be4e261e74
## Overview
This rather extensive PR achieves two primary goals:
1. Uses the finalized/justified checkpoints of fork choice (FC), rather than that of the head state.
2. Refactors fork choice, block production and block processing to `async` functions.
Additionally, it achieves:
- Concurrent forkchoice updates to the EL and cache pruning after a new head is selected.
- Concurrent "block packing" (attestations, etc) and execution payload retrieval during block production.
- Concurrent per-block-processing and execution payload verification during block processing.
- The `Arc`-ification of `SignedBeaconBlock` during block processing (it's never mutated, so why not?):
- I had to do this to deal with sending blocks into spawned tasks.
- Previously we were cloning the beacon block at least 2 times during each block processing, these clones are either removed or turned into cheaper `Arc` clones.
- We were also `Box`-ing and un-`Box`-ing beacon blocks as they moved throughout the networking crate. This is not a big deal, but it's nice to avoid shifting things between the stack and heap.
- Avoids cloning *all the blocks* in *every chain segment* during sync.
- It also has the potential to clean up our code where we need to pass an *owned* block around so we can send it back in the case of an error (I didn't do much of this, my PR is already big enough 😅)
- The `BeaconChain::HeadSafetyStatus` struct was removed. It was an old relic from prior merge specs.
For motivation for this change, see https://github.com/sigp/lighthouse/pull/3244#issuecomment-1160963273
## Changes to `canonical_head` and `fork_choice`
Previously, the `BeaconChain` had two separate fields:
```
canonical_head: RwLock<Snapshot>,
fork_choice: RwLock<BeaconForkChoice>
```
Now, we have grouped these values under a single struct:
```
canonical_head: CanonicalHead {
cached_head: RwLock<Arc<Snapshot>>,
fork_choice: RwLock<BeaconForkChoice>
}
```
Apart from ergonomics, the only *actual* change here is wrapping the canonical head snapshot in an `Arc`. This means that we no longer need to hold the `cached_head` (`canonical_head`, in old terms) lock when we want to pull some values from it. This was done to avoid deadlock risks by preventing functions from acquiring (and holding) the `cached_head` and `fork_choice` locks simultaneously.
## Breaking Changes
### The `state` (root) field in the `finalized_checkpoint` SSE event
Consider the scenario where epoch `n` is just finalized, but `start_slot(n)` is skipped. There are two state roots we might in the `finalized_checkpoint` SSE event:
1. The state root of the finalized block, which is `get_block(finalized_checkpoint.root).state_root`.
4. The state root at slot of `start_slot(n)`, which would be the state from (1), but "skipped forward" through any skip slots.
Previously, Lighthouse would choose (2). However, we can see that when [Teku generates that event](de2b2801c8/data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v1/events/EventSubscriptionManager.java (L171-L182)) it uses [`getStateRootFromBlockRoot`](de2b2801c8/data/provider/src/main/java/tech/pegasys/teku/api/ChainDataProvider.java (L336-L341)) which uses (1).
I have switched Lighthouse from (2) to (1). I think it's a somewhat arbitrary choice between the two, where (1) is easier to compute and is consistent with Teku.
## Notes for Reviewers
I've renamed `BeaconChain::fork_choice` to `BeaconChain::recompute_head`. Doing this helped ensure I broke all previous uses of fork choice and I also find it more descriptive. It describes an action and can't be confused with trying to get a reference to the `ForkChoice` struct.
I've changed the ordering of SSE events when a block is received. It used to be `[block, finalized, head]` and now it's `[block, head, finalized]`. It was easier this way and I don't think we were making any promises about SSE event ordering so it's not "breaking".
I've made it so fork choice will run when it's first constructed. I did this because I wanted to have a cached version of the last call to `get_head`. Ensuring `get_head` has been run *at least once* means that the cached values doesn't need to wrapped in an `Option`. This was fairly simple, it just involved passing a `slot` to the constructor so it knows *when* it's being run. When loading a fork choice from the store and a slot clock isn't handy I've just used the `slot` that was saved in the `fork_choice_store`. That seems like it would be a faithful representation of the slot when we saved it.
I added the `genesis_time: u64` to the `BeaconChain`. It's small, constant and nice to have around.
