In our application_startup, we seed up our database with some fake data, if no data exists.
To do this, we're using the Async methods to store the data. Great. Only problem is, we're not sure how to do this in the application_startup because that's not an async method.
I've spent soooo much time trying to understand #StevenCleary's tutorials and I'm always getting deadlocks. I totally grok what he consistently says:
As a general rule, you should use "async all the way down"; that is, don't block on async code
but I just don't get how I can do that, in this case :(
Lets imagine this is the code I'm trying to play with...
protected void Application_Start()
{
var someFakeData = LoadSomeFakeData();
var documentStore = new DocumentStore();
await documentStore.InitializeAsync(someFakeData);
...
// Registers this database as a singleton.
Container.Register(documentStore);
}
and later on .. some code that uses this documentStore. It is injected via construction injection ...
public SomeController(IDocumentStore documentStore)
{
_documentStore = documentStore;
}
public ViewModel GetFoos()
{
using (var session = _documentStore.OpenSession())
{
... db code goes in here ...
}
}
Clarification
I'm not trying to do some async code in here. I'm actually trying to call this async method, synchronously. Sure, i loose the benefits of async blah blah de blah.. but i'm happy with that. This is start up and I'm happy to block on startup.
In this case, you're asynchronously initializing a shared resource. So, I recommend that you either save the Task itself, or introduce an asynchronous wrapper type.
Using Task:
protected void Application_Start()
{
var someFakeData = LoadSomeFakeData();
var documentStore = new DocumentStore();
var documentStoreTask = documentStore.InitializeAsync(someFakeData);
...
// Registers this database task as a singleton.
Container.Register(documentStoreTask);
}
That may be too awkward, though, depending on Container. In that case, you can introduce an asynchronous wrapper type:
public sealed class DocumentStoreWrapper
{
private readonly Task<DocumentStore> _documentStore;
public DocumentStoreWrapper(Data data)
{
_documentStore = CreateDocumentStoreAsync(data);
}
private static async Task<DocumentStore> CreateDocumentStoreAsync(Data data)
{
var result = new DocumentStore();
await documentStore.InitializeAsync(data);
...
return result;
}
public Task<DocumentStore> DocumentStoreTask { get { return _documentStore; } }
}
protected void Application_Start()
{
var someFakeData = LoadSomeFakeData();
var documentStoreWrapper = new DocumentStoreWrapper(someFakeData);
...
// Registers this database wrapper as a singleton.
Container.Register(documentStoreWrapper);
}
Or, you could use AsyncLazy<T>, which does much the same thing but uses a background thread to execute the initialization code.
You can use of Task.Run(() => YourAsyncMethod()); inside of none async method like:
protected void Application_Start()
{
Task.Run(() => MyAsyncMethod(true));
}
This is an old topic, but it's popped up in my search and maybe it will for others.
For what the OP has requested (ie. To run an async method in a synchronous way from inside a synchronous method, and block until it's finished), is there some reason that the use of Task.WaitAll would not be a simple and adequate way of addressing this?
protected void Application_Start()
{
Task.WaitAll(MyAsyncMethod(true));
}
public static class AsyncHelper
{
private static readonly TaskFactory MyTaskFactory = new
TaskFactory(CancellationToken.None,
TaskCreationOptions.None,
TaskContinuationOptions.None,
TaskScheduler.Default);
public static TResult RunSync<TResult>(Func<Task<TResult>> func)
{
return MyTaskFactory
.StartNew(func)
.Unwrap()
.GetAwaiter()
.GetResult();
}
public static void RunSync(Func<Task> func)
{
MyTaskFactory
.StartNew(func)
.Unwrap()
.GetAwaiter()
.GetResult();
}
}
then use as
AsyncHelper.RunSync(ProcessAsync);
private async Task ProcessAsync(){ ....
Related
I am creating a Xamarin Forms application, and I am using the Xamarin Profiler to show that I have a memory leak. I have tracked the memory leak down to where it is happening, but I can't understand WHY it is happening.
I have a class (we will call it MyClass for now). And that class is using a Timer to call a service once every second. That service makes a REST call to retrieve a bunch of information, and then serializes the results back into an object....
