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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start():
 """ Start recording stats. Call this from a benchmark script when your setup is done. Call this at most once. @raise RuntimeError: Raised if the parent process responds with anything other than an acknowledgement of this message. """

    os.write(BenchmarkProcess.BACKCHANNEL_OUT, BenchmarkProcess.START)
    response = util.untilConcludes(os.read, BenchmarkProcess.BACKCHANNEL_IN, 1)
    if response != BenchmarkProcess.START:
        raise RuntimeError(
            "Parent process responded with %r instead of START " % (response,))