xref: /external/tensorflow/tensorflow/core/lib/io/table.h

/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef TENSORFLOW_LIB_IO_TABLE_H_
#define TENSORFLOW_LIB_IO_TABLE_H_

#include <stdint.h>
#include "tensorflow/core/lib/io/iterator.h"

namespace tensorflow {
class RandomAccessFile;

namespace table {

class Block;
class BlockHandle;
class Footer;
struct Options;

// A Table is a sorted map from strings to strings.  Tables are
// immutable and persistent.  A Table may be safely accessed from
// multiple threads without external synchronization.
class Table {
 public:
  // Attempt to open the table that is stored in bytes [0..file_size)
  // of "file", and read the metadata entries necessary to allow
  // retrieving data from the table.
  //
  // If successful, returns ok and sets "*table" to the newly opened
  // table.  The client should delete "*table" when no longer needed.
  // If there was an error while initializing the table, sets "*table"
  // to NULL and returns a non-ok status.  Does not take ownership of
  // "*file", but the client must ensure that "file" remains live
  // for the duration of the returned table's lifetime.
  static Status Open(const Options& options, RandomAccessFile* file,
                     uint64 file_size, Table** table);

  ~Table();

  // Returns a new iterator over the table contents.
  // The result of NewIterator() is initially invalid (caller must
  // call one of the Seek methods on the iterator before using it).
  Iterator* NewIterator() const;

  // Given a key, return an approximate byte offset in the file where
  // the data for that key begins (or would begin if the key were
  // present in the file).  The returned value is in terms of file
  // bytes, and so includes effects like compression of the underlying data.
  // E.g., the approximate offset of the last key in the table will
  // be close to the file length.
  uint64 ApproximateOffsetOf(const StringPiece& key) const;

 private:
  struct Rep;
  Rep* rep_;

  explicit Table(Rep* rep) { rep_ = rep; }
  static Iterator* BlockReader(void*, const StringPiece&);

  // Calls (*handle_result)(arg, ...) with the entry found after a call
  // to Seek(key).  May not make such a call if filter policy says
  // that key is not present.
  Status InternalGet(const StringPiece& key, void* arg,
                     void (*handle_result)(void* arg, const StringPiece& k,
                                           const StringPiece& v));

  // No copying allowed
  Table(const Table&);
  void operator=(const Table&);
};

}  // namespace table
}  // namespace tensorflow

#endif  // TENSORFLOW_LIB_IO_TABLE_H_