qt: implement FutureScheduler, always await async code to complete

src/qt/FutureScheduler.cpp

@@ -0,0 +1,89 @@
+#include "FutureScheduler.h"
+
+FutureScheduler::FutureScheduler(QObject *parent)
+    : QObject(parent), Alive(0), Stopping(false)
+{
+}
+
+FutureScheduler::~FutureScheduler()
+{
+    shutdownWaitForFinished();
+}
+
+void FutureScheduler::shutdownWaitForFinished() noexcept
+{
+    QMutexLocker locker(&Mutex);
+
+    Stopping = true;
+    while (Alive > 0)
+    {
+        Condition.wait(&Mutex);
+    }
+}
+
+QPair<bool, QFuture<void>> FutureScheduler::run(std::function<void()> function) noexcept
+{
+    return execute<void>([this, function](QFutureWatcher<void> *) {
+        return QtConcurrent::run([this, function] {
+            try
+            {
+                function();
+            }
+            catch (const std::exception &exception)
+            {
+                qWarning() << "Exception thrown from async function: " << exception.what();
+            }
+            done();
+        });
+    });
+}
+
+QPair<bool, QFuture<QJSValueList>> FutureScheduler::run(std::function<QJSValueList() noexcept> function, const QJSValue &callback) noexcept
+{
+    if (!callback.isCallable())
+    {
+        throw std::runtime_error("js callback must be callable");
+    }
+
+    return execute<QJSValueList>([this, function, callback](QFutureWatcher<QJSValueList> *watcher) {
+        connect(watcher, &QFutureWatcher<QJSValueList>::finished, [watcher, callback] {
+            QJSValue(callback).call(watcher->future().result());
+        });
+        return QtConcurrent::run([this, function] {
+            QJSValueList result;
+            try
+            {
+                result = function();
+            }
+            catch (const std::exception &exception)
+            {
+                qWarning() << "Exception thrown from async function: " << exception.what();
+            }
+            done();
+            return result;
+        });
+    });
+}
+
+bool FutureScheduler::add() noexcept
+{
+    QMutexLocker locker(&Mutex);
+
+    if (Stopping)
+    {
+        return false;
+    }
+
+    ++Alive;
+    return true;
+}
+
+void FutureScheduler::done() noexcept
+{
+    {
+        QMutexLocker locker(&Mutex);
+        --Alive;
+    }
+
+    Condition.wakeAll();
+}