Is this a good, cross-platform way of spawning processes in Ruby 1.9?

Question

Below is a function I am using to spawn subprocesses in a cross-platform manner on Ruby 1.9 with optional timeout support.

It works well most of the time. However I am experiencing a weird issue where process.spawn does not return (i.e. blocks) in some cases.

def execute!(args)
  raise "invalid command specified" if args[:command].nil? or args[:command].empty?

  command = args[:command]
  timeout = args[:timeout] ? args[:timeout] : 60

  readpipe, writepipe = IO.pipe
  begin
    pid = Process.spawn(command, :out => writepipe, :err => writepipe)
    writepipe.close
  rescue
    readpipe.close
    return "Execution of #{command} unsuccessful", 1
  end

  puts pid

  process_output = ""
  process_exitstatus = 1
  begin
    timeout_status = Timeout::timeout(timeout) {
      _, process_status = Process.waitpid2(pid)
      process_exitstatus = process_status.exitstatus
      process_output = readpipe.readlines.join("")
      process_output = "" if process_output.nil?
    }
  rescue Timeout::Error
    process_output = "ERROR: #{command} took longer to execute than specified timeout! Killing process..."
    process_exitstatus = 1
    Process.kill('KILL', pid)
  ensure
    readpipe.close
  end

  return process_output, process_exitstatus
end

Can anyone spot any potential issues with this code that may be causing the problem I've described?