/* * 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 <stddef.h> #include <sys/uio.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 { unsigned char *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. * * @return total number of bytes readable into both vec elements */ size_t 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. * * @return total number of bytes writable in both vec elements */ size_t 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); /** * Reset the write pointer to the read pointer, making an empty buffer. * * This should only be called by the writer * * @param rb a pointer to the ringbuffer structure. */ void ringbuf_writer_reset(struct ringbuf * rb); /** * Reset the read pointer to the write pointer, making an empty buffer. * * This should only be called by the reader * * @param rb a pointer to the ringbuffer structure. */ void ringbuf_reader_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 */