I've edited some lines: 
* I changed tileSize from 512 to 256. 
* In worker_base_tiles i removed zoom_limits.put(gdal2tiles.tminz) and tmaxz, because in main at 2601 line queue became empty and thrown me an error. 
* I've changed tminz\tmaxz = gdal2tiles.tminz\tmaxz. i didn't find reason to use put method, because in main you initiate GDAL2Tiles class which has tminz and tmaxz parameters.