path: root/Alc/ringbuffer.c

/**
 * OpenAL cross platform audio library
 * Copyright (C) 1999-2007 by authors.
 * This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Library General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 *  Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 *  License along with this library; if not, write to the
 *  Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 * Or go to http://www.gnu.org/copyleft/lgpl.html
 */

#include "config.h"

#include <string.h>
#include <stdlib.h>

#include "ringbuffer.h"
#include "align.h"
#include "atomic.h"
#include "threads.h"
#include "almalloc.h"
#include "compat.h"


/* NOTE: This lockless ringbuffer implementation is copied from JACK, extended
 * to include an element size. Consequently, parameters and return values for a
 * size or count is in 'elements', not bytes. Additionally, it only supports
 * single-consumer/single-provider operation. */
struct ll_ringbuffer {
    ATOMIC(size_t) write_ptr;
    ATOMIC(size_t) read_ptr;
    size_t size;
    size_t size_mask;
    size_t elem_size;

    alignas(16) char buf[];
};

/* Create a new ringbuffer to hold at least `sz' elements of `elem_sz' bytes.
 * The number of elements is rounded up to the next power of two. */
ll_ringbuffer_t *ll_ringbuffer_create(size_t sz, size_t elem_sz)
{
    ll_ringbuffer_t *rb;
    size_t power_of_two = 0;

    if(sz > 0)
    {
        power_of_two = sz - 1;
        power_of_two |= power_of_two>>1;
        power_of_two |= power_of_two>>2;
        power_of_two |= power_of_two>>4;
        power_of_two |= power_of_two>>8;
        power_of_two |= power_of_two>>16;
#if SIZE_MAX > UINT_MAX
        power_of_two |= power_of_two>>32;
#endif
    }
    power_of_two++;
    if(power_of_two < sz) return NULL;

    rb = al_malloc(16, sizeof(*rb) + power_of_two*elem_sz);
    if(!rb) return NULL;

    ATOMIC_INIT(&rb->write_ptr, 0);
    ATOMIC_INIT(&rb->read_ptr, 0);
    rb->size = power_of_two;
    rb->size_mask = rb->size - 1;
    rb->elem_size = elem_sz;
    return rb;
}

/* Free all data associated with the ringbuffer `rb'. */
void ll_ringbuffer_free(ll_ringbuffer_t *rb)
{
    al_free(rb);
}

/* Reset the read and write pointers to zero. This is not thread safe. */
void ll_ringbuffer_reset(ll_ringbuffer_t *rb)
{
    ATOMIC_STORE(&rb->write_ptr, 0, almemory_order_release);
    ATOMIC_STORE(&rb->read_ptr, 0, almemory_order_release);
    memset(rb->buf, 0, rb->size*rb->elem_size);
}

/* Return the number of elements available for reading. This is the number of
 * elements in front of the read pointer and behind the write pointer. */
size_t ll_ringbuffer_read_space(const ll_ringbuffer_t *rb)
{
    size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
    size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
    return (w-r) & rb->size_mask;
}
/* Return the number of elements available for writing. This is the number of
 * elements in front of the write pointer and behind the read pointer. */
size_t ll_ringbuffer_write_space(const ll_ringbuffer_t *rb)
{
    size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
    size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
    return (r-w-1) & rb->size_mask;
}

/* The copying data reader. Copy at most `cnt' elements from `rb' to `dest'.
 * Returns the actual number of elements copied. */
size_t ll_ringbuffer_read(ll_ringbuffer_t *rb, char *dest, size_t cnt)
{
    size_t read_ptr;
    size_t free_cnt;
    size_t cnt2;
    size_t to_read;
    size_t n1, n2;

    free_cnt = ll_ringbuffer_read_space(rb);
    if(free_cnt == 0) return 0;

    to_read = (cnt > free_cnt) ? free_cnt : cnt;
    read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;

    cnt2 = read_ptr + to_read;
    if(cnt2 > rb->size)
    {
        n1 = rb->size - read_ptr;
        n2 = cnt2 & rb->size_mask;
    }
    else
    {
        n1 = to_read;
        n2 = 0;
    }

    memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
    read_ptr += n1;
    if(n2)
    {
        memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
               n2*rb->elem_size);
        read_ptr += n2;
    }
    ATOMIC_STORE(&rb->read_ptr, read_ptr, almemory_order_release);
    return to_read;
}

