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1# Copyright 2013 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5"""This is a helper module to get and manipulate histogram data.
6
7The histogram data is the same data as is visible from "chrome://histograms".
8More information can be found at: chromium/src/base/metrics/histogram.h
9"""
10
11import json
12import logging
13
14BROWSER_HISTOGRAM = 'browser_histogram'
15RENDERER_HISTOGRAM = 'renderer_histogram'
16
17
18def CustomizeBrowserOptions(options):
19  """Allows histogram collection."""
20  options.AppendExtraBrowserArgs(['--enable-stats-collection-bindings'])
21
22
23def SubtractHistogram(histogram_json, start_histogram_json):
24  """Subtracts a previous histogram from a histogram.
25
26  Both parameters and the returned result are json serializations.
27  """
28  start_histogram = json.loads(start_histogram_json)
29  # It's ok if the start histogram is empty (we had no data, maybe even no
30  # histogram at all, at the start of the test).
31  if 'buckets' not in start_histogram:
32    return histogram_json
33
34  histogram = json.loads(histogram_json)
35  if ('pid' in start_histogram and 'pid' in histogram
36      and start_histogram['pid'] != histogram['pid']):
37    raise Exception(
38        'Trying to compare histograms from different processes (%d and %d)'
39        % (start_histogram['pid'], histogram['pid']))
40
41  start_histogram_buckets = dict()
42  for b in start_histogram['buckets']:
43    start_histogram_buckets[b['low']] = b['count']
44
45  new_buckets = []
46  for b in histogram['buckets']:
47    new_bucket = b
48    low = b['low']
49    if low in start_histogram_buckets:
50      new_bucket['count'] = b['count'] - start_histogram_buckets[low]
51      if new_bucket['count'] < 0:
52        logging.error('Histogram subtraction error, starting histogram most '
53                      'probably invalid.')
54    if new_bucket['count']:
55      new_buckets.append(new_bucket)
56  histogram['buckets'] = new_buckets
57  histogram['count'] -= start_histogram['count']
58
59  return json.dumps(histogram)
60
61
62def GetHistogram(histogram_type, histogram_name, tab):
63  """Get a json serialization of a histogram."""
64  assert histogram_type in [BROWSER_HISTOGRAM, RENDERER_HISTOGRAM]
65  function = 'getHistogram'
66  if histogram_type == BROWSER_HISTOGRAM:
67    function = 'getBrowserHistogram'
68  histogram_json = tab.EvaluateJavaScript(
69      'statsCollectionController.%s("%s")' %
70      (function, histogram_name))
71  if histogram_json:
72    return histogram_json
73  return None
74
75
76def GetHistogramCount(histogram_type, histogram_name, tab):
77  """Get the count of events for the given histograms."""
78  histogram_json = GetHistogram(histogram_type, histogram_name, tab)
79  histogram = json.loads(histogram_json)
80  if 'count' in histogram:
81    return histogram['count']
82  else:
83    return 0
84
85def GetHistogramSum(histogram_type, histogram_name, tab):
86  """Get the sum of events for the given histograms."""
87  histogram_json = GetHistogram(histogram_type, histogram_name, tab)
88  histogram = json.loads(histogram_json)
89  if 'sum' in histogram:
90    return histogram['sum']
91  else:
92    return 0
93