Why does this not work?
What I am trying to do: I need a way to run specific methods in a specific thread that lives on till the end of the program.
My other possible options: As I understand a possible way to do it would be to implement a queue. Into which I could push in methods I want to be run in the specific thread. In the specific thread, I would be spinning and sleeping / monitor.pulse to see if there are delegates waiting to be run in the queue.
My objective: Is to avoid all the hardwork to create the delegate queue, maintain lock etc. It appears that a ready made solution exists in the WPF world called Dispatcher. WPF controls mostly inherit from DispatcherObject and somehow the whole thing works. What do I have to do to get this work?
using System;
using System.Threading;
using System.Windows.Threading;
namespace ThreadingTrials
{
class Program
{
[STAThread]
static void Main(string[] args)
{
Thread.CurrentThread.Name = "mainThread";
Engine engine = new Engine();
Console.WriteLine("initializing SpecialEngine from {0}", Thread.CurrentThread.Name);
engine.initialize();
engine.doWork();
}
}
class Engine:DispatcherObject
{
private EventWaitHandle InitializationComplete;
private EventWaitHandle newWorkComplete;
//private Dispatcher dispatcher;
public Engine()
{
}
public void initialize()
{
InitializationComplete = new EventWaitHandle(false, EventResetMode.ManualReset);
Thread thread = new Thread(new ParameterizedThreadStart((hwnd)=>
{
InitializeSpecialEngineObject();
while (true) ;
}));
thread.Name = "Special Engine Thread";
thread.SetApartmentState(ApartmentState.STA);
thread.Priority = ThreadPriority.Normal;
thread.Start();
Console.WriteLine("waiting for initialize at {0}", Thread.CurrentThread.Name);
InitializationComplete.WaitOne();
}
private void InitializeSpecialEngineObject()
{
Console.WriteLine("doing initialization at {0}", Thread.CurrentThread.Name);
Thread.Sleep(500);
//dispatcher = Dispatcher.CurrentDispatcher;
InitializationComplete.Set();
}
internal void doWork()
{
newWorkComplete = new EventWaitHandle(false, EventResetMode.AutoReset);
//Dispatcher.Thread.Suspend();
Dispatcher.Invoke((SendOrPostCallback)delegate
{
Console.WriteLine("dispatched to {0}", Thread.CurrentThread.Name);
Thread.Sleep(500);
newWorkComplete.Set();
},DispatcherPriority.Background, null);
Dispatcher.Thread.Resume();
Console.WriteLine("waiting for new work to complete at {0}", Thread.CurrentThread.Name);
newWorkComplete.WaitOne();
}
private void doingWork()
{
Console.WriteLine("Doing work in {0}", Thread.CurrentThread.Name);
Thread.Sleep(500);
}
}
}
Thanks for the input. Fair enough. It was actually very little work to make a simple worker thread that waits for an event signifying a new task in queue of void() delegates, and runs them as they become available. I copied most of the code from a website online... Sorry lost reference. I had done it on that day, and should have edited this post earlier.
using System;
using System.Threading;
using System.Collections.Generic;
class ProducerConsumerQueue : IDisposable
{
EventWaitHandle _wh = new AutoResetEvent(false);
Thread _worker;
readonly object _locker = new object();
Queue<Action> _tasks = new Queue<Action>();
public delegate void Action();
public ProducerConsumerQueue()
{
_worker = new Thread(Work);
_worker.Start();
}
public void EnqueueTask(Action work)
{
lock (_locker) _tasks.Enqueue(work);
_wh.Set();
}
public void Dispose()
{
EnqueueTask(null); // Signal the consumer to exit.
_worker.Join(); // Wait for the consumer's thread to finish.
_wh.Close(); // Release any OS resources.
}
void Work()
{
while (true)
{
Action task = null;
lock (_locker)
if (_tasks.Count > 0)
{
task = _tasks.Dequeue();
if (task == null) return;
}
if (task != null)
{
task.Invoke();
}
else
_wh.WaitOne(); // No more tasks - wait for a signal
}
}
}
class Program
{
static void Main()
{
using (ProducerConsumerQueue q = new ProducerConsumerQueue())
{
q.EnqueueTask(delegate
{
Console.WriteLine("Performing task: Hello");
Thread.Sleep(1000); // simulate work...
});
for (int i = 0; i < 10; i++) q.EnqueueTask(delegate
{
Console.WriteLine("Performing task: "+ i);
Thread.Sleep(1000); // simulate work...
});
q.EnqueueTask(delegate
{
Console.WriteLine("Performing task: Goodbye!");
Thread.Sleep(1000); // simulate work...
});
}
// Exiting the using statement calls q's Dispose method, which
// enqueues a null task and waits until the consumer finishes.
}
}
You don't call Dispatcher.Run. You're assuming that a Dispatcher contains a Thread that does its work, but this is backwards. The first time that Dispatcher.CurrentDispatcher is called, a Dispatcher is created bound to the current thread. Note that even though your code doesn't call CurrentDispatcher directly, it does do so indirectly by constructing a DispatcherObject (which captures CurrentDispatcher into a field).
Review the WPF threading model docs, which contain all the details you need.
If you want dispatcher-like functionality in a child thread but don't want to take a dependency on WPF, you can use the ActionThread class from Nito.Async, which is roughly equivalent to a Dispatcher plus a dedicated Thread.