Merge branch '4.7' of scm.dev.nokia.troll.no:qt/oslo-staging-1 into 4.7-integration

* '4.7' of scm.dev.nokia.troll.no:qt/oslo-staging-1:
  Fix potential networking crash due to null-pointer dereference
  Revert "Improve timer ID safety by using a serial counter per ID."
  Invalidate QScriptPrograms when engine is destroyed
  Fix alignment issue causing crash in QtScript/JavaScriptCore
  Restore Qt 4.6 behaviour: exec() always enters the event loop.
  Make syncqt not complain about missing header macros.

12 files changed, 138 insertions, 122 deletions

diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog b/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
index c2b1155..9cbf0c1 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
@@ -358,6 +358,31 @@
 
         * wtf/AlwaysInline.h:
 
+2010-02-12  Gavin Barraclough  <barraclough@apple.com>
+
+        Reviewed by Darin Adler.
+
+        https://bugs.webkit.org/show_bug.cgi?id=33731
+        Many false leaks in release builds due to PtrAndFlags
+
+        Remove UntypedPtrAndBitfield (similar to PtrAndFlags) in UStringImpl,
+        and steal bits from the refCount instead.
+
+        * runtime/UStringImpl.cpp:
+        (JSC::UStringImpl::baseSharedBuffer):
+        (JSC::UStringImpl::~UStringImpl):
+        * runtime/UStringImpl.h:
+        (JSC::UStringImpl::cost):
+        (JSC::UStringImpl::isIdentifier):
+        (JSC::UStringImpl::setIsIdentifier):
+        (JSC::UStringImpl::ref):
+        (JSC::UStringImpl::deref):
+        (JSC::UStringImpl::UStringImpl):
+        (JSC::UStringImpl::bufferOwnerString):
+        (JSC::UStringImpl::bufferOwnership):
+        (JSC::UStringImpl::isStatic):
+        (JSC::UStringImpl::):
+
 2010-02-12  Kwang Yul Seo  <skyul@company100.net>
 
         Reviewed by Adam Barth.
diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
index 4b0d1c9..4fde49e 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
@@ -38,12 +38,14 @@ namespace JSC {
 SharedUChar* UStringImpl::baseSharedBuffer()
 {
     ASSERT((bufferOwnership() == BufferShared)
-        || ((bufferOwnership() == BufferOwned) && !m_dataBuffer.asPtr<void*>()));
+        || ((bufferOwnership() == BufferOwned) && !m_buffer));
 
-    if (bufferOwnership() != BufferShared)
-        m_dataBuffer = UntypedPtrAndBitfield(SharedUChar::create(new OwnFastMallocPtr<UChar>(m_data)).releaseRef(), BufferShared);
+    if (bufferOwnership() != BufferShared) {
+        m_refCountAndFlags = (m_refCountAndFlags & ~s_refCountMaskBufferOwnership) | BufferShared;
+        m_bufferShared = SharedUChar::create(new OwnFastMallocPtr<UChar>(m_data)).releaseRef();
+    }
 
-    return m_dataBuffer.asPtr<SharedUChar*>();
+    return m_bufferShared;
 }
 
 SharedUChar* UStringImpl::sharedBuffer()
@@ -71,10 +73,10 @@ UStringImpl::~UStringImpl()
         if (bufferOwnership() == BufferOwned)
             fastFree(m_data);
         else if (bufferOwnership() == BufferSubstring)
-            m_dataBuffer.asPtr<UStringImpl*>()->deref();
+            m_bufferSubstring->deref();
         else {
             ASSERT(bufferOwnership() == BufferShared);
-            m_dataBuffer.asPtr<SharedUChar*>()->deref();
+            m_bufferShared->deref();
         }
     }
 }
diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
index 4e1ddc7..e6d1a8a 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
@@ -40,48 +40,6 @@ class IdentifierTable;
   
 typedef CrossThreadRefCounted<OwnFastMallocPtr<UChar> > SharedUChar;
 
