Copy stack until safepoint *before* notifying other threads at safepoints.

Source/heap/ThreadState.cpp

Index: Source/heap/ThreadState.cpp
diff --git a/Source/heap/ThreadState.cpp b/Source/heap/ThreadState.cpp
index fa886557d507ce03fd22cf801cd4b4d805906902..6d8aa23ca52db6429c9b5444dc7082004fb6879d 100644
--- a/Source/heap/ThreadState.cpp
+++ b/Source/heap/ThreadState.cpp
@@ -181,6 +181,7 @@ public:
     void doEnterSafePoint(ThreadState* state, intptr_t* stackEnd)
     {
         state->recordStackEnd(stackEnd);
+        state->copyStackUntilSafePointScope();
         // m_unparkedThreadCount tracks amount of unparked threads. It is
         // positive if and only if we have requested other threads to park
         // at safe-points in preparation for GC. The last thread to park
@@ -193,7 +194,6 @@ public:
             MutexLocker locker(m_mutex);
             m_parked.signal(); // Safe point reached.
         }
-        state->copyStackUntilSafePointScope();
     }
 
     void enterSafePoint(ThreadState* state)