class _DHTNode(object):
def __init__(self, n=8, ff=0.80, direction=LEFT_TO_RIGHT, parent=None):
"""
Defines an instance of a new Dynamic Hash Table.
:param n: The max number of entries per bucket.
:param ff: The fill factor for each bucket.
:param direction: The direction to consume the key from.
:param parent: A reference to the parent node.
"""
if n < 3:
n = 3
self.n = n
if ff < 0.25:
ff = 0.25
self.ff = ff
if not (direction == LEFT_TO_RIGHT or direction == RIGHT_TO_LEFT):
direction = LEFT_TO_RIGHT
self.n = n
self.ff = ff
self.direction = direction
self.parent = parent
self.left = SortedList(key=extract_key)
self.right = SortedList(key=extract_key)
def add(self, key, value, bkey):
"""
Adds a key-value pair to the DHT.
:param key: The key to add.
:param value: The corresponding value.
:param bkey: A binary representation of the key.
"""
bit, ck = consume_bkey(bkey, self.direction)
if bit == LEFT_BIT:
if isinstance(self.left, SortedList):
self.left.add(_IndexEntry(key, value, ck))
if len(self.left) > self.n * self.ff:
self._overflow(LEFT_BIT)
elif isinstance(self.left, _DHTNode):
self.left.add(key, value, ck)
else:
raise Exception()
elif bit == RIGHT_BIT:
if isinstance(self.right, SortedList):
self.right.add(_IndexEntry(key, value, ck))
if len(self.right) > self.n * self.ff:
self._overflow(RIGHT_BIT)
elif isinstance(self.right, _DHTNode):
self.right.add(key, value, ck)
else:
raise Exception()
else:
raise Exception()
def contains(self, key, bkey):
"""
Determines if the DHT contains at lest one key-value entry with the given key.
:param key: The key to lookup.
:param bkey: The binary representation of the key.
:return: True if at least one key-value entry is found corresponding to the given key, False otherwise.
"""
bit, ck = consume_bkey(bkey, self.direction)
if bit == LEFT_BIT:
if isinstance(self.left, SortedList):
for entry in self.left:
if key == entry.key:
return True
return False
elif isinstance(self.left, _DHTNode):
return self.left.contains(key, ck)
else:
raise Exception()
elif bit == RIGHT_BIT:
if isinstance(self.right, SortedList):
for entry in self.right:
if key == entry.key:
return True
return False
elif isinstance(self.right, _DHTNode):
return self.right.contains(key, ck)
else:
raise Exception()
else:
raise Exception()
def delete(self, key, bkey):
"""
Deletes the first matching key-value entry from the DHT.
:param key: The key to lookup.
:param bkey: The binary representation of the key.
"""
bit, ck = consume_bkey(bkey, self.direction)
if bit == LEFT_BIT:
if isinstance(self.left, SortedList):
discard = None
for entry in self.left:
if key == entry.key:
discard = entry
break
if discard:
self.left.discard(discard)
elif isinstance(self.left, _DHTNode):
self.left.delete(key, ck)
else:
raise Exception()
elif bit == RIGHT_BIT:
if isinstance(self.right, SortedList):
discard = None
for entry in self.right:
if key == entry.key:
discard = entry
break
if discard:
self.right.discard(discard)
elif isinstance(self.right, _DHTNode):
self.right.delete(key, ck)
else:
raise Exception()
else:
raise Exception()
if (isinstance(self.left, SortedList) and not self.left
and isinstance(self.right, SortedList) and not self.right):
self._underflow()
def get(self, key, bkey):
"""
Gets the first matching key-value entry from the key
:param key: The key to lookup.
:param bkey: The binary representation of the key.
:return: True if at least one key-value entry is found corresponding to the given key, False otherwise.
"""
bit, ck = consume_bkey(bkey, self.direction)
if bit == LEFT_BIT:
if isinstance(self.left, SortedList):
for entry in self.left:
if key == entry.key:
return entry.value
return None
elif isinstance(self.left, _DHTNode):
return self.left.get(key, ck)
else:
raise Exception()
elif bit == RIGHT_BIT:
if isinstance(self.right, SortedList):
for entry in self.right:
if key == entry.key:
return entry.value
return None
elif isinstance(self.right, _DHTNode):
return self.right.get(key, ck)
else:
raise Exception()
else:
raise Exception()
def height(self):
"""
Gets the height of the DHT.
:return: The height of the DHT.
"""
if isinstance(self.left, SortedList) and isinstance(
self.right, SortedList):
return 1
left = 0
right = 0
if isinstance(self.left, _DHTNode):
left = self.left.height() + 1
if isinstance(self.right, _DHTNode):
right = self.right.height() + 1
return max(left, right)
def traverse(self):
"""
Traverses the DHT yielding key-value pairs as a Python generator.
:return: A Python generator over the key-value pairs in the DHT.
"""
if isinstance(self.left, SortedList):
for entry in self.left:
yield entry.key, entry.value
elif isinstance(self.left, _DHTNode):
yield from self.left.traverse()
else:
raise Exception()
if isinstance(self.right, SortedList):
for entry in self.right:
yield entry.key, entry.value
elif isinstance(self.right, _DHTNode):
yield from self.right.traverse()
else:
raise Exception()
def _overflow(self, bit):
"""
Redistributes the indicated buckets keys to a new left and right bucket. An overflow happens when a bucket
grows to large, i.e. its total length is greater than its maximum number of entries times its fill factor.
:param bit: The bit representing the buck that overflowed. One of {LEFT_BIT, RIGHT_BIT}.
"""
if bit == LEFT_BIT and isinstance(self.left, SortedList):
new_left = _DHTNode(n=self.n,
ff=self.ff,
direction=self.direction,
parent=self)
for entry in self.left:
new_left.add(entry.key, entry.value, entry.bkey)
self.left.clear()
self.left = new_left
elif bit == RIGHT_BIT and isinstance(self.right, SortedList):
new_right = _DHTNode(n=self.n,
ff=self.ff,
direction=self.direction,
parent=self)
for entry in self.right:
new_right.add(entry.key, entry.value, entry.bkey)
self.right.clear()
self.right = new_right
else:
raise Exception()
def _underflow(self):
"""
Coalesces the two buckets pointed to by this this into a single bucket. An underflow occurs when a deletion
causes a state where by both buckets pointed to by this node are empty. This rule is ignored for the root node.
"""
# only underflow if we are not the root node, root node cannot underflow
if self.parent:
if self.parent.left == self:
self.parent.left = SortedList(key=extract_key)
elif self.parent.right == self:
self.parent.right = SortedList(key=extract_key)
else:
raise Exception()
