/*
* This file is originally from JACK Audio Connection Kit
*
* Copyright (C) 2000 Paul Davis
* Copyright (C) 2003 Rohan Drape
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* ISO/POSIX C version of Paul Davis's lock free ringbuffer C++ code.
* This is safe for the case of one read thread and one write thread.
*/
#include "ringbuf.h"
#include "utils.h"
#define advance_ptr(ptr,cnt,mask) ptr = (ptr + cnt) & mask
/*
* Create a new ringbuffer to hold at least `sz' bytes of data. The
* actual buffer size is rounded up to the next power of two.
*/
struct ringbuf *ringbuf_create(size_t sz)
{
struct ringbuf *rb = xmalloc(sizeof(struct ringbuf));
size_t power_of_two;
for (power_of_two = 1; 1 << power_of_two < sz; power_of_two++)
/* next power_of_two... */;
rb->size = 1 << power_of_two;
rb->size_mask = rb->size;
rb->size_mask -= 1;
rb->buf = xmalloc(rb->size);
ringbuf_reset(rb);
return rb;
}
/* Free all data associated with the ringbuffer `rb'. */
void ringbuf_free(struct ringbuf * rb)
{
free(rb->buf);
free(rb);
}
/* Reset the read and write pointers to zero. This is not thread safe. */
void ringbuf_reset(struct ringbuf * rb)
{
rb->read_ptr = 0;
rb->write_ptr = 0;
}
/*
* Return the number of bytes available for reading. This is the
* number of bytes in front of the read pointer and behind the write
* pointer.
*/
size_t ringbuf_read_space(const struct ringbuf * rb)
{
size_t w = rb->write_ptr;
size_t r = rb->read_ptr;
if (w > r)
return w - r;
else
return (w - r + rb->size) & rb->size_mask;
}
/*
* Return the number of bytes available for writing. This is the
* number of bytes in front of the write pointer and behind the read
* pointer.
*/
size_t ringbuf_write_space(const struct ringbuf * rb)
{
size_t w = rb->write_ptr;
size_t r = rb->read_ptr;
if (w > r)
return ((r - w + rb->size) & rb->size_mask) - 1;
else if (w < r)
return (r - w) - 1;
else
return rb->size - 1;
}
/*
* The copying data reader. Copy at most `cnt' bytes from `rb' to
* `dest'. Returns the actual number of bytes copied.
*/
size_t ringbuf_read(struct ringbuf * rb, void *dest, size_t cnt)
{
size_t free_cnt;
size_t cnt2;
size_t to_read;
size_t n1, n2;
if ((free_cnt = ringbuf_read_space(rb)) == 0)
return 0;
to_read = cnt > free_cnt ? free_cnt : cnt;
cnt2 = rb->read_ptr + to_read;
if (cnt2 > rb->size) {
n1 = rb->size - rb->read_ptr;
n2 = cnt2 & rb->size_mask;
} else {
n1 = to_read;
n2 = 0;
}
memcpy(dest, rb->buf + rb->read_ptr, n1);
ringbuf_read_advance(rb, n1);
if (n2) {
memcpy(dest + n1, rb->buf + rb->read_ptr, n2);
ringbuf_read_advance(rb, n2);
}
return to_read;
}
/*
* The copying data reader w/o read pointer advance. Copy at most
* `cnt' bytes from `rb' to `dest'. Returns the actual number of bytes
* copied.
*/
size_t ringbuf_peek(struct ringbuf * rb, void *dest, size_t cnt)
{
size_t free_cnt;
size_t cnt2;
size_t to_read;
size_t n1, n2;
size_t tmp_read_ptr = rb->read_ptr;
if ((free_cnt = ringbuf_read_space(rb)) == 0)
return 0;
to_read = cnt > free_cnt ? free_cnt : cnt;
cnt2 = tmp_read_ptr + to_read;
if (cnt2 > rb->size) {
n1 = rb->size - tmp_read_ptr;
n2 = cnt2 & rb->size_mask;
} else {
n1 = to_read;
n2 = 0;
}
memcpy(dest, rb->buf + tmp_read_ptr, n1);
advance_ptr(tmp_read_ptr, n1, rb->size_mask);
if (n2) {
memcpy(dest + n1, rb->buf + tmp_read_ptr, n2);
advance_ptr(tmp_read_ptr, n2, rb->size_mask);
}
return to_read;
}
/*
* The copying data writer. Copy at most `cnt' bytes to `rb' from
* `src'. Returns the actual number of bytes copied.
*/
size_t ringbuf_write(struct ringbuf * rb, const void *src, size_t cnt)
{
size_t free_cnt;
size_t cnt2;
size_t to_write;
size_t n1, n2;
if ((free_cnt = ringbuf_write_space(rb)) == 0)
return 0;
to_write = cnt > free_cnt ? free_cnt : cnt;
cnt2 = rb->write_ptr + to_write;
if (cnt2 > rb->size) {
n1 = rb->size - rb->write_ptr;
n2 = cnt2 & rb->size_mask;
} else {
n1 = to_write;
n2 = 0;
}
memcpy(rb->buf + rb->write_ptr, src, n1);
ringbuf_write_advance(rb, n1);
if (n2) {
memcpy(rb->buf + rb->write_ptr, src + n1, n2);
ringbuf_write_advance(rb, n2);
}
return to_write;
}
/* Advance the read pointer `cnt' places. */
void ringbuf_read_advance(struct ringbuf * rb, size_t cnt)
{
advance_ptr(rb->read_ptr, cnt, rb->size_mask);
}
/* Advance the write pointer `cnt' places. */
void ringbuf_write_advance(struct ringbuf * rb, size_t cnt)
{
advance_ptr(rb->write_ptr, cnt, rb->size_mask);
}
/*
* 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.
*/
size_t ringbuf_get_read_vector(const struct ringbuf * rb, struct iovec * vec)
{
size_t free_cnt;
size_t cnt2;
size_t w = rb->write_ptr;
size_t r = rb->read_ptr;
if (w > r)
free_cnt = w - r;
else
free_cnt = (w - r + rb->size) & 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].iov_base = rb->buf + r;
vec[0].iov_len = rb->size - r;
vec[1].iov_base = rb->buf;
vec[1].iov_len = cnt2 & rb->size_mask;
} else {
/* Single part vector: just the rest of the buffer */
vec[0].iov_base = rb->buf + r;
vec[0].iov_len = free_cnt;
vec[1].iov_len = 0;
}
return vec[0].iov_len + vec[1].iov_len;
}
/*
* 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.
*/
size_t ringbuf_get_write_vector(const struct ringbuf * rb, struct iovec * vec)
{
size_t free_cnt;
size_t cnt2;
size_t w = rb->write_ptr;
size_t r = rb->read_ptr;
if (w > r)
free_cnt = ((r - w + rb->size) & rb->size_mask) - 1;
else if (w < r)
free_cnt = (r - w) - 1;
else
free_cnt = rb->size - 1;
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].iov_base = rb->buf + w;
vec[0].iov_len = rb->size - w;
vec[1].iov_base = rb->buf;
vec[1].iov_len = cnt2 & rb->size_mask;
} else {
vec[0].iov_base = rb->buf + w;
vec[0].iov_len = free_cnt;
vec[1].iov_len = 0;
}
return vec[0].iov_len + vec[1].iov_len;
}
