Provide a logical view of VM-internal maps in Observatory.

runtime/vm/object.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 7215 matching lines @@
   RawSmi* deleted_keys() const {
     return raw_ptr()->deleted_keys_;
   }
   void SetDeletedKeys(intptr_t value) const {
     StoreSmi(&raw_ptr()->deleted_keys_, Smi::New(value));
   }
   static intptr_t deleted_keys_offset() {
     return OFFSET_OF(RawLinkedHashMap, deleted_keys_);
   }
 
+  intptr_t Length() const {
+    intptr_t used = Smi::Value(raw_ptr()->used_data_);
+    intptr_t deleted = Smi::Value(raw_ptr()->deleted_keys_);
+    return (used >> 1) - deleted;
+  }
+
+  class Iterator : ValueObject {

[koda, 2015/06/02 16:42:37]

Add comment to note how this differs from its Dart counterpart:
1. does not check for concurrent modifications.
2. crashes, rather than returns null, when the iterator is before beginning or
after end

[rmacnak, 2015/06/02 17:33:31]

Done.

+   public:
+    explicit Iterator(const LinkedHashMap& map)
+      : map_(map)
+      , data_(Array::Handle(map.data()))

[koda, 2015/06/02 16:42:37]

I think our code usually has these commas at the end of the lines.

[rmacnak, 2015/06/02 17:33:31]

Ah, yes. Before is Blink.

+      , scratch_(Object::Handle())
+      , offset_(-2)
+      , length_(Smi::Handle(map.used_data()).Value()) {}

[koda, 2015/06/02 16:42:37]

Avoid handle creation: Smi::Value(map.used_data())

[rmacnak, 2015/06/02 17:33:31]

Done.

+
+    bool MoveNext() {
+      // Cf. _CompactIterator in runtime/lib/compact_hash.dart.
+      while (true) {
+        offset_ += 2;
+        if (offset_ >= length_) {
+          return false;
+        }
+        scratch_ = data_.At(offset_);
+        if (scratch_.raw() != data_.raw()) {
+          // Slot is not deleted (self-reference indicates deletion).
+          return true;
+        }
+      }
+    }
+
+    RawObject* CurrentKey() const {
+      return data_.At(offset_);
+    }
+
+    RawObject* CurrentValue() const {
+      return data_.At(offset_ + 1);
+    }
+
+   private:
+    const LinkedHashMap& map_;
+    const Array& data_;
+    Object& scratch_;
+    intptr_t offset_;
+    const intptr_t length_;
+  };
+
  private:
   FINAL_HEAP_OBJECT_IMPLEMENTATION(LinkedHashMap, Instance);
 
   // Allocate a map, but leave all fields set to null.
   // Used during deserialization (since map might contain itself as key/value).
   static RawLinkedHashMap* NewUninitialized(Heap::Space space = Heap::kNew);
 
   friend class Class;
 };
 
@@ skipping 546 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_