Using Rx, I desire pause and resume functionality in the following code:
How to implement Pause() and Resume() ?
static IDisposable _subscription;
static void Main(string[] args)
{
Subscribe();
Thread.Sleep(500);
// Second value should not be shown after two seconds:
Pause();
Thread.Sleep(5000);
// Continue and show second value and beyond now:
Resume();
}
static void Subscribe()
{
var list = new List<int> { 1, 2, 3, 4, 5 };
var obs = list.ToObservable();
_subscription = obs.SubscribeOn(Scheduler.NewThread).Subscribe(p =>
{
Console.WriteLine(p.ToString());
Thread.Sleep(2000);
},
err => Console.WriteLine("Error"),
() => Console.WriteLine("Sequence Completed")
);
}
static void Pause()
{
// Pseudocode:
//_subscription.Pause();
}
static void Resume()
{
// Pseudocode:
//_subscription.Resume();
}
Rx Solution?
I believe I could make it work with some kind of Boolean field gating combined with thread locking (Monitor.Wait and Monitor.Pulse)
But is there an Rx operator or some other reactive shorthand to achieve the same aim?
Here's a reasonably simple Rx way to do what you want. I've created an extension method called Pausable that takes a source observable and a second observable of boolean that pauses or resumes the observable.
public static IObservable<T> Pausable<T>(
this IObservable<T> source,
IObservable<bool> pauser)
{
return Observable.Create<T>(o =>
{
var paused = new SerialDisposable();
var subscription = Observable.Publish(source, ps =>
{
var values = new ReplaySubject<T>();
Func<bool, IObservable<T>> switcher = b =>
{
if (b)
{
values.Dispose();
values = new ReplaySubject<T>();
paused.Disposable = ps.Subscribe(values);
return Observable.Empty<T>();
}
else
{
return values.Concat(ps);
}
};
return pauser.StartWith(false).DistinctUntilChanged()
.Select(p => switcher(p))
.Switch();
}).Subscribe(o);
return new CompositeDisposable(subscription, paused);
});
}
It can be used like this:
var xs = Observable.Generate(
0,
x => x < 100,
x => x + 1,
x => x,
x => TimeSpan.FromSeconds(0.1));
var bs = new Subject<bool>();
var pxs = xs.Pausable(bs);
pxs.Subscribe(x => { /* Do stuff */ });
Thread.Sleep(500);
bs.OnNext(true);
Thread.Sleep(5000);
bs.OnNext(false);
Thread.Sleep(500);
bs.OnNext(true);
Thread.Sleep(5000);
bs.OnNext(false);
It should be fairly easy for you to put this in your code with the Pause & Resume methods.
Here it is as an application of IConnectableObservable that I corrected slightly for the newer api (original here):
public static class ObservableHelper {
public static IConnectableObservable<TSource> WhileResumable<TSource>(Func<bool> condition, IObservable<TSource> source) {
var buffer = new Queue<TSource>();
var subscriptionsCount = 0;
var isRunning = System.Reactive.Disposables.Disposable.Create(() => {
lock (buffer)
{
subscriptionsCount--;
}
});
var raw = Observable.Create<TSource>(subscriber => {
lock (buffer)
{
subscriptionsCount++;
if (subscriptionsCount == 1)
{
while (buffer.Count > 0) {
subscriber.OnNext(buffer.Dequeue());
}
Observable.While(() => subscriptionsCount > 0 && condition(), source)
.Subscribe(
v => { if (subscriptionsCount == 0) buffer.Enqueue(v); else subscriber.OnNext(v); },
e => subscriber.OnError(e),
() => { if (subscriptionsCount > 0) subscriber.OnCompleted(); }
);
}
}
return isRunning;
});
return raw.Publish();
}
}
Here is my answer. I believe there may be a race condition around pause resume, however this can be mitigated by serializing all activity onto a scheduler. (favor Serializing over synchronizing).
