bccu#1893 - [PERFORMANCE] .uno:ViewRowColumnHeaders too slow

For very large spreadsheets, the boost json generator
(property_tree) is extremely slow and memory-inefficient.

There is little need for generic json generator, however,
since there are exactly two nodes (rows and columns)
and each is an array of size/text pairs.

The new logic uses a string with reserved capacity
to accomodate the output and generates it in one
step.

The speed improvement is orders of magnitude (hours to seconds)
for very large spreadsheets.

Change-Id: Ifaf316c270ed6e4b923ec44189a315f69e7e9b0e
Reviewed-on: https://gerrit.libreoffice.org/26480
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>

1 files changed, 22 insertions, 23 deletions

diff --git a/sc/source/ui/view/tabview.cxx b/sc/source/ui/view/tabview.cxx
index c7cf4cbbba02..1a6810733a30 100644
--- a/sc/source/ui/view/tabview.cxx
+++ b/sc/source/ui/view/tabview.cxx
@@ -2319,15 +2319,20 @@ OUString ScTabView::getRowColumnHeaders(const Rectangle& rRectangle)
     SCROW nEndRow = 0;
     pDoc->GetTiledRenderingArea(aViewData.GetTabNo(), nEndCol, nEndRow);
 
-    boost::property_tree::ptree aRows;
+    std::string os;
+    os.reserve(256 + (50 * nEndRow) + (50 * nEndCol));
+
+    os.append("{ \"commandName\": \".uno:ViewRowColumnHeaders\",\n");
+    os.append("\"rows\": [\n");
+
     long nTotal = 0;
     long nTotalPixels = 0;
     for (SCROW nRow = 0; nRow <= nEndRow; ++nRow)
     {
         // nSize will be 0 for hidden rows.
-        sal_uInt16 nSize = pDoc->GetRowHeight(nRow, aViewData.GetTabNo());
-        long nSizePixels = ScViewData::ToPixel(nSize, aViewData.GetPPTY());
-        OUString aText = pRowBar[SC_SPLIT_BOTTOM]->GetEntryText(nRow);
+        const sal_uInt16 nSize = pDoc->GetRowHeight(nRow, aViewData.GetTabNo());
+        const long nSizePixels = ScViewData::ToPixel(nSize, aViewData.GetPPTY());
+        const OUString aText = pRowBar[SC_SPLIT_BOTTOM]->GetEntryText(nRow);
 
         bool bSkip = false;
         if (!rRectangle.IsEmpty())
@@ -2340,23 +2345,23 @@ OUString ScTabView::getRowColumnHeaders(const Rectangle& rRectangle)
         }
         if (!bSkip)
         {
-            boost::property_tree::ptree aRow;
-            aRow.put("size", OString::number((nTotalPixels + nSizePixels) / aViewData.GetPPTY()).getStr());
-            aRow.put("text", aText.toUtf8().getStr());
-            aRows.push_back(std::make_pair("", aRow));
+            os.append("{ \"text\": \"").append(aText.toUtf8().getStr()).append("\", ");
+            os.append("\"size\": \"").append(OString::number((nTotalPixels + nSizePixels) / aViewData.GetPPTY()).getStr()).append("\" }, ");
         }
         nTotal += nSize;
         nTotalPixels += nSizePixels;
     }
 
-    boost::property_tree::ptree aCols;
+    os.erase(os.size() - 2);
+    os.append("],\n\"columns\":\n[");
+
     nTotal = 0;
     nTotalPixels = 0;
     for (SCCOL nCol = 0; nCol <= nEndCol; ++nCol)
     {
-        sal_uInt16 nSize = pDoc->GetColWidth(nCol, aViewData.GetTabNo());
-        long nSizePixels = ScViewData::ToPixel(nSize, aViewData.GetPPTX());
-        OUString aText = pColBar[SC_SPLIT_LEFT]->GetEntryText(nCol);
+        const sal_uInt16 nSize = pDoc->GetColWidth(nCol, aViewData.GetTabNo());
+        const long nSizePixels = ScViewData::ToPixel(nSize, aViewData.GetPPTX());
+        const OUString aText = pColBar[SC_SPLIT_LEFT]->GetEntryText(nCol);
 
         bool bSkip = false;
         if (!rRectangle.IsEmpty())
@@ -2369,22 +2374,16 @@ OUString ScTabView::getRowColumnHeaders(const Rectangle& rRectangle)
         }
         if (!bSkip)
         {
-            boost::property_tree::ptree aCol;
-            aCol.put("size", OString::number((nTotalPixels + nSizePixels) / aViewData.GetPPTX()).getStr());
-            aCol.put("text", aText.toUtf8().getStr());
-            aCols.push_back(std::make_pair("", aCol));
+            os.append("{ \"text\": \"").append(aText.toUtf8().getStr()).append("\", ");
+            os.append("\"size\": \"").append(OString::number((nTotalPixels + nSizePixels) / aViewData.GetPPTX()).getStr()).append("\" }, ");
         }
         nTotal += nSize;
         nTotalPixels += nSizePixels;
     }
 
-    boost::property_tree::ptree aTree;
-    aTree.put("commandName", ".uno:ViewRowColumnHeaders");
-    aTree.add_child("rows", aRows);
-    aTree.add_child("columns", aCols);
-    std::stringstream aStream;
-    boost::property_tree::write_json(aStream, aTree);
-    return OUString::fromUtf8(aStream.str().c_str());
+    os.erase(os.size() - 2);
+    os.append("]\n}");
+    return OUString::fromUtf8(os.c_str());
 }
 
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