Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 81 insertions, 0 deletions

diff --git a/include/osl/doublecheckedlocking.h b/include/osl/doublecheckedlocking.h
new file mode 100644
index 000000000..f89ab3620
--- /dev/null
+++ b/include/osl/doublecheckedlocking.h
@@ -0,0 +1,81 @@
+/* -*- 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: */