using System;
using System.Reactive.Concurrency;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Reactive.Subjects;
using Microsoft.Reactive.Testing;
using NUnit.Framework;
namespace StackOverflow.Tests.Q7620182_PauseResume
{
[TestFixture]
public class PauseAndResumeTests
{
[Test]
public void Should_pause_and_resume()
{
//Arrange
var scheduler = new TestScheduler();
var isRunningTrigger = new BehaviorSubject<bool>(true);
Action pause = () => isRunningTrigger.OnNext(false);
Action resume = () => isRunningTrigger.OnNext(true);
var source = scheduler.CreateHotObservable(
ReactiveTest.OnNext(0.1.Seconds(), 1),
ReactiveTest.OnNext(2.0.Seconds(), 2),
ReactiveTest.OnNext(4.0.Seconds(), 3),
ReactiveTest.OnNext(6.0.Seconds(), 4),
ReactiveTest.OnNext(8.0.Seconds(), 5));
scheduler.Schedule(TimeSpan.FromSeconds(0.5), () => { pause(); });
scheduler.Schedule(TimeSpan.FromSeconds(5.0), () => { resume(); });
//Act
var sut = Observable.Create<IObservable<int>>(o =>
{
var current = source.Replay();
var connection = new SerialDisposable();
connection.Disposable = current.Connect();
return isRunningTrigger
.DistinctUntilChanged()
.Select(isRunning =>
{
if (isRunning)
{
//Return the current replayed values.
return current;
}
else
{
//Disconnect and replace current.
current = source.Replay();
connection.Disposable = current.Connect();
//yield silence until the next time we resume.
return Observable.Never<int>();
}
})
.Subscribe(o);
}).Switch();
var observer = scheduler.CreateObserver<int>();
using (sut.Subscribe(observer))
{
scheduler.Start();
}
//Assert
var expected = new[]
{
ReactiveTest.OnNext(0.1.Seconds(), 1),
ReactiveTest.OnNext(5.0.Seconds(), 2),
ReactiveTest.OnNext(5.0.Seconds(), 3),
ReactiveTest.OnNext(6.0.Seconds(), 4),
ReactiveTest.OnNext(8.0.Seconds(), 5)
};
CollectionAssert.AreEqual(expected, observer.Messages);
}
}
}
It just works:
class SimpleWaitPulse
{
static readonly object _locker = new object();
static bool _go;
static void Main()
{ // The new thread will block
new Thread (Work).Start(); // because _go==false.
Console.ReadLine(); // Wait for user to hit Enter
lock (_locker) // Let's now wake up the thread by
{ // setting _go=true and pulsing.
_go = true;
Monitor.Pulse (_locker);
}
}
static void Work()
{
lock (_locker)
while (!_go)
Monitor.Wait (_locker); // Lock is released while we’re waiting
Console.WriteLine ("Woken!!!");
}
}
Please, see How to Use Wait and Pulse for more details
Related
So, when I develop new feature for my system, I try too do a TDD - the code is to big to do that for old features right now, sadly.
However, I find that sometimes I hit a brick wall during the tests - especially when using Delay and Throttle.
I did a lot of reading and I think I know much more than week before, but I wanted to put all of this into pracitce. I wrote some experiments:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive;
using System.Reactive.Concurrency;
using System.Reactive.Linq;
using System.Reactive.Threading.Tasks;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Reactive.Testing;
using NUnit.Framework;
using NUnit.Framework.Internal.Commands;
using ReactiveUI;
using ReactiveUI.Testing;
namespace UtilsTests
{
[TestFixture]
public class SchedulersTests
{
private int SecondsN = 1;
[Test]
public async Task NoScheduler()
{
var t = Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), RxApp.MainThreadScheduler)
.ObserveOn(RxApp.MainThreadScheduler)
.ToTask();
await t;
}
[Test]
public Task ImmediateSchedulerExperiment()
{
return Scheduler.Immediate.With(async s =>
{
var t = Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), RxApp.MainThreadScheduler).ToTask();
await t;
});
}
[Test]
public Task ImmediateSchedulerExperiment2()
{
return Scheduler.Immediate.With(async s =>
{
var t = Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), s).FirstAsync().ToTask();
await t;
});
}
[Test]
public void ImmediateSchedulerExperiment3()
{
Scheduler.Immediate.With(s =>
{
var t = false;
Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), s)
.Subscribe(_ =>
{
t = true;
});
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_SchedulersNotSpecified()
