Use async code when interacting with EL (#3244)

## 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>

beacon_node/network/src/sync/block_lookups/mod.rs

@@ -7,6 +7,7 @@ use lighthouse_network::{PeerAction, PeerId};
 use lru_cache::LRUTimeCache;
 use slog::{crit, debug, error, trace, warn, Logger};
 use smallvec::SmallVec;
+use std::sync::Arc;
 use store::{Hash256, SignedBeaconBlock};
 use tokio::sync::mpsc;
 
@@ -105,7 +106,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
 
     pub fn search_parent(
         &mut self,
-        block: Box<SignedBeaconBlock<T::EthSpec>>,
+        block: Arc<SignedBeaconBlock<T::EthSpec>>,
         peer_id: PeerId,
         cx: &mut SyncNetworkContext<T::EthSpec>,
     ) {
@@ -129,7 +130,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
             return;
         }
 
-        let parent_lookup = ParentLookup::new(*block, peer_id);
+        let parent_lookup = ParentLookup::new(block, peer_id);
         self.request_parent(parent_lookup, cx);
     }
 
@@ -139,7 +140,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
         &mut self,
         id: Id,
         peer_id: PeerId,
-        block: Option<Box<SignedBeaconBlock<T::EthSpec>>>,
+        block: Option<Arc<SignedBeaconBlock<T::EthSpec>>>,
         seen_timestamp: Duration,
         cx: &mut SyncNetworkContext<T::EthSpec>,
     ) {
@@ -203,7 +204,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
         &mut self,
         id: Id,
         peer_id: PeerId,
-        block: Option<Box<SignedBeaconBlock<T::EthSpec>>>,
+        block: Option<Arc<SignedBeaconBlock<T::EthSpec>>>,
         seen_timestamp: Duration,
         cx: &mut SyncNetworkContext<T::EthSpec>,
     ) {
@@ -496,7 +497,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
             Err(BlockError::ParentUnknown(block)) => {
                 // need to keep looking for parents
                 // add the block back to the queue and continue the search
-                parent_lookup.add_block(*block);
+                parent_lookup.add_block(block);
                 self.request_parent(parent_lookup, cx);
             }
             Ok(_) | Err(BlockError::BlockIsAlreadyKnown { .. }) => {
@@ -618,7 +619,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
 
     fn send_block_for_processing(
         &mut self,
-        block: Box<SignedBeaconBlock<T::EthSpec>>,
+        block: Arc<SignedBeaconBlock<T::EthSpec>>,
         duration: Duration,
         process_type: BlockProcessType,
     ) -> Result<(), ()> {

beacon_node/network/src/sync/block_lookups/parent_lookup.rs

@@ -1,4 +1,5 @@
 use lighthouse_network::PeerId;
+use std::sync::Arc;
 use store::{EthSpec, Hash256, SignedBeaconBlock};
 use strum::IntoStaticStr;
 
@@ -21,7 +22,7 @@ pub(crate) struct ParentLookup<T: EthSpec> {
     /// The root of the block triggering this parent request.
     chain_hash: Hash256,
     /// The blocks that have currently been downloaded.
-    downloaded_blocks: Vec<SignedBeaconBlock<T>>,
+    downloaded_blocks: Vec<Arc<SignedBeaconBlock<T>>>,
     /// Request of the last parent.
     current_parent_request: SingleBlockRequest<PARENT_FAIL_TOLERANCE>,
     /// Id of the last parent request.
@@ -48,10 +49,10 @@ impl<T: EthSpec> ParentLookup<T> {
     pub fn contains_block(&self, block: &SignedBeaconBlock<T>) -> bool {
         self.downloaded_blocks
             .iter()
-            .any(|d_block| d_block == block)
+            .any(|d_block| d_block.as_ref() == block)
     }
 
-    pub fn new(block: SignedBeaconBlock<T>, peer_id: PeerId) -> Self {
+    pub fn new(block: Arc<SignedBeaconBlock<T>>, peer_id: PeerId) -> Self {
         let current_parent_request = SingleBlockRequest::new(block.parent_root(), peer_id);
 
         Self {
@@ -86,7 +87,7 @@ impl<T: EthSpec> ParentLookup<T> {
         self.current_parent_request.check_peer_disconnected(peer_id)
     }
 
-    pub fn add_block(&mut self, block: SignedBeaconBlock<T>) {
+    pub fn add_block(&mut self, block: Arc<SignedBeaconBlock<T>>) {
         let next_parent = block.parent_root();
         self.downloaded_blocks.push(block);
         self.current_parent_request.hash = next_parent;
@@ -108,7 +109,7 @@ impl<T: EthSpec> ParentLookup<T> {
         self.current_parent_request_id = None;
     }
 
-    pub fn chain_blocks(&mut self) -> Vec<SignedBeaconBlock<T>> {
+    pub fn chain_blocks(&mut self) -> Vec<Arc<SignedBeaconBlock<T>>> {
         std::mem::take(&mut self.downloaded_blocks)
     }
 
