If it were on a local machine I'd suggest waiting for the other process, but that's not really an option in this case (unless you can wait for the local process? I don't know how P::FM works in any detail, nor how you're set up, so this might be totally useless). Looking at the problem as a whole, rather than the specific solution you've already tried, you might want to change your remote process to send an acknowledgement of some kind back at you when it's done—it requires a little more coding and a little more network traffic, but it seems likely to me that it would work, which appears to be an advantage over the current approach.