Thanks. Now I really understand. But there is another question if I may. Suppose that instead of @command array, I have a list (array) of files, @files_list. In a loop, I open a file from the list, read through it, set some counters, close the file, then get the 2nd file from the list, do the same thing and so on. The processing of each file takes time, and I have a lot of files. So I use the parallel fork to start four children ($manager->start and next) where each child would process a file from a list. Between’ $manager->start and next’ and $manager->finish, I set some counters, say how many files could not be opened. That counter is not global to all the children, so my counter would not be accurate. My question is what do I do if I need a variable to be shared (or global) between all the children, so each child would be able to update the same variable. I don't want to store the counter in some temp file that I would be able to access after all children are finished. Thanks much.