Rework of background task set up for rendering the thumbnails of the pages in the background.

these are stored and swapped in and out of the page collection that is viewed as the user goes through
the flip view.  had some issues with respect to getting the background tasks shut down and mupdf
cleaned up when someone opens a new file. that is now all resolved.   This all simplified the code
significantly.

7 files changed, 160 insertions, 262 deletions

diff --git a/winrt/mupdf_cpp/MainPage.xaml b/winrt/mupdf_cpp/MainPage.xaml
index b9af3dd9..abaf7d36 100644
--- a/winrt/mupdf_cpp/MainPage.xaml
+++ b/winrt/mupdf_cpp/MainPage.xaml
@@ -14,7 +14,7 @@
                     <ColumnDefinition Width="*"/>
                     <ColumnDefinition Width="Auto"/>
                 </Grid.ColumnDefinitions>
-                <Slider x:Name="xaml_PageSlider" Minimum="0"  Maximum="10" ValueChanged="Slider_ValueChanged" LostFocus="Slider_Released" Grid.Column="0" Margin="10,0" VerticalAlignment="Center" />
+                <Slider x:Name="xaml_PageSlider" Minimum="0"  Maximum="10" ValueChanged="Slider_ValueChanged" Grid.Column="0" Margin="10,0" VerticalAlignment="Center" />
                 <Button x:Name="Find_File" Style="{StaticResource OpenFileAppBarButtonStyle}" Tag="OpenFile"  HorizontalAlignment="Right" Grid.Column="1" Click="Picker"/>
             </Grid>
         </AppBar>
diff --git a/winrt/mupdf_cpp/MainPage.xaml.cpp b/winrt/mupdf_cpp/MainPage.xaml.cpp
index 5cb2298f..ffd8bd52 100644
--- a/winrt/mupdf_cpp/MainPage.xaml.cpp
+++ b/winrt/mupdf_cpp/MainPage.xaml.cpp
@@ -7,6 +7,7 @@
 #include "MainPage.xaml.h"
 
 #define LOOK_AHEAD 1 /* A +/- count on the pages to pre-render */
+#define THUMB_PREADD 30
 #define MIN_SCALE 0.5
 #define MAX_SCALE 4
 #define MARGIN_BUFF 400
@@ -90,11 +91,9 @@ MainPage::MainPage()
     // Create the image brush
     mu_doc = nullptr;
     m_docPages = ref new Platform::Collections::Vector<DocumentPage^>();
+    m_thumbnails = ref new Platform::Collections::Vector<DocumentPage^>();
     CleanUp();
     RecordMainThread();
-    mu_doc = ref new mudocument(); 
-    if (mu_doc == nullptr)
-        throw ref new FailureException("Document allocation failed!");
 }
 
 /// <summary>
@@ -179,7 +178,7 @@ void mupdf_cpp::MainPage::Picker(Platform::Object^ sender, Windows::UI::Xaml::Ro
 	create_task(openPicker->PickSingleFileAsync()).then([this](StorageFile^ file) 
 	{ 
 		if (file) 
-		{ 		
+		{ 	
             this->OpenDocumentPrep(file);
 		} 
 		else 
@@ -215,6 +214,7 @@ void MainPage::UpdatePage(int page_num, InMemoryRandomAccessStream^ ras,
 
     /* We do not want flipview change notification to occur for ourselves */
     m_page_update = true;
+    //this->m_docPages->BindableSetAt(page_num, doc_page);
     this->m_docPages->SetAt(page_num, doc_page);
     m_page_update = false;
 
@@ -313,13 +313,6 @@ void MainPage::ReleasePages(int old_page, int new_page)
     }
 }
 
-void MainPage::InitThumbnails()
-{
-    this->m_thumbnails.raster = ref new Array<InMemoryRandomAccessStream^>(m_num_pages);
-    this->m_thumbnails.scale = ref new Array<double>(m_num_pages);
-    this->m_thumbnails.size = ref new Array<Point>(m_num_pages);
-}
-
 /* Return this page from a full res image to the thumb image or only set to thumb
    if it has not already been set */
 void MainPage::SetThumb(int page_num, bool replace)
@@ -327,10 +320,14 @@ void MainPage::SetThumb(int page_num, bool replace)
     /* See what is there now */
     auto doc = this->m_docPages->GetAt(page_num);
     if (doc->Content == THUMBNAIL) return;
+    if (doc->Content == FULL_RESOLUTION && replace == false) return;
 
