[CalendarServer-changes] [7256] CalendarServer/branches/users/glyph/subtransactions/txdav/common

[source_changes at macosforge.org]

Revision: 7256
          http://trac.macosforge.org/projects/calendarserver/changeset/7256
Author:   glyph at apple.com
Date:     2011-03-24 13:36:51 -0700 (Thu, 24 Mar 2011)
Log Message:
-----------
subtransaction API.

Modified Paths:
--------------
    CalendarServer/branches/users/glyph/subtransactions/txdav/common/datastore/sql.py
    CalendarServer/branches/users/glyph/subtransactions/txdav/common/icommondatastore.py

Modified: CalendarServer/branches/users/glyph/subtransactions/txdav/common/datastore/sql.py
===================================================================
--- CalendarServer/branches/users/glyph/subtransactions/txdav/common/datastore/sql.py	2011-03-24 20:36:40 UTC (rev 7255)
+++ CalendarServer/branches/users/glyph/subtransactions/txdav/common/datastore/sql.py	2011-03-24 20:36:51 UTC (rev 7256)
@@ -36,6 +36,7 @@
 from twisted.python import hashlib
 from twisted.python.modules import getModule
 from twisted.python.util import FancyEqMixin
+from twisted.python.failure import Failure
 
 from twisted.internet.defer import inlineCallbacks, returnValue, succeed
 
@@ -54,11 +55,12 @@
 from txdav.common.icommondatastore import HomeChildNameNotAllowedError, \
     HomeChildNameAlreadyExistsError, NoSuchHomeChildError, \
     ObjectResourceNameNotAllowedError, ObjectResourceNameAlreadyExistsError, \
-    NoSuchObjectResourceError
+    NoSuchObjectResourceError, AllRetriesFailed
 from txdav.common.inotifications import INotificationCollection, \
     INotificationObject
 
 from twext.python.clsprop import classproperty
+from twext.enterprise.ienterprise import AlreadyFinishedError
 from twext.enterprise.dal.syntax import Delete
 from twext.enterprise.dal.syntax import Insert
 from twext.enterprise.dal.syntax import Len
@@ -238,6 +240,85 @@
         self._postCommitOperations.append(operation)
 
 
+    _savepointCounter = 0
+
+    def _savepoint(self):
+        """
+        Generate a new SavepointAction whose name is unique in this transaction.
+        """
+        self._savepointCounter += 1
+        return SavepointAction('sp%d' % (self._savepointCounter,))
+
+
+    @inlineCallbacks
+    def subtransaction(self, thunk, retries=1):
+        """
+        Create a limited transaction object, which provides only SQL execution,
+        and run a function in a sub-transaction (savepoint) context, with that
+        object to execute SQL on.
+
+        @param thunk: a 1-argument callable which returns a Deferred when it is
+            done.  If this Deferred fails, 
+
+        @param retries: the number of times to re-try C{thunk} before deciding
+            that it's legitimately failed.
+
+        @return: a L{Deferred} which fires or fails according to the logic in
+            C{thunk}.  If it succeeds, it will return the value that C{thunk}
+            returned.
+        """
+        # Right now this code is covered mostly by the automated property store
+        # tests.  It should have more direct test coverage.
+
+        # TODO: we should really have a list of acceptable exceptions for
+        # failure and not blanket catch, but that involves more knowledge of the
+        # database driver in use than we currently possess at this layer.
+        block = self._sqlTxn.commandBlock()
+        sp = self._savepoint()
+        failuresToMaybeLog = []
+        triesLeft = retries + 1
+        try:
+            while True:
+                yield sp.acquire(block)
+                try:
+                    result = yield thunk(block)
+                except:
+                    failuresToMaybeLog.append(Failure())
+                    yield sp.rollback(block)
+                    if triesLeft:
+                        triesLeft -= 1
+                        # Important to get the new block before the old one has
+                        # been completed; since we almost certainly have some
+                        # writes to do, the caller of commit() will expect that
+                        # they actually get done, even if they didn't actually
+                        # block or yield to wait for them!  (c.f. property
+                        # store writes.)
+                        newBlock = self._sqlTxn.commandBlock()
+                        block.end()
+                        block = newBlock
+                        sp = self._savepoint()
+                    else:
+                        block.end()
+                        for f in failuresToMaybeLog:
+                            # TODO: direct tests, to make sure error logging
+                            # happens correctly in all cases.
+                            log.err(f)
+                        raise AllRetriesFailed()
+                else:
+                    yield sp.release(block)
+                    block.end()
+                    returnValue(result)
+        except AlreadyFinishedError:
+            # Interfering agents may disrupt our plans by calling abort()
+            # halfway through trying to do this subtransaction.  In that case -
+            # and only that case - acquire() or release() or commandBlock() may
+            # raise an AlreadyFinishedError (either synchronously, or in the
+            # case of the first two, possibly asynchronously as well).  We can
+            # safely ignore this, because it can't have any real effect; our
+            # caller shouldn't be paying attention anyway.
+            block.end()
+
+
     def execSQL(self, *a, **kw):
         """
         Execute some SQL (delegate to L{IAsyncTransaction}).

Modified: CalendarServer/branches/users/glyph/subtransactions/txdav/common/icommondatastore.py
===================================================================
--- CalendarServer/branches/users/glyph/subtransactions/txdav/common/icommondatastore.py	2011-03-24 20:36:40 UTC (rev 7255)
+++ CalendarServer/branches/users/glyph/subtransactions/txdav/common/icommondatastore.py	2011-03-24 20:36:51 UTC (rev 7256)
@@ -108,6 +108,12 @@
     Uh, oh.
     """
 
+class AllRetriesFailed(CommonStoreError):
+    """
+    In a re-tried subtransaction, all attempts failed to produce useful
+    progress.  Other exceptions will be logged.
+    """
+
 # Indexing / sync tokens
 
 class ReservationError(LookupError):
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