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Add a generic ring buffer implementation

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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
This commit is contained in:
Eric Wong 2008-06-30 02:42:40 +00:00
parent 3a932bf388
commit bec0835836
3 changed files with 503 additions and 0 deletions
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2
src/Makefile.am
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@ -66,6 +66,7 @@ mpd_headers = \
playerData.h \
playlist.h \
replayGain.h \
ringbuf.h \
signal_check.h \
sig_handlers.h \
sllist.h \
@ -122,6 +123,7 @@ mpd_SOURCES = \
playerData.c \
playlist.c \
replayGain.c \
ringbuf.c \
sig_handlers.c \
signal_check.c \
sllist.c \

296
src/ringbuf.c Normal file
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@ -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;
}
}

205
src/ringbuf.h Normal file
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@ -0,0 +1,205 @@
/*
* 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.
*/
#ifndef RINGBUF_H
#define RINGBUF_H
#include "os_compat.h"
/** @file ringbuf.h
*
* A set of library functions to make lock-free ringbuffers available
* to JACK clients. The `capture_client.c' (in the example_clients
* directory) is a fully functioning user of this API.
*
* The key attribute of a ringbuffer is that it can be safely accessed
* by two threads simultaneously -- one reading from the buffer and
* the other writing to it -- without using any synchronization or
* mutual exclusion primitives. For this to work correctly, there can
* only be a single reader and a single writer thread. Their
* identities cannot be interchanged.
*/
struct ringbuf {
void *buf;
size_t write_ptr;
size_t read_ptr;
size_t size;
size_t size_mask;
};
/**
* Allocates a ringbuffer data structure of a specified size. The
* caller must arrange for a call to ringbuf_free() to release
* the memory associated with the ringbuffer.
*
* @param sz the ringbuffer size in bytes.
*
* @return a pointer to a new struct ringbuf, if successful; NULL
* otherwise.
*/
struct ringbuf *ringbuf_create(size_t sz);
/**
* Frees the ringbuffer data structure allocated by an earlier call to
* ringbuf_create().
*
* @param rb a pointer to the ringbuffer structure.
*/
void ringbuf_free(struct ringbuf * rb);
/**
* Fill a data structure with a description of the current readable
* data held in the ringbuffer. This description is returned in a two
* element array of struct iovec. Two elements are needed
* because the data to be read may be split across the end of the
* ringbuffer.
*
* The first element will always contain a valid @a len field, which
* may be zero or greater. If the @a len field is non-zero, then data
* can be read in a contiguous fashion using the address given in the
* corresponding @a buf field.
*
* If the second element has a non-zero @a len field, then a second
* contiguous stretch of data can be read from the address given in
* its corresponding @a buf field.
*
* @param rb a pointer to the ringbuffer structure.
* @param vec a pointer to a 2 element array of struct iovec.
*
*/
void ringbuf_get_read_vector(const struct ringbuf * rb, struct iovec * vec);
/**
* Fill a data structure with a description of the current writable
* space in the ringbuffer. The description is returned in a two
* element array of struct iovec. Two elements are needed
* because the space available for writing may be split across the end
* of the ringbuffer.
*
* The first element will always contain a valid @a len field, which
* may be zero or greater. If the @a len field is non-zero, then data
* can be written in a contiguous fashion using the address given in
* the corresponding @a buf field.
*
* If the second element has a non-zero @a len field, then a second
* contiguous stretch of data can be written to the address given in
* the corresponding @a buf field.
*
* @param rb a pointer to the ringbuffer structure.
* @param vec a pointer to a 2 element array of struct iovec.
*/
void ringbuf_get_write_vector(const struct ringbuf * rb, struct iovec * vec);
/**
* Read data from the ringbuffer.
*
* @param rb a pointer to the ringbuffer structure.
* @param dest a pointer to a buffer where data read from the
* ringbuffer will go.
* @param cnt the number of bytes to read.
*
* @return the number of bytes read, which may range from 0 to cnt.
*/
size_t ringbuf_read(struct ringbuf * rb, void *dest, size_t cnt);
/**
* Read data from the ringbuffer. Opposed to ringbuf_read()
* this function does not move the read pointer. Thus it's
* a convenient way to inspect data in the ringbuffer in a
* continous fashion. The price is that the data is copied
* into a user provided buffer. For "raw" non-copy inspection
* of the data in the ringbuffer use ringbuf_get_read_vector().
*
* @param rb a pointer to the ringbuffer structure.
* @param dest a pointer to a buffer where data read from the
* ringbuffer will go.
* @param cnt the number of bytes to read.
*
* @return the number of bytes read, which may range from 0 to cnt.
*/
size_t ringbuf_peek(struct ringbuf * rb, void *dest, size_t cnt);
/**
* Advance the read pointer.
*
* After data have been read from the ringbuffer using the pointers
* returned by ringbuf_get_read_vector(), use this function to
* advance the buffer pointers, making that space available for future
* write operations.
*
* @param rb a pointer to the ringbuffer structure.
* @param cnt the number of bytes read.
*/
void ringbuf_read_advance(struct ringbuf * rb, size_t cnt);
/**
* Return the number of bytes available for reading.
*
* @param rb a pointer to the ringbuffer structure.
*
* @return the number of bytes available to read.
*/
size_t ringbuf_read_space(const struct ringbuf * rb);
/**
* Reset the read and write pointers, making an empty buffer.
*
* This is not thread safe.
*
* @param rb a pointer to the ringbuffer structure.
*/
void ringbuf_reset(struct ringbuf * rb);
/**
* Write data into the ringbuffer.
*
* @param rb a pointer to the ringbuffer structure.
* @param src a pointer to the data to be written to the ringbuffer.
* @param cnt the number of bytes to write.
*
* @return the number of bytes write, which may range from 0 to cnt
*/
size_t ringbuf_write(struct ringbuf * rb, const void *src, size_t cnt);
/**
* Advance the write pointer.
*
* After data have been written the ringbuffer using the pointers
* returned by ringbuf_get_write_vector(), use this function
* to advance the buffer pointer, making the data available for future
* read operations.
*
* @param rb a pointer to the ringbuffer structure.
* @param cnt the number of bytes written.
*/
void ringbuf_write_advance(struct ringbuf * rb, size_t cnt);
/**
* Return the number of bytes available for writing.
*
* @param rb a pointer to the ringbuffer structure.
*
* @return the amount of free space (in bytes) available for writing.
*/
size_t ringbuf_write_space(const struct ringbuf * rb);
#endif /* RINGBUF_H */