/*  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 <config.h>#include <stdlib.h>#include <string.h>#ifdef USE_MLOCK#include <sys/mman.h>#endif /* USE_MLOCK */#include "rb.h"/* 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.  */rb_t *rb_create (size_t sz){  int power_of_two;  rb_t *rb;  rb = calloc (1, sizeof (rb_t));  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;  rb->buf = calloc (1, rb->size);  rb->mlocked = 0;  return rb;}/* Free all data associated with the ringbuffer `rb'. */voidrb_free (rb_t * rb){#ifdef USE_MLOCK  if (rb->mlocked) {    munlock (rb->buf, rb->size);  }#endif /* USE_MLOCK */  free (rb->buf);}/* Lock the data block of `rb' using the system call 'mlock'.  */intrb_mlock (rb_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. */voidrb_reset (rb_t * 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_trb_read_space (const rb_t * rb){  size_t w, r;  w = rb->write_ptr;  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_trb_write_space (const rb_t * rb){  size_t w, r;  w = rb->write_ptr;  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_trb_read (rb_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 = rb_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);  rb->read_ptr += n1;  rb->read_ptr &= rb->size_mask;  if (n2) {    memcpy (dest + n1, &(rb->buf[rb->read_ptr]), n2);    rb->read_ptr += n2;    rb->read_ptr &= 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. */size_trb_peek (rb_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 = rb_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 += n1;  tmp_read_ptr &= rb->size_mask;  if (n2) {    memcpy (dest + n1, &(rb->buf[tmp_read_ptr]), n2);    tmp_read_ptr += n2;    tmp_read_ptr &= 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_trb_write (rb_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 = rb_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);  rb->write_ptr += n1;  rb->write_ptr &= rb->size_mask;  if (n2) {    memcpy (&(rb->buf[rb->write_ptr]), src + n1, n2);    rb->write_ptr += n2;    rb->write_ptr &= rb->size_mask;  }  return to_write;}/* Advance the read pointer `cnt' places. */voidrb_read_advance (rb_t * rb, size_t cnt){  rb->read_ptr += cnt;  rb->read_ptr &= rb->size_mask;}/* Advance the write pointer `cnt' places. */voidrb_write_advance (rb_t * rb, size_t cnt){  rb->write_ptr += cnt;  rb->write_ptr &= 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.  */voidrb_get_read_vector (const rb_t * rb,		    rb_data_t * vec){  size_t free_cnt;  size_t cnt2;  size_t w, r;  w = rb->write_ptr;  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].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.  */voidrb_get_write_vector (const rb_t * rb,		     rb_data_t * vec){  size_t free_cnt;  size_t cnt2;  size_t w, r;  w = rb->write_ptr;  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].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;  }}