3 files changed, 13 insertions, 4 deletions
diff --git a/src/qml/debugger/qqmldebug.cpp b/src/qml/debugger/qqmldebug.cpp
index 58b8ea2c4f..0ca56f3a70 100644
--- a/src/qml/debugger/qqmldebug.cpp
+++ b/src/qml/debugger/qqmldebug.cpp
@@ -44,17 +44,26 @@
 #include <private/qqmlengine_p.h>
 #include <private/qv4compileddata_p.h>
 
+#include <atomic>
 #include <cstdio>
 
 QT_REQUIRE_CONFIG(qml_debug);
 
 QT_BEGIN_NAMESPACE
 
+#if __cplusplus >= 202002L
+# define Q_ATOMIC_FLAG_INIT {}
+#else
+# define Q_ATOMIC_FLAG_INIT ATOMIC_FLAG_INIT // deprecated in C++20
+#endif
+
+static std::atomic_flag s_printedWarning = Q_ATOMIC_FLAG_INIT;
+
 QQmlDebuggingEnabler::QQmlDebuggingEnabler(bool printWarning)
 {
-    if (!QQmlEnginePrivate::qml_debugging_enabled && printWarning)
+    if (printWarning && !s_printedWarning.test_and_set(std::memory_order_relaxed))
         fprintf(stderr, "QML debugging is enabled. Only use this in a safe environment.\n");
-    QQmlEnginePrivate::qml_debugging_enabled = true;
+    QQmlEnginePrivate::qml_debugging_enabled.store(true, std::memory_order_relaxed);
 }
 
 /*!
diff --git a/src/qml/debugger/qqmldebugconnector.cpp b/src/qml/debugger/qqmldebugconnector.cpp
index 0ef40d6911..01a0723b76 100644
--- a/src/qml/debugger/qqmldebugconnector.cpp
+++ b/src/qml/debugger/qqmldebugconnector.cpp
@@ -111,7 +111,7 @@ QQmlDebugConnector *QQmlDebugConnector::instance()
     if (!params)
         return nullptr;
 
-    if (!QQmlEnginePrivate::qml_debugging_enabled) {
+    if (!QQmlEnginePrivate::qml_debugging_enabled.load(std::memory_order_relaxed)) {
         if (!params->arguments.isEmpty()) {
             qWarning().noquote() << QString::fromLatin1(
                                         "QML Debugger: Ignoring \"-qmljsdebugger=%1\". Debugging "
diff --git a/src/qml/debugger/qqmlprofiler_p.h b/src/qml/debugger/qqmlprofiler_p.h
index d3eedab1c6..ed1e011830 100644
--- a/src/qml/debugger/qqmlprofiler_p.h
+++ b/src/qml/debugger/qqmlprofiler_p.h
@@ -176,7 +176,7 @@ public:
 
         RefLocation(QV4::ExecutableCompilationUnit *ref, const QUrl &url,
                     const QV4::CompiledData::Object *obj, const QString &type)
-            : Location(QQmlSourceLocation(type, obj->location.line, obj->location.column), url),
+            : Location(QQmlSourceLocation(type, obj->location.line(), obj->location.column()), url),
               locationType(Creating), sent(false)
         {
             unit = ref;