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C# cross threading with no form

i have an application which turns your webcam on and off. It turns it on, on a new thread and im trying to make a button work from the main code to turn it off buts cross threading doesnt work and as their is no form, i cant invoke. here is the code:
public class Program
{
public static FilterInfoCollection CaptureDevicesList;
public static VideoSourcePlayer videoSourcePlayer = new VideoSourcePlayer();
public static VideoCaptureDevice videoSource;
public static System.Timers.Timer TimerClose = new System.Timers.Timer();
[STAThread]
static void Main()
{
TimerClose.Elapsed += (o, e) => TimerClose_Tick();
TimerClose.Interval = 10000;
TimerClose.Start();
new Thread(() =>
{
Thread.CurrentThread.IsBackground = true;
CaptureDevicesList = new FilterInfoCollection(FilterCategory.VideoInputDevice);
Class1.oncam();
}).Start();
Application.Run();
}
private static void TimerClose_Tick()
{
Class1.CloseCurrentVideoSource(); // <--- function cant run
}
}
So what im trying to do is get the close function to work which is trying to turn the webcam off which is running on a different thread. Here is class1:
class Class1
{
public static void oncam()
{
Program.videoSource = new VideoCaptureDevice(Program.CaptureDevicesList[0].MonikerString);
OpenVideoSource(Program.videoSource);
}
public static void OpenVideoSource(IVideoSource source)
{
CloseCurrentVideoSource();
Program.videoSourcePlayer.VideoSource = source;
Program.videoSourcePlayer.Start();
}
public static void CloseCurrentVideoSource()
{
if (Program.videoSourcePlayer.VideoSource != null)
{
Program.videoSourcePlayer.SignalToStop();
for (int i = 0; i < 30; i++)
{
if (!Program.videoSourcePlayer.IsRunning)
break;
System.Threading.Thread.Sleep(100);
}
if (Program.videoSourcePlayer.IsRunning)
{
Program.videoSourcePlayer.Stop();
}
Program.videoSourcePlayer.VideoSource = null;
}
}
}
Any help is appriciated

VideoSourcePlayer inherits from System.Windows.Forms.Control and thus requires synchronization for cross-thread access.
Call Invoke on this control when accessing it from another thread.

Notify multiple background workers with a property change C#

I have a global variable called:
string tweet;
I run several background workers, that does nothing but wait on value change of the tweet variable. Then run a function called: ProcessTweet( object sender, MyCustomEventArgs args )
My question is what is the best way to handle the property changed event from all those background workers, and later process the results based on the tweet value and another argument passed to the ProcessTweet function.
I tried to take a look at INotifyPropertyChanged but I am not sure how to handle OnValueChange event from each background worker. Will it run the same ProcessTweet function once or each background worker will run an instance of that function?
EDIT:
private ITweet _LastTweet;
public ITweet LastTweet
{
get { return this._LastTweet; }
set
{
this._LastTweet = value;
}
}
Still not sure how to handle property change event the best way ^
And below is the rest of the code
private void bgworker_DoWork(object sender, DoWorkEventArgs e)
{
MyCustomClass myCustomClass = e.Argument as MyCustomClass;
//here I want to listen on the LastTweet Value Change event and handle it
}
List<BackgroundWorker> listOfBGWorkers = new List<BackgroundWorker>();
private BackgroundWorker CreateBackgroundWorker()
{
BackgroundWorker bgworker = new BackgroundWorker();
//add the DoWork etc..
bgworker.DoWork += new System.ComponentModel.DoWorkEventHandler(bgworker_DoWork);
return bgworker;
}
private void buttonStart_Click(object sender, EventArgs e)
{
for (int i = 0; i < 10; i++)
{
//Create the background workers
var bgworker = CreateBackgroundWorker();
listOfBGWorkers.Add(bgworker);
//get the MYCustomClass value;
var myCustomClass = SomeFunction();
bgworker.RunWorkerAsync(myCustomClass);
}
}

Ok - here's a small console app that demonstrates what I think you're trying to do.
It creates a 'source of tweets' in a thread.
You can subscribe to this 'source' and be notified when a new tweet 'arrives'.
You create TweetHandlers which have internal queues of tweets to process
You subscribe these TweetHandlers to the source
When a new tweet arrives, it is added to the queues of all the TweetHandlers by the event subscription
The TweetHandlers are set to run in their own Tasks. Each TweetHandler has its own delegate for performing a customizable action on a Tweet.
The code is as follows:
interface ITweet
{
object someData { get; }
}
class Tweet : ITweet
{
public object someData { get; set; }
}
class TweetSource
{
public event Action<ITweet> NewTweetEvent = delegate { };
private Task tweetSourceTask;
public void Start()
{
tweetSourceTask = new TaskFactory().StartNew(createTweetsForever);
}
private void createTweetsForever()
{
while (true)
{
Thread.Sleep(1000);
var tweet = new Tweet{ someData = Guid.NewGuid().ToString() };
NewTweetEvent(tweet);
}
}
}
class TweetHandler
{
public TweetHandler(Action<ITweet> handleTweet)
{
HandleTweet = handleTweet;
}
public void AddTweetToQueue(ITweet tweet)
{
queueOfTweets.Add(tweet);
}
public void HandleTweets(CancellationToken token)
{
ITweet item;
while (queueOfTweets.TryTake(out item, -1, token))
{
HandleTweet(item);
}
}
private BlockingCollection<ITweet> queueOfTweets = new BlockingCollection<ITweet>();
private Action<ITweet> HandleTweet;
}
class Program
{
static void Main(string[] args)
{
var handler1 = new TweetHandler(TweetHandleMethod1);
var handler2 = new TweetHandler(TweetHandleMethod2);
var source = new TweetSource();
source.NewTweetEvent += handler1.AddTweetToQueue;
source.NewTweetEvent += handler2.AddTweetToQueue;
// start up the task threads (2 of them)!
var tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;
var taskFactory = new TaskFactory(token);
var task1 = taskFactory.StartNew(() => handler1.HandleTweets(token));
var task2 = taskFactory.StartNew(() => handler2.HandleTweets(token));
// fire up the source
source.Start();
Thread.Sleep(10000);
tokenSource.Cancel();
}
static void TweetHandleMethod1(ITweet tweet)
{
Console.WriteLine("Did action 1 on tweet {0}", tweet.someData);
}
static void TweetHandleMethod2(ITweet tweet)
{
Console.WriteLine("Did action 2 on tweet {0}", tweet.someData);
}
}
The output looks like this:
Did action 2 on tweet 892dd6c1-392c-4dad-8708-ca8c6e180907
Did action 1 on tweet 892dd6c1-392c-4dad-8708-ca8c6e180907
Did action 2 on tweet 8bf97417-5511-4301-86db-3ff561d53f49
Did action 1 on tweet 8bf97417-5511-4301-86db-3ff561d53f49
Did action 2 on tweet 9c902b1f-cfab-4839-8bb0-cc21dfa301d5

Joining a thread started with StartNew()

