Merge bitcoin-core/gui#598: Avoid recalculating the wallet balance - use model cache

4584d300a40bfd84517072f7a6eee114fb7cab08 GUI: remove now unneeded 'm_balances' field from overviewpage (furszy)
050e8b139145d6991e740b0e5f2b3364663dd348 GUI: 'getAvailableBalance', use cached balance if the user did not select UTXO manually (furszy)
96e3264a82c51b456703f500bd98e8cb98115697 GUI: use cached balance in overviewpage and sendcoinsdialog (furszy)
321335bf0292034d79afa6c44f7f072942b6cc3c GUI: add getter for WalletModel::m_cached_balances field (furszy)
e62958dc81d215a1c56318d0914dfd9a33d45973 GUI: sendCoinsDialog, remove duplicate wallet().getBalances() call (furszy)

Pull request description:

  As per the title says, we are recalculating the entire wallet balance on different situations calling to `wallet().getBalances()`, when should instead make use of the wallet model cached balance.

  This has the benefits of (1) not spending resources calculating a balance that we already have cached, and (2) avoid blocking the main thread for a long time, in case of big wallets, walking through the entire wallet's tx map more than what it's really needed.

  Changes:

  1) Fix: `SendCoinsDialog` was calling `wallet().getBalances()` twice during `setModel`.
  2) Use the cached balance if the user did not select any UTXO manually inside the wallet model `getAvailableBalance` call.

  -----------------------
  As an extra note, this work born in [#25005](https://github.com/bitcoin/bitcoin/pull/25005) but grew out of scope of it.

ACKs for top commit:
  jarolrod:
    ACK 4584d300a40bfd84517072f7a6eee114fb7cab08
  hebasto:
    re-ACK 4584d300a40bfd84517072f7a6eee114fb7cab08, only suggested changes and commit message formatting since my [recent](https://github.com/bitcoin-core/gui/pull/598#pullrequestreview-1071268192) review.

Tree-SHA512: 6633ce7f9a82a3e46e75aa7295df46c80a4cd4a9f3305427af203c9bc8670573fa8a1927f14a279260c488cc975a08d238faba2e9751588086fea1dcf8ea2b28

7 files changed, 54 insertions, 39 deletions

diff --git a/src/qt/overviewpage.cpp b/src/qt/overviewpage.cpp
index a8133f481e..85a3c36f39 100644
--- a/src/qt/overviewpage.cpp
+++ b/src/qt/overviewpage.cpp
@@ -147,8 +147,6 @@ OverviewPage::OverviewPage(const PlatformStyle *platformStyle, QWidget *parent)
 {
     ui->setupUi(this);
 
-    m_balances.balance = -1;
-
     // use a SingleColorIcon for the "out of sync warning" icon
     QIcon icon = m_platform_style->SingleColorIcon(QStringLiteral(":/icons/warning"));
     ui->labelTransactionsStatus->setIcon(icon);
@@ -177,8 +175,9 @@ void OverviewPage::handleTransactionClicked(const QModelIndex &index)
 void OverviewPage::setPrivacy(bool privacy)
 {
     m_privacy = privacy;
-    if (m_balances.balance != -1) {
-        setBalance(m_balances);
+    const auto& balances = walletModel->getCachedBalance();
+    if (balances.balance != -1) {
+        setBalance(balances);
     }
 
     ui->listTransactions->setVisible(!m_privacy);
@@ -197,7 +196,6 @@ OverviewPage::~OverviewPage()
 void OverviewPage::setBalance(const interfaces::WalletBalances& balances)
 {
     BitcoinUnit unit = walletModel->getOptionsModel()->getDisplayUnit();
-    m_balances = balances;
     if (walletModel->wallet().isLegacy()) {
         if (walletModel->wallet().privateKeysDisabled()) {
             ui->labelBalance->setText(BitcoinUnits::formatWithPrivacy(unit, balances.watch_only_balance, BitcoinUnits::SeparatorStyle::ALWAYS, m_privacy));
@@ -276,14 +274,13 @@ void OverviewPage::setWalletModel(WalletModel *model)
         ui->listTransactions->setModelColumn(TransactionTableModel::ToAddress);
 
         // Keep up to date with wallet
-        interfaces::Wallet& wallet = model->wallet();
-        interfaces::WalletBalances balances = wallet.getBalances();
-        setBalance(balances);
+        setBalance(model->getCachedBalance());
         connect(model, &WalletModel::balanceChanged, this, &OverviewPage::setBalance);
 
         connect(model->getOptionsModel(), &OptionsModel::displayUnitChanged, this, &OverviewPage::updateDisplayUnit);
 
-        updateWatchOnlyLabels(wallet.haveWatchOnly() && !model->wallet().privateKeysDisabled());
+        interfaces::Wallet& wallet = model->wallet();
+        updateWatchOnlyLabels(wallet.haveWatchOnly() && !wallet.privateKeysDisabled());
         connect(model, &WalletModel::notifyWatchonlyChanged, [this](bool showWatchOnly) {
             updateWatchOnlyLabels(showWatchOnly && !walletModel->wallet().privateKeysDisabled());
         });
@@ -306,10 +303,10 @@ void OverviewPage::changeEvent(QEvent* e)
 
 void OverviewPage::updateDisplayUnit()
 {
-    if(walletModel && walletModel->getOptionsModel())
-    {
-        if (m_balances.balance != -1) {
-            setBalance(m_balances);
+    if (walletModel && walletModel->getOptionsModel()) {
+        const auto& balances = walletModel->getCachedBalance();
+        if (balances.balance != -1) {
+            setBalance(balances);
         }
 
         // Update txdelegate->unit with the current unit
diff --git a/src/qt/overviewpage.h b/src/qt/overviewpage.h
index 058df1a8c5..56f45907db 100644
--- a/src/qt/overviewpage.h
+++ b/src/qt/overviewpage.h
@@ -52,7 +52,6 @@ private:
     Ui::OverviewPage *ui;
     ClientModel *clientModel;
     WalletModel *walletModel;
-    interfaces::WalletBalances m_balances;
     bool m_privacy{false};
 
     const PlatformStyle* m_platform_style;
diff --git a/src/qt/sendcoinsdialog.cpp b/src/qt/sendcoinsdialog.cpp
index bd44d12781..a75c1098a5 100644
--- a/src/qt/sendcoinsdialog.cpp
+++ b/src/qt/sendcoinsdialog.cpp
@@ -164,11 +164,9 @@ void SendCoinsDialog::setModel(WalletModel *_model)
             }
         }
 
-        interfaces::WalletBalances balances = _model->wallet().getBalances();
-        setBalance(balances);
         connect(_model, &WalletModel::balanceChanged, this, &SendCoinsDialog::setBalance);
-        connect(_model->getOptionsModel(), &OptionsModel::displayUnitChanged, this, &SendCoinsDialog::updateDisplayUnit);
-        updateDisplayUnit();
+        connect(_model->getOptionsModel(), &OptionsModel::displayUnitChanged, this, &SendCoinsDialog::refreshBalance);
+        refreshBalance();
 
         // Coin Control
         connect(_model->getOptionsModel(), &OptionsModel::displayUnitChanged, this, &SendCoinsDialog::coinControlUpdateLabels);
@@ -711,9 +709,9 @@ void SendCoinsDialog::setBalance(const interfaces::WalletBalances& balances)
     }
 }
 
-void SendCoinsDialog::updateDisplayUnit()
+void SendCoinsDialog::refreshBalance()
 {
-    setBalance(model->wallet().getBalances());
+    setBalance(model->getCachedBalance());
     ui->customFee->setDisplayUnit(model->getOptionsModel()->getDisplayUnit());
     updateSmartFeeLabel();
 }
@@ -786,7 +784,7 @@ void SendCoinsDialog::useAvailableBalance(SendCoinsEntry* entry)
     m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner();
 
     // Calculate available amount to send.
-    CAmount amount = model->wallet().getAvailableBalance(*m_coin_control);
+    CAmount amount = model->getAvailableBalance(m_coin_control.get());
     for (int i = 0; i < ui->entries->count(); ++i) {
         SendCoinsEntry* e = qobject_cast<SendCoinsEntry*>(ui->entries->itemAt(i)->widget());
         if (e && !e->isHidden() && e != entry) {
diff --git a/src/qt/sendcoinsdialog.h b/src/qt/sendcoinsdialog.h
index 400503d0c0..b58d4690a0 100644
--- a/src/qt/sendcoinsdialog.h
+++ b/src/qt/sendcoinsdialog.h
@@ -97,7 +97,7 @@ private Q_SLOTS:
     void on_buttonMinimizeFee_clicked();
     void removeEntry(SendCoinsEntry* entry);
     void useAvailableBalance(SendCoinsEntry* entry);
-    void updateDisplayUnit();
+    void refreshBalance();
     void coinControlFeatureChanged(bool);
     void coinControlButtonClicked();
     void coinControlChangeChecked(int);
diff --git a/src/qt/test/wallettests.cpp b/src/qt/test/wallettests.cpp
index b8ae62ecab..7e39829038 100644
--- a/src/qt/test/wallettests.cpp
+++ b/src/qt/test/wallettests.cpp
@@ -129,6 +129,13 @@ void BumpFee(TransactionView& view, const uint256& txid, bool expectDisabled, st
     QVERIFY(text.indexOf(QString::fromStdString(expectError)) != -1);
 }
 
+void CompareBalance(WalletModel& walletModel, CAmount expected_balance, QLabel* balance_label_to_check)
+{
+    BitcoinUnit unit = walletModel.getOptionsModel()->getDisplayUnit();
+    QString balanceComparison = BitcoinUnits::formatWithUnit(unit, expected_balance, false, BitcoinUnits::SeparatorStyle::ALWAYS);
+    QCOMPARE(balance_label_to_check->text().trimmed(), balanceComparison);
+}
+
 //! Simple qt wallet tests.
 //
 // Test widgets can be debugged interactively calling show() on them and
@@ -195,15 +202,10 @@ void TestGUI(interfaces::Node& node)
     sendCoinsDialog.setModel(&walletModel);
     transactionView.setModel(&walletModel);
 
