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IAsyncEnumerable like a Source for akka streams

I want to use IAsyncEnumerable like a Source for akka streams. But I not found, how do it.
No sutiable method in Source class for this code.
using System.Collections.Generic;
using System.Threading.Tasks;
using Akka.Streams.Dsl;
namespace ConsoleApp1
{
class Program
{
static async Task Main(string[] args)
{
Source.From(await AsyncEnumerable())
.Via(/*some action*/)
//.....
}
private static async IAsyncEnumerable<int> AsyncEnumerable()
{
//some async enumerable
}
}
}
How use IAsyncEnumerbale for Source?

This has been done in the past as a part of Akka.NET Streams contrib package, but since I don't see it there anymore, let's go through on how to implement such source. The topic can be quite long, as:
Akka.NET Streams is really about graph processing - we're talking about many-inputs/many-outputs configurations (in Akka.NET they're called inlets and outlets) with support for cycles in graphs.
Akka.NET is not build on top of .NET async/await or even on top of .NET standard thread pool library - they're both pluggable, which means that the lowest barier is basically using callbacks and encoding what C# compiler sometimes does for us.
Akka.NET streams is capable of both pushing and pulling values between stages/operators. IAsyncEnumerable<T> can only pull data while IObservable<T> can only push it, so we get more expressive power here, but this comes at a cost.
The basics of low level API used to implement custom stages can be found in the docs.
The starter boilerplate looks like this:
public static class AsyncEnumerableExtensions {
// Helper method to change IAsyncEnumerable into Akka.NET Source.
public static Source<T, NotUsed> AsSource<T>(this IAsyncEnumerable<T> source) =>
Source.FromGraph(new AsyncEnumerableSource<T>(source));
}
// Source stage is description of a part of the graph that doesn't consume
// any data, only produce it using a single output channel.
public sealed class AsyncEnumerableSource<T> : GraphStage<SourceShape<T>>
{
private readonly IAsyncEnumerable<T> _enumerable;
public AsyncEnumerableSource(IAsyncEnumerable<T> enumerable)
{
_enumerable = enumerable;
Outlet = new Outlet<T>("asyncenumerable.out");
Shape = new SourceShape<T>(Outlet);
}
public Outlet<T> Outlet { get; }
public override SourceShape<T> Shape { get; }
/// Logic if to a graph stage, what enumerator is to enumerable.
protected override GraphStageLogic CreateLogic(Attributes inheritedAttributes) =>
new Logic(this);
sealed class Logic: OutGraphStageLogic
{
public override void OnPull()
{
// method called whenever a consumer asks for new data
}
public override void OnDownstreamFinish()
{
// method called whenever a consumer stage finishes,used for disposals
}
}
}
As mentioned, we don't use async/await straight away here: even more, calling Logic methods in asynchronous context is unsafe. To make it safe we need to register out methods that may be called from other threads using GetAsyncCallback<T> and call them via returned wrappers. This will ensure, that not data races will happen when executing asynchronous code.
sealed class Logic : OutGraphStageLogic
{
private readonly Outlet<T> _outlet;
// enumerator we'll call for MoveNextAsync, and eventually dispose
private readonly IAsyncEnumerator<T> _enumerator;
// callback called whenever _enumerator.MoveNextAsync completes asynchronously
private readonly Action<Task<bool>> _onMoveNext;
// callback called whenever _enumerator.DisposeAsync completes asynchronously
private readonly Action<Task> _onDisposed;
// cache used for errors thrown by _enumerator.MoveNextAsync, that
// should be rethrown after _enumerator.DisposeAsync
private Exception? _failReason = null;
public Logic(AsyncEnumerableSource<T> source) : base(source.Shape)
{
_outlet = source.Outlet;
_enumerator = source._enumerable.GetAsyncEnumerator();
_onMoveNext = GetAsyncCallback<Task<bool>>(OnMoveNext);
_onDisposed = GetAsyncCallback<Task>(OnDisposed);
}
// ... other methods
}
The last part to do are methods overriden on `Logic:
OnPull used whenever the downstream stage calls for new data. Here we need to call for next element of async enumerator sequence.
OnDownstreamFinish called whenever the downstream stage has finished and will not ask for any new data. It's the place for us to dispose our enumerator.
Thing is these methods are not async/await, while their enumerator's equivalent are. What we basically need to do there is to:
Call corresponding async methods of underlying enumerator (OnPull → MoveNextAsync and OnDownstreamFinish → DisposeAsync).
See, if we can take their results immediately - it's important part that usually is done for us as part of C# compiler in async/await calls.
If not, and we need to wait for the results - call ContinueWith to register our callback wrappers to be called once async methods are done.
sealed class Logic : OutGraphStageLogic
{
// ... constructor and fields
public override void OnPull()
{
var hasNext = _enumerator.MoveNextAsync();
if (hasNext.IsCompletedSuccessfully)
{
// first try short-path: values is returned immediately
if (hasNext.Result)
// check if there was next value and push it downstream
Push(_outlet, _enumerator.Current);
else
// if there was none, we reached end of async enumerable
// and we can dispose it
DisposeAndComplete();
}
else
// we need to wait for the result
hasNext.AsTask().ContinueWith(_onMoveNext);
}
// This method is called when another stage downstream has been completed
public override void OnDownstreamFinish() =>
// dispose enumerator on downstream finish
DisposeAndComplete();
private void DisposeAndComplete()
{
var disposed = _enumerator.DisposeAsync();
if (disposed.IsCompletedSuccessfully)
{
// enumerator disposal completed immediately
if (_failReason is not null)
// if we close this stream in result of error in MoveNextAsync,
// fail the stage
FailStage(_failReason);
else
// we can close the stage with no issues
CompleteStage();
}
else
// we need to await for enumerator to be disposed
disposed.AsTask().ContinueWith(_onDisposed);
}
private void OnMoveNext(Task<bool> task)
{
// since this is callback, it will always be completed, we just need
// to check for exceptions
if (task.IsCompletedSuccessfully)
{
if (task.Result)
// if task returns true, it means we read a value
Push(_outlet, _enumerator.Current);
else
// otherwise there are no more values to read and we can close the source
DisposeAndComplete();
}
else
{
// task either failed or has been cancelled
_failReason = task.Exception as Exception ?? new TaskCanceledException(task);
FailStage(_failReason);
}
}
private void OnDisposed(Task task)
{
if (task.IsCompletedSuccessfully) CompleteStage();
else {
var reason = task.Exception as Exception
?? _failReason
?? new TaskCanceledException(task);
FailStage(reason);
}
}
}

