http://invest2fghrk7zf5ae4kie6pc573htvvc24yoilmxb2wd6pwkzvrglid.onion/bitcoin-difficulty/index22.html
That’s how banks maintain money balances and transfers; they briefly lock access (or decrease the balance) while they make a transfer, then update the other side, then re-open access (or update again). With Google Docs (or Google Sheets), both parties have access to the same document at the same time, and the single version of that document is always visible to both of them.