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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2002 by Björn Stenberg
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include "kernel-internal.h"
#include "semaphore.h"
/****************************************************************************
* Simple semaphore functions ;)
****************************************************************************/
/* Initialize the semaphore object.
* max = maximum up count the semaphore may assume (max >= 1)
* start = initial count of semaphore (0 <= count <= max) */
void semaphore_init(struct semaphore *s, int max, int start)
{
KERNEL_ASSERT(max > 0 && start >= 0 && start <= max,
"semaphore_init->inv arg\n");
wait_queue_init(&s->queue);
s->max = max;
s->count = start;
corelock_init(&s->cl);
}
/* Down the semaphore's count or wait for 'timeout' ticks for it to go up if
* it is already 0. 'timeout' as TIMEOUT_NOBLOCK (0) will not block and may
* safely be used in an ISR. */
int semaphore_wait(struct semaphore *s, int timeout)
{
int ret = OBJ_WAIT_TIMEDOUT;
int oldlevel = disable_irq_save();
corelock_lock(&s->cl);
int count = s->count;
if(LIKELY(count > 0))
{
/* count is not zero; down it */
s->count = count - 1;
ret = OBJ_WAIT_SUCCEEDED;
}
else if(timeout != 0)
{
/* too many waits - block until count is upped... */
struct thread_entry *current = __running_self_entry();
block_thread(current, timeout, &s->queue, NULL);
corelock_unlock(&s->cl);
/* ...and turn control over to next thread */
switch_thread();
/* if explicit wake indicated; do no more */
if(LIKELY(!wait_queue_ptr(current)))
return OBJ_WAIT_SUCCEEDED;
disable_irq();
corelock_lock(&s->cl);
/* see if anyone got us after the expired wait */
if(wait_queue_try_remove(current))
{
count = s->count;
if(count > 0)
{
/* down it lately */
s->count = count - 1;
ret = OBJ_WAIT_SUCCEEDED;
}
}
}
/* else just polling it */
corelock_unlock(&s->cl);
restore_irq(oldlevel);
return ret;
}
/* Up the semaphore's count and release any thread waiting at the head of the
* queue. The count is saturated to the value of the 'max' parameter specified
* in 'semaphore_init'. */
void semaphore_release(struct semaphore *s)
{
unsigned int result = THREAD_NONE;
int oldlevel = disable_irq_save();
corelock_lock(&s->cl);
struct thread_entry *thread = WQ_THREAD_FIRST(&s->queue);
if(LIKELY(thread != NULL))
{
/* a thread was queued - wake it up and keep count at 0 */
KERNEL_ASSERT(s->count == 0,
"semaphore_release->threads queued but count=%d!\n", s->count);
result = wakeup_thread(thread, WAKEUP_DEFAULT);
}
else
{
int count = s->count;
if(count < s->max)
{
/* nothing waiting - up it */
s->count = count + 1;
}
}
corelock_unlock(&s->cl);
restore_irq(oldlevel);
#if defined(HAVE_PRIORITY_SCHEDULING) && defined(is_thread_context)
/* No thread switch if not thread context */
if((result & THREAD_SWITCH) && is_thread_context())
switch_thread();
#endif
(void)result;
}
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