MyClass:
public class MyClass : ContentPage
{
private readonly IMyService myService;
public MyClass() : base()
{
}
protected override async void OnAppearing()
{
StartTimer();
}
private void StartTimer()
{
Task.Run(async() =>
{
while(true)
{
myService = ((App)App.Current)
.serviceProvider
.GetRequiredService<IMyService>();
//--- everytime I call myService.GetSystemStatus(), my allocated memory continues to rise
MyResponse response = await myService.GetSystemStatus();
Device.BeginInvokeOnMainThread(() =>
{
// update the UI here...
});
await Task.Delay(1000);
}
});
}
}
MyService (Singleton):
public class MyService : IMyService
{
private readonly IMyHttpClientFactory httpClientFactory;
public MyService(IMyHttpClientFactory httpClientFactory)
{
this.httpClientFactory = httpClientFactory;
}
public async Task<MyResponse> GetSystemStatus()
{
return await httpClientFactory.Create().GetAsync<MyResponse>(
"http://example.com/api/status"
);
}
}
MyHttpClientFactory (Singleton):
public class MyHttpClientFactory : IMyHttpClientFactory
{
private readonly IServiceProvider _serviceProvider;
public MyHttpClientFactory(IServiceProvider serviceProvider)
{
_serviceProvider = serviceProvider;
}
public MyHttpClient Create()
{
return _serviceProvider.GetRequiredService<MyHttpClient>();
}
}
MyHttpClient:
public class MyHttpClient : IDisposable
{
private HttpClient _httpClient;
public MyHttpClient ()
{
_httpClient = new HttpClient();
_httpClient.Timeout = TimeSpan.FromSeconds(10);
}
public async Task<T> GetAsync<T>(string url) where T : new()
{
string s = await GetStringAsync(url);
return JsonConvert.DeserializeObject<T>(s);
}
public async Task<string> GetStringAsync(string url)
{
using (var response = await _httpClient.GetAsync(url))
{
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
}
My services are defined as follows:
public partial class App : Application
public ServiceProvider serviceProvider;
public App()
{
IServiceCollection services = new ServiceCollection();
ConfigureServices(services);
serviceProvider = services.BuildServiceProvider();
InitializeComponent();
}
private void ConfigureServices(IServiceCollection services)
{
services.AddHttpClient<MyHttpClient>("MyHttpClient", x =>
{
x.Timeout = TimeSpan.FromSeconds(5);
});
services.AddSingleton<IMyHttpClientFactory, MyHttpClientFactory>();
services.AddSingleton<IMyService, MyService>();
}
}
Best I can tell, the memory is going up because I am referencing the DI MyService inside a separate thread. But I am not sure if this is the reason or if there is something else that would be causing the leak?
Any advice would be greatly appreciated!!!
Thanks!
From what I understand from your code and your comments, it looks like you're looping by calling StartTimer() inside the Device.StartTimer() method.
According to the documentation, Device.StartTimer() is recurring and will occur every X seconds, depending of your interval parameter.
By removing the call to StartTimer() (the one between t.Dispose() and return false of MyClass.StartTimer, your code should work as expected and you will not create a new timer every x seconds
What could be the cause of the leak:
Your MyHttpClient class implements the IDisposable interface, yet the code to use an instance of this class is not leveraging the disposable nature of the object.
Even though the internal HttpClient instance is wrapped in a using statement, the MyHttpClient instance will not be disposed of as you would expect.
// from MyHttpClient class
public async Task<MyResponse> GetSystemStatus()
{
// no using statement here
return await httpClientFactory.Create().GetAsync<MyResponse>(
"http://example.com/api/status"
);
}
// should be:
public async Task<MyResponse> GetSystemStatus()
{
using (var client = await httpClientFactory.Create())
{
return await client.GetAsync<MyResponse>("http://example.com/api/status");
}
}
Another thing to try is to change the location of the resolution of the MyService instance to inside the Task since this is where it is used. This will allow the task to own the resource, and allow it to be collected when the task is complete.
private void StartTimer()
{
Device.StartTimer(TimeSpan.FromSeconds(1), () =>
{
Task t = Task.Run(async() =>
{
// resolve the service here
myService = ((App)App.Current)
.serviceProvider
.GetRequiredService<IMyService>();
MyResponse response = await myService.GetSystemStatus();
Device.BeginInvokeOnMainThread(() =>
{
// update the UI here...
});
});
t.Wait();
t.Dispose();
StartTimer();
return false;
});
}
A couple of additional observations of your code:
In your HttpClientFactory's Create() method, you are resolving an instance of your client from the DI container.
Your MyHttpClient class has a default constructor which means the resolution is not needed since there are no additional dependencies requiring DI support.
Your code could simply return a new MyHttpClient() instance from the Create() method without the need for DI.
Your MyHttpClient also implements the IMyHttpClient interface, but your factory returns the concrete type. This means you need to either remove the interface as unnecessary or change the return type to be the interface type since the interface is redundant unless it is used.
Thank you all for your answers....
I finally figured out the source of the memory leak.
The problem was that I was referencing "MyService" like this:
myService = ((App)App.Current)
.serviceProvider
.GetRequiredService<IMyService>();
The problem was that the serviceProvider object was a public property on my App. So each time I referenced the provider inside my loop, it was creating the leak.
To get around this, I added an abstract method to each of my pages that implemented MyClass to return the service correctly using DI. This has corrected my memory leak issue....
Thanks all for the help!
I don't think that your timer logic is the cause of the leak.
But in case it is useful to you, here is a clean way to do work periodically, yet if work takes a long time, avoid events "piling up".
Given await/async, no Timer is needed.
(There is an alternative solution that starts/stops a single System.Timers.Timer, but I won't go into that here.)
Replace StartTimer() declaration with the following:
/// <summary> Runs until keepRunning() returns false.
/// Delays by "msecDelay" AFTER finishing the previous loop's non-UI work. </summary>
private void StartTaskLoopWhileKeepRunning(Func<bool> keepRunning, int msecDelay = 250)
{
Task.Run(async () =>
{
while (keepRunning())
{
// Do non-UI work here.
// ... possibly slow work ...
Device.BeginInvokeOnMainThread(() =>
{
// NOTE: This work will run in parallel with the next delay.
// ... Do UI work here. ...
});
// Non-UI thread sleeps for msec.
await Task.Delay(msecDelay);
}
});
}
In a lot of our services, the OnStart method calls a neverEnding async Task and .Wait() which does all the service work until it gets manually shut down. We do something like the following (and have been since before I came onto the scene).
MyServiceClass service;
protected override void OnStart(string[] args)
{
eventLog.WriteEntry("MyService service is starting up.");
service = new MyServiceClass(this.ServiceName);
}
...
public class MyServiceClass
{
public MyServiceClass() {
Task.Run(() => DoServiceWork()).Wait();
}
public async Task DoServiceWork() {
while (true)
{
await Task.Delay(1000);//pretend this is actual work being done
}
}
}
Is there any reason not to just store the task and move on? (assuming the main method has appropriate exception handling)
public class MyServiceClass
{
public Task taskToBeAwaitedOnServiceStop;
public MyServiceClass() {
taskToBeAwaitedOnServiceStop = Task.Run(() => DoServiceWork());
}
}
or just to ignore the task entirely
public class MyServiceClass
{
public MyServiceClass() {
_ = DoServiceWork();
}
}
I'm considering the options as we don't like having .waits floating around (and having less means less to check when we go hunting). I'm asking here to be certain my alternatives won't cause strange service logic if implemented.
I hope this isn't too stupid a question, thanks for any help :)
I have a this code
public class ClassToTest
{
private readonly IRepository repository;
public ClassToTest(DI GOES HERE){...}
public DoSomething()
{
Task.Run(async () => {
//some code
repository.ExecuteAsync();
}
}
}
public class Repository : IRepository
{
public Task ExecuteAsync()
{
using (var connection = new SqlConnection(DbConfiguration.DatabaseConnection))
{
return connection.ExecuteAsync(storedProcedure, parameters, commandType: CommandType.StoredProcedure, commandTimeout: Configuration.TransactionTimeout);
}
}
}
[Test]
public void TestMethod()
{
var repository = new Mock<IRepository>;
var classToTest = new ClassToTest();
classToTest.DoSomething();
repository.Veryfy(p => p.ExecuteAsync(), Times.Once());
}
The test fails with this message
Expected invocation on the mock once, but was 0 times: p => p.ExecuteAsync()
Does anyone knows why?
Thanks
As others have alluded, because you're calling Task.Run and not waiting for a response, the Unit test will likely complete before the background task is even started, hence the Moq Verify failure.
Also, your code won't compile as is - when asking a Q on StackOverflow, be sure to give a complete, compilable MVP.
Of special importance is the bug in the code you are trying to test. Repository.ExecuteAsync calls connection.ExecuteAsync, inside a using scope, but this isn't awaited. This will mean that the connection will be disposed before the task completes. You'll need to change the method to async and await the call to defer disposal of the connection.
The wrapper method DoSomething method shouldn't use Task.Run(), although, because it adds no value to the repository Task, it doesn't need to repeat the async / return await, either.
The caller (your Unit test, in this instance) can then await DoSomething (or if the caller genuinely wants to do further processing without awaiting the Task, then leave it to the caller to decide. At least this way, the caller gets a handle to the Task, to check on completion).
The final state of your code might look more like this:
public class ClassToTest
{
private readonly IRepository _repository;
public ClassToTest(IRepository repository)
{
_repository = repository;
}
// Doesn't necessarily need to be async
public Task DoSomething()
{
// We're return the wrapped task directly, and adding no additional value.
return repository.ExecuteAsync();
}
}
public class Repository : IRepository
{
public async Task ExecuteAsync()
{
using (var connection = new SqlConnection(DbConfiguration.DatabaseConnection))
{
// Here we do need to await, otherwise we'll dispose the connection
return await connection.ExecuteAsync(storedProcedure, parameters,
commandType: CommandType.StoredProcedure,
commandTimeout: Configuration.TransactionTimeout);
}
}
}
// NUnit has full support for async / await
[Test]
public async Task TestMethod()
{
var repository = new Mock<IRepository>();
var classToTest = new ClassToTest(repository.Object);
repository.Setup(_ => _.ExecuteAsync()).Returns(Task.FromResult((object)null));
// Moq also has support for async, e.g. .ReturnsAsync
// You need to await the test.
await classToTest.DoSomething();
repository.Verify(p => p.ExecuteAsync(), Times.Once());
}
Suppose I'm writing a custom MVC filter which does some asynchronous calls within the method overrides, like so:
public class MyActionFilter : System.Web.Mvc.ActionFilterAttribute
{
public override void OnActionExecuted(ActionExecutedContext ctx)
{
var stuff = ConfigureAwaitHelper1().Result;
// do stuff
}
public override void OnActionExecuting(ActionExecutingContext ctx)
{
var stuff = ConfigureAwaitHelper2().Result;
// do stuff
}
private async Task<string> ConfigureAwaitHelper1()
{
var result = await client.GetAsStringAsync("blah.com").ConfigureAwait(false);
return result;
}
private async Task<string> ConfigureAwaitHelper2()
{
return await client.GetAsStringAsync("blah.com").ConfigureAwait(false);
}
}
Why does OnActionExecuting deadlock, whereas OnActionExecuted does not? I don't see the fundamental difference between the two. The act of returning happens only after the asynchronous task is complete, which is rather like putting the result into an "anonymous return" local var before returning it, so I don't see why the former should deadlock.
Why does OnActionExecuting deadlock, whereas OnActionExecuted does not?
I'm surprised it works at all. The reason you're experiencing the deadlock is due to the fact that you're invoking a .Result on a Task. This is evil and you should only ever invoke .Result and .Wait in console applications.
I am using MvvmLight and have implemented communication between some of my ViewModels using the MessengerInstance.Send(...) method. It works great!
Recently, though, I have moved from using Synchronous methods to async methods to retrieve data and it looks like this breaks messaging (probably because it executes on a different thread). For example:
public ICommand SomeCommand { get { return new RelayCommand(DoSomething); } }
private async void DoSomething(object obj)
{
//Used to be SomeWcfService.DoSomething(); with some logic afterward
await SomeWcfService.DoSomethingAsync().ContinueWith(task => { //Some logic after method completes });
MessengerInstance.Send(SomeDataToSend, MessageIdentifer.DoSomething);
}
Instead of using a continuation, just put it after the await:
private async void DoSomething(object obj)
{
//Used to be SomeWcfService.DoSomething(); with some logic afterward
var result = await SomeWcfService.DoSomethingAsync();
// .ContinueWith(task => { //Some logic after method completes });
// use result here!
MessengerInstance.Send(SomeDataToSend, MessageIdentifer.DoSomething);
}
If there is no result returned from DoSomethingAsync, you can just leave out the result, and put your code in place.
The continuation, as you wrote it, will not run on the same synchronization context. The await keyword is actually asynchronously waiting your continuation, not the async method from WCF, as well.
If your "some logic" is asynchronous, you can use await within that code, as well.