As of Akka.NET v1.4.30 this is now natively supported inside Akka.Streams via the RunAsAsyncEnumerable method:
var input = Enumerable.Range(1, 6).ToList();
var cts = new CancellationTokenSource();
var token = cts.Token;
var asyncEnumerable = Source.From(input).RunAsAsyncEnumerable(Materializer);
var output = input.ToArray();
bool caught = false;
try
{
await foreach (var a in asyncEnumerable.WithCancellation(token))
{
cts.Cancel();
}
}
catch (OperationCanceledException e)
{
caught = true;
}
caught.ShouldBeTrue();
I copied that sample from the Akka.NET test suite, in case you're wondering.

You can also use an existing primitive for streaming large collections of data. Here is an example of using Source.unfoldAsync to stream pages of data - in this case github repositories using Octokit - until there is no more.
var source = Source.UnfoldAsync<int, RepositoryPage>(startPage, page =>
{
var pageTask = client.GetRepositoriesAsync(page, pageSize);
var next = pageTask.ContinueWith(task =>
{
var page = task.Result;
if (page.PageNumber * pageSize > page.Total) return Option<(int, RepositoryPage)>.None;
else return new Option<(int, RepositoryPage)>((page.PageNumber + 1, page));
});
return next;
});
To run
using var sys = ActorSystem.Create("system");
using var mat = sys.Materializer();
int startPage = 1;
int pageSize = 50;
var client = new GitHubClient(new ProductHeaderValue("github-search-app"));
var source = ...
var sink = Sink.ForEach<RepositoryPage>(Console.WriteLine);
var result = source.RunWith(sink, mat);
await result.ContinueWith(_ => sys.Terminate());
class Page<T>
{
public Page(IReadOnlyList<T> contents, int page, long total)
{
Contents = contents;
PageNumber = page;
Total = total;
}
public IReadOnlyList<T> Contents { get; set; } = new List<T>();
public int PageNumber { get; set; }
public long Total { get; set; }
}
class RepositoryPage : Page<Repository>
{
public RepositoryPage(IReadOnlyList<Repository> contents, int page, long total)
: base(contents, page, total)
{
}
public override string ToString() =>
$"Page {PageNumber}\n{string.Join("", Contents.Select(x => x.Name + "\n"))}";
}
static class GitHubClientExtensions
{
public static async Task<RepositoryPage> GetRepositoriesAsync(this GitHubClient client, int page, int size)
{
// specify a search term here
var request = new SearchRepositoriesRequest("bootstrap")
{
Page = page,
PerPage = size
};
var result = await client.Search.SearchRepo(request);
return new RepositoryPage(result.Items, page, result.TotalCount);
}
}

Proper way to empty semaphore property after initialization usage

I'm using the following c# code to initialize some properties:
class MyClass
{
private static readonly string _myLuaScript = "...";
private SemaphoreSlim _myLuaScriptSemaphore = new SemaphoreSlim(1, 1);
private LoadedLuaScript? _myLoadedLuaScript = null;
public async Task<LoadedLuaScript> GetMyLoadedLuaScript
{
if (_myLoadedLuaScript == null)
{
await _myLuaScriptSemaphore.WaitAsync();
try
{
if (_myLoadedLuaScript == null)
{
_myLoadedLuaScript = await LoadAsync();
}
}
finally
{
_myLuaScriptSemaphore.Release();
}
}
return _myLoadedLuaScript;
}
}
My question is, how do I properly get rid of _myLuaScriptSemaphore, since there is a point where I no longer need it.