When using the StartNew() method to kick off a process on a new thread, I need to figure out how to make another call into this object in that same thread (I assume this would be some sort of Join operation?).
The following example is dumbed down to illustrate the meat of what I am trying to do. I am well aware it is severely lacking in basic concurrency considerations. But I didn't want to cloud the code with all of that logic, so please forgive me on that.
The following console app shows what I am trying to accomplish. Assume on the StartNew() call a new thread with ID 9976 is created and the method invoked there. I would like the subsequent call to ProcessImmediate() in the file system watcher change event handler to be made on thread 9976 as well. As it stands, the call would share the same thread that is used for the file system watcher change event.
Can this be done, and if so, how?
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var runner = new Runner();
runner.Run();
Console.ReadKey();
}
}
public class Runner
{
private Activity _activity = null;
private FileSystemWatcher _fileSystemWatcher;
public void Run()
{
_activity = new Activity();
// start activity on a new thread
Task.Factory.StartNew(() => _activity.Go());
_fileSystemWatcher = new FileSystemWatcher();
_fileSystemWatcher.Filter = "*.watcher";
_fileSystemWatcher.Path = "c:\temp";
_fileSystemWatcher.Changed += FileSystemWatcher_Changed;
_fileSystemWatcher.EnableRaisingEvents = true;
}
private void FileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
{
// WANT TO CALL THIS FOR ACTIVITY RUNNING ON PREVIOUSLY CALLED THREAD
_activity.ProcessImmediate();
}
}
public class Activity
{
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
System.Threading.Thread.Sleep(2000);
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate()
{
// for purposes of this example, assume that Go is magically in its sleep state when ProcessImmediate is called
DoSomethingInteresting();
}
public bool Stop { get; set; }
}
}
* UPDATE *
Thanks for the excellent responses. I took Mike's suggestion and implemented it for my console app. Below is the full working code which also includes the use of a cancellation token. I post this in case someone else might find it useful.
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var runner = new Runner();
runner.Run();
Console.ReadKey();
runner.Stop();
Console.ReadKey();
}
}
public class Runner
{
private Activity _activity = null;
private FileSystemWatcher _fileSystemWatcher;
private CancellationTokenSource _cts = new CancellationTokenSource();
public void Stop() { _cts.Cancel(); }
public void Run()
{
_activity = new Activity();
// start activity on a new thread
var task = new Task(() => _activity.Go(_cts.Token), _cts.Token, TaskCreationOptions.LongRunning);
task.Start();
_fileSystemWatcher = new FileSystemWatcher();
_fileSystemWatcher.Filter = "*.watcher";
_fileSystemWatcher.Path = "C:\\Temp\\FileSystemWatcherPath";
_fileSystemWatcher.Changed += FileSystemWatcher_Changed;
_fileSystemWatcher.EnableRaisingEvents = true;
}
private void FileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
{
// WANT TO CALL THIS FOR ACTIVITY RUNNING ON PREVIOUSLY CALLED THREAD
_activity.ProcessImmediate();
}
}
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
public void Go(CancellationToken ct)
{
Thread.CurrentThread.Name = "Go";
while (!ct.IsCancellationRequested)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(5000);
}
Console.WriteLine("Exiting");
}
protected virtual void DoSomethingInteresting()
{
Console.WriteLine(string.Format("Doing Something Interesting on thread {0}", Thread.CurrentThread.ManagedThreadId));
}
public void ProcessImmediate()
{
// for purposes of this example, assume that Go is magically in its sleep state when ProcessImmediate is called
_processing.Set();
}
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}
}

First, you should use TaskCreationOptions.LongRunning if you are creating a task that will not complete quickly. Second, use an AutoResetEvent to signal the waiting thread to wake up. Note that below ProcessImmediate will return before DoSomethingInteresting has completed running on the other thread. Example:
using System.Threading;
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(2000);
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate()
{
_processing.Set();
}
public bool Stop { get; set; }
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}

User mike has given a better solution, which will be appropriate when you like to call the same method immediately. If you want to call a different methods immediately I'll expand mike's answer to achieve that.
using System.Threading;
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
private ConcurrentQueue<Action> actionsToProcess = new ConcurrentQueue<Action>();
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(2000);
while(!actionsToProcess.IsEmpty)
{
Action action;
if(actionsToProcess.TryDeque(out action))
action();
}
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate(Action action)
{
actionsToProcess.Enqueue(action);
_processing.Set();
}
public bool Stop { get; set; }
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}

To execute different methods on the same thread you can use a message loop that dispatches incoming requests. A simple option would be to use the event loop scheduler of the Reactive Extensions and to "recursively" schedule your Go() function - if in the mean time a different operation is scheduled it would be processed before the next Go() operation.
Here is a sample:
class Loop
: IDisposable
{
IScheduler scheduler = new EventLoopScheduler();
MultipleAssignmentDisposable stopper = new MultipleAssignmentDisposable();
public Loop()
{
Next();
}
void Next()
{
if (!stopper.IsDisposed)
stopper.Disposable = scheduler.Schedule(Handler);
}
void Handler()
{
Thread.Sleep(1000);
Console.WriteLine("Handler: {0}", Thread.CurrentThread.ManagedThreadId);
Next();
}
public void Notify()
{
scheduler.Schedule(() =>
{
Console.WriteLine("Notify: {0}", Thread.CurrentThread.ManagedThreadId);
});
}
public void Dispose()
{
stopper.Dispose();
}
}
static void Main(string[] args)
{
using (var l = new Loop())
{
Console.WriteLine("Press 'q' to quit.");
while (Console.ReadKey().Key != ConsoleKey.Q)
l.Notify();
}
}

How to wait for a thread to finish execution in C#?

I have a function that is called in rapid succession that has a open database connection.
my issue is that before one database connection is closed, another instance of the function is called and i could possibly receive a deadlock in the database.
I have tried:
private static WaitHandle[] waitHandles = new WaitHandle[]
{
new AutoResetEvent(false)
};
protected override void Broadcast(Data data, string updatedBy)
{
Action newAction = new Action(() =>
{
DataManagerFactory.PerformWithDataManager(
dataManager =>
{
// Update status and broadcast the changes
data.UpdateModifiedColumns(dataManager, updatedBy);
BroadcastManager.Instance().PerformBroadcast(
data,
BroadcastAction.Update,
Feature.None);
},
e => m_log.Error(ServerLog.ConfigIdlingRequestHandler_UpdateFailed() + e.Message));
}
);
Thread workerThread = new Thread(new ThreadStart(newAction));
ThreadPool.QueueUserWorkItem(workerThread.Start, waitHandles[0]);
WaitHandle.WaitAll(waitHandles);
}
but i recieve a thread error and the program freezes. It has something to do with the thread start function having no parameters i believe.
Thanks for any help

This is how it's done. Create class that does the job:
public class MyAsyncClass
{
public delegate void NotifyComplete(string message);
public event NotifyComplete NotifyCompleteEvent;
//Starts async thread...
public void Start()
{
System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ThreadStart(DoSomeJob));
t.Start();
}
void DoSomeJob()
{
//just wait 5 sec for nothing special...
System.Threading.Thread.Sleep(5000);
if (NotifyCompleteEvent != null)
{
NotifyCompleteEvent("My job is completed!");
}
}
}
Now this is code from another class, that calls first one:
MyAsyncClass myClass = null;
private void button2_Click(object sender, EventArgs e)
{
myClass = new MyAsyncClass();
myClass.NotifyCompleteEvent += new MyAsyncClass.NotifyComplete(myClass_NotifyCompleteEvent);
//here I start the job inside working class...
myClass.Start();
}
//here my class is notified from working class when job is completed...
delegate void myClassDelegate(string message);
void myClass_NotifyCompleteEvent(string message)
{
if (this.InvokeRequired)
{
Delegate d = new myClassDelegate(myClass_NotifyCompleteEvent);
this.Invoke(d, new object[] { message });
}
else
{
MessageBox.Show(message);
}
}
Let me know if I need to explain some details.
Alternative to this is BackgroudWorker:

C# Threading Mechanism

Let's say I have an exposed interface as such:
interface IMyService
{
MyResult MyOperation();
}
This operation is synchronous and returns a value.
My implemented interface has to do the following:
Call an asynchronous method
Wait for event #1
Wait for event #2
This is due to a 3rd party COM object I am working with.
This code looks similar to the following
public MyResult MyOperation()
{
_myCOMObject.AsyncOperation();
//Here I need to wait for both events to fire before returning
}
private void MyEvent1()
{
//My Event 1 is fired in this handler
}
private void MyEvent2()
{
//My Event 2 is fired in this handler
}
My two events can happen in either order, it is quite random.
What is the proper threading mechanism I can use to synchronize this? I was using ManualResetEvent before I had to start waiting for the second event, and have not seen an easy way to use it for both events. These 2 events set variables that allow me to create the return value for MyOperation().
Any ideas on a good implementation for this? I have no control over the way the 3rd party object is implemented.

