Lib/bsddb/dbutils.py

   1 #------------------------------------------------------------------------
   2 #
   3 # Copyright (C) 2000 Autonomous Zone Industries
   4 #
   5 # License:      This is free software.  You may use this software for any
   6 #               purpose including modification/redistribution, so long as
   7 #               this header remains intact and that you do not claim any
   8 #               rights of ownership or authorship of this software.  This
   9 #               software has been tested, but no warranty is expressed or
  10 #               implied.
  11 #
  12 # Author: Gregory P. Smith <greg@electricrain.com>
  13 #
  14 # Note: I don't know how useful this is in reality since when a
  15 #       DBLockDeadlockError happens the current transaction is supposed to be
  16 #       aborted.  If it doesn't then when the operation is attempted again
  17 #       the deadlock is still happening...
  18 #       --Robin
  19 #
  20 #------------------------------------------------------------------------
  21
  22
  23 #
  24 # import the time.sleep function in a namespace safe way to allow
  25 # "from bsddb.db import *"
  26 #
  27 from time import sleep as _sleep
  28
  29 try:
  30     # For Python 2.3
  31     from bsddb import db
  32 except ImportError:
  33     # For earlier Pythons w/distutils pybsddb
  34     from bsddb3 import db
  35
  36 # always sleep at least N seconds between retrys
  37 _deadlock_MinSleepTime = 1.0/64
  38 # never sleep more than N seconds between retrys
  39 _deadlock_MaxSleepTime = 3.14159
  40
  41 # Assign a file object to this for a "sleeping" message to be written to it
  42 # each retry
  43 _deadlock_VerboseFile = None
  44
  45
  46 def DeadlockWrap(function, *_args, **_kwargs):
  47     """DeadlockWrap(function, *_args, **_kwargs) - automatically retries
  48     function in case of a database deadlock.
  49
  50     This is a function intended to be used to wrap database calls such
  51     that they perform retrys with exponentially backing off sleeps in
  52     between when a DBLockDeadlockError exception is raised.
  53
  54     A 'max_retries' parameter may optionally be passed to prevent it
  55     from retrying forever (in which case the exception will be reraised).
  56
  57         d = DB(...)
  58         d.open(...)
  59         DeadlockWrap(d.put, "foo", data="bar")  # set key "foo" to "bar"
  60     """
  61     sleeptime = _deadlock_MinSleepTime
  62     max_retries = _kwargs.get('max_retries', -1)
  63     if _kwargs.has_key('max_retries'):
  64         del _kwargs['max_retries']
  65     while 1:
  66         try:
  67             return function(*_args, **_kwargs)
  68         except db.DBLockDeadlockError:
  69             if _deadlock_VerboseFile:
  70                 _deadlock_VerboseFile.write(
  71                     'dbutils.DeadlockWrap: sleeping %1.3f\n' % sleeptime)
  72             _sleep(sleeptime)
  73             # exponential backoff in the sleep time
  74             sleeptime *= 2
  75             if sleeptime > _deadlock_MaxSleepTime:
  76                 sleeptime = _deadlock_MaxSleepTime
  77             max_retries -= 1
  78             if max_retries == -1:
  79                 raise
  80
  81
  82 #------------------------------------------------------------------------