jack2/common/jack/ringbuffer.h

/*
  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 _RINGBUFFER_H
#define _RINGBUFFER_H

#ifdef __cplusplus
extern "C"
{
#endif

#include <sys/types.h>

    /** @file ringbuffer.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.
     */

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

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

    /**
     * Allocates a ringbuffer data structure of a specified size. The
     * caller must arrange for a call to jack_ringbuffer_free() to release
     * the memory associated with the ringbuffer.
     *
     * @param sz the ringbuffer size in bytes.
     *
     * @return a pointer to a new jack_ringbuffer_t, if successful; NULL
     * otherwise.
     */
    jack_ringbuffer_t *jack_ringbuffer_create(size_t sz);

    /**
     * Frees the ringbuffer data structure allocated by an earlier call to
     * jack_ringbuffer_create().
     *
     * @param rb a pointer to the ringbuffer structure.
     */
    void jack_ringbuffer_free(jack_ringbuffer_t *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 jack_ringbuffer_data_t.  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 jack_ringbuffer_data_t.
     *
     */
    void jack_ringbuffer_get_read_vector(const jack_ringbuffer_t *rb,
                                         jack_ringbuffer_data_t *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 jack_ringbuffer_data_t.  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 jack_ringbuffer_data_t.
     */
    void jack_ringbuffer_get_write_vector(const jack_ringbuffer_t *rb,
                                          jack_ringbuffer_data_t *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 jack_ringbuffer_read(jack_ringbuffer_t *rb, char *dest, size_t cnt);

    /**
     * Read data from the ringbuffer. Opposed to jack_ringbuffer_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 jack_ringbuffer_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 jack_ringbuffer_peek(jack_ringbuffer_t *rb, char *dest, size_t cnt);

    /**
     * Advance the read pointer.
     *
     * After data have been read from the ringbuffer using the pointers
     * returned by jack_ringbuffer_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 jack_ringbuffer_read_advance(jack_ringbuffer_t *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 jack_ringbuffer_read_space(const jack_ringbuffer_t *rb);

    /**
     * Lock a ringbuffer data block into memory.
     *
     * Uses the mlock() system call.  This is not a realtime operation.
     *
     * @param rb a pointer to the ringbuffer structure.
     */
    int jack_ringbuffer_mlock(jack_ringbuffer_t *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 jack_ringbuffer_reset(jack_ringbuffer_t *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 jack_ringbuffer_write(jack_ringbuffer_t *rb, const char *src,
                                 size_t cnt);

    /**
     * Advance the write pointer.
     *
     * After data have been written the ringbuffer using the pointers
     * returned by jack_ringbuffer_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 jack_ringbuffer_write_advance(jack_ringbuffer_t *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 jack_ringbuffer_write_space(const jack_ringbuffer_t *rb);


#ifdef __cplusplus
}
#endif

#endif