Two ManualResetEvents should do the trick for you. Just initialize them to false before you call the _myCOMObject.AsyncOperation(). Like this:
private ManualResetEvent event1;
private ManualResetEvent event2;
public MyResult MyOperation()
{
event1 = new ManualResetEvent(false);
event2 = new ManualResetEvent(false);
_myCOMObject.AsyncOperation();
WaitHandle.WaitAll(new WaitHandle[] { event1, event2 });
}
private void MyEvent1()
{
event1.Set();
}
private void MyEvent2()
{
event2.Set();
}
Edit
Thanks for the comments. I've changed the wait call to use WaitAll

My implementation example is as follows:
namespace ConsoleApplication1
{
class Program
{
private static WaitHandle[] waitHandles;
private static event EventHandler Evt1;
private static event EventHandler Evt2;
static void Main(string[] args)
{
waitHandles = new WaitHandle[]{
new ManualResetEvent(false),
new ManualResetEvent(false)
};
Evt1 += new EventHandler(Program_Evt1);
Evt2 += new EventHandler(Program_Evt2);
OnEvt1();
OnEvt2();
WaitHandle.WaitAll(waitHandles);
Console.WriteLine("Finished");
Console.ReadLine();
}
static void Program_Evt2(object sender, EventArgs e)
{
Thread.Sleep(2000);
((ManualResetEvent)waitHandles[0]).Set();
}
static void Program_Evt1(object sender, EventArgs e)
{
((ManualResetEvent)waitHandles[1]).Set();
}
static void OnEvt1()
{
if (Evt1 != null)
Evt1(null, EventArgs.Empty);
}
static void OnEvt2()
{
if (Evt2 != null)
Evt2(null, EventArgs.Empty);
}
}
}
I make it sleep for the purposes of this example and the WaitAll functionality
Cheers,
Andrew
P.S. another example would be using AsyncCallback, really quick and dirty example, but gives you more keys to open the door with :-) . Hope this helps!!
namespace ConsoleApplication1
{
class Program
{
private static WaitHandle[] waitHandles;
private static event EventHandler Evt1;
private static event EventHandler Evt2;
static void Main(string[] args)
{
waitHandles = new WaitHandle[]{
new ManualResetEvent(false),
new ManualResetEvent(false)
};
var callabck1 = new AsyncCallback(OnEvt1);
var callabck2 = new AsyncCallback(OnEvt2);
callabck1.Invoke(new ManualResetResult(null, (ManualResetEvent)waitHandles[0]));
callabck2.Invoke(new ManualResetResult(null, (ManualResetEvent)waitHandles[1]));
WaitHandle.WaitAll(waitHandles);
Console.WriteLine("Finished");
Console.ReadLine();
}
static void OnEvt1(IAsyncResult result)
{
Console.WriteLine("Setting1");
var handle = result.AsyncWaitHandle;
((ManualResetEvent)handle).Set();
}
static void OnEvt2(IAsyncResult result)
{
Thread.Sleep(2000);
Console.WriteLine("Setting2");
var handle = result.AsyncWaitHandle;
((ManualResetEvent)handle).Set();
}
}
public class ManualResetResult : IAsyncResult
{
private object _state;
private ManualResetEvent _handle;
public ManualResetResult(object state, ManualResetEvent handle)
{
_state = state;
_handle = handle;
}
#region IAsyncResult Members
public object AsyncState
{
get { return _state; }
}
public WaitHandle AsyncWaitHandle
{
get { return _handle; }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
#endregion
}
}

I am not sure I understood your question, but AutoResetEvent.WaitAll seems to solve your problem, if I got it right. It allows you to set more than one handler and it will only be released when all are set.
http://msdn.microsoft.com/en-us/library/z6w25xa6.aspx