Allow destroying QJSValues from other threads

QVariants are commonly passed around between threads and QVariants can
wrap QJSValues. Therefore we need to allow this. The persistent value is
freed immediately if we're still in the same thread. Otherwise a
message is passed to the QJSEngine that owns it. If there is no
QJSEngine we assume that we can free the value immediately. As such a
thing can only happen via private API we can make sure this assumption
holds.

Fixes: QTBUG-75939
Change-Id: I14c09fd5d6ef7ba689f66656f2bcbb5c88bacf89
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
 

3 files changed, 40 insertions, 3 deletions

diff --git a/tests/auto/qml/qjsvalue/qjsvalue.pro b/tests/auto/qml/qjsvalue/qjsvalue.pro
index 3bbbbd4787..a01cffa100 100644
--- a/tests/auto/qml/qjsvalue/qjsvalue.pro
+++ b/tests/auto/qml/qjsvalue/qjsvalue.pro
@@ -1,6 +1,6 @@
 CONFIG += testcase
 TARGET = tst_qjsvalue
 macx:CONFIG -= app_bundle
-QT += qml widgets testlib gui-private
+QT += qml widgets testlib gui-private qml-private
 SOURCES  += tst_qjsvalue.cpp
 HEADERS  += tst_qjsvalue.h
diff --git a/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp b/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
index f9718e3699..ebbc9f7e0a 100644
--- a/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
+++ b/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
@@ -27,7 +27,14 @@
 ****************************************************************************/
 
 #include "tst_qjsvalue.h"
+
+#include <private/qv4engine_p.h>
+#include <private/qjsvalue_p.h>
+
 #include <QtWidgets/QPushButton>
+#include <QtCore/qthread.h>
+
+#include <memory>
 
 tst_QJSValue::tst_QJSValue()
     : engine(nullptr)
@@ -2610,4 +2617,34 @@ void tst_QJSValue::nestedObjectToVariant()
     QCOMPARE(o.toVariant(), expected);
 }
 
+void tst_QJSValue::deleteFromDifferentThread()
+{
+#if !QT_CONFIG(thread)
+    QSKIP("Need thread support to destroy QJSValues from different threads");
+#else
+    QV4::PersistentValueStorage storage(engine->handle());
+    QCOMPARE(storage.firstPage, nullptr);
+    QJSValue jsval;
+    QJSValuePrivate::setRawValue(&jsval, storage.allocate());
+    QVERIFY(storage.firstPage != nullptr);
+
+    QMutex mutex;
+    QWaitCondition condition;
+
+    std::unique_ptr<QThread> thread(QThread::create([&]() {
+        QMutexLocker locker(&mutex);
+        QJSValuePrivate::free(&jsval);
+        QJSValuePrivate::setRawValue(&jsval, nullptr);
+        QVERIFY(storage.firstPage != nullptr);
+        condition.wakeOne();
+    }));
+
+    QMutexLocker locker(&mutex);
+    thread->start();
+    condition.wait(&mutex);
+    QTRY_VERIFY(thread->isFinished());
+    QTRY_COMPARE(storage.firstPage, nullptr);
+#endif
+}
+
 QTEST_MAIN(tst_QJSValue)
diff --git a/tests/auto/qml/qjsvalue/tst_qjsvalue.h b/tests/auto/qml/qjsvalue/tst_qjsvalue.h
index b8b9f4403c..ccbacb3acc 100644
--- a/tests/auto/qml/qjsvalue/tst_qjsvalue.h
+++ b/tests/auto/qml/qjsvalue/tst_qjsvalue.h
@@ -35,8 +35,6 @@
 #include <qjsvalue.h>
 #include <QtTest/QtTest>
 
-Q_DECLARE_METATYPE(QVariant)
-
 class tst_QJSValue : public QObject
 {
     Q_OBJECT
@@ -143,6 +141,8 @@ private slots:
     void nestedObjectToVariant_data();
     void nestedObjectToVariant();
 
+    void deleteFromDifferentThread();
+
 private:
     void newEngine()
     {