| # Copyright 2015 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| """Tools for gradually enabling a feature on a deterministic set of machines. |
| |
| Add a flag to your program to control the percentage of machines that a new |
| feature should be enabled on:: |
| |
| def add_argparse_options(self, parser): |
| parser.add_argument('--myfeature-percent', type=int, default=0) |
| |
| def main(self, opts): |
| if experiments.is_active_for_host('myfeature', opts.myfeature_percent): |
| # do myfeature |
| """ |
| |
| import hashlib |
| import logging |
| import socket |
| import struct |
| |
| |
| def _is_active(labels, percent): |
| h = hashlib.md5() |
| for label, value in sorted(labels.iteritems()): |
| h.update(label) |
| h.update(value) |
| |
| # The first 8 bytes of the hash digest as an unsigned integer. |
| hash_num = struct.unpack_from('Q', h.digest())[0] |
| |
| return (hash_num % 100) < percent |
| |
| |
| def is_active_for_host(experiment_name, percent): |
| ret = _is_active({ |
| 'name': experiment_name, |
| 'host': socket.getfqdn(), |
| }, percent) |
| |
| if ret: |
| logging.info('Experiment "%s" is active', experiment_name) |
| |
| return ret |