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 <[email protected]>
Task-number: QTBUG-119274
Change-Id: I1d94f41bc7a434fad67de0fd46454b6db285f2eb
Reviewed-by: Ulf Hermann <[email protected]>

7 files changed, 49 insertions, 6 deletions

diff --git a/src/qml/jsruntime/qv4enginebase_p.h b/src/qml/jsruntime/qv4enginebase_p.h
index 721a024efb..68e906baa1 100644
--- a/src/qml/jsruntime/qv4enginebase_p.h
+++ b/src/qml/jsruntime/qv4enginebase_p.h
@@ -45,7 +45,8 @@ struct Q_QML_EXPORT EngineBase {
 
     quint8 isExecutingInRegExpJIT = false;
     quint8 isInitialized = false;
-    quint8 padding[2];
+    quint8 inShutdown = false;
+    quint8 isGCOngoing = false; // incremental gc is ongoing (but mutator might be running)
     MemoryManager *memoryManager = nullptr;
 
     union {
diff --git a/src/qml/jsruntime/qv4identifiertable.cpp b/src/qml/jsruntime/qv4identifiertable.cpp
index d8999951dc..4c915442f4 100644
--- a/src/qml/jsruntime/qv4identifiertable.cpp
+++ b/src/qml/jsruntime/qv4identifiertable.cpp
@@ -36,7 +36,7 @@ void IdentifierTable::addEntry(Heap::StringOrSymbol *str)
     if (str->subtype == Heap::String::StringType_ArrayIndex)
         return;
 
-    str->identifier = PropertyKey::fromStringOrSymbol(str);
+    str->identifier = PropertyKey::fromStringOrSymbol(engine, str);
 
     bool grow = (alloc <= size*2);
 
@@ -165,6 +165,9 @@ PropertyKey IdentifierTable::asPropertyKeyImpl(const Heap::String *str)
     while (Heap::StringOrSymbol *e = entriesByHash[idx]) {
         if (e->stringHash == hash && e->toQString() == str->toQString()) {
             str->identifier = e->identifier;
+            QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack) {
+                e->identifier.asStringOrSymbol()->mark(stack);
+            });
             return e->identifier;
         }
         ++idx;
diff --git a/src/qml/jsruntime/qv4internalclass.cpp b/src/qml/jsruntime/qv4internalclass.cpp
index e4c401f5a7..ddf38c968d 100644
--- a/src/qml/jsruntime/qv4internalclass.cpp
+++ b/src/qml/jsruntime/qv4internalclass.cpp
@@ -122,6 +122,11 @@ PropertyKey SharedInternalClassDataPrivate<PropertyKey>::at(uint i) const
 void SharedInternalClassDataPrivate<PropertyKey>::set(uint i, PropertyKey t)
 {
     Q_ASSERT(data && i < size());
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack) {
+        if constexpr (QV4::WriteBarrier::isInsertionBarrier)
+            if (auto string = t.asStringOrSymbol())
+                string->mark(stack);
+    });
     data->values.values[i].rawValueRef() = t.id();
 }
 
@@ -256,6 +261,11 @@ void InternalClass::init(Heap::InternalClass *other)
     protoId = engine->newProtoId();
 
     internalClass.set(engine, other->internalClass);
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack) {
+        if constexpr (QV4::WriteBarrier::isInsertionBarrier) {
+            other->mark(stack);
+        }
+    });
 }
 
 void InternalClass::destroy()
@@ -476,6 +486,10 @@ Heap::InternalClass *InternalClass::changePrototypeImpl(Heap::Object *proto)
 
     // create a new class and add it to the tree
     Heap::InternalClass *newClass = engine->newClass(this);
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack) {
+        if (proto && QV4::WriteBarrier::isInsertionBarrier)
+            proto->mark(stack);
+    });
     newClass->prototype = proto;
 
     t.lookup = newClass;
diff --git a/src/qml/jsruntime/qv4persistent.cpp b/src/qml/jsruntime/qv4persistent.cpp
index 75353935a1..3cbaec1dac 100644
--- a/src/qml/jsruntime/qv4persistent.cpp
+++ b/src/qml/jsruntime/qv4persistent.cpp
@@ -171,7 +171,7 @@ Value *PersistentValueStorage::allocate()
     Value *v = p->values + p->header.freeList;
     p->header.freeList = v->int_32();
 
