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WCF Web Socket Service - lock not working correctly

In my web socket wcf service I'm using timer elapsed event to do some logic on my object and after that send information to client (by callback object). I also track callback closed event to clean all object that I'm using in timer elapsed event handler. The problem that i occured is that, when I'm trying to dispose my object i get errors that is still working and to prevent that i try to use lock in both code (timer elapsed event and closed channel event) but it not working correctly (i'm still getting errors that i'm calling method on my object that is no allowed for this moment - this mean that timer elapsed and also call it in the same time).
Is WCF do something special which causes to lock don't work as I expected ?
Here is some of my code:
[ServiceContract(CallbackContract = typeof(IWebSocketsCallback))]
public interface IWebSockets
{
[OperationContract(IsOneWay = true, Action = "*")]
void Start(Message msg);
}
[ServiceContract]
public interface IWebSocketsCallback
{
[OperationContract(IsOneWay = true, Action = "*")]
void SendToClient(Message msg);
}
public class WebSockets : IWebSockets
{
private IWebSocketsCallback callback;
private bool handlePIChanges = false;
private PIDataPipe pipe;
private PIEventsProducer piEventsProducer;
private Timer timer;
private readonly object timerLock = new object();
private readonly object pipeLock = new object();
private bool isPipeClosed = false;
public WebSockets()
{
callback = OperationContext.Current.GetCallbackChannel<IWebSocketsCallback>();
((IChannel)callback).Closed += WebSockets_Closed;
}
public void Start(Message msg)
{
// some custom logic that i ommited ...
timer = CreateTimer();
timer.Elapsed += (sender, e) => PIQueryingCallback(pipe, timer);
}
private void WebSockets_Closed(object sender, EventArgs e)
{
lock (timerLock)
{
handlePIChanges = false;
if (timer != null)
{
timer.Stop();
timer.Dispose();
piEventsProducer.Clear();
}
}
lock (pipeLock)
{
if (pipe != null)
{
pipe.RemoveSignups(pipe.AsReadOnly()); // this cause error, because GetObserverEvents not stopped working
pipe.Close();
isPipeClosed = true;
}
}
}
private void PIQueryingCallback(PIDataPipe pipe, Timer myTimer)
{
bool moreIndicator;
AFErrors<PIPoint> errors;
lock (pipeLock)
{
do
{
if (handlePIChanges && !isPipeClosed)
{
try
{
errors = pipe.GetObserverEvents(2000, out moreIndicator); // this method calls make block for other call on this object untill it return results
}
catch (Exception e)
{
moreIndicator = false;
continue;
}
}
else
{
moreIndicator = false;
}
}
while (moreIndicator);
}
if (handlePIChanges)
{
lock (timerLock)
{
if (handlePIChanges)
{
myTimer.Start();
}
}
}
}
// this method is called after GetObserveEventsCompleted
private void HandlePIDataEventProducerChanges(string msg)
{
if (handlePIChanges && !isPipeClosed)
{
if (((IChannel)callback).State == CommunicationState.Opened)
{
try
{
callback?.SendPIDataChangesToClient(CreateMessage(msg));
}
catch (Exception ex)
{
}
}
}
}
}

How to write NFC tags while preventing WP from launching the action which is currently stored on NFC tag

I trying to allow people to write to NFC tags using my app, so that my app gets launched with a custom parameter. I want to be able to reprogram NFC tags which already have data on them.
I am using the following code but the problem is, that WP always recognizes the action which is already on the NFC tag and interrupts because it wants to launch the NFC tag action which was written anytime before.
How can I tell the OS to stop triggering the action of the tag so that I can immediately rewrite it?
public enum NfcHelperState
{
Initializing,
Waiting,
Ready,
Writing,
Finished,
Error,
NoDeviceFound
}
public class NfcHelper
{
private NfcHelperState _state = NfcHelperState.Initializing;
public NfcHelperState State
{
get { return _state; }
}
private ProximityDevice _nfcDevice;
private long _subscriptionId;
public NfcHelper()
{
Init();
}
public void Init()
{
UpdateState();
_nfcDevice = ProximityDevice.GetDefault();
if (_nfcDevice == null)
{
UpdateState(NfcHelperState.NoDeviceFound);
return;
}
UpdateState(NfcHelperState.Waiting);
}
private void UpdateState(NfcHelperState? state = null)
{
if (state.HasValue)
{
_state = state.Value;
}
if (OnStatusMessageChanged != null)
{
OnStatusMessageChanged(this, _state);
}
}
public void WriteToTag()
{
UpdateState(NfcHelperState.Ready);
_subscriptionId = _nfcDevice.SubscribeForMessage("WriteableTag", WriteableTagDetected);
}
private void WriteableTagDetected(ProximityDevice sender, ProximityMessage message)
{
UpdateState(NfcHelperState.Writing);
try
{
var str = "action=my_custom_action";
str += "\tWindowsPhone\t";
str += CurrentApp.AppId;
_nfcDevice.PublishBinaryMessage("LaunchApp:WriteTag", GetBufferFromString(str),
WriteToTagComplete);
}
catch (Exception e)
{
UpdateState(NfcHelperState.Error);
StopWaitingForTag();
}
}
private void WriteToTagComplete(ProximityDevice sender, long messageId)
{
sender.StopPublishingMessage(messageId);
UpdateState(NfcHelperState.Finished);
StopWaitingForTag();
}
private void StopWaitingForTag()
{
_nfcDevice.StopSubscribingForMessage(_subscriptionId);
}
private static IBuffer GetBufferFromString(string str)
{
using (var dw = new DataWriter())
{
dw.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf16LE;
dw.WriteString(str);
return dw.DetachBuffer();
}
}
public delegate void NfcStatusMessageChangedHandler(object myObject, NfcHelperState newState);
public event NfcStatusMessageChangedHandler OnStatusMessageChanged;
}
WriteToTag is called when a button in my app is tapped and the app waits for a writable tag. If a writable tag is recognized, WriteableTagDetected gets called and immediately starts the writing process. However, this is interrupted by the WP dialog which asks whether to perform the NFC action or not. After writing, WriteToTagComplete should be called, where StopWaitingForTag gets called and ends the write process.
I hope you guys can help me :)

Turns out I thought the wrong way. I didn't need to wait for a tag to arrive in order to rewrite it. In fact, there's no need to do _nfcDevice.SubscribeForMessage("WriteableTag", WriteableTagDetected); before writing. Just start using PublishBinaryMessage and it will write to the tag once it arrives at the device.
My final code looks like the following:
public enum NfcHelperState
{
Initializing,
Ready,
WaitingForWriting,
FinishedWriting,
ErrorWriting,
NoDeviceFound
}
public class NfcHelper
{
private NfcHelperState _state = NfcHelperState.Initializing;
public NfcHelperState State
{
get { return _state; }
}
private ProximityDevice _nfcDevice;
private long? _writingMessageId;
public NfcHelper()
{
Init();
}
public void Init()
{
UpdateState();
_nfcDevice = ProximityDevice.GetDefault();
if (_nfcDevice == null)
{
UpdateState(NfcHelperState.NoDeviceFound);
return;
}
UpdateState(NfcHelperState.Ready);
}
private void UpdateState(NfcHelperState? state = null)
{
if (state.HasValue)
{
_state = state.Value;
}
if (OnStatusMessageChanged != null)
{
OnStatusMessageChanged(this, _state);
}
}
public void WriteToTag()
{
StopWritingMessage();
UpdateState(NfcHelperState.WaitingForWriting);
try
{
var str = new StringBuilder();
str.Append("action=my_custom_action");
str.Append("\tWindowsPhone\t{");
str.Append(CurrentApp.AppId);
str.Append("}");
_writingMessageId = _nfcDevice.PublishBinaryMessage("LaunchApp:WriteTag", GetBufferFromString(str.ToString()),
WriteToTagComplete);
}
catch
{
UpdateState(NfcHelperState.ErrorWriting);
StopWritingMessage();
}
}
private void WriteToTagComplete(ProximityDevice sender, long messageId)
{
UpdateState(NfcHelperState.FinishedWriting);
StopWritingMessage();
}
private void StopWritingMessage()
{
if (_writingMessageId.HasValue)
{
_nfcDevice.StopPublishingMessage(_writingMessageId.Value);
_writingMessageId = null;
}
}
private static IBuffer GetBufferFromString(string str)
{
using (var dw = new DataWriter())
{
dw.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf16LE;
dw.WriteString(str);
return dw.DetachBuffer();
}
}
public delegate void NfcStatusMessageChangedHandler(object myObject, NfcHelperState newState);
public event NfcStatusMessageChangedHandler OnStatusMessageChanged;
}

A While Loop Thread

So I've been trying to create a bit of code that sends data on a while loop, specifically an alive packet to a server through a UdpClient.
static void doSend(string ip, int port)
{
while (isSending)
{
_sockMain = new UdpClient(ip, port);
// Code for datagram here, took it out
_sockMain.Send(arr_bData, arr_bData.Length);
}
}
But when I call the "Stop" method, it gets stuck in a constant loop and doesn't come out. How can I put the while loop into a Thread? So I can abort the thread on stop, cancelling the loop?

