recipe_modules/utils/api.py

# Copyright 2020 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Helper functions for common boilerplate tasks.

Top-level functions stored in __init__.py can be imported and used directly
(without needing a `RecipeApi` object) using `RECIPE_MODULES` imports. E.g.:

  ```
  from RECIPE_MODULES.fuchsia.utils import memoize

  @memoize
  def expensive_computation(inputs):
    return do_work(inputs)

  def RunSteps(api, ...):
    expensive_computation(...)
  ```
"""

from recipe_engine import recipe_api


class UtilsApi(recipe_api.RecipeApi):
    def retry(self, func, max_attempts, sleep=5.0, backoff_factor=1.5):
        """Retry the given function with exponential backoff.

        Args:
            func (callable): A function that performs the action that should
                be retried on failure. If it raises a `StepFailure` it will
                be retried. Any other exception will end the retry loop and
                bubble up.
            max_attempts (int): How many times to try before giving up.
            sleep (int or float): The time to sleep after the first attempt.
            backoff_factor (int or float): The factor by which the sleep time
                will be multiplied after each attempt.
        """
        for attempt in range(max_attempts):
            try:
                return func()
            except self.m.step.StepFailure:
                if attempt == max_attempts - 1:
                    raise

            self.m.time.sleep(sleep)
            sleep *= backoff_factor