Ideally, I would want to use a struct/class Loader to handle this logic, but I can't seem to see a way that elegantly does not leave something allocated behind.
Bonus question, but I don't I don't think it's nicely doable, is there a way to somehow return a LoadedLuaScript after the initialization stage ?

Triggering DynamicData cache update using Reactive Subject

As a caveat I'm a novice with Rx (2 weeks) and have been experimenting with using Rx, RxUI and Roland Pheasant's DynamicData.
I have a service that initially loads data from local persistence and then, upon some user (or system) instruction will contact the server (TriggerServer in the example) to get additional or replacement data. The solution I've come up with uses a Subject and I've come across many a site discussing the pros/cons of using them. Although I understand the basics of hot/cold it's all based on reading rather than real world.
So, using the below as a simplified version, is this 'right' way of going about this problem or is there something I haven't properly understood somewhere?
NB: I'm not sure how important it is, but the actual code is taken from a Xamarin.Forms app, that uses RxUI, the user input being a ReactiveCommand.
Example:
using DynamicData;
using System;
using System.Linq;
using System.Reactive;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Reactive.Subjects;
using System.Threading.Tasks;
public class MyService : IDisposable
{
private CompositeDisposable _cleanup;
private Subject<Unit> _serverSubject = new Subject<Unit>();
public MyService()
{
var data = Initialise().Publish();
AllData = data.AsObservableCache();
_cleanup = new CompositeDisposable(AllData, data.Connect());
}
public IObservableCache<MyData, Guid> AllData { get; }
public void TriggerServer()
{
// This is what I'm not sure about...
_serverSubject.OnNext(Unit.Default);
}
private IObservable<IChangeSet<MyData, Guid>> Initialise()
{
return ObservableChangeSet.Create<MyData, Guid>(async cache =>
{
// inital load - is this okay?
cache.AddOrUpdate(await LoadLocalData());
// is this a valid way of doing this?
var sync = _serverSubject.Select(_ => GetDataFromServer())
.Subscribe(async task =>
{
var data = await task.ConfigureAwait(false);
cache.AddOrUpdate(data);
});
return new CompositeDisposable(sync);
}, d=> d.Id);
}
private IObservable<MyData> LoadLocalData()
{
return Observable.Timer(TimeSpan.FromSeconds(3)).Select(_ => new MyData("localdata"));
}
private async Task<MyData> GetDataFromServer()
{
await Task.Delay(2000).ConfigureAwait(true);
return new MyData("serverdata");
}
public void Dispose()
{
_cleanup?.Dispose();
}
}
public class MyData
{
public MyData(string value)
{
Value = value;
}
public Guid Id { get; } = Guid.NewGuid();
public string Value { get; set; }
}
And a simple Console app to run:
public static class TestProgram
{
public static void Main()
{
var service = new MyService();
service.AllData.Connect()
.Bind(out var myData)
.Subscribe(_=> Console.WriteLine("data in"), ()=> Console.WriteLine("COMPLETE"));
while (Continue())
{
Console.WriteLine("");
Console.WriteLine("");
Console.WriteLine($"Triggering Server Call, current data is: {string.Join(", ", myData.Select(x=> x.Value))}");
service.TriggerServer();
}
}
private static bool Continue()
{
Console.WriteLine("Press any key to call server, x to exit");
var key = Console.ReadKey();
return key.Key != ConsoleKey.X;
}
}