-    if ((replace || doc->Content == DUMMY) && this->m_thumbnails.raster[page_num] != nullptr) 
-        UpdatePage(page_num, this->m_thumbnails.raster[page_num], 
-                   this->m_thumbnails.size[page_num], THUMBNAIL);
+    if (this->m_thumbnails->Size > page_num)
+    {
+        m_page_update = true;
+        this->m_docPages->SetAt(page_num, this->m_thumbnails->GetAt(page_num));
+        m_page_update = false;
+    }
 }
 
 /* Create white image for us to use as place holder in large document for flip
@@ -380,6 +377,15 @@ void mupdf_cpp::MainPage::CleanUp()
     /* Remove current pages in the flipviews */
     if (m_docPages != nullptr && m_docPages->Size > 0)
         m_docPages->Clear();
+    if (m_thumbnails != nullptr && m_thumbnails->Size > 0)
+        m_thumbnails->Clear();
+
+    if (this->mu_doc != nullptr) 
+        mu_doc->CleanUp();
+
+    mu_doc = ref new mudocument(); 
+    if (mu_doc == nullptr)
+        throw ref new FailureException("Document allocation failed!");
 
     this->m_curr_flipView = nullptr;
     m_currpage = -1;
@@ -396,8 +402,6 @@ void mupdf_cpp::MainPage::CleanUp()
     m_search_rect_count = 0;
     ResetSearch();
     m_ren_status = REN_AVAILABLE;
-    m_thumb_page_start = 0;
-    m_thumb_page_stop = 0;
     m_links_on = false;
 
     this->xaml_PageSlider->Minimum = m_slider_min;
@@ -410,86 +414,77 @@ void mupdf_cpp::MainPage::RenderThumbs()
 {
     spatial_info_t spatial_info = this->InitSpatial(1);
     int num_pages = this->m_num_pages;
-    int thumb_pages = this->m_thumb_page_start;
     cancellation_token_source cts;
     auto token = cts.get_token();
     m_ThumbCancel = cts;
 
     this->m_ren_status = REN_THUMBS;
-    thumbs_t thumbnails = m_thumbnails;
-    DWORD thread0_id = GetCurrentThreadId();
-
-    create_task([spatial_info, num_pages, thumb_pages, thumbnails, this, thread0_id]()-> int
+    Vector<DocumentPage^>^ thumbnails = m_thumbnails;
+    auto ui = task_continuation_context::use_current();
+    create_task([spatial_info, num_pages, thumbnails, this, ui, token]()-> int
     {
         spatial_info_t spatial_info_local = spatial_info;
         spatial_info_local.scale_factor = SCALE_THUMB;
 
-        InMemoryRandomAccessStream ^ras = ref new InMemoryRandomAccessStream();
-
-        for (int k = thumb_pages; k < num_pages; k++)
+        for (int k = 0; k < num_pages; k++)
         {
             Point ras_size = ComputePageSize(spatial_info_local, k);
             bool done = false;
             DWORD thread1_id = GetCurrentThreadId();
-            auto task = create_task(mu_doc->RenderPage(k, ras_size.X, ras_size.Y)).then([this, k, ras_size, thumbnails, &done, thread1_id, thread0_id] (InMemoryRandomAccessStream^ ras)
-            {
-                DWORD thread2_id = GetCurrentThreadId();
-                thumbnails.raster[k] = ras;
-                thumbnails.scale[k] = SCALE_THUMB;
-                thumbnails.size[k] = ras_size;
-                done = true;
-            }, task_continuation_context::use_current());  
+            auto task2 = create_task(mu_doc->RenderPage(k, ras_size.X, ras_size.Y));
 
