Long live incremental garbage collection in QML!

The design of the garbage collector is described in
src/qml/memory/design.md.

The gc and gcdone test helpers are adjusted to drive the gc to
completion, even when in incremental mode.

Parts of tst_qv4mm and tst_qqmlqt need to run with the incremental gc
disabled, as they call gc inside QML and assumes that the GC finishes
before returning.

Initial-patch-by: Rafal Chomentowski <rafal.chomentowski@ge.com>
Task-number: QTBUG-119274
Change-Id: I1d94f41bc7a434fad67de0fd46454b6db285f2eb
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/qml/memory/qv4mmdefs_p.h b/src/qml/memory/qv4mmdefs_p.h
index a7fc7bb7cb..277b1adcc5 100644
--- a/src/qml/memory/qv4mmdefs_p.h
+++ b/src/qml/memory/qv4mmdefs_p.h
@@ -21,6 +21,8 @@
 
 QT_BEGIN_NAMESPACE
 
+class QDeadlineTimer;
+
 namespace QV4 {
 
 struct MarkStack;
@@ -229,7 +231,7 @@ Q_STATIC_ASSERT((1 << Chunk::BitShift) == Chunk::Bits);
 
 struct Q_QML_PRIVATE_EXPORT MarkStack {
     MarkStack(ExecutionEngine *engine);
-    ~MarkStack() { drain(); }
+    ~MarkStack() { /* we drain manually */ }
 
     void push(Heap::Base *m) {
         *(m_top++) = m;
@@ -250,17 +252,28 @@ struct Q_QML_PRIVATE_EXPORT MarkStack {
         }
     }
 
+    bool isEmpty() const { return m_top == m_base; }
+
+    qptrdiff remainingBeforeSoftLimit() const
+    {
+        return m_softLimit - m_top;
+    }
+
     ExecutionEngine *engine() const { return m_engine; }
 
+    void drain();
+    enum class DrainState { Ongoing, Complete };
+    DrainState drain(QDeadlineTimer deadline);
 private:
     Heap::Base *pop() { return *(--m_top); }
-    void drain();
 
     Heap::Base **m_top = nullptr;
     Heap::Base **m_base = nullptr;
     Heap::Base **m_softLimit = nullptr;
     Heap::Base **m_hardLimit = nullptr;
+
     ExecutionEngine *m_engine = nullptr;
+
     quintptr m_drainRecursion = 0;
 };