#------------------------------------------------------------------------
#
# Copyright (C) 2000 Autonomous Zone Industries
#
# License: This is free software. You may use this software for any
# purpose including modification/redistribution, so long as
# this header remains intact and that you do not claim any
# rights of ownership or authorship of this software. This
# software has been tested, but no warranty is expressed or
# implied.
#
# Author: Gregory P. Smith <[email protected]>
#
# Note: I don't know how useful this is in reality since when a
# DBLockDeadlockError happens the current transaction is supposed to be
# aborted. If it doesn't then when the operation is attempted again
# the deadlock is still happening...
# --Robin
#
#------------------------------------------------------------------------


#
# import the time.sleep function in a namespace safe way to allow
# "from bsddb.dbutils import *"
#
from time import sleep as _sleep

import sys
absolute_import = (sys.version_info[0] >= 3)
if absolute_import :
# Because this syntaxis is not valid before Python 2.5
exec("from . import db")
else :
import db

# always sleep at least N seconds between retrys
_deadlock_MinSleepTime = 1.0/128
# never sleep more than N seconds between retrys
_deadlock_MaxSleepTime = 3.14159

# Assign a file object to this for a "sleeping" message to be written to it
# each retry
_deadlock_VerboseFile = None


def DeadlockWrap(function, *_args, **_kwargs):
"""DeadlockWrap(function, *_args, **_kwargs) - automatically retries
function in case of a database deadlock.

This is a function intended to be used to wrap database calls such
that they perform retrys with exponentially backing off sleeps in
between when a DBLockDeadlockError exception is raised.

A 'max_retries' parameter may optionally be passed to prevent it
from retrying forever (in which case the exception will be reraised).

d = DB(...)
d.open(...)
DeadlockWrap(d.put, "foo", data="bar") # set key "foo" to "bar"
"""
sleeptime = _deadlock_MinSleepTime
max_retries = _kwargs.get('max_retries', -1)
if 'max_retries' in _kwargs:
del _kwargs['max_retries']
while True:
try:
return function(*_args, **_kwargs)
except db.DBLockDeadlockError:
if _deadlock_VerboseFile:
_deadlock_VerboseFile.write(
'dbutils.DeadlockWrap: sleeping %1.3f\n' % sleeptime)
_sleep(sleeptime)
# exponential backoff in the sleep time
sleeptime *= 2
if sleeptime > _deadlock_MaxSleepTime:
sleeptime = _deadlock_MaxSleepTime
max_retries -= 1
if max_retries == -1:
raise


#------------------------------------------------------------------------