Retain previously added breadcrumbs whenever a new breadcrumb is added

[fractalwrench]

This changeset avoids clearing all breadcrumbs everytime a new breadcrumb is added, by omitting a call to bugsnag_event_clear_breadcrumbs. Previously this method freed memory, then allocated new memory for each breadcrumb.

Reducing this churn by retaining previously added values will partially address #10, which is caused by multiple threads attempting to free/allocate memory at the same time. I've found that running the reproduction case results in less frequent signals when this fix is applied.

One concern with this change is that we should be careful it hasn't introduced any memory leaks. I believe the bugsnag_event_add_breadcrumb method was freeing the required memory in the first place so bugsnag_event_clear_breadcrumbs wasn't necessary, but it would be good to confirm this.

[Pezzah]

I think we might need two different methods here, one for just adding a new breadcrumb (where we assume that the others are already in sync) and one for cloning / copying all existing breadcrumbs.

This method is not always called when adding a new breadcrumb, it is also called when initializing the NDK notifier, and also to clear all breadcrumbs (see https://github.com/bugsnag/bugsnag-android/blob/master/sdk/src/main/java/com/bugsnag/android/Client.java#L1221).

[kattrali]

Ditto @Pezzah's comment, adding resolution of in-person conversation. The way forward is to:

• Clear and iterate over breadcrumbs when doing the initial population and when clearBreadcrumbs() is called from the Java side
• Separate adding a breadcrumb into a different event which only appends to the collection

[Pezzah]

When adding a breadcrumb will it be thread safe to assume that it is the last breadcrumb in the list that needs to be added? or does the addBreadcrumb method need to pass through parameters for the name / type?

[maltzj]

gentle poke from a concerned citizen

[maltzj]

gentle nudge

[fractalwrench]

Hi @maltzj - sorry for missing this. This ticket is currently still in progress, as it has a bit wider an impact than initially thought.

[maltzj]

Thanks for the update @fractalwrench. Let me know if there's any other insight I can provide here.

[fractalwrench]

Closing as this will be addressed by bugsnag/bugsnag-android#369