Merge 129796 - Rewrite multithreaded filter job dispatching

Source/WebCore/platform/graphics/filters/FETurbulence.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005 Rob Buis <buis@kde.org>
  * Copyright (C) 2005 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Renata Hodovan <reni@inf.u-szeged.hu>
  * Copyright (C) 2011 Gabor Loki <loki@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 358 matching lines @@
     initPaint(paintingData);
 
     int optimalThreadNumber = (absolutePaintRect().width() * absolutePaintRect().height()) / s_minimalRectDimension;
     if (optimalThreadNumber > 1) {
         // Initialize parallel jobs
         WTF::ParallelJobs<FillRegionParameters> parallelJobs(&WebCore::FETurbulence::fillRegionWorker, optimalThreadNumber);
 
         // Fill the parameter array
         int i = parallelJobs.numberOfJobs();
         if (i > 1) {
+            // Split the job into "stepY"-sized jobs but there a few jobs that need to be slightly larger since
+            // stepY * jobs < total size. These extras are handled by the remainder "jobsWithExtra".
+            const int stepY = absolutePaintRect().height() / i;
+            const int jobsWithExtra = absolutePaintRect().height() % i;
+
             int startY = 0;
-            int stepY = absolutePaintRect().height() / i;
             for (; i > 0; --i) {
                 FillRegionParameters& params = parallelJobs.parameter(i-1);
                 params.filter = this;
                 params.pixelArray = pixelArray;
                 params.paintingData = &paintingData;
                 params.startY = startY;
-                if (i != 1) {
-                    params.endY = startY + stepY;
-                    startY = startY + stepY;
-                } else
-                    params.endY = absolutePaintRect().height();
+                startY += i < jobsWithExtra ? stepY + 1 : stepY;
+                params.endY = startY;
             }
 
             // Execute parallel jobs
             parallelJobs.execute();
             return;
         }
     }
 
     // Fallback to single threaded mode if there is no room for a new thread or the paint area is too small.
     fillRegion(pixelArray, paintingData, 0, absolutePaintRect().height());
@@ skipping 28 matching lines @@
        << "baseFrequency=\"" << baseFrequencyX() << ", " << baseFrequencyY() << "\" "
        << "seed=\"" << seed() << "\" "
        << "numOctaves=\"" << numOctaves() << "\" "
        << "stitchTiles=\"" << stitchTiles() << "\"]\n";
     return ts;
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(FILTERS)