Allow TaskExecutor to be used in async tests (#3178)

# Description

Since the `TaskExecutor` currently requires a `Weak<Runtime>`, it's impossible to use it in an async test where the `Runtime` is created outside our scope. Whilst we *could* create a new `Runtime` instance inside the async test, dropping that `Runtime` would cause a panic (you can't drop a `Runtime` in an async context).

To address this issue, this PR creates the `enum Handle`, which supports either:

- A `Weak<Runtime>` (for use in our production code)
- A `Handle` to a runtime (for use in testing)

In theory, there should be no change to the behaviour of our production code (beyond some slightly different descriptions in HTTP 500 errors), or even our tests. If there is no change, you might ask *"why bother?"*. There are two PRs (#3070 and #3175) that are waiting on these fixes to introduce some new tests. Since we've added the EL to the `BeaconChain` (for the merge), we are now doing more async stuff in tests.

I've also added a `RuntimeExecutor` to the `BeaconChainTestHarness`. Whilst that's not immediately useful, it will become useful in the near future with all the new async testing.

beacon_node/execution_layer/src/lib.rs

@@ -304,11 +304,7 @@ impl ExecutionLayer {
         T: Fn(&'a Self) -> U,
         U: Future<Output = Result<V, Error>>,
     {
-        let runtime = self
-            .executor()
-            .runtime()
-            .upgrade()
-            .ok_or(Error::ShuttingDown)?;
+        let runtime = self.executor().handle().ok_or(Error::ShuttingDown)?;
         // TODO(merge): respect the shutdown signal.
         runtime.block_on(generate_future(self))
     }
@@ -322,11 +318,7 @@ impl ExecutionLayer {
         T: Fn(&'a Self) -> U,
         U: Future<Output = V>,
     {
-        let runtime = self
-            .executor()
-            .runtime()
-            .upgrade()
-            .ok_or(Error::ShuttingDown)?;
+        let runtime = self.executor().handle().ok_or(Error::ShuttingDown)?;
         // TODO(merge): respect the shutdown signal.
         Ok(runtime.block_on(generate_future(self)))
     }
@@ -1263,13 +1255,15 @@ impl ExecutionLayer {
 mod test {
     use super::*;
     use crate::test_utils::MockExecutionLayer as GenericMockExecutionLayer;
+    use task_executor::test_utils::TestRuntime;
     use types::MainnetEthSpec;
 
     type MockExecutionLayer = GenericMockExecutionLayer<MainnetEthSpec>;
 
     #[tokio::test]
     async fn produce_three_valid_pos_execution_blocks() {
-        MockExecutionLayer::default_params()
+        let runtime = TestRuntime::default();
+        MockExecutionLayer::default_params(runtime.task_executor.clone())
             .move_to_terminal_block()
             .produce_valid_execution_payload_on_head()
             .await
@@ -1281,7 +1275,8 @@ mod test {
 
     #[tokio::test]
     async fn finds_valid_terminal_block_hash() {
-        MockExecutionLayer::default_params()
+        let runtime = TestRuntime::default();
+        MockExecutionLayer::default_params(runtime.task_executor.clone())
             .move_to_block_prior_to_terminal_block()
             .with_terminal_block(|spec, el, _| async move {
                 el.engines().upcheck_not_synced(Logging::Disabled).await;
@@ -1300,7 +1295,8 @@ mod test {
 
     #[tokio::test]
     async fn verifies_valid_terminal_block_hash() {
-        MockExecutionLayer::default_params()
+        let runtime = TestRuntime::default();
+        MockExecutionLayer::default_params(runtime.task_executor.clone())
             .move_to_terminal_block()
             .with_terminal_block(|spec, el, terminal_block| async move {
                 el.engines().upcheck_not_synced(Logging::Disabled).await;
@@ -1316,7 +1312,8 @@ mod test {
 
     #[tokio::test]
     async fn rejects_invalid_terminal_block_hash() {
-        MockExecutionLayer::default_params()
+        let runtime = TestRuntime::default();
+        MockExecutionLayer::default_params(runtime.task_executor.clone())
             .move_to_terminal_block()
             .with_terminal_block(|spec, el, terminal_block| async move {
                 el.engines().upcheck_not_synced(Logging::Disabled).await;
@@ -1334,7 +1331,8 @@ mod test {
 
