feat: child db for concurrent state (#87)

* fix: restore commit bounds to drivers

* feat: child db for concurrent state

* tests: write em

* test: even more stuff

* chore: bump version

* chore: lints and doclinks

Author: prestwich

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "trevm"
-version = "0.19.9"
+version = "0.19.10"
 rust-version = "1.83.0"
 edition = "2021"
 authors = ["init4"]

src/db/sync/cache.rs

@@ -44,6 +44,18 @@ impl ConcurrentCacheState {
         Self { accounts: DashMap::default(), contracts: DashMap::default(), has_state_clear }
     }
 
+    /// Absorb other into self, overwriting any existing values.
+    pub fn absorb(&self, other: Self) {
+        // NB: the `Extend` trait takes self by `&mut self`, so we have inlined
+        // it here
+        for pair in other.accounts.into_iter() {
+            self.accounts.insert(pair.0, pair.1);
+        }
+        for pair in other.contracts.into_iter() {
+            self.contracts.insert(pair.0, pair.1);
+        }
+    }
+
     /// Set state clear flag. EIP-161.
     pub fn set_state_clear_flag(&mut self, has_state_clear: bool) {
         self.has_state_clear = has_state_clear;

src/db/sync/child.rs

@@ -0,0 +1 @@
+

src/db/sync/error.rs

@@ -0,0 +1,25 @@
+use crate::db::ArcUpgradeError;
+
+/// Errors that can occur when working with a concurrent state.
+#[derive(Debug, thiserror::Error, Clone, Copy, PartialEq, Eq)]
+pub enum ConcurrentStateError {
+    /// Failed to upgrade the arc.
+    #[error("{0}")]
+    Arc(#[from] ArcUpgradeError),
+
+    /// This DB is not the parent of the child.
+    #[error("Child belongs to a different parent")]
+    NotParent,
+}
+
+impl ConcurrentStateError {
+    /// Create a new error for when the DB is not the parent of the child.
+    pub const fn not_parent() -> Self {
+        Self::NotParent
+    }
+
+    /// Create a new error for when the arc upgrade fails.
+    pub const fn not_unique() -> Self {
+        Self::Arc(ArcUpgradeError::NotUnique)
+    }
+}

src/db/sync/mod.rs

@@ -1,12 +1,14 @@
 mod builder;
-
 pub use builder::ConcurrentStateBuilder;
 
 mod cache;
 pub use cache::ConcurrentCacheState;
 
+mod error;
+pub use error::ConcurrentStateError;
+
 mod state;
-pub use state::{ConcurrentState, ConcurrentStateInfo};
+pub use state::{Child, ConcurrentState, ConcurrentStateInfo};
 
 use crate::db::StateAcc;
 use revm::{