SDK: Add sysvar to expose recent block hashes to programs (#6663)

* SDK: Add sysvar to expose recent block hashes to programs

* Blockhashes is one word

* Missed one

* Avoid allocs on update

* unwrap_or_else

* Use iterators

* Add microbench

* Revert "unwrap_or_else"

This reverts commit a8f8c3bfbe.

* Revert "Avoid allocs on update"

This reverts commit 486f01790c.

runtime/benches/bank.rs

@@ -9,6 +9,7 @@ use solana_runtime::loader_utils::create_invoke_instruction;
 use solana_sdk::account::KeyedAccount;
 use solana_sdk::client::AsyncClient;
 use solana_sdk::client::SyncClient;
+use solana_sdk::clock::MAX_RECENT_BLOCKHASHES;
 use solana_sdk::genesis_block::create_genesis_block;
 use solana_sdk::instruction::InstructionError;
 use solana_sdk::pubkey::Pubkey;
@@ -173,3 +174,26 @@ fn bench_bank_async_process_builtin_transactions(bencher: &mut Bencher) {
 fn bench_bank_async_process_native_loader_transactions(bencher: &mut Bencher) {
     do_bench_transactions(bencher, &async_bencher, &create_native_loader_transactions);
 }
+
+#[bench]
+#[ignore]
+fn bench_bank_update_recent_blockhashes(bencher: &mut Bencher) {
+    let (genesis_block, _mint_keypair) = create_genesis_block(100);
+    let mut bank = Arc::new(Bank::new(&genesis_block));
+    goto_end_of_slot(Arc::get_mut(&mut bank).unwrap());
+    let genesis_blockhash = bank.last_blockhash();
+    // Prime blockhash_queue
+    for i in 0..(MAX_RECENT_BLOCKHASHES + 1) {
+        bank = Arc::new(Bank::new_from_parent(
+            &bank,
+            &Pubkey::default(),
+            (i + 1) as u64,
+        ));
+        goto_end_of_slot(Arc::get_mut(&mut bank).unwrap());
+    }
+    // Verify blockhash_queue is full (genesis blockhash has been kicked out)
+    assert!(!bank.check_hash_age(&genesis_blockhash, MAX_RECENT_BLOCKHASHES));
+    bencher.iter(|| {
+        bank.update_recent_blockhashes();
+    });
+}

runtime/src/bank.rs

@@ -291,6 +291,7 @@ impl Bank {
         bank.update_clock();
         bank.update_rent();
         bank.update_epoch_schedule();
+        bank.update_recent_blockhashes();
         bank
     }
 
@@ -385,6 +386,7 @@ impl Bank {
         new.update_stake_history(Some(parent.epoch()));
         new.update_clock();
         new.update_fees();
+        new.update_recent_blockhashes();
         new
     }
 
@@ -539,6 +541,15 @@ impl Bank {
         );
     }
 
+    pub fn update_recent_blockhashes(&self) {
+        let blockhash_queue = self.blockhash_queue.read().unwrap();
+        let recent_blockhash_iter = blockhash_queue.get_recent_blockhashes();
+        self.store_account(
+            &sysvar::recent_blockhashes::id(),
+            &sysvar::recent_blockhashes::create_account_with_data(1, recent_blockhash_iter),
+        );
+    }
+
     // If the point values are not `normal`, bring them back into range and
     // set them to the last value or 0.
     fn check_point_values(
@@ -1599,6 +1610,18 @@ impl Drop for Bank {
     }
 }
 
+pub fn goto_end_of_slot(bank: &mut Bank) {
+    let mut tick_hash = bank.last_blockhash();
+    loop {
+        tick_hash = hashv(&[&tick_hash.as_ref(), &[42]]);
+        bank.register_tick(&tick_hash);
+        if tick_hash == bank.last_blockhash() {
+            bank.freeze();
+            return;
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -2023,18 +2046,6 @@ mod tests {
         assert_eq!(bank.get_balance(&key.pubkey()), 1);
     }
 
-    fn goto_end_of_slot(bank: &mut Bank) {
-        let mut tick_hash = bank.last_blockhash();
-        loop {
-            tick_hash = hashv(&[&tick_hash.as_ref(), &[42]]);
-            bank.register_tick(&tick_hash);
-            if tick_hash == bank.last_blockhash() {
-                bank.freeze();
-                return;
-            }
-        }
-    }
-
     #[test]
     fn test_bank_tx_fee() {
         let arbitrary_transfer_amount = 42;
@@ -3322,4 +3333,22 @@ mod tests {
         // Non-native loader accounts can not be used for instruction processing
         bank.add_instruction_processor(mint_keypair.pubkey(), mock_ix_processor);
     }
+
+    #[test]
+    fn test_recent_blockhashes_sysvar() {
+        let (genesis_block, _mint_keypair) = create_genesis_block(500);
+        let mut bank = Arc::new(Bank::new(&genesis_block));
+        for i in 1..5 {
+            let bhq_account = bank.get_account(&sysvar::recent_blockhashes::id()).unwrap();
+            let recent_blockhashes =
+                sysvar::recent_blockhashes::RecentBlockhashes::from_account(&bhq_account).unwrap();
+            // Check length
+            assert_eq!(recent_blockhashes.len(), i);
+            let most_recent_hash = recent_blockhashes.iter().nth(0).unwrap();
+            // Check order
+            assert!(bank.check_hash_age(most_recent_hash, 0));
+            goto_end_of_slot(Arc::get_mut(&mut bank).unwrap());
+            bank = Arc::new(new_from_parent(&bank));
+        }
+    }
 }

runtime/src/blockhash_queue.rs

@@ -114,11 +114,16 @@ impl BlockhashQueue {
         }
         None
     }
+
+    pub fn get_recent_blockhashes(&self) -> impl Iterator<Item = (u64, &Hash)> {
+        (&self.ages).iter().map(|(k, v)| (v.hash_height, k))
+    }
 }
 #[cfg(test)]
 mod tests {
     use super::*;
     use bincode::serialize;
+    use solana_sdk::clock::MAX_RECENT_BLOCKHASHES;
     use solana_sdk::hash::hash;
 
     #[test]
@@ -150,4 +155,21 @@ mod tests {
         assert_eq!(last_hash, hash_queue.last_hash());
         assert!(hash_queue.check_hash_age(&last_hash, 0));
     }
+
+    #[test]
+    fn test_get_recent_blockhashes() {
+        let mut blockhash_queue = BlockhashQueue::new(MAX_RECENT_BLOCKHASHES);
+        let recent_blockhashes = blockhash_queue.get_recent_blockhashes();
+        // Sanity-check an empty BlockhashQueue
+        assert_eq!(recent_blockhashes.count(), 0);
+        for i in 0..MAX_RECENT_BLOCKHASHES {
+            let hash = hash(&serialize(&i).unwrap());
+            blockhash_queue.register_hash(&hash, &FeeCalculator::default());
+        }
+        let recent_blockhashes = blockhash_queue.get_recent_blockhashes();
+        // Verify that the returned hashes are most recent
+        for (_slot, hash) in recent_blockhashes {
+            assert!(blockhash_queue.check_hash_age(hash, MAX_RECENT_BLOCKHASHES));
+        }
+    }
 }