     #[tokio::test]
     async fn rejects_unknown_terminal_block_hash() {
-        MockExecutionLayer::default_params()
+        let runtime = TestRuntime::default();
+        MockExecutionLayer::default_params(runtime.task_executor.clone())
             .move_to_terminal_block()
             .with_terminal_block(|spec, el, _| async move {
                 el.engines().upcheck_not_synced(Logging::Disabled).await;

beacon_node/execution_layer/src/test_utils/mock_execution_layer.rs

@@ -2,61 +2,22 @@ use crate::{
     test_utils::{MockServer, DEFAULT_TERMINAL_BLOCK, DEFAULT_TERMINAL_DIFFICULTY, JWT_SECRET},
     Config, *,
 };
-use environment::null_logger;
 use sensitive_url::SensitiveUrl;
-use std::sync::Arc;
 use task_executor::TaskExecutor;
 use tempfile::NamedTempFile;
 use types::{Address, ChainSpec, Epoch, EthSpec, FullPayload, Hash256, Uint256};
 
-pub struct ExecutionLayerRuntime {
-    pub runtime: Option<Arc<tokio::runtime::Runtime>>,
-    pub _runtime_shutdown: exit_future::Signal,
-    pub task_executor: TaskExecutor,
-    pub log: Logger,
-}
-
-impl Default for ExecutionLayerRuntime {
-    fn default() -> Self {
-        let runtime = Arc::new(
-            tokio::runtime::Builder::new_multi_thread()
-                .enable_all()
-                .build()
-                .unwrap(),
-        );
-        let (runtime_shutdown, exit) = exit_future::signal();
-        let (shutdown_tx, _) = futures::channel::mpsc::channel(1);
-        let log = null_logger().unwrap();
-        let task_executor =
-            TaskExecutor::new(Arc::downgrade(&runtime), exit, log.clone(), shutdown_tx);
-
-        Self {
-            runtime: Some(runtime),
-            _runtime_shutdown: runtime_shutdown,
-            task_executor,
-            log,
-        }
-    }
-}
-
-impl Drop for ExecutionLayerRuntime {
-    fn drop(&mut self) {
-        if let Some(runtime) = self.runtime.take() {
-            Arc::try_unwrap(runtime).unwrap().shutdown_background()
-        }
-    }
-}
-
 pub struct MockExecutionLayer<T: EthSpec> {
     pub server: MockServer<T>,
     pub el: ExecutionLayer,
-    pub el_runtime: ExecutionLayerRuntime,
+    pub executor: TaskExecutor,
     pub spec: ChainSpec,
 }
 
 impl<T: EthSpec> MockExecutionLayer<T> {
-    pub fn default_params() -> Self {
+    pub fn default_params(executor: TaskExecutor) -> Self {
         Self::new(
+            executor,
             DEFAULT_TERMINAL_DIFFICULTY.into(),
             DEFAULT_TERMINAL_BLOCK,
             ExecutionBlockHash::zero(),
@@ -65,13 +26,13 @@ impl<T: EthSpec> MockExecutionLayer<T> {
     }
 
     pub fn new(
+        executor: TaskExecutor,
         terminal_total_difficulty: Uint256,
         terminal_block: u64,
         terminal_block_hash: ExecutionBlockHash,
         terminal_block_hash_activation_epoch: Epoch,
     ) -> Self {
-        let el_runtime = ExecutionLayerRuntime::default();
-        let handle = el_runtime.runtime.as_ref().unwrap().handle();
+        let handle = executor.handle().unwrap();
 
         let mut spec = T::default_spec();
         spec.terminal_total_difficulty = terminal_total_difficulty;
@@ -79,7 +40,7 @@ impl<T: EthSpec> MockExecutionLayer<T> {
         spec.terminal_block_hash_activation_epoch = terminal_block_hash_activation_epoch;
 
         let server = MockServer::new(
-            handle,
+            &handle,
             terminal_total_difficulty,
             terminal_block,
             terminal_block_hash,
@@ -97,17 +58,13 @@ impl<T: EthSpec> MockExecutionLayer<T> {
             suggested_fee_recipient: Some(Address::repeat_byte(42)),
             ..Default::default()
         };
-        let el = ExecutionLayer::from_config(
-            config,
-            el_runtime.task_executor.clone(),
-            el_runtime.log.clone(),
-        )
-        .unwrap();
+        let el =
+            ExecutionLayer::from_config(config, executor.clone(), executor.log().clone()).unwrap();
 
         Self {
             server,
             el,
-            el_runtime,
+            executor,
             spec,
         }
     }

beacon_node/execution_layer/src/test_utils/mod.rs

@@ -22,7 +22,7 @@ use types::{EthSpec, ExecutionBlockHash, Uint256};
 use warp::{http::StatusCode, Filter, Rejection};
 
 pub use execution_block_generator::{generate_pow_block, ExecutionBlockGenerator};
-pub use mock_execution_layer::{ExecutionLayerRuntime, MockExecutionLayer};
+pub use mock_execution_layer::MockExecutionLayer;
 
 pub const DEFAULT_TERMINAL_DIFFICULTY: u64 = 6400;
 pub const DEFAULT_TERMINAL_BLOCK: u64 = 64;