new comphelper::SingletonRef

to replace salhelper::SingletonRef, but using a std::mutex instead of an
osl::Mutex

Change-Id: Ibf88a3778f47300c08b8ec9ee58ed24eb83aed7b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/147046
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

3 files changed, 165 insertions, 4 deletions

diff --git a/include/comphelper/singletonref.hxx b/include/comphelper/singletonref.hxx
new file mode 100644
index 000000000000..5e90fc78cdc1
--- /dev/null
+++ b/include/comphelper/singletonref.hxx
@@ -0,0 +1,161 @@
+/* -*- 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 <cstddef>
+#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 ->
+        std::unique_lock aLock(SingletonRef::ownStaticLock());
+        return m_pInstance;
+        // <- GLOBAL SAFE
+    }
+
+    /** @short  Allows (*rSingle).someBodyOp().
+         */
+    SingletonClass& operator*() const
+    {
+        // GLOBAL SAFE ->
+        std::unique_lock aLock(SingletonRef::ownStaticLock());
+        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: */
diff --git a/include/connectivity/DriversConfig.hxx b/include/connectivity/DriversConfig.hxx
index 239259313a72..8dd8d23ca846 100644
--- a/include/connectivity/DriversConfig.hxx
+++ b/include/connectivity/DriversConfig.hxx
@@ -26,7 +26,7 @@
 
 #include <com/sun/star/uno/Sequence.h>
 #include <connectivity/dbtoolsdllapi.hxx>
-#include <salhelper/singletonref.hxx>
+#include <comphelper/singletonref.hxx>
 #include <comphelper/namedvaluecollection.hxx>
 #include <unotools/confignode.hxx>
 
@@ -56,7 +56,7 @@ namespace connectivity
 
     class OOO_DLLPUBLIC_DBTOOLS DriversConfig
     {
-        typedef salhelper::SingletonRef<DriversConfigImpl> OSharedConfigNode;
+        typedef comphelper::SingletonRef<DriversConfigImpl> OSharedConfigNode;
 
         const ::comphelper::NamedValueCollection& impl_get(std::u16string_view _sURL,sal_Int32 _nProps) const;
     public:
diff --git a/include/connectivity/sqlparse.hxx b/include/connectivity/sqlparse.hxx
index 7e55d41e339f..0a8523e436a8 100644
--- a/include/connectivity/sqlparse.hxx
+++ b/include/connectivity/sqlparse.hxx
@@ -28,7 +28,7 @@
 #include <connectivity/IParseContext.hxx>
 #include <connectivity/dbtoolsdllapi.hxx>
 #include <connectivity/sqlerror.hxx>
-#include <salhelper/singletonref.hxx>
+#include <comphelper/singletonref.hxx>
 
 #include <map>
 
@@ -94,7 +94,7 @@ namespace connectivity
         void clearAndDelete();
     };
 
-    typedef salhelper::SingletonRef<OSQLParseNodesContainer> OSQLParseNodesGarbageCollector;
+    typedef comphelper::SingletonRef<OSQLParseNodesContainer> OSQLParseNodesGarbageCollector;
 
     //= OSQLParser