-
-            try
-            {
-                task.get();  // get exception
-            }
-            catch (Exception^ exception)
-            {
-            }
-
-             /* Don't start new thumb until this one is finished, lest we launch a
-               thousand thumbnail renderings */
-            while (!done) 
+            task2.then([this, k, thumbnails, ras_size](InMemoryRandomAccessStream^ ras)
             {
-            }
+                assert(IsMainThread());
+                WriteableBitmap ^bmp = ref new WriteableBitmap(ras_size.X, ras_size.Y);
+                bmp->SetSource(ras);
+                DocumentPage^ doc_page = ref new DocumentPage();
+                doc_page->Image = bmp;
+                doc_page->Height = ras_size.Y / SCALE_THUMB;
+                doc_page->Width = ras_size.X / SCALE_THUMB;
+                doc_page->Content = THUMBNAIL;
+                if (this->m_ren_status == REN_THUMBS) {
+                    m_thumbnails->Append(doc_page);
+                    /* Flipview object get overwhelmed unless I do this */
+                    if ((k < THUMB_PREADD))
+                        SetThumb(k, false);
+                }
+            }, ui).then([this] (task<void> t)
+                {
+                try
+                {
+                    t.get();
+                }
+                catch(Platform::InvalidArgumentException^ e)
+                {
+                    //TODO handle error.
+                }
+            }, token); //end task chain */
 
             /* If cancelled then save the last one as the continuation will not
                have occured.  */
             if (is_task_cancellation_requested()) 
             {
-                thumbnails.raster[k] = ras;
-                thumbnails.scale[k] = SCALE_THUMB;
-                thumbnails.size[k] = ras_size;
-                this->m_thumb_page_stop = k + 1;
-                
                 cancel_current_task();
             }
         }
         return num_pages; /* all done with thumbnails! */
     }, token).then([this](task<int> the_task) 
     {
-        int new_end;
+        /* Finish adding them, but not if we were cancelled. */
+        bool is_cancelled = false;
         try
         {
-           new_end = the_task.get();
+           the_task.get();
         } 
         catch (const task_canceled& e)
         {
-            new_end = this->m_thumb_page_stop;
+            is_cancelled = true;
         }
-
-        int old_end = this->m_thumb_page_start;
-
-        /* Now go ahead and create the proper stuctures */
-        this->m_ren_status = REN_UPDATE_THUMB_CANVAS;
-        this->m_thumb_page_start = new_end;
-
-        for (int k = old_end; k < new_end; k++)
+        if (!is_cancelled)
         {
-            assert(IsMainThread());
-            SetThumb(k, false);
+            for (int k = THUMB_PREADD; k < m_num_pages; k++)
+                SetThumb(k, false);
         }
         this->m_ren_status = REN_AVAILABLE;
     }, task_continuation_context::use_current());
@@ -500,6 +495,11 @@ void mupdf_cpp::MainPage::OpenDocumentPrep(StorageFile^ file)
     if (this->m_num_pages != -1) 
     {
         m_init_done = false;
+
+        /* Set the index to the start of the document */
+        this->xaml_vert_flipView->SelectedIndex = 0;
+        this->xaml_horiz_flipView->SelectedIndex = 0;
+
         /* If the thumbnail thread is running then we need to end that first */
         RenderingStatus_t *ren_status = &m_ren_status;
         cancellation_token_source *ThumbCancel = &m_ThumbCancel;
@@ -572,7 +572,6 @@ void mupdf_cpp::MainPage::OpenDocument(StorageFile^ file)
 
         /* Do the first few pages, then start the thumbs */
         spatial_info_t spatial_info = InitSpatial(1);
-
         for (int k = 0; k < LOOK_AHEAD + 2; k++) 
         {
             if (m_num_pages > k ) 
@@ -590,7 +589,6 @@ void mupdf_cpp::MainPage::OpenDocument(StorageFile^ file)
                 }, task_continuation_context::use_current());
             }
         }
-
         /* Update the slider settings, if more than one page */
         if (m_num_pages > 1) 
         {
@@ -608,89 +606,58 @@ void mupdf_cpp::MainPage::OpenDocument(StorageFile^ file)
         this->m_init_done = true;
     }).then([this]
     {
-        InitThumbnails();
         this->RenderThumbs();
     }, task_continuation_context::use_current());
 }
 
-task<int> mupdf_cpp::MainPage::RenderRange(int curr_page)
+
+void mupdf_cpp::MainPage::RenderRange(int curr_page)
 {
     /* Render +/- the look ahead from where we are if blank page is present */
     spatial_info_t spatial_info = InitSpatial(1);
 
-    RenderingStatus_t *ren_status = &m_ren_status;
-    cancellation_token_source *ThumbCancel = &m_ThumbCancel;
-
-    /* Create a task to wait until the renderer is available */
-    auto t = create_task([ren_status, ThumbCancel]()
-    {
-        if (*ren_status == REN_THUMBS)
-            ThumbCancel->cancel();
-        while (*ren_status != REN_AVAILABLE) {
-        }
-    });
-        
-    return t.then([this, curr_page, spatial_info]()
+    assert(IsMainThread());
+    for (int k = curr_page - LOOK_AHEAD; k <= curr_page + LOOK_AHEAD; k++) 
     {
-        assert(IsMainThread());
-        int val = 0;
-        /* This runs on the main ui thread */
-        for (int k = curr_page - LOOK_AHEAD; k <= curr_page + LOOK_AHEAD; k++) 
+        if (k >= 0 && k < m_num_pages) 
         {
-            if (k >= 0 && k < m_num_pages) 
+            /* Check if page is already rendered */
+            auto doc = this->m_docPages->GetAt(k);
+            if (doc->Content != FULL_RESOLUTION) 
             {
-                /* Check if page is already rendered */
-                auto doc = this->m_docPages->GetAt(k);
-                if (doc->Content != FULL_RESOLUTION) 
+                Point ras_size = ComputePageSize(spatial_info, k);
+                auto render_task = 
+                    create_task(mu_doc->RenderPage(k, ras_size.X, ras_size.Y));
+
+                render_task.then([this, k, ras_size] (InMemoryRandomAccessStream^ ras)
                 {
-                    Point ras_size = ComputePageSize(spatial_info, k);
-                    auto render_task = 
-                        create_task(mu_doc->RenderPage(k, ras_size.X, ras_size.Y));
-
-                    render_task.then([this, k, ras_size] (InMemoryRandomAccessStream^ ras)
-                    {
-                        /* Set up the image brush when rendering is completed, must be on
-                           UI thread */
-                        UpdatePage(k, ras, ras_size, FULL_RESOLUTION);
-                        this->m_ren_status = REN_AVAILABLE;                    
-                    }, task_continuation_context::use_current());
-                }
-            }
-        } 
-        Canvas^ link_canvas = (Canvas^) (this->FindName("linkCanvas"));
-        if (link_canvas != nullptr)
-        {
-            Canvas^ Parent_Canvas = (Canvas^) link_canvas->Parent;
-            if (Parent_Canvas != nullptr)
-            {
-                Parent_Canvas->Children->RemoveAtEnd();
-                delete link_canvas;
+                    /* Set up the image brush when rendering is completed, must be on
+                        UI thread */
+                    UpdatePage(k, ras, ras_size, FULL_RESOLUTION);
+                }, task_continuation_context::use_current());
             }
         }
-        m_currpage = curr_page;
-        if (this->m_links_on) 
+    } 
+    Canvas^ link_canvas = (Canvas^) (this->FindName("linkCanvas"));
+    if (link_canvas != nullptr)
+    {
+        Canvas^ Parent_Canvas = (Canvas^) link_canvas->Parent;
+        if (Parent_Canvas != nullptr)
         {
-            AddLinkCanvas();
+            Parent_Canvas->Children->RemoveAtEnd();
+            delete link_canvas;
         }
-        /* Check if thumb rendering is done.  If not then restart */
-        if (this->m_num_pages != this->m_thumb_page_start)
-            this->RenderThumbs();
-        return val;
-    }, task_continuation_context::use_current());
-}
-
-void mupdf_cpp::MainPage::Slider_Released(Platform::Object^ sender, Windows::UI::Xaml::Controls::Primitives::RangeBaseValueChangedEventArgs^ e)
-{
-    /* Check if thumb rendering is done.  If not then restart */
-    if (this->m_num_pages != this->m_thumb_page_start)
-        this->RenderThumbs();
+    }
+    m_currpage = curr_page;
+    if (this->m_links_on) 
+    {
+        AddLinkCanvas();
+    }
 }
 
 void mupdf_cpp::MainPage::Slider_ValueChanged(Platform::Object^ sender, Windows::UI::Xaml::Controls::Primitives::RangeBaseValueChangedEventArgs^ e)
 {
     int newValue = (int) this->xaml_PageSlider->Value - 1;  /* zero based */
-    RenderingStatus_t *ren_status = &m_ren_status;
-    cancellation_token_source *ThumbCancel = &m_ThumbCancel;
 
     if (m_update_flip)
     {
@@ -702,28 +669,19 @@ void mupdf_cpp::MainPage::Slider_ValueChanged(Platform::Object^ sender, Windows:
         auto doc = this->m_docPages->GetAt(newValue);
         if (doc->Content != FULL_RESOLUTION) 
         {
-            create_task([ren_status, ThumbCancel]()
-            {
-                if (*ren_status == REN_THUMBS)
-                    ThumbCancel->cancel();
-                while (*ren_status != REN_AVAILABLE) {
-                }
-            }).then([this, newValue]() 
-            {
-                spatial_info_t spatial_info = InitSpatial(1);
-                Point ras_size = ComputePageSize(spatial_info, newValue);
-                auto render_task = 
-                    create_task(mu_doc->RenderPage(newValue, ras_size.X, ras_size.Y));
+            spatial_info_t spatial_info = InitSpatial(1);
+            Point ras_size = ComputePageSize(spatial_info, newValue);
+            auto render_task = 
+                create_task(mu_doc->RenderPage(newValue, ras_size.X, ras_size.Y));
 
-                render_task.then([this, newValue, ras_size] (InMemoryRandomAccessStream^ ras)
-                {
-                    UpdatePage(newValue, ras, ras_size, FULL_RESOLUTION);
-                    this->m_ren_status = REN_AVAILABLE;  
-                    this->m_currpage = newValue;
-                    m_sliderchange = true;
-                    this->m_curr_flipView->SelectedIndex = newValue;
-                    ResetSearch(); 
-                }, task_continuation_context::use_current());
+            render_task.then([this, newValue, ras_size] (InMemoryRandomAccessStream^ ras)
+            {
+                UpdatePage(newValue, ras, ras_size, FULL_RESOLUTION);
+                this->m_ren_status = REN_AVAILABLE;  
+                this->m_currpage = newValue;
+                m_sliderchange = true;
+                this->m_curr_flipView->SelectedIndex = newValue;
+                ResetSearch(); 
             }, task_continuation_context::use_current());
         }
     }
@@ -758,11 +716,8 @@ void mupdf_cpp::MainPage::FlipView_SelectionChanged(Object^ sender, SelectionCha
             }
             /* Get the current page */
             int curr_page = this->m_currpage;
-            task<int> task = this->RenderRange(pos);
-            task.then([this, curr_page, pos](int val)
-            {
-                this->ReleasePages(curr_page, pos);
-            }, task_continuation_context::use_current());
+            this->RenderRange(pos);
+            this->ReleasePages(curr_page, pos);
         }
     }
 }
@@ -898,21 +853,9 @@ void mupdf_cpp::MainPage::SearchNext(Platform::Object^ sender, Windows::UI::Xaml
     StackPanel^ leftPanel = (StackPanel^) this->TopAppBar->FindName("LeftPanel");
     TextBox^ findBox = (TextBox^) leftPanel->FindName("findBox");
     String^ textToFind = findBox->Text;
-    RenderingStatus_t *ren_status = &m_ren_status;
-    cancellation_token_source *ThumbCancel = &m_ThumbCancel;
 
-    /* Create a task to wait until the renderer is available */
-    create_task([ren_status, ThumbCancel]()
-    {
-        if (*ren_status == REN_THUMBS)
-            ThumbCancel->cancel();
-        while (*ren_status != REN_AVAILABLE) {
-            }
-    }).then([this, textToFind]() 
-    {
-        if (this->m_search_active == false)
-            SearchInDirection(1, textToFind);
-    }, task_continuation_context::use_current());
+    if (this->m_search_active == false)
+        SearchInDirection(1, textToFind);
 }
 
 void mupdf_cpp::MainPage::SearchPrev(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
@@ -920,21 +863,9 @@ void mupdf_cpp::MainPage::SearchPrev(Platform::Object^ sender, Windows::UI::Xaml
     StackPanel^ leftPanel = (StackPanel^) this->TopAppBar->FindName("LeftPanel");
     TextBox^ findBox = (TextBox^) leftPanel->FindName("findBox");
     String^ textToFind = findBox->Text;
-    RenderingStatus_t *ren_status = &m_ren_status;
-    cancellation_token_source *ThumbCancel = &m_ThumbCancel;
 
-    /* Create a task to wait until the renderer is available */
-    create_task([ren_status, ThumbCancel]()
-    {
-        if (*ren_status == REN_THUMBS)
-            ThumbCancel->cancel();
-        while (*ren_status != REN_AVAILABLE) {
-        }
-    }).then([this, textToFind]() 
-    {
-        if (this->m_search_active == false)
-            SearchInDirection(-1, textToFind);
-    }, task_continuation_context::use_current());
+    if (this->m_search_active == false)
+        SearchInDirection(-1, textToFind);
 }
 
 void mupdf_cpp::MainPage::CancelSearch(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
@@ -1148,24 +1079,9 @@ void mupdf_cpp::MainPage::ClearLinksCanvas()
 void mupdf_cpp::MainPage::Linker(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
 {
     m_links_on = !m_links_on;
-    RenderingStatus_t *ren_status = &m_ren_status;
-    cancellation_token_source *ThumbCancel = &m_ThumbCancel;
         
     if (m_links_on)
-    {
-       auto t = create_task([ren_status, ThumbCancel]()
-        {
-            if (*ren_status == REN_THUMBS)
-                ThumbCancel->cancel();
-            while (*ren_status != REN_AVAILABLE) {
-            }
-        });
-        
-        t.then([this]()
-        {
-            AddLinkCanvas();
-        }, task_continuation_context::use_current());
-    }
+        AddLinkCanvas();
     else
         ClearLinksCanvas();
 }
@@ -1345,37 +1261,20 @@ void mupdf_cpp::MainPage::ContentDisplay(Platform::Object^ sender, Windows::UI::
     {
         if (xaml_ListView->Items->Size == 0)
         {
-            /* Make sure we are good to go */
-            RenderingStatus_t *ren_status = &m_ren_status;
-            cancellation_token_source *ThumbCancel = &m_ThumbCancel;
-
-            /* Create a task to wait until the renderer is available */
-            auto t = create_task([ren_status, ThumbCancel]()
+            int size_content = mu_doc->ComputeContents();
+            /* Bring up the content now */
+            for (int k = 0; k < size_content; k++)
             {
-                if (*ren_status == REN_THUMBS)
-                    ThumbCancel->cancel();
-                while (*ren_status != REN_AVAILABLE) {
-                }
-            }).then([this]()
+                ContentItem^ item = mu_doc->GetContent(k);
+                this->xaml_ListView->Items->Append(item);
+            }
+            if (size_content > 0)
             {
-                int size_content = mu_doc->ComputeContents();
-                /* Bring up the content now */
-                for (int k = 0; k < size_content; k++)
-                {
-                    ContentItem^ item = mu_doc->GetContent(k);
-                    this->xaml_ListView->Items->Append(item);
-                }
-                if (size_content > 0)
-                {
-                    this->xaml_ListView->Opacity = 1.0;
-                    this->xaml_ListView->IsEnabled = true;
-                    this->m_curr_flipView->Opacity = 0.0;
-                    this->m_curr_flipView->IsEnabled = false;
-                }
-                /* Check if thumb rendering is done.  If not then restart */
-                if (this->m_num_pages != this->m_thumb_page_start)
-                    this->RenderThumbs();
-            }, task_continuation_context::use_current());
+                this->xaml_ListView->Opacity = 1.0;
+                this->xaml_ListView->IsEnabled = true;
+                this->m_curr_flipView->Opacity = 0.0;
+                this->m_curr_flipView->IsEnabled = false;
+            }
         }  
         else 
         {
@@ -1421,27 +1320,13 @@ void mupdf_cpp::MainPage::Reflower(Platform::Object^ sender, Windows::UI::Xaml::
     } 
     else if (this->m_curr_flipView->IsEnabled)
     {
-        /* Only go from flip view to reflow */
-        RenderingStatus_t *ren_status = &m_ren_status;
-        cancellation_token_source *ThumbCancel = &m_ThumbCancel;
-        /* Create a task to wait until the renderer is available */
-        auto t = create_task([ren_status, ThumbCancel]()
-        {
-            if (*ren_status == REN_THUMBS)
-                ThumbCancel->cancel();
-            while (*ren_status != REN_AVAILABLE) {
-            }
-        }).then([this]()
-        {
-            String^ html_string = mu_doc->ComputeHTML(this->m_currpage);
-            xaml_WebView->Visibility = Windows::UI::Xaml::Visibility::Visible;
-            this->xaml_MainGrid->Opacity = 0.0;
-            this->m_curr_flipView->IsEnabled = false;
-            this->xaml_WebView->NavigateToString(html_string);
-            /* Check if thumb rendering is done.  If not then restart */
-            if (this->m_num_pages != this->m_thumb_page_start)
-                this->RenderThumbs();
-        }, task_continuation_context::use_current());
+        String^ html_string = mu_doc->ComputeHTML(this->m_currpage);
+        xaml_WebView->Visibility = Windows::UI::Xaml::Visibility::Visible;
+        this->xaml_MainGrid->Opacity = 0.0;
+        this->m_curr_flipView->IsEnabled = false;
+        this->xaml_WebView->NavigateToString(html_string);
+        this->xaml_WebView->Height = this->ActualHeight - 2 * this->BottomAppBar->ActualHeight;
+        /* Check if thumb rendering is done.  If not then restart */
     }
 }
 
diff --git a/winrt/mupdf_cpp/MainPage.xaml.h b/winrt/mupdf_cpp/MainPage.xaml.h
index e858ebe8..0b8f48fe 100644
--- a/winrt/mupdf_cpp/MainPage.xaml.h
+++ b/winrt/mupdf_cpp/MainPage.xaml.h
@@ -56,13 +56,6 @@ typedef struct spatial_info_s
     double scale_factor;
 } spatial_info_t;
 
-typedef struct thumbs_s
-{
-    Array<InMemoryRandomAccessStream^>^ raster;  
-    Array<double>^ scale;
-    Array<Point>^  size;
-} thumbs_t;
-
 namespace mupdf_cpp
 {
 	/// <summary>
@@ -79,6 +72,7 @@ namespace mupdf_cpp
     /* added */
     private:
         Vector<DocumentPage^>^ m_docPages;
+        Vector<DocumentPage^>^ m_thumbnails;
         mudocument^ mu_doc; 
         bool m_file_open;
         int  m_currpage;
@@ -91,17 +85,13 @@ namespace mupdf_cpp
         bool m_links_on;
         int m_search_rect_count;
         cancellation_token_source m_searchcts;
-        cancellation_token_source m_thumbcts;
         bool m_page_update;
         long long m_memory_use;
         WriteableBitmap ^m_BlankBmp;
         SolidColorBrush^ m_textcolor_brush; 
         SolidColorBrush^ m_linkcolor_brush; 
         FlipView^ m_curr_flipView;
-        thumbs_t m_thumbnails;
         RenderingStatus_t m_ren_status;
-        int m_thumb_page_start;
-        int m_thumb_page_stop;
         cancellation_token_source m_ThumbCancel;
         bool m_zoom_mode;  // remove
         bool m_insearch;  /* Used for UI display */
@@ -113,7 +103,7 @@ namespace mupdf_cpp
         void Searcher(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e);
         void OpenDocumentPrep(StorageFile^ file);
         void OpenDocument(StorageFile^ file);
-        task<int> RenderRange(int curr_page);
+        void RenderRange(int curr_page);
         void CleanUp();
         void UpdatePage(int page_num, InMemoryRandomAccessStream^ ras, Point ras_size, Page_Content_t content_type);
         void CreateBlank(int width, int height);
@@ -136,7 +126,6 @@ namespace mupdf_cpp
         void Canvas_ManipulationCompleted(Platform::Object^ sender, Windows::UI::Xaml::Input::ManipulationCompletedRoutedEventArgs^ e);
         void AddThumbNail(int page_num, FlipView^ flip_view);
         spatial_info_t InitSpatial(double scale);
-        void InitThumbnails();
         void RenderThumbs();
         void SetThumb(int page_num, bool replace);
         void ReleasePages(int old_page, int new_page);
diff --git a/winrt/mupdfwinrt/muctx.cpp b/winrt/mupdfwinrt/muctx.cpp
index a26ddffa..128b35e0 100644
--- a/winrt/mupdfwinrt/muctx.cpp
+++ b/winrt/mupdfwinrt/muctx.cpp
@@ -88,6 +88,23 @@ static void unlock_mutex(void *user, int lock)
 	LeaveCriticalSection((LPCRITICAL_SECTION)user);
 }
 
+void muctx::CleanUp(void)
+{
+    free(this->mu_cookie);
+    if (mu_outline != NULL)
+		fz_free_outline(mu_ctx, mu_outline);
+    if (mu_doc != NULL)
+		fz_close_document(mu_doc);
+    if (mu_ctx != NULL)
+		fz_free_context(mu_ctx);
+
+    this->mu_cookie = NULL;
+    this->mu_ctx = NULL;
+    this->mu_doc = NULL;
+    this->mu_outline = NULL;
+    this->mu_stream = NULL;
+}
+
 /* Set up the context, mutex and cookie */
 HRESULT muctx::InitializeContext()
 {
diff --git a/winrt/mupdfwinrt/muctx.h b/winrt/mupdfwinrt/muctx.h
index 112d6cb5..c738593f 100644
--- a/winrt/mupdfwinrt/muctx.h
+++ b/winrt/mupdfwinrt/muctx.h
@@ -84,6 +84,7 @@ private:
 public:
     muctx(void);
     ~muctx(void);
+    void CleanUp(void);
     HRESULT InitializeStream(IRandomAccessStream^ readStream, char *ext);
     int GetPageCount();   
     HRESULT InitializeContext();
diff --git a/winrt/mupdfwinrt/mudocument.cpp b/winrt/mupdfwinrt/mudocument.cpp
index c9b4e33d..fef09612 100644
--- a/winrt/mupdfwinrt/mudocument.cpp
+++ b/winrt/mupdfwinrt/mudocument.cpp
@@ -17,6 +17,11 @@ mudocument::mudocument()
     this->links = nullptr;
 }
 
+void mudocument::CleanUp()
+{
+    this->mu_object.CleanUp();
+}
+
 int mudocument::GetNumPages()
 {
     return this->mu_object.GetPageCount();
@@ -97,7 +102,7 @@ static void Prepare_bmp(int width, int height, DataWriter ^dw)
 Windows::Foundation::IAsyncOperation<InMemoryRandomAccessStream^>^ 
     mudocument::RenderPage(int page_num, int width, int height)
 {
-    return create_async([this, width, height, page_num]() -> InMemoryRandomAccessStream^
+    return create_async([this, width, height, page_num](cancellation_token ct) -> InMemoryRandomAccessStream^
     {
         /* Allocate space for bmp */
         Array<unsigned char>^ bmp_data = ref new Array<unsigned char>(height * 4 * width);
diff --git a/winrt/mupdfwinrt/mudocument.h b/winrt/mupdfwinrt/mudocument.h
index 2c96888d..48b8c301 100644
--- a/winrt/mupdfwinrt/mudocument.h
+++ b/winrt/mupdfwinrt/mudocument.h
@@ -28,6 +28,7 @@ namespace mupdfwinrt
             Platform::Collections::Vector<ContentItem^>^ contents;
         public:
             mudocument();
+            void CleanUp();
             Windows::Foundation::IAsyncAction^ OpenFile(StorageFile^ file);
             int GetNumPages(void);
             Point GetPageSize(int page_num);