From 41106a50d2be9358ab19e75c1d6d075a773525b7 Mon Sep 17 00:00:00 2001
From: "Wladimir J. van der Laan" <laanwj@gmail.com>
Date: Wed, 23 Apr 2014 08:40:48 +0200
Subject: [PATCH] qt: get required locks upfront in polling functions

This avoids the GUI from getting stuck on
periodical polls if the core is holding the locks for a longer time -
for example, during a wallet rescan.
---
 src/qt/clientmodel.cpp           |  6 ++++++
 src/qt/transactiontablemodel.cpp | 21 ++++++++++++++-------
 src/qt/walletmodel.cpp           | 25 ++++++++++++++-----------
 3 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index 287296644c2..3c0564c2081 100644
--- a/src/qt/clientmodel.cpp
+++ b/src/qt/clientmodel.cpp
@@ -92,6 +92,12 @@ double ClientModel::getVerificationProgress() const
 
 void ClientModel::updateTimer()
 {
+    // Get required lock upfront. This avoids the GUI from getting stuck on
+    // periodical polls if the core is holding the locks for a longer time -
+    // for example, during a wallet rescan.
+    TRY_LOCK(cs_main, lockMain);
+    if(!lockMain)
+        return;
     // Some quantities (such as number of blocks) change so fast that we don't want to be notified for each change.
     // Periodically check and update with a timer.
     int newNumBlocks = getNumBlocks();
diff --git a/src/qt/transactiontablemodel.cpp b/src/qt/transactiontablemodel.cpp
index aaecf88c258..df412650d8c 100644
--- a/src/qt/transactiontablemodel.cpp
+++ b/src/qt/transactiontablemodel.cpp
@@ -24,7 +24,6 @@
 #include <QDebug>
 #include <QIcon>
 #include <QList>
-#include <QTimer>
 
 // Amount column is right-aligned it contains numbers
 static int column_alignments[] = {
@@ -187,17 +186,25 @@ public:
         {
             TransactionRecord *rec = &cachedWallet[idx];
 
+            // Get required locks upfront. This avoids the GUI from getting
+            // stuck if the core is holding the locks for a longer time - for
+            // example, during a wallet rescan.
+            //
             // If a status update is needed (blocks came in since last check),
             //  update the status of this transaction from the wallet. Otherwise,
             // simply re-use the cached status.
-            LOCK2(cs_main, wallet->cs_wallet);
-            if(rec->statusUpdateNeeded())
+            TRY_LOCK(cs_main, lockMain);
+            if(lockMain)
             {
-                std::map<uint256, CWalletTx>::iterator mi = wallet->mapWallet.find(rec->hash);
-
-                if(mi != wallet->mapWallet.end())
+                TRY_LOCK(wallet->cs_wallet, lockWallet);
+                if(lockWallet && rec->statusUpdateNeeded())
                 {
-                    rec->updateStatus(mi->second);
+                    std::map<uint256, CWalletTx>::iterator mi = wallet->mapWallet.find(rec->hash);
+
+                    if(mi != wallet->mapWallet.end())
+                    {
+                        rec->updateStatus(mi->second);
+                    }
                 }
             }
             return rec;
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 61f26107afc..37d82ec0633 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -98,18 +98,21 @@ void WalletModel::updateStatus()
 
 void WalletModel::pollBalanceChanged()
 {
-    bool heightChanged = false;
-    {
-        LOCK(cs_main);
-        if(chainActive.Height() != cachedNumBlocks)
-        {
-            // Balance and number of transactions might have changed
-            cachedNumBlocks = chainActive.Height();
-            heightChanged = true;
-        }
-    }
-    if(heightChanged)
+    // Get required locks upfront. This avoids the GUI from getting stuck on
+    // periodical polls if the core is holding the locks for a longer time -
+    // for example, during a wallet rescan.
+    TRY_LOCK(cs_main, lockMain);
+    if(!lockMain)
+        return;
+    TRY_LOCK(wallet->cs_wallet, lockWallet);
+    if(!lockWallet)
+        return;
+
+    if(chainActive.Height() != cachedNumBlocks)
     {
+        // Balance and number of transactions might have changed
+        cachedNumBlocks = chainActive.Height();
+
         checkBalanceChanged();
         if(transactionTableModel)
             transactionTableModel->updateConfirmations();