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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-15 05:54:39 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-15 05:54:39 +0000
commit267c6f2ac71f92999e969232431ba04678e7437e (patch)
tree358c9467650e1d0a1d7227a21dac2e3d08b622b2 /include/comphelper/singletonref.hxx
parentInitial commit. (diff)
downloadlibreoffice-267c6f2ac71f92999e969232431ba04678e7437e.tar.xz
libreoffice-267c6f2ac71f92999e969232431ba04678e7437e.zip
Adding upstream version 4:24.2.0.upstream/4%24.2.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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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 .
+ */
+#pragma once
+
+#include <sal/config.h>
+#include <osl/diagnose.h>
+#include <mutex>
+
+namespace comphelper
+{
+/** @short Template for implementing singleton classes.
+ This is a replacement for salhelper::SingletonRef, but which uses std::mutex instead of osl::Mutex.
+
+ Such classes can be instantiated every time they
+ are needed. But the internal wrapped object will
+ be created one times only. Of course it's used
+ resources are referenced one times only too.
+ This template hold it alive till the last
+ reference is gone. Further all operations
+ on this reference are threadsafe. Only
+ calls directly to the internal object (which modify
+ its state) must be made threadsafe by the object itself
+ or from outside.
+
+ @attention To prevent the code against race conditions, it's not
+ allowed to start operations inside the ctor
+ of the internal wrapped object - especially operations
+ which needs a reference to the same singleton too.
+
+ The only chance to suppress such strange constellations
+ is a lazy-init mechanism.
+
+ <ul>
+ <li>a) The singleton class can provide a special init()
+ method, which must be called as first after creation.</li>
+ <li>b) The singleton class can call a special impl_init()
+ method implicit for every called interface method.</li>
+ </ul>
+
+ Note further that this singleton pattern can work only, if
+ all user of such singleton are located inside the same library!
+ Because static values can't be exported - e.g. from windows libraries.
+ */
+template <class SingletonClass> class SingletonRef
+{
+ // member
+
+private:
+ /** @short pointer to the internal wrapped singleton. */
+ static SingletonClass* m_pInstance;
+
+ /** @short ref count, which regulate creation and removing of m_pInstance. */
+ static sal_Int32 m_nRef;
+
+ // interface
+
+public:
+ /** @short standard ctor.
+
+ The internal wrapped object is created only,
+ if its ref count was 0. Otherwise this method
+ does nothing ... except increasing of the internal
+ ref count!
+ */
+ SingletonRef()
+ {
+ // GLOBAL SAFE ->
+ std::unique_lock aLock(SingletonRef::ownStaticLock());
+
+ // must be increased before(!) the check is done.
+ // Otherwise this check can fail inside the same thread ...
+ ++m_nRef;
+ if (m_nRef == 1)
+ m_pInstance = new SingletonClass();
+
+ OSL_ENSURE(m_nRef > 0 && m_pInstance,
+ "Race? Ref count of singleton >0, but instance is NULL!");
+ // <- GLOBAL SAFE
+ }
+
+ /** @short standard dtor.
+
+ The internal wrapped object is removed only,
+ if its ref count will be 0. Otherwise this method
+ does nothing ... except decreasing of the internal
+ ref count!
+ */
+ ~SingletonRef()
+ {
+ // GLOBAL SAFE ->
+ std::unique_lock aLock(SingletonRef::ownStaticLock());
+
+ // must be decreased before(!) the check is done.
+ // Otherwise this check can fail inside the same thread ...
+ --m_nRef;
+ if (m_nRef == 0)
+ {
+ delete m_pInstance;
+ m_pInstance = nullptr;
+ }
+ // <- GLOBAL SAFE
+ }
+
+ SingletonRef& operator=(SingletonRef const&) = default;
+
+ /** @short Allows rSingle->someBodyOp().
+ */
+ SingletonClass* operator->() const
+ {
+ // GLOBAL SAFE ->
+ return m_pInstance;
+ // <- GLOBAL SAFE
+ }
+
+ /** @short Allows (*rSingle).someBodyOp().
+ */
+ SingletonClass& operator*() const
+ {
+ // GLOBAL SAFE ->
+ return *m_pInstance;
+ // <- GLOBAL SAFE
+ }
+
+ // helper
+
+private:
+ SingletonRef(SingletonRef&) = delete;
+
+ static std::mutex& ownStaticLock()
+ {
+ static std::mutex aInstance;
+ return aInstance;
+ }
+};
+
+template <class SingletonClass> SingletonClass* SingletonRef<SingletonClass>::m_pInstance = nullptr;
+
+template <class SingletonClass> sal_Int32 SingletonRef<SingletonClass>::m_nRef = 0;
+
+} // namespace comphelper
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */