On Windows, set current thread in TLS to NULL before deleting the thread.

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 260f59088ae169ec397713235d46287c90f0e43b..18c062dc90744f19bc8473e7fce41b0e72626801 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -93,9 +93,9 @@ void Thread::EnsureInit() {
 void Thread::CleanUp() {
   Thread* current = Current();
   if (current != NULL) {
+    SetCurrent(NULL);
     delete current;

[Ivan Posva, 2015/08/21 03:23:56]

Are we sure the destructor will not touch anything that tries to reference
Thread::Current()?

[koda, 2015/08/21 17:15:42]

I can't guarantee it won't, but if it did, we'd already have a problem with
pthreads on Linux and Mac. This CL just makes Windows consistent with their
behavior.

It's fine for the destructor to call Thread::Current as long as it guards
against null. The same is true for any initialization code that might run before
Thread::EnsureInit.

   }
-  SetCurrent(NULL);
 }
 #endif