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I can't understand the difference between Thread.Sleep() and synchronous methods. Please explain..
Is synchronous method in C# is similar to Thread.Sleep()?.
No, other than Thread.Sleep is a synchronous method.
A synchronous method is one where the entirety of their functionality happens before returning control to the caller.
Thread.Sleep is a function which causes the executing thread to block for the specified number of milliseconds (not exactly, but close due to the CPU thread scheduler). It executes synchronously and wouldn't be as useful in an asynchronous method.
However, saying they are the same thing would be a misnomer, as there are plenty of synchronous methods that are not Thread.Sleep and do not use it either.
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Is it safe to call File.WriteAllTextAsync to write to a single file multiple times without awaiting the result, as long as all the calls are made in a single thread?
By safe I mean:
no IO exception will be thrown
afterwards the file will have the content of the last call made
This seems to run fine, but is it guaranteed to do so?
for (var i = 0; i < 1000; ++i)
{
File.WriteAllTextAsync(fileName, i.ToString());
}
No, it is not safe. You may get "File already in use " exception.
Either you need await or do it synchronously.
No, it's not safe. It is not guaranteed that no exceptions will be thrown¹ or that all text will be written in the file. The only reason that it seems to work is because the asynchronous filesystem APIs are not implemented efficiently in .NET, and most of them block the calling thread instead of launching the operations asynchronously as they should. My suggestion is to use the synchronous API instead (File.WriteAllText).
¹ It is possible though that the thrown exceptions will remain unobserved, since the asynchronous operations are launched in a fire-and-forget fashion.
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I have multi-core laptop and I wanna make my application more faster on that machine, I think async-await and parallel programming help to achieve that feat.
Typically, Async and await is more about not blocking the current thread during a long-running operation.
Typically, parallel processing is used when the goal is to achieve an increase in performance.
That said, I think it's not uncommon to see both used together--you might have a desktop app that you want to ensure the UI thread is not blocked while you perform a long-running operation
so you could use Async and await to start the long-running operation on a non-UI thread (this way, your desktop app's GUI can still be responsive while the long-running operation is running on another thread
and you might also decide to introduce parallelism in the implementation of that long-running operation to have it complete faster
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I am new to asynchronous programming in .Net using C#. All I have understood so far is :
With asynchronous programming, threads that are waiting for a web service or database to return data are freed up to service new requests until the data the is received.
Once the data is received, the thread is restarted and continue processing the code that comes after that call.
Now , I wanted to know in details How the state is managed for the thread so that it can start executing from the point the async call was made.
If it uses a stack to handle that, Can some one please give me an insight into the process?
Thanks,
Mayank
Now , I wanted to know in details How the state is managed for the thread so that it can start executing from the point the async call was made.
Async method are divided into smaller chunks. Basically, when compiling async method, for every await keyword new method is generated.
Keep in mind, that this is a big simplification and it's all done behind the scenes and you really don't need to know how it works in order to use it.
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I'm in the process of converting our data layer for a fairly large and complex WCF application to talk to the database asynchronously.
This has resulted in async and awaits being littered everywhere in the calling/consuming code.
Looking at the stack trace for a typical request I can already see many sections for the System.Runtime.CompilerServices.TaskAwaiter doing it's thing with await. And I have only just started this task!
I understand what .net does when it encounters async/await, so my question is the following: Is the extra overhead associated working with async/await worth it when the result is quite a few async methods from the beginning of a request to the end? I understand the benefits of calling the database asynchronously but is there a limit? Particularly when the calling application is fairly large and complex (or more appropriately a large and long call-stack).
Thanks.
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Can we say that the C# async/await pattern is some kind of
(smart) sugar syntax ?
Because as far as I can see, at the very end, it "just" hides all the implementation of an (internal) worker thread for the programmer.
Yes, there is no CLR support for await. It goes away on compilation. Anything you can write with await you can write without it.
Awaiting tasks it is a fancy way of calling ContinueWith :)
Decompile an assembly that uses await to see how it works under the covers.
async/await is indeed syntactic sugar, however, it doesn't just hide threads. Just because you use async and await in a method does not mean that you are creating threads.
From the MSDN Article Asynchronous Programming with Async and Await (C# and Visual Basic):
The async and await keywords don't cause additional threads to be
created. Async methods don't require multithreading because an async
method doesn't run on its own thread. The method runs on the current
synchronization context and uses time on the thread only when the
method is active. You can use Task.Run to move CPU-bound work to a
background thread, but a background thread doesn't help with a process
that's just waiting for results to become available.