Currently, new transactions take a very long time to be included in each block (or reach the intended recipient), because each node has to obtain a repository lock and import the transaction before it notifies its peers. This can take a long time due to the lock being held by the block minter or synchronizer, and this compounds with every peer that the transaction is routed through.
Validating signatures doesn't require a lock, and so can take place very soon after receipt of a new transaction. This change causes each node to broadcast a new transaction to its peers as soon as its signature is validated, rather than waiting until after the import.
When a notified peer then makes a request for the transaction data itself, this can now be loaded from the sig-valid import queue as an alternative to the repository (since they won't be in the repository until after the import, which likely won't have happened yet).
One small downside to this approach is that each unconfirmed transaction is now notified twice - once after the signature is deemed valid, and again in Controller.onNewTransaction(), but this should be an acceptable trade off given the speed improvements it should achieve. Another downside is that it could cause invalid transactions (with valid signatures) to propagate, but these would quickly be added to each peer's invalidUnconfirmedTransactions list after the import failure, and therefore be ignored.
Importing has to be single threaded since it requires the database lock, but there's nothing to stop us from validating signatures on multiple threads, as no lock is required. So it makes sense to separate these two functions to allow for possible multi threaded signature validation in the future, to speed up the process.
Everything remains single threaded in this commit. It should be functionally the same as before, to reduce risk.
Also removed CrossChainDigibyteACCTv1Resource, since this is unused, and it seems excessive to maintain support of this for every coin (and potentially every ACCT version).
Direct connections for arbitrary data are currently unlikely to succeed, because those allowing incoming connections generally have their slots maxed out and have reached maxPeers. The idea here is that some connections remain reserved for dedicated arbitrary data transfers, therefore temporarily circumventing the limit (up to a defined maximum number of reserved connections).
Arbitrary data connections will auto disconnect after 2 minutes (we might be able to reduce this at a later date), and it also probably makes sense for the requesting node to disconnect as soon as it has all the chunks that it needs (this part isn't implemented yet).
One downside of this feature is that the listen socket is now going to be accepting connections most of the time, since it is unlikely that we will regularly have 4 data peers connected. This could be improved by modifying the OP_ACCEPT behaviour based on whether we are expecting any data peers to connect. In most cases, this would allow it to remain closed. But for the sake of simplicity I will leave that optimization for a future commit.
This is used to force a quick disconnect for peers that are only connecting for the purposes of requesting data for a specific arbitrary transaction signature.
