Using .NET StreamReader ReadAsync

[BramB]

I am trying to use the .NET streamReader to read byte arrays from a device. This works fine when using the Read() function.

The buffer is (partly) filled with all available data, but when connection is lost when entering the Read function, Labview get locked (off course).

Therefore I want to use the ReadAsync() method.

This works fine as the task is completed and I see the number of available bytes in Result, IsCompleted is True and Status = Ran to Completion. But how can I extract the read bytes. The buffer output of the ReadAsync method contains all zero off course because at that point the task hadn't been finished.

In .NET documentation the following example in C# is shown using the await opeartor, but I can't find out how I can implement this in Labview.

[wiebe@CARYA]

You probably should tell it what to read, and if it succeeds, you don't get an error.

Mildly tested, not completely working. Because I use the ReadAsync, I probably have to wait... As it is I still get zeros.

The do something like await, you probably use getAwaiter:

[wiebe@CARYA]

Note that a .net wait (any wait) will block LabVIEW for the wait time. I've even seen blocked FPs, event structures not working and other weirdness.

I'd use a LabVIEW wait if possible. 

The async .net proccess shouldn't be blocking LabVIEW.

[BramB]

Thanks for the suggestions, but I couldn't get it working perfectly either. I have implemented some extra check with the ordinarly Read function and that works fine upto now. But it is not completely save I guess in case connection is lost right between the 'EndOfStream" check en the Read.

[wiebe@CARYA]

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@BramB wrote:

But it is not completely save I guess in case connection is lost right between the 'EndOfStream" check en the Read.

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You can check with a breakpoint between the nodes.

I wouldn't be too surprised if the streamreader handles that asynchronously. Reading data might just work even if the writer was closed.

[JimB.]

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@BramB wrote:

I am trying to use the .NET streamReader to read byte arrays from a device. This works fine when using the Read() function.

If I may, what sort of device is this and why do you wish to use a StreamReader to read "byte arrays" from it?

Are you able to implement this reliably in .NET? If so, the easiest way may be to just build a wrapper library for it.

Unfortunately, I don't think you can really use ReadAsync() in LabVIEW. LabVIEW is being a little too helpful here by allowing you to pass an U16 Array as the buffer argument. I say this because I do believe this would work if you could pass the buffer argument as a .NET object, but I do not believe LabVIEW allows this. The issue is that the method call is already automatically marshaling back and forth between the LabVIEW array and the .NET char[]. What you really want is to hold a reference to the .NET char[] object and then convert it to LabVIEW data after the async operation completes.

There might be a way to force it to work, but I suspect there may be a better solution.