Implement a real write barrier

Implement a Steel write barrier for our objects. The barrier is
interesting as it can also be used for incremental GC runs by
simply turning the barrier on and leaving old objects marked as
black.

Change-Id: I0b273974d94a990dee3cd9298089b8b202c75bf2
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/qml/memory/qv4heap_p.h b/src/qml/memory/qv4heap_p.h
index bcd1af7705..7bedd705f9 100644
--- a/src/qml/memory/qv4heap_p.h
+++ b/src/qml/memory/qv4heap_p.h
@@ -113,6 +113,12 @@ struct Q_QML_EXPORT Base {
         Q_ASSERT(!Chunk::testBit(c->extendsBitmap, h - c->realBase()));
         return Chunk::setBit(c->blackBitmap, h - c->realBase());
     }
+    inline void setGrayBit() {
+        const HeapItem *h = reinterpret_cast<const HeapItem *>(this);
+        Chunk *c = h->chunk();
+        Q_ASSERT(!Chunk::testBit(c->extendsBitmap, h - c->realBase()));
+        return Chunk::setBit(c->grayBitmap, h - c->realBase());
+    }
 
     inline bool inUse() const {
         const HeapItem *h = reinterpret_cast<const HeapItem *>(this);