Avoid infinite growth of linked hash map implementation

dart/runtime/lib/compact_hash.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:typed_data';
 
 // Hash table with open addressing that separates the index from keys/values.
 abstract class _HashBase {
   // Each occupied entry in _index is a fixed-size integer that encodes a pair:
   //   [ hash pattern for key | index of entry in _data ]
   // The hash pattern is based on hashCode, but is guaranteed to be non-zero.
   // The length of _index is always a power of two, and there is always at
   // least one unoccupied entry.
   Uint32List _index;
 
   // The number of bits used for each component is determined by table size.
   // The length of _index is twice the number of entries in _data, and both
   // are doubled when _data is full. Thus, _index will have a max load factor
   // of 1/2, which enables one more bit to be used for the hash.
-  // TODO(koda): Consider growing _data by factor sqrt(2), twice as often. 
+  // TODO(koda): Consider growing _data by factor sqrt(2), twice as often.
   static const int _INITIAL_INDEX_BITS = 3;
   static const int _INITIAL_INDEX_SIZE = 1 << (_INITIAL_INDEX_BITS + 1);
-  
+
   // Unused and deleted entries are marked by 0 and 1, respectively.
   static const int _UNUSED_PAIR = 0;
   static const int _DELETED_PAIR = 1;
-  
+
   // Cached in-place mask for the hash pattern component. On 32-bit, the top
   // bits are wasted to avoid Mint allocation.
   // TODO(koda): Reclaim the bits by making the compiler treat hash patterns
   // as unsigned words.
   int _hashMask = int.is64Bit() ?
       (1 << (32 - _INITIAL_INDEX_BITS)) - 1 :
       (1 << (30 - _INITIAL_INDEX_BITS)) - 1;
 
   static int _hashPattern(int fullHash, int hashMask, int size) {
     final int maskedHash = fullHash & hashMask;
     // TODO(koda): Consider keeping bit length and use left shift.
     return (maskedHash == 0) ? (size >> 1) : maskedHash * (size >> 1);
   }
 
   // Linear probing.
   static int _firstProbe(int fullHash, int sizeMask) {
     final int i = fullHash & sizeMask;
     // Light, fast shuffle to mitigate bad hashCode (e.g., sequential).
     return ((i << 1) + i) & sizeMask;
   }
   static int _nextProbe(int i, int sizeMask) => (i + 1) & sizeMask;
-  
+
   // Fixed-length list of keys (set) or key/value at even/odd indices (map).
   List _data;
   // Length of _data that is used (i.e., keys + values for a map).
   int _usedData = 0;
   // Number of deleted keys.
   int _deletedKeys = 0;
-  
+
   // A self-loop is used to mark a deleted key or value.
   static bool _isDeleted(List data, Object keyOrValue) =>
       identical(keyOrValue, data);
   static void _setDeletedAt(List data, int d) {
     data[d] = data;
   }
 
   // Concurrent modification detection relies on this checksum monotonically
   // increasing between reallocations of _data.
   int get _checkSum => _usedData + _deletedKeys;
@@ skipping 15 matching lines @@
 // appended to _data.
 class _CompactLinkedHashMap<K, V>
     extends MapBase<K, V> with _HashBase, _OperatorEqualsAndHashCode
     implements LinkedHashMap<K, V> {
 
   _CompactLinkedHashMap() {
     assert(_HashBase._UNUSED_PAIR == 0);
     _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
     _data = new List(_HashBase._INITIAL_INDEX_SIZE);
   }
-  
+
   int get length => (_usedData >> 1) - _deletedKeys;
   bool get isEmpty => length == 0;
   bool get isNotEmpty => !isEmpty;
-  
+
   void _rehash() {
-    if ((_deletedKeys << 1) > _usedData) {
+    if ((_deletedKeys << 2) > _usedData) {

[koda, 2015/03/24 16:27:57]

Perhaps expressing this in terms of 'length' instead would have made the bug
easier to spot:

if (_deletedKeys > length)
...

[kustermann, 2015/03/24 16:44:01]

Good point. Ivan wanted me to submit the CL as is -  sorry for not addressing
the comment - in order to get it cherry-picked to dev channel.

If you'll add a test, I guess you can rename it to length.

You could use the VMOptions setting from our test runner to reduce old space
size. i.e. something like:

$ cat tests/standalone/map_literal_oom_test.dart
// VMOptions=--old_gen_heap_size=10

main() {
  var x = {};
  for (int i = 0; i < 1000000000; i++) {
    x[i] = 10;
    x.remove(i);
  }
}

       // TODO(koda): Consider shrinking.
       // TODO(koda): Consider in-place compaction and more costly CME check.
       _init(_index.length, _hashMask, _data, _usedData);
     } else {
       // TODO(koda): Support 32->64 bit transition (and adjust _hashMask).
       _init(_index.length << 1, _hashMask >> 1, _data, _usedData);
     }
   }
-  
+
   void clear() {
     if (!isEmpty) {
       _init(_index.length, _hashMask);
     }
   }
 
   // Allocate new _index and _data, and optionally copy existing contents.
   void _init(int size, int hashMask, [List oldData, int oldUsed]) {
     assert(size & (size - 1) == 0);
     assert(_HashBase._UNUSED_PAIR == 0);
     _index = new Uint32List(size);
     _hashMask = hashMask;
     _data = new List(size);
     _usedData = 0;
     _deletedKeys = 0;
     if (oldData != null) {
       for (int i = 0; i < oldUsed; i += 2) {
         var key = oldData[i];
         if (!_HashBase._isDeleted(oldData, key)) {
           // TODO(koda): While there are enough hash bits, avoid hashCode calls.
           this[key] = oldData[i + 1];
         }
       }
     }
   }
-  
+
   void _insert(K key, V value, int hashPattern, int i) {
     if (_usedData == _data.length) {
       _rehash();
       this[key] = value;
     } else {
       assert(1 <= hashPattern && hashPattern <  (1 << 32));
       final int index = _usedData >> 1;
       assert((index & hashPattern) == 0);
       _index[i] = hashPattern | index;
       _data[_usedData++] = key;
       _data[_usedData++] = value;
     }
   }
-  
+
   // If key is present, returns the index of the value in _data, else returns
   // the negated insertion point in _index.
   int _findValueOrInsertPoint(K key, int fullHash, int hashPattern, int size) {
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int firstDeleted = -1;
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair == _HashBase._DELETED_PAIR) {
         if (firstDeleted < 0){
           firstDeleted = i;
         }
       } else {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             return d + 1;
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return firstDeleted >= 0 ? -firstDeleted : -i;
   }
-  
+
   void operator[]=(K key, V value) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
     if (d > 0) {
       _data[d] = value;
     } else {
       final int i = -d;
       _insert(key, value, hashPattern, i);
     }
   }
-  
+
   V putIfAbsent(K key, V ifAbsent()) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
     if (d > 0) {
       return _data[d];
     }
     // 'ifAbsent' is allowed to modify the map.
     List oldData = _data;
     int oldCheckSum = _checkSum;
     V value = ifAbsent();
     if (_isModifiedSince(oldData, oldCheckSum)) {
       this[key] = value;
     } else {
       final int i = -d;
       _insert(key, value, hashPattern, i);
     }
     return value;
   }
-  
+
   V remove(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             _index[i] = _HashBase._DELETED_PAIR;
             _HashBase._setDeletedAt(_data, d);
             V value = _data[d + 1];
             _HashBase._setDeletedAt(_data, d + 1);
             ++_deletedKeys;
             return value;
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return null;
   }
-  
+
   // If key is absent, return _data (which is never a value).
   Object _getValueOrData(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             return _data[d + 1];
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return _data;
   }
-  
+
   bool containsKey(Object key) => !identical(_data, _getValueOrData(key));
-  
+
   V operator[](Object key) {
     var v = _getValueOrData(key);
     return identical(_data, v) ? null : v;
   }
-  
+
   bool containsValue(Object value) {
     for (var v in values) {
       // Spec. says this should always use "==", also for identity maps, etc.
       if (v == value) {
         return true;
       }
     }
     return false;
   }
 
@@ skipping 18 matching lines @@
 
 class _CompactLinkedCustomHashMap<K, V>
     extends _CompactLinkedHashMap<K, V> {
   final _equality;
   final _hasher;
   final _validKey;
 