{
new TestScheduler().With(s =>
{
var t = false;
Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), s)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_DeylaOn_RxMainThread()
{
new TestScheduler().With(s =>
{
var t = false;
Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), RxApp.MainThreadScheduler)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_DeylaOn_RxTaskPool()
{
new TestScheduler().With(s =>
{
var t = false;
Observable.Return(Unit.Default).Delay(TimeSpan.FromSeconds(SecondsN), RxApp.TaskpoolScheduler)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_RunOnTaskPool_ObserveOnMainThread()
{
new TestScheduler().With(s =>
{
var t = false;
Observable.Return(Unit.Default)
.Delay(TimeSpan.FromSeconds(SecondsN), RxApp.TaskpoolScheduler)
.ObserveOn(RxApp.MainThreadScheduler)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_RunOnTaskPool_ObserveOnTaskpool()
{
new TestScheduler().With(s =>
{
var t = false;
Observable.Return(Unit.Default)
.Delay(TimeSpan.FromSeconds(SecondsN), RxApp.TaskpoolScheduler)
.ObserveOn(RxApp.TaskpoolScheduler)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
s.AdvanceByMs(1);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_RunOnTaskPool_ObserveOnMainThread_MainThreadIsAnotherInstance()
{
new TestScheduler().With(s =>
{
var mainThreadScheduler = new TestScheduler();
RxApp.MainThreadScheduler = mainThreadScheduler;
var t = false;
Observable.Return(Unit.Default)
.Delay(TimeSpan.FromSeconds(SecondsN), RxApp.TaskpoolScheduler)
.ObserveOn(RxApp.MainThreadScheduler)
.Subscribe(_ =>
{
t = true;
});
s.AdvanceByMs(SecondsN * 1000);
mainThreadScheduler.AdvanceBy(1);
Assert.IsTrue(t);
});
}
[Test]
public void TestSchedulerExperiment_RunOnTest_ObserveOnTest()
{
new TestScheduler().With(s =>
{
var t = false;
var obs = Observable.Return(Unit.Default)
.Delay(TimeSpan.FromSeconds(SecondsN), s)
.ObserveOn(s);
obs
.Subscribe(_ =>
{
t = true;
});
// s.AdvanceByMs(SecondsN * 1000);
// s.AdvanceBy(1);
s.AdvanceUntil(obs);
Assert.IsTrue(t);
});
}
}
}
At first, I thought that Scheduler.Immediate will do the trick, executing things after delay right on the spot, and boy, that's wrong. I found this article, which explained things rather nicely. I found also this post, explaining which operator uses which scheduler.
I know now, that when playing with time, I should use TestScheduler. Otherwise, don't change the schedulers.
I know now, that you DO NOT do anything async in contructor, instead you create a command called let's say Init that does that on activation and you can await it in a test (for example delayd collection creation based on constructor argument to allow smooth UI animations when the view is comples)
BUT, when I run those tests from above, I get that:
There are few things I do not understand.
1) Why with Scheduler.Immediate the tests take twice the time? I think I get why Take(1) does not make difference, but still...
2) When using TestSchduler, how do I determine how much to step forward?
I noticed that in test TestSchedulerExperiment_RunOnTest_ObserveOnTest I have to do additional AdvanceBy(1), becuase it's also the observer. So, when the chain is longer, has more observers, it's really hard to count them.
Is it common practice to do scheduler.AdvanceBy(10000000000000);?
I tried to create AdvanceUntil extension, but I know it sucks for many reasons (cold observables for example).
public static void AdvanceUntil<TIgnore>(this TestScheduler s, IObservable<TIgnore> obs, double? advanceByMs = null)
{
var done = false;
obs.Subscribe(_ => done = true, (ex) => done = true, () => done = true);
while(!done)
s.AdvanceByMs(advanceByMs ?? 100);
}
Or maybe there is a "flush" method that I don't know?
Also, I learned to await stuff inside the TestScheduler.With:
[Test]
public Task TestSchedulerExperiment_await()
{
return new TestScheduler().With(async s =>
{
var v = false;
var t = Observable.Return(true).Delay(TimeSpan.FromSeconds(SecondsN), s)
.Take(1) // without hits the test never ends
.ToTask();
s.AdvanceByMs(SecondsN * 1000);
v = await t;
Assert.IsTrue(v);
});
but I still need to know the time.
