annotate base/RingBuffer.h @ 490:c3fb8258e34d

* Make it possible to import an entire session from an RDF document.
  However, at the moment the timings of events appear to be constrained
  by how far the audio decoder has got through its audio file at the
  time the event is queried -- need to investigate.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

/*
   This is a modified version of a source file from the 
   Rosegarden MIDI and audio sequencer and notation editor.
   This file copyright 2000-2006 Chris Cannam.
*/

#ifndef _RINGBUFFER_H_
#define _RINGBUFFER_H_

#include <sys/types.h>

#include "system/System.h"
#include "Scavenger.h"

#include <cstring> // memcpy, memset &c

//#define DEBUG_RINGBUFFER 1

#ifdef DEBUG_RINGBUFFER
#include <iostream>
#endif

/**
 * RingBuffer implements a lock-free ring buffer for one writer and N
 * readers, that is to be used to store a sample type T.
 *
 * For efficiency, RingBuffer frequently initialises samples by
 * writing zeroes into their memory space, so T should normally be a
 * simple type that can safely be set to zero using memset.
 */

template <typename T, int N = 1>
class RingBuffer
{
public:
    /**
     * Create a ring buffer with room to write n samples.
     *
     * Note that the internal storage size will actually be n+1
     * samples, as one element is unavailable for administrative
     * reasons.  Since the ring buffer performs best if its size is a
     * power of two, this means n should ideally be some power of two
     * minus one.
     */
    RingBuffer(size_t n);

    virtual ~RingBuffer();

    /**
     * Return the total capacity of the ring buffer in samples.
     * (This is the argument n passed to the constructor.)
     */
    size_t getSize() const;

    /**
     * Resize the ring buffer.  This also empties it.  Actually swaps
     * in a new, larger buffer; the old buffer is scavenged after a
     * seemly delay.  Should be called from the write thread.
     */
    void resize(size_t newSize);

    /**
     * Lock the ring buffer into physical memory.  Returns true
     * for success.
     */
    bool mlock();

    /**
     * Reset read and write pointers, thus emptying the buffer.
     * Should be called from the write thread.
     */
    void reset();

    /**
     * Return the amount of data available for reading by reader R, in
     * samples.
     */
    size_t getReadSpace(int R = 0) const;

    /**
     * Return the amount of space available for writing, in samples.
     */
    size_t getWriteSpace() const;

    /**
     * Read n samples from the buffer, for reader R.  If fewer than n
     * are available, the remainder will be zeroed out.  Returns the
     * number of samples actually read.
     */
    size_t read(T *destination, size_t n, int R = 0);

    /**
     * Read n samples from the buffer, for reader R, adding them to
     * the destination.  If fewer than n are available, the remainder
     * will be left alone.  Returns the number of samples actually
     * read.
     */
    size_t readAdding(T *destination, size_t n, int R = 0);

    /**
     * Read one sample from the buffer, for reader R.  If no sample is
     * available, this will silently return zero.  Calling this
     * repeatedly is obviously slower than calling read once, but it
     * may be good enough if you don't want to allocate a buffer to
     * read into.
     */
    T readOne(int R = 0);

    /**
     * Read n samples from the buffer, if available, for reader R,
     * without advancing the read pointer -- i.e. a subsequent read()
     * or skip() will be necessary to empty the buffer.  If fewer than
     * n are available, the remainder will be zeroed out.  Returns the
     * number of samples actually read.
     */
    size_t peek(T *destination, size_t n, int R = 0) const;

    /**
     * Read one sample from the buffer, if available, without
     * advancing the read pointer -- i.e. a subsequent read() or
     * skip() will be necessary to empty the buffer.  Returns zero if
     * no sample was available.
     */
    T peekOne(int R = 0) const;

    /**
     * Pretend to read n samples from the buffer, for reader R,
     * without actually returning them (i.e. discard the next n
     * samples).  Returns the number of samples actually available for
     * discarding.
     */
    size_t skip(size_t n, int R = 0);

    /**
     * Write n samples to the buffer.  If insufficient space is
     * available, not all samples may actually be written.  Returns
     * the number of samples actually written.
     */
    size_t write(const T *source, size_t n);

    /**
     * Write n zero-value samples to the buffer.  If insufficient
     * space is available, not all zeros may actually be written.
     * Returns the number of zeroes actually written.
     */
    size_t zero(size_t n);

protected:
    T               *m_buffer;
    volatile size_t  m_writer;
    volatile size_t  m_readers[N];
    size_t           m_size;
    bool             m_mlocked;

    static Scavenger<ScavengerArrayWrapper<T> > m_scavenger;

private:
    RingBuffer(const RingBuffer &); // not provided
    RingBuffer &operator=(const RingBuffer &); // not provided
};

template <typename T, int N>
Scavenger<ScavengerArrayWrapper<T> > RingBuffer<T, N>::m_scavenger;

template <typename T, int N>
RingBuffer<T, N>::RingBuffer(size_t n) :
    m_buffer(new T[n + 1]),
    m_writer(0),
    m_size(n + 1),
    m_mlocked(false)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::RingBuffer(" << n << ")" << std::endl;
#endif

    for (int i = 0; i < N; ++i) m_readers[i] = 0;

    m_scavenger.scavenge();
}

template <typename T, int N>
RingBuffer<T, N>::~RingBuffer()
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::~RingBuffer" << std::endl;
#endif

    if (m_mlocked) {
	MUNLOCK((void *)m_buffer, m_size * sizeof(T));
    }
    delete[] m_buffer;

    m_scavenger.scavenge();
}

template <typename T, int N>
size_t
RingBuffer<T, N>::getSize() const
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::getSize(): " << m_size-1 << std::endl;
#endif

    return m_size - 1;
}

template <typename T, int N>
void
RingBuffer<T, N>::resize(size_t newSize)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::resize(" << newSize << ")" << std::endl;
#endif

    m_scavenger.scavenge();

    if (m_mlocked) {
	MUNLOCK((void *)m_buffer, m_size * sizeof(T));
    }

    m_scavenger.claim(new ScavengerArrayWrapper<T>(m_buffer));

    reset();
    m_buffer = new T[newSize + 1];
    m_size = newSize + 1;

    if (m_mlocked) {
	if (MLOCK((void *)m_buffer, m_size * sizeof(T))) {
	    m_mlocked = false;
	}
    }
}

template <typename T, int N>
bool
RingBuffer<T, N>::mlock()
{
    if (MLOCK((void *)m_buffer, m_size * sizeof(T))) return false;
    m_mlocked = true;
    return true;
}

template <typename T, int N>
void
RingBuffer<T, N>::reset()
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::reset" << std::endl;
#endif

    m_writer = 0;
    for (int i = 0; i < N; ++i) m_readers[i] = 0;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::getReadSpace(int R) const
{
    size_t writer = m_writer;
    size_t reader = m_readers[R];
    size_t space = 0;

    if (writer > reader) space = writer - reader;
    else space = ((writer + m_size) - reader) % m_size;

#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::getReadSpace(" << R << "): " << space << std::endl;
#endif

    return space;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::getWriteSpace() const
{
    size_t space = 0;
    for (int i = 0; i < N; ++i) {
	size_t here = (m_readers[i] + m_size - m_writer - 1) % m_size;
	if (i == 0 || here < space) space = here;
    }

#ifdef DEBUG_RINGBUFFER
    size_t rs(getReadSpace()), rp(m_readers[0]);

    std::cerr << "RingBuffer: write space " << space << ", read space "
	      << rs << ", total " << (space + rs) << ", m_size " << m_size << std::endl;
    std::cerr << "RingBuffer: reader " << rp << ", writer " << m_writer << std::endl;
#endif

#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::getWriteSpace(): " << space << std::endl;
#endif

    return space;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::read(T *destination, size_t n, int R)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::read(dest, " << n << ", " << R << ")" << std::endl;
#endif

    size_t available = getReadSpace(R);
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only " << available << " samples available"
		  << std::endl;
#endif
	memset(destination + available, 0, (n - available) * sizeof(T));
	n = available;
    }
    if (n == 0) return n;

    size_t here = m_size - m_readers[R];
    if (here >= n) {
	memcpy(destination, m_buffer + m_readers[R], n * sizeof(T));
    } else {
	memcpy(destination, m_buffer + m_readers[R], here * sizeof(T));
	memcpy(destination + here, m_buffer, (n - here) * sizeof(T));
    }

    m_readers[R] = (m_readers[R] + n) % m_size;

