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diff --git a/include/unotools/readwritemutexguard.hxx b/include/unotools/readwritemutexguard.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#ifndef INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
+#define INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
+
+#include <osl/mutex.hxx>
+#include <o3tl/typed_flags_set.hxx>
+
+enum class ReadWriteGuardMode {
+    ReadOnly       = 0x00,
+    Write          = 0x01,
+    CriticalChange = 0x02 | Write,
+    BlockCritical  = 0x04,     // only a block, not a read, exclusive flag!
+};
+namespace o3tl {
+    template<> struct typed_flags<ReadWriteGuardMode> : is_typed_flags<ReadWriteGuardMode, 0x7> {};
+}
+
+namespace utl {
+
+class ReadWriteMutex
+{
+    friend class ReadWriteGuard;
+
+            sal_uInt32          nReadCount;
+            sal_uInt32          nBlockCriticalCount;
+            ::osl::Mutex        maMutex;
+            ::osl::Mutex        maWriteMutex;
+
+public:
+                                ReadWriteMutex()
+                                    : nReadCount(0)
+                                    , nBlockCriticalCount(0)
+                                    {}
+};
+
+/** Enable multiple threads to read simultaneously, but a write blocks all
+    other reads and writes, and a read blocks any write.
+    Used in I18N wrappers to be able to maintain a single instance of a wrapper
+    for the standard Office locale.
+    NEVER construct a writing guard if there is already a reading guard in the
+    same context, the following will dead lock EVEN IN THE SAME THREAD!
+    void foo()
+    {
+        ReadWriteGuard aGuard1( aMutex );
+        bar();
+    }
+    void bar()
+    {
+        // waits forever for aGuard1
+        ReadWriteGuard aGuard2( aMutex, ReadWriteGuardMode::nWrite );
+    }
+ */
+class ReadWriteGuard
+{
+            ReadWriteMutex&     rMutex;
+            ReadWriteGuardMode  nMode;
+public:
+                                ReadWriteGuard(
+                                    ReadWriteMutex& rMutex,
+                                    ReadWriteGuardMode nRequestMode = ReadWriteGuardMode::ReadOnly  // read only
+                                    );
+                                ~ReadWriteGuard();
+
+    /** Be careful with this, it does wait for ANY read to complete.
+        The following will dead lock EVEN IN THE SAME THREAD!
+        void foo()
+        {
+            ReadWriteGuard aGuard1( aMutex );
+            bar();
+        }
+        void bar()
+        {
+            ReadWriteGuard aGuard2( aMutex );
+            aGuard2.changeReadToWrite();    // waits forever for aGuard1
+        }
+     */
+            void                changeReadToWrite();
+};
+
+}   // namespace utl
+
+#endif // INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */