From 5659e73493fcdfb5d0cb9d686c24c4fbe1c217ed Mon Sep 17 00:00:00 2001
From: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>
Date: Fri, 14 Aug 2020 20:46:32 +0300
Subject: [PATCH 1/3] qt: Add ObjectInvoke template function

This is a replacement of the QMetaObject::invokeMethod functor overload
which is available in Qt 5.10+.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
---
 src/qt/guiutil.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/qt/guiutil.h b/src/qt/guiutil.h
index c976b4b4bb0..d7bd1248844 100644
--- a/src/qt/guiutil.h
+++ b/src/qt/guiutil.h
@@ -340,6 +340,18 @@ namespace GUIUtil
     #endif
     }
 
+    /**
+     * Queue a function to run in an object's event loop. This can be
+     * replaced by a call to the QMetaObject::invokeMethod functor overload after Qt 5.10, but
+     * for now use a QObject::connect for compatibility with older Qt versions, based on
+     * https://stackoverflow.com/questions/21646467/how-to-execute-a-functor-or-a-lambda-in-a-given-thread-in-qt-gcd-style
+     */
+    template <typename Fn>
+    void ObjectInvoke(QObject* object, Fn&& function, Qt::ConnectionType connection = Qt::QueuedConnection)
+    {
+        QObject source;
+        QObject::connect(&source, &QObject::destroyed, object, std::forward<Fn>(function), connection);
+    }
 
 } // namespace GUIUtil
 

From 5fcfee68af47d4a891ae9c9964d73886f0f01d7d Mon Sep 17 00:00:00 2001
From: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>
Date: Fri, 14 Aug 2020 20:53:35 +0300
Subject: [PATCH 2/3] qt: Call setParent() in the parent's context

setParent(parent) calls sendEvent(parent, QChildEvent) that implies
running in the thread which created the parent object.
---
 src/qt/walletcontroller.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/qt/walletcontroller.cpp b/src/qt/walletcontroller.cpp
index d9e0274d01b..a59f33b785f 100644
--- a/src/qt/walletcontroller.cpp
+++ b/src/qt/walletcontroller.cpp
@@ -131,7 +131,11 @@ WalletModel* WalletController::getOrCreateWallet(std::unique_ptr<interfaces::Wal
     WalletModel* wallet_model = new WalletModel(std::move(wallet), m_client_model, m_platform_style, nullptr);
     // Handler callback runs in a different thread so fix wallet model thread affinity.
     wallet_model->moveToThread(thread());
-    wallet_model->setParent(this);
+    // setParent(parent) must be called in the thread which created the parent object. More details in #18948.
+    GUIUtil::ObjectInvoke(this, [wallet_model, this] {
+        wallet_model->setParent(this);
+    }, GUIUtil::blockingGUIThreadConnection());
+
     m_wallets.push_back(wallet_model);
 
     // WalletModel::startPollBalance needs to be called in a thread managed by

From 8963b2c71f120b2746396c4987392f0105c8dd60 Mon Sep 17 00:00:00 2001
From: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>
Date: Mon, 11 May 2020 17:12:59 +0300
Subject: [PATCH 3/3] qt: Improve comments in
 WalletController::getOrCreateWallet()

---
 src/qt/walletcontroller.cpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/qt/walletcontroller.cpp b/src/qt/walletcontroller.cpp
index a59f33b785f..83f3cccbff0 100644
--- a/src/qt/walletcontroller.cpp
+++ b/src/qt/walletcontroller.cpp
@@ -128,8 +128,14 @@ WalletModel* WalletController::getOrCreateWallet(std::unique_ptr<interfaces::Wal
     }
 
     // Instantiate model and register it.
-    WalletModel* wallet_model = new WalletModel(std::move(wallet), m_client_model, m_platform_style, nullptr);
-    // Handler callback runs in a different thread so fix wallet model thread affinity.
+    WalletModel* wallet_model = new WalletModel(std::move(wallet), m_client_model, m_platform_style,
+                                                nullptr /* required for the following moveToThread() call */);
+
+    // Move WalletModel object to the thread that created the WalletController
+    // object (GUI main thread), instead of the current thread, which could be
+    // an outside wallet thread or RPC thread sending a LoadWallet notification.
+    // This ensures queued signals sent to the WalletModel object will be
+    // handled on the GUI event loop.
     wallet_model->moveToThread(thread());
     // setParent(parent) must be called in the thread which created the parent object. More details in #18948.
     GUIUtil::ObjectInvoke(this, [wallet_model, this] {
@@ -161,7 +167,6 @@ WalletModel* WalletController::getOrCreateWallet(std::unique_ptr<interfaces::Wal
     // Re-emit coinsSent signal from wallet model.
     connect(wallet_model, &WalletModel::coinsSent, this, &WalletController::coinsSent);
 
-    // Notify walletAdded signal on the GUI thread.
     Q_EMIT walletAdded(wallet_model);
 
     return wallet_model;