mariadb/storage/tokudb/tokudb_buffer.h

/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
#ident "$Id$"
/*======
This file is part of TokuDB


Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved.

    TokuDBis is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 2,
    as published by the Free Software Foundation.

    TokuDB is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with TokuDB.  If not, see <http://www.gnu.org/licenses/>.

======= */

#ident "Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved."

#ifndef _TOKUDB_BUFFER_H
#define _TOKUDB_BUFFER_H

#include "hatoku_defines.h"
#include "tokudb_debug.h"
#include "tokudb_thread.h"
#include "tokudb_vlq.h"

namespace tokudb {

// A Buffer manages a contiguous chunk of memory and supports appending new
// data to the end of the buffer, and consuming chunks from the beginning of
// the buffer.  The buffer will reallocate memory when appending new data to
// a full buffer. 

class buffer {
public:
    inline buffer(
        void* the_data,
        size_t s,
        size_t l) :
        m_data(the_data),
        m_size(s),
        m_limit(l),
        m_is_static(true) {
    }
    inline buffer() :
        m_data(NULL),
        m_size(0),
        m_limit(0),
        m_is_static(false) {
    }
    virtual ~buffer() {
        if (!m_is_static)
            free(m_data);
    }

    // Return a pointer to the end of the buffer suitable for appending a
    // fixed number of bytes.
    void* append_ptr(size_t s) {
        maybe_realloc(s);
        void* p = (char*)m_data + m_size;
        m_size += s;
        return p;
    }

    // Append bytes to the buffer
    void append(void* p, size_t s) {
        memcpy(append_ptr(s), p, s);
    }

    // Append an unsigned int to the buffer.
    // Returns the number of bytes used to encode the number.
    // Returns 0 if the number could not be encoded.
    template<class T> size_t append_ui(T n) {
        maybe_realloc(10); // 10 bytes is big enough for up to 64 bit number
        size_t s = tokudb::vlq_encode_ui<T>(n, (char *) m_data + m_size, 10);
        m_size += s;
        return s;
    }

    // Return a pointer to the next location in the buffer where bytes are
    // consumed from.
    void* consume_ptr(size_t s) {
        if (m_size + s > m_limit)
            return NULL;
        void* p = (char*)m_data + m_size;
        m_size += s;
        return p;
    }

    // Consume bytes from the buffer.
    void consume(void* p, size_t s) {
        memcpy(p, consume_ptr(s), s);
    }

    // Consume an unsigned int from the buffer.
    // Returns 0 if the unsigned int could not be decoded, probably because
    // the buffer is too short.
    // Otherwise return the number of bytes consumed, and stuffs the decoded
    // number in *p.
    template<class T> size_t consume_ui(T* p) {
        size_t s = tokudb::vlq_decode_ui<T>(
            p,
            (char*)m_data + m_size,
            m_limit - m_size);
        m_size += s;
        return s;
    }

    // Write p_length bytes at an offset in the buffer
    void write(void* p, size_t p_length, size_t offset) {
        assert_always(offset + p_length <= m_size);
        memcpy((char*)m_data + offset, p, p_length);
    }

    // Read p_length bytes at an offset in the buffer
    void read(void* p, size_t p_length, size_t offset) {
        assert_always(offset + p_length <= m_size);
        memcpy(p, (char*)m_data + offset, p_length);
    }

    // Replace a field in the buffer with new data.  If the new data size is
    // different, then readjust the size of the buffer and move things around.
    void replace(size_t offset, size_t old_s, void* new_p, size_t new_s) {
        assert_always(offset + old_s <= m_size);
        if (new_s > old_s)
            maybe_realloc(new_s - old_s);
        char* data_offset = (char*)m_data + offset;
        if (new_s != old_s) {
            size_t n = m_size - (offset + old_s);
            assert_always(offset + new_s + n <= m_limit);
            assert_always(offset + old_s + n <= m_limit);
            memmove(data_offset + new_s, data_offset + old_s, n);
            if (new_s > old_s)
                m_size += new_s - old_s;
            else
                m_size -= old_s - new_s;
            assert_always(m_size <= m_limit);
        }
        memcpy(data_offset, new_p, new_s);
    }

    // Return a pointer to the data in the buffer
    void* data() const {
        return m_data;
    }

    // Return the size of the data in the buffer
    size_t size() const {
        return m_size;
    }

    // Return the size of the underlying memory in the buffer
    size_t limit() const {
        return m_limit;
    }

private:
    // Maybe reallocate the buffer when it becomes full by doubling its size.
    void maybe_realloc(size_t s) {
        if (m_size + s > m_limit) {
            size_t new_limit = m_limit * 2;
            if (new_limit < m_size + s)
                new_limit = m_size + s;
            assert_always(!m_is_static);
            void *new_data = realloc(m_data, new_limit);
            assert_always(new_data != NULL);
            m_data = new_data;
            m_limit = new_limit;
        }
    }   
private:
    void* m_data;
    size_t m_size;
    size_t m_limit;
    bool m_is_static;
};

};

#endif