A transaction handler that performs retries

snf-astakos-app/astakos/im/retry_xctx.py

+# Copyright 2013 GRNET S.A. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or
+# without modification, are permitted provided that the following
+# conditions are met:
+#
+#   1. Redistributions of source code must retain the above
+#      copyright notice, this list of conditions and the following
+#      disclaimer.
+#
+#   2. Redistributions in binary form must reproduce the above
+#      copyright notice, this list of conditions and the following
+#      disclaimer in the documentation and/or other materials
+#      provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS
+# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+# The views and conclusions contained in the software and
+# documentation are those of the authors and should not be
+# interpreted as representing official policies, either expressed
+# or implied, of GRNET S.A.
+
+from synnefo.lib.db.xctx import TransactionHandler
+from time import sleep
+
+class RetryException(Exception):
+    pass
+
+class RetryTransactionHandler(TransactionHandler):
+    def __init__(self, retries=3, retry_wait=1.0, on_fail=None, **kwargs):
+        self.retries    = retries
+        self.retry_wait = retry_wait
+        self.on_fail    = on_fail
+        TransactionHandler.__init__(self, **kwargs)
+
+    def __call__(self, func):
+        def wrap(*args, **kwargs):
+            while True:
+                try:
+                    f = TransactionHandler.__call__(self, func)
+                    return f(*args, **kwargs)
+                except RetryException:
+                    self.retries -= 1
+                    if self.retries <= 0:
+                        f = self.on_fail
+                        if not callable(f):
+                            raise
+                        return f(*args, **kwargs)
+                    sleep(self.retry_wait)
+        return wrap