[SES-1931] - Fix debouncer crash

[simophin]

Description

The ConversationNotificationDebouncer doesn't handle threaded code correctly, added sync block manually.

This PR also makes sure no activity context is ever stored inside this singleton object.

[bemusementpark]

LGTM, although there's probably a nice coroutine operator to collect and debounce.

[bemusementpark]

nice

[simophin]

LGTM, although there's probably a nice coroutine operator to collect and debounce.

I'd love to use Kotlin Flow in the hopefully not very far future

[bemusementpark]

I was just thinking, you can save the list copy by making it a var:

private fun publish() {
    synchronized(this) {
        threadIDs.also { threadIDs = mutableSetOf() }
    }.forEach {
context.contentResolver.notifyChange(DatabaseContentProviders.Conversation.getUriForThread(it), null)
}

but it needs the same synchronized(this) in notify.

Creating a new instance still needs an allocation, but toList needs an allocation and an O(n) copy. Probably negligible performance, so don't feel obliged to change it, but the syntax is nice-ish too.

[simophin]

I actually went down this path to avoid the copying and using AtomicReference to avoid synchronization but had since decided against it, as I think easier to read code is more important than a few nanoseconds off the hotspot.

[simophin]

Also considered using a sorted long[] to avoid boxing but feel really unnecessary here, most of the time you only see a few items in the list really...