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216 lines
7.4 KiB
C#
216 lines
7.4 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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namespace POSV.LoadBalance
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{
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/// <summary>
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/// Consistent Hashing node ring implementation
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/// </summary>
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/// <typeparam name="T"></typeparam>
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public class ConsistentHash<T>
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{
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private readonly SortedDictionary<int, T> _circle;
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private readonly int _virtualNodesFactor;
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public ConsistentHash(SortedDictionary<int, T> nodeHashCircle, int virtualNodesFactor)
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{
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if (nodeHashCircle == null)
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throw new ArgumentNullException("nodeHashCircle");
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if (virtualNodesFactor < 1)
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throw new ArgumentException("virtualNodesFactor must be >= 1");
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_circle = nodeHashCircle;
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_virtualNodesFactor = virtualNodesFactor;
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}
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/// <summary>
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/// arrays for fast binary search access
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/// </summary>
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private Tuple<int[], T[]> _ring = null;
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private Tuple<int[], T[]> RingTuple
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{
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get { return _ring ?? (_ring = Tuple.Create(_circle.Keys.ToArray(), _circle.Values.ToArray())); }
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}
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/// <summary>
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/// Sorted hash values of the nodes
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/// </summary>
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private int[] NodeHashRing
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{
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get { return RingTuple.Item1; }
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}
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/// <summary>
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/// NodeRing is the nodes sorted in the same order as <see cref="NodeHashRing"/>, i.e. same index
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/// </summary>
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private T[] NodeRing
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{
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get { return RingTuple.Item2; }
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}
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/// <summary>
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/// Add a node to the hash ring.
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///
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/// Note that <see cref="ConsistentHash{T}"/> is immutable and
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/// this operation returns a new instance.
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/// </summary>
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public ConsistentHash<T> Add(T node)
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{
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return this + node;
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}
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/// <summary>
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/// Removes a node from the hash ring.
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///
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/// Note that <see cref="ConsistentHash{T}"/> is immutable and
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/// this operation returns a new instance.
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/// </summary>
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public ConsistentHash<T> Remove(T node)
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{
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return this - node;
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}
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/// <summary>
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/// Converts the result of <see cref="Array.BinarySearch{T}(T[], T)"/> into an index in the
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/// <see cref="RingTuple"/> array.
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/// </summary>
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/// <param name="i"></param>
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/// <returns></returns>
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private int Idx(int i)
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{
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if (i >= 0)
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return i; //exact match
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else
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{
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var j = Math.Abs(i + 1);
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if (j >= NodeHashRing.Length)
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return 0; //after last, use first
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else
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return j; //next node clockwise
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}
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}
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/// <summary>
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/// Get the node responsible for the data key.
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/// Can only be used if nodes exist in the node ring.
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/// Otherwise throws <see cref="ArgumentException"/>.
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/// </summary>
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public T NodeFor(byte[] key)
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{
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if (IsEmpty)
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throw new InvalidOperationException(string.Format("Can't get node for [{0}] from an empty node ring", key));
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return NodeRing[Idx(Array.BinarySearch(NodeHashRing, ConsistentHash.HashFor(key)))];
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}
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/// <summary>
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/// Get the node responsible for the data key.
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/// Can only be used if nodes exist in the node ring.
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/// Otherwise throws <see cref="ArgumentException"/>.
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/// </summary>
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public T NodeFor(string key)
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{
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if (IsEmpty)
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throw new InvalidOperationException(string.Format("Can't get node for [{0}] from an empty node ring", key));
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return NodeRing[Idx(Array.BinarySearch(NodeHashRing, ConsistentHash.HashFor(key)))];
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}
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/// <summary>
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/// Is the node ring empty? i.e. no nodes added or all removed
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/// </summary>
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public bool IsEmpty
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{
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get { return !_circle.Any(); }
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}
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#region Operator overloads
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/// <summary>
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/// Add a node to the hash ring.
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///
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/// Note that <see cref="ConsistentHash{T}"/> is immutable and
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/// this operation returns a new instance.
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/// </summary>s
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public static ConsistentHash<T> operator +(ConsistentHash<T> hash, T node)
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{
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var nodeHash = ConsistentHash.HashFor(node.GetHashCode().ToString());
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var vNodeHashCircle = Enumerable.Range(1, hash._virtualNodesFactor)
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.Select(x => new KeyValuePair<int, T>(ConsistentHash.ConcatenateNodeHash(nodeHash, x), node));
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var newNodeHashCircle = new SortedDictionary<int, T>();
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foreach (var item in hash._circle.Concat(vNodeHashCircle))
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newNodeHashCircle.Add(item.Key, item.Value);
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return new ConsistentHash<T>(newNodeHashCircle, hash._virtualNodesFactor);
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}
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/// <summary>
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/// Removes a node from the hash ring.
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///
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/// Note that <see cref="ConsistentHash{T}"/> is immutable and
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/// this operation returns a new instance.
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/// </summary>
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public static ConsistentHash<T> operator -(ConsistentHash<T> hash, T node)
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{
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var nodeHash = ConsistentHash.HashFor(node.GetHashCode().ToString());
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var vNodeHashCircle = Enumerable.Range(1, hash._virtualNodesFactor)
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.Select(x => new KeyValuePair<int, T>(ConsistentHash.ConcatenateNodeHash(nodeHash, x), node));
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var newNodeHashCircle = new SortedDictionary<int, T>();
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foreach (var item in hash._circle.Except(vNodeHashCircle))
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newNodeHashCircle.Add(item.Key, item.Value);
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return new ConsistentHash<T>(newNodeHashCircle, hash._virtualNodesFactor);
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}
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#endregion
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}
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/// <summary>
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/// Static helper class for creating <see cref="ConsistentHash{T}"/> instances.
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/// </summary>
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public static class ConsistentHash
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{
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/// <summary>
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/// Factory method to create a <see cref="ConsistentHash{T}"/> instance.
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/// </summary>
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public static ConsistentHash<T> Create<T>(IEnumerable<T> nodes, int virtualNodesFactor)
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{
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var nodeHashCircle = new SortedDictionary<int, T>();
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foreach (var node in nodes)
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{
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var nodeHash = HashFor(node.GetHashCode().ToString());
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var vNodeHashs = Enumerable.Range(1, virtualNodesFactor)
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.Select(x => ConcatenateNodeHash(nodeHash, x)).ToList();
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foreach (var vNodeHash in vNodeHashs)
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nodeHashCircle.Add(vNodeHash, node);
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}
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return new ConsistentHash<T>(nodeHashCircle, virtualNodesFactor);
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}
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#region Hashing methods
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internal static int ConcatenateNodeHash(int nodeHash, int vnode)
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{
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unchecked
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{
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var h = MurmurHash.StartHash((uint)nodeHash);
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h = MurmurHash.ExtendHash(h, (uint)vnode, MurmurHash.StartMagicA, MurmurHash.StartMagicB);
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return (int)MurmurHash.FinalizeHash(h);
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}
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}
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internal static int HashFor(string hashKey)
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{
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return MurmurHash.StringHash(hashKey);
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}
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internal static int HashFor(byte[] bytes)
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{
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return MurmurHash.ByteHash(bytes);
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}
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#endregion
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}
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}
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