Merge bitcoin-core/gui#381: refactor: Make BitcoinCore class reusable

8169fc4e73a87331e02502fc24e293831765c8b1 qt, refactor: Fix code styling of moved InitExecutor class (Hennadii Stepanov)
c82165a55701fe4ff604d7f30163051cd47c2363 qt, refactor: Move InitExecutor class into its own module (Hennadii Stepanov)
dbcf56b6c6e939923673b3f07bed7bb3632dbeb1 scripted-diff: Rename BitcoinCore class to InitExecutor (Hennadii Stepanov)
19a1d008310f250b69b7aa764a9f26384d5a4a85 qt: Add BitcoinCore::m_thread member (Hennadii Stepanov)

Pull request description:

  This PR makes the `BitcoinCore` class reusable, i.e., it can be used by the widget-based GUI or by the [QML-based](https://github.com/bitcoin-core/gui-qml/tree/main/src/qml) one, and it makes the divergence between these two repos minimal.

  The small benefit to the current branch is more structured code.

  Actually, this PR is ported from https://github.com/bitcoin-core/gui-qml/pull/10.
  The example of the re-using of the `BitcoinCore` class is https://github.com/bitcoin-core/gui-qml/pull/11.

ACKs for top commit:
  laanwj:
    ACK 8169fc4e73a87331e02502fc24e293831765c8b1
  ryanofsky:
    Code review ACK 8169fc4e73a87331e02502fc24e293831765c8b1. Only change is switching from `m_executor` from pointer to optional type (thanks for update!)

Tree-SHA512: a0552c32d26d9acf42921eb12bcdf68f02d52f7183c688c43257b1a58679f64e45f193ee2d316850c7f0f516561e17abe989fe545bfa05e158ad3f4c66d19bca

5 files changed, 140 insertions, 106 deletions

diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
index 442c813a5a..4ab4e388d9 100644
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -7,12 +7,19 @@
 #endif
 
 #include <qt/bitcoin.h>
-#include <qt/bitcoingui.h>
 
 #include <chainparams.h>
+#include <init.h>
+#include <interfaces/handler.h>
+#include <interfaces/node.h>
+#include <node/context.h>
+#include <node/ui_interface.h>
+#include <noui.h>
+#include <qt/bitcoingui.h>
 #include <qt/clientmodel.h>
 #include <qt/guiconstants.h>
 #include <qt/guiutil.h>
+#include <qt/initexecutor.h>
 #include <qt/intro.h>
 #include <qt/networkstyle.h>
 #include <qt/optionsmodel.h>
@@ -20,6 +27,11 @@
 #include <qt/splashscreen.h>
 #include <qt/utilitydialog.h>
 #include <qt/winshutdownmonitor.h>
+#include <uint256.h>
+#include <util/system.h>
+#include <util/threadnames.h>
+#include <util/translation.h>
+#include <validation.h>
 
 #ifdef ENABLE_WALLET
 #include <qt/paymentserver.h>
@@ -27,18 +39,6 @@
 #include <qt/walletmodel.h>
 #endif // ENABLE_WALLET
 
-#include <init.h>
-#include <interfaces/handler.h>
-#include <interfaces/node.h>
-#include <node/context.h>
-#include <node/ui_interface.h>
-#include <noui.h>
-#include <uint256.h>
-#include <util/system.h>
-#include <util/threadnames.h>
-#include <util/translation.h>
-#include <validation.h>
-
 #include <boost/signals2/connection.hpp>
 #include <memory>
 
@@ -155,54 +155,11 @@ void DebugMessageHandler(QtMsgType type, const QMessageLogContext& context, cons
     }
 }
 
-BitcoinCore::BitcoinCore(interfaces::Node& node) :
-    QObject(), m_node(node)
-{
-}
-
-void BitcoinCore::handleRunawayException(const std::exception *e)
-{
-    PrintExceptionContinue(e, "Runaway exception");
-    Q_EMIT runawayException(QString::fromStdString(m_node.getWarnings().translated));
-}
-
-void BitcoinCore::initialize()
-{
-    try
-    {
-        util::ThreadRename("qt-init");
-        qDebug() << __func__ << ": Running initialization in thread";
-        interfaces::BlockAndHeaderTipInfo tip_info;
-        bool rv = m_node.appInitMain(&tip_info);
-        Q_EMIT initializeResult(rv, tip_info);
-    } catch (const std::exception& e) {
-        handleRunawayException(&e);
-    } catch (...) {
-        handleRunawayException(nullptr);
-    }
-}
-
-void BitcoinCore::shutdown()
-{
-    try
-    {
-        qDebug() << __func__ << ": Running Shutdown in thread";
-        m_node.appShutdown();
-        qDebug() << __func__ << ": Shutdown finished";
-        Q_EMIT shutdownResult();
-    } catch (const std::exception& e) {
-        handleRunawayException(&e);
-    } catch (...) {
-        handleRunawayException(nullptr);
-    }
-}
-
 static int qt_argc = 1;
 static const char* qt_argv = "bitcoin-qt";
 
 BitcoinApplication::BitcoinApplication():
     QApplication(qt_argc, const_cast<char **>(&qt_argv)),
-    coreThread(nullptr),
     optionsModel(nullptr),
     clientModel(nullptr),
     window(nullptr),
@@ -230,13 +187,7 @@ void BitcoinApplication::setupPlatformStyle()
 
 BitcoinApplication::~BitcoinApplication()
 {
-    if(coreThread)
-    {
-        qDebug() << __func__ << ": Stopping thread";
-        coreThread->quit();
-        coreThread->wait();
-        qDebug() << __func__ << ": Stopped thread";
-    }
+    m_executor.reset();
 
     delete window;
     window = nullptr;
@@ -291,22 +242,15 @@ bool BitcoinApplication::baseInitialize()
 
 void BitcoinApplication::startThread()
 {
-    if(coreThread)
-        return;
-    coreThread = new QThread(this);
-    BitcoinCore *executor = new BitcoinCore(node());
-    executor->moveToThread(coreThread);
+    assert(!m_executor);
+    m_executor.emplace(node());
 
     /*  communication to and from thread */
-    connect(executor, &BitcoinCore::initializeResult, this, &BitcoinApplication::initializeResult);
-    connect(executor, &BitcoinCore::shutdownResult, this, &BitcoinApplication::shutdownResult);
-    connect(executor, &BitcoinCore::runawayException, this, &BitcoinApplication::handleRunawayException);
-    connect(this, &BitcoinApplication::requestedInitialize, executor, &BitcoinCore::initialize);
-    connect(this, &BitcoinApplication::requestedShutdown, executor, &BitcoinCore::shutdown);
-    /*  make sure executor object is deleted in its own thread */
-    connect(coreThread, &QThread::finished, executor, &QObject::deleteLater);
-
-    coreThread->start();
+    connect(&m_executor.value(), &InitExecutor::initializeResult, this, &BitcoinApplication::initializeResult);
+    connect(&m_executor.value(), &InitExecutor::shutdownResult, this, &BitcoinApplication::shutdownResult);
+    connect(&m_executor.value(), &InitExecutor::runawayException, this, &BitcoinApplication::handleRunawayException);
+    connect(this, &BitcoinApplication::requestedInitialize, &m_executor.value(), &InitExecutor::initialize);
+    connect(this, &BitcoinApplication::requestedShutdown, &m_executor.value(), &InitExecutor::shutdown);
 }
 
 void BitcoinApplication::parameterSetup()
@@ -339,7 +283,6 @@ void BitcoinApplication::requestShutdown()
     shutdownWindow.reset(ShutdownWindow::showShutdownWindow(window));
 
     qDebug() << __func__ << ": Requesting shutdown";
-    startThread();
     window->hide();
     // Must disconnect node signals otherwise current thread can deadlock since
     // no event loop is running.
diff --git a/src/qt/bitcoin.h b/src/qt/bitcoin.h
index f9fab0534b..ed2f26b7f3 100644
--- a/src/qt/bitcoin.h
+++ b/src/qt/bitcoin.h
@@ -9,11 +9,14 @@
 #include <config/bitcoin-config.h>
 #endif
 
-#include <QApplication>
+#include <interfaces/node.h>
+#include <qt/initexecutor.h>
+
 #include <assert.h>
 #include <memory>
+#include <optional>
 
-#include <interfaces/node.h>
+#include <QApplication>
 
 class BitcoinGUI;
 class ClientModel;
@@ -26,31 +29,6 @@ class WalletController;
 class WalletModel;
 
