smplockseq.h

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/*
 * Copyright (c) 2016 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.org/license/LICENSE.
 */

#ifndef _RTEMS_SCORE_SMPLOCKSEQ_H
#define _RTEMS_SCORE_SMPLOCKSEQ_H

#include <rtems/score/cpuopts.h>

#if defined(RTEMS_SMP)

#include <rtems/score/assert.h>
#include <rtems/score/atomic.h>

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

typedef struct {
  Atomic_Uint sequence;
} SMP_sequence_lock_Control;

#define SMP_SEQUENCE_LOCK_INITIALIZER { ATOMIC_INITIALIZER_UINT( 0 ) }

static inline void _SMP_sequence_lock_Initialize( SMP_sequence_lock_Control *lock )
{
  _Atomic_Init_uint( &lock->sequence, 0 );
}

static inline void _SMP_sequence_lock_Destroy( SMP_sequence_lock_Control *lock )
{
  (void) lock;
}

static inline unsigned int _SMP_sequence_lock_Write_begin(
  SMP_sequence_lock_Control *lock
)
{
  unsigned int seq;

  seq = _Atomic_Load_uint( &lock->sequence, ATOMIC_ORDER_RELAXED );
  _Assert( seq % 2 == 0 );

  _Atomic_Store_uint( &lock->sequence, seq + 1, ATOMIC_ORDER_RELAXED );

  /* There is no atomic store with acquire/release semantics */
  _Atomic_Fence( ATOMIC_ORDER_ACQ_REL );

  return seq;
}

static inline void _SMP_sequence_lock_Write_end(
  SMP_sequence_lock_Control *lock,
  unsigned int               seq
)
{
  _Atomic_Store_uint( &lock->sequence, seq + 2, ATOMIC_ORDER_RELEASE );
}

static inline unsigned int _SMP_sequence_lock_Read_begin(
  const SMP_sequence_lock_Control *lock
)
{
  return _Atomic_Load_uint( &lock->sequence, ATOMIC_ORDER_ACQUIRE );
}

static inline bool _SMP_sequence_lock_Read_retry(
  SMP_sequence_lock_Control *lock,
  unsigned int               seq
)
{
  unsigned int seq2;

  seq2 = _Atomic_Fetch_add_uint( &lock->sequence, 0, ATOMIC_ORDER_RELEASE );
  return seq != seq2 || seq % 2 != 0;
}

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* RTEMS_SMP */

#endif /* _RTEMS_SCORE_SMPLOCKSEQ_H */