ringbuffer.c

/*
  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 <stdlib.h>
#include <string.h>
#ifdef USE_MLOCK
#include <sys/mman.h>
#endif /* USE_MLOCK */
#include "JackCompilerDeps.h"

/* Portable definitions for acquire and release fences */
#if defined(_MSC_VER)
	#if defined(_M_AMD64) || defined(_M_IX86) || defined(_M_X64)
		/* Only compiler fences are needed on x86. In fact, GCC
		 * will generate no instructions for acq/rel fences on
		 * x86 */
		#include <intrin.h>
		#define JACK_ACQ_FENCE() _ReadBarrier()
		#define JACK_REL_FENCE() _WriteBarrier()
	#else
		/* Use full memory fence for non-x86 systems with msvc */
		#include <windows.h>
		#define JACK_ACQ_FENCE() MemoryBarrier()
		#define JACK_REL_FENCE() MemoryBarrier()
	#endif
#elif defined(__GNUC__)
	#ifdef __ATOMIC_ACQUIRE
		#define JACK_ACQ_FENCE() __atomic_thread_fence(__ATOMIC_ACQUIRE)
		#define JACK_REL_FENCE() __atomic_thread_fence(__ATOMIC_RELEASE)
	#else
		/* Fallback to the legacy __sync builtin (full memory fence) */
		#define JACK_ACQ_FENCE() __sync_synchronize()
		#define JACK_REL_FENCE() __sync_synchronize()
	#endif
#else
	#define JACK_ACQ_FENCE()
	#define JACK_REL_FENCE()
#endif

typedef struct {
    char *buf;
    size_t len;
}
jack_ringbuffer_data_t ;

typedef struct {
    char	*buf;
    size_t	write_ptr;
    size_t	read_ptr;
    size_t	size;
    size_t	size_mask;
    int	mlocked;
}
jack_ringbuffer_t ;

LIB_EXPORT jack_ringbuffer_t *jack_ringbuffer_create(size_t sz);
LIB_EXPORT void jack_ringbuffer_free(jack_ringbuffer_t *rb);
LIB_EXPORT void jack_ringbuffer_get_read_vector(const jack_ringbuffer_t *rb,
                                         jack_ringbuffer_data_t *vec);
LIB_EXPORT void jack_ringbuffer_get_write_vector(const jack_ringbuffer_t *rb,
                                          jack_ringbuffer_data_t *vec);
LIB_EXPORT size_t jack_ringbuffer_read(jack_ringbuffer_t *rb, char *dest, size_t cnt);
LIB_EXPORT size_t jack_ringbuffer_peek(jack_ringbuffer_t *rb, char *dest, size_t cnt);
LIB_EXPORT void jack_ringbuffer_read_advance(jack_ringbuffer_t *rb, size_t cnt);
LIB_EXPORT size_t jack_ringbuffer_read_space(const jack_ringbuffer_t *rb);
LIB_EXPORT int jack_ringbuffer_mlock(jack_ringbuffer_t *rb);
LIB_EXPORT void jack_ringbuffer_reset(jack_ringbuffer_t *rb);
LIB_EXPORT void jack_ringbuffer_reset_size (jack_ringbuffer_t * rb, size_t sz);
LIB_EXPORT size_t jack_ringbuffer_write(jack_ringbuffer_t *rb, const char *src,
                                 size_t cnt);
void jack_ringbuffer_write_advance(jack_ringbuffer_t *rb, size_t cnt);
size_t jack_ringbuffer_write_space(const jack_ringbuffer_t *rb);

/* 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.  */

LIB_EXPORT jack_ringbuffer_t *
jack_ringbuffer_create (size_t sz)
{
	int power_of_two;
	jack_ringbuffer_t *rb;

	if ((rb = (jack_ringbuffer_t *) malloc (sizeof (jack_ringbuffer_t))) == NULL) {
		return NULL;
	}

	for (power_of_two = 1; 1 << power_of_two < sz; power_of_two++);

	rb->size = 1 << power_of_two;
	rb->size_mask = rb->size;
	rb->size_mask -= 1;
	rb->write_ptr = 0;
	rb->read_ptr = 0;
	if ((rb->buf = (char *) malloc (rb->size)) == NULL) {
		free (rb);
		return NULL;
	}
	rb->mlocked = 0;

	return rb;
}

/* Free all data associated with the ringbuffer `rb'. */

LIB_EXPORT void
jack_ringbuffer_free (jack_ringbuffer_t * rb)
{
#ifdef USE_MLOCK
	if (rb->mlocked) {
		munlock (rb->buf, rb->size);
	}
#endif /* USE_MLOCK */
	free (rb->buf);
	free (rb);
}

/* Lock the data block of `rb' using the system call 'mlock'.  */

LIB_EXPORT int
jack_ringbuffer_mlock (jack_ringbuffer_t * rb)
{
#ifdef USE_MLOCK
	if (mlock (rb->buf, rb->size)) {
		return -1;
	}
#endif /* USE_MLOCK */
	rb->mlocked = 1;
	return 0;
}

/* Reset the read and write pointers to zero. This is not thread
   safe. */

LIB_EXPORT void
jack_ringbuffer_reset (jack_ringbuffer_t * rb)
{
	rb->read_ptr = 0;
	rb->write_ptr = 0;
	memset(rb->buf, 0, rb->size);
}

/* Reset the read and write pointers to zero. This is not thread
   safe. */

LIB_EXPORT void
jack_ringbuffer_reset_size (jack_ringbuffer_t * rb, size_t sz)
{
    rb->size = sz;
    rb->size_mask = rb->size;
    rb->size_mask -= 1;
    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.  */

LIB_EXPORT size_t
jack_ringbuffer_read_space (const jack_ringbuffer_t * rb)
{
	size_t w, r;

	w = rb->write_ptr;
	JACK_ACQ_FENCE();
	r = rb->read_ptr;

	return (w - r) & 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.  */

LIB_EXPORT size_t
jack_ringbuffer_write_space (const jack_ringbuffer_t * rb)
{
	size_t w, r;

	w = rb->write_ptr;
	r = rb->read_ptr;
	JACK_ACQ_FENCE();

	return (r - w - 1) & rb->size_mask;
}

/* The copying data reader.  Copy at most `cnt' bytes from `rb' to
   `dest'.  Returns the actual number of bytes copied. */

LIB_EXPORT size_t
jack_ringbuffer_read (jack_ringbuffer_t * rb, char *dest, size_t cnt)
{
	size_t free_cnt;
	size_t cnt2;
	size_t to_read;
	size_t n1, n2;

	if ((free_cnt = jack_ringbuffer_read_space (rb)) == 0) {
		return 0;
	}

	to_read = cnt > free_cnt ? free_cnt : cnt;

	/* note: relaxed load here, rb->read_ptr cannot be
	 * modified from writing thread  */
	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);
	JACK_REL_FENCE(); /* ensure pointer increment happens after copy */
	rb->read_ptr = (rb->read_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (dest + n1, &(rb->buf[rb->read_ptr]), n2);
		JACK_REL_FENCE(); /* ensure pointer increment happens after copy */
		rb->read_ptr = (rb->read_ptr + n2) & rb->size_mask;
	}

	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. */

LIB_EXPORT size_t
jack_ringbuffer_peek (jack_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 tmp_read_ptr;

	tmp_read_ptr = rb->read_ptr;

	if ((free_cnt = jack_ringbuffer_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);
	tmp_read_ptr = (tmp_read_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (dest + n1, &(rb->buf[tmp_read_ptr]), n2);
	}

	return to_read;
}

/* The copying data writer.  Copy at most `cnt' bytes to `rb' from
   `src'.  Returns the actual number of bytes copied. */

LIB_EXPORT size_t
jack_ringbuffer_write (jack_ringbuffer_t * rb, const char *src, size_t cnt)
{
	size_t free_cnt;
	size_t cnt2;
	size_t to_write;
	size_t n1, n2;

	if ((free_cnt = jack_ringbuffer_write_space (rb)) == 0) {
		return 0;
	}

	to_write = cnt > free_cnt ? free_cnt : cnt;

	/* note: relaxed load here, rb->write_ptr cannot be
	 * modified from reading thread  */
	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);
	JACK_REL_FENCE(); /* ensure pointer increment happens after copy */
	rb->write_ptr = (rb->write_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (&(rb->buf[rb->write_ptr]), src + n1, n2);
		JACK_REL_FENCE(); /* ensure pointer increment happens after copy */
		rb->write_ptr = (rb->write_ptr + n2) & rb->size_mask;
	}

	return to_write;
}

/* Advance the read pointer `cnt' places. */

LIB_EXPORT void
jack_ringbuffer_read_advance (jack_ringbuffer_t * rb, size_t cnt)
{
	size_t tmp = (rb->read_ptr + cnt) & rb->size_mask;
	JACK_REL_FENCE(); /* ensure pointer increment happens after copy (by user) */
	rb->read_ptr = tmp;
}

/* Advance the write pointer `cnt' places. */

LIB_EXPORT void
jack_ringbuffer_write_advance (jack_ringbuffer_t * rb, size_t cnt)
{
	size_t tmp = (rb->write_ptr + cnt) & rb->size_mask;
	JACK_REL_FENCE(); /* ensure pointer increment happens after copy (by user) */
	rb->write_ptr = tmp;
}

/* 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.  */

LIB_EXPORT void
jack_ringbuffer_get_read_vector (const jack_ringbuffer_t * rb,
				 jack_ringbuffer_data_t * vec)
{
	size_t free_cnt;
	size_t cnt2;
	size_t r;

	r = rb->read_ptr;
	free_cnt = jack_ringbuffer_read_space(rb);
	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 = &(rb->buf[r]);
		vec[0].len = rb->size - r;
		vec[1].buf = rb->buf;
		vec[1].len = cnt2 & rb->size_mask;

	} else {

		/* Single part vector: just the rest of the buffer */

		vec[0].buf = &(rb->buf[r]);
		vec[0].len = free_cnt;
		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.  */

LIB_EXPORT void
jack_ringbuffer_get_write_vector (const jack_ringbuffer_t * rb,
				  jack_ringbuffer_data_t * vec)
{
	size_t free_cnt;
	size_t cnt2;
	size_t w;

	w = rb->write_ptr;
	free_cnt = jack_ringbuffer_write_space(rb);
	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 = &(rb->buf[w]);
		vec[0].len = rb->size - w;
		vec[1].buf = rb->buf;
		vec[1].len = cnt2 & rb->size_mask;
	} else {
		vec[0].buf = &(rb->buf[w]);
		vec[0].len = free_cnt;
		vec[1].len = 0;
	}
}