-    if (p->header.freeList != -1 && p != firstPage) {
+    if (p->header.freeList != -1 && p != firstPage && !engine->isGCOngoing) {
         unlink(p);
         insertInFront(this, p);
     }
@@ -304,6 +304,10 @@ void PersistentValue::set(ExecutionEngine *engine, const Value &value)
 {
     if (!val)
         val = engine->memoryManager->m_persistentValues->allocate();
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack){
+        if (QV4::WriteBarrier::isInsertionBarrier && value.isManaged())
+            stack->push(value.heapObject());
+    });
     *val = value;
 }
 
@@ -311,6 +315,13 @@ void PersistentValue::set(ExecutionEngine *engine, ReturnedValue value)
 {
     if (!val)
         val = engine->memoryManager->m_persistentValues->allocate();
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack){
+        if constexpr (!QV4::WriteBarrier::isInsertionBarrier)
+            return;
+        auto val = Value::fromReturnedValue(value);
+        if (val.isManaged())
+            stack->push(val.heapObject());
+    });
     *val = value;
 }
 
@@ -318,6 +329,11 @@ void PersistentValue::set(ExecutionEngine *engine, Heap::Base *obj)
 {
     if (!val)
         val = engine->memoryManager->m_persistentValues->allocate();
+    QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack){
+        if constexpr (QV4::WriteBarrier::isInsertionBarrier)
+            stack->push(obj);
+    });
+
     *val = obj;
 }
 
diff --git a/src/qml/jsruntime/qv4propertykey.cpp b/src/qml/jsruntime/qv4propertykey.cpp
index d93ff8e794..65dd7e7fc1 100644
--- a/src/qml/jsruntime/qv4propertykey.cpp
+++ b/src/qml/jsruntime/qv4propertykey.cpp
@@ -7,6 +7,7 @@
 #include <qv4string_p.h>
 #include <qv4engine_p.h>
 #include <qv4scopedvalue_p.h>
+#include <private/qv4mm_p.h>
 
 using namespace Qt::Literals::StringLiterals;
 
diff --git a/src/qml/jsruntime/qv4propertykey_p.h b/src/qml/jsruntime/qv4propertykey_p.h
index 0b8ad084d2..d6d15e402d 100644
--- a/src/qml/jsruntime/qv4propertykey_p.h
+++ b/src/qml/jsruntime/qv4propertykey_p.h
@@ -14,6 +14,7 @@
 // We mean it.
 //
 
+#include <private/qv4writebarrier_p.h>
 #include <private/qv4global_p.h>
 #include <private/qv4staticvalue_p.h>
 #include <QtCore/qhashfunctions.h>
@@ -70,11 +71,18 @@ public:
     // We cannot #include the declaration of Heap::StringOrSymbol here.
     // Therefore we do some gymnastics to enforce the type safety.
 
-    template<typename StringOrSymbol = Heap::StringOrSymbol>
-    static PropertyKey fromStringOrSymbol(StringOrSymbol *b)
+    template<typename StringOrSymbol = Heap::StringOrSymbol, typename Engine = QV4::EngineBase>
+    static PropertyKey fromStringOrSymbol(Engine *engine, StringOrSymbol *b)
     {
         static_assert(std::is_base_of_v<Heap::StringOrSymbol, StringOrSymbol>);
         PropertyKey key;
+        QV4::WriteBarrier::markCustom(engine, [&](QV4::MarkStack *stack) {
+            if constexpr (QV4::WriteBarrier::isInsertionBarrier) {
+                // treat this as an insertion - the StringOrSymbol becomes reachable
+                // via the propertykey, so we consequently need to mark it durnig gc
+                b->mark(stack);
+            }
+        });
         key.val.setM(b);
         Q_ASSERT(key.isManaged());
         return key;
diff --git a/src/qml/jsruntime/qv4symbol.cpp b/src/qml/jsruntime/qv4symbol.cpp
index 585038937e..5f7ec89fd2 100644
--- a/src/qml/jsruntime/qv4symbol.cpp
+++ b/src/qml/jsruntime/qv4symbol.cpp
@@ -16,7 +16,7 @@ void Heap::Symbol::init(const QString &s)
     Q_ASSERT(s.at(0) == QLatin1Char('@'));
     QString desc(s);
     StringOrSymbol::init(desc.data_ptr());
-    identifier = PropertyKey::fromStringOrSymbol(this);
+    identifier = PropertyKey::fromStringOrSymbol(internalClass->engine, this);
 }
 
 void Heap::SymbolCtor::init(QV4::ExecutionContext *scope)