And why there has to be Take(1)?
scheduler.Start() executes everything that has been scheduled, so you don't need that extension method.
I recommend not mixing async/await with Rx most of the time, especially for time-based functionality, which is basically all of your tests because of the Delay operator. Otherwise, you could potentially be waiting minutes for a single test to complete. So async/await serves no purpose in any of them.
For example, in a scenario like your TestSchedulerExperiment await test, the test scheduler along with a subscription is all you need. That test would simply become:
// Passing test
[Test]
public void TestSchedulerExperiment()
{
new TestScheduler().With(s =>
{
var v = false;
Observable
.Return(true)
.Delay(TimeSpan.FromSeconds(1), s)
.Subscribe(_ => v = true);
s.Start();
Console.WriteLine("Scheduler clock value: {0}", s.Clock);
Assert.True(v);
});
}
Why with Scheduler.Immediate the tests take twice the time?
If you really want to delve in and see what's happening under the hood I highly recommend this Spy extension by James and add timestamps.
var t = Observable
.Return(Unit.Default).Spy("Return")
.Delay(TimeSpan.FromSeconds(2), RxApp.MainThreadScheduler).Spy("Delay")
.ToTask();
await t;
// Partial output
Return: OnNext(()) on Thread: 1, 23:22:41.2631845
Delay: OnNext(()) on Thread: 1, 23:22:43.2891836
Return: OnCompleted() on Thread: 1, 23:22:43.2921808
Delay: OnCompleted() on Thread: 1, 23:22:45.2958130
Return uses ImmediateScheduler and as you may know, RxApp.MainThreadScheduler = ImmediateScheduler in a unit test runner. Because this scheduler is synchronous Return and Delay notifications both have to wait on each other. Return can't fire its OnCompleted until Delay fires OnNext, and then Delay's OnCompleted notification delays for another 2 seconds.
I have following code:
public class Batcher<TPayload> : IBatcher<TPayload>
{
private static readonly BufferBlock<BatchElement<TPayload>> BufferBlock = new BufferBlock<BatchElement<TPayload>>(new DataflowBlockOptions
{
EnsureOrdered = true
});
private readonly TransformBlock<BatchElement<TPayload>, BatchElement<TPayload>> BufferInterceptor;
private readonly TransformBlock<BatchElement<TPayload>, BatchElement<TPayload>> TimeoutInterceptor;
public EventsBatcher(int size, int interval, IMagicService magicService, ILogger<Batcher<TPayload, TStrategy>> logger)
{
BufferInterceptor =
new TransformBlock<BatchElement<TPayload>, BatchElement<TPayload>>(x =>
{
logger.LogInformation($"Get a message with value: {x}");
return x;
});
TimeoutInterceptor =
new TransformBlock<BatchElement<TPayload>, BatchElement<TPayload>>(x =>
{
logger.LogInformation($"Move out from transformation block with a value: {x}");
return x;
});
var batchBlock = new BatchBlock<BatchElement<TPayload>>(size, new GroupingDataflowBlockOptions()
{
EnsureOrdered = true
});
var timer = new Timer(async _ =>
{
try
{
batchBlock.TriggerBatch();
var data = await batchBlock.ReceiveAsync();
if (!data.Any() && data.SomeLogic())
return;
await magicService.PushMessageAsync(batchElement.Payload);
}
catch (Exception e)
{
logger.LogError($"Error occurs while trying to invoke action on batch", e);
}
}, null, 0, 500);
var timeoutBlock = new TransformBlock<BatchElement<TPayload>, BatchElement<TPayload>>(v =>
{
timer.Change(interval, Timeout.Infinite);
return v;
});
TimeoutInterceptor.LinkTo(batchBlock);
timeoutBlock.LinkTo(TimeoutInterceptor);
BufferInterceptor.LinkTo(timeoutBlock);
BufferBlock.LinkTo(BufferInterceptor);
}
public async Task<Result<Unit>> SendAsync(BatchElement<TPayload> msg, CancellationToken token = new CancellationToken())
