From aebfad19b475eb41cc20d3439123f8759861e100 Mon Sep 17 00:00:00 2001
From: Ivailo Monev <xakepa10@gmail.com>
Date: Tue, 26 Jan 2016 17:32:18 +0200
Subject: [PATCH] Ensure QObject wrappers are garbage-collected if appropriate

upstrema commits:
https://github.com/qtproject/qtscript/commit/378416af7542e34196908896c9a69573b995adb0

Signed-off-by: Ivailo Monev <xakepa10@gmail.com>
---
 .../JavaScriptCore/runtime/Collector.cpp             |  6 +++---
 src/script/api/qscriptengine.cpp                     |  3 +++
 src/script/bridge/qscriptqobject.cpp                 | 18 +++++++++++++-----
 src/script/bridge/qscriptqobject_p.h                 | 20 ++++++++++++++++++++
 4 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/Collector.cpp b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/Collector.cpp
index cc17f07fe..0db970375 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/Collector.cpp
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/Collector.cpp
@@ -1102,9 +1102,6 @@ void Heap::markRoots()
     // Mark explicitly registered roots.
     markProtectedObjects(markStack);
 
-    if (m_globalData->clientData)
-        m_globalData->clientData->mark(markStack);
-
     // Mark misc. other roots.
     if (m_markListSet && m_markListSet->size())
         MarkedArgumentBuffer::markLists(markStack, *m_markListSet);
@@ -1116,6 +1113,9 @@ void Heap::markRoots()
     if (m_globalData->firstStringifierToMark)
         JSONObject::markStringifiers(markStack, m_globalData->firstStringifierToMark);
 
+    if (m_globalData->clientData)
+        m_globalData->clientData->mark(markStack);
+
     markStack.drain();
     markStack.compact();
 
diff --git a/src/script/api/qscriptengine.cpp b/src/script/api/qscriptengine.cpp
index 9f9f7c981..a16703adc 100644
--- a/src/script/api/qscriptengine.cpp
+++ b/src/script/api/qscriptengine.cpp
@@ -1258,6 +1258,9 @@ void QScriptEnginePrivate::setContextFlags(JSC::ExecState *exec, uint flags)
 }
 
 
+// This function is called by JSC after all objects reachable by JSC itself
+// have been processed (see JSC::Heap::markRoots()).
+// Here we should mark additional objects managed by QtScript.
 void QScriptEnginePrivate::mark(JSC::MarkStack& markStack)
 {
     Q_Q(QScriptEngine);
diff --git a/src/script/bridge/qscriptqobject.cpp b/src/script/bridge/qscriptqobject.cpp
index 1a0f87d6a..e4601c6f7 100644
--- a/src/script/bridge/qscriptqobject.cpp
+++ b/src/script/bridge/qscriptqobject.cpp
@@ -96,7 +96,7 @@ struct QObjectConnection
                 QObjectDelegate *inst = static_cast<QObjectDelegate*>(delegate);
                 if ((inst->ownership() == QScriptEngine::ScriptOwnership)
                     || ((inst->ownership() == QScriptEngine::AutoOwnership)
-                        && inst->value() && !inst->value()->parent())) {
+                        && !inst->hasParent())) {
                     senderWrapper = JSC::JSValue();
                 } else {
                     markStack.append(senderWrapper);
@@ -2319,6 +2319,10 @@ QObjectData::~QObjectData()
     }
 }
 
+// This function assumes all objects reachable elsewhere in the JS environment
+// (stack, heap) have been marked already (see QScriptEnginePrivate::mark()).
+// This determines whether any of QtScript's internal QObject wrappers are only
+// weakly referenced and can be discarded.
 void QObjectData::mark(JSC::MarkStack& markStack)
 {
     if (connectionManager)
@@ -2327,10 +2331,14 @@ void QObjectData::mark(JSC::MarkStack& markStack)
         QList<QScript::QObjectWrapperInfo>::iterator it;
         for (it = wrappers.begin(); it != wrappers.end(); ) {
             const QScript::QObjectWrapperInfo &info = *it;
-            // ### don't mark if there are no other references.
-            // we need something like isMarked()
-            markStack.append(info.object);
-            ++it;
+            if (JSC::Heap::isCellMarked(info.object)) {
+                ++it;
+            } else if (info.isCollectableWhenWeaklyReferenced()) {
+                it = wrappers.erase(it);
+            } else {
+                markStack.append(info.object);
+                ++it;
+            }
         }
     }
 }
diff --git a/src/script/bridge/qscriptqobject_p.h b/src/script/bridge/qscriptqobject_p.h
index c635c91e0..cf44de996 100644
--- a/src/script/bridge/qscriptqobject_p.h
+++ b/src/script/bridge/qscriptqobject_p.h
@@ -95,6 +95,7 @@ public:
 
     inline QObject *value() const { return data->value; }
     inline void setValue(QObject* value) { data->value = value; }
+    inline bool hasParent() const { return data->value && data->value->parent(); }
 
     inline QScriptEngine::ValueOwnership ownership() const
         { return data->ownership; }
@@ -138,6 +139,25 @@ struct QObjectWrapperInfo
     QScriptObject *object;
     QScriptEngine::ValueOwnership ownership;
     QScriptEngine::QObjectWrapOptions options;
+
+    // Returns true if this wrapper can be garbage-collected when there are no
+    // other references to it in the JS environment (weak reference), otherwise
+    // returns false (should not be collected).
+    bool isCollectableWhenWeaklyReferenced() const
+    {
+        switch (ownership) {
+        case QScriptEngine::ScriptOwnership:
+            return true;
+        case QScriptEngine::AutoOwnership: {
+            QScriptObjectDelegate *delegate = object->delegate();
+            Q_ASSERT(delegate && (delegate->type() == QScriptObjectDelegate::QtObject));
+            return !static_cast<QObjectDelegate *>(delegate)->hasParent();
+        }
+        default:
+            break;
+        }
+        return false;
+    }
 };
 
 class QObjectData // : public QObjectUserData
-- 
2.11.0