smplockseq.h

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/* SPDX-License-Identifier: BSD-2-Clause */
 
/*
 * Copyright (c) 2016 embedded brains GmbH & Co. KG
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
 
#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 */