Reduce database blocking in light-mode

[HeinrichApfelmus]

Issue number

ADP-2012

Overview

This pull request fixes an issue in light-mode where a lock on the database was kept while fetching transactions from an external blockchain data source.

Details

• The field atomically of the DBLayer allows us to do atomic database operations.
• Instead of wrapping the entire body of restoreBlocks into a call to atomically, we now wrap the reading and writing separately.
  • In principle, this could lead to trouble when two calls to restoreBlocks interleave — the checkpoint which we have read need no longer agree with the one we are writing to.
  • However, the old code also assumes that the calls to restoreBlocks are not interleaved. More generally, we expect that the callbacks stored in a ChainFollower are called sequentially.

[paolino]

LGTM

[piotr-iohk]

LGTM.

Creating a wallet does not "hold" the postWallet nor blocks the listWallets endpoints any longer.
(I have some further observations, but will share them in the Jira ticket)

[HeinrichApfelmus]

bors merge

[iohk-bors]

Build succeeded:

• buildkite/cardano-wallet
• ci/hydra-build:required