Looks very good for first try with Rx
I would suggest few changes:
1) Remove the Initialize() call from the constructor and make it a public method - helps a lot with unit tests and now you can await it if you need to
public static void Main()
{
var service = new MyService();
service.Initialize();
2) Add Throttle to you trigger - this fixes parallel calls to the server returning the same results
3) Don't do anything that can throw in Subscribe, use Do instead:
var sync = _serverSubject
.Throttle(Timespan.FromSeconds(0.5), RxApp.TaskPoolScheduler) // you can pass a scheduler via arguments, or use TestScheduler in unit tests to make time pass faster
.Do(async _ =>
{
var data = await GetDataFromServer().ConfigureAwait(false); // I just think this is more readable, your way was also correct
cache.AddOrUpdate(data);
})
// .Retry(); // or anything alese to handle failures
.Subscribe();

I'm putting what I've come to as my solution just in case there's others that find this while they're wandering the internets.
I ended up removing the Subjects all together and chaining together several SourceCache, so when one changed it pushed into the other and so on. I've removed some code for brevity:
public class MyService : IDisposable
{
private SourceCache<MyData, Guid> _localCache = new SourceCache<MyData, Guid>(x=> x.Id);
private SourceCache<MyData, Guid> _serverCache = new SourceCache<MyData, Guid>(x=> x.Id);
public MyService()
{
var localdata = _localCache.Connect();
var serverdata = _serverCache.Connect();
var alldata = localdata.Merge(serverdata);
AllData = alldata.AsObservableCache();
}
public IObservableCache<MyData, Guid> AllData { get; }
public IObservable<Unit> TriggerLocal()
{
return LoadLocalAsync().ToObservable();
}
public IObservable<Unit> TriggerServer()
{
return LoadServerAsync().ToObservable();
}
}
EDIT: I've changed this again to remove any chaining of caches - I just manage the one cache internally. Lesson is not to post too early.

C# Trying to wrap a function with a stopwatch

I've been attempting to see how long functions take to execute in my code as practice to see where I can optimize. Right now I use a helper class that is essentially a stopwatch with a message to check these. The goal of this is that I should be able to wrap whatever method call I want in the helper and I'll get it's duration.
public class StopwatcherData
{
public long Time { get; set; }
public string Message { get; set; }
public StopwatcherData(long time, string message)
{
Time = time;
Message = message;
}
}
public class Stopwatcher
{
public delegate void CompletedCallBack(string result);
public static List<StopwatcherData> Data { get; set; }
private static Stopwatch stopwatch { get; set;}
public Stopwatcher()
{
Data = new List<StopwatcherData>();
stopwatch = new Stopwatch();
stopwatch.Start();
}
public static void Click(string message)
{
Data.Add(new StopwatcherData(stopwatch.ElapsedMilliseconds, message));
}
public static void Reset()
{
stopwatch.Reset();
stopwatch.Start();
}
}
Right now to use this, I have to call the Reset before the function I want so that the timer is restarted, and then call the click after it.
Stopwatcher.Reset()
MyFunction();
Stopwatcher.Click("MyFunction");
I've read a bit about delegates and actions, but I'm unsure of how to apply them to this situation. Ideally, I would pass the function as part of the Stopwatcher call.
//End Goal:
Stopwatcher.Track(MyFunction(), "MyFunction Time");
Any help is welcome.

