Develop Reference

Async thread dies on TPL await

I'm writing a simple producer/consumer application, but I'm noticing a really strange behaviour..This is the code:
private Thread _timelineThread = null;
private BufferBlock<RtpPacket> _queue = null;
private AutoResetEvent _stopping = new AutoResetEvent(false);
static void Main(string[] args)
{
// Start consumer thread
Consume();
// Produce
var t = new Thread(() =>
{
while (true)
{
var packet = RtpPacket.GetNext();
_queue.Post(packet);
Thread.Sleep(70);
}
}
t.Join();
}
static void Consume()
{
_timelineThread = new Thread(async () =>
{
while (_stopping.WaitOne(0) == false)
{
// Start consuming...
while (await _queue.OutputAvailableAsync())
{
var packet = await _queue.ReceiveAsync();
// Some processing...
}
}
});
_timelineThread.Start();
}
This is intended to be an infinite loop (until I route the _stopping signal). But, when _timelineThread hits the first await _queue.OutputAvailableAsync(), the thread changes state to 'Stopped'. There is something wrong that I'm not considering ?
If I change the Consume() function to this:
static void Consume()
{
_timelineThread = new Thread(() =>
{
while (_stopping.WaitOne(0) == false)
{
// Start consuming...
while (_queue.OutputAvailableAsync().GetAwaiter().GetResult())
{
var packet = _queue.ReceiveAsync().GetAwaiter().GetResult();
// Some processing...
}
}
});
_timelineThread.Start();
}
the thread runs without any problem..but the code is almost identical to the previous one..
EDIT: after one hour also this 'hack' doesn't seems to work..thread is 'Running' but I don't receive any data from the queue..

The Thread constructor does not understand async delegates. You can read about this here:
Is it OK to use "async" with a ThreadStart method?
Async thread body loop, It just works, but how?
My suggestion is to use a synchronous BlockingCollection<RtpPacket> instead of the BufferBlock<RtpPacket>, and consume it by enumerating the GetConsumingEnumerable method:
var _queue = new BlockingCollection<RtpPacket>();
var producer = new Thread(() =>
{
while (true)
{
var packet = RtpPacket.GetNext();
if (packet == null) { _queue.CompleteAdding(); break; }
_queue.Add(packet);
Thread.Sleep(70);
}
});
var consumer = new Thread(() =>
{
foreach (var packet in _queue.GetConsumingEnumerable())
{
// Some processing...
}
});
producer.Start();
consumer.Start();
producer.Join();
consumer.Join();

Call a Method from thread1 to thread2?

First: What I want to do?
I want to run multiple jobs on one thread, for example, I want to make a thread for calculations and always run methods inside of that.
Get a pointer like SynchronizationContext.Current or Thread.CurrentThread to access current job working.
3.A Cross-Platform way like Net Standard.
Second: Example-1 (CrossPlatform-Working) My example not working, because Post and Send method in SynchronizationContext don't work
class Program
{
static void Main(string[] args)
{
SynchronizationContext contextThread1 = null;
SynchronizationContext contextThread2 = null;
Thread thread1, thread2 = null;
thread1 = new Thread(() =>
{
SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
contextThread1 = SynchronizationContext.Current;
while (true)
{
Thread.Sleep(1000);
if (contextThread2 != null)
{
contextThread2.Post((state) =>
{
//Thread.CurrentThread == thread2 always false because the method is not runnig from thread 2
Console.WriteLine("call a method from thread 1 for thread 2 :" + (Thread.CurrentThread == thread2));
}, null);
}
}
});
thread1.IsBackground = true;
thread1.Start();
thread2 = new Thread(() =>
{
SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
contextThread2 = SynchronizationContext.Current;
while (true)
{
Thread.Sleep(1000);
if (contextThread1 != null)
{
contextThread1.Post((state) =>
{
//Thread.CurrentThread == thread1 always false because the method is not runnig from thread 1
Console.WriteLine("call a method from thread 2 for thread 1 :"+(Thread.CurrentThread == thread1));
}, null);
}
}
});
thread2.IsBackground = true;
thread2.Start();
Console.ReadKey();
}
}
Example-2: (No Cross PLatform because Windowsbase.dll): this example works fine but this is not cross platform.
class Program
{
static void Main(string[] args)
{
Dispatcher contextThread1 = null;
Dispatcher contextThread2 = null;
Thread thread1, thread2 = null;
thread1 = new Thread(() =>
{
contextThread1 = Dispatcher.CurrentDispatcher;
Dispatcher.Run();
});
thread1.IsBackground = true;
thread1.Start();
thread2 = new Thread(() =>
{
contextThread2 = Dispatcher.CurrentDispatcher;
Dispatcher.Run();
});
thread2.IsBackground = true;
thread2.Start();
while (true)
{
Thread.Sleep(1000);
if (contextThread2 != null)
{
contextThread2.Invoke(new Action(() =>
{
//Thread.CurrentThread == thread2 always false because the method is not runnig from thread 2
Console.WriteLine("call a method from thread 1 for thread 2 :" + (Thread.CurrentThread == thread2));
}));
}
if (contextThread1 != null)
{
contextThread1.Invoke(new Action(() =>
{
Console.WriteLine("call a method from thread 2 for thread 1 :" + (Thread.CurrentThread == thread1));
}));
}
}
Console.ReadKey();
}
}

You should always use a tool these days to make your life easier where possible. In this case you should use Microsoft's Reactive Framework. Just NuGet "System.Reactive" and add using System.Reactive.Linq;.
Then you can do this:
void Main()
{
var thread1 = new EventLoopScheduler();
var thread2 = new EventLoopScheduler();
Action action = () => Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
action();
thread1.Schedule(action);
Thread.Sleep(1000);
thread2.Schedule(action);
Thread.Sleep(1000);
thread2.Schedule(() =>
{
action();
thread1.Schedule(action);
});
Thread.Sleep(1000);
action();
}
The kind of output I get is:
11
12
14
14
12
11
If you follow along with the code you can see it is correctly scheduling to each thread.
When you want to shut down just call .Dispose() on each EventLoopScheduler.

Wait for RunOnUIThread to finish and continue executing the rest of the task

im developing an app for android via c#(xamarin.visual studio) , the problem is that i have some task to do that running in other threads , and when it should update the layout it should call Activity.RunOnUIThread , everything it's working well but the thread dont wait this method to finnish and continue executing the rest withuout waiting.
The question is : How to wait for RunOnUIThread to finish and after that continue executing rest of the commands of the task. ?
public void start(int threadCounter)
{
for (int i = 0; i < threadCounter; i++)
{
Thread thread1 = new Thread(new ThreadStart(RunScanTcp));
thread1.Start();
}
}
public void RunScanTcp()
{
int port;
//while there are more ports to scan
while ((port = portList.NextPort()) != -1)
{
count = port;
Thread.Sleep(1000); //lets be a good citizen to the cpu
Console.WriteLine("Current Port Count : " + count.ToString());
try
{
Connect(host, port, tcpTimeout);
}
catch
{
continue;
}
Activity.RunOnUiThread(() =>
{
mdata.Add(new data() { titulli = "Port : " + port, sekuenca = "Sequence : ", ttl = "Connection Sucessfull !", madhesia = "", koha = "Time : " });
mAdapter.NotifyItemInserted(mdata.Count() - 1);
if (ndaluar == false)
{
mRecyclerView.ScrollToPosition(mdata.Count() - 1);
}
}); // in that point i want to wait this to finish and than continue below...
Console.WriteLine("TCP Port {0} is open ", port);
}

First of all you should avoid creating new Threads.
In you case you must use ThreadPool.QueueUserWorkItem to enqueue the CPU bound operation.
Then you could use a ManualResetEventSlim or TaskCompletionSource to synchronize the the UI thread and the Worker Thread.
Example:
// mre is used to block and release threads manually. It is
// created in the unsignaled state.
ManualResetEventSlim mre = new ManualResetEventSlim(false);
RunOnUiThread(() =>
{
// Update UI here.
// Release Manual reset event.
mre.Set();
});
// Wait until UI operations end.
mre.Wait();
In your specific case:
for (int i = 0; i < threadCounter; i++)
{
ThreadPool.QueueUserWorkItem(RunScanTcp);
}
private void RunScanTcp(object stateInfo)
{
// Do CPU bound operation here.
var a = 100;
while (--a != 0)
{
// mre is used to block and release threads manually. It is
// created in the unsignaled state.
ManualResetEventSlim mre = new ManualResetEventSlim(false);
Activity.RunOnUiThread(() =>
{
// Update UI here.
// Release Manual reset event.
mre.Set();
});
// Wait until UI operation ends.
mre.WaitOne();
}
}
If you prefer to use TaskCompletionSource you could use an alternative approach:
private async void RunScanTcp(object stateInfo)
{
// Do CPU bound operation here.
var a = 100;
while (--a != 0)
{
// using TaskCompletionSource
var tcs = new TaskCompletionSource<bool>();
RunOnUiThread(() =>
{
// Update UI here.
// Set result
tcs.TrySetResult(true);
});
// Wait until UI operationds.
tcs.Task.Wait();
}
}

