nuttx: add seqlock.h

This commit added seqlock.h.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

include/nuttx/seqlock.h

@@ -0,0 +1,189 @@
+/****************************************************************************
+ * include/nuttx/seqlock.h
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __INCLUDE_NUTTX_SEQLOCK_H
+#define __INCLUDE_NUTTX_SEQLOCK_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/spinlock.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+ #define SEQLOCK_INITIALIZER {0, SP_UNLOCKED}
+
+/****************************************************************************
+ * Public Data Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Sequence counters (seqcount_t)
+ ****************************************************************************/
+
+typedef struct seqclock
+{
+  volatile unsigned int sequence;
+  spinlock_t lock;
+} seqcount_t;
+
+#undef EXTERN
+#if defined(__cplusplus)
+#define EXTERN extern "C"
+extern "C"
+{
+#else
+#define EXTERN extern
+#endif
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: seqlock_init
+ *
+ * Description:
+ *   init seqlock
+ *
+ * Input Parameters:
+ *   seqcount_t
+ *
+ * Returned Value:
+ *   None
+ *
+ ****************************************************************************/
+
+static inline_function void seqlock_init(FAR seqcount_t *s)
+{
+  s->sequence = 0;
+  spin_lock_init(&s->lock);
+}
+
+/****************************************************************************
+ * Name: read_seqbegin
+ *
+ * Description:
+ *   This is a primitive counting synchronization mechanism
+ *   that enables lock-free reading.
+ *
+ * Input Parameters:
+ *   seqcount_t
+ *
+ * Returned Value:
+ *   seq - Used to determine whether the state has changed during reading.
+ *
+ ****************************************************************************/
+
+static inline_function
+unsigned int read_seqbegin(FAR const seqcount_t *s)
+{
+  unsigned int seq;
+
+  while ((seq = s->sequence) & 1);
+
+  UP_DMB();
+  return seq;
+}
+
+/****************************************************************************
+ * Name: read_seqretry
+ *
+ * Description:
+ *   This is a primitive counting synchronization mechanism
+ *   that enables lock-free reading.
+ *
+ * Input Parameters:
+ *   seqcount_t
+ *   start - Used to determine whether the state has changed during reading.
+ *
+ * Returned Value:
+ *   0 indicate need retry
+ *
+ ****************************************************************************/
+
+static inline_function
+unsigned int read_seqretry(FAR const seqcount_t *s, unsigned int start)
+{
+  unsigned int seq;
+
+  UP_DMB();
+  seq = s->sequence;
+  return seq != start;
+}
+
+/****************************************************************************
+ * Name: write_seqlock_irqsave
+ *
+ * Description:
+ *   This is a primitive counting synchronization mechanism
+ *   that enables lock-free reading. write need spinlock to protect
+ *
+ * Input Parameters:
+ *   seqcount_t
+ *
+ * Returned Value:
+ *   irqstate
+ *
+ ****************************************************************************/
+
+static inline_function
+irqstate_t write_seqlock_irqsave(FAR seqcount_t *s)
+{
+  irqstate_t flags = spin_lock_irqsave(&s->lock);
+
+  s->sequence++;
+  return flags;
+}
+
+/****************************************************************************
+ * Name: write_sequnlock_irqrestore
+ *
+ * Description:
+ *   This is a primitive counting synchronization mechanism
+ *   that enables lock-free reading. write need spinlock to protect
+ *
+ * Input Parameters:
+ *   seqcount_t
+ *   irqstate_t - irqstate used to restore
+ *
+ * Returned Value:
+ *   None
+ *
+ ****************************************************************************/
+
+static inline_function
+void write_sequnlock_irqrestore(seqcount_t *s, irqstate_t flags)
+{
+  s->sequence++;
+  spin_unlock_irqrestore(&s->lock, flags);
+}
+
+#undef EXTERN
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* __INCLUDE_NUTTX_SEQLOCK_H */