/****************************************************************************
*
* Copyright (C) 2013 PX4 Development Team. All rights reserved.
* Author: Lorenz Meier <lm@inf.ethz.ch>
*
* 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.h
*
* A simple ringbuffer template.
*/
#pragma once
template<typename T>
class RingBuffer {
public:
RingBuffer(unsigned size);
virtual ~RingBuffer();
/**
* Put an item into the buffer.
*
* @param val Item to put
* @return true if the item was put, false if the buffer is full
*/
bool put(T &val);
/**
* Put an item into the buffer if there is space.
*
* @param val Item to put
* @return true if the item was put, false if the buffer is full
*/
bool put(const T &val);
/**
* Force an item into the buffer, discarding an older item if there is not space.
*
* @param val Item to put
* @return true if an item was discarded to make space
*/
bool force(T &val);
/**
* Force an item into the buffer, discarding an older item if there is not space.
*
* @param val Item to put
* @return true if an item was discarded to make space
*/
bool force(const T &val);
/**
* Get an item from the buffer.
*
* @param val Item that was gotten
* @return true if an item was got, false if the buffer was empty.
*/
bool get(T &val);
/**
* Get an item from the buffer (scalars only).
*
* @return The value that was fetched. If the buffer is empty,
* returns zero.
*/
T get(void);
/*
* Get the number of slots free in the buffer.
*
* @return The number of items that can be put into the buffer before
* it becomes full.
*/
unsigned space(void);
/*
* Get the number of items in the buffer.
*
* @return The number of items that can be got from the buffer before
* it becomes empty.
*/
unsigned count(void);
/*
* Returns true if the buffer is empty.
*/
bool empty();
/*
* Returns true if the buffer is full.
*/
bool full();
/*
* Returns the capacity of the buffer, or zero if the buffer could
* not be allocated.
*/
unsigned size();
/*
* Empties the buffer.
*/
void flush();
/*
* resize the buffer. This is unsafe to be called while
* a producer or consuming is running. Caller is responsible
* for any locking needed
*
* @param new_size new size for buffer
* @return true if the resize succeeds, false if
* not (allocation error)
*/
bool resize(unsigned new_size);
/*
* printf() some info on the buffer
*/
void print_info(const char *name);
private:
T *_buf;
unsigned _size;
volatile unsigned _head; /**< insertion point */
volatile unsigned _tail; /**< removal point */
unsigned _next(unsigned index);
};
template <typename T>
RingBuffer<T>::RingBuffer(unsigned with_size) :
_buf(new T[with_size + 1]),
_size(with_size),
_head(with_size),
_tail(with_size)
{}
template <typename T>
RingBuffer<T>::~RingBuffer()
{
if (_buf != nullptr)
delete[] _buf;
}
template <typename T>
bool RingBuffer<T>::empty()
{
return _tail == _head;
}
template <typename T>
bool RingBuffer<T>::full()
{
return _next(_head) == _tail;
}
template <typename T>
unsigned RingBuffer<T>::size()
{
return (_buf != nullptr) ? _size : 0;
}
template <typename T>
void RingBuffer<T>::flush()
{
T junk;
while (!empty())
get(junk);
}
template <typename T>
unsigned RingBuffer<T>::_next(unsigned index)
{
return (0 == index) ? _size : (index - 1);
}
template <typename T>
bool RingBuffer<T>::put(T &val)
{
unsigned next = _next(_head);
if (next != _tail) {
_buf[_head] = val;
_head = next;
return true;
} else {
return false;
}
}
template <typename T>
bool RingBuffer<T>::put(const T &val)
{
unsigned next = _next(_head);
if (next != _tail) {
_buf[_head] = val;
_head = next;
return true;
} else {
return false;
}
}
template <typename T>
bool RingBuffer<T>::force(T &val)
{
bool overwrote = false;
for (;;) {
if (put(val))
break;
T junk;
get(junk);
overwrote = true;
}
return overwrote;
}
template <typename T>
bool RingBuffer<T>::force(const T &val)
{
bool overwrote = false;
for (;;) {
if (put(val))
break;
T junk;
get(junk);
overwrote = true;
}
return overwrote;
}
template <typename T>
bool RingBuffer<T>::get(T &val)
{
if (_tail != _head) {
unsigned candidate;
unsigned next;
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 */
val = _buf[candidate];
/* if the tail pointer didn't change, we got our item */
} while (!__sync_bool_compare_and_swap(&_tail, candidate, next));
return true;
} else {
return false;
}
}
template <typename T>
T RingBuffer<T>::get(void)
{
T val;
return get(val) ? val : 0;
}
template <typename T>
unsigned RingBuffer<T>::space(void)
{
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) ? (_size - (tail - head)) : (head - tail - 1);
}
template <typename T>
unsigned RingBuffer<T>::count(void)
{
/*
* Note that due to the conservative nature of space(), this may
* over-estimate the number of items in the buffer.
*/
return _size - space();
}
template <typename T>
bool RingBuffer<T>::resize(unsigned new_size)
{
T *old_buffer;
T *new_buffer = new T[new_size + 1];
if (new_buffer == nullptr) {
return false;
}
old_buffer = _buf;
_buf = new_buffer;
_size = new_size;
_head = new_size;
_tail = new_size;
delete[] old_buffer;
return true;
}
template <typename T>
void RingBuffer<T>::print_info(const char *name)
{
printf("%s %u (%u/%u @ %p)\n",
name, _size, _head, _tail, _buf);
}
