code: public static int getRegionSize(Region<?, ?> region) {
  		Function function = new RegionSizeFunction();
  
  		FunctionService.registerFunction(function);
  
  		ResultCollector<?, ?> rc = FunctionService.onRegion(region)
  				.withCollector(new RegionSizeResultCollector())
  				.execute(function);
  
  		return (Integer) rc.getResult();
  	}
docs: Returns approximate number of entries in the region. As the function
  counts number of entries on different nodes in parallel, per node values
  may be captured on different moments. So the value may never be valid.
  
  @param region
  the region.
  @returns approximate number of objects in the given region.