Introduce EmbedderHeapTracer

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 6f2bba09bf14d88060da0225f417f3d7b40df098..99cc4a9bdd82de7d9601cb400287289534f47650 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5158,6 +5158,8 @@ enum GCCallbackFlags {
 };
 
 typedef void (*GCCallback)(GCType type, GCCallbackFlags flags);
+typedef void (*GCPutOnMarkingDequeCallback)(PersistentBase<Object>* handle,
+                                            Isolate* isolate);
 
 typedef void (*InterruptCallback)(Isolate* isolate, void* data);
 
@@ -5350,6 +5352,30 @@ class V8_EXPORT PersistentHandleVisitor {  // NOLINT
                                      uint16_t class_id) {}
 };
 
+/**
+ * Interface for tracing through the embedder heap. During the v8 garbage
+ * collection, the embedder is notified that some object he has a reference to
+ * is still alive, and is expected to trace through its heap and call callback
+ * function for each dependent js object.
+ *
+ * After the v8 garbage collection is finished, ClearTracingMarks is called so
+ * the embedder can clear its temporary data.
+ */
+class EmbedderHeapTracer {
+ public:
+  virtual ~EmbedderHeapTracer() {}
+  /**
+   * V8 will call this method with every wrapper. Embedder is expected to call
+   * the provided callback (synchronously) with every dependent wrapper so the
+   * v8 will keep it alive.
+   */
+  virtual void TraceWrappableFrom(Isolate* isolate, Persistent<Object>* value,
+                                  GCPutOnMarkingDequeCallback callback);

[jochen (gone - plz use gerrit), 2016/03/24 14:31:36]

as discussed offline, I'd propose to not add callbacks we don't need yet

+  /**
+   * V8 allocation is *not* allowed in the ClearTracingMarks.
+   */
+  virtual void ClearTracingMarks(Isolate* isolate) {}
+};
 
 /**
  * Isolate represents an isolated instance of the V8 engine.  V8 isolates have
@@ -5812,6 +5838,11 @@ class V8_EXPORT Isolate {
   void RemoveGCPrologueCallback(GCCallback callback);
 
   /**
+   * Sets the embedder heap tracer for the isolate.
+   */
+  void SetEmbedderHeapTracer(EmbedderHeapTracer* tracer);
+
+  /**
    * Enables the host application to receive a notification after a
    * garbage collection. Allocations are allowed in the callback function,
    * but the callback is not re-entrant: if the allocation inside it will