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diff --git a/sd/source/ui/sidebar/MasterPageContainerQueue.hxx b/sd/source/ui/sidebar/MasterPageContainerQueue.hxx
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+++ b/sd/source/ui/sidebar/MasterPageContainerQueue.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 "MasterPageContainer.hxx"
+#include "MasterPageDescriptor.hxx"
+
+#include <vcl/timer.hxx>
+
+#include <memory>
+
+namespace sd::sidebar {
+
+/** The queue stores and processes all requests from a MasterPageContainer
+    for the creation of previews.
+    The order of request processing and its timing is controlled by a
+    heuristic that uses values given with each request and which is
+    controlled by various parameters that are described below.
+*/
+class MasterPageContainerQueue final
+{
+public:
+    class ContainerAdapter {
+    public:
+        virtual bool UpdateDescriptor (
+            const SharedMasterPageDescriptor& rpDescriptor,
+            bool bForcePageObject,
+            bool bForcePreview,
+            bool bSendEvents) = 0;
+
+    protected:
+        ~ContainerAdapter() {}
+    };
+
+    static MasterPageContainerQueue* Create (
+        const std::weak_ptr<ContainerAdapter>& rpContainer);
+    ~MasterPageContainerQueue();
+
+    /** This method is typically called for entries in the container for
+        which GetPreviewState() returns OS_CREATABLE.  The creation of the
+        preview is then scheduled to be executed asynchronously at a later
+        point in time.  When the preview is available the change listeners
+        will be notified.
+    */
+    bool RequestPreview (const SharedMasterPageDescriptor& rDescriptor);
+
+    /** Return <TRUE/> when there is a request currently in the queue for
+        the given token.
+    */
+    bool HasRequest (MasterPageContainer::Token aToken) const;
+
+    /** Return <TRUE/> when there is at least one request in the queue.
+    */
+    bool IsEmpty() const;
+
+    /** After this call the queue does not wait anymore for requests with
+        higher priority when only a small number of requests with lower
+        priority are present.  This method should be called when all
+        templates are inserted into the MasterPageContainer.
+    */
+    void ProcessAllRequests();
+
+private:
+    std::weak_ptr<ContainerAdapter> mpWeakContainer;
+    class PreviewCreationRequest;
+    class RequestQueue;
+    std::unique_ptr<RequestQueue> mpRequestQueue;
+    Timer maDelayedPreviewCreationTimer;
+    sal_uInt32 mnRequestsServedCount;
+
+    // There are a couple of values that define various aspects of the
+    // heuristic that defines the order and timing in which requests for
+    // preview creation are processed.
+
+    /** The time to wait (in milliseconds) between the creation of previews.
+    */
+    static const sal_Int32 snDelayedCreationTimeout;
+
+    /** The time to wait when the system is not idle.
+    */
+    static const sal_Int32 snDelayedCreationTimeoutWhenNotIdle;
+
+    /** Requests for previews of master pages in a document have their
+        priority increased by this value.
+    */
+    static const sal_Int32 snMasterPagePriorityBoost;
+
+    /** When only requests which a priority lower than this threshold exist
+        and not many requests have been made yet then wait with processing
+        them until more requests are present.
+    */
+    static const sal_Int32 snWaitForMoreRequestsPriorityThreshold;
+
+    /** When only requests which a priority lower than a threshold exist
+        and not more requests than this number have been made or already
+        processed then wait with processing them until more requests are
+        present.
+    */
+    static sal_uInt32 snWaitForMoreRequestsCount;
+
+    explicit MasterPageContainerQueue (const std::weak_ptr<ContainerAdapter>& rpContainer);
+    void LateInit();
+
+    /** Calculate the priority that defines the order in which requests
+        are processed.
+    */
+    static sal_Int32 CalculatePriority (const SharedMasterPageDescriptor& rDescriptor);
+
+    DECL_LINK(DelayedPreviewCreation, Timer *, void);
+};
+
+} // end of namespace sd::sidebar
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */