From 754f25ae99bfdbd97beab44b884bca12272c34f3 Mon Sep 17 00:00:00 2001
From: Justin Starry <justin@solana.com>
Date: Fri, 5 Jun 2020 10:06:01 +0800
Subject: [PATCH] Avoid AccountInUse errors when simulating transactions
 (#10391)

automerge
---
 core/src/rpc.rs                  | 12 +++++-------
 runtime/src/bank.rs              |  9 +++++++++
 runtime/src/transaction_batch.rs | 17 +++++++++++++++++
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/core/src/rpc.rs b/core/src/rpc.rs
index a76cbe8635..f303e26a75 100644
--- a/core/src/rpc.rs
+++ b/core/src/rpc.rs
@@ -718,13 +718,11 @@ fn verify_signature(input: &str) -> Result<Signature> {
 }
 
 /// Run transactions against a frozen bank without committing the results
-fn run_transaction_simulation(
-    bank: &Bank,
-    transactions: &[Transaction],
-) -> transaction::Result<()> {
+fn run_transaction_simulation(bank: &Bank, transaction: Transaction) -> transaction::Result<()> {
     assert!(bank.is_frozen(), "simulation bank must be frozen");
 
-    let batch = bank.prepare_batch(transactions, None);
+    let txs = &[transaction];
+    let batch = bank.prepare_simulation_batch(txs);
     let (_loaded_accounts, executed, _retryable_transactions, _transaction_count, _signature_count) =
         bank.load_and_execute_transactions(&batch, solana_sdk::clock::MAX_PROCESSING_AGE);
     executed[0].0.clone().map(|_| ())
@@ -1454,7 +1452,7 @@ impl RpcSol for RpcSolImpl {
             }
 
             let bank = &*meta.request_processor.read().unwrap().bank(None)?;
-            if let Err(err) = run_transaction_simulation(&bank, &[transaction]) {
+            if let Err(err) = run_transaction_simulation(&bank, transaction) {
                 // Note: it's possible that the transaction simulation failed but the actual
                 // transaction would succeed, such as when a transaction depends on an earlier
                 // transaction that has yet to reach max confirmations. In these cases the user
@@ -1501,7 +1499,7 @@ impl RpcSol for RpcSolImpl {
         let bank = &*meta.request_processor.read().unwrap().bank(None)?;
 
         if result.is_ok() {
-            result = run_transaction_simulation(&bank, &[transaction]);
+            result = run_transaction_simulation(&bank, transaction);
         }
 
         new_response(
diff --git a/runtime/src/bank.rs b/runtime/src/bank.rs
index 8959f236ac..b1515adb82 100644
--- a/runtime/src/bank.rs
+++ b/runtime/src/bank.rs
@@ -1058,6 +1058,15 @@ impl Bank {
         TransactionBatch::new(results, &self, txs, iteration_order)
     }
 
+    pub fn prepare_simulation_batch<'a, 'b>(
+        &'a self,
+        txs: &'b [Transaction],
+    ) -> TransactionBatch<'a, 'b> {
+        let mut batch = TransactionBatch::new(vec![Ok(()); txs.len()], &self, txs, None);
+        batch.needs_unlock = false;
+        batch
+    }
+
     pub fn unlock_accounts(&self, batch: &mut TransactionBatch) {
         if batch.needs_unlock {
             batch.needs_unlock = false;
diff --git a/runtime/src/transaction_batch.rs b/runtime/src/transaction_batch.rs
index 597de36274..9f03ad33fa 100644
--- a/runtime/src/transaction_batch.rs
+++ b/runtime/src/transaction_batch.rs
@@ -81,6 +81,23 @@ mod tests {
         assert!(batch2.lock_results().iter().all(|x| x.is_ok()));
     }
 
+    #[test]
+    fn test_simulation_batch() {
+        let (bank, txs) = setup();
+
+        // Prepare batch without locks
+        let batch = bank.prepare_simulation_batch(&txs);
+        assert!(batch.lock_results().iter().all(|x| x.is_ok()));
+
+        // Grab locks
+        let batch2 = bank.prepare_batch(&txs, None);
+        assert!(batch2.lock_results().iter().all(|x| x.is_ok()));
+
+        // Prepare another batch without locks
+        let batch3 = bank.prepare_simulation_batch(&txs);
+        assert!(batch3.lock_results().iter().all(|x| x.is_ok()));
+    }
+
     fn setup() -> (Bank, Vec<Transaction>) {
         let dummy_leader_pubkey = Pubkey::new_rand();
         let GenesisConfigInfo {