From Lionel Lagarde, "Support for paging and shared PBO"

"The attached file contains:
- a per-context read counter in GLBufferObject::BufferEntry
- a global client counter in BufferData
- the glue between Texture* and Image client counter
"

src/osg/Texture.cpp

@@ -2089,8 +2089,12 @@ void Texture::applyTexImage2D_load(State& state, GLenum target, const Image* ima
         const BufferObject* bo = image->getBufferObject();
         if (bo->getCopyDataAndReleaseGLBufferObject())
         {
-            //OSG_NOTICE<<"Release PBO"<<std::endl;
-            bo->releaseGLObjects(&state);
+            pbo->setBufferDataHasBeenRead(image);
+            if (pbo->hasAllBufferDataBeenRead())
+            {
+                //OSG_NOTICE<<"Release PBO"<<std::endl;
+                bo->releaseGLObjects(&state);
+            }
         }
     }