First of all, that won't work. If either pipes fill up, the child will block and never exit. You also don't kill the child on timeout. (I'm blind!)

So let's examine what your original solution doesn't work on Windows:

• You can only select() sockets on Windows.
• alarm() is emulated by Perl, so it may not work in this circumstance.

Using sockets instead of pipes to communicate with the child (as demonstrated here) would solve the first problem, so all that's left would be to use select()'s timeout argument instead of alarm.

And now we'll forget everything I said because we don't want to reinvent the wheel. Just use IPC::Run.