--- /dev/null	2018-12-27 16:32:15.144191626 -0500
+++ new/src/hotspot/share/gc/g1/g1FreeIdSet.hpp	2019-01-08 20:20:53.242037831 -0500
@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2019, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_GC_G1_G1FREEIDSET_HPP
+#define SHARE_GC_G1_G1FREEIDSET_HPP
+
+#include "memory/allocation.hpp"
+#include "runtime/semaphore.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+// Represents a set of small integer ids, from which elements can be
+// temporarily allocated for exclusive use.  The ids are in a
+// contiguous range from 'start' to 'start + size'.  Used to obtain a
+// distinct worker_id value for a mutator thread that doesn't normally
+// have such an id.
+class G1FreeIdSet : public CHeapObj<mtGC> {
+  Semaphore _sem;
+  uint* _next;
+  uint _start;
+  uint _size;
+  uintx _head_index_mask;
+  volatile uintx _head;
+
+  uint head_index(uintx head) const;
+  uintx make_head(uint index, uintx old_head) const;
+
+  // Noncopyable.
+  G1FreeIdSet(const G1FreeIdSet&);
+  G1FreeIdSet& operator=(const G1FreeIdSet&);
+
+public:
+  G1FreeIdSet(uint start, uint size);
+  ~G1FreeIdSet();
+
+  // Returns an unclaimed parallel id (waiting for one to be released if
+  // necessary).  Must not safepoint while holding a claimed id.
+  uint claim_par_id();
+
+  void release_par_id(uint id);
+
+  struct TestSupport;           // For unit test access.
+};
+
+#endif // SHARE_GC_G1_G1FREEIDSET_HPP