Since we're using FC for the fin/just checkpoints, we no longer get the `0x00..00` roots at genesis. You can see I had to remove a work-around in `ef-tests` here: b56be3bc2. I can't find any reason why this would be an issue, if anything I think it'll be better since the genesis-alias has caught us out a few times (0x00..00 isn't actually a real root). Edit: I did find a case where the `network` expected the 0x00..00 alias and patched it here: 3f26ac3e2.
You'll notice a lot of changes in tests. Generally, tests should be functionally equivalent. Here are the things creating the most diff-noise in tests:
- Changing tests to be `tokio::async` tests.
- Adding `.await` to fork choice, block processing and block production functions.
- Refactor of the `canonical_head` "API" provided by the `BeaconChain`. E.g., `chain.canonical_head.cached_head()` instead of `chain.canonical_head.read()`.
- Wrapping `SignedBeaconBlock` in an `Arc`.
- In the `beacon_chain/tests/block_verification`, we can't use the `lazy_static` `CHAIN_SEGMENT` variable anymore since it's generated with an async function. We just generate it in each test, not so efficient but hopefully insignificant.
I had to disable `rayon` concurrent tests in the `fork_choice` tests. This is because the use of `rayon` and `block_on` was causing a panic.
Co-authored-by: Mac L <mjladson@pm.me>
70 lines
2.3 KiB
Rust
70 lines
2.3 KiB
Rust
#![recursion_limit = "128"] // For lazy-static
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pub mod attestation_verification;
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mod attester_cache;
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mod beacon_chain;
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mod beacon_fork_choice_store;
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pub mod beacon_proposer_cache;
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mod beacon_snapshot;
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pub mod block_reward;
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mod block_times_cache;
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mod block_verification;
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pub mod builder;
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pub mod canonical_head;
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pub mod chain_config;
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mod early_attester_cache;
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mod errors;
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pub mod eth1_chain;
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pub mod events;
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mod execution_payload;
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pub mod fork_choice_signal;
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pub mod fork_revert;
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mod head_tracker;
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pub mod historical_blocks;
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mod metrics;
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pub mod migrate;
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mod naive_aggregation_pool;
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mod observed_aggregates;
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mod observed_attesters;
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mod observed_block_producers;
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pub mod observed_operations;
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mod persisted_beacon_chain;
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mod persisted_fork_choice;
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mod pre_finalization_cache;
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pub mod proposer_prep_service;
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pub mod schema_change;
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mod shuffling_cache;
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mod snapshot_cache;
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pub mod state_advance_timer;
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pub mod sync_committee_verification;
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pub mod test_utils;
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mod timeout_rw_lock;
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pub mod validator_monitor;
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mod validator_pubkey_cache;
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pub use self::beacon_chain::{
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AttestationProcessingOutcome, BeaconChain, BeaconChainTypes, BeaconStore, ChainSegmentResult,
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ForkChoiceError, ProduceBlockVerification, StateSkipConfig, WhenSlotSkipped,
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INVALID_JUSTIFIED_PAYLOAD_SHUTDOWN_REASON, MAXIMUM_GOSSIP_CLOCK_DISPARITY,
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};
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pub use self::beacon_snapshot::BeaconSnapshot;
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pub use self::chain_config::ChainConfig;
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pub use self::errors::{BeaconChainError, BlockProductionError};
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pub use self::historical_blocks::HistoricalBlockError;
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pub use attestation_verification::Error as AttestationError;
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pub use beacon_fork_choice_store::{BeaconForkChoiceStore, Error as ForkChoiceStoreError};
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pub use block_verification::{BlockError, ExecutionPayloadError, GossipVerifiedBlock};
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pub use canonical_head::{CachedHead, CanonicalHead, CanonicalHeadRwLock};
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pub use eth1_chain::{Eth1Chain, Eth1ChainBackend};
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pub use events::ServerSentEventHandler;
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pub use fork_choice::ExecutionStatus;
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pub use metrics::scrape_for_metrics;
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pub use parking_lot;
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pub use slot_clock;
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pub use state_processing::per_block_processing::errors::{
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AttestationValidationError, AttesterSlashingValidationError, DepositValidationError,
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ExitValidationError, ProposerSlashingValidationError,
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};
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pub use store;
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pub use timeout_rw_lock::TimeoutRwLock;
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pub use types;
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