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Viewing changes to bzrlib/transactions.py

  • Committer: Robert Collins
  • Date: 2005-10-11 01:05:24 UTC
  • mto: This revision was merged to the branch mainline in revision 1438.
  • Revision ID: robertc@robertcollins.net-20051011010524-e258bc8d051cc9d2
add a cache bound to Transactions, and a precious facility, so that we keep inventory.weave in memory, but can discard weaves for other such files.

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bzrlib/transactions.py
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repeated reads cannot be obtained if the object is ejected.
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"""
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import sys
 
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import bzrlib.errors as errors
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from bzrlib.identitymap import IdentityMap, NullIdentityMap
 
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from bzrlib.trace import mutter
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class ReadOnlyTransaction(object):
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        """
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    def __init__(self):
 
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        super(ReadOnlyTransaction, self).__init__()
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        self.map = IdentityMap()
 
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        self._clean_objects = set()
 
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        self._clean_queue = []
 
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        self._limit = -1
 
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        self._precious_objects = set()
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    def register_clean(self, an_object):
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        """Register an_object as being clean."""
 
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    def register_clean(self, an_object, precious=False):
 
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        """Register an_object as being clean.
 
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        If the precious hint is True, the object will not
 
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        be ejected from the object identity map ever.
 
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        """
 
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        self._clean_objects.add(an_object)
 
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        self._clean_queue.append(an_object)
 
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        if precious:
 
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            self._precious_objects.add(an_object)
 
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        self._trim()
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    def register_dirty(self, an_object):
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        """Register an_object as being dirty."""
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    def rollback(self):
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        """Let people call this even though nothing has to happen."""
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    def set_cache_size(self, size):
 
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        """Set a new cache size."""
 
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        assert -1 <= size
 
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        self._limit = size
 
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        self._trim()
 
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    def _trim(self):
 
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        """Trim the cache back if needed."""
 
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        if self._limit < 0 or self._limit - len(self._clean_objects) > 0:
 
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            return
 
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        needed = len(self._clean_objects) - self._limit
 
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        offset = 0
 
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        while needed and offset < len(self._clean_objects):
 
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            # references we know of:
 
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            # temp passed to getrefcount in our frame
 
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            # temp in getrefcount's frame
 
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            # the map forward
 
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            # the map backwards
 
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            # _clean_objects
 
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            # _clean_queue
 
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            # 1 missing ?
 
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            if (sys.getrefcount(self._clean_queue[offset]) <= 7 and
 
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                not self._clean_queue[offset] in self._precious_objects):
 
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                removed = self._clean_queue[offset]
 
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                self._clean_objects.remove(removed)
 
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                del self._clean_queue[offset]
 
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                self.map.remove_object(removed)
 
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                mutter('removed object %r', removed)
 
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                needed -= 1
 
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            else:
 
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                offset += 1
 
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class PassThroughTransaction(object):
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    """A pass through transaction
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        """
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    def __init__(self):
 
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        super(PassThroughTransaction, self).__init__()
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        self.map = NullIdentityMap()
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    def register_clean(self, an_object):
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        """Register an_object as being clean."""
 
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    def register_clean(self, an_object, precious=False):
 
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        """Register an_object as being clean.
 
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        Note that precious is only a hint, and PassThroughTransaction
 
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        ignores it.
 
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        """
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    def register_dirty(self, an_object):
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        """Register an_object as being dirty."""
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    def rollback(self):
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        """Cannot rollback a pass through transaction."""
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        raise errors.AlreadyCommitted
 
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    def set_cache_size(self, ignored):
 
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        """Do nothing, we are passing through."""