ringbufferNPT.h

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/*
 * Copyright (C) 2000 Paul Davis & Benno Senoner
 * Copyright (C) 2013 John Emmas <john@creativepost.co.uk>
 * Copyright (C) 2015-2016 Robin Gareus <robin@gareus.org>
 *
 * 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.
 *
 * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
#pragma once
 
//#include <sys/mman.h>
 
#include <atomic>
#include <cstring>
#include <glib.h>
 
#include "pbd/libpbd_visibility.h"
 
namespace PBD {
 
/* ringbuffer class where the element size is not required to be a power of two */
 
template<class T>
class /*LIBPBD_API*/ RingBufferNPT
{
  public:
        RingBufferNPT (size_t sz) {
                size = sz;
                buf = new T[size];
                reset ();
        }
 
        virtual ~RingBufferNPT () {
                delete [] buf;
        }
 
        void reset () {
                /* !!! NOT THREAD SAFE !!! */
                write_ptr.store (0);
                read_ptr.store (0);
        }
 
        void set (size_t r, size_t w) {
                /* !!! NOT THREAD SAFE !!! */
                write_ptr.store (w);
                read_ptr.store (r);
        }
 
        size_t  read  (T *dest, size_t cnt);
        size_t  write (const T *src, size_t cnt);
        size_t  write_one (const T src);
 
        struct rw_vector {
            T *buf[2];
            size_t len[2];
        };
 
        void get_read_vector (rw_vector *);
        void get_write_vector (rw_vector *);
 
        void decrement_read_ptr (size_t cnt) {
                read_ptr.store ((read_ptr.load () - cnt) % size);
        }
 
        void increment_read_ptr (size_t cnt) {
                read_ptr.store ((read_ptr.load () + cnt) % size);
        }
 
        void increment_write_ptr (size_t cnt) {
                write_ptr.store ((write_ptr.load () + cnt) % size);
        }
 
        size_t write_space () {
                size_t w, r;
 
                w = write_ptr.load ();
                r = read_ptr.load ();
 
                if (w > r) {
                        return ((r - w + size) % size) - 1;
                } else if (w < r) {
                        return (r - w) - 1;
                } else {
                        return size - 1;
                }
        }
 
        size_t read_space () {
                size_t w, r;
 
                w = write_ptr.load ();
                r = read_ptr.load ();
 
                if (w > r) {
                        return w - r;
                } else {
                        return (w - r + size) % size;
                }
        }
 
        T *buffer () { return buf; }
        size_t get_write_ptr () const { return write_ptr.load (); }
        size_t get_read_ptr () const { return read_ptr.load (); }
        size_t bufsize () const { return size; }
 
  protected:
        T *buf;
        size_t size;
        mutable std::atomic<int> write_ptr;
        mutable std::atomic<int> read_ptr;
 
private:
        RingBufferNPT (RingBufferNPT const&);
};
 
template<class T> /*LIBPBD_API*/ size_t
RingBufferNPT<T>::read (T *dest, size_t cnt)
{
        size_t free_cnt;
        size_t cnt2;
        size_t to_read;
        size_t n1, n2;
        size_t priv_read_ptr;
 
        priv_read_ptr = read_ptr.load ();
 
        if ((free_cnt = read_space ()) == 0) {
                return 0;
        }
 
        to_read = cnt > free_cnt ? free_cnt : cnt;
 
        cnt2 = priv_read_ptr + to_read;
 
        if (cnt2 > size) {
                n1 = size - priv_read_ptr;
                n2 = cnt2 % size;
        } else {
                n1 = to_read;
                n2 = 0;
        }
 
        memcpy (dest, &buf[priv_read_ptr], n1 * sizeof (T));
        priv_read_ptr = (priv_read_ptr + n1) % size;
 
        if (n2) {
                memcpy (dest+n1, buf, n2 * sizeof (T));
                priv_read_ptr = n2;
        }
 
        read_ptr.store (priv_read_ptr);
        return to_read;
}
 
template<class T> /*LIBPBD_API*/ size_t
RingBufferNPT<T>::write (const T *src, size_t cnt)
{
        size_t free_cnt;
        size_t cnt2;
        size_t to_write;
        size_t n1, n2;
        size_t priv_write_ptr;
 
        priv_write_ptr = write_ptr.load ();
 
        if ((free_cnt = write_space ()) == 0) {
                return 0;
        }
 
        to_write = cnt > free_cnt ? free_cnt : cnt;
 
        cnt2 = priv_write_ptr + to_write;
 
        if (cnt2 > size) {
                n1 = size - priv_write_ptr;
                n2 = cnt2 % size;
        } else {
                n1 = to_write;
                n2 = 0;
        }
 
        memcpy (&buf[priv_write_ptr], src, n1 * sizeof (T));
        priv_write_ptr = (priv_write_ptr + n1) % size;
 
        if (n2) {
                memcpy (buf, src+n1, n2 * sizeof (T));
                priv_write_ptr = n2;
        }
 
        write_ptr.store (priv_write_ptr);
        return to_write;
}
 
template<class T> /*LIBPBD_API*/ size_t
RingBufferNPT<T>::write_one (const T src)
{
        return write (&src, 1);
}
 
template<class T> /*LIBPBD_API*/ void
RingBufferNPT<T>::get_read_vector (typename RingBufferNPT<T>::rw_vector *vec)
{
        size_t free_cnt;
        size_t cnt2;
        size_t w, r;
 
        w = write_ptr.load ();
        r = read_ptr.load ();
 
        if (w > r) {
                free_cnt = w - r;
        } else {
                free_cnt = (w - r + size) % size;
        }
 
        cnt2 = r + free_cnt;
 
        if (cnt2 > size) {
                /* Two part vector: the rest of the buffer after the
                   current write ptr, plus some from the start of
                   the buffer.
                */
 
                vec->buf[0] = &buf[r];
                vec->len[0] = size - r;
                vec->buf[1] = buf;
                vec->len[1] = cnt2 % size;
 
        } else {
 
                /* Single part vector: just the rest of the buffer */
 
                vec->buf[0] = &buf[r];
                vec->len[0] = free_cnt;
                vec->buf[1] = 0;
                vec->len[1] = 0;
        }
}
 
template<class T> /*LIBPBD_API*/ void
RingBufferNPT<T>::get_write_vector (typename RingBufferNPT<T>::rw_vector *vec)
{
        size_t free_cnt;
        size_t cnt2;
        size_t w, r;
 
        w = write_ptr.load ();
        r = read_ptr.load ();
 
        if (w > r) {
                free_cnt = ((r - w + size) % size) - 1;
        } else if (w < r) {
                free_cnt = (r - w) - 1;
        } else {
                free_cnt = size - 1;
        }
 
        cnt2 = w + free_cnt;
 
        if (cnt2 > size) {
 
                /* Two part vector: the rest of the buffer after the
                   current write ptr, plus some from the start of
                   the buffer.
                */
 
                vec->buf[0] = &buf[w];
                vec->len[0] = size - w;
                vec->buf[1] = buf;
                vec->len[1] = cnt2 % size;
        } else {
                vec->buf[0] = &buf[w];
                vec->len[0] = free_cnt;
                vec->len[1] = 0;
        }
}
 
} /* namespace */