#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::read: read " << n << ", reader now " << m_readers[R] << std::endl;
#endif

    return n;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::readAdding(T *destination, size_t n, int R)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::readAdding(dest, " << n << ", " << R << ")" << std::endl;
#endif

    size_t available = getReadSpace(R);
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only " << available << " samples available"
		  << std::endl;
#endif
	n = available;
    }
    if (n == 0) return n;

    size_t here = m_size - m_readers[R];

    if (here >= n) {
	for (size_t i = 0; i < n; ++i) {
	    destination[i] += (m_buffer + m_readers[R])[i];
	}
    } else {
	for (size_t i = 0; i < here; ++i) {
	    destination[i] += (m_buffer + m_readers[R])[i];
	}
	for (size_t i = 0; i < (n - here); ++i) {
	    destination[i + here] += m_buffer[i];
	}
    }

    m_readers[R] = (m_readers[R] + n) % m_size;
    return n;
}

template <typename T, int N>
T
RingBuffer<T, N>::readOne(int R)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::readOne(" << R << ")" << std::endl;
#endif

    if (m_writer == m_readers[R]) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: No sample available"
		  << std::endl;
#endif
	T t;
	memset(&t, 0, sizeof(T));
	return t;
    }
    T value = m_buffer[m_readers[R]];
    if (++m_readers[R] == m_size) m_readers[R] = 0;
    return value;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::peek(T *destination, size_t n, int R) const
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::peek(dest, " << n << ", " << R << ")" << std::endl;
#endif

    size_t available = getReadSpace(R);
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only " << available << " samples available"
		  << std::endl;
#endif
	memset(destination + available, 0, (n - available) * sizeof(T));
	n = available;
    }
    if (n == 0) return n;

    size_t here = m_size - m_readers[R];
    if (here >= n) {
	memcpy(destination, m_buffer + m_readers[R], n * sizeof(T));
    } else {
	memcpy(destination, m_buffer + m_readers[R], here * sizeof(T));
	memcpy(destination + here, m_buffer, (n - here) * sizeof(T));
    }

#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::peek: read " << n << std::endl;
#endif

    return n;
}

template <typename T, int N>
T
RingBuffer<T, N>::peekOne(int R) const
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::peek(" << R << ")" << std::endl;
#endif

    if (m_writer == m_readers[R]) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: No sample available"
		  << std::endl;
#endif
	T t;
	memset(&t, 0, sizeof(T));
	return t;
    }
    T value = m_buffer[m_readers[R]];
    return value;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::skip(size_t n, int R)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::skip(" << n << ", " << R << ")" << std::endl;
#endif

    size_t available = getReadSpace(R);
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only " << available << " samples available"
		  << std::endl;
#endif
	n = available;
    }
    if (n == 0) return n;
    m_readers[R] = (m_readers[R] + n) % m_size;
    return n;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::write(const T *source, size_t n)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::write(" << n << ")" << std::endl;
#endif

    size_t available = getWriteSpace();
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only room for " << available << " samples"
		  << std::endl;
#endif
	n = available;
    }
    if (n == 0) return n;

    size_t here = m_size - m_writer;
    if (here >= n) {
	memcpy(m_buffer + m_writer, source, n * sizeof(T));
    } else {
	memcpy(m_buffer + m_writer, source, here * sizeof(T));
	memcpy(m_buffer, source + here, (n - here) * sizeof(T));
    }

    m_writer = (m_writer + n) % m_size;

#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::write: wrote " << n << ", writer now " << m_writer << std::endl;
#endif

    return n;
}

template <typename T, int N>
size_t
RingBuffer<T, N>::zero(size_t n)
{
#ifdef DEBUG_RINGBUFFER
    std::cerr << "RingBuffer<T," << N << ">[" << this << "]::zero(" << n << ")" << std::endl;
#endif

    size_t available = getWriteSpace();
    if (n > available) {
#ifdef DEBUG_RINGBUFFER
	std::cerr << "WARNING: Only room for " << available << " samples"
		  << std::endl;
#endif
	n = available;
    }
    if (n == 0) return n;

    size_t here = m_size - m_writer;
    if (here >= n) {
	memset(m_buffer + m_writer, 0, n * sizeof(T));
    } else {
	memset(m_buffer + m_writer, 0, here * sizeof(T));
	memset(m_buffer, 0, (n - here) * sizeof(T));
    }

    m_writer = (m_writer + n) % m_size;
    return n;
}

#endif // _RINGBUFFER_H_