It's not really a good idea to profile your application like that, but if you insist, you can at least make some improvements.
First, don't reuse Stopwatch, just create new every time you need.
Second, you need to handle two cases - one when delegate you pass returns value and one when it does not.
Since your Track method is static - it's a common practice to make it thread safe. Non-thread-safe static methods are quite bad idea. For that you can store your messages in a thread-safe collection like ConcurrentBag, or just use lock every time you add item to your list.
In the end you can have something like this:
public class Stopwatcher {
private static readonly ConcurrentBag<StopwatcherData> _data = new ConcurrentBag<StopwatcherData>();
public static void Track(Action action, string message) {
var w = Stopwatch.StartNew();
try {
action();
}
finally {
w.Stop();
_data.Add(new StopwatcherData(w.ElapsedMilliseconds, message));
}
}
public static T Track<T>(Func<T> func, string message) {
var w = Stopwatch.StartNew();
try {
return func();
}
finally {
w.Stop();
_data.Add(new StopwatcherData(w.ElapsedMilliseconds, message));
}
}
}
And use it like this:
Stopwatcher.Track(() => SomeAction(param1), "test");
bool result = Stopwatcher.Track(() => SomeFunc(param2), "test");
If you are going to use that with async delegates (which return Task or Task<T>) - you need to add two more overloads for that case.

Yes, you can create a timer function that accepts any action as a delegate. Try this block:
public static long TimeAction(Action action)
{
var timer = new Stopwatch();
timer.Start();
action();
timer.Stop();
return timer.ElapsedMilliseconds;
}
This can be used like this:
var elapsedMilliseconds = TimeAction(() => MyFunc(param1, param2));
This is a bit more awkward if your wrapped function returns a value, but you can deal with this by assigning a variable from within the closure, like this:
bool isSuccess ;
var elapsedMilliseconds = TimeToAction(() => {
isSuccess = MyFunc(param1, param2);
});

I've had this problem a while ago as well and was always afraid of the case that I'll leave errors when I change Stopwatcher.Track(() => SomeFunc(), "test")(See Evk's answer) back to SomeFunc(). So I tought about something that wraps it without changing it!
I came up with a using, which is for sure not the intended purpose.
public class OneTimeStopwatch : IDisposable
{
private string _logPath = "C:\\Temp\\OneTimeStopwatch.log";
private readonly string _itemname;
private System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
public OneTimeStopwatch(string itemname)
{
_itemname = itemname;
sw.Start();
}
public void Dispose()
{
sw.Stop();
System.IO.File.AppendAllText(_logPath, string.Format($"{_itemname}: {sw.ElapsedMilliseconds}ms{Environment.NewLine}"));
}
}
This can be used a easy way
using (new OneTimeStopwatch("test"))
{
//some sensible code not to touch
System.Threading.Thread.Sleep(1000);
}
//logfile with line "test: 1000ms"
I only need to remove 2 lines (and auto format) to make it normal again.
Plus I can easily wrap multiple lines here which isn't possible without defining new functions in the other approach.
Again, this is not recommended for terms of few miliseconds.

