From 0084d4684fc4d51bfe7ae561ca2bd0e647d29ae4 Mon Sep 17 00:00:00 2001
From: Job Evers-Meltzer <jobevers@users.noreply.github.com>
Date: Tue, 13 Dec 2016 20:53:24 -0600
Subject: [PATCH] Add distance optimization

---
 lbrynet/dht/node.py | 88 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 74 insertions(+), 14 deletions(-)

diff --git a/lbrynet/dht/node.py b/lbrynet/dht/node.py
index 866f6c82e..6f8d12a2b 100644
--- a/lbrynet/dht/node.py
+++ b/lbrynet/dht/node.py
@@ -6,10 +6,16 @@
 #
 # The docstrings in this module contain epytext markup; API documentation
 # may be created by processing this file with epydoc: http://epydoc.sf.net
-
-import hashlib, random, struct, time, binascii
 import argparse
+import binascii
+import hashlib
+import operator
+import random
+import struct
+import time
+
 from twisted.internet import defer, error
+
 import constants
 import routingtable
 import datastore
@@ -645,6 +651,9 @@ class _IterativeFindHelper(object):
         self.key = key
         self.find_value = find_value
         self.rpc = rpc
+        # all distance operations in this class only care about the distance
+        # to self.key, so this makes it easier to calculate those
+        self.distance = Distance(key)
         # List of active queries; len() indicates number of active probes
         #
         # n.b: using lists for these variables, because Python doesn't
@@ -725,10 +734,7 @@ class _IterativeFindHelper(object):
             self.find_value_result['closestNodeNoValue'] = aContact
 
     def _is_closer(self, responseMsg):
-        return (
-            self.node._routingTable.distance(self.key, responseMsg.nodeID) <
-            self.node._routingTable.distance(self.key, self.active_contacts[0].id)
-        )
+        return self.distance.is_closer(responseMsg.nodeID, self.active_contacts[0].id)
 
     def _addIfValid(self, contactTriple):
         if isinstance(contactTriple, (list, tuple)) and len(contactTriple) == 3:
@@ -753,17 +759,15 @@ class _IterativeFindHelper(object):
             del self.pending_iteration_calls[0]
             self.searchIteration()
 
+    def sortByDistance(self, contact_list):
+        """Sort the list of contacts in order by distance from key"""
+        ExpensiveSort(contact_list, self.distance.to_contact).sort()
+
     # Send parallel, asynchronous FIND_NODE RPCs to the shortlist of contacts
     def searchIteration(self):
         self.slow_node_count[0] = len(self.active_probes)
-        # TODO: move sort_key to be a method on the class
-        def sort_key(firstContact, secondContact, targetKey=self.key):
-            return cmp(
-                self.node._routingTable.distance(firstContact.id, targetKey),
-                self.node._routingTable.distance(secondContact.id, targetKey)
-            )
         # Sort the discovered active nodes from closest to furthest
-        self.active_contacts.sort(sort_key)
+        self.sortByDistance(self.active_contacts)
         # This makes sure a returning probe doesn't force calling this function by mistake
         while len(self.pending_iteration_calls):
             del self.pending_iteration_calls[0]
@@ -784,7 +788,7 @@ class _IterativeFindHelper(object):
         if len(self.active_contacts):
             self.prev_closest_node[0] = self.active_contacts[0]
         contactedNow = 0
-        self.shortlist.sort(sort_key)
+        self.sortByDistance(self.shortlist)
         # Store the current shortList length before contacting other nodes
         prevShortlistLength = len(self.shortlist)
         for contact in self.shortlist:
@@ -837,6 +841,62 @@ class _IterativeFindHelper(object):
         )
 
 
+class Distance(object):
+    """Calculate the XOR result between two string variables.
+
+    Frequently we re-use one of the points so as an optimization
+    we pre-calculate the long value of that point.
+    """
+    def __init__(self, key):
+        self.key = key
+        self.val_key_one = long(key.encode('hex'), 16)
+
+    def __call__(self, key_two):
+        val_key_two = long(key_two.encode('hex'), 16)
+        return self.val_key_one ^ val_key_two
+
+    def is_closer(self, a, b):
+        """Returns true is `a` is closer to `key` than `b` is"""
+        return self(a) < self(b)
+
+    def to_contact(self, contact):
+        """A convenience function for calculating the distance to a contact"""
+        return self(contact.id)
+
+
+class ExpensiveSort(object):
+    """Sort a list in place.
+
+    The result of `key(item)` is cached for each item in the `to_sort`
+    list as an optimization.  This can be useful when `key` is
+    expensive.
+
+    Attributes:
+        to_sort: a list of items to sort
+        key: callable, like `key` in normal python sort
+        attr: the attribute name used to cache the value on each item.
+    """
+    def __init__(self, to_sort, key, attr='__value'):
+        self.to_sort = to_sort
+        self.key = key
+        self.attr = attr
+
+    def sort(self):
+        self._cacheValues()
+        self._sortByValue()
+        self._removeValue()
+
+    def _cacheValues(self):
+        for item in self.to_sort:
+            setattr(item, self.attr, self.key(item))
+
+    def _sortByValue(self):
+        self.to_sort.sort(key=operator.attrgetter(self.attr))
+
+    def _removeValue(self):
+        for item in self.to_sort:
+            delattr(item, self.attr)
+
 
 def main():
     parser = argparse.ArgumentParser(description="Launch a dht node")