Prepare for white allocation during gc (0/9): Engine

When inserting compilation units into the engine, we don't have any
write barrier, as those are treaded as roots. However, we still have to
be careful when an executable compilation unit is created while the gc
is already ongoing. Thus, when we insert a CU into the engine, we mark
it.

Change-Id: I5e7c7e9518190dd6943cf57b0a82229d6be8d3b9
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>

2 files changed, 17 insertions, 6 deletions

diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 6f91712bb4..09c763e956 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -2123,8 +2123,23 @@ QQmlRefPointer<ExecutableCompilationUnit> ExecutionEngine::executableCompilation
             return *it;
     }
 
-    return *m_compilationUnits.insert(
+    auto executableUnit =  m_compilationUnits.insert(
             url, ExecutableCompilationUnit::create(std::move(unit), this));
+    // runtime data should not be initialized yet, so we don't need to mark the CU
+    Q_ASSERT(!(*executableUnit)->runtimeStrings);
+    return *executableUnit;
+}
+
+QQmlRefPointer<ExecutableCompilationUnit> ExecutionEngine::insertCompilationUnit(QQmlRefPointer<CompiledData::CompilationUnit> &&unit) {
+    QUrl url = unit->finalUrl();
+    auto executableUnit = ExecutableCompilationUnit::create(std::move(unit), this);
+    /* Compilation Units stored in the engine are part of the gc roots,
+      so we don't trigger any write-barrier when they are added. Use
+      markCustom to make sure they are still marked when we insert them */
+    QV4::WriteBarrier::markCustom(this, [&executableUnit](QV4::MarkStack *ms) {
+        executableUnit->markObjects(ms);
+    });
+    return *m_compilationUnits.insert(std::move(url), std::move(executableUnit));
 }
 
 void ExecutionEngine::trimCompilationUnits()
diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 1f4622d154..102700e25b 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -759,11 +759,7 @@ public:
             QQmlRefPointer<QV4::CompiledData::CompilationUnit> &&unit);
 
     QQmlRefPointer<ExecutableCompilationUnit> insertCompilationUnit(
-            QQmlRefPointer<QV4::CompiledData::CompilationUnit> &&unit) {
-        QUrl url = unit->finalUrl();
-        return *m_compilationUnits.insert(
-                std::move(url), ExecutableCompilationUnit::create(std::move(unit), this));
-    }
+            QQmlRefPointer<QV4::CompiledData::CompilationUnit> &&unit);
 
     QMultiHash<QUrl, QQmlRefPointer<ExecutableCompilationUnit>> compilationUnits() const
     {