Scavenge watched objects by scavenging their watchers.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/scavenger.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
@@ skipping 104 matching lines @@
       return;
     }
 
     // Read the header word of the object and determine if the object has
     // already been copied.
     uword header = *reinterpret_cast<uword*>(raw_addr);
     uword new_addr = 0;
     if (IsForwarding(header)) {
       // Get the new location of the object.
       new_addr = ForwardedAddr(header);
+    } 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 {
-      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();
-      }
       intptr_t size = raw_obj->Size();
       // Check whether object should be promoted.
       if (scavenger_->survivor_end_ <= raw_addr) {
         // Not a survivor of a previous scavenge. Just copy the object into the
         // to space.
         new_addr = scavenger_->TryAllocate(size);
       } else {
         // TODO(iposva): Experiment with less aggressive promotion. For example
         // a coin toss determines if an object is promoted or whether it should
         // survive in this generation.
@@ skipping 480 matching lines @@
   PeerTable::iterator it = peer_table_.find(raw_obj);
   return (it == peer_table_.end()) ? NULL : it->second;
 }
 
 
 int64_t Scavenger::PeerCount() const {
   return static_cast<int64_t>(peer_table_.size());
 }
 
 }  // namespace dart