ringbuffer.cpp

Go to the documentation of this file.

/****************************************************************************
 *
 *   Copyright (C) 2013-2015 PX4 Development Team. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/**
 * @file ringbuffer.cpp
 *
 * A flexible ringbuffer class.
 */

#include "ringbuffer.h"
#include <string.h>

namespace ringbuffer
{

RingBuffer::RingBuffer(unsigned num_items, size_t item_size) :
    _num_items(num_items),
    _item_size(item_size),
    _buf(new char[(_num_items + 1) * item_size]),
    _head(_num_items),
    _tail(_num_items)
{}

RingBuffer::~RingBuffer()
{
    delete[] _buf;
}

unsigned
RingBuffer::_next(unsigned index)
{
    return (0 == index) ? _num_items : (index - 1);
}

bool
RingBuffer::empty()
{
    return _tail == _head;
}

bool
RingBuffer::full()
{
    return _next(_head) == _tail;
}

unsigned
RingBuffer::size()
{
    return (_buf != nullptr) ? _num_items : 0;
}

void
RingBuffer::flush()
{
    while (!empty()) {
        get(nullptr);
    }
}

bool
RingBuffer::put(const void *val, size_t val_size)
{
    unsigned next = _next(_head);

    if (next != _tail) {
        if ((val_size == 0) || (val_size > _item_size)) {
            val_size = _item_size;
        }

        memcpy(&_buf[_head * _item_size], val, val_size);
        _head = next;
        return true;

    } else {
        return false;
    }
}

bool
RingBuffer::put(int8_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(uint8_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(int16_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(uint16_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(int32_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(uint32_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(int64_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(uint64_t val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(float val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::put(double val)
{
    return put(&val, sizeof(val));
}

bool
RingBuffer::force(const void *val, size_t val_size)
{
    bool overwrote = false;

    for (;;) {
        if (put(val, val_size)) {
            break;
        }

        get(nullptr);
        overwrote = true;
    }

    return overwrote;
}

bool
RingBuffer::force(int8_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(uint8_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(int16_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(uint16_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(int32_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(uint32_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(int64_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(uint64_t val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(float val)
{
    return force(&val, sizeof(val));
}

bool
RingBuffer::force(double val)
{
    return force(&val, sizeof(val));
}

// FIXME - clang crashes on this get() call
#ifdef __PX4_QURT
#define __PX4_SBCAP my_sync_bool_compare_and_swap
static inline bool my_sync_bool_compare_and_swap(volatile unsigned *a, unsigned b, unsigned c)
{
    if (*a == b) {
        *a = c;
        return true;
    }

    return false;
}

#else
#define __PX4_SBCAP __sync_bool_compare_and_swap
#endif
bool
RingBuffer::get(void *val, size_t val_size)
{
    if (_tail != _head) {
        unsigned candidate;
        unsigned next;

        if ((val_size == 0) || (val_size > _item_size)) {
            val_size = _item_size;
        }

        do {
            /* decide which element we think we're going to read */
            candidate = _tail;

            /* and what the corresponding next index will be */
            next = _next(candidate);

            /* go ahead and read from this index */
            if (val != nullptr) {
                memcpy(val, &_buf[candidate * _item_size], val_size);
            }

            /* if the tail pointer didn't change, we got our item */
        } while (!__PX4_SBCAP(&_tail, candidate, next));

        return true;

    } else {
        return false;
    }
}

bool
RingBuffer::get(int8_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(uint8_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(int16_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(uint16_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(int32_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(uint32_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(int64_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(uint64_t &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(float &val)
{
    return get(&val, sizeof(val));
}

bool
RingBuffer::get(double &val)
{
    return get(&val, sizeof(val));
}

unsigned
RingBuffer::space()
{
    unsigned tail, head;

    /*
     * Make a copy of the head/tail pointers in a fashion that
     * may err on the side of under-estimating the free space
     * in the buffer in the case that the buffer is being updated
     * asynchronously with our check.
     * If the head pointer changes (reducing space) while copying,
     * re-try the copy.
     */
    do {
        head = _head;
        tail = _tail;
    } while (head != _head);

    return (tail >= head) ? (_num_items - (tail - head)) : (head - tail - 1);
}

unsigned
RingBuffer::count()
{
    /*
     * Note that due to the conservative nature of space(), this may
     * over-estimate the number of items in the buffer.
     */
    return _num_items - space();
}

bool
RingBuffer::resize(unsigned new_size)
{
    char *old_buffer;
    char *new_buffer = new char [(new_size + 1) * _item_size];

    if (new_buffer == nullptr) {
        return false;
    }

    old_buffer = _buf;
    _buf = new_buffer;
    _num_items = new_size;
    _head = new_size;
    _tail = new_size;
    delete[] old_buffer;
    return true;
}

void
RingBuffer::print_info(const char *name)
{
    printf("%s  %u/%lu (%u/%u @ %p)\n",
           name,
           _num_items,
           (unsigned long)_num_items * _item_size,
           _head,
           _tail,
           _buf);
}

} // namespace ringbuffer