{
try
{
var result = await BufferBlock.SendAsync(msg, token);
return result
? ResultFactory.CreateSuccess()
: ResultFactory.CreateFailure<Unit>("Message was refused by queue");
}
catch (Exception e)
{
return ResultFactory.CreateFailure<Unit>(e.Message);
}
}
}
Which responsibility is to evaluate somehow data every x milliseconds. I try to write unit tests to that to be sure that everything works fine. Those tests are here:
public class BatcherTests
{
public EventsBatcher<int> Initialize(Dictionary<DateTime, int> output)
{
var busMock = new Mock<IMagicService>();
busMock.Setup(x => x.PushMessageAsync(It.IsAny<int>()))
.Callback<Data>((data) =>
{
output.Add(DateTime.Now, data);
}).Returns(Task.CompletedTask);
var loggerMock = new Mock<ILogger<Batcher<int>>>();
return new Batcher<int>(
2,
5000,
busMock.Object,
loggerMock.Object
);
}
[Fact]
public async Task Batcher_ShouldRemoveDuplicatedMessages()
{
var output = new Dictionary<DateTime, int>();
var batcher = Initialize(output);
var first = await batcher.SendAsync(new MockEvent { Payload = 1 });
var second = await batcher.SendAsync(new MockEvent { Payload = 1 });
(first.IsSuccess && second.IsSuccess).ShouldBeTrue();
while (output.Count != 2)
{
}
output.Count.ShouldBe(2);
output.First().Value.ShouldBe(1);
output.Last().Value.ShouldBe(1);
output.Clear();
}
[Fact]
public async Task Batcher_WhenSizeIsSetTo2AndWeSend3Items_ReturnTwoBatchedItemsWithDateIntervalPlusMinus5000msAndAllSendRequestsEndsWithSuccess()
{
var output = new Dictionary<DateTime, int>();
var batcher = Initialize(output);
var first = await batcher.SendAsync(new MockEvent { Payload = 1 });
var second = await batcher.SendAsync(new MockEvent { Payload = 1 });
var third = await batcher.SendAsync(new MockEvent { Payload = 1 });
(first.IsSuccess && second.IsSuccess && third.IsSuccess).ShouldBeTrue();
while (output.Count != 2) //never ends because there are already two elements in output dictionary
{
}
output.Count.ShouldBe(2);
output.First().Value.ShouldBe(2);
output.Last().Value.ShouldBe(1);
var interval = (output.Last().Key - output.First().Key).TotalSeconds;
(interval >= 4.5d && interval <= 5.5d).ShouldBeTrue();
output.Clear();
}
}
But the strange thing is that when I run them separately they end up with a success status. But when I run them all together one of them seems to stuck. This is because a dictionary which is passed to a logic method has 2 elements inside while starting a test. I don't see here a possibility of shared context since stub class is created at the beginning of test cases, the same with a dictionary. Is there something that I missing? I also try to split those test cases to separe classes but the same behavior occurs.
There is shared stated, but it is not in the test (directly).
Your BufferBlock is declared as static in the class Batcher<TPayload>. There is your shared state.
private static readonly BufferBlock<BatchElement<TPayload>> BufferBlock = new BufferBlock<BatchElement<TPayload>>(new DataflowBlockOptions
{
EnsureOrdered = true
});
When multiple tests are executed that shared block is linked to the other blocks multiple times.
I am having an issue with my code below. I have a cold source that begins when you subscribe. I want to run Observable once, so I am using a replay call on it. What I found is that when it hits the conditional branch to write the header, it starts the Observable on the call to FirstAsync, and then starts the Observable again in a new thread at the ForEachAsync call. I end up with the observable running concurently in two threads. I am not sure why this is occuring.
public async Task WriteToFileAsync(string filename, IObservable<IFormattableTestResults> source, bool overwrite)
{
ThrowIfInvalidFileName(filename);
var path = Path.Combine(_path, filename);
bool fileExists = File.Exists(path);
using (var writer = new StreamWriter(path, !overwrite))
{
var replay = source.Replay().RefCount();
if (overwrite || !fileExists)
{
var first = await replay.FirstAsync();
var header = GetCsvHeader(first.GetResults());
await writer.WriteLineAsync(header);
}
await replay.ForEachAsync(result => writer.WriteLineAsync(FormatCsv(result.GetResults())));
}
}
Edit 10/22/2015: Adding more code
private Task RunIVBoardCurrentAdjust(IVBoardAdjustment test)
{
logger.Info("Loading IV board current adjustment test.");
var testCases = _testCaseLoader.GetIVBoardCurrentAdjustTests().ToArray();
var source = test.RunCurrentAdjustment(testCases);
return _fileResultsService.WriteToFileAsync("IVBoardCurrentAdjust.csv", source, false);
}
public IObservable<IVBoardCurrentAdjustTestResults> RunCurrentAdjustment(IEnumerable<IVBoardCurrentAdjustTestCase> testCases)
{
return
testCases
.Select(RunCurrentAdjustment)
.Concat();
}
public IObservable<IVBoardCurrentAdjustTestResults> RunCurrentAdjustment(IVBoardCurrentAdjustTestCase testCase)
{
logger.Debug("Preparing IV board current adjustment procedure.");
return Observable.Create<IVBoardCurrentAdjustTestResults>(
(observer, cancelToken) =>
{
var results =
RunAdjustment(testCase)
.Do(result => logger.Trace(""))
.Select(
(output, i) =>
new IVBoardCurrentAdjustTestResults(i, testCase, output)
{
Component = "IV Board",
Description = "Characterization (Secant Method)"
})
.Replay();
results.Subscribe(observer, cancelToken);
var task = StoreResultInBTD(results, testCase, 1/testCase.Load);
results.Connect();
return task;
});
}
private IObservable<IRootFindingResult> RunAdjustment<T>(IVBoardAdjustTestCase<T> testCase) where T : DacCharacterizationSecantInput
{
logger.Debug("Initializing IV board test.");
SetupTest(testCase);
return
new DacCharacterization()
.RunSecantMethod(
code => _yellowCake.IVBoard.DacRegister.Value = code,
() => _dmm.Read(),
GetTestInputs(testCase));
}
private async Task StoreResultInBTD(IObservable<IVBoardAdjustTestResults> results, IVBoardAdjustTestCase testCase, double targetScalingFactor = 1)
{
var points =
results
.Select(
result =>
new IVBoardCharacteristicCurveTestPoint(
(result.Output.Target - result.Output.Error) * targetScalingFactor,
(int)result.Output.Root));
var curve = await points.ToArray();
_yellowCake.BoardTest.WriteIVBoardAjust(curve, testCase.Mode, testCase.Range);
_yellowCake.BoardTest.SaveToFile();
}
private IEnumerable<DacCharacterizationSecantInput> GetTestInputs<T>(IVBoardAdjustTestCase<T> testCase) where T : DacCharacterizationSecantInput
{
foreach (var input in testCase.Inputs)
{
logger.Debug("Getting next test input.");
_dmm.Config.PowerLineCycles.Value = input.IntegrationTime;
yield return input.Input;
}
}
public IObservable<IRootFindingResult> RunSecantMethod(
Action<int> setDacOutput,
Func<double> readMeanOutput,
IEnumerable<DacCharacterizationSecantInput> inputs)
{
var search = new SecantSearch();
var param = SecantMethodParameter.Create(setDacOutput, readMeanOutput);
return
Observable
.Create<IRootFindingResult>(
(observer, cancelToken) =>
Task.Run(() =>
{
foreach (var input in inputs)
{
cancelToken.ThrowIfCancellationRequested();
var result =
search.FindRoot(
param.SearchFunction,
input.FirstGuess,
input.SecondGuess,
input.Target,
input.SearchOptions,
cancelToken,
() => param.AdaptedDacCode);
if (!result.Converged)
{
observer.OnError(new FailedToConvergeException(result));
}
observer.OnNext(result);
}
}, cancelToken));
}
I have a little problem with Threads in this code..
I just want to run a lot of tasks together, and continue when all of them finish.
while (true)
{
// Run tasks together:
foreach (object T in objectsList)
{
if (T.something>0)
var task = Task.Factory.StartNew(() => T.RunObject());
task.ContinueWith(delegate { ChangeObject(T, 1); }, TaskContinuationOptions.NotOnFaulted);
}
// <-- Here I want to wait for all the task to be finish.
// I know its task.Wait() but how to waitAll()?
System.Threading.Thread.Sleep(this.GetNextTime());
var RefreshObjects = new Task(loadObjectsList); RefreshObjects .Start(); RefreshObjects.Wait();
}
I don't know how many objects will be in objectsList and I don't know if T.something will be > 0.
so I can't just use:
Task[] Tasks = new Task[objectsList.count()]
for (int T=0; T<objectsList.count(); ++T)
{
if (objectsList[T].something>0)
var task = Task.Factory.StartNew(() => objectsList[T].RunObject());
task.ContinueWith(delegate { ChangeObject(objectsList[T], 1); }, ...);
}
Task.WaitAll(Tasks);
Because Tasks will contains nulls when objectsList[T].something!>0...
Thanks for any advice!
Just switch the condition and create a List of tasks only for the objects which matches your criteria.
var tasks = objectsList
.Where(x => x.Something() > 0)
.Select(x => {
var task = Task.Factory.StartNew(() => x.RunObject());
task.ContinueWith(t => ChangeObject(....));
return task;
})
.ToArray();
Task.WaitAll(tasks);
Your code sample just waits for RunObject()to complete! If this is desired skip the rest of my answer. If you want to wait for the continuation to complete, too you can use this
var tasks = objectsList
.Where(x => x.Something() > 0)
.Select(x => Task.Factory.StartNew(() => x.RunObject()).ContinueWith(t => ChangeObject(....)))
.ToArray();
Task.WaitAll(tasks);
because ContinueWith generates a new Task.
If objectsList implements IEnumerable, (as an array does),
(And there are less than 64 objects in the list), you can use this:
public delegate void SyncDelegatesInParallelDelegate<in T>(T item);
public static class ParallelLinqExtensions
{
public static void SyncDelegatesInParallel<T>(
this IEnumerable<T> list,
SyncDelegatesInParallelDelegate<T> action)
{
var foundCriticalException = false;
Exception exception = null;
var waitHndls = new List<WaitHandle>();
foreach (var item in list)
{
// Temp copy of session for modified closure
var localItem = item;
var txEvnt = new ManualResetEvent(false);
// Temp copy of session for closure
ThreadPool.QueueUserWorkItem(
depTx =>
{
try { if (!foundCriticalException) action(localItem); }
catch (Exception gX)
{ exception = gX; foundCriticalException = true; }
finally { txEvnt.Set(); }
}, null);
waitHndls.Add(txEvnt);
}
if (waitHndls.Count > 0) WaitHandle.WaitAll(waitHndls.ToArray());
if (exception != null) throw exception;
}
}
you would call it like this
objectsList.SyncDelegatesInParallel(delegate { ChangeObject(T, 1);});
I want to process something using parallel loop like this :
public void FillLogs(IEnumerable<IComputer> computers)
{
Parallel.ForEach(computers, cpt=>
{
cpt.Logs = cpt.GetRawLogs().ToList();
});
}
Ok, it works fine. But How to do if I want the FillLogs method return an IEnumerable ?
public IEnumerable<IComputer> FillLogs(IEnumerable<IComputer> computers)
{
Parallel.ForEach(computers, cpt=>
{
cpt.Logs = cpt.GetRawLogs().ToList();
yield return cpt // KO, don't work
});
}
EDIT
It seems not to be possible... but I use something like this :
public IEnumerable<IComputer> FillLogs(IEnumerable<IComputer> computers)
{
return computers.AsParallel().Select(cpt => cpt);
}
But where I put the cpt.Logs = cpt.GetRawLogs().ToList(); instruction
Short version - no, that isn't possible via an iterator block; the longer version probably involves synchronized queue/dequeue between the caller's iterator thread (doing the dequeue) and the parallel workers (doing the enqueue); but as a side note - logs are usually IO-bound, and parallelising things that are IO-bound often doesn't work very well.
If the caller is going to take some time to consume each, then there may be some merit to an approach that only processes one log at a time, but can do that while the caller is consuming the previous log; i.e. it begins a Task for the next item before the yield, and waits for completion after the yield... but that is again, pretty complex. As a simplified example:
static void Main()
{
foreach(string s in Get())
{
Console.WriteLine(s);
}
}
static IEnumerable<string> Get() {
var source = new[] {1, 2, 3, 4, 5};
Task<string> outstandingItem = null;
Func<object, string> transform = x => ProcessItem((int) x);
foreach(var item in source)
{
var tmp = outstandingItem;
// note: passed in as "state", not captured, so not a foreach/capture bug
outstandingItem = new Task<string>(transform, item);
outstandingItem.Start();
if (tmp != null) yield return tmp.Result;
}
if (outstandingItem != null) yield return outstandingItem.Result;
}
static string ProcessItem(int i)
{
return i.ToString();
}
I don't want to be offensive, but maybe there is a lack of understanding. Parallel.ForEach means that the TPL will run the foreach according to the available hardware in several threads. But that means, that ii is possible to do that work in parallel! yield return gives you the opportunity to get some values out of a list (or what-so-ever) and give them back one-by-one as they are needed. It prevents of the need to first find all items matching the condition and then iterate over them. That is indeed a performance advantage, but can't be done in parallel.
Although the question is old I've managed to do something just for fun.
class Program
{
static void Main(string[] args)
{
foreach (var message in GetMessages())
{
Console.WriteLine(message);
}
}
// Parallel yield
private static IEnumerable<string> GetMessages()
{
int total = 0;
bool completed = false;
var batches = Enumerable.Range(1, 100).Select(i => new Computer() { Id = i });
var qu = new ConcurrentQueue<Computer>();
Task.Run(() =>
{
try
{
Parallel.ForEach(batches,
() => 0,
(item, loop, subtotal) =>
{
Thread.Sleep(1000);
qu.Enqueue(item);
return subtotal + 1;
},
result => Interlocked.Add(ref total, result));
}
finally
{
completed = true;
}
});
int current = 0;
while (current < total || !completed)
{
SpinWait.SpinUntil(() => current < total || completed);
if (current == total) yield break;
current++;
qu.TryDequeue(out Computer computer);
yield return $"Completed {computer.Id}";
}
}
}
public class Computer
{
public int Id { get; set; }
}
Compared to Koray's answer this one really uses all the CPU cores.
You can use the following extension method
public static class ParallelExtensions
{
public static IEnumerable<T1> OrderedParallel<T, T1>(this IEnumerable<T> list, Func<T, T1> action)
{
var unorderedResult = new ConcurrentBag<(long, T1)>();
Parallel.ForEach(list, (o, state, i) =>
{
unorderedResult.Add((i, action.Invoke(o)));
});
var ordered = unorderedResult.OrderBy(o => o.Item1);
return ordered.Select(o => o.Item2);
}
}
use like:
public void FillLogs(IEnumerable<IComputer> computers)
{
cpt.Logs = computers.OrderedParallel(o => o.GetRawLogs()).ToList();
}
Hope this will save you some time.
How about
Queue<string> qu = new Queue<string>();
bool finished = false;
Task.Factory.StartNew(() =>
{
Parallel.ForEach(get_list(), (item) =>
{
string itemToReturn = heavyWorkOnItem(item);
lock (qu)
qu.Enqueue(itemToReturn );
});
finished = true;
});
while (!finished)
{
lock (qu)
while (qu.Count > 0)
yield return qu.Dequeue();
//maybe a thread sleep here?
}
Edit:
I think this is better:
public static IEnumerable<TOutput> ParallelYieldReturn<TSource, TOutput>(this IEnumerable<TSource> source, Func<TSource, TOutput> func)
{
ConcurrentQueue<TOutput> qu = new ConcurrentQueue<TOutput>();
bool finished = false;
AutoResetEvent re = new AutoResetEvent(false);
Task.Factory.StartNew(() =>
{
Parallel.ForEach(source, (item) =>
{
qu.Enqueue(func(item));
re.Set();
});
finished = true;
re.Set();
});
while (!finished)
{
re.WaitOne();
while (qu.Count > 0)
{
TOutput res;
if (qu.TryDequeue(out res))
yield return res;
}
}
}
Edit2: I agree with the short No answer. This code is useless; you cannot break the yield loop.