async-await – Page 3

Getting a meaningful stack trace when using async code

January 6, 2024 by Tarik

So – is there any way to get a more meaningful stack trace when running async tasks? Yes, you can use ExceptionDispatchInfo.Capture that was introduced in .NET 4.5 for async-await speficially: private static void ThrowError(Task t) { if (t.IsFaulted) { Exception exception = t.Exception.InnerExceptions != null && t.Exception.InnerExceptions.Count == 1 ? t.Exception.InnerExceptions[0] : t.Exception; ExceptionDispatchInfo.Capture(exception).Throw(); … Read more

Is there ever a reason to `return await …` in python asyncio?

January 4, 2024 by Tarik

Given: async def foo() -> str: return ‘bar’ What you get when calling foo is an Awaitable, which obviously you’d want to await. What you need to think about is the return value of your function. You can for example do this: def bar() -> Awaitable[str]: return foo() # foo as defined above There, bar … Read more

‘async’ call in a function that does not support concurrency

January 3, 2024 by Tarik

The answer here is that the “await getSomethingLater” must be called from an async context. Literally that means changing this: let result = await tryThis.getSomethingLater(3.141592653589793238462) print(“result: \(result)”) into this: Task { let result = await tryThis.getSomethingLater(3.141592653589793238462) print(“result: \(result)”) } So the whole thing becomes: class TryThis { func getSomethingLater(_ number: Double) async -> String { … Read more

Why does Java have no async/await?

January 2, 2024 by Tarik

The short answer is that the designers of Java try to eliminate the need for asynchronous methods instead of facilitating their use. According to Ron Pressler’s talk asynchronous programming using CompletableFuture causes three main problems. branching or looping over the results of asynchronous method calls is not possible stacktraces cannot be used to identify the … Read more

Does this.setState return promise in react

January 2, 2024 by Tarik

You can promisify this.setState so that you can use the React API as a promise. This is how I got it to work: class LyricsGrid extends Component { setAsyncState = (newState) => new Promise((resolve) => this.setState(newState, resolve)); Later, I call this.setAsyncState using the standard Promise API: this.setAsyncState({ lyricsCorpus, matrix, count }) .then(foo1) .then(foo2) .catch(err => … Read more

Why is .json() asynchronous? [duplicate]

January 1, 2024 by Tarik

After the initial fetch() call, only the headers have been read. So, to parse the body as JSON, first the body data has to be read from the incoming stream. And, since reading from the TCP stream is asynchronous, the .json() operation ends up asynchronous. Note: the actual parsing of the JSON itself is not … Read more

Async function returning promise, instead of value [duplicate]

January 1, 2024 by Tarik

Async prefix is a kind of wrapper for Promises. async function latestTime() { const bl = await web3.eth.getBlock(‘latest’); console.log(bl.timestamp); // Returns a primitive console.log(typeof bl.timestamp.then == ‘function’); //Returns false – not a promise return bl.timestamp; } Is the same as function latestTime() { return new Promise(function(resolve,success){ const bl = web3.eth.getBlock(‘latest’); bl.then(function(result){ console.log(result.timestamp); // Returns a … Read more

LINQ ToListAsync expression with a DbSet

January 1, 2024 by Tarik

As noted in the comments, add using System.Data.Entity (under the Entity Framework package) to get the QueryableExtensions. For .NET Core, these methods are under Microsoft.EntityFrameworkCore

How is an IAsyncCursor used for iteration with the mongodb c# driver?

January 1, 2024 by Tarik

You have 3 options: Use the built-in driver method (e.g. ForEachAsync, ToListAsync). On C# 8.0 and above you can convert the IAsyncCursor into an IAsyncEnumerable and use await foreach or any async LINQ operator. Iterate over the IAsyncCursor. Built-in Driver Methods The driver has some LINQ-like extension methods for IAsyncCursor, like AnyAsync, ToListAsync, etc. For … Read more

How can I wait for an async function from synchronous function in Swift 5.5?

December 28, 2023 by Tarik

You could maybe argue that asynchronous code doesn’t belong in setUp(), but it seems to me that to do so would be to conflate synchronicity with sequential…icity? The point of setUp() is to run before anything else begins running, but that doesn’t mean it has to be written synchronously, only that everything else needs to … Read more