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+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#ifndef STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
+#define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
+
+namespace leveldb {
+
+// A internal wrapper class with an interface similar to Iterator that
+// caches the valid() and key() results for an underlying iterator.
+// This can help avoid virtual function calls and also gives better
+// cache locality.
+class IteratorWrapper {
+ public:
+ IteratorWrapper(): iter_(NULL), valid_(false) { }
+ explicit IteratorWrapper(Iterator* iter): iter_(NULL) {
+ Set(iter);
+ }
+ ~IteratorWrapper() { delete iter_; }
+ Iterator* iter() const { return iter_; }
+
+ // Takes ownership of "iter" and will delete it when destroyed, or
+ // when Set() is invoked again.
+ void Set(Iterator* iter) {
+ delete iter_;
+ iter_ = iter;
+ if (iter_ == NULL) {
+ valid_ = false;
+ } else {
+ Update();
+ }
+ }
+
+
+ // Iterator interface methods
+ bool Valid() const { return valid_; }
+ Slice key() const { assert(Valid()); return key_; }
+ Slice value() const { assert(Valid()); return iter_->value(); }
+ // Methods below require iter() != NULL
+ Status status() const { assert(iter_); return iter_->status(); }
+ void Next() { assert(iter_); iter_->Next(); Update(); }
+ void Prev() { assert(iter_); iter_->Prev(); Update(); }
+ void Seek(const Slice& k) { assert(iter_); iter_->Seek(k); Update(); }
+ void SeekToFirst() { assert(iter_); iter_->SeekToFirst(); Update(); }
+ void SeekToLast() { assert(iter_); iter_->SeekToLast(); Update(); }
+
+ private:
+ void Update() {
+ valid_ = iter_->Valid();
+ if (valid_) {
+ key_ = iter_->key();
+ }
+ }
+
+ Iterator* iter_;
+ bool valid_;
+ Slice key_;
+};
+
+} // namespace leveldb
+
+#endif // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_