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diff --git a/sd/source/ui/slidesorter/inc/cache/SlsPageCacheManager.hxx b/sd/source/ui/slidesorter/inc/cache/SlsPageCacheManager.hxx
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+++ b/sd/source/ui/slidesorter/inc/cache/SlsPageCacheManager.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 .
+ */
+
+#pragma once
+
+#include <sal/types.h>
+#include <com/sun/star/uno/XInterface.hpp>
+#include <memory>
+#include <vector>
+
+class Size;
+class SdrPage;
+
+namespace sd::slidesorter::cache {
+
+class BitmapCache;
+
+/** Provide and manage the preview bitmap caches for all slide sorter
+    instances.  There is one cache per active slide sorter plus a small
+    number of caches that are no longer in use.  The later are kept to speed
+    up the switching between views.
+*/
+class PageCacheManager
+{
+public:
+    typedef std::vector< std::pair<Size, std::shared_ptr<BitmapCache> > > BestFittingPageCaches;
+    typedef css::uno::Reference<css::uno::XInterface> DocumentKey;
+
+    /** Return the one instance of the PageCacheManager class.
+    */
+    static std::shared_ptr<PageCacheManager> Instance();
+
+    /** Look up the cache for the given model in which the previews have the
+        specified size.  If no such cache exists, then one is created.  When
+        a new BitmapCache is created its Recycle() method is called with a
+        sorted list of existing caches from which the new one initialize its
+        previews.
+        @return
+            The returned cache lives as long as somebody keeps a shared
+            pointer and the ReleaseCache() method has not been called.
+    */
+    std::shared_ptr<BitmapCache> GetCache (
+        const  DocumentKey& pDocument,
+        const Size& rPreviewSize);
+
+    /** Tell the cache manager to release its own reference to the specified
+        cache.  After that the cache will live as long as the caller (and
+        maybe others) holds its reference.
+    */
+    void ReleaseCache (const std::shared_ptr<BitmapCache>& rpCache);
+
+    /** This is an information to the cache manager that the size of preview
+        bitmaps in the specified cache has changed.
+
+    */
+    std::shared_ptr<BitmapCache> ChangeSize (
+        const std::shared_ptr<BitmapCache>& rpCache,
+        const Size& rOldPreviewSize,
+        const Size& rNewPreviewSize);
+
+    /** Invalidate the preview bitmap for one slide that belongs to the
+        specified document.  The bitmaps for this slide in all caches are
+        marked as out-of-date and will be re-created when they are requested
+        the next time.
+    */
+    bool InvalidatePreviewBitmap (
+        const DocumentKey& pDocument,
+        const SdrPage* pPage);
+
+    /** Invalidate the preview bitmaps for all slides that belong to the
+        specified document.  This is necessary after model changes that
+        affect e.g. page number fields.
+    */
+    void InvalidateAllPreviewBitmaps (const DocumentKey& pDocument);
+
+    /** Invalidate all the caches that are currently in use and destroy
+        those that are not.  This is used for example when the high contrast
+        mode is turned on or off.
+    */
+    void InvalidateAllCaches();
+
+    /** Call this method when a page has been deleted and its preview
+        is not needed anymore.
+    */
+    void ReleasePreviewBitmap (const SdrPage* pPage);
+
+private:
+    /** Singleton instance of the cache manager.  Note that this is a weak
+        pointer.  The (implementation class of) ViewShellBase holds a
+        shared_ptr so that the cache manager has the same life time as the
+        ViewShellBase.
+    */
+    static std::weak_ptr<PageCacheManager> mpInstance;
+
+    /// List of active caches.
+    class PageCacheContainer;
+    std::unique_ptr<PageCacheContainer> mpPageCaches;
+
+    /// List of inactive, recently used caches.
+    class RecentlyUsedPageCaches;
+    std::unique_ptr<RecentlyUsedPageCaches> mpRecentlyUsedPageCaches;
+
+    /** The maximal number of recently used caches that are kept alive after
+        they have become inactive, i.e. after they are not used anymore by a
+        slide sorter.
+    */
+    static const sal_uInt32 mnMaximalRecentlyCacheCount = 2;
+
+    PageCacheManager();
+    ~PageCacheManager();
+
+    class Deleter;
+    friend class Deleter;
+
+    std::shared_ptr<BitmapCache> GetRecentlyUsedCache(
+        const DocumentKey& pDocument,
+        const Size& rSize);
+
+    /** Add the given cache to the list of recently used caches for the
+        document.  There is one such list per document.  Each least has at
+        most mnMaximalRecentlyCacheCount members.
+    */
+    void PutRecentlyUsedCache(
+        DocumentKey const & pDocument,
+        const Size& rPreviewSize,
+        const std::shared_ptr<BitmapCache>& rpCache);
+
+    /** This method is used internally to initialize a newly created
+        BitmapCache with already existing previews.
+    */
+    void Recycle (
+        const std::shared_ptr<BitmapCache>& rpCache,
+        const DocumentKey& pDocument,
+        const Size& rPreviewSize);
+};
+
+} // end of namespace ::sd::slidesorter::cache
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */