tkProgressBar without progress in foreach %dopar%

I have a list (temp.data) with many raster data and some computations are in
parallel. n is the number of raster data and target is the mask. I'd like to
use a progress bar. It is created but while the loop is running the progress
is not showed. The loop ends and the progress bar is closed. I've tried to
use the functions pdCreate/pdStep in raster package, but without success...

Someone have any idea...

     mypb <- tkProgressBar(title = "R progress bar", label = "",  min = 0,
max = n, initial = 0, width = 300)



     #creating a computing cluster

     cl <- makeCluster(detectCores(),type='SOCK')

     registerDoParallel(cl, cores = detectCores())



     foreach(i=1:n,.packages=c('tcltk','rgdal','raster')) %dopar% {

       Sys.sleep(.1)

       setTkProgressBar(mypb, i, title = "R progress bar", label = NULL)




temp.data[[i]]<-mask(temp.data[[i]],target,maskvalue=as.numeric(class.outsid
e))


writeRaster(temp.data[[i]],filename=files.list[i],format='GTiff',overwrite=T
)

     }



     stopCluster(cl)

     close(mypb)





Thanks

Alexsandro