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/*
* @file
*
* @brief Wait for Spinlock
* @ingroup ScoreSpinlock
*/
/*
* COPYRIGHT (c) 1989-2009.
* On-Line Applications Research Corporation (OAR).
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
#if HAVE_CONFIG_H
#include "config.h"
#endif
#include <rtems/score/corespinlockimpl.h>
#include <rtems/score/percpu.h>
Status_Control _CORE_spinlock_Seize(
CORE_spinlock_Control *the_spinlock,
bool wait,
Watchdog_Interval timeout,
ISR_lock_Context *lock_context
)
{
Thread_Control *executing;
#if defined(FUNCTIONALITY_NOT_CURRENTLY_USED_BY_ANY_API)
Watchdog_Interval limit = _Watchdog_Ticks_since_boot + timeout;
#endif
executing = _Thread_Executing;
_CORE_spinlock_Acquire_critical( the_spinlock, lock_context );
if ( the_spinlock->lock == CORE_SPINLOCK_LOCKED &&
the_spinlock->holder == executing ) {
_CORE_spinlock_Release( the_spinlock, lock_context );
return STATUS_NESTING_NOT_ALLOWED;
}
the_spinlock->users += 1;
for ( ;; ) {
if ( the_spinlock->lock == CORE_SPINLOCK_UNLOCKED ) {
the_spinlock->lock = CORE_SPINLOCK_LOCKED;
the_spinlock->holder = executing;
_CORE_spinlock_Release( the_spinlock, lock_context );
return STATUS_SUCCESSFUL;
}
/*
* Spinlock is unavailable. If not willing to wait, return.
*/
if ( !wait ) {
the_spinlock->users -= 1;
_CORE_spinlock_Release( the_spinlock, lock_context );
return STATUS_UNAVAILABLE;
}
#if defined(FUNCTIONALITY_NOT_CURRENTLY_USED_BY_ANY_API)
/*
* They are willing to wait but there could be a timeout.
*/
if ( timeout && (limit <= _Watchdog_Ticks_since_boot) ) {
the_spinlock->users -= 1;
_CORE_spinlock_Release( the_spinlock, lock_context );
return STATUS_TIMEOUT;
}
#endif
/*
* The thread is willing to spin so let's set things up so
* another thread has a chance of running. This spinlock has
* to be released by either another thread or an ISR. Since
* POSIX does not say anything about ISRs, that implies that
* another thread must be able to run while spinning. We are
* not blocking so that implies we are at least preemptible
* and possibly time-sliced.
*
* So first, we will enable interrpts to allow for them to happen.
* Then we will "flash" the thread dispatching critical section
* so other threads have a chance to run.
*
* A spinlock cannot be deleted while it is being used so we are
* safe from deletion.
*/
_CORE_spinlock_Release( the_spinlock, lock_context );
/*
* An ISR could occur here. Another thread could get dispatched here.
* Reenter the critical sections so we can attempt the lock again.
*/
_ISR_lock_ISR_disable( lock_context );
_CORE_spinlock_Acquire_critical( the_spinlock, lock_context );
}
}
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