Make Scope data global on desktop and mobile

[bruno-garcia]

This came up a few times, more recently on SO:

https://stackoverflow.com/questions/65066020/c-xamarin-forms-and-sentrysdk-context-info-not-making-it-to-sentry-errors

Currently the Hub is stored in a AsyncLocal field so data forks on new asynchronous flows.
This causes problems for Desktop and Mobile apps that want to push work to a back ground thread but would like that data available in case of an error anywhere.

This is how the Android and iOS SDKs of Sentry work, with a static global Hub.

An attempt to simulate that happened in this PR #448 but we the general approach needs to be discussed.

Resolves: #221

More context: https://forum.sentry.io/t/accessing-and-ensuring-global-shared-scope-in-net/11709/2

[jairbubbles]

Hello @bruno-garcia,

I was hit by the same issue and I must say it took me time to figure out what was going on (and get the source code). It's really counter-intuitive.

I wanted to track events and I was receiving them through different callbacks on different threads. As a workaround I ended up creating a specific scope that I use as a container for my events:

private readonly BaseScope _breadCrumbsScope = new Scope(null);

When I need to report an exception I fill everything I need just before sending it so I'm sure it's on the good scope:

SentrySdk.ConfigureScope(scope =>
{
  foreach (var breadCrumb in _breadCrumbsScope.Breadcrumbs)
  {
    scope.AddBreadcrumb(message: breadCrumb.Message, category: breadCrumb.Category, type: breadCrumb.Type, data: (Dictionary<string, string>)breadCrumb.Data, level: breadCrumb.Level);
   }
});

// Fill other things like user info and meta data

SentrySdk.CaptureException(exception);

As a side note, I do not use the embedded exception handling.

[bruno-garcia]

Thanks for sharing your work around @jairbubbles and sorry you hit this issue and took time to trace down.
This is a serious issue in usability from Desktop and Mobile users and really needs addressing. @rhcarvalho while working on tracing API became aware of the single/global state vs local state issues different SDKs have and we're discussing new APIs we can introduce to support both modes. A state change that that should be local to the local scope or globally visible to the whole process.

We'll hopefully get to this soon with a solution.

[bruno-garcia]

Customers also have the need to change data globally outside desktop apps. When they want to add such tags for data that's resolved only later in the program's executing. After a call to the backend for example that runs parallel to the process bootstrapping.

[jairbubbles]

In my case I wouldn't mind managing the global scope on my own, exposing static functions is nice but can be misleading.