-class UntypedPtrAndBitfield {
-public:
-    UntypedPtrAndBitfield() {}
-
-    UntypedPtrAndBitfield(void* ptrValue, uintptr_t bitValue)
-        : m_value(reinterpret_cast<uintptr_t>(ptrValue) | bitValue)
-#ifndef NDEBUG
-        , m_leaksPtr(ptrValue)
-#endif
-    {
-        ASSERT(ptrValue == asPtr<void*>());
-        ASSERT((*this & ~s_alignmentMask) == bitValue);
-    }
-
-    template<typename T>
-    T asPtr() const { return reinterpret_cast<T>(m_value & s_alignmentMask); }
-
-    UntypedPtrAndBitfield& operator&=(uintptr_t bits)
-    {
-        m_value &= bits | s_alignmentMask;
-        return *this;
-    }
-
-    UntypedPtrAndBitfield& operator|=(uintptr_t bits)
-    {
-        m_value |= bits & ~s_alignmentMask;
-        return *this;
-    }
-
-    uintptr_t operator&(uintptr_t mask) const
-    {
-        return m_value & mask & ~s_alignmentMask;
-    }
-
-private:
-    static const uintptr_t s_alignmentMask = ~static_cast<uintptr_t>(0x7);
-    uintptr_t m_value;
-#ifndef NDEBUG
-        void* m_leaksPtr; // Only used to allow tools like leaks on OSX to detect that the memory is referenced.
-#endif
-};
-
 class UStringImpl : Noncopyable {
 public:
     template<size_t inlineCapacity>
@@ -151,21 +109,27 @@ public:
     {
         // For substrings, return the cost of the base string.
         if (bufferOwnership() == BufferSubstring)
-            return m_dataBuffer.asPtr<UStringImpl*>()->cost();
+            return m_bufferSubstring->cost();
 
-        if (m_dataBuffer & s_reportedCostBit)
+        if (m_refCountAndFlags & s_refCountFlagHasReportedCost)
             return 0;
-        m_dataBuffer |= s_reportedCostBit;
+        m_refCountAndFlags |= s_refCountFlagHasReportedCost;
         return m_length;
     }
     unsigned hash() const { if (!m_hash) m_hash = computeHash(data(), m_length); return m_hash; }
     unsigned existingHash() const { ASSERT(m_hash); return m_hash; } // fast path for Identifiers
     void setHash(unsigned hash) { ASSERT(hash == computeHash(data(), m_length)); m_hash = hash; } // fast path for Identifiers
-    bool isIdentifier() const { return m_isIdentifier; }
-    void setIsIdentifier(bool isIdentifier) { m_isIdentifier = isIdentifier; }
+    bool isIdentifier() const { return m_refCountAndFlags & s_refCountFlagIsIdentifier; }
+    void setIsIdentifier(bool isIdentifier)
+    {
+        if (isIdentifier)
+            m_refCountAndFlags |= s_refCountFlagIsIdentifier;
+        else
+            m_refCountAndFlags &= ~s_refCountFlagIsIdentifier;
+    }
 
-    UStringImpl* ref() { m_refCount += s_refCountIncrement; return this; }
-    ALWAYS_INLINE void deref() { if (!(m_refCount -= s_refCountIncrement)) delete this; }
+    UStringImpl* ref() { m_refCountAndFlags += s_refCountIncrement; return this; }
+    ALWAYS_INLINE void deref() { m_refCountAndFlags -= s_refCountIncrement; if (!(m_refCountAndFlags & s_refCountMask)) delete this; }
 
     static void copyChars(UChar* destination, const UChar* source, unsigned numCharacters)
     {
@@ -205,11 +169,10 @@ private:
     // Used to construct normal strings with an internal or external buffer.
     UStringImpl(UChar* data, int length, BufferOwnership ownership)
         : m_data(data)
+        , m_buffer(0)
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | ownership)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(0, ownership)
     {
         ASSERT((ownership == BufferInternal) || (ownership == BufferOwned));
         checkConsistency();
@@ -221,11 +184,10 @@ private:
     enum StaticStringConstructType { ConstructStaticString };
     UStringImpl(UChar* data, int length, StaticStringConstructType)
         : m_data(data)
+        , m_buffer(0)
         , m_length(length)
-        , m_refCount(s_staticRefCountInitialValue)
+        , m_refCountAndFlags(s_refCountFlagStatic | BufferOwned)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(0, BufferOwned)
     {
         checkConsistency();
     }
@@ -233,28 +195,26 @@ private:
     // Used to create new strings that are a substring of an existing string.
     UStringImpl(UChar* data, int length, PassRefPtr<UStringImpl> base)
         : m_data(data)
+        , m_bufferSubstring(base.releaseRef())
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | BufferSubstring)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(base.releaseRef(), BufferSubstring)
     {
         // Do use static strings as a base for substrings; UntypedPtrAndBitfield assumes
         // that all pointers will be at least 8-byte aligned, we cannot guarantee that of
         // UStringImpls that are not heap allocated.
-        ASSERT(m_dataBuffer.asPtr<UStringImpl*>()->size());
-        ASSERT(!m_dataBuffer.asPtr<UStringImpl*>()->isStatic());
+        ASSERT(m_bufferSubstring->size());
+        ASSERT(!m_bufferSubstring->isStatic());
         checkConsistency();
     }
 