Async result handle to return to callers

I have a method that queues some work to be executed asynchronously. I'd like to return some sort of handle to the caller that can be polled, waited on, or used to fetch the return value from the operation, but I can't find a class or interface that's suitable for the task.
BackgroundWorker comes close, but it's geared to the case where the worker has its own dedicated thread, which isn't true in my case. IAsyncResult looks promising, but the provided AsyncResult implementation is also unusable for me. Should I implement IAsyncResult myself?
Clarification:
I have a class that conceptually looks like this:
class AsyncScheduler
{
private List<object> _workList = new List<object>();
private bool _finished = false;
public SomeHandle QueueAsyncWork(object workObject)
{
// simplified for the sake of example
_workList.Add(workObject);
return SomeHandle;
}
private void WorkThread()
{
// simplified for the sake of example
while (!_finished)
{
foreach (object workObject in _workList)
{
if (!workObject.IsFinished)
{
workObject.DoSomeWork();
}
}
Thread.Sleep(1000);
}
}
}
The QueueAsyncWork function pushes a work item onto the polling list for a dedicated work thread, of which there will only over be one. My problem is not with writing the QueueAsyncWork function--that's fine. My question is, what do I return to the caller? What should SomeHandle be?
The existing .Net classes for this are geared towards the situation where the asynchronous operation can be encapsulated in a single method call that returns. That's not the case here--all of the work objects do their work on the same thread, and a complete work operation might span multiple calls to workObject.DoSomeWork(). In this case, what's a reasonable approach for offering the caller some handle for progress notification, completion, and getting the final outcome of the operation?

Yes, implement IAsyncResult (or rather, an extended version of it, to provide for progress reporting).
public class WorkObjectHandle : IAsyncResult, IDisposable
{
private int _percentComplete;
private ManualResetEvent _waitHandle;
public int PercentComplete {
get {return _percentComplete;}
set
{
if (value < 0 || value > 100) throw new InvalidArgumentException("Percent complete should be between 0 and 100");
if (_percentComplete = 100) throw new InvalidOperationException("Already complete");
if (value == 100 && Complete != null) Complete(this, new CompleteArgs(WorkObject));
_percentComplete = value;
}
public IWorkObject WorkObject {get; private set;}
public object AsyncState {get {return WorkObject;}}
public bool IsCompleted {get {return _percentComplete == 100;}}
public event EventHandler<CompleteArgs> Complete; // CompleteArgs in a usual pattern
// you may also want to have Progress event
public bool CompletedSynchronously {get {return false;}}
public WaitHandle
{
get
{
// initialize it lazily
if (_waitHandle == null)
{
ManualResetEvent newWaitHandle = new ManualResetEvent(false);
if (Interlocked.CompareExchange(ref _waitHandle, newWaitHandle, null) != null)
newWaitHandle.Dispose();
}
return _waitHandle;
}
}
public void Dispose()
{
if (_waitHandle != null)
_waitHandle.Dispose();
// dispose _workObject too, if needed
}
public WorkObjectHandle(IWorkObject workObject)
{
WorkObject = workObject;
_percentComplete = 0;
}
}
public class AsyncScheduler
{
private Queue<WorkObjectHandle> _workQueue = new Queue<WorkObjectHandle>();
private bool _finished = false;
public WorkObjectHandle QueueAsyncWork(IWorkObject workObject)
{
var handle = new WorkObjectHandle(workObject);
lock(_workQueue)
{
_workQueue.Enqueue(handle);
}
return handle;
}
private void WorkThread()
{
// simplified for the sake of example
while (!_finished)
{
WorkObjectHandle handle;
lock(_workQueue)
{
if (_workQueue.Count == 0) break;
handle = _workQueue.Dequeue();
}
try
{
var workObject = handle.WorkObject;
// do whatever you want with workObject, set handle.PercentCompleted, etc.
}
finally
{
handle.Dispose();
}
}
}
}

