Thread A: DirectoryHelper#updateContactsDatabase() acquires database lock
Thread B: LiveRecipientCache#getSelf() acquires lock on LiveRecipientCache
Thread A: DirectoryHelper#updateContactsDatabase() calls Recipient.externalContact(), which eventually needs LiveRecipientCache lock
Thread B: Needs to read the database (e.g. line 120) to get information about itself
So A has the DB lock but needs the LiveRecipientCache lock, and B has
the LiveRecipientCache lock but needs the DB lock.
In general, we need to avoid acquiring any new locks in a transaction,
but for now, this specific instance looks like it could be solved by
using a unique lock for LiveRecipientCache#getSelf().
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