Scavenge watched objects by scavenging their watchers.

runtime/vm/scavenger.cc

Index: runtime/vm/scavenger.cc
diff --git a/runtime/vm/scavenger.cc b/runtime/vm/scavenger.cc
index 9767e03c6760ecca0f233b057a1b4a3ccda67af5..0c2364a212f7fbc15a05d8a88d009392037c8f03 100644
--- a/runtime/vm/scavenger.cc
+++ b/runtime/vm/scavenger.cc
@@ -122,18 +122,22 @@ class ScavengerVisitor : public ObjectPointerVisitor {
     if (IsForwarding(header)) {
       // Get the new location of the object.
       new_addr = ForwardedAddr(header);
-    } else {
-      if (raw_obj->IsWatched()) {
-        std::pair<DelaySet::iterator, DelaySet::iterator> ret;
-        // Visit all elements with a key equal to raw_obj.
-        ret = delay_set_.equal_range(raw_obj);
-        for (DelaySet::iterator it = ret.first; it != ret.second; ++it) {
-          // Visit through the associated WeakProperty at this time.
-          it->second->VisitPointers(this);
-        }
-        delay_set_.erase(ret.first, ret.second);
-        raw_obj->ClearWatchedBit();
+    } else if (raw_obj->IsWatched()) {
+      // Forward the object by scavenging its watchers.

[Ivan Posva, 2012/10/02 23:02:31]

Can you add a comment here that we delayed visiting the pointers when we
initially encountered the weak property object? Essentially at this point we
know that the key is reachable so we should visit the pointers in the weak
property.

[cshapiro, 2012/10/03 01:39:42]

Done.

+      raw_obj->ClearWatchedBit();
+      std::pair<DelaySet::iterator, DelaySet::iterator> ret;
+      // Visit all elements with a key equal to raw_obj.
+      ret = delay_set_.equal_range(raw_obj);
+      for (DelaySet::iterator it = ret.first; it != ret.second; ++it) {
+        // Visit through the associated WeakProperty at this time.
+        it->second->VisitPointers(this);
       }
+      delay_set_.erase(ret.first, ret.second);
+      // Reread the header word to get the new location of the object.
+      header = *reinterpret_cast<uword*>(raw_addr);
+      ASSERT(IsForwarding(header));
+      new_addr = ForwardedAddr(header);
+    } else {
       intptr_t size = raw_obj->Size();
       // Check whether object should be promoted.
       if (scavenger_->survivor_end_ <= raw_addr) {