2. change(state): Run AwaitUtxo read requests without shared mutable chain state

[teor2345]

Motivation

This PR runs StateService::AwaitUtxo read requests without accessing shared mutable chain state.
As a useful side-effect, this makes all StateService read requests concurrent.

Closes #5102.

Designs

See #4937 and https://docs.google.com/drawings/d/1FXpAUlenDAjl8nkftrypdAPsj0jr-Ut9gZlSP57nuyc/edit

Solution

Don't access shared mutable chain state in StateService read requests:

• Re-Implement AwaitUtxo without accessing shared mutable chain state, using StateService.pending_utxos and ReadStateService::AnyUtxo
  • Send the whole NonFinalizedState to the ReadStateService
  • Rename the ChainUtxo request to BestChainUtxo
  • Add an AnyChainUtxo request

Related documentation:

• Update the state service module documentation
• Explain how spent UTXOs are treated by the state
• Clarify how cached Chains impact state read requests

Related Cleanups:

• Move AwaitUtxos next to the other shared writeable state requests
• Rename ReadResponse::Utxos to ReadResponse::AddressUtxos
• Rename an out_point variable to outpoint for consistency
• Rename transparent_utxos to address_utxos
• Move the QueuedBlock type into the queued_blocks module

Testing

We should run a full sync on this before we merge, and make sure it is not significantly slower than the main branch.

Review

This PR is part of regular scheduled work.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

Actually create a separate task to commit blocks to the state.

[codecov]

Codecov Report

Merging #5107 (019a75a) into main (806dd0f) will decrease coverage by 0.05%.
The diff coverage is 79.74%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5107      +/-   ##
==========================================
- Coverage   79.35%   79.29%   -0.06%     
==========================================
  Files         307      307              
  Lines       39259    39323      +64     
==========================================
+ Hits        31153    31181      +28     
- Misses       8106     8142      +36     

[teor2345]

I'm running a full sync and a checkpoint sync here:
https://github.com/ZcashFoundation/zebra/actions/runs/3018034862

[teor2345]

I did a full sync and an update sync locally:

• both succeeded on testnet
• update sync succeeded on mainnet
• full sync is still going on mainnet, it seems to be about the same speed, there are no warnings

[teor2345]

I'm running a full sync here, but we don't need to wait for it before we merge this PR:
https://github.com/ZcashFoundation/zebra/actions/runs/3047965824

[upbqdn]

All looks good. I left some minor comments.