Make StakeHistory clone-on-write (solana-labs#21573)

Author: brooksprumo

runtime/src/lib.rs

@@ -49,6 +49,7 @@ pub mod snapshot_package;
 pub mod snapshot_utils;
 pub mod sorted_storages;
 pub mod stake_delegations;
+pub mod stake_history;
 pub mod stake_weighted_timestamp;
 pub mod stakes;
 pub mod status_cache;

runtime/src/serde_snapshot/tests.rs

@@ -312,7 +312,7 @@ mod test_bank_serialize {
 
     // This some what long test harness is required to freeze the ABI of
     // Bank's serialization due to versioned nature
-    #[frozen_abi(digest = "FBhQnLvFHaCkXN8ZL8MaR6yQUhLgyvWqdoFeBRwsmbBo")]
+    #[frozen_abi(digest = "Fv5AFJSnZi9sssiE7Jn8bH2iTPnqu3UNc3np62r1sTsr")]
     #[derive(Serialize, AbiExample)]
     pub struct BankAbiTestWrapperFuture {
         #[serde(serialize_with = "wrapper_future")]

runtime/src/stake_history.rs

@@ -0,0 +1,84 @@
+//! This module implements clone-on-write semantics for the SDK's `StakeHistory` to reduce
+//! unnecessary cloning of the underlying vector.
+use std::{
+    ops::{Deref, DerefMut},
+    sync::Arc,
+};
+
+/// The SDK's stake history with clone-on-write semantics
+#[derive(Default, Clone, PartialEq, Debug, Deserialize, Serialize, AbiExample)]
+pub struct StakeHistory(Arc<StakeHistoryInner>);
+
+impl Deref for StakeHistory {
+    type Target = StakeHistoryInner;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for StakeHistory {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        Arc::make_mut(&mut self.0)
+    }
+}
+
+/// The inner type, which is the SDK's stake history
+type StakeHistoryInner = solana_sdk::stake_history::StakeHistory;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use solana_sdk::stake_history::StakeHistoryEntry;
+
+    fn rand_stake_history_entry() -> StakeHistoryEntry {
+        StakeHistoryEntry {
+            effective: rand::random(),
+            activating: rand::random(),
+            deactivating: rand::random(),
+        }
+    }
+
+    #[test]
+    fn test_stake_history_is_cow() {
+        let mut stake_history = StakeHistory::default();
+        (100..109).for_each(|epoch| {
+            let entry = rand_stake_history_entry();
+            stake_history.add(epoch, entry);
+        });
+
+        // Test: Clone the stake history and **do not modify**.  Assert the underlying instances
+        // are the same.
+        {
+            let stake_history2 = stake_history.clone();
+            assert_eq!(stake_history, stake_history2);
+            assert!(
+                Arc::ptr_eq(&stake_history.0, &stake_history2.0),
+                "Inner Arc must point to the same underlying instance"
+            );
+            assert!(
+                std::ptr::eq(stake_history.deref(), stake_history2.deref()),
+                "Deref must point to the same underlying instance"
+            );
+        }
+
+        // Test: Clone the stake history and then modify.  Assert the underlying instances are
+        // unique.
+        {
+            let mut stake_history2 = stake_history.clone();
+            assert_eq!(stake_history, stake_history2);
+            (200..209).for_each(|epoch| {
+                let entry = rand_stake_history_entry();
+                stake_history2.add(epoch, entry);
+            });
+            assert_ne!(stake_history, stake_history2);
+            assert!(
+                !Arc::ptr_eq(&stake_history.0, &stake_history2.0),
+                "Inner Arc must point to a different underlying instance"
+            );
+            assert!(
+                !std::ptr::eq(stake_history.deref(), stake_history2.deref()),
+                "Deref must point to a different underlying instance"
+            );
+        }
+    }
+}

runtime/src/stakes.rs

@@ -3,6 +3,7 @@
 use {
     crate::{
         stake_delegations::StakeDelegations,
+        stake_history::StakeHistory,
         vote_account::{VoteAccount, VoteAccounts, VoteAccountsHashMap},
     },
     rayon::{
@@ -17,7 +18,6 @@ use {
             self,
             state::{Delegation, StakeActivationStatus, StakeState},
         },
-        stake_history::StakeHistory,
     },
     solana_stake_program::stake_state,
     solana_vote_program::vote_state::VoteState,