   // TODO(koda): Ask gbracha why I cannot have fields _equals/_hashCode.
   int _hashCode(e) => _hasher(e);
   bool _equals(e1, e2) => _equality(e1, e2);
-      
+
   bool containsKey(Object o) => _validKey(o) ? super.containsKey(o) : false;
   V operator[](Object o) => _validKey(o) ? super[o] : null;
   V remove(Object o) => _validKey(o) ? super.remove(o) : null;
 
   _CompactLinkedCustomHashMap(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<K>().test;
 }
-      
+
 // Iterates through _data[_offset + _step], _data[_offset + 2*_step], ...
 // and checks for concurrent modification.
 class _CompactIterable<E> extends IterableBase<E> {
   final _table;
   final List _data;
   final int _len;
   final int _offset;
   final int _step;
 
   _CompactIterable(this._table, this._data, this._len,
@@ skipping 49 matching lines @@
 
   int get length => _usedData - _deletedKeys;
 
   void _rehash() {
     if ((_deletedKeys << 1) > _usedData) {
       _init(_index.length, _hashMask, _data, _usedData);
     } else {
       _init(_index.length << 1, _hashMask >> 1, _data, _usedData);
     }
   }
-  
+
   void clear() {
     if (!isEmpty) {
       _init(_index.length, _hashMask);
     }
   }
-  
+
   void _init(int size, int hashMask, [List oldData, int oldUsed]) {
     _index = new Uint32List(size);
     _hashMask = hashMask;
     _data = new List(size >> 1);
     _usedData = 0;
     _deletedKeys = 0;
     if (oldData != null) {
       for (int i = 0; i < oldUsed; i += 1) {
         var key = oldData[i];
         if (!_HashBase._isDeleted(oldData, key)) {
@@ skipping 31 matching lines @@
       add(key);
     } else {
       final int insertionPoint = (firstDeleted >= 0) ? firstDeleted : i;
       assert(1 <= hashPattern && hashPattern < (1 << 32));
       assert((hashPattern & _usedData) == 0);
       _index[insertionPoint] = hashPattern | _usedData;
       _data[_usedData++] = key;
     }
     return true;
   }
-  
+
   // If key is absent, return _data (which is never a value).
   Object _getKeyOrData(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int d = hashPattern ^ pair;
         if (d < maxEntries && _equals(key, _data[d])) {
           return _data[d];  // Note: Must return the existing key.
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
-    return _data;    
+    return _data;
   }
 
   E lookup(Object key) {
     var k = _getKeyOrData(key);
     return identical(_data, k) ? null : k;
   }
-  
+
   bool contains(Object key) => !identical(_data, _getKeyOrData(key));
 
   bool remove(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int d = hashPattern ^ pair;
         if (d < maxEntries && _equals(key, _data[d])) {
           _index[i] = _HashBase._DELETED_PAIR;
           _HashBase._setDeletedAt(_data, d);
           ++_deletedKeys;
           return true;
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return false;
   }
-                                                
+
   Iterator<E> get iterator =>
       new _CompactIterator<E>(this, _data, _usedData, -1, 1);
 
   // Returns a set of the same type, although this
   // is not required by the spec. (For instance, always using an identity set
   // would be technically correct, albeit surprising.)
   Set<E> toSet() => new _CompactLinkedHashSet<E>()..addAll(this);
 }
-    
+
 class _CompactLinkedIdentityHashSet<E>
     extends _CompactLinkedHashSet<E> with _IdenticalAndIdentityHashCode {
   Set<E> toSet() => new _CompactLinkedIdentityHashSet<E>()..addAll(this);
 }
-    
+
 class _CompactLinkedCustomHashSet<E>
     extends _CompactLinkedHashSet<E> {
   final _equality;
   final _hasher;
   final _validKey;
 
   int _hashCode(e) => _hasher(e);
   bool _equals(e1, e2) => _equality(e1, e2);
-  
+
   bool contains(Object o) => _validKey(o) ? super.contains(o) : false;
   E lookup(Object o) => _validKey(o) ? super.lookup(o) : null;
   bool remove(Object o) => _validKey(o) ? super.remove(o) : false;
 
   _CompactLinkedCustomHashSet(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<E>().test;
 
   Set<E> toSet() =>
       new _CompactLinkedCustomHashSet<E>(_equality, _hasher, _validKey)
           ..addAll(this);
 }