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/*! \file semaphore.c
\brief Implementation: POSIX 1003.1b semaphores for process synchronization.
\author Markus L. Noga <markus@noga.de>
*/
/*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
* License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is legOS code, released October 17, 1999.
*
* The Initial Developer of the Original Code is Markus L. Noga.
* Portions created by Markus L. Noga are Copyright (C) 1999
* Markus L. Noga. All Rights Reserved.
*
* Contributor(s): Markus L. Noga <markus@noga.de>
*/
#include <semaphore.h>
#ifdef CONF_SEMAPHORES
#include <unistd.h>
///////////////////////////////////////////////////////////////////////////////
//
// Functions
//
///////////////////////////////////////////////////////////////////////////////
//! the semaphore event wakeup function for wait_event().
/*! \param data pointer to the semaphore passed as a wakeup_t
*/
wakeup_t sem_event_wait(wakeup_t data) {
sem_t *sem=(sem_t*) ((unsigned)data);
// we're called by the scheduler, therefore in an IRQ handler,
// so no worrying about IRQs.
//
if(*sem) {
(*sem)--;
return 1; // sem!=0 -> wakeup
}
return 0;
}
//! wait on a semaphore
/*! \param sem a valid semaphore
suspends the calling thread until the semaphore
has non-zero count. It then atomically
decreases the semaphore count.
implemented with wait_event().
*/
int sem_wait(sem_t * sem) {
// check if semaphore is available, if not, go to sleep
if(sem_trywait(sem))
if (wait_event(sem_event_wait,(unsigned long) ((unsigned)sem)) == 0)
return -1;
return 0;
}
typedef struct {
sem_t *sem;
time_t abs_timeout;
} timeout_sem_data_t;
static wakeup_t sem_event_timeout_wait(wakeup_t data) {
timeout_sem_data_t *tsem = (timeout_sem_data_t*) ((unsigned)data);
// we're called by the scheduler, therefore in an IRQ handler,
// so no worrying about IRQs.
//
if (*tsem->sem) {
(*tsem->sem)--;
return 1; // sem!=0 -> wakeup
}
if (tsem->abs_timeout <= get_system_up_time()) {
return 2; // timeout reached -> wakeup
}
return 0;
}
int sem_timedwait(sem_t *sem,
const time_t abs_timeout) {
timeout_sem_data_t data;
data.sem = sem;
data.abs_timeout = abs_timeout;
if (sem_trywait(sem)) {
if (wait_event(sem_event_timeout_wait,
(wakeup_t) ((unsigned) &data)) != 1) {
return -1; // timeout reached.
}
}
return 0;
}
//! non-blocking check on a semaphore
/*! \param sem a valid semaphore
a non-blocking variant of sem_wait. If the
semaphore has non-zero count, the count
is atomically decreased and sem_trywait immediately
returns 0. If the semaphore count is zero, sem_trywait
immediately returns with error EAGAIN.
this is IRQ handler safe.
*/
int sem_trywait(sem_t * sem);
#ifndef DOXYGEN_SHOULD_SKIP_THIS
__asm__("\n\
.text\n\
.align 1\n\
.globl _sem_trywait\n\
_sem_trywait:\n\
stc ccr,r1h ; save flags \n\
orc #0x80,ccr ; block all but NMI\n\
mov.b @r0,r1l\n\
beq sem_fail ; !=0 -> decrease, return 0\n\
dec r1l\n\
mov.b r1l,@r0\n\
sub.w r0,r0 ; return 0\n\
bra sem_ok\n\
\n\
sem_fail:\n\
mov #0xffff,r0 ; else return 0xffff\n\
\n\
sem_ok:\n\
ldc r1h,ccr ; restore flags\n\
rts\n\
");
#endif // DOXYGEN_SHOULD_SKIP_THIS
#endif // CONF_SEMAPHORES
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