Okay here's an architecture for you:
Wrap your application in an independent server program that will be long-running, and then instead of invoking your application (which you said was expensive) you can open a unix socket to your application server program and talk with it that way. See perldoc perlipc for examples of clients and servers.
Unix sockets live in the file system but programs relate to them like sockets instead of like files.
Depending on the application, using a fifo instead of a socket might work. your long-running application server would sit on the other side of the fifo and would give exactly one burst of data whenever the fifo is read.
Both of these approaches will take some research.
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