Properly dispose of event producer from a different thread - c#

This is SIMPLIFIED code just illustrating a problem I am trying to solve (haven't compiled it so please ignore any syntax errors). Suppose I have a ProducerProxy like:
public class ProducerProxy : IDisposable {
public event EventHandler<EventArgs> NotificationEvent;
private volatile bool itsKeepProducing = true;
public DoStuff() {
Task.Factory.StartNew(() => {
while (itsKeepProducing) {
RaiseNotificationEvent();
Thread.Sleep(100);
}
}
}
public void Dispose() {
itsKeepProducing = false;
DestroySomeStuff();
}
}
Suppose I now have a class that uses this ProducerProxy:
public class Consumer : IDisposable {
private ProducerProxy itsProducerProxy;
public void Consumer() {
itsProducerProxy = new ProducerProxy();
itsProducerProxy.NotificationEvent += OnNotificationEvent;
}
public void Start() {
itsProducerProxy.DoStuff();
}
public void OnNotificationEvent(object sender, EventArgs args) {
DealWithNotification(args); //this could take some time maybe 1-2 seconds
}
public void Dispose() {
//how do I dispose of the producer here?
//I can't just do the following because notifications might still be processing in OnNotification event:
if (itsProducerProxy != null) {
itsProducerProxy.NotificationEvent -= OnNotificationEvent;
itsProducerProxy.Dispose();
itsProducerProxy = null;
}
}
So my use case is (yes, it should be done using try/catch or using using but that distracts from the question -- just illustrating a point)
var consumer = new Consumer();
consumer.Start();
... //do some stuff
consumer.Dispose();
What is the correct/proper thread-safe implementation for Consumer.Dispose()? or maybe for Producer.Dispose()?

You can use the cooperative thread cancellation pattern by passing in a CancellationToken into your process...
public class Consumer : IDisposable {
private ProducerProxy itsProducerProxy;
// how we signal others that we are disposed
private CancellationTokenSource _cts = new CancellationTokenSource();
/* SNIP */
public void OnNotificationEvent(object sender, EventArgs args) {
// We now provide the inner process with the cancellation token
DealWithNotification(_cts.Token);
}
public void Dispose()
{
// not thread safe but you get the gist
if (_cts!= null) {
_cts.Cancel();
_cts.Dispose();
_cts = null;
}
/* SNIP */
}
}
where the inner process short circuits when cancellation has been requested
private void DealWithNotification(CancellationToken token)
{
if(token.IsCancellationRequested) return;
var foo = "omgwtflol" + bar;
if(token.IsCancellationRequested) return;
Thread.Sleep(2);
if(token.IsCancellationRequested) return;
var reallyEveryTime = File.ReadAllBytes(foo);
if(token.IsCancellationRequested) return;
foreach(var b in reallyEveryTime)
{
if(token.IsCancellationRequested) return;
InnerProcess(token);
}
// etc etc etc you get the idea
}

Related

Object received as null when dispatched through an event

I have a fairly basic Logger
public class Logger: ILogger
{
public event EventHandler<MessageLoggedArgs> MessageLogged;
...
public void LogMessage(string msg, LogType logType)
{
var logItem = new LogItem(msg, logType);
addLogMessage(logItem);
}
private void addLogMessage(LogItem logItem)
{
MessageLogged?.Invoke(this, new MessageLoggedArgs(logItem));
}
}
public class MessageLoggedArgs
{
public LogItem LogItem {get;}
public MessageLoggedArgs(LogItem logitem)
{
LogItem = logItem;
}
}
public class LogsProcessor
{
public LogsProcessor(ILogger logger)
{
_logger = logger;
_logger.MessageLogged += OnMessageLogged;
}
private volatile List<LogItem> buffer = new List<LogItem>();
private ManualResetEvent ev = new ManualResetEvent(true);
private void OnMessageLogged(object sender, MessageLoggerArgs e)
{
buffer.Add(e.LogItem);
ev.Set();
}
//Runs on a thread
private void process()
{
while(true)
{
ev.WaitOne(Timeout.Infinite);
if(buffer.Count != 0)
{
while(buffer.Count != 0)
{
var item = logbuffer[0];
buffer.RemoveAt(0);
Application.Current.Dispatcher.BeginInvoke
( new Action( () => { //Log to UI }));
}
}
else
ev.Reset();
}
}
}
The consumer of this class receives some null objects when a lot of logs are generated. Is it possible that the objects are being garbage collected? If yes, then how is it possible that the logs are garbage collected, even though there is always a reference to the object alive inside of the MessageLoggedAgs.
This has me baffled.
Edit: Turns out that the problem is somehow because of accessing the buffer using a thread. I was able to eliminate the issue by using a ConcurrentQueue. However, I don't know where exactly the issue was earlier. I thought it wouldn't be an issue if I was accessing buffer using a single thread.

