mariadb/locktree/keyrange.h

/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
#ident "$Id$"
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  TokuDB, Tokutek Fractal Tree Indexing Library.
  Copyright (C) 2007-2013 Tokutek, Inc.

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  The technology is licensed by the Massachusetts Institute of
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  United States of America Serial No. 11/760379 and to the patents
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  This software is covered by US Patent No. 8,185,551.
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#ident "Copyright (c) 2007-2013 Tokutek Inc.  All rights reserved."
#ident "The technology is licensed by the Massachusetts Institute of Technology, Rutgers State University of New Jersey, and the Research Foundation of State University of New York at Stony Brook under United States of America Serial No. 11/760379 and to the patents and/or patent applications resulting from it."

#ifndef KEYRANGE_H
#define KEYRANGE_H

#include <ft/comparator.h>

namespace toku {

// A keyrange has a left and right key as endpoints.
//
// When a keyrange is created it owns no memory, but when it copies
// or extends another keyrange, it copies memory as necessary. This
// means it is cheap in the common case.

class keyrange {
public:

    // effect: constructor that borrows left and right key pointers.
    //         no memory is allocated or copied.
    void create(const DBT *left_key, const DBT *right_key);

    // effect: constructor that allocates and copies another keyrange's points.
    void create_copy(const keyrange &range);

    // effect: destroys the keyrange, freeing any allocated memory
    void destroy(void);

    // effect: extends the keyrange by choosing the leftmost and rightmost
    //         endpoints from this range and the given range.
    //         replaced keys in this range are freed, new keys are copied.
    void extend(comparator *cmp, const keyrange &range);

    // returns: the amount of memory this keyrange takes. does not account
    //          for point optimizations or malloc overhead.
    uint64_t get_memory_size(void) const;

    // returns: pointer to the left key of this range
    const DBT *get_left_key(void) const;

    // returns: pointer to the right key of this range
    const DBT *get_right_key(void) const;

    // two ranges are either equal, lt, gt, or overlapping
    enum comparison {
        EQUALS,
        LESS_THAN,
        GREATER_THAN,
        OVERLAPS
    };

    // effect: compares this range to the given range
    // returns: LESS_THAN    if given range is strictly to the left
    //          GREATER_THAN if given range is strictly to the right
    //          EQUALS       if given range has the same left and right endpoints
    //          OVERLAPS     if at least one of the given range's endpoints falls
    //                       between this range's endpoints
    comparison compare(comparator *cmp, const keyrange &range) const;

    // returns: true if the range and the given range are equal or overlapping
    bool overlaps(comparator *cmp, const keyrange &range) const;

    // returns: a keyrange representing -inf, +inf
    static keyrange get_infinite_range(void);

private:
    // some keys should be copied, some keys should not be.
    //
    // to support both, we use two DBTs for copies and two pointers
    // for temporaries. the access rule is:
    // - if a pointer is non-null, then it reprsents the key.
    // - otherwise the pointer is null, and the key is in the copy.
    DBT m_left_key_copy;
    DBT m_right_key_copy;
    const DBT *m_left_key;
    const DBT *m_right_key;

    // if this range is a point range, then m_left_key == m_right_key
    // and the actual data is stored exactly once in m_left_key_copy.
    bool m_point_range;

    // effect: initializes a keyrange to be empty
    void init_empty(void);

    // effect: copies the given key once into the left key copy
    //         and sets the right key copy to share the left.
    // rationale: optimization for point ranges to only do one malloc
    void set_both_keys(const DBT *key);

    // effect: destroys the current left key. sets and copies the new one.
    void replace_left_key(const DBT *key);

    // effect: destroys the current right key. sets and copies the new one.
    void replace_right_key(const DBT *key);
};

} /* namespace toku */

#endif /* KEYRANGE_H */