Signal the private state thread. First we should copy this is case the
-    // thread starts exiting since the private state thread will NULL this out
-    // when it exits
+    // Signal the private state thread
+    if (m_private_state_thread.IsJoinable())
     {
-        HostThread private_state_thread(m_private_state_thread);
-        if (private_state_thread.IsJoinable())
+        // Broadcast the event.
+        // It is important to do this outside of the if below, because
+        // it's possible that the thread state is invalid but that the
+        // thread is waiting on a control event instead of simply being
+        // on its way out (this should not happen, but it apparently can).
+        if (log)
+            log->Printf ("Sending control event of type: %d.", signal);
+        std::shared_ptr<EventDataReceipt> event_receipt_sp(new EventDataReceipt());
+        m_private_state_control_broadcaster.BroadcastEvent(signal, event_receipt_sp);
+
+        // Wait for the event receipt or for the private state thread to exit
+        bool receipt_received = false;
+        if (PrivateStateThreadIsValid())
         {
-            if (log)
-                log->Printf ("Sending control event of type: %d.", signal);
-            // Send the control event and wait for the receipt or for the private state
-            // thread to exit
-            std::shared_ptr<EventDataReceipt> event_receipt_sp(new EventDataReceipt());
-            m_private_state_control_broadcaster.BroadcastEvent(signal, event_receipt_sp);
-
-            bool receipt_received = false;
             while (!receipt_received)
             {
                 bool timed_out = false;
@@ -4137,23 +4139,24 @@
                 if (!receipt_received)
                 {
                     // Check if the private state thread is still around. If it isn't then we are done waiting
-                    if (!m_private_state_thread.IsJoinable())
-                        break; // Private state thread exited, we are done
+                    if (!PrivateStateThreadIsValid())
+                        break; // Private state thread exited or is exiting, we are done
                 }
             }
-
-            if (signal == eBroadcastInternalStateControlStop)
-            {
-                thread_result_t result = NULL;
-                private_state_thread.Join(&result);
-            }
         }
-        else
+
+        if (signal == eBroadcastInternalStateControlStop)
         {
-            if (log)
-                log->Printf ("Private state thread already dead, no need to signal it to stop.");
+            thread_result_t result = NULL;
+            m_private_state_thread.Join(&result);
+            m_private_state_thread.Reset();
         }
     }
+    else
+    {
+        if (log)
+            log->Printf("Private state thread already dead, no need to signal it to stop.");
+    }
 }
 
 void
@@ -4446,7 +4449,6 @@
     // try to change it on the way out.
     if (!is_secondary_thread)
         m_public_run_lock.SetStopped();
-    m_private_state_thread.Reset();
     return NULL;
 }