Fixes for OSThread creation shutdown race.

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
diff --git a/runtime/vm/dart.cc b/runtime/vm/dart.cc
index 96dc5986e72bae70741b1dab41c73609d28e8544..8a5e91b53ed0f86162fcc9da2480d55eac14cc76 100644
--- a/runtime/vm/dart.cc
+++ b/runtime/vm/dart.cc
@@ -248,15 +248,18 @@ const char* Dart::Cleanup() {
     // before shutting down the thread pool.
     WaitForIsolateShutdown();
 
+    // Shutdown the thread pool. On return, all thread pool threads have exited.
+    delete thread_pool_;
+    thread_pool_ = NULL;
+
     // Disable creation of any new OSThread structures which means no more new
     // threads can do an EnterIsolate. This must come after isolate shutdown
     // because new threads may need to be spawned to shutdown the isolates.
+    // This must come after deletion of the thread pool to avoid a race in which
+    // a thread spawned by the thread pool does not exit through the thread
+    // pool, messing up its bookkeeping.
     OSThread::DisableOSThreadCreation();
 
-    // Shutdown the thread pool. On return, all thread pool threads have exited.
-    delete thread_pool_;
-    thread_pool_ = NULL;
-
     // Set the VM isolate as current isolate.
     bool result = Thread::EnterIsolate(vm_isolate_);
     ASSERT(result);