Process async BankClient transactions in batches (#3738)

* Process async transactions in batches

This aims to process transactions at least as fast as LocalCluster

* Add benchmark

runtime/src/bank_client.rs

@@ -1,5 +1,5 @@
 use crate::bank::Bank;
-use solana_sdk::client::{AsyncClient, SyncClient};
+use solana_sdk::client::{AsyncClient, Client, SyncClient};
 use solana_sdk::hash::Hash;
 use solana_sdk::instruction::Instruction;
 use solana_sdk::message::Message;
@@ -10,17 +10,22 @@ use solana_sdk::system_instruction;
 use solana_sdk::transaction::{self, Transaction};
 use solana_sdk::transport::Result;
 use std::io;
+use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::Arc;
+use std::thread::Builder;
 
 pub struct BankClient {
-    bank: Bank,
+    bank: Arc<Bank>,
+    transaction_sender: Sender<Transaction>,
 }
 
+impl Client for BankClient {}
+
 impl AsyncClient for BankClient {
     fn async_send_transaction(&self, transaction: Transaction) -> io::Result<Signature> {
-        // Ignore the result. Client must use get_signature_status() instead.
-        let _ = self.bank.process_transaction(&transaction);
-
-        Ok(transaction.signatures.get(0).cloned().unwrap_or_default())
+        let signature = transaction.signatures.get(0).cloned().unwrap_or_default();
+        self.transaction_sender.send(transaction).unwrap();
+        Ok(signature)
     }
 
     fn async_send_message(
@@ -104,8 +109,29 @@ impl SyncClient for BankClient {
 }
 
 impl BankClient {
+    fn run(bank: &Bank, transaction_receiver: Receiver<Transaction>) {
+        while let Ok(tx) = transaction_receiver.recv() {
+            let mut transactions = vec![tx];
+            while let Ok(tx) = transaction_receiver.try_recv() {
+                transactions.push(tx);
+            }
+            let _ = bank.process_transactions(&transactions);
+        }
+    }
+
     pub fn new(bank: Bank) -> Self {
-        Self { bank }
+        let bank = Arc::new(bank);
+        let (transaction_sender, transaction_receiver) = channel();
+        let thread_bank = bank.clone();
+        let bank = bank.clone();
+        Builder::new()
+            .name("solana-bank-client".to_string())
+            .spawn(move || Self::run(&thread_bank, transaction_receiver))
+            .unwrap();
+        Self {
+            bank,
+            transaction_sender,
+        }
     }
 }