@@ -116,9 +117,9 @@ impl<T: EthSpec> ParentLookup<T> {
     /// the processing result of the block.
     pub fn verify_block(
         &mut self,
-        block: Option<Box<SignedBeaconBlock<T>>>,
+        block: Option<Arc<SignedBeaconBlock<T>>>,
         failed_chains: &mut lru_cache::LRUTimeCache<Hash256>,
-    ) -> Result<Option<Box<SignedBeaconBlock<T>>>, VerifyError> {
+    ) -> Result<Option<Arc<SignedBeaconBlock<T>>>, VerifyError> {
         let block = self.current_parent_request.verify_block(block)?;
 
         // check if the parent of this block isn't in the failed cache. If it is, this chain should

beacon_node/network/src/sync/block_lookups/single_block_lookup.rs

@@ -1,4 +1,5 @@
 use std::collections::HashSet;
+use std::sync::Arc;
 
 use lighthouse_network::{rpc::BlocksByRootRequest, PeerId};
 use rand::seq::IteratorRandom;
@@ -82,8 +83,8 @@ impl<const MAX_ATTEMPTS: u8> SingleBlockRequest<MAX_ATTEMPTS> {
     /// Returns the block for processing if the response is what we expected.
     pub fn verify_block<T: EthSpec>(
         &mut self,
-        block: Option<Box<SignedBeaconBlock<T>>>,
-    ) -> Result<Option<Box<SignedBeaconBlock<T>>>, VerifyError> {
+        block: Option<Arc<SignedBeaconBlock<T>>>,
+    ) -> Result<Option<Arc<SignedBeaconBlock<T>>>, VerifyError> {
         match self.state {
             State::AwaitingDownload => {
                 self.register_failure();
@@ -195,7 +196,7 @@ mod tests {
 
         let mut sl = SingleBlockRequest::<4>::new(block.canonical_root(), peer_id);
         sl.request_block().unwrap();
-        sl.verify_block(Some(Box::new(block))).unwrap().unwrap();
+        sl.verify_block(Some(Arc::new(block))).unwrap().unwrap();
     }
 
     #[test]

beacon_node/network/src/sync/block_lookups/tests.rs

@@ -158,7 +158,7 @@ fn test_single_block_lookup_happy_path() {
 
     // The peer provides the correct block, should not be penalized. Now the block should be sent
     // for processing.
-    bl.single_block_lookup_response(id, peer_id, Some(Box::new(block)), D, &mut cx);
+    bl.single_block_lookup_response(id, peer_id, Some(Arc::new(block)), D, &mut cx);
     rig.expect_empty_network();
     rig.expect_block_process();
 
@@ -204,7 +204,7 @@ fn test_single_block_lookup_wrong_response() {
 
     // Peer sends something else. It should be penalized.
     let bad_block = rig.rand_block();
-    bl.single_block_lookup_response(id, peer_id, Some(Box::new(bad_block)), D, &mut cx);
+    bl.single_block_lookup_response(id, peer_id, Some(Arc::new(bad_block)), D, &mut cx);
     rig.expect_penalty();
     rig.expect_block_request(); // should be retried
 
@@ -243,7 +243,7 @@ fn test_single_block_lookup_becomes_parent_request() {
 
     // The peer provides the correct block, should not be penalized. Now the block should be sent
     // for processing.
-    bl.single_block_lookup_response(id, peer_id, Some(Box::new(block.clone())), D, &mut cx);
+    bl.single_block_lookup_response(id, peer_id, Some(Arc::new(block.clone())), D, &mut cx);
     rig.expect_empty_network();
     rig.expect_block_process();
 
@@ -252,7 +252,7 @@ fn test_single_block_lookup_becomes_parent_request() {
 
     // Send the stream termination. Peer should have not been penalized, and the request moved to a
     // parent request after processing.
-    bl.single_block_processed(id, Err(BlockError::ParentUnknown(Box::new(block))), &mut cx);
+    bl.single_block_processed(id, Err(BlockError::ParentUnknown(Arc::new(block))), &mut cx);
     assert_eq!(bl.single_block_lookups.len(), 0);
     rig.expect_parent_request();
     rig.expect_empty_network();
@@ -269,11 +269,11 @@ fn test_parent_lookup_happy_path() {
     let peer_id = PeerId::random();
 
     // Trigger the request
-    bl.search_parent(Box::new(block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(block), peer_id, &mut cx);
     let id = rig.expect_parent_request();
 
     // Peer sends the right block, it should be sent for processing. Peer should not be penalized.
-    bl.parent_lookup_response(id, peer_id, Some(Box::new(parent)), D, &mut cx);
+    bl.parent_lookup_response(id, peer_id, Some(Arc::new(parent)), D, &mut cx);
     rig.expect_block_process();
     rig.expect_empty_network();
 
@@ -294,12 +294,12 @@ fn test_parent_lookup_wrong_response() {
     let peer_id = PeerId::random();
 
     // Trigger the request
-    bl.search_parent(Box::new(block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(block), peer_id, &mut cx);
     let id1 = rig.expect_parent_request();
 
