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从X ++调用异步方法 / Calling async method from X++

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There is a trend in the .NET world to make time-consuming calls asynchronous, to prevent applications from getting blocked when waiting for a response from a web service and things like that. Many existing APIs were enhanced with asynchronous variants of previously synchronous actions and some newer APIs offer only asynchronous methods. So… how can we call such asynchronous methods from X++? For a demo, imagine that I want to read the content of a file. I can use StreamReader.ReadToEnd() or the asynchronous alternative, ReadToEndAsync(). ReadToEnd() returns a string, therefore I can simply assign the result to a string variable.
str file = "devenv.exe.config";
 
using (var reader = new System.IO.StreamReader(file))
{
    str s = reader.ReadToEnd();
}
By the way, the code is written for F&O, where we can simplify our code with using and var keywords, but the core logic can be used in older versions of AX as well. .NET Interop as such was introduced in AX 4.0. ReadToEndAsync() doesn’t return a string, it returns a task returning a string (Task<string>). A task represent a piece of work to be done, in this case reading the file. In normal .NET development, you could use threads for parallel processing for a long time before tasks (Task Parallel Library) were introduced, but tasks make it all much easier. It’s been further enhanced by adding async and await keyworks to languages such as C#, which allows writing code for dealing with asynchronous methods in a very succinct way. We don’t have async/await in X++, but we surely can work with tasks directly. When I call an async method, I get a task object and the easiest thing I can do with it it is waiting for completion and then accessing the result:
str file = "devenv.exe.config";
 
using (var reader = new System.IO.StreamReader(file))
{
    var task = reader.ReadToEndAsync();
    task.Wait();
    str s = task.Result;
}
I’ll get exactly the same result as in the synchronous variant mentioned above. This is actually a synchronous execution of an asynchronous API, therefore it doesn’t bring many advantages for parallelism, but it’s often what you want anyway. For instance, you call your logic from a batch job (you don’t mind blocking), you can’t continue without the result and the API doesn’t support synchronous operations. You can build something more interesting on top of this simple example. For instance, you can create several tasks (without calling Wait()), put them into an array and then use Task.WaitAll() to execute all of them at once (in parallel if possible) and wait for completion. To make things truly asynchronous, you would need callback methods instead of waiting for completion.
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