Background thread support

[konraddysput]

Why

Our users would like to start using backtraceClient instance from background threads/coroutines/async methods. In examples that we saw in the past they're sharing an instance of backtraceClient between threads - which is kinda not safe, and use it to send reports when an exception occurs.

Our users would like to use Backtrace to detect and capture exceptions that background threads generate.

With this approach, when they will use backtraceClient to send a report from any background thread, because of Unity engine dependency we won't be able to use Unity API to generate the report - for example, we won't be able to start coroutine or generate attributes.

This diff adds background exception cache with the respect of exception information (so everything related to the background thread will be still available). Once Update method fire in the Backtrace client we will be able to send it from main thread.

Testing strategy

Send report/exception/message from Backtrace client from background thread

• previously it generated an exception
• now it stores a report that will be ready to send on the next update method
• Please see unit tests to validate the behavior

Capture unhandled thread exception generated by background thread in Backtrace

• previously Backtrace client didn't support it
• now it allows to capture them and use unhandled exception flow like skip report etc.
• Please see unit tests to validate the behavior.

Example code that previously didn't work

    private async Task<WWW> MakeHttpRequest()
    {
        var www = await new WWW("https://jsonplaceholder.typicode.com/usersa");
        return www;

    }

    private async Task DownloadUsers()
    {
        var www = await MakeHttpRequest();


        if (!string.IsNullOrEmpty(www.error))
        {
            throw new Exception(www.error);
        }
    }
    private async Task PushAsyncStateMachineToLimits()
    {
            try
            {
                await DownloadUsers();
            }
            catch (Exception e)
            {
                _client.Send(e);
            }
            return;
    }

    private IEnumerator TestAsyncStateMachine()
    {
        PushAsyncStateMachineToLimits();
        yield return null;
    }

or

        var thread = new Thread(() =>
            {
                var exception = new InvalidOperationException(exceptionMessage);
                client.Send(exception);
            });

[rqbacktrace]

Why is this Stack instead of Queue?

[konraddysput]

Hmm yes, you're right. Queue makes more sense here

[rqbacktrace]

This seems to be repeated 3 times. Can we pull this into a function?

[konraddysput]

Not really because of different parameters that this function require and cost of BacktraceReport creation

[rqbacktrace]

Okay I see. Since this gets called in Update method we need to consider cost of BacktraceReport creation.

[rqbacktrace]

Why is this LateUpdate now? What happens in Update?

[konraddysput]

To give main thread to update before an anr thread

[rqbacktrace]

Ah okay that makes sense

[rqbacktrace]

Looks good to me! Just had a few questions

[vlussenburg]

didn't fully understand the issue but seeing the test made it clear! 👌