Implement #15

PythonHome/Lib/bsddb/dbutils.py

@@ -0,0 +1,83 @@
+#------------------------------------------------------------------------
+#
+# 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@krypto.org>
+#
+# 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
+
+
+#------------------------------------------------------------------------