Add option for start up crashes

[philipphofmann]

Description

Add an option enableStartupCrashDetection with a default of true, so users can disable the start up crahes detection added with #2220.

Please also add this option to the docs.

[kevinrenskers]

Why would someone want to disable this feature?

[philipphofmann]

If it causes problems, or you never want your app to be blocked at start-up. Ideally, you should never use it. @romtsn, I think @kevinrenskers has a point. Should we maybe also remove it from getsentry/sentry-java#2277?

[romtsn]

you never want your app to be blocked at start-up.

I think this is the reason we should have it. Because we made some assumptions on the flush timeout and startup crash threshold, doesn't mean that they are correct. 2 seconds threshold might very well be enough for most of the apps in developed countries to flush out the envelopes, so that they don't even need to block and would like to disable this altogether.

Another point is - we care so much about performance and talk how we should make it a nobrainer for our customers to buy, yet introducing a feature that potentially degrades one of the core mobile vitals (app start) without a possibility to disable it. That doesn't sound right to me.

[kevinrenskers]

Then the question becomes: why would anyone want to enable it, if it causes problems? To me adding flags and options is not necessarily a good thing. The feature should either be useful and not cause problems, or should be made that way, so there is no reason to disable it. Not sure if that is possible here, but just adding a boolean seems weird to me.

[romtsn]

yeah, this feature is more-or-less a tradeoff between getting a crash on Sentry no-matter-what and potential performance quirks caused by this. The problem is that this tradeoff is decided by us and we don't leave any room for the users to change this decision, although it ultimately affects their performance.

Initially I wanted to make both the flushTimeout and the crashThreshold configurable, so the users could set their own numeric values and tweak them at their disposal, but Philipp was opposed to this. Also, the original issue states:

The SDK init function doesn't return until the start-up crash is sent to Sentry or until a configurable timeout is reached.

In any case, I don't wanna spend more time on bikeshedding here, so I can remove those options or keep those 2 options only on Android, but this would lead to misalignment between SDKs.

[philipphofmann]

As discussed on a call with @romtsn, we decided that we don't add this option for now. We think that this feature should be on by default, and there should be no good reason to disable it, as you accept the app start being blocked if there was a crash shortly after the app start on a previous run. We can always add this option later.