--- old/src/share/vm/gc_implementation/shared/suspendibleThreadSet.cpp	2015-05-07 18:07:49.869760936 -0400
+++ new/src/share/vm/gc_implementation/shared/suspendibleThreadSet.cpp	2015-05-07 18:07:48.441679245 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -33,16 +33,20 @@
 double SuspendibleThreadSet::_suspend_all_start = 0.0;
 
 void SuspendibleThreadSet::join() {
+  assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");
   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
   while (_suspend_all) {
     ml.wait(Mutex::_no_safepoint_check_flag);
   }
   _nthreads++;
+  DEBUG_ONLY(Thread::current()->set_suspendible_thread();)
 }
 
 void SuspendibleThreadSet::leave() {
+  assert(Thread::current()->is_suspendible_thread(), "Thread not joined");
   MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
   assert(_nthreads > 0, "Invalid");
+  DEBUG_ONLY(Thread::current()->clear_suspendible_thread();)
   _nthreads--;
   if (_suspend_all) {
     ml.notify_all();
@@ -50,6 +54,7 @@
 }
 
 void SuspendibleThreadSet::yield() {
+  assert(Thread::current()->is_suspendible_thread(), "Must have joined");
   if (_suspend_all) {
     MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
     if (_suspend_all) {
--- old/src/share/vm/runtime/thread.cpp	2015-05-07 18:07:53.705980388 -0400
+++ new/src/share/vm/runtime/thread.cpp	2015-05-07 18:07:52.521912652 -0400
@@ -190,6 +190,7 @@
   set_stack_size(0);
   set_self_raw_id(0);
   set_lgrp_id(-1);
+  DEBUG_ONLY(clear_suspendible_thread();)
 
   // allocated data structures
   set_osthread(NULL);
--- old/src/share/vm/runtime/thread.hpp	2015-05-07 18:07:58.322244465 -0400
+++ new/src/share/vm/runtime/thread.hpp	2015-05-07 18:07:56.454137596 -0400
@@ -206,11 +206,25 @@
  private:
   int _num_nested_signal;
 
+  DEBUG_ONLY(bool _suspendible_thread;)
+
  public:
   void enter_signal_handler() { _num_nested_signal++; }
   void leave_signal_handler() { _num_nested_signal--; }
   bool is_inside_signal_handler() const { return _num_nested_signal > 0; }
 
+#ifdef ASSERT
+  void set_suspendible_thread() {
+    _suspendible_thread = true;
+  }
+
+  void clear_suspendible_thread() {
+    _suspendible_thread = false;
+  }
+
+  bool is_suspendible_thread() { return _suspendible_thread; }
+#endif
+
  private:
   // Active_handles points to a block of handles
   JNIHandleBlock* _active_handles;