From 486f01790c271cf09ac3dbffba0e40e526e81324 Mon Sep 17 00:00:00 2001
From: Trent Nelson <trent@solana.com>
Date: Thu, 31 Oct 2019 16:19:49 -0600
Subject: [PATCH] Avoid allocs on update

---
 runtime/src/bank.rs                  | 19 +++++++++----------
 sdk/src/sysvar/recent_blockhashes.rs | 20 ++++++++++++++------
 2 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/runtime/src/bank.rs b/runtime/src/bank.rs
index ab7793319a..318017e2bb 100644
--- a/runtime/src/bank.rs
+++ b/runtime/src/bank.rs
@@ -543,10 +543,13 @@ impl Bank {
             .read()
             .unwrap()
             .get_recent_blockhashes(sysvar::recent_blockhashes::MAX_ENTRIES);
-        self.store_account(
-            &sysvar::recent_blockhashes::id(),
-            &sysvar::recent_blockhashes::create_account(1, recent_blockhashes),
-        );
+        let id = sysvar::recent_blockhashes::id();
+        let mut account = self
+            .get_account(&id)
+            .or_else(|| Some(sysvar::recent_blockhashes::create_account(1)))
+            .unwrap();
+        sysvar::recent_blockhashes::update_account(&mut account, recent_blockhashes).unwrap();
+        self.store_account(&id, &account);
     }
 
     // If the point values are not `normal`, bring them back into range and
@@ -3360,17 +3363,13 @@ mod tests {
     fn test_recent_blockhashes_sysvar() {
         let (genesis_block, _mint_keypair) = create_genesis_block(500);
         let mut bank = Arc::new(Bank::new(&genesis_block));
-        let bhq_account = bank
-            .get_account(&sysvar::recent_blockhashes::id())
-            .unwrap();
+        let bhq_account = bank.get_account(&sysvar::recent_blockhashes::id()).unwrap();
         let recent_blockhashes =
             sysvar::recent_blockhashes::RecentBlockhashes::from_account(&bhq_account).unwrap();
         assert_eq!(recent_blockhashes.len(), 1);
         goto_end_of_slot(Arc::get_mut(&mut bank).unwrap());
         let bank = Arc::new(new_from_parent(&bank));
-        let bhq_account = bank
-            .get_account(&sysvar::recent_blockhashes::id())
-            .unwrap();
+        let bhq_account = bank.get_account(&sysvar::recent_blockhashes::id()).unwrap();
         let recent_blockhashes =
             sysvar::recent_blockhashes::RecentBlockhashes::from_account(&bhq_account).unwrap();
         assert_eq!(recent_blockhashes.len(), 2);
diff --git a/sdk/src/sysvar/recent_blockhashes.rs b/sdk/src/sysvar/recent_blockhashes.rs
index 1a8742592d..e3902b2956 100644
--- a/sdk/src/sysvar/recent_blockhashes.rs
+++ b/sdk/src/sysvar/recent_blockhashes.rs
@@ -46,10 +46,18 @@ impl Deref for RecentBlockhashes {
     }
 }
 
-pub fn create_account(lamports: u64, recent_blockhashes: Vec<Hash>) -> Account {
-    let mut account = Account::new(lamports, RecentBlockhashes::size_of(), &sysvar::id());
+pub fn create_account(lamports: u64) -> Account {
+    Account::new(lamports, RecentBlockhashes::size_of(), &sysvar::id())
+}
+
+pub fn update_account(account: &mut Account, recent_blockhashes: Vec<Hash>) -> Option<()> {
     let recent_blockhashes = RecentBlockhashes(recent_blockhashes);
-    recent_blockhashes.to_account(&mut account).unwrap();
+    recent_blockhashes.to_account(account)
+}
+
+pub fn create_account_with_data(lamports: u64, recent_blockhashes: Vec<Hash>) -> Account {
+    let mut account = create_account(lamports);
+    update_account(&mut account, recent_blockhashes).unwrap();
     account
 }
 
@@ -60,14 +68,14 @@ mod tests {
 
     #[test]
     fn test_create_account_empty() {
-        let account = create_account(42, vec![]);
+        let account = create_account_with_data(42, vec![]);
         let recent_blockhashes = RecentBlockhashes::from_account(&account).unwrap();
         assert_eq!(recent_blockhashes, RecentBlockhashes::default());
     }
 
     #[test]
     fn test_create_account_full() {
-        let account = create_account(42, vec![Hash::default(); MAX_ENTRIES]);
+        let account = create_account_with_data(42, vec![Hash::default(); MAX_ENTRIES]);
         let recent_blockhashes = RecentBlockhashes::from_account(&account).unwrap();
         assert_eq!(recent_blockhashes.len(), MAX_ENTRIES);
     }
@@ -75,7 +83,7 @@ mod tests {
     #[test]
     #[should_panic]
     fn test_create_account_too_big() {
-        let account = create_account(42, vec![Hash::default(); MAX_ENTRIES + 1]);
+        let account = create_account_with_data(42, vec![Hash::default(); MAX_ENTRIES + 1]);
         RecentBlockhashes::from_account(&account).unwrap();
     }
 }