     // Peer sends the wrong block, peer should be penalized and the block re-requested.
     let bad_block = rig.rand_block();
-    bl.parent_lookup_response(id1, peer_id, Some(Box::new(bad_block)), D, &mut cx);
+    bl.parent_lookup_response(id1, peer_id, Some(Arc::new(bad_block)), D, &mut cx);
     rig.expect_penalty();
     let id2 = rig.expect_parent_request();
 
@@ -308,7 +308,7 @@ fn test_parent_lookup_wrong_response() {
     rig.expect_empty_network();
 
     // Send the right block this time.
-    bl.parent_lookup_response(id2, peer_id, Some(Box::new(parent)), D, &mut cx);
+    bl.parent_lookup_response(id2, peer_id, Some(Arc::new(parent)), D, &mut cx);
     rig.expect_block_process();
 
     // Processing succeeds, now the rest of the chain should be sent for processing.
@@ -328,7 +328,7 @@ fn test_parent_lookup_empty_response() {
     let peer_id = PeerId::random();
 
     // Trigger the request
-    bl.search_parent(Box::new(block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(block), peer_id, &mut cx);
     let id1 = rig.expect_parent_request();
 
     // Peer sends an empty response, peer should be penalized and the block re-requested.
@@ -337,7 +337,7 @@ fn test_parent_lookup_empty_response() {
     let id2 = rig.expect_parent_request();
 
     // Send the right block this time.
-    bl.parent_lookup_response(id2, peer_id, Some(Box::new(parent)), D, &mut cx);
+    bl.parent_lookup_response(id2, peer_id, Some(Arc::new(parent)), D, &mut cx);
     rig.expect_block_process();
 
     // Processing succeeds, now the rest of the chain should be sent for processing.
@@ -357,7 +357,7 @@ fn test_parent_lookup_rpc_failure() {
     let peer_id = PeerId::random();
 
     // Trigger the request
-    bl.search_parent(Box::new(block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(block), peer_id, &mut cx);
     let id1 = rig.expect_parent_request();
 
     // The request fails. It should be tried again.
@@ -365,7 +365,7 @@ fn test_parent_lookup_rpc_failure() {
     let id2 = rig.expect_parent_request();
 
     // Send the right block this time.
-    bl.parent_lookup_response(id2, peer_id, Some(Box::new(parent)), D, &mut cx);
+    bl.parent_lookup_response(id2, peer_id, Some(Arc::new(parent)), D, &mut cx);
     rig.expect_block_process();
 
     // Processing succeeds, now the rest of the chain should be sent for processing.
@@ -385,7 +385,7 @@ fn test_parent_lookup_too_many_attempts() {
     let peer_id = PeerId::random();
 
     // Trigger the request
-    bl.search_parent(Box::new(block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(block), peer_id, &mut cx);
     for i in 1..=parent_lookup::PARENT_FAIL_TOLERANCE + 1 {
         let id = rig.expect_parent_request();
         match i % 2 {
@@ -397,7 +397,7 @@ fn test_parent_lookup_too_many_attempts() {
             _ => {
                 // Send a bad block this time. It should be tried again.
                 let bad_block = rig.rand_block();
-                bl.parent_lookup_response(id, peer_id, Some(Box::new(bad_block)), D, &mut cx);
+                bl.parent_lookup_response(id, peer_id, Some(Arc::new(bad_block)), D, &mut cx);
                 rig.expect_penalty();
             }
         }
@@ -427,12 +427,12 @@ fn test_parent_lookup_too_deep() {
     let peer_id = PeerId::random();
     let trigger_block = blocks.pop().unwrap();
     let chain_hash = trigger_block.canonical_root();
-    bl.search_parent(Box::new(trigger_block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(trigger_block), peer_id, &mut cx);
 
     for block in blocks.into_iter().rev() {
         let id = rig.expect_parent_request();
         // the block
-        bl.parent_lookup_response(id, peer_id, Some(Box::new(block.clone())), D, &mut cx);
+        bl.parent_lookup_response(id, peer_id, Some(Arc::new(block.clone())), D, &mut cx);
         // the stream termination
         bl.parent_lookup_response(id, peer_id, None, D, &mut cx);
         // the processing request
@@ -440,7 +440,7 @@ fn test_parent_lookup_too_deep() {
         // the processing result
         bl.parent_block_processed(
             chain_hash,
-            Err(BlockError::ParentUnknown(Box::new(block))),
+            Err(BlockError::ParentUnknown(Arc::new(block))),
             &mut cx,
         )
     }
@@ -454,7 +454,7 @@ fn test_parent_lookup_disconnection() {
     let (mut bl, mut cx, mut rig) = TestRig::test_setup(None);
     let peer_id = PeerId::random();
     let trigger_block = rig.rand_block();
-    bl.search_parent(Box::new(trigger_block), peer_id, &mut cx);
+    bl.search_parent(Arc::new(trigger_block), peer_id, &mut cx);
     bl.peer_disconnected(&peer_id, &mut cx);
     assert!(bl.parent_queue.is_empty());
 }