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

#

# 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 <greg@electricrain.com>

#

# 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 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 _kwargs.has_key('max_retries'):

        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

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