/* The copying data reader w/o read pointer advance. Copy at most `cnt'
 * elements from `rb' to `dest'. Returns the actual number of elements copied.
 */
size_t ll_ringbuffer_peek(ll_ringbuffer_t *rb, char *dest, size_t cnt)
{
    size_t free_cnt;
    size_t cnt2;
    size_t to_read;
    size_t n1, n2;
    size_t read_ptr;

    free_cnt = ll_ringbuffer_read_space(rb);
    if(free_cnt == 0) return 0;

    to_read = (cnt > free_cnt) ? free_cnt : cnt;
    read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;

    cnt2 = read_ptr + to_read;
    if(cnt2 > rb->size)
    {
        n1 = rb->size - read_ptr;
        n2 = cnt2 & rb->size_mask;
    }
    else
    {
        n1 = to_read;
        n2 = 0;
    }

    memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
    if(n2)
    {
        read_ptr += n1;
        memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
               n2*rb->elem_size);
    }
    return to_read;
}

/* The copying data writer. Copy at most `cnt' elements to `rb' from `src'.
 * Returns the actual number of elements copied. */
size_t ll_ringbuffer_write(ll_ringbuffer_t *rb, const char *src, size_t cnt)
{
    size_t write_ptr;
    size_t free_cnt;
    size_t cnt2;
    size_t to_write;
    size_t n1, n2;

    free_cnt = ll_ringbuffer_write_space(rb);
    if(free_cnt == 0) return 0;

    to_write = (cnt > free_cnt) ? free_cnt : cnt;
    write_ptr = ATOMIC_LOAD(&rb->write_ptr, almemory_order_relaxed) & rb->size_mask;

    cnt2 = write_ptr + to_write;
    if(cnt2 > rb->size)
    {
        n1 = rb->size - write_ptr;
        n2 = cnt2 & rb->size_mask;
    }
    else
    {
        n1 = to_write;
        n2 = 0;
    }

    memcpy(&rb->buf[write_ptr*rb->elem_size], src, n1*rb->elem_size);
    write_ptr += n1;
    if(n2)
    {
        memcpy(&rb->buf[(write_ptr&rb->size_mask)*rb->elem_size], src + n1*rb->elem_size,
               n2*rb->elem_size);
        write_ptr += n2;
    }
    ATOMIC_STORE(&rb->write_ptr, write_ptr, almemory_order_release);
    return to_write;
}

/* Advance the read pointer `cnt' places. */
void ll_ringbuffer_read_advance(ll_ringbuffer_t *rb, size_t cnt)
{
    ATOMIC_ADD(&rb->read_ptr, cnt, almemory_order_acq_rel);
}

/* Advance the write pointer `cnt' places. */
void ll_ringbuffer_write_advance(ll_ringbuffer_t *rb, size_t cnt)
{
    ATOMIC_ADD(&rb->write_ptr, cnt, almemory_order_acq_rel);
}

/* The non-copying data reader. `vec' is an array of two places. Set the values
 * at `vec' to hold the current readable data at `rb'. If the readable data is
 * in one segment the second segment has zero length. */
void ll_ringbuffer_get_read_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t * vec)
{
    size_t free_cnt;
    size_t cnt2;
    size_t w, r;

    w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
    r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
    w &= rb->size_mask;
    r &= rb->size_mask;
    free_cnt = (w-r) & rb->size_mask;

    cnt2 = r + free_cnt;
    if(cnt2 > rb->size)
    {
        /* Two part vector: the rest of the buffer after the current write ptr,
         * plus some from the start of the buffer. */
        vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
        vec[0].len = rb->size - r;
        vec[1].buf = (char*)rb->buf;
        vec[1].len = cnt2 & rb->size_mask;
    }
    else
    {
        /* Single part vector: just the rest of the buffer */
        vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
        vec[0].len = free_cnt;
        vec[1].buf = NULL;
        vec[1].len = 0;
    }
}

/* The non-copying data writer. `vec' is an array of two places. Set the values
 * at `vec' to hold the current writeable data at `rb'. If the writeable data
 * is in one segment the second segment has zero length. */
void ll_ringbuffer_get_write_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t *vec)
{
    size_t free_cnt;
    size_t cnt2;
    size_t w, r;

    w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
    r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
    w &= rb->size_mask;
    r &= rb->size_mask;
    free_cnt = (r-w-1) & rb->size_mask;

    cnt2 = w + free_cnt;
    if(cnt2 > rb->size)
    {
        /* Two part vector: the rest of the buffer after the current write ptr,
         * plus some from the start of the buffer. */
        vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
        vec[0].len = rb->size - w;
        vec[1].buf = (char*)rb->buf;
        vec[1].len = cnt2 & rb->size_mask;
    }
    else
    {
        vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
        vec[0].len = free_cnt;
        vec[1].buf = NULL;
        vec[1].len = 0;
    }
}