wallet_descriptor intermittent error "Please enter the wallet passphrase with walletpassphrase first. (-13)" #18811

https://travis-ci.org/github/MarcoFalke/btc_nightly/jobs/680655419#L412

In that run it took more than 10 seconds which is the unlock timeout.

2020-04-28T17:12:01.196000Z TestFramework (INFO): Test that unlock is needed when deriving only hardened keys in an encrypted wallet
2020-04-28T17:12:01.345000Z TestFramework (ERROR): JSONRPC error

And on my system it took around 3 seconds.

So maybe just increase the timeout (if this happens often) in https://github.com/bitcoin/bitcoin/blob/ba348dbc518b8e082a5dc3a225432fdacf859a13/test/functional/wallet_descriptor.py#L114

No? It took 0.149000 seconds?

Oh right!

The issue is a race between the 2nd walletpassphrase and the 1st lock callback. This was introduced in #18481.

From the logs

2020-04-28T17:11:50.607000Z TestFramework (INFO): Test encryption
2020-04-28T17:11:51.349000Z TestFramework (INFO): Test that getnewaddress still works after keypool is exhausted in an encrypted wallet
2020-04-28T17:12:01.196000Z TestFramework (INFO): Test that unlock is needed when deriving only hardened keys in an encrypted wallet
2020-04-28T17:12:01.345000Z TestFramework (ERROR): JSONRPC error

Little more than 10 seconds passed between the 1st walletpassphrase and the error, so in practice, the 2nd walletpassphrase was canceled by the 1st timeout.

I'll submit a possible fix.