It hangs because your doSend method works on UI thread. You can use something like the below class to make it run on a seperate thread or you can use BackgroundWorkerClass
public class DataSender
{
public DataSender(string ip, int port)
{
IP = ip;
Port = port;
}
private string IP;
private int Port;
System.Threading.Thread sender;
private bool issending = false;
public void StartSending()
{
if (issending)
{
// it is already started sending. throw an exception or do something.
}
issending = true;
sender = new System.Threading.Thread(SendData);
sender.IsBackground = true;
sender.Start();
}
public void StopSending()
{
issending = false;
if (sender.Join(200) == false)
{
sender.Abort();
}
sender = null;
}
private void SendData()
{
System.Net.Sockets.UdpClient _sockMain = new System.Net.Sockets.UdpClient(IP, Port);
while (issending)
{
// Define and assign arr_bData somewhere in class
_sockMain.Send(arr_bData, arr_bData.Length);
}
}
}

You can use the backgroundworker thread http://www.dotnetperls.com/backgroundworker
and inside dowork() put your while loop.
You can stop the code by using CancelAsync() and set backgroundWorker1.WorkerSupportsCancellation == true
BackgroundWorker bw = new BackgroundWorker();
if (bw.IsBusy != true)
{
bw.RunWorkerAsync();
}
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
// Run your while loop here and return result.
result = // your time consuming function (while loop)
}
// when you click on some cancel button
bw.CancelAsync();

static bool _isSending;
static void doSend(string ip, int port)
{
_isSending = true;
while (_isSending)
{
_sockMain = new UdpClient(ip, port);
// ...
_sockMain.Send(arr_bData, arr_bData.Length);
}
}
static void Stop()
{
// set flag for exiting loop here
_isSending = false;
}
Also consider to name your methods in PascalCase, i.e. DoSend (even StartSending will be better), StopSending.

How about using BREAK statement?

How to use a mutex

I have one thread, that is sending data stored in a buffer of type List< string> via tcp. Another thread is writing into the buffer. As I am not very familiar with c# I'd like to know how I should use lock or Mutex correctly.
This is the code I'd like to use eventually:
while(buffer.isLocked())
{
buffer.wait();
}
buffer.lockBuffer();
buffer.add(tcpPacket);
buffer.unlockBuffer();
buffer.notify();
This is my current code. I hope someone can help me complete it.
public class Buffer
{
private Mutex mutex;
private List<string> buffer;
private bool locked = false;
public Buffer()
{
mutex = new Mutex(false);
buffer = new List<string>();
}
public bool isLocked()
{
return locked;
}
public void lockBuffer()
{
if (!locked)
{
//...
locked = true;
}
}
public void unlockBuffer()
{
if(locked)
{
mutex.ReleaseMutex();
locked = false;
}
}
public void wait()
{
mutex.WaitOne();
}
public void notify()
{
//...
}
}

It would be better if you use System.Collections.Concurrent.BlockingCollection. It doesn't require an external sync.
For those who don't use 4.0
using System;
using System.Collections.Generic;
using System.Threading;
namespace MyCollections
{
public class BlockingQueue<T> : IDisposable
{
Queue<T> _Queue = new Queue<T>();
SemaphoreSlim _ItemsInQueue = null;
SemaphoreSlim _FreeSlots = null;
int _MaxItems = -1;
public BlockingQueue(int maxItems=Int32.MaxValue)
{
_MaxItems = maxItems;
_ItemsInQueue = new SemaphoreSlim(0, maxItems);
_FreeSlots = new SemaphoreSlim(maxItems, maxItems);
}
public void Dispose()
{
if (_ItemsInQueue != null) _ItemsInQueue.Dispose();
if (_FreeSlots != null) _FreeSlots.Dispose();
}
public int Count
{
get { return _ItemsInQueue.CurrentCount; }
}
public void Add(T item)
{
if(_MaxItems != Int32.MaxValue) _FreeSlots.Wait();
lock (this)
{
_Queue.Enqueue(item);
_ItemsInQueue.Release();
}
}
public T Take()
{
T item = default(T);
_ItemsInQueue.Wait();
lock (this)
{
item = _Queue.Dequeue();
if (_MaxItems != Int32.MaxValue) _FreeSlots.Release();
}
return item;
}
}
}

