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  Better memory mapped buffers  (Read 1831 times)
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Offline Gorgorath

Junior Devvie




Java games rock!


« Posted 2007-01-19 10:01:14 »

Because of the way java/jni treats memory mapped files i had to come with a better way of rendering/stream my pointclouds efficiently. The java memory mapped  buffers are not cleared. Even not when setting the buffers to null. the only way to free memory was to explicitly call System.gc() which is a severe penalty. so i've written a small c++ program that will let the user create a file map then map a portion of this file and finally return a bytebuffer.

this is my innermost streaming loop
int handle = DTStreamFiles.createFile(
                  sceneGraphDir + node.getDataFile(),
                  DTStreamFiles.GENERIC_READ,
                  DTStreamFiles.FILE_SHARE_READ,
                  DTStreamFiles.OPEN_EXIST,
                  DTStreamFiles.FILE_ATTRIBUTE_NORMAL);
            
            
            if (handle != -1)
            {
               int byteLength = node.wantedPoints*MathConstants.VERTEX_SIZE;
               int mapHandle = DTStreamFiles.createFileMapping(handle,
                     DTStreamFiles.PAGE_READONLY, 0, 0);
               
               if (mapHandle != 0)
               {
   
                  int valPointer = DTStreamFiles.mapViewOfFile(
                        mapHandle,
                        DTStreamFiles.FILE_MAP_READ,
                        0,
                        0,
                        byteLength);
   
                  if (valPointer != 0)
                  {
                     ByteBuffer buf = DTStreamFiles.getDirectBuffer(valPointer, byteLength);
//DO WHAT U WANT WITH THIS BUFFER it isn't valid anymore after unmapping the file

   //unmap view of file
                  DTStreamFiles.unMapViewOfFile(valPointer);
                  //close mapping handle
                  DTStreamFiles.closeHandle(mapHandle);   
               }
               //close handle
               DTStreamFiles.closeHandle(handle);


it can be found here :
http://home.hccnet.nl/pj.holverda/better_file_mapping.rar


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