public async Task Start()
{
if (_hasStarted)
{
throw new InvalidOperationException("This scheduler is already started.");
}
_hasStarted = true;
_failedJobQueue.Monitor();
_recoverableAction.Monitor();
var tasks = _jobPumps.Select(p => p.Start()).ToArray();
await Task.WhenAny(tasks).FailFastOnException();
}