QSignalSpy: make args member const

This means it's implicitly thread-safe now and we don't need to
protect accesses to it with the mutex.

Task-number: QTBUG-123544
Change-Id: I9f826003dca6fb81e7a75e283482c81ecff09be0
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/testlib/qsignalspy.cpp

@@ -258,7 +258,6 @@ bool QSignalSpy::connectToSignal(const QObject *sender, int sigIndex)
 
 void QSignalSpy::appendArgs(void **a)
 {
-    QMutexLocker locker(&m_mutex);
     QList<QVariant> list;
     list.reserve(args.size());
     for (qsizetype i = 0; i < args.size(); ++i) {
@@ -268,6 +267,7 @@ void QSignalSpy::appendArgs(void **a)
         else
             list << QVariant(QMetaType(type), a[i + 1]);
     }
+    QMutexLocker locker(&m_mutex);
     append(std::move(list));
 
     if (m_waiting) {

src/testlib/qsignalspy.h

@@ -12,8 +12,6 @@
 #include <QtCore/qvariant.h>
 #include <QtCore/qmutex.h>
 
-#include <mutex>
-
 QT_BEGIN_NAMESPACE
 
 
@@ -65,15 +63,11 @@ public:
 
 private:
     explicit QSignalSpy(ObjectSignal os)
+        : args(os.obj ? makeArgs(os.sig, os.obj) : QList<int>{})
     {
         if (!os.obj)
             return;
 
-        auto tmp = makeArgs(os.sig, os.obj);
-        {
-            const auto lock = std::scoped_lock(m_mutex);
-            args = std::move(tmp);
-        }
         if (!connectToSignal(os.obj, os.sig.methodIndex()))
             return;
 
@@ -92,11 +86,11 @@ private:
     // the full, normalized signal name
     QByteArray sig;
     // holds the QMetaType types for the argument list of the signal
-    QList<int> args;
+    const QList<int> args;
 
     QTestEventLoop m_loop;
     bool m_waiting = false;
-    QMutex m_mutex; // protects m_waiting, args and the QList base class, between appendArgs() and wait()
+    QMutex m_mutex; // protects m_waiting and the QList base class, between appendArgs() and wait()
 };
 
 QT_END_NAMESPACE