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();
}
}

Waiting for a 3rd party thread to finish

I need to call a 3rd party code that optionally starts a new thread, performs some processing, and then calls a different method on my object. What I need is wait for the 3rd party processing to be finished, then return from the original method. In other words, I have a class like this (C#):
class MyClass: IThirdPartyInterface {
void MyMethod() {
//some preprocessing
//call a 3rd party static method
ThirdParty.DoSomething(this);
}
void FinishedProcessing() {
//some postprocessing
//???
}
}
I want to modify MyMethod so that it return only after the thread that started in DoSomething has finished its execution and called the FinishedProcessing method. Since the thread is started by the third party code, I don't have access to it, so I cannot use Thread.Join here. So, what do I do instead?
You need to use an System.Threading.AutoResetEvent, it would be like this:
class MyClass: IThirdPartyInterface {
AutoResetEvent _event = new AutoResetEvent(false);
void MyMethod() {
ThirdParty.DoSomething(this);
_event.WaitOne();
}
void FinishedProcessing() {
_event.Set();
}
}
If the thread continues running after your FinishedProcessing method is called by the 3rdparty class, it would be a little diferent:
class MyClass: IThirdPartyInterface {
AutoResetEvent _event = new AutoResetEvent(false);
Thread _thread;
void MyMethod() {
ThirdParty.DoSomething(this);
_event.WaitOne();
_thread.Join();
}
void FinishedProcessing() {
_thread = Thread.CurrentThread;
_event.Set();
}
}
Make your MyMethod() async and then run thirdparty method inside your custom await method, moething like this:
private async void MyMethod()
{
var result = await WaitAsynchronouslyAsync();
}
public async Task<string> WaitAsynchronouslyAsync()
{
await ThirdParty.DoSomething(this);
return "Finished";
}
If ThirdParty.DoSomething does not support async pattern
you can use additional proxy with finalizer.
But it could affect application performance like a "while(myBoolFlag){}".
class Program
{
static void Main(string[] args)
{
var list = new List<ManualResetEvent>();
for (var i = 0; i < 10000; i++)
{
var m = new ManualResetEvent(false);
list.Add(m);
new Thread(Start).Start(m);
if (i > 0 && (i % 10) == 0)
for (int j = i - 10; j < i; j++)
{
list[j].WaitOne(1000);// wait signal
GC.Collect(); //force finalizer
A.Print();
}
}
}
private static void Start(object obj)
{
new A(obj as ManualResetEvent, null);
}
}
public class A : IThirdPartyInterface
{
public static long time1;
public static long count1;
private DateTime start = DateTime.Now;
private ManualResetEvent _stop;
private IThirdPartyInterface _origin;
public A(ManualResetEvent stop, IThirdPartyInterface origin)
{
_stop = stop;
_origin = origin;
}
~A()
{
Interlocked.Increment(ref count1);
Interlocked.Add(ref time1, (long)(DateTime.Now - start).TotalMilliseconds);
_stop.Set(); //send signal
}
public static void Print()
{
Console.Write("\r" + A.time1 + "\\" + A.count1 + " ");
if (A.count1 != 0)
Console.Write((A.time1 / A.count1).ToString());
}
}

Should i pass a Backgroundworker to method

I have an app that has several methods that take a long time to complete. I am using a backgroundworker to run these methods and keep my UI responsive. My methods look something like
public void DoSomething()
{
while( HaveMoreWork )
{
// do work
}
}
Now i want the UI to be able to cancel this at any time so I have changed my methods to take a Backgroundworker like so
public void DoSomething(Backgroundworker worker)
{
while( HaveMoreWork && !worker.CancelationPending )
{
// do work
}
}
My question is, is there a better way to do this. Seems like passing a Backgroundwoker as an argument to all these methods is a bit messy. What is best practice for this?
I am using global variable
private BackgroundWorker _bwSearch = new BackgroundWorker();
private void InitializeBackgroundWorker()
{
_bwSearch = new BackgroundWorker();
_bwSearch.WorkerSupportsCancellation = true;
_bwSearch.DoWork += bwSearch_DoWork;
_bwSearch.RunWorkerCompleted += bwSearch_RunWorkerCompleted;
}
when clicked on stop button
private void btnCancel_Click(object sender, EventArgs e)
{
_bwSearch.Abort();
}
Updated:
Also I am using this simple helper class that is inherited from BackgroundWorker
public class AbortableBackgroundWorker : BackgroundWorker
{
private Thread _workerThread;
protected override void OnDoWork(DoWorkEventArgs e)
{
_workerThread = Thread.CurrentThread;
try
{
base.OnDoWork(e);
}
catch (ThreadAbortException)
{
e.Cancel = true;
Thread.ResetAbort();
}
}
public void Abort()
{
if (_workerThread != null)
{
_workerThread.Abort();
_workerThread = null;
}
}
}
public class DoSomethingService
{
private volatile bool _stopped = false;
public void Start(object socketQueueObject)
{
while (!_stopped)
{
...
}
}
public void Stop()
{
_stopped = true;
}
}
...
var doSomethingService = DoSomethingService();
doSomethingService.Start();
...
doSomethingService.Stop();

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

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