The following code is not thread-safe. If two threads are entering this method at the same time, both might pass the if condition successfully.
public void lockBuffer()
{
if (!locked)
{
//...
locked = true;
}
}
You simply might want to do something like this:
lock (_sycnObject)
{
buffer.lockBuffer();
buffer.add(tcpPacket);
buffer.unlockBuffer();
buffer.notify();
}
I don't think you're doing something sophisticated that requires more than the simple to use lock-statement.

I wouldn't use Mutexes since I suppose you aren't dealing with multiple processes synchronization. Locks are pretty fine and simpler to implement:
class Buffer
{
private readonly object syncObject = new object();
private readonly List<string> buffer = new List<string>();
public void AddPacket(string packet)
{
lock (syncObject)
{
buffer.Add(packet);
}
}
public void Notify()
{
// Do something, if needed lock again here
// lock (syncObject)
// {
// Notify Implementation
// }
}
}
The usage is obviously (as you requested):
var myBuffer = new Buffer();
myBuffer.Add("Hello, World!");
myBuffer.Notify();

How do I track down a synchronization error?

I've recently made my simple graphics library multi-threaded. It is now faster - And the simulation jitters a lot, as if various places had cached old position data and then applied it after it had gone "stale".
Basically, the boxes move, then jerk back, then move, then jerk back...There's no collision as of yet, so it's not that.
Not sure what code to post.
Thanks.
Edit: Whatever it is, also causes lag spikes.
Edit2:
TaskManager:
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));
foreach (var handler in handlers)
handler.Start();
this.value = 0;
}
public void Start()
{
foreach (var handler in handlers)
handler.Wake();
}
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;
}
public 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); }
}
}
TaskHandler:
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;
}
private void Run()
{
TaskManager.MethodDel curMethod;
while (true)
{
while (!stopWhenDone || manager.GetQueueCount() > 0)
{
if (manager.GetFromQueue(out curMethod))
{
curMethod(manager.Value);
}
}
waitHandle.Set();
waitHandle.WaitOne();
}
}
public void Wake()
{
waitHandle.Set();
}
}
The main Update loop:
public virtual void Update(float timestep)
{
taskManager.Value = timestep; taskManager.Start();
foreach (Camera camera in cameraLookup.Values)
// camera.Update(timestep);
taskManager.AddToQueue(camera.Update);
taskManager.StopWhenDone();
taskManager.Wait();
/* foreach (IAffector affector in affectorLookup.Values)
affector.Update(timestep); */
foreach (IAffector affector in affectorLookup.Values)
taskManager.AddToQueue(affector.Update);
taskManager.StopWhenDone();
taskManager.Wait();
// taskManager.StopWhenDone();
// taskManager.Wait();
foreach (IConstraint constraint in constraintLookup.Values)
// constraint.Update(timestep);
taskManager.AddToQueue(constraint.Update);
taskManager.StopWhenDone();
taskManager.Wait();
foreach (Physic physic in physicLookup.Values)
// physic.Update(timestep);
taskManager.AddToQueue(physic.Update);
taskManager.StopWhenDone();
taskManager.Wait();
foreach (Body body in bodyLookup.Values)
// body.Update(timestep);
taskManager.AddToQueue(body.Update);
taskManager.StopWhenDone();
taskManager.Wait();
foreach (Model model in modelLookup.Values)
// model.Update(timestep);
taskManager.AddToQueue(model.Update);
taskManager.StopWhenDone();
taskManager.Wait();
}

How are you managing the data, can you test at the point it is read to tell if it is stale? Providing advice on a multi-threaded app is pretty difficult. You could try setting up some tracing and log the specific pieces where you think the problem might be. If you logged when data is changed and when it is read you might be able to figure out where it is going wrong.
Post some example code to show us how you manage the data and we can take it from there.

If the data is going "stale", then you need to fix your caching system to evict/update old data.
Threading really isn't that hard, the logic is simple. The problem with threading is identifying your data that is shared and not shared, tracking this data, and make sure this data is updated in the correct order. Most of this has to do with your program's structure. Structure is much much more important when you add threads into your program.