Method _start

src/state/log.cpp:258–293

Future<Nothing> LogStorageProcess::_start(
    const Option<Log::Position>& position)
{
  CHECK_SOME(starting);

  if (position.isNone()) {
    VLOG(2) << "Writer failed to get elected, retrying";

    starting = None(); // Reset 'starting' so we try again.
    return start(); // TODO(benh): Don't try again forever?
  }

  VLOG(2) << "Writer got elected at position " << position->identity();

  // Now read and apply log entries. Since 'start' can be called
  // multiple times (i.e., since we reset 'starting' after getting a
  // None position returned after 'set', 'expunge', etc) we need to
  // check and see if we've already successfully read the log at least
  // once by checking 'index'. If we haven't yet read the log (i.e.,
  // this is the first call to 'start' and 'index' is None) then we
  // get the beginning of the log first so we can read from that up to
  // what ever position was known at the time we started the
  // writer. Note that it should always be safe to read a truncated
  // entry since a subsequent operation in the log should invalidate
  // that entry when we read it instead.
  if (index.isSome()) {
    // If we've started before (i.e., have an 'index' position) we
    // should also expect to know the last 'truncated' position.
    CHECK_SOME(truncated);
    return reader.read(index.get(), position.get())
      .then(defer(self(), &Self::apply, lambda::_1));
  }

  return reader.beginning()
    .then(defer(self(), &Self::__start, lambda::_1, position.get()));
}


Future<Nothing> LogStorageProcess::__start(