Fix memory leak on TaskManager due to continuous growth of knownHashe…

…s (2.x) (#865)

* First draft with knownhashes as dictionary

* Remove first known hash - searching by value

* Parameters calibration and code style

* Fix tasks removal and limits

* Avoid the same hash value

* With fifo (#867)

* Update TaskManager.cs

* Update FIFOSet.cs

* Remove lock

* Update FIFOSet.cs

* Rename

neo/IO/Caching/FIFOSet.cs

@@ -1,9 +1,12 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace Neo.IO.Caching
 {
- internal class FIFOSet<T> where T : IEquatable<T>
+ internal class FIFOSet<T> : IEnumerable<T> where T : IEquatable<T>
  {
  private readonly int maxCapacity;
  private readonly int removeCount;
@@ -37,5 +40,21 @@ public bool Add(T item)
  dictionary.Add(item, null);
  return true;
  }
+
+ public void ExceptWith(IEnumerable<UInt256> hashes)
+ {
+ foreach (var hash in hashes)
+ {
+ dictionary.Remove(hash);
+ }
+ }
+
+ public IEnumerator<T> GetEnumerator()
+ {
+ var entries = dictionary.Values.Cast<T>().ToArray();
+ foreach (var entry in entries) yield return entry;
+ }
+
+ IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
  }
 }

neo/Network/P2P/TaskManager.cs

@@ -1,6 +1,7 @@
 using Akka.Actor;
 using Akka.Configuration;
 using Neo.IO.Actors;
+using Neo.IO.Caching;
 using Neo.Ledger;
 using Neo.Network.P2P.Payloads;
 using System;
@@ -24,7 +25,14 @@ private class Timer { }
 
  private readonly NeoSystem system;
  private const int MaxConncurrentTasks = 3;
- private readonly HashSet<UInt256> knownHashes = new HashSet<UInt256>();
+
+ /// <summary>
+ /// Max GetBlocks and Headers are limmited to 500 each
+ /// Blockchain.Singleton.MemPool.Capacity * 2 was the same value used in ProtocolHandler
+ /// </summary>
+ private static readonly int MaxCachedHashes = Blockchain.Singleton.MemPool.Capacity * 2;
+ private readonly FIFOSet<UInt256> knownHashes = new FIFOSet<UInt256>(MaxCachedHashes);
+
  private readonly Dictionary<UInt256, int> globalTasks = new Dictionary<UInt256, int>();
  private readonly Dictionary<IActorRef, TaskSession> sessions = new Dictionary<IActorRef, TaskSession>();
  private readonly ICancelable timer = Context.System.Scheduler.ScheduleTellRepeatedlyCancelable(TimerInterval, TimerInterval, Context.Self, new Timer(), ActorRefs.NoSender);