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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 .
+ */
+
+/*
+ * This file is part of LibreOffice published API.
+ */
+
+#ifndef INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
+#define INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
+
+#if defined __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/** A platform specific macro needed to make double-checked locking work.
+
+ See
+ <http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
+ for a description of double-checked locking, why it is broken, and how it
+ can be fixed. On platforms where it is necessary, this macro will expand
+ to some memory barrier instruction. On many platforms, double-checked
+ locking works as it is, though, so on those platforms this macro will be
+ empty. This is a macro instead of a (C++ inline) function to allow for
+ maximum performance in both C and C++.
+
+ If possible, use the rtl_Instance template instead of explicitly spelling
+ out the double-checked locking pattern. There are few cases where you
+ will have to spell it out explicitly (e.g., the logic of a certain
+ instance of the pattern is too complex to be mapped to the template, or
+ some compiler refuses to compile a template instantiation due to internal
+ compiler errors), though, and you should always call this macro at the
+ right places then:
+
+ @code{.cpp}
+ static T * pInstance = 0;
+
+ T * p = pInstance;
+ if (!p)
+ {
+ Guard aGuard(aMutex);
+ p = pInstance;
+ if (!p)
+ {
+ p = ...;
+ OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
+ pInstance = p;
+ }
+ }
+ else
+ OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
+ return p;
+ @endcode
+
+ One extra advantage of this macro is that it makes it easier to find all
+ places where double-checked locking is used.
+ */
+#define OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() /* empty */
+
+#if defined __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* INCLUDED_OSL_DOUBLECHECKEDLOCKING_H */
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */