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Processing received UDP data in another thread in C#

I have a class which contains a method for receiving UDP data in a separate thread. I do this to avoid the main application (which is running in Unity3D) from stalling.
I need to pass the data that is received in the separate thread to another class, which runs on the original thread and, as such, is able to interact with Unity3D.
Here is roughly what the UDPReceiver looks like:
public class UDPReciever {
//...
public UDPReciever() {
m_Port = 12345;
m_Worker = new Thread(new ThreadStart(recvData));
m_Worker.IsBackground = true;
m_Worker.Start();
}
void recvData() {
m_UDPClient = new UdpClient(m_Port);
while (true) {
try {
IPEndPoint anyIP = new IPEndPoint(IPAddress.Any, 0);
byte[] data = (m_UDPClient.Receive(ref anyIP));
// TODO: Hand 'data' to NetworkController class (running in the original thread) for processing
} catch (Exception err) {
print(err.ToString());
}
}
}
}
This is roughly what the NetworkController class needs to look like. Ideally the "OnNewData" method would be called every time a new packet is received with the data passed as an argument.
public class NetworkController {
//...
void OnNewData(pData) {
// Process the data in this thread
}
}
How would I go about achieving this? Thanks in advance.

Here is how it could be done (not tested):
public class Dispatcher : MonoBehaviour
{
private static readonly BlockingCollection<Action> tasks = new BlockingCollection<Action>();
public static Dispatcher Instance = null;
static Dispatcher()
{
Instance = new Dispatcher();
}
private Dispatcher()
{
}
public void InvokeLater(Action task)
{
tasks.Add(task);
}
void FixedUpdate()
{
if (tasks.Count > 0)
{
foreach (Action task in tasks.GetConsumingEnumerable())
{
task();
}
}
}
}
...
NetworkController networkControllerInstance;
void recvData()
{
m_UDPClient = new UdpClient(m_Port);
while (true)
{
try
{
IPEndPoint anyIP = new IPEndPoint(IPAddress.Any, 0);
byte[] data = (m_UDPClient.Receive(ref anyIP));
Dispatcher.Instance.InvokeLater(() => networkControllerInstance.OnNewData(data));
}
catch (Exception err)
{
print(err.ToString());
}
}
}
EDIT:
A version that should be compliant with .Net 3.5:
public class Dispatcher : MonoBehaviour
{
private static readonly Queue<Action> tasks = new Queue<Action>();
public static Dispatcher Instance = null;
static Dispatcher()
{
Instance = new Dispatcher();
}
private Dispatcher()
{
}
public void InvokeLater(Action task)
{
lock (tasks)
{
tasks.Enqueue(task);
}
}
void FixedUpdate()
{
while (tasks.Count > 0)
{
Action task = null;
lock (tasks)
{
if (tasks.Count > 0)
{
task = tasks.Dequeue();
}
}
task();
}
}
}
EDIT 2:
if you want to avoid freezing the main thread during a too long period:
void FixedUpdate()
{
if (tasks.Count != 0)
{
Action task = null;
lock (tasks)
{
if (tasks.Count != 0)
{
task = tasks.Dequeue();
}
}
task();
}
}

Frequent lag spikes in multi-threaded code

I'm attempting to make my simple C# graphics library multi-threaded. However, after the introduction of this code:
/* foreach (IAffector affector in affectorLookup.Values)
affector.Update(timestep); */
taskManager.Value = timestep; taskManager.Start();
foreach (IAffector affector in affectorLookup.Values)
taskManager.AddToQueue(affector.Update);
taskManager.StopWhenDone();
taskManager.Wait();
the simulation starts experiencing sharp lag-spikes, which seem to originate in TaskHandler.Run (I can't tell for sure, because adding the previous code makes my code profiler ignore anything outside TaskHandler.Run).
The task manager:
public class TaskManager
{
public delegate void MethodDel(float timestep);
private Queue<MethodDel> queue;
private List<TaskHandler> handlers;
private float value;
public float Value
{
get
{
return value;
}
set
{
this.value = value;
}
}
public TaskManager()
{
this.queue = new Queue<MethodDel>();
this.handlers = new List<TaskHandler>(System.Environment.ProcessorCount);
for (int t = 0; t < this.handlers.Capacity; ++t)
this.handlers.Add(new TaskHandler(this));
this.value = 0;
}
public void Start()
{
foreach (var handler in handlers)
handler.Start();
}
public void Stop()
{
lock (queue)
queue.Clear();
foreach (var handler in handlers)
handler.StopWhenDone();
}
public void StopWhenDone()
{
foreach (var handler in handlers)
handler.StopWhenDone();
}
public void AddToQueue(MethodDel method)
{
lock (queue)
queue.Enqueue(method);
}
public bool GetFromQueue(out MethodDel method)
{
lock (queue)
{
if (queue.Count == 0) { method = null; return false; }
method = queue.Dequeue();
return true;
}
}
public int GetQueueCount()
{
return queue.Count;
}
internal void Wait()
{
// Have to wait for them one at a time because the main thread is STA.
WaitHandle[] waitHandles = new WaitHandle[1];
// for (int t = 0; t < handlers.Count; ++t)
// waitHandles[t] = handlers[t].WaitHandle;
// WaitHandle.WaitAll(waitHandles);
for (int t = 0; t < handlers.Count; ++t)
{ waitHandles[0] = handlers[t].WaitHandle; WaitHandle.WaitAll(waitHandles); }
}
}
And the task handler:
public class TaskHandler
{
private TaskManager manager;
private Thread thread;
private bool stopWhenDone;
private ManualResetEvent waitHandle;
public ManualResetEvent WaitHandle
{
get
{
return waitHandle;
}
}
public TaskHandler(TaskManager manager)
{
this.manager = manager;
}
public void Start()
{
waitHandle = new ManualResetEvent(false);
stopWhenDone = false;
thread = new Thread(Run);
thread.IsBackground = true;
thread.SetApartmentState(ApartmentState.MTA);
thread.Start();
}
public void StopWhenDone()
{
this.stopWhenDone = true;
}
// Possible source of slowdown
private void Run()
{
TaskManager.MethodDel curMethod;
while (!stopWhenDone || manager.GetQueueCount() > 0)
{
if (manager.GetFromQueue(out curMethod))
{
curMethod(manager.Value);
}
}
waitHandle.Set();
}
}

Starting a thread is a heavy operation. Not sure if it's as heavy as you are experiencing, but that could be it. Also, having all your processing run parallel can be putting a big strain on your system with possibly little benefit...

I'm going to venture that the spikes have something to do with waitHandle.Set();
I like the overall design, but I have not used WaitHandle before, so I am unsure how this interacts with your design.

Implementation of processing items asynchronously

Is there any good implementation of processing queue items asynchronously?

If you're using .NET 4, a lot of this comes for free out of the box.
If you've already got all the items, you can use Parallel.ForEach. If you need a producer/consumer queue, you can use BlockingCollection<T> to wrap one of the concurrent collections (such as ConcurrentQueue<T> or ConcurrentStack<T>). How you use that is up to you; there's a blog post here going into a detailed example, and there are probably other similar posts around too. (You might want to look at the Parallel Team Blog for a lot more material.)

You could take a look at a Producer/Consumer pattern if you are unfortunate enough not to be using .net 4.
Here is my code I have disassembled, my apologies for the mess but you should be able to use this by adding to a project and recompiling, then creating your process using the resulting dll.
Enum for ChannelState:
public enum ChannelState
{
WaitingForSend,
WaitingForReceive,
Open
}
Interfaces:
public interface IChannel<TMessage>
{
// Methods
TMessage Receive();
void Send(TMessage message);
// Properties
bool CanReceive { get; }
bool CanSend { get; }
ChannelState State { get; }
}
using System;
public interface IReceiver<TMessage>
{
// Events
event EventHandler<MessageReceivedEventArgs<TMessage>> MessageReceived;
// Methods
void Activate();
void Deactivate();
// Properties
bool IsActive { get; }
}
Concrete classes:
using System.Collections.Generic;
using System.Threading;
using System;
public class BufferedChannel<TMessage> : IChannel<TMessage>
{
// Fields
private int _blockedReceivers;
private int _blockedSenders;
private Queue<TMessage> _buffer;
private int _capacity;
private EventWaitHandle _capacityAvailableEvent;
private EventWaitHandle _messagesAvailableEvent;
// Methods
public BufferedChannel()
{
this._buffer = new Queue<TMessage>();
this._messagesAvailableEvent = new EventWaitHandle(false, EventResetMode.AutoReset);
this._capacityAvailableEvent = new EventWaitHandle(true, EventResetMode.AutoReset);
this._capacity = 50;
}
public BufferedChannel(int bufferSize)
{
this._buffer = new Queue<TMessage>();
this._messagesAvailableEvent = new EventWaitHandle(false, EventResetMode.AutoReset);
this._capacityAvailableEvent = new EventWaitHandle(true, EventResetMode.AutoReset);
this._capacity = 50;
if (bufferSize <= 0)
{
throw new ArgumentOutOfRangeException("bufferSize", bufferSize, ExceptionMessages.ChannelsBufferSizeMustBeGreaterThanZero);
}
this._capacity = bufferSize;
}
public TMessage Receive()
{
Interlocked.Increment(ref this._blockedReceivers);
try
{
this._messagesAvailableEvent.WaitOne();
}
catch
{
lock (this._buffer)
{
Interlocked.Decrement(ref this._blockedReceivers);
}
throw;
}
lock (this._buffer)
{
Interlocked.Decrement(ref this._blockedReceivers);
this._capacityAvailableEvent.Set();
if ((this._buffer.Count - 1) > this._blockedReceivers)
{
this._messagesAvailableEvent.Set();
}
return this._buffer.Dequeue();
}
}
public void Send(TMessage message)
{
Interlocked.Increment(ref this._blockedSenders);
try
{
this._capacityAvailableEvent.WaitOne();
}
catch
{
lock (this._buffer)
{
Interlocked.Decrement(ref this._blockedSenders);
}
throw;
}
lock (this._buffer)
{
Interlocked.Decrement(ref this._blockedSenders);
this._buffer.Enqueue(message);
if (this._buffer.Count < this.BufferSize)
{
this._capacityAvailableEvent.Set();
}
this._messagesAvailableEvent.Set();
}
}
// Properties
public int BufferCount
{
get
{
lock (this._buffer)
{
return this._buffer.Count;
}
}
}
public int BufferSize
{
get
{
lock (this._buffer)
{
return this._capacity;
}
}
set
{
lock (this._buffer)
{
if (value <= 0)
{
throw new ArgumentOutOfRangeException("BufferSize", value, ExceptionMessages.ChannelsBufferSizeMustBeGreaterThanZero);
}
this._capacity = value;
if ((this._blockedSenders > 0) && (this._capacity > this._buffer.Count))
{
this._capacityAvailableEvent.Set();
}
}
}
}
public bool CanReceive
{
get
{
return true;
}
}
public bool CanSend
{
get
{
return true;
}
}
public ChannelState State
{
get
{
if (this._blockedSenders > 0)
{
return ChannelState.WaitingForReceive;
}
if (this._blockedReceivers > 0)
{
return ChannelState.WaitingForSend;
}
return ChannelState.Open;
}
}
}
using System;
using System.Collections.Generic;
using System.Threading;
using System.ComponentModel;
using System.Runtime.CompilerServices;
public sealed class Receiver<TMessage> : Component, IReceiver<TMessage>
{
// Fields
private volatile bool _continue;
private object _controlLock;
private volatile bool _disposed;
private Thread _receiverThread;
private bool _receiving;
private object _receivingLock;
private object _threadLock;
[CompilerGenerated]
private IChannel<TMessage> channel;
// Events
public event EventHandler<MessageReceivedEventArgs<TMessage>> MessageReceived;
// Methods
public Receiver(IChannel<TMessage> channel)
{
this._controlLock = new object();
this._threadLock = new object();
this._receivingLock = new object();
if (channel == null)
{
throw new ArgumentNullException("channel");
}
this.Channel = channel;
}
public void Activate()
{
this.CheckDisposed();
lock (this._controlLock)
{
if (this._receiverThread != null)
{
throw new InvalidOperationException();
}
this._continue = true;
this._receiverThread = new Thread(new ThreadStart(this.RunAsync));
this._receiverThread.IsBackground = true;
this._receiverThread.Start();
}
}
private void CheckDisposed()
{
if (this._disposed)
{
throw new ObjectDisposedException(base.GetType().Name);
}
}
public void Deactivate()
{
lock (this._controlLock)
{
if (this._continue)
{
this._continue = false;
lock (this._threadLock)
{
if (this._receiverThread != null)
{
this.SafeInterrupt();
this._receiverThread.Join();
this._receiverThread = null;
}
}
}
}
}
protected override void Dispose(bool disposing)
{
base.Dispose(disposing);
if (disposing)
{
this.Deactivate();
this._disposed = true;
}
}
private void OnMessageReceived(TMessage message)
{
EventHandler<MessageReceivedEventArgs<TMessage>> messageReceived = this.MessageReceived;
if (messageReceived != null)
{
messageReceived(this, new MessageReceivedEventArgs<TMessage>(message));
}
}
private void RunAsync()
{
while (this._continue)
{
TMessage message = default(TMessage);
bool flag = false;
try
{
lock (this._receivingLock)
{
this._receiving = true;
}
message = this.Channel.Receive();
flag = true;
lock (this._receivingLock)
{
this._receiving = false;
}
Thread.Sleep(0);
}
catch (ThreadInterruptedException)
{
}
if (!this._continue)
{
if (flag)
{
this.Channel.Send(message);
return;
}
break;
}
this.OnMessageReceived(message);
}
}
private void SafeInterrupt()
{
lock (this._receivingLock)
{
lock (this._threadLock)
{
if (this._receiving && (this._receiverThread != null))
{
this._receiverThread.Interrupt();
}
}
}
}
// Properties
protected override bool CanRaiseEvents
{
get
{
return true;
}
}
public IChannel<TMessage> Channel
{
[CompilerGenerated]
get
{
return this.channel;
}
[CompilerGenerated]
private set
{
this.channel = value;
}
}
public bool IsActive
{
get
{
lock (this._controlLock)
{
return (this._receiverThread != null);
}
}
}
}
using System;
using System.Runtime.CompilerServices;
public class MessageReceivedEventArgs<TMessage> : EventArgs
{
// Fields
[CompilerGenerated]
private TMessage message;
// Methods
public MessageReceivedEventArgs(TMessage message)
{
this.Message = message;
}
// Properties
public TMessage Message
{
[CompilerGenerated]
get
{
return this.message;
}
[CompilerGenerated]
private set
{
this.message = value;
}
}
}
using System.Threading;
public class BlockingChannel<TMessage> : IChannel<TMessage>
{
// Fields
private TMessage _message;
private EventWaitHandle _messageReceiveEvent;
private EventWaitHandle _messageReceiveyEvent;
private object _sendLock;
private ChannelState _state;
private object _stateLock;
// Methods
public BlockingChannel()
{
this._state = ChannelState.Open;
this._stateLock = new object();
this._messageReceiveyEvent = new EventWaitHandle(false, EventResetMode.AutoReset);
this._messageReceiveEvent = new EventWaitHandle(false, EventResetMode.AutoReset);
this._sendLock = new object();
}
public TMessage Receive()
{
this.State = ChannelState.WaitingForSend;
this._messageReceiveyEvent.WaitOne();
this._messageReceiveEvent.Set();
this.State = ChannelState.Open;
return this._message;
}
public void Send(TMessage message)
{
lock (this._sendLock)
{
this._message = message;
this.State = ChannelState.WaitingForReceive;
this._messageReceiveyEvent.Set();
this._messageReceiveEvent.WaitOne();
}
}
// Properties
public bool CanReceive
{
get
{
return true;
}
}
public bool CanSend
{
get
{
return true;
}
}
public ChannelState State
{
get
{
lock (this._stateLock)
{
return this._state;
}
}
private set
{
lock (this._stateLock)
{
this._state = value;
}
}
}
}

Pretty old but this is the good one that I know off http://www.codeproject.com/KB/cs/inprocessasynservicesincs.aspx

Use .NET 4 tasks.
var t = Task<int>.Factory.StartNew(() => ProcessItem());
Use the ConcurrencyOptions to set the maximum degree of parallelism on that processing.
If you want to roll it yourself, use BlockingCollection<T> which provides blocking and bounding capabilities for thread-safe collections and implement a separate thread (or threads) for the consumer.

How to share data between different threads In C# using AOP?

How to share data between different threads In C# without using the static variables?
Can we create a such machanism using attribute?
Will Aspect oriented programming help in such cases?
To acheive this all the different threads should work on single object?

You can't beat the simplicity of a locked message queue. I say don't waste your time with anything more complex.
Read up on the lock statement.
lock
EDIT
Here is an example of the Microsoft Queue object wrapped so all actions against it are thread safe.
public class Queue<T>
{
/// <summary>Used as a lock target to ensure thread safety.</summary>
private readonly Locker _Locker = new Locker();
private readonly System.Collections.Generic.Queue<T> _Queue = new System.Collections.Generic.Queue<T>();
/// <summary></summary>
public void Enqueue(T item)
{
lock (_Locker)
{
_Queue.Enqueue(item);
}
}
/// <summary>Enqueues a collection of items into this queue.</summary>
public virtual void EnqueueRange(IEnumerable<T> items)
{
lock (_Locker)
{
if (items == null)
{
return;
}
foreach (T item in items)
{
_Queue.Enqueue(item);
}
}
}
/// <summary></summary>
public T Dequeue()
{
lock (_Locker)
{
return _Queue.Dequeue();
}
}
/// <summary></summary>
public void Clear()
{
lock (_Locker)
{
_Queue.Clear();
}
}
/// <summary></summary>
public Int32 Count
{
get
{
lock (_Locker)
{
return _Queue.Count;
}
}
}
/// <summary></summary>
public Boolean TryDequeue(out T item)
{
lock (_Locker)
{
if (_Queue.Count > 0)
{
item = _Queue.Dequeue();
return true;
}
else
{
item = default(T);
return false;
}
}
}
}
EDIT 2
I hope this example helps.
Remember this is bare bones.
Using these basic ideas you can safely harness the power of threads.
public class WorkState
{
private readonly Object _Lock = new Object();
private Int32 _State;
public Int32 GetState()
{
lock (_Lock)
{
return _State;
}
}
public void UpdateState()
{
lock (_Lock)
{
_State++;
}
}
}
public class Worker
{
private readonly WorkState _State;
private readonly Thread _Thread;
private volatile Boolean _KeepWorking;
public Worker(WorkState state)
{
_State = state;
_Thread = new Thread(DoWork);
_KeepWorking = true;
}
public void DoWork()
{
while (_KeepWorking)
{
_State.UpdateState();
}
}
public void StartWorking()
{
_Thread.Start();
}
public void StopWorking()
{
_KeepWorking = false;
}
}
private void Execute()
{
WorkState state = new WorkState();
Worker worker = new Worker(state);
worker.StartWorking();
while (true)
{
if (state.GetState() > 100)
{
worker.StopWorking();
break;
}
}
}

You can pass an object as argument to the Thread.Start and use it as a shared data storage between the current thread and the initiating thread.
You can also just directly access (with the appropriate locking of course) your data members, if you started the thread using the instance form of the ThreadStart delegate.
You can't use attributes to create shared data between threads. You can use the attribute instances attached to your class as a data storage, but I fail to see how that is better than using static or instance data members.

Look at the following example code:
public class MyWorker
{
public SharedData state;
public void DoWork(SharedData someData)
{
this.state = someData;
while (true) ;
}
}
public class SharedData {
X myX;
public getX() { etc
public setX(anX) { etc
}
public class Program
{
public static void Main()
{
SharedData data = new SharedDate()
MyWorker work1 = new MyWorker(data);
MyWorker work2 = new MyWorker(data);
Thread thread = new Thread(new ThreadStart(work1.DoWork));
thread.Start();
Thread thread2 = new Thread(new ThreadStart(work2.DoWork));
thread2.Start();
}
}
In this case, the thread class MyWorker has a variable state. We initialise it with the same object. Now you can see that the two workers access the same SharedData object. Changes made by one worker are visible to the other.
You have quite a few remaining issues. How does worker 2 know when changes have been made by worker 1 and vice-versa? How do you prevent conflicting changes? Maybe read: this tutorial.

