Merge #12330: Reduce scope of cs_main and cs_wallet locks in listtransactions

c409b1adac [rpc] Reduce scope of cs_main and cs_wallet locks in listtransactions (João Barbosa)

Pull request description:

  Trivial change, no behaviour change.

  Benchmark done as follow:
   - run with `-regtest`
   - wallet with 5000 transactions
   - measured the time spent with the lock and the total time
   - times are an average of 100 `listtransactions --count=...` calls

  | `--count` | lock (ms) | total (ms) | saving |
  |--:|--:|--:|--:|
  | 10 | 0.2230 | 0.2510 | 11% |
  | 100 | 2.5150 | 2.8690 | 12% |
  | 1000 | 20.0320 | 23.3490 | 14% |
  | 10000 | 105.2070 | 125.5310 | 16% |

Tree-SHA512: ebedfeeb4c8ad75c89128e53cae976a82967dbb5ffd129da0f7204ccf9c3c15070b3d509f3767bebd745512e410200cc546147c836e82409f95fc9b8d14fc3ed

src/wallet/rpcwallet.cpp

@@ -1794,8 +1794,6 @@ UniValue listtransactions(const JSONRPCRequest& request)
     // the user could have gotten from another RPC command prior to now
     pwallet->BlockUntilSyncedToCurrentChain();
 
-    LOCK2(cs_main, pwallet->cs_wallet);
-
     std::string strAccount = "*";
     if (!request.params[0].isNull())
         strAccount = request.params[0].get_str();
@@ -1817,6 +1815,9 @@ UniValue listtransactions(const JSONRPCRequest& request)
 
     UniValue ret(UniValue::VARR);
 
+    {
+        LOCK2(cs_main, pwallet->cs_wallet);
+
         const CWallet::TxItems & txOrdered = pwallet->wtxOrdered;
 
         // iterate backwards until we have nCount items to return:
@@ -1831,6 +1832,8 @@ UniValue listtransactions(const JSONRPCRequest& request)
 
             if ((int)ret.size() >= (nCount+nFrom)) break;
         }
+    }
+
     // ret is newest to oldest
 
     if (nFrom > (int)ret.size())