--- a/src/share/vm/runtime/thread.hpp	Wed Feb 01 07:59:01 2012 -0800
+++ b/src/share/vm/runtime/thread.hpp	Wed Feb 01 16:57:08 2012 -0800
@@ -182,7 +182,8 @@
     _ext_suspended          = 0x40000000U, // thread has self-suspended
     _deopt_suspend          = 0x10000000U, // thread needs to self suspend for deopt
 
-    _has_async_exception    = 0x00000001U  // there is a pending async exception
+    _has_async_exception    = 0x00000001U, // there is a pending async exception
+    _critical_native_unlock = 0x00000002U  // Must call back to unlock JNI critical lock
   };
 
   // various suspension related flags - atomically updated
@@ -350,6 +351,15 @@
     clear_suspend_flag(_has_async_exception);
   }
 
+  bool do_critical_native_unlock() const { return (_suspend_flags & _critical_native_unlock) != 0; }
+
+  void set_critical_native_unlock() {
+    set_suspend_flag(_critical_native_unlock);
+  }
+  void clear_critical_native_unlock() {
+    clear_suspend_flag(_critical_native_unlock);
+  }
+
   // Support for Unhandled Oop detection
 #ifdef CHECK_UNHANDLED_OOPS
  private:
@@ -1038,6 +1048,11 @@
   // Check for async exception in addition to safepoint and suspend request.
   static void check_special_condition_for_native_trans(JavaThread *thread);
 
+  // Same as check_special_condition_for_native_trans but finishes the
+  // transition into thread_in_Java mode so that it can potentially
+  // block.
+  static void check_special_condition_for_native_trans_and_transition(JavaThread *thread);
+
   bool is_ext_suspend_completed(bool called_by_wait, int delay, uint32_t *bits);
   bool is_ext_suspend_completed_with_lock(uint32_t *bits) {
     MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);
@@ -1311,8 +1326,9 @@
   // JNI critical regions. These can nest.
   bool in_critical()    { return _jni_active_critical > 0; }
   bool in_last_critical()  { return _jni_active_critical == 1; }
-  void enter_critical() { assert(Thread::current() == this,
-                                 "this must be current thread");
+  void enter_critical() { assert(Thread::current() == this ||
+                                 Thread::current()->is_VM_thread() && SafepointSynchronize::is_synchronizing(),
+                                 "this must be current thread or synchronizing");
                           _jni_active_critical++; }
   void exit_critical()  { assert(Thread::current() == this,
                                  "this must be current thread");