 
-/** Class encapsulating Bitcoin Core startup and shutdown.
- * Allows running startup and shutdown in a different thread from the UI thread.
- */
-class BitcoinCore: public QObject
-{
-    Q_OBJECT
-public:
-    explicit BitcoinCore(interfaces::Node& node);
-
-public Q_SLOTS:
-    void initialize();
-    void shutdown();
-
-Q_SIGNALS:
-    void initializeResult(bool success, interfaces::BlockAndHeaderTipInfo tip_info);
-    void shutdownResult();
-    void runawayException(const QString &message);
-
-private:
-    /// Pass fatal exception message to UI thread
-    void handleRunawayException(const std::exception *e);
-
-    interfaces::Node& m_node;
-};
-
 /** Main Bitcoin application object */
 class BitcoinApplication: public QApplication
 {
@@ -112,7 +90,7 @@ Q_SIGNALS:
     void windowShown(BitcoinGUI* window);
 
 private:
-    QThread *coreThread;
+    std::optional<InitExecutor> m_executor;
     OptionsModel *optionsModel;
     ClientModel *clientModel;
     BitcoinGUI *window;
diff --git a/src/qt/initexecutor.cpp b/src/qt/initexecutor.cpp
new file mode 100644
index 0000000000..7060f74dab
--- /dev/null
+++ b/src/qt/initexecutor.cpp
@@ -0,0 +1,66 @@
+// Copyright (c) 2014-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <qt/initexecutor.h>
+
+#include <interfaces/node.h>
+#include <util/system.h>
+#include <util/threadnames.h>
+
+#include <exception>
+
+#include <QDebug>
+#include <QObject>
+#include <QString>
+#include <QThread>
+
+InitExecutor::InitExecutor(interfaces::Node& node)
+    : QObject(), m_node(node)
+{
+    this->moveToThread(&m_thread);
+    m_thread.start();
+}
+
+InitExecutor::~InitExecutor()
+{
+    qDebug() << __func__ << ": Stopping thread";
+    m_thread.quit();
+    m_thread.wait();
+    qDebug() << __func__ << ": Stopped thread";
+}
+
+void InitExecutor::handleRunawayException(const std::exception* e)
+{
+    PrintExceptionContinue(e, "Runaway exception");
+    Q_EMIT runawayException(QString::fromStdString(m_node.getWarnings().translated));
+}
+
+void InitExecutor::initialize()
+{
+    try {
+        util::ThreadRename("qt-init");
+        qDebug() << __func__ << ": Running initialization in thread";
+        interfaces::BlockAndHeaderTipInfo tip_info;
+        bool rv = m_node.appInitMain(&tip_info);
+        Q_EMIT initializeResult(rv, tip_info);
+    } catch (const std::exception& e) {
+        handleRunawayException(&e);
+    } catch (...) {
+        handleRunawayException(nullptr);
+    }
+}
+
+void InitExecutor::shutdown()
+{
+    try {
+        qDebug() << __func__ << ": Running Shutdown in thread";
+        m_node.appShutdown();
+        qDebug() << __func__ << ": Shutdown finished";
+        Q_EMIT shutdownResult();
+    } catch (const std::exception& e) {
+        handleRunawayException(&e);
+    } catch (...) {
+        handleRunawayException(nullptr);
+    }
+}
diff --git a/src/qt/initexecutor.h b/src/qt/initexecutor.h
new file mode 100644
index 0000000000..319ce40465
--- /dev/null
+++ b/src/qt/initexecutor.h
@@ -0,0 +1,46 @@
+// Copyright (c) 2014-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_QT_INITEXECUTOR_H
+#define BITCOIN_QT_INITEXECUTOR_H
+
+#include <interfaces/node.h>
+
+#include <exception>
+
+#include <QObject>
+#include <QThread>
+
+QT_BEGIN_NAMESPACE
+class QString;
+QT_END_NAMESPACE
+
+/** Class encapsulating Bitcoin Core startup and shutdown.
+ * Allows running startup and shutdown in a different thread from the UI thread.
+ */
+class InitExecutor : public QObject
+{
+    Q_OBJECT
+public:
+    explicit InitExecutor(interfaces::Node& node);
+    ~InitExecutor();
+
+public Q_SLOTS:
+    void initialize();
+    void shutdown();
+
+Q_SIGNALS:
+    void initializeResult(bool success, interfaces::BlockAndHeaderTipInfo tip_info);
+    void shutdownResult();
+    void runawayException(const QString& message);
+
+private:
+    /// Pass fatal exception message to UI thread
+    void handleRunawayException(const std::exception* e);
+
+    interfaces::Node& m_node;
+    QThread m_thread;
+};
+
+#endif // BITCOIN_QT_INITEXECUTOR_H
diff --git a/src/qt/test/test_main.cpp b/src/qt/test/test_main.cpp
index eb86f027ef..7d66f67f8a 100644
--- a/src/qt/test/test_main.cpp
+++ b/src/qt/test/test_main.cpp
@@ -8,6 +8,7 @@
 
 #include <interfaces/node.h>
 #include <qt/bitcoin.h>
+#include <qt/initexecutor.h>
 #include <qt/test/apptests.h>
 #include <qt/test/rpcnestedtests.h>
 #include <qt/test/uritests.h>