     // Used to construct new strings sharing an existing shared buffer.
     UStringImpl(UChar* data, int length, PassRefPtr<SharedUChar> sharedBuffer)
         : m_data(data)
+        , m_bufferShared(sharedBuffer.releaseRef())
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | BufferShared)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(sharedBuffer.releaseRef(), BufferShared)
     {
         checkConsistency();
     }
@@ -277,26 +237,31 @@ private:
     // This number must be at least 2 to avoid sharing empty, null as well as 1 character strings from SmallStrings.
     static const int s_minLengthToShare = 10;
     static const unsigned s_copyCharsInlineCutOff = 20;
-    static const uintptr_t s_bufferOwnershipMask = 3;
-    static const uintptr_t s_reportedCostBit = 4;
     // We initialize and increment/decrement the refCount for all normal (non-static) strings by the value 2.
     // We initialize static strings with an odd number (specifically, 1), such that the refCount cannot reach zero.
-    static const int s_refCountIncrement = 2;
-    static const int s_staticRefCountInitialValue = 1;
-
-    UStringImpl* bufferOwnerString() { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
-    const UStringImpl* bufferOwnerString() const { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
+    static const unsigned s_refCountMask = 0xFFFFFFF0;
+    static const int s_refCountIncrement = 0x20;
+    static const int s_refCountFlagStatic = 0x10;
+    static const unsigned s_refCountFlagHasReportedCost = 0x8;
+    static const unsigned s_refCountFlagIsIdentifier = 0x4;
+    static const unsigned s_refCountMaskBufferOwnership = 0x3;
+
+    UStringImpl* bufferOwnerString() { return (bufferOwnership() == BufferSubstring) ? m_bufferSubstring :  this; }
+    const UStringImpl* bufferOwnerString() const { return (bufferOwnership() == BufferSubstring) ? m_bufferSubstring :  this; }
     SharedUChar* baseSharedBuffer();
-    unsigned bufferOwnership() const { return m_dataBuffer & s_bufferOwnershipMask; }
-    bool isStatic() const { return m_refCount & 1; }
+    unsigned bufferOwnership() const { return m_refCountAndFlags & s_refCountMaskBufferOwnership; }
+    bool isStatic() const { return m_refCountAndFlags & s_refCountFlagStatic; }
 
     // unshared data
     UChar* m_data;
+    union {
+        void* m_buffer;
+        UStringImpl* m_bufferSubstring;
+        SharedUChar* m_bufferShared;
+    };
     int m_length;
-    unsigned m_refCount;
-    mutable unsigned m_hash : 31;
-    mutable unsigned m_isIdentifier : 1;
-    UntypedPtrAndBitfield m_dataBuffer;
+    unsigned m_refCountAndFlags;
+    mutable unsigned m_hash;
 
     JS_EXPORTDATA static UStringImpl* s_null;
     JS_EXPORTDATA static UStringImpl* s_empty;
diff --git a/src/3rdparty/javascriptcore/VERSION b/src/3rdparty/javascriptcore/VERSION
index b4744b7..13943b2 100644
--- a/src/3rdparty/javascriptcore/VERSION
+++ b/src/3rdparty/javascriptcore/VERSION
@@ -4,8 +4,8 @@ This is a snapshot of JavaScriptCore from
 
 The commit imported was from the
 
-        javascriptcore-snapshot-24012011 branch/tag
+        javascriptcore-snapshot-27012011 branch/tag
 
 and has the sha1 checksum
 
-        d143bde5ae8cff229aebd43487a2fce5e713e990
+        3ab0f621048fbeb480b687a28ed31d92d8506150
diff --git a/src/corelib/kernel/qabstracteventdispatcher.cpp b/src/corelib/kernel/qabstracteventdispatcher.cpp
index cc08f092..e79f87a 100644
--- a/src/corelib/kernel/qabstracteventdispatcher.cpp
+++ b/src/corelib/kernel/qabstracteventdispatcher.cpp
@@ -137,12 +137,6 @@ void QAbstractEventDispatcherPrivate::init()
 // free list). As an added protection, we use the cell to store an invalid
 // (negative) value that we can later check for integrity.
 //
-// ABA prevention simply adds a value to 7 of the top 8 bits when resetting
-// nextFreeTimerId.
-//
-// The extra code is the bucket allocation which allows us to start with a
-// very small bucket size and grow as needed.
-//
 // (continues below).
 int QAbstractEventDispatcherPrivate::allocateTimerId()
 {
@@ -170,8 +164,6 @@ int QAbstractEventDispatcherPrivate::allocateTimerId()
         newTimerId = prepareNewValueWithSerialNumber(timerId, b[at]);
     } while (!nextFreeTimerId.testAndSetRelaxed(timerId, newTimerId));
 
-    timerId &= TimerIdMask;
-    timerId |= b[at] & TimerSerialMask;
     b[at] = -timerId;
 
     return timerId;
@@ -182,13 +174,12 @@ int QAbstractEventDispatcherPrivate::allocateTimerId()
 //    X[timerId] = nextFreeTimerId;
 // then we update nextFreeTimerId to the timer we've just released
 //
+// The extra code in allocateTimerId and releaseTimerId are ABA prevention
+// and bucket memory. The buckets are simply to make sure we allocate only
+// the necessary number of timers. See above.
+//
 // ABA prevention simply adds a value to 7 of the top 8 bits when resetting
 // nextFreeTimerId.
-//
-// In addition to that, we update the same 7 bits in each entry in the bucket
-// as a counter. That way, a timer ID allocated and released will always be
-// returned with a different ID. This reduces the chances of timers being released
-// erroneously by application code.
 void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId)
 {
     int which = timerId & TimerIdMask;
@@ -196,21 +187,12 @@ void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId)
     int at = bucketIndex(bucket, which);
     int *b = timerIds[bucket];
 
-#ifndef QT_NO_DEBUG
-    // debug code
-    Q_ASSERT_X(timerId == -b[at], "QAbstractEventDispatcher::releaseTimerId", "Timer ID was not found, fix application");
-#else
-    if (timerId != -b[at]) {
-        // release code
-        qWarning("Timer ID %d was not found, fix application", timerId);
-        return;
-    }
-#endif
+    Q_ASSERT(b[at] == -timerId);
 
     int freeId, newTimerId;
     do {
         freeId = nextFreeTimerId;//.loadAcquire(); // ### FIXME Proper memory ordering semantics
-        b[at] = prepareNewValueWithSerialNumber(-b[at], freeId);
+        b[at] = freeId & TimerIdMask;
 
         newTimerId = prepareNewValueWithSerialNumber(freeId, timerId);
     } while (!nextFreeTimerId.testAndSetRelease(freeId, newTimerId));
diff --git a/src/corelib/thread/qthread.cpp b/src/corelib/thread/qthread.cpp
index f368192..f4bfa5d 100644
--- a/src/corelib/thread/qthread.cpp
+++ b/src/corelib/thread/qthread.cpp
@@ -482,10 +482,7 @@ int QThread::exec()
     Q_D(QThread);
     QMutexLocker locker(&d->mutex);
     d->data->quitNow = false;
-    if (d->exited) {
-        d->exited = false;
-        return d->returnCode;
-    }
+    d->exited = false;
     locker.unlock();
 