You could use Monitor.Wait and Monitor.Pulse with a shared myLock object to wait for the UI execution.
Activity.RunOnUiThread(() =>
{
mdata.Add(new data() { titulli = "Port : " + port, sekuenca = "Sequence : ", ttl = "Connection Sucessfull !", madhesia = "", koha = "Time : " });
mAdapter.NotifyItemInserted(mdata.Count() - 1);
if (ndaluar == false)
{
mRecyclerView.ScrollToPosition(mdata.Count() - 1);
}
lock(myLock) Monitor.Pulse(myLock)
});
lock(myLock) Monitor.Wait(myLock)
Console.WriteLine("TCP Port {0} is open ", port);

For those interested in an async/await solution, there is Stephen Cleary's AsyncManualResetEvent, e.g.:
var mre = new AsyncManualResetEvent();
this.context.RunOnUiThread(() =>
{
// Do awesome UI stuff
mre.Set();
});
await mre.WaitAsync();

Multithreading in C# with Win.Forms control

I'm beginner in C#. And i have problem with threads when i using win.forms. My application freezes. What the problem with this code? I'm using microsoft example from msdn.
Here's my code:
delegate void SetTextCallback(object text);
private void WriteString(object text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(WriteString);
this.Invoke(d, new object[] { text });
}
else
{
for (int i = 0; i <= 1000; i++)
{
this.textBox1.Text = text.ToString();
}
}
}
private void button1_Click(object sender, EventArgs e)
{
Thread th_1 = new Thread(WriteString);
Thread th_2 = new Thread(WriteString);
Thread th_3 = new Thread(WriteString);
Thread th_4 = new Thread(WriteString);
th_1.Priority = ThreadPriority.Highest; // самый высокий
th_2.Priority = ThreadPriority.BelowNormal; // выше среднего
th_3.Priority = ThreadPriority.Normal; // средний
th_4.Priority = ThreadPriority.Lowest; // низкий
th_1.Start("1");
th_2.Start("2");
th_3.Start("3");
th_4.Start("4");
th_1.Join();
th_2.Join();
th_3.Join();
th_4.Join();
}

There is a deadlock - UI thread is waiting for threads to complete with Thread.Join() while the worker threads are trying to send a message to UI using blocking Control.Invoke(). Replacing the Invoke in the thread code by BeginInvoke() will make the deadlock go away
if (this.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(WriteString);
// BeginInvoke posts message to UI thread asyncronously
this.BeginInvoke(d, new object[] { text });
}
else
{
this.textBox1.Text = text.ToString();
}

It freezes because of the Join calls. Thread.Join() makes the current thread wait after another one is complete.

Measuring thread running time

public void Foo(IRB inR) {
Stopwatch sw = new Stopwatch();
sw.Start();
System.Threading.Thread theThread = new System.Threading.Thread(delegate() {
if (inR.Ready) {
inR.ABC();
while (!inR.Ready) { Thread.Sleep(100); }
}
mP.CP = false;
});
theThread.Name = "aaabbbccc";
theThread.Start();
}
So, I want use StopWatch measuring the time that "theThread" running. (Actually, I want to measure time from creating of this thread to end of thread.)
I already put stopwatch.start() where I want. But where should I put my stopwatch.stop()?
Thank you.

Why not put the stopwatch code in the thread itself? For example:
public class ThreadTimer
{
private readonly ThreadStart realWork;
public ThreadTimer(ThreadStart realWork)
{
this.realWork = realWork;
}
public void TimeAndExecute()
{
Stopwatch stopwatch = Stopwatch.StartNew();
try
{
realWork();
}
finally
{
stopwatch.Stop();
// Log or whatever here
}
}
}
Then:
ThreadStart work = delegate() {
if (inR.Ready) {
inR.ABC();
while (!inR.Ready) { Thread.Sleep(100); }
}
mP.CP = false;
};
ThreadTimer timer = new ThreadTimer(work);
Thread thread = new Thread(timer.TimeAndExecute);
thread.Start();

Can you put it at the end of your delegate?
You'd have to join the background thread with the running thread if you create the Stopwatch object as a variable local to your function. Or, you can create it outside the function to let the thread run without joining.
public void ConditionPlate(IRB inR)
{
Stopwatch sw = new Stopwatch();
sw.Start();
System.Threading.Thread theThread = new System.Threading.Thread(delegate()
{
if (inR.Ready)
{
inR.ABC();
while (!inR.Ready) { Thread.Sleep(100); }
}
mP.CP = false;
// ********************************
// This will stop the stopwatch.
// ********************************
sw.Stop();
});
theThread.Name = "aaabbbccc";
theThread.Start();
// Wait for the thread to stop (necessary if 'sw' is created here, locally)
theThread.Join();
// gets time required for creation of thread to thread completion.
var elapsed = sw.Elapsed;
}