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diff --git a/sd/source/ui/slidesorter/cache/SlsRequestQueue.hxx b/sd/source/ui/slidesorter/cache/SlsRequestQueue.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 "SlsRequestPriorityClass.hxx"
+#include <cache/SlsCacheContext.hxx>
+#include <osl/mutex.hxx>
+#include <svx/sdrpageuser.hxx>
+
+#include <memory>
+
+namespace sd::slidesorter::cache
+{
+/** The request queue stores requests that are described by the Request
+    sorted according to priority class and then priority.
+*/
+class RequestQueue : public sdr::PageUser
+{
+public:
+    explicit RequestQueue(SharedCacheContext pCacheContext);
+    virtual ~RequestQueue();
+
+    /** Insert a request with highest or lowest priority in its priority
+        class.  When the request is already present then it is first
+        removed.  This effect is then a re-prioritization.
+        @param aKey
+            The request.
+        @param eRequestClass
+            The priority class in which to insert the request with highest
+            or lowest priority.
+        @param bInsertWithHighestPriority
+            When this flag is <TRUE/> the request is inserted with highest
+            priority in its class.  When <FALSE/> the request is inserted
+            with lowest priority.
+    */
+    void AddRequest(CacheKey aKey, RequestPriorityClass eRequestClass);
+
+    /** Remove the specified request from the queue.
+        @param aKey
+            It is OK when the specified request is not a member of the
+            queue.
+    */
+#if OSL_DEBUG_LEVEL >= 2
+    bool
+#else
+    void
+#endif
+    RemoveRequest(CacheKey aKey);
+
+    /** Change the priority class of the specified request.
+    */
+    void ChangeClass(CacheKey aKey, RequestPriorityClass eNewRequestClass);
+
+    /** Get the request with the highest priority int the highest priority class.
+    */
+    CacheKey GetFront();
+
+    // For debugging.
+    RequestPriorityClass GetFrontPriorityClass();
+
+    /** Really a synonym for RemoveRequest(GetFront());
+    */
+    void PopFront();
+
+    /** Returns <TRUE/> when there is no element in the queue.
+    */
+    bool IsEmpty();
+
+    /** Remove all requests from the queue.  This resets the minimum and
+        maximum priorities to their default values.
+    */
+    void Clear();
+
+    /** Return the mutex that guards the access to the priority queue.
+    */
+    ::osl::Mutex& GetMutex() { return maMutex; }
+
+    /** Ensure we don't hand out a page deleted before anyone got a
+        chance to process it
+    */
+    virtual void PageInDestruction(const SdrPage& rPage) override;
+
+private:
+    ::osl::Mutex maMutex;
+    class Container;
+    std::unique_ptr<Container> mpRequestQueue;
+    SharedCacheContext mpCacheContext;
+
+    /** A lower bound of the lowest priority of all elements in the queues.
+        The start value is 0.  It is assigned and then decreased every time
+        when an element is inserted or marked as the request with lowest
+        priority.
+    */
+    int mnMinimumPriority;
+    /** An upper bound of the highest priority of all elements in the queues.
+        The start value is 1.  It is assigned and then increased every time
+        when an element is inserted or marked as the request with highest
+        priority.
+    */
+    int mnMaximumPriority;
+};
+
+} // end of namespace ::sd::slidesorter::cache
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */