SubscriptionCallback::ReportData needs to capture its callbacks in block vars.

[bzbarsky-apple]

Problem

SubscriptionCallback::ReportData (in MTRBaseDevice.mm) does this:

    if (mAttributeReportCallback && attributeReports.count) {
        dispatch_async(mQueue, ^{
            mAttributeReportCallback(attributeReports);

but by the time the async block runs, mAttributeReportCallback can have become null, right? And in general, this is doing racy access to the callback....

We have crashes on that call to mAttributeReportCallback that I bet are due to this.

Proposed Solution

The callback should be getting captured into a block var, like the attributeReports are.

[aajain-com]

@bzbarsky-apple @woody-apple this seems very similar to #21142 that I filed given that SubscriptionCallback::OnReportEnd ends up calling ReportData() as per the code. WDYT?

[bzbarsky-apple]

@aajain-com Yes, I expect #21142 is the same issue, with mEventReportCallback having become null.