Add a generic ring buffer implementation

This piece of code is from the JACK Audio Connection Kit
(trimmed down a bit for better readability).

The vector functions now reuse the common iovec struct used by
writev/readv instead of reinventing an identical but
differently-named struct.

From the comments:
> 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.

License is LGPL 2.1 or later

git-svn-id: https://svn.musicpd.org/mpd/trunk@7386 09075e82-0dd4-0310-85a5-a0d7c8717e4f

1 files changed, 296 insertions, 0 deletions

diff --git a/src/ringbuf.c b/src/ringbuf.c
new file mode 100644
index 000000000..517a4c216
--- /dev/null
+++ b/src/ringbuf.c
@@ -0,0 +1,296 @@
+/*
+ * 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.
+ */
+void 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;
+	}
+}
+
+/*
+ * 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 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;
+	}
+}
+