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#ifndef foopulsecoreaupdatehfoo
#define foopulsecoreaupdatehfoo
/***
This file is part of PulseAudio.
Copyright 2009 Lennart Poettering
PulseAudio 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.
PulseAudio 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
General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with PulseAudio; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
USA.
***/
typedef struct pa_aupdate pa_aupdate;
pa_aupdate *pa_aupdate_new(void);
void pa_aupdate_free(pa_aupdate *a);
/* Will return 0, or 1, depending on which copy of the data the caller
* should look at */
unsigned pa_aupdate_read_begin(pa_aupdate *a);
void pa_aupdate_read_end(pa_aupdate *a);
/* Will return 0, or 1, depending which copy of the data the caller
* should modify */
unsigned pa_aupdate_write_begin(pa_aupdate *a);
void pa_aupdate_write_end(pa_aupdate *a);
/* Will return 0, or 1, depending which copy of the data the caller
* should modify. Each time called this will return the opposite of
* the previous pa_aupdate_write_begin() / pa_aupdate_write_swap()
* call. Should only be called between pa_aupdate_write_begin() and
* pa_aupdate_write_end() */
unsigned pa_aupdate_write_swap(pa_aupdate *a);
/*
* This infrastructure allows lock-free updates of arbitrary data
* structures in an rcu'ish way: two copies of the data structure
* should be existing. One side ('the reader') has read access to one
* of the two data structure at a time. It does not have to lock it,
* however it needs to signal that it is using it/stopped using
* it. The other side ('the writer') modifies the second data structure,
* and then atomically swaps the two data structures, followed by a
* modification of the other one.
*
* This is intended to be used for cases where the reader side needs
* to be fast while the writer side can be slow.
*
* The reader side is signal handler safe.
*
* The writer side lock is not recursive. The reader side is.
*
* There may be multiple readers and multiple writers at the same
* time.
*
* Usage is like this:
*
* static struct foo bar[2];
* static pa_aupdate *a;
*
* reader() {
* unsigned j;
*
* j = pa_update_read_begin(a);
*
* ... read the data structure bar[j] ...
*
* pa_update_read_end(a);
* }
*
* writer() {
* unsigned j;
*
* j = pa_update_write_begin(a);
*
* ... update the data structure bar[j] ...
*
* j = pa_update_write_swap(a);
*
* ... update the data structure bar[j], the same way as above ...
*
* pa_update_write_end(a)
* }
*
* In some cases keeping both structures up-to-date might not be
* necessary, since they are fully rebuilt on each iteration
* anyway. In that case you may leave the _write_swap() call out, it
* will then be done implicitly in the _write_end() invocation.
*/
#endif
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