fix: potential race condition between add_block and sync #4677
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Description
This fixes a potential race condition.
It is possible for
add_block
to pass theis_add_block_disabled()
, start doing orphan validation (which can take quite long).While this is happening,
sync
sets theadd_block_disabled
flag and acquires a read_lock to then do pre-processing to determine sync mode, etc. While this is busy,add_block
asks for a write_lock.Add_block
gets its write_lock beforesync
gets its write_block because of the prioritization of RWLock.Also moved the
if db.contains(&DbKey::BlockHash(block_hash))
before the orphan validation as this is a much cheaper operation.