lib/metrics.py

# Copyright 2016 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Wrapper library around ts_mon.

This library provides some wrapper functionality around ts_mon, to make it more
friendly to developers. It also provides import safety, in case ts_mon is not
deployed with your code.
"""

from __future__ import print_function

try:
  from infra_libs.ts_mon.common import metrics
  from infra_libs.ts_mon.common import interface
except (ImportError, RuntimeError):
  metrics = None
  interface = None


class MockMetric(object):
  """Mock metric object, to be returned if ts_mon is not set up."""

  def _mock_method(self, *args, **kwargs):
    pass

  def __getattr__(self, _):
    return self._mock_method


def _ImportSafe(fn):
  """Decorator which causes |fn| to return MockMetric if ts_mon not imported."""
  def wrapper(*args, **kwargs):
    if metrics:
      return fn(*args, **kwargs)
    else:
      return MockMetric()

  return wrapper


def _GetOrConstructMetric(name, constructor):
  """Returns an existing metric handle or constructs a new one.

  Args:
    name: Name of the metric to construct.
    constructor: Callable constructor object, if that metric doesn't exist.

  Returns:
    A metric handle, or a MockMetric if ts_mon was not imported.
  """
  return interface.state.metrics.get(name) or constructor(name)


@_ImportSafe
def Counter(name):
  """Returns a metric handle for a counter named |name|."""
  return _GetOrConstructMetric(name, metrics.CounterMetric)


@_ImportSafe
def Gauge(name):
  """Returns a metric handle for a gauge named |name|."""
  return _GetOrConstructMetric(name, metrics.GaugeMetric)


@_ImportSafe
def String(name):
  """Returns a metric handle for a string named |name|."""
  return _GetOrConstructMetric(name, metrics.StringMetric)


@_ImportSafe
def Boolean(name):
  """Returns a metric handle for a boolean named |name|."""
  return _GetOrConstructMetric(name, metrics.BooleanMetric)


@_ImportSafe
def Float(name):
  """Returns a metric handle for a float named |name|."""
  return _GetOrConstructMetric(name, metrics.FloatMetric)


@_ImportSafe
def CumulativeDistribution(name):
  """Returns a metric handle for a cumulative distribution named |name|."""
  return _GetOrConstructMetric(name, metrics.CumulativeDistributionMetric)