def start():
os.write(BenchmarkProcess.BACKCHANNEL_OUT, BenchmarkProcess.START)<EOL>response = util.untilConcludes(os.read, BenchmarkProcess.BACKCHANNEL_IN, <NUM_LIT:1>)<EOL>if response != BenchmarkProcess.START:<EOL><INDENT>raise RuntimeError(<EOL>"<STR_LIT>" % (response,))<EOL><DEDENT>
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.