     QEventLoop eventLoop;
diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index 2404d2a..0337c1f 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/src/corelib/tools/qsharedpointer_impl.h
@@ -44,7 +44,17 @@
 #ifndef QSHAREDPOINTER_H
 #error Do not include qsharedpointer_impl.h directly
 #endif
+
 #if 0
+// These macros are duplicated here to make syncqt not complain a about
+// this header, as we have a "qt_sync_stop_processing" below, which in turn
+// is here because this file contains a template mess and duplicates the
+// classes found in qsharedpointer.h
+QT_BEGIN_HEADER
+QT_BEGIN_NAMESPACE
+QT_MODULE(Core)
+QT_END_NAMESPACE
+QT_END_HEADER
 #pragma qt_sync_stop_processing
 #endif
 
diff --git a/src/network/access/qnetworkreplyimpl.cpp b/src/network/access/qnetworkreplyimpl.cpp
index 9d7082c..343f344 100644
--- a/src/network/access/qnetworkreplyimpl.cpp
+++ b/src/network/access/qnetworkreplyimpl.cpp
@@ -109,7 +109,7 @@ void QNetworkReplyImplPrivate::_q_startOperation()
     }
 #endif
 
-    if (backend->isSynchronous()) {
+    if (backend && backend->isSynchronous()) {
         state = Finished;
     } else {
         if (state != Finished) {
@@ -296,7 +296,7 @@ void QNetworkReplyImplPrivate::setup(QNetworkAccessManager::Operation op, const
     // in QtWebKit.
     QVariant synchronousHttpAttribute = req.attribute(
             static_cast<QNetworkRequest::Attribute>(QNetworkRequest::DownloadBufferAttribute + 1));
-    if (synchronousHttpAttribute.toBool()) {
+    if (backend && synchronousHttpAttribute.toBool()) {
         backend->setSynchronous(true);
         if (outgoingData && outgoingData->isSequential()) {
             outgoingDataBuffer = new QRingBuffer();
@@ -351,7 +351,7 @@ void QNetworkReplyImplPrivate::setup(QNetworkAccessManager::Operation op, const
             QMetaObject::invokeMethod(q, "_q_startOperation", Qt::QueuedConnection);
         }
 #else
-        if (backend->isSynchronous())
+        if (backend && backend->isSynchronous())
             _q_startOperation();
         else
             QMetaObject::invokeMethod(q, "_q_startOperation", Qt::QueuedConnection);
diff --git a/src/script/api/qscriptengine.cpp b/src/script/api/qscriptengine.cpp
index 9e338d4..54039c0 100644
--- a/src/script/api/qscriptengine.cpp
+++ b/src/script/api/qscriptengine.cpp
@@ -1022,6 +1022,7 @@ QScriptEnginePrivate::~QScriptEnginePrivate()
     while (!ownedAgents.isEmpty())
         delete ownedAgents.takeFirst();
 
+    detachAllRegisteredScriptPrograms();
     detachAllRegisteredScriptValues();
     detachAllRegisteredScriptStrings();
     qDeleteAll(m_qobjectData);
@@ -1576,6 +1577,14 @@ bool QScriptEnginePrivate::scriptDisconnect(JSC::JSValue signal, JSC::JSValue re
 
 #endif
 
+void QScriptEnginePrivate::detachAllRegisteredScriptPrograms()
+{
+    QSet<QScriptProgramPrivate*>::const_iterator it;
+    for (it = registeredScriptPrograms.constBegin(); it != registeredScriptPrograms.constEnd(); ++it)
+        (*it)->detachFromEngine();
+    registeredScriptPrograms.clear();
+}
+
 void QScriptEnginePrivate::detachAllRegisteredScriptValues()
 {
     QScriptValuePrivate *it;
diff --git a/src/script/api/qscriptengine_p.h b/src/script/api/qscriptengine_p.h
index 05a8901..f8144e9 100644
--- a/src/script/api/qscriptengine_p.h
+++ b/src/script/api/qscriptengine_p.h
@@ -87,6 +87,7 @@ class QScriptEngineAgent;
 class QScriptEnginePrivate;
 class QScriptSyntaxCheckResult;
 class QScriptEngine;
+class QScriptProgramPrivate;
 
 namespace QScript
 {
@@ -273,6 +274,10 @@ public:
     static QScriptSyntaxCheckResult checkSyntax(const QString &program);
     static bool canEvaluate(const QString &program);
 
+    inline void registerScriptProgram(QScriptProgramPrivate *program);
+    inline void unregisterScriptProgram(QScriptProgramPrivate *program);
+    void detachAllRegisteredScriptPrograms();
+
     inline QScriptValuePrivate *allocateScriptValuePrivate(size_t);
     inline void freeScriptValuePrivate(QScriptValuePrivate *p);
 