When you start a thread you are executing a method of some chosen class. All attributes of that class are visible.
Worker myWorker = new Worker( /* arguments */ );
Thread myThread = new Thread(new ThreadStart(myWorker.doWork));
myThread.Start();
Your thread is now in the doWork() method and can see any atrributes of myWorker, which may themselves be other objects. Now you just need to be careful to deal with the cases of having several threads all hitting those attributes at the same time.

Automatically terminating non essential threads in C#

I have an object in C# on which I need to execute a method on a regular basis. I would like this method to be executed only when other people are using my object, as soon as people stop using my object I would like this background operation to stop.
So here is a simple example is this (which is broken):
class Fish
{
public Fish()
{
Thread t = new Thread(new ThreadStart(BackgroundWork));
t.IsBackground = true;
t.Start();
}
public void BackgroundWork()
{
while(true)
{
this.Swim();
Thread.Sleep(1000);
}
}
public void Swim()
{
Console.WriteLine("The fish is Swimming");
}
}
The problem is that if I new a Fish object anywhere, it never gets garbage collected, cause there is a background thread referencing it. Here is an illustrated version of broken code.
public void DoStuff()
{
Fish f = new Fish();
}
// after existing from this method my Fish object keeps on swimming.
I know that the Fish object should be disposable and I should clean up the thread on dispose, but I have no control over my callers and can not ensure dispose is called.
How do I work around this problem and ensure the background threads are automatically disposed even if Dispose is not called explicitly?

Here is my proposed solution to this problem:
class Fish : IDisposable
{
class Swimmer
{
Thread t;
WeakReference fishRef;
public ManualResetEvent terminate = new ManualResetEvent(false);
public Swimmer(Fish3 fish)
{
this.fishRef = new WeakReference(fish);
t = new Thread(new ThreadStart(BackgroundWork));
t.IsBackground = true;
t.Start();
}
public void BackgroundWork()
{
bool done = false;
while(!done)
{
done = Swim();
if (!done)
{
done = terminate.WaitOne(1000, false);
}
}
}
// this is pulled out into a helper method to ensure
// the Fish object is referenced for the minimal amount of time
private bool Swim()
{
bool done;
Fish fish = Fish;
if (fish != null)
{
fish.Swim();
done = false;
}
else
{
done = true;
}
return done;
}
public Fish Fish
{
get { return fishRef.Target as Fish3; }
}
}
Swimmer swimmer;
public Fish()
{
swimmer = new Swimmer(this);
}
public void Swim()
{
Console.WriteLine("The third fish is Swimming");
}
volatile bool disposed = false;
public void Dispose()
{
if (!disposed)
{
swimmer.terminate.Set();
disposed = true;
GC.SuppressFinalize(this);
}
}
~Fish()
{
if(!disposed)
{
Dispose();
}
}
}

I think the IDisposable solution is the correct one.
If the users of your class don't follow the guidelines for using classes that implement IDisposable it's their fault - and you can make sure that the documentation explicitly mentions how the class should be used.
Another, much messier, option would be a "KeepAlive" DateTime field that each method called by your client would update. The worker thread then checks the field periodically and exits if it hasn't been updated for a certain amount of time. When a method is setting the field the thread will be restarted if it has exited.

This is how I would do it:
class Fish3 : IDisposable
{
Thread t;
private ManualResetEvent terminate = new ManualResetEvent(false);
private volatile int disposed = 0;
public Fish3()
{
t = new Thread(new ThreadStart(BackgroundWork));
t.IsBackground = true;
t.Start();
}
public void BackgroundWork()
{
while(!terminate.WaitOne(1000, false))
{
Swim();
}
}
public void Swim()
{
Console.WriteLine("The third fish is Swimming");
}
public void Dispose()
{
if(Interlocked.Exchange(ref disposed, 1) == 0)
{
terminate.Set();
t.Join();
GC.SuppressFinalize(this);
}
}
~Fish3()
{
if(Interlocked.Exchange(ref disposed, 1) == 0)
{
Dispose();
}
}
}