您最多选择25个主题
主题必须以字母或数字开头，可以包含连字符 (-)，并且长度不得超过35个字符
112 行
3.9 KiB
112 行
3.9 KiB
// 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.
|
|
//
|
|
// An iterator yields a sequence of key/value pairs from a source.
|
|
// The following class defines the interface. Multiple implementations
|
|
// are provided by this library. In particular, iterators are provided
|
|
// to access the contents of a Table or a DB.
|
|
//
|
|
// Multiple threads can invoke const methods on an Iterator without
|
|
// external synchronization, but if any of the threads may call a
|
|
// non-const method, all threads accessing the same Iterator must use
|
|
// external synchronization.
|
|
|
|
#ifndef STORAGE_LEVELDB_INCLUDE_ITERATOR_H_
|
|
#define STORAGE_LEVELDB_INCLUDE_ITERATOR_H_
|
|
|
|
#include "leveldb/export.h"
|
|
#include "leveldb/slice.h"
|
|
#include "leveldb/status.h"
|
|
|
|
namespace leveldb {
|
|
|
|
class LEVELDB_EXPORT Iterator {
|
|
public:
|
|
Iterator();
|
|
|
|
Iterator(const Iterator&) = delete;
|
|
Iterator& operator=(const Iterator&) = delete;
|
|
|
|
virtual ~Iterator();
|
|
|
|
// An iterator is either positioned at a key/value pair, or
|
|
// not valid. This method returns true iff the iterator is valid.
|
|
virtual bool Valid() const = 0;
|
|
|
|
// Position at the first key in the source. The iterator is Valid()
|
|
// after this call iff the source is not empty.
|
|
virtual void SeekToFirst() = 0;
|
|
|
|
// Position at the last key in the source. The iterator is
|
|
// Valid() after this call iff the source is not empty.
|
|
virtual void SeekToLast() = 0;
|
|
|
|
// Position at the first key in the source that is at or past target.
|
|
// The iterator is Valid() after this call iff the source contains
|
|
// an entry that comes at or past target.
|
|
virtual void Seek(const Slice& target) = 0;
|
|
|
|
// Moves to the next entry in the source. After this call, Valid() is
|
|
// true iff the iterator was not positioned at the last entry in the source.
|
|
// REQUIRES: Valid()
|
|
virtual void Next() = 0;
|
|
|
|
// Moves to the previous entry in the source. After this call, Valid() is
|
|
// true iff the iterator was not positioned at the first entry in source.
|
|
// REQUIRES: Valid()
|
|
virtual void Prev() = 0;
|
|
|
|
// Return the key for the current entry. The underlying storage for
|
|
// the returned slice is valid only until the next modification of
|
|
// the iterator.
|
|
// REQUIRES: Valid()
|
|
virtual Slice key() const = 0;
|
|
|
|
// Return the value for the current entry. The underlying storage for
|
|
// the returned slice is valid only until the next modification of
|
|
// the iterator.
|
|
// REQUIRES: Valid()
|
|
virtual Slice value() const = 0;
|
|
|
|
// If an error has occurred, return it. Else return an ok status.
|
|
virtual Status status() const = 0;
|
|
|
|
// Clients are allowed to register function/arg1/arg2 triples that
|
|
// will be invoked when this iterator is destroyed.
|
|
//
|
|
// Note that unlike all of the preceding methods, this method is
|
|
// not abstract and therefore clients should not override it.
|
|
using CleanupFunction = void (*)(void* arg1, void* arg2);
|
|
void RegisterCleanup(CleanupFunction function, void* arg1, void* arg2);
|
|
|
|
private:
|
|
// Cleanup functions are stored in a single-linked list.
|
|
// The list's head node is inlined in the iterator.
|
|
struct CleanupNode {
|
|
// True if the node is not used. Only head nodes might be unused.
|
|
bool IsEmpty() const { return function == nullptr; }
|
|
// Invokes the cleanup function.
|
|
void Run() {
|
|
assert(function != nullptr);
|
|
(*function)(arg1, arg2);
|
|
}
|
|
|
|
// The head node is used if the function pointer is not null.
|
|
CleanupFunction function;
|
|
void* arg1;
|
|
void* arg2;
|
|
CleanupNode* next;
|
|
};
|
|
CleanupNode cleanup_head_;
|
|
};
|
|
|
|
// Return an empty iterator (yields nothing).
|
|
LEVELDB_EXPORT Iterator* NewEmptyIterator();
|
|
|
|
// Return an empty iterator with the specified status.
|
|
LEVELDB_EXPORT Iterator* NewErrorIterator(const Status& status);
|
|
|
|
} // namespace leveldb
|
|
|
|
#endif // STORAGE_LEVELDB_INCLUDE_ITERATOR_H_
|