1 files changed, 176 insertions, 0 deletions
diff --git a/cpukit/include/rtems/score/smplockseq.h b/cpukit/include/rtems/score/smplockseq.h
new file mode 100644
index 0000000000..5daaee9c6e
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+++ b/cpukit/include/rtems/score/smplockseq.h
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+/**
+ * @file
+ *
+ * @ingroup ScoreSMPLock
+ *
+ * @brief SMP Lock API
+ */
+
+/*
+ * 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 */
+
+/**
+ * @addtogroup ScoreSMPLock
+ *
+ * @{
+ */
+
+/**
+ * @brief SMP sequence lock control.
+ *
+ * The sequence lock offers a consistent data set for readers in the presence
+ * of at most one concurrent writer.  Due to the read-modify-write operation in
+ * _SMP_sequence_lock_Read_retry() the data corresponding to the last written
+ * sequence number is observed.  To allow multiple writers an additional SMP
+ * lock is necessary to serialize writes.
+ *
+ * See also Hans-J. Boehm, HP Laboratories,
+ * "Can Seqlocks Get Along With Programming Language Memory Models?",
+ * http://www.hpl.hp.com/techreports/2012/HPL-2012-68.pdf
+ */
+typedef struct {
+  /**
+   * @brief The sequence number.
+   *
+   * An odd value indicates that a write is in progress.
+   */
+  Atomic_Uint sequence;
+} SMP_sequence_lock_Control;
+
+/**
+ * @brief SMP sequence lock control initializer for static initialization.
+ */
+#define SMP_SEQUENCE_LOCK_INITIALIZER { ATOMIC_INITIALIZER_UINT( 0 ) }
+
+/**
+ * @brief Initializes an SMP sequence lock.
+ *
+ * Concurrent initialization leads to unpredictable results.
+ *
+ * @param lock The SMP sequence lock control.
+ */
+static inline void _SMP_sequence_lock_Initialize( SMP_sequence_lock_Control *lock )
+{
+  _Atomic_Init_uint( &lock->sequence, 0 );
+}
+
+/**
+ * @brief Destroys an SMP sequence lock.
+ *
+ * Concurrent destruction leads to unpredictable results.
+ *
+ * @param lock The SMP sequence lock control.
+ */
+static inline void _SMP_sequence_lock_Destroy( SMP_sequence_lock_Control *lock )
+{
+  (void) lock;
+}
+
+/**
+ * @brief Begins an SMP sequence lock write operation.
+ *
+ * This function will not disable interrupts.  The caller must ensure that the
+ * current thread of execution is not interrupted indefinite since this would
+ * starve readers.
+ *
+ * @param lock The SMP sequence lock control.
+ *
+ * @return The current sequence number.
+ */
+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;
+}
+
+/**
+ * @brief Ends an SMP sequence lock write operation.
+ *
+ * @param lock The SMP sequence lock control.
+ * @param seq The sequence number returned by _SMP_sequence_lock_Write_begin().
+ */
+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 );
+}
+
+/**
+ * @brief Begins an SMP sequence lock read operation.
+ *
+ * This function will not disable interrupts.
+ *
+ * @param lock The SMP sequence lock control.
+ *
+ * @return The current sequence number.
+ */
+static inline unsigned int _SMP_sequence_lock_Read_begin(
+  const SMP_sequence_lock_Control *lock
+)
+{
+  return _Atomic_Load_uint( &lock->sequence, ATOMIC_ORDER_ACQUIRE );
+}
+
+/**
+ * @brief Ends an SMP sequence lock read operation and indicates if a retry is
+ * necessary.
+ *
+ * @param lock The SMP sequence lock control.
+ * @param seq The sequence number returned by _SMP_sequence_lock_Read_begin().
+ *
+ * @retval true The read operation must be retried with a call to
+ *   _SMP_sequence_lock_Read_begin().
+ * @retval false Otherwise.
+ */
+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 */