From 08215dd21ebefe41f30e43d630a68d644419d021 Mon Sep 17 00:00:00 2001
From: Ulf Hermann <ulf.hermann@qt.io>
Date: Tue, 4 Jun 2019 13:24:28 +0200
Subject: 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>
---
 src/qml/jsapi/qjsvalue_p.h | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

(limited to 'src/qml/jsapi')

diff --git a/src/qml/jsapi/qjsvalue_p.h b/src/qml/jsapi/qjsvalue_p.h
index bcf0a9d12d..2faffffbae 100644
--- a/src/qml/jsapi/qjsvalue_p.h
+++ b/src/qml/jsapi/qjsvalue_p.h
@@ -60,6 +60,8 @@
 #include <private/qv4mm_p.h>
 #include <private/qv4persistent_p.h>
 
+#include <QtCore/qthread.h>
+
 QT_BEGIN_NAMESPACE
 
 class Q_AUTOTEST_EXPORT QJSValuePrivate
@@ -79,6 +81,11 @@ public:
         return nullptr;
     }
 
+    static inline void setRawValue(QJSValue *jsval, QV4::Value *v)
+    {
+        jsval->d = reinterpret_cast<quintptr>(v);
+    }
+
     static inline void setVariant(QJSValue *jsval, const QVariant &v) {
         QVariant *val = new QVariant(v);
         jsval->d = reinterpret_cast<quintptr>(val) | 1;
@@ -169,10 +176,20 @@ public:
     }
 
     static inline void free(QJSValue *jsval) {
-        if (QV4::Value *v = QJSValuePrivate::getValue(jsval))
+        if (QV4::Value *v = QJSValuePrivate::getValue(jsval)) {
+            if (QV4::ExecutionEngine *e = engine(jsval)) {
+                if (QJSEngine *jsEngine = e->jsEngine()) {
+                    if (jsEngine->thread() != QThread::currentThread()) {
+                        QMetaObject::invokeMethod(
+                                jsEngine, [v](){ QV4::PersistentValueStorage::free(v); });
+                        return;
+                    }
+                }
+            }
             QV4::PersistentValueStorage::free(v);
-        else if (QVariant *v = QJSValuePrivate::getVariant(jsval))
+        } else if (QVariant *v = QJSValuePrivate::getVariant(jsval)) {
             delete v;
+        }
     }
 };
 
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