@@ -368,6 +373,7 @@ public:
     static const int maxFreeScriptValues = 256;
     int freeScriptValuesCount;
     QScriptStringPrivate *registeredScriptStrings;
+    QSet<QScriptProgramPrivate*> registeredScriptPrograms;
     QHash<int, QScriptTypeInfo*> m_typeInfos;
     int processEventsInterval;
     QScriptValue abortResult;
@@ -566,6 +572,18 @@ inline QByteArray convertToLatin1(const JSC::UString &str)
 
 } // namespace QScript
 
+inline void QScriptEnginePrivate::registerScriptProgram(QScriptProgramPrivate *program)
+{
+    Q_ASSERT(!registeredScriptPrograms.contains(program));
+    registeredScriptPrograms.insert(program);
+}
+
+inline void QScriptEnginePrivate::unregisterScriptProgram(QScriptProgramPrivate *program)
+{
+    Q_ASSERT(registeredScriptPrograms.contains(program));
+    registeredScriptPrograms.remove(program);
+}
+
 inline QScriptValuePrivate *QScriptEnginePrivate::allocateScriptValuePrivate(size_t size)
 {
     if (freeScriptValues) {
diff --git a/src/script/api/qscriptprogram.cpp b/src/script/api/qscriptprogram.cpp
index da103bb..31af9a0 100644
--- a/src/script/api/qscriptprogram.cpp
+++ b/src/script/api/qscriptprogram.cpp
@@ -64,6 +64,7 @@ QScriptProgramPrivate::~QScriptProgramPrivate()
     if (engine) {
         QScript::APIShim shim(engine);
         _executable.clear();
+        engine->unregisterScriptProgram(this);
     }
 }
 
@@ -78,7 +79,10 @@ JSC::EvalExecutable *QScriptProgramPrivate::executable(JSC::ExecState *exec,
     if (_executable) {
         if (eng == engine)
             return _executable.get();
-        _executable = 0;
+        // "Migrating" to another engine; clean up old state
+        QScript::APIShim shim(engine);
+        _executable.clear();
+        engine->unregisterScriptProgram(this);
     }
     WTF::PassRefPtr<QScript::UStringSourceProviderWithFeedback> provider
         = QScript::UStringSourceProviderWithFeedback::create(sourceCode, fileName, firstLineNumber, eng);
@@ -86,10 +90,19 @@ JSC::EvalExecutable *QScriptProgramPrivate::executable(JSC::ExecState *exec,
     JSC::SourceCode source(provider, firstLineNumber); //after construction of SourceCode provider variable will be null.
     _executable = JSC::EvalExecutable::create(exec, source);
     engine = eng;
+    engine->registerScriptProgram(this);
     isCompiled = false;
     return _executable.get();
 }
 
+void QScriptProgramPrivate::detachFromEngine()
+{
+    _executable.clear();
+    sourceId = -1;
+    isCompiled = false;
+    engine = 0;
+}
+
 /*!
   Constructs a null QScriptProgram.
 */
@@ -122,9 +135,6 @@ QScriptProgram::QScriptProgram(const QScriptProgram &other)
 */
 QScriptProgram::~QScriptProgram()
 {
-    //    Q_D(QScriptProgram);
-    //    if (d->engine && (d->ref == 1))
-    //      d->engine->unregisterScriptProgram(d);
 }
 
 /*!
@@ -132,9 +142,6 @@ QScriptProgram::~QScriptProgram()
 */
 QScriptProgram &QScriptProgram::operator=(const QScriptProgram &other)
 {
-  //    if (d_func() && d_func()->engine && (d_func()->ref == 1))
-      //        d_func()->engine->unregisterScriptProgram(d_func());
-  //    }
     d_ptr = other.d_ptr;
     return *this;
 }
diff --git a/src/script/api/qscriptprogram_p.h b/src/script/api/qscriptprogram_p.h
index d2fd234..e7809ab 100644
--- a/src/script/api/qscriptprogram_p.h
+++ b/src/script/api/qscriptprogram_p.h
@@ -61,6 +61,7 @@ public:
 
     JSC::EvalExecutable *executable(JSC::ExecState *exec,
                                     QScriptEnginePrivate *engine);
+    void detachFromEngine();
 
     QBasicAtomicInt ref;