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/**
* @file
*
* @ingroup ScoreSMPLock
*
* @brief SMP Lock API
*/
/*
* COPYRIGHT (c) 1989-2011.
* On-Line Applications Research Corporation (OAR).
*
* Copyright (c) 2013-2014 embedded brains GmbH
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.com/license/LICENSE.
*/
#ifndef _RTEMS_SCORE_SMPLOCK_H
#define _RTEMS_SCORE_SMPLOCK_H
#include <rtems/score/cpuopts.h>
#if defined( RTEMS_SMP )
#include <rtems/score/atomic.h>
#include <rtems/score/isrlevel.h>
#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
/**
* @defgroup ScoreSMPLock SMP Locks
*
* @ingroup Score
*
* @brief The SMP lock provides mutual exclusion for SMP systems at the lowest
* level.
*
* The SMP lock is implemented as a ticket lock. This provides fairness in
* case of concurrent lock attempts.
*
* This SMP lock API has a flaw. It does not provide the ability to use a
* local context for acquire and release pairs. Such a context is necessary to
* implement for example the Mellor-Crummey and Scott (MCS) locks. The SMP
* lock is currently used in _Thread_Disable_dispatch() and
* _Thread_Enable_dispatch() and makes them to a giant lock acquire and
* release. Since these functions do not pass state information via a local
* context there is currently no use case for such a feature.
*
* @{
*/
/**
* @brief SMP lock control.
*/
typedef struct {
Atomic_Uint next_ticket;
Atomic_Uint now_serving;
} SMP_lock_Control;
/**
* @brief SMP lock control initializer for static initialization.
*/
#define SMP_LOCK_INITIALIZER \
{ ATOMIC_INITIALIZER_UINT( 0U ), ATOMIC_INITIALIZER_UINT( 0U ) }
/**
* @brief Initializes a SMP lock control.
*
* Concurrent initialization leads to unpredictable results.
*
* @param[out] lock The SMP lock control.
*/
static inline void _SMP_lock_Initialize( SMP_lock_Control *lock )
{
_Atomic_Init_uint( &lock->next_ticket, 0U );
_Atomic_Init_uint( &lock->now_serving, 0U );
}
/**
* @brief Acquires a SMP lock.
*
* This function will not disable interrupts. The caller must ensure that the
* current thread of execution is not interrupted indefinite once it obtained
* the SMP lock.
*
* @param[in,out] lock The SMP lock control.
*/
static inline void _SMP_lock_Acquire( SMP_lock_Control *lock )
{
unsigned int my_ticket =
_Atomic_Fetch_add_uint( &lock->next_ticket, 1U, ATOMIC_ORDER_RELAXED );
unsigned int now_serving;
do {
now_serving =
_Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_ACQUIRE );
} while ( now_serving != my_ticket );
}
/**
* @brief Releases a SMP lock.
*
* @param[in,out] lock The SMP lock control.
*/
static inline void _SMP_lock_Release( SMP_lock_Control *lock )
{
unsigned int current_ticket =
_Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_RELAXED );
unsigned int next_ticket = current_ticket + 1U;
_Atomic_Store_uint( &lock->now_serving, next_ticket, ATOMIC_ORDER_RELEASE );
}
/**
* @brief Disables interrupts and acquires the SMP lock.
*
* @param[in,out] lock The SMP lock control.
* @param[out] isr_cookie The ISR cookie.
*/
#define _SMP_lock_ISR_disable_and_acquire( lock, isr_cookie ) \
do { \
_ISR_Disable_without_giant( isr_cookie ); \
_SMP_lock_Acquire( lock ); \
} while (0)
/**
* @brief Releases the SMP lock and enables interrupts.
*
* @param[in,out] lock The SMP lock control.
* @param[in] isr_cookie The ISR cookie.
*/
#define _SMP_lock_Release_and_ISR_enable( lock, isr_cookie ) \
do { \
_SMP_lock_Release( lock ); \
_ISR_Enable_without_giant( isr_cookie ); \
} while (0)
/**@}*/
#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif /* defined( RTEMS_SMP ) */
#endif /* _RTEMS_SCORE_SMPLOCK_H */
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