# Copyright (c) 2012 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.
import logging
import random
import signal
import sys
import threading
import time
from autotest_lib.client.common_lib import error
def handler(signum, frame):
"""
Register a handler for the timeout.
"""
raise error.TimeoutException('Call is timed out.')
def install_sigalarm_handler(new_handler):
"""
Try installing a sigalarm handler.
In order to protect apache, wsgi intercepts any attempt to install a
sigalarm handler, so our function will feel the full force of a sigalarm
even if we try to install a pacifying signal handler. To avoid this we
need to confirm that the handler we tried to install really was installed.
@param new_handler: The new handler to install. This must be a callable
object, or signal.SIG_IGN/SIG_DFL which correspond to
the numbers 1,0 respectively.
@return: True if the installation of new_handler succeeded, False otherwise.
"""
if (new_handler is None or
(not callable(new_handler) and
new_handler != signal.SIG_IGN and
new_handler != signal.SIG_DFL)):
logging.warning('Trying to install an invalid sigalarm handler.')
return False
signal.signal(signal.SIGALRM, new_handler)
installed_handler = signal.getsignal(signal.SIGALRM)
return installed_handler == new_handler
def set_sigalarm_timeout(timeout_secs, default_timeout=60):
"""
Set the sigalarm timeout.
This methods treats any timeout <= 0 as a possible error and falls back to
using it's default timeout, since negative timeouts can have 'alarming'
effects. Though 0 is a valid timeout, it is often used to cancel signals; in
order to set a sigalarm of 0 please call signal.alarm directly as there are
many situations where a 0 timeout is considered invalid.
@param timeout_secs: The new timeout, in seconds.
@param default_timeout: The default timeout to use, if timeout <= 0.
@return: The old sigalarm timeout
"""
timeout_sec_n = int(timeout_secs)
if timeout_sec_n <= 0:
timeout_sec_n = int(default_timeout)
return signal.alarm(timeout_sec_n)
def timeout(func, args=(), kwargs={}, timeout_sec=60.0, default_result=None):
"""
This function run the given function using the args, kwargs and
return the given default value if the timeout_sec is exceeded.
@param func: function to be called.
@param args: arguments for function to be called.
@param kwargs: keyword arguments for function to be called.
@param timeout_sec: timeout setting for call to exit, in seconds.
@param default_result: default return value for the function call.
@return 1: is_timeout 2: result of the function call. If
is_timeout is True, the call is timed out. If the
value is False, the call is finished on time.
"""
old_alarm_sec = 0
old_handler = signal.getsignal(signal.SIGALRM)
installed_handler = install_sigalarm_handler(handler)
if installed_handler:
old_alarm_sec = set_sigalarm_timeout(timeout_sec, default_timeout=60)
# If old_timeout_time = 0 we either didn't install a handler, or sigalrm
# had a signal.SIG_DFL handler with 0 timeout. In the latter case we still
# need to restore the handler/timeout.
old_timeout_time = (time.time() + old_alarm_sec) if old_alarm_sec > 0 else 0
try:
default_result = func(*args, **kwargs)
return False, default_result
except error.TimeoutException:
return True, default_result
finally:
# If we installed a sigalarm handler, cancel it since our function
# returned on time. If we can successfully restore the old handler,
# reset the old timeout, or, if the old timeout's deadline has passed,
# set the sigalarm to fire in one second. If the old_timeout_time is 0
# we don't need to set the sigalarm timeout since we have already set it
# as a byproduct of cancelling the current signal.
if installed_handler:
signal.alarm(0)
if install_sigalarm_handler(old_handler) and old_timeout_time:
set_sigalarm_timeout(int(old_timeout_time - time.time()),
default_timeout=1)
def retry(ExceptionToCheck, timeout_min=1.0, delay_sec=3, blacklist=None):
"""Retry calling the decorated function using a delay with jitter.
Will raise RPC ValidationError exceptions from the decorated
function without retrying; a malformed RPC isn't going to
magically become good. Will raise exceptions in blacklist as well.
If the retry is done in a child thread, timeout may not be enforced as
signal only works in main thread. Therefore, the retry inside a child
thread may run longer than timeout or even hang.
original from:
http://www.saltycrane.com/blog/2009/11/trying-out-retry-decorator-python/
@param ExceptionToCheck: the exception to check. May be a tuple of
exceptions to check.
@param timeout_min: timeout in minutes until giving up.
@param delay_sec: pre-jittered delay between retries in seconds. Actual
delays will be centered around this value, ranging up to
50% off this midpoint.
@param blacklist: a list of exceptions that will be raised without retrying
"""
def deco_retry(func):
random.seed()
def delay():
"""
'Jitter' the delay, up to 50% in either direction.
"""
random_delay = random.uniform(.5 * delay_sec, 1.5 * delay_sec)
logging.warning('Retrying in %f seconds...', random_delay)
time.sleep(random_delay)
def func_retry(*args, **kwargs):
# Used to cache exception to be raised later.
exc_info = None
delayed_enabled = False
exception_tuple = () if blacklist is None else tuple(blacklist)
start_time = time.time()
remaining_time = timeout_min * 60
is_main_thread = isinstance(threading.current_thread(),
threading._MainThread)
while remaining_time > 0:
if delayed_enabled:
delay()
else:
delayed_enabled = True
try:
# Clear the cache
exc_info = None
if is_main_thread:
is_timeout, result = timeout(func, args, kwargs,
remaining_time)
if not is_timeout:
return result
else:
return func(*args, **kwargs)
except exception_tuple:
raise
except error.CrosDynamicSuiteException:
raise
except ExceptionToCheck as e:
logging.warning('%s(%s)', e.__class__, e)
# Cache the exception to be raised later.
exc_info = sys.exc_info()
remaining_time = int(timeout_min*60 -
(time.time() - start_time))
# The call must have timed out or raised ExceptionToCheck.
if not exc_info:
raise error.TimeoutException('Call is timed out.')
# Raise the cached exception with original backtrace.
raise exc_info[0], exc_info[1], exc_info[2]
return func_retry # true decorator
return deco_retry