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https://github.com/alsa-project/alsa-lib.git
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85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
/*
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* Atomic read/write
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* Copyright (c) 2001 by Abramo Bagnara <abramo@alsa-project.org>
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Library General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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#include <asm/system.h>
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/* Max number of times we must spin on a spinlock calling sched_yield().
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After MAX_SPIN_COUNT iterations, we put the calling thread to sleep. */
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#ifndef MAX_SPIN_COUNT
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#define MAX_SPIN_COUNT 50
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#endif
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/* Duration of sleep (in nanoseconds) when we can't acquire a spinlock
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after MAX_SPIN_COUNT iterations of sched_yield().
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This MUST BE > 2ms.
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(Otherwise the kernel does busy-waiting for realtime threads,
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giving other threads no chance to run.) */
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#ifndef SPIN_SLEEP_DURATION
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#define SPIN_SLEEP_DURATION 2000001
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#endif
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typedef struct {
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unsigned int begin, end;
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} snd_atomic_write_t;
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typedef struct {
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volatile const snd_atomic_write_t *write;
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unsigned int end;
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} snd_atomic_read_t;
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void snd_atomic_read_wait(snd_atomic_read_t *t);
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static inline void snd_atomic_write_init(snd_atomic_write_t *w)
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{
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w->begin = 0;
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w->end = 0;
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}
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static inline void snd_atomic_write_begin(snd_atomic_write_t *w)
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{
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w->begin++;
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wmb();
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}
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static inline void snd_atomic_write_end(snd_atomic_write_t *w)
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{
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wmb();
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w->end++;
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}
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static inline void snd_atomic_read_init(snd_atomic_read_t *r, snd_atomic_write_t *w)
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{
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r->write = w;
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}
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static inline void snd_atomic_read_begin(snd_atomic_read_t *r)
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{
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r->end = r->write->end;
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rmb();
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}
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static inline int snd_atomic_read_ok(snd_atomic_read_t *r)
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{
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rmb();
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return r->end == r->write->begin;
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}
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