If I understand correctly you have a collection of work objects (IWorkObject) that each complete a task via multiple calls to a DoSomeWork method. When an IWorkObject object has finished its work you'd like to respond to that somehow and during the process you'd like to respond to any reported progress?
In that case I'd suggest you take a slightly different approach. You could take a look at the Parallel Extension framework (blog). Using the framework, you could write something like this:
public void QueueWork(IWorkObject workObject)
{
Task.TaskFactory.StartNew(() =>
{
while (!workObject.Finished)
{
int progress = workObject.DoSomeWork();
DoSomethingWithReportedProgress(workObject, progress);
}
WorkObjectIsFinished(workObject);
});
}
Some things to note:
QueueWork now returns void. The reason for this is that the actions that occur when progress is reported or when the task completes have become part of the thread that executes the work. You could of course return the Task that the factory creates and return that from the method (to enable polling for example).
The progress-reporting and finish-handling are now part of the thread because you should always avoid polling when possible. Polling is more expensive because usually you either poll too frequently (too early) or not often enough (too late). There is no reason you can't report on the progress and finishing of the task from within the thread that is running the task.
The above could also be implemented using the (lower level) ThreadPool.QueueUserWorkItem method.
Using QueueUserWorkItem:
public void QueueWork(IWorkObject workObject)
{
ThreadPool.QueueUserWorkItem(() =>
{
while (!workObject.Finished)
{
int progress = workObject.DoSomeWork();
DoSomethingWithReportedProgress(workObject, progress);
}
WorkObjectIsFinished(workObject);
});
}

The WorkObject class can contain the properties that need to be tracked.
public class WorkObject
{
public PercentComplete { get; private set; }
public IsFinished { get; private set; }
public void DoSomeWork()
{
// work done here
this.PercentComplete = 50;
// some more work done here
this.PercentComplete = 100;
this.IsFinished = true;
}
}
Then in your example:
Change the collection from a List to a Dictionary that can hold Guid values (or any other means of uniquely identifying the value).
Expose the correct WorkObject's properties by having the caller pass the Guid that it received from QueueAsyncWork.
I'm assuming that you'll start WorkThread asynchronously (albeit, the only asynchronous thread); plus, you'll have to make retrieving the dictionary values and WorkObject properties thread-safe.
private Dictionary<Guid, WorkObject> _workList =
new Dictionary<Guid, WorkObject>();
private bool _finished = false;
public Guid QueueAsyncWork(WorkObject workObject)
{
Guid guid = Guid.NewGuid();
// simplified for the sake of example
_workList.Add(guid, workObject);
return guid;
}
private void WorkThread()
{
// simplified for the sake of example
while (!_finished)
{
foreach (WorkObject workObject in _workList)
{
if (!workObject.IsFinished)
{
workObject.DoSomeWork();
}
}
Thread.Sleep(1000);
}
}
// an example of getting the WorkObject's property
public int GetPercentComplete(Guid guid)
{
WorkObject workObject = null;
if (!_workList.TryGetValue(guid, out workObject)
throw new Exception("Unable to find Guid");
return workObject.PercentComplete;
}

The simplest way to do this is described here. Suppose you have a method string DoSomeWork(int). You then create a delegate of the correct type, for example:
Func<int, string> myDelegate = DoSomeWork;
Then you call the BeginInvoke method on the delegate:
int parameter = 10;
myDelegate.BeginInvoke(parameter, Callback, null);
The Callback delegate will be called once your asynchronous call has completed. You can define this method as follows:
void Callback(IAsyncResult result)
{
var asyncResult = (AsyncResult) result;
var #delegate = (Func<int, string>) asyncResult.AsyncDelegate;
string methodReturnValue = #delegate.EndInvoke(result);
}
Using the described scenario, you can also poll for results or wait on them. Take a look at the url I provided for more info.
Regards,
Ronald

If you don't want to use async callbacks, you can use an explicit WaitHandle, such as a ManualResetEvent:
public abstract class WorkObject : IDispose
{
ManualResetEvent _waitHandle = new ManualResetEvent(false);
public void DoSomeWork()
{
try
{
this.DoSomeWorkOverride();
}
finally
{
_waitHandle.Set();
}
}
protected abstract DoSomeWorkOverride();
public void WaitForCompletion()
{
_waitHandle.WaitOne();
}
public void Dispose()
{
_waitHandle.Dispose();
}
}
And in your code you could say
using (var workObject = new SomeConcreteWorkObject())
{
asyncScheduler.QueueAsyncWork(workObject);
workObject.WaitForCompletion();
}
Don't forget to call Dispose on your workObject though.
You can always use alternate implementations which create a wrapper like this for every work object, and who call _waitHandle.Dispose() in WaitForCompletion(), you can lazily instantiate the wait handle (careful: race conditions ahead), etc. (That's pretty much what BeginInvoke does for delegates.)