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diff --git a/gcc-4.9/libitm/config/linux/rwlock.h b/gcc-4.9/libitm/config/linux/rwlock.h
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+/* Copyright (C) 2011-2014 Free Software Foundation, Inc.
+   Contributed by Torvald Riegel <triegel@redhat.com>.
+
+   This file is part of the GNU Transactional Memory Library (libitm).
+
+   Libitm is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   Libitm 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 for
+   more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef GTM_RWLOCK_H
+#define GTM_RWLOCK_H
+
+#include "local_atomic"
+#include "common.h"
+
+namespace GTM HIDDEN {
+
+struct gtm_thread;
+
+// This datastructure is the blocking, futex-based version of the Dekker-style
+// reader-writer lock used to provide mutual exclusion between active and
+// serial transactions.
+// See libitm's documentation for further details.
+//
+// In this implementation, writers are given highest priority access but
+// read-to-write upgrades do not have a higher priority than writers.
+//
+// Do not change the layout of this class; it must remain a POD type with
+// standard layout, and the WRITERS field must be first (i.e., so the
+// assembler code can assume that its address is equal to the address of the
+// respective instance of the class).
+
+class gtm_rwlock
+{
+  // TODO Put futexes on different cachelines?
+  std::atomic<int> writers;       // Writers' futex.
+  std::atomic<int> writer_readers;// A confirmed writer waits here for readers.
+  std::atomic<int> readers;       // Readers wait here for writers (iff true).
+
+ public:
+  gtm_rwlock() : writers(0), writer_readers(0), readers(0) {};
+
+  void read_lock (gtm_thread *tx);
+  void read_unlock (gtm_thread *tx);
+
+  void write_lock ();
+  void write_unlock ();
+
+  bool write_upgrade (gtm_thread *tx);
+  void write_upgrade_finish (gtm_thread *tx);
+
+  // Returns true iff there is a concurrent active or waiting writer.
+  // This is primarily useful for simple HyTM approaches, and the value being
+  // checked is loaded with memory_order_relaxed.
+  bool is_write_locked()
+  {
+    return writers.load (memory_order_relaxed) != 0;
+  }
+
+ protected:
+  bool write_lock_generic (gtm_thread *tx);
+};
+
+} // namespace GTM
+
+#endif // GTM_RWLOCK_H