-    {
-        // Check balance in send dialog
-        QLabel* balanceLabel = sendCoinsDialog.findChild<QLabel*>("labelBalance");
-        QString balanceText = balanceLabel->text();
-        BitcoinUnit unit = walletModel.getOptionsModel()->getDisplayUnit();
-        CAmount balance = walletModel.wallet().getBalance();
-        QString balanceComparison = BitcoinUnits::formatWithUnit(unit, balance, false, BitcoinUnits::SeparatorStyle::ALWAYS);
-        QCOMPARE(balanceText, balanceComparison);
-    }
+    // Update walletModel cached balance which will trigger an update for the 'labelBalance' QLabel.
+    walletModel.pollBalanceChanged();
+    // Check balance in send dialog
+    CompareBalance(walletModel, walletModel.wallet().getBalance(), sendCoinsDialog.findChild<QLabel*>("labelBalance"));
 
     // Send two transactions, and verify they are added to transaction list.
     TransactionTableModel* transactionTableModel = walletModel.getTransactionTableModel();
@@ -223,12 +225,8 @@ void TestGUI(interfaces::Node& node)
     // Check current balance on OverviewPage
     OverviewPage overviewPage(platformStyle.get());
     overviewPage.setWalletModel(&walletModel);
-    QLabel* balanceLabel = overviewPage.findChild<QLabel*>("labelBalance");
-    QString balanceText = balanceLabel->text().trimmed();
-    BitcoinUnit unit = walletModel.getOptionsModel()->getDisplayUnit();
-    CAmount balance = walletModel.wallet().getBalance();
-    QString balanceComparison = BitcoinUnits::formatWithUnit(unit, balance, false, BitcoinUnits::SeparatorStyle::ALWAYS);
-    QCOMPARE(balanceText, balanceComparison);
+    walletModel.pollBalanceChanged(); // Manual balance polling update
+    CompareBalance(walletModel, walletModel.wallet().getBalance(), overviewPage.findChild<QLabel*>("labelBalance"));
 
     // Check Request Payment button
     ReceiveCoinsDialog receiveCoinsDialog(platformStyle.get());
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index ac6c8bea46..c6f3f5b00c 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -67,6 +67,10 @@ WalletModel::~WalletModel()
 
 void WalletModel::startPollBalance()
 {
+    // Update the cached balance right away, so every view can make use of it,
+    // so them don't need to waste resources recalculating it.
+    pollBalanceChanged();
+
     // This timer will be fired repeatedly to update the balance
     // Since the QTimer::timeout is a private signal, it cannot be used
     // in the GUIUtil::ExceptionSafeConnect directly.
@@ -120,12 +124,17 @@ void WalletModel::pollBalanceChanged()
 
 void WalletModel::checkBalanceChanged(const interfaces::WalletBalances& new_balances)
 {
-    if(new_balances.balanceChanged(m_cached_balances)) {
+    if (new_balances.balanceChanged(m_cached_balances)) {
         m_cached_balances = new_balances;
         Q_EMIT balanceChanged(new_balances);
     }
 }
 
+interfaces::WalletBalances WalletModel::getCachedBalance() const
+{
+    return m_cached_balances;
+}
+
 void WalletModel::updateTransaction()
 {
     // Balance and number of transactions might have changed
@@ -194,7 +203,9 @@ WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransact
         return DuplicateAddress;
     }
 
-    CAmount nBalance = m_wallet->getAvailableBalance(coinControl);
+    // If no coin was manually selected, use the cached balance
+    // Future: can merge this call with 'createTransaction'.
+    CAmount nBalance = getAvailableBalance(&coinControl);
 
     if(total > nBalance)
     {
@@ -602,3 +613,8 @@ uint256 WalletModel::getLastBlockProcessed() const
 {
     return m_client_model ? m_client_model->getBestBlockHash() : uint256{};
 }
+
+CAmount WalletModel::getAvailableBalance(const CCoinControl* control)
+{
+    return control && control->HasSelected() ? wallet().getAvailableBalance(*control) : getCachedBalance().balance;
+}
diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index 0184fb8ec2..73dfe0386a 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -155,6 +155,13 @@ public:
 
     uint256 getLastBlockProcessed() const;
 
+    // Retrieve the cached wallet balance
+    interfaces::WalletBalances getCachedBalance() const;
+
+    // If coin control has selected outputs, searches the total amount inside the wallet.
+    // Otherwise, uses the wallet's cached available balance.
+    CAmount getAvailableBalance(const wallet::CCoinControl* control);
+
 private:
     std::unique_ptr<interfaces::Wallet> m_wallet;
     std::unique_ptr<interfaces::Handler> m_handler_unload;