One method is to keep pipes open to the children - if you have a pipe which the parent reads and the child writes, you can send your dots (valid progess indicators :) down the pipe. You then remove file locking problems (which you have with writing dots to a file). You end up with a parent with a whole bunch of pipes - just do a select() on these, and you'll get woken up whenever there's anything to read from them.

Pipes were pretty much invented for this - they survive fork (i.e., both child and parent can still see it!). Pipes rock :) Programming Perl has some other good examples of IPC - shared memory, sockets, etc., but all that's a bit overboard for what you want. The usual pipe way is:

pipe(READHANDLE, WRITEHANDLE);
my $result = fork();
if ($result>0) {
    # child process, we write to the pipe
} else {
    # parent process, or error - might want to check before
    # we try to read from pipe :))
}

[download]

If you want more than one child, just keep the handles in an array so you don't lose them, and do a select() in the parent when all the children are active.

Oh, and beware of buffering - probably best to turn that off when debugging :)

In reply to Re: Using signals in Perl by kal
in thread Using signals in Perl by leons

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