Merge 129796 - Rewrite multithreaded filter job dispatching

Source/WebCore/platform/graphics/filters/FEMorphology.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) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 155 matching lines @@
     param->filter->platformApplyGeneric(param->paintingData, param->startY, param->endY);
 }
 
 void FEMorphology::platformApply(PaintingData* paintingData)
 {
     int optimalThreadNumber = (paintingData->width * paintingData->height) / s_minimalArea;
     if (optimalThreadNumber > 1) {
         ParallelJobs<PlatformApplyParameters> parallelJobs(&WebCore::FEMorphology::platformApplyWorker, optimalThreadNumber);
         int numOfThreads = parallelJobs.numberOfJobs();
         if (numOfThreads > 1) {
-            const int deltaY = 1 + paintingData->height / numOfThreads;
+            // Split the job into "jobSize"-sized jobs but there a few jobs that need to be slightly larger since
+            // jobSize * jobs < total size. These extras are handled by the remainder "jobsWithExtra".
+            const int jobSize = paintingData->height / numOfThreads;
+            const int jobsWithExtra = paintingData->height % numOfThreads;
             int currentY = 0;
             for (int job = numOfThreads - 1; job >= 0; --job) {
                 PlatformApplyParameters& param = parallelJobs.parameter(job);
                 param.filter = this;
                 param.startY = currentY;
-                currentY += deltaY;
-                param.endY = job ? currentY : paintingData->height;
+                currentY += job < jobsWithExtra ? jobSize + 1 : jobSize;
+                param.endY = currentY;
                 param.paintingData = paintingData;
             }
             parallelJobs.execute();
             return;
         }
         // Fallback to single thread model
     }
 
     platformApplyGeneric(paintingData, 0, paintingData->height);
 }
@@ skipping 58 matching lines @@
     FilterEffect::externalRepresentation(ts);
     ts << " operator=\"" << morphologyOperator() << "\" "
        << "radius=\"" << radiusX() << ", " << radiusY() << "\"]\n";
     inputEffect(0)->externalRepresentation(ts, indent + 1);
     return ts;
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(FILTERS)