misc/rwlock:Implementing read/write locks.

A new locking mechanism: read/write locks
When there is a writer it is not possible to put on a read lock or a write lock; when there is a reader it is possible to reenter the read lock but not the write lock.
Writers are exclusive locks, readers are shared locks.
At the same time through the waiter count to determine whether there is currently a blocked task, if there is then in the unlock time to wake up all the waiter, through the priority of the competition to complete the blocked lock execution.
For example:
When we have a reader blocking two waiter writers, when the reader is unlocked it wakes up both writers. The writer with higher priority wakes up and checks for a successful condition and locks the lock, the second writer wakes up and fails to check for a condition and continues to block the lock.

Signed-off-by: chenrun1 <chenrun1@xiaomi.com>

include/nuttx/rwsem.h

@@ -0,0 +1,162 @@
+/****************************************************************************
+ * include/nuttx/rwsem.h
+ *
+ * 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_RWSEM_H
+#define __INCLUDE_NUTTX_RWSEM_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/mutex.h>
+
+/****************************************************************************
+ * Public Type Definitions
+ ****************************************************************************/
+
+typedef struct
+{
+  mutex_t protected; /* Protecting Locks for Read/Write Locked Tables */
+  sem_t   waiting;   /* Reader/writer Waiting queue */
+  int     waiter;    /* Waiter Count */
+  int     writer;    /* Writer Count */
+  int     reader;    /* Reader Count */
+} rw_semaphore_t;
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: down_read_trylock
+ *
+ * Description:
+ *   Acquire a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   Return 1 if successful, 0 if failed
+ *
+ ****************************************************************************/
+
+int down_read_trylock(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: down_read
+ *
+ * Description:
+ *   Acquire a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void down_read(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: up_read
+ *
+ * Description:
+ *   Unlock a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void up_read(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: down_write_trylock
+ *
+ * Description:
+ *   Acquire a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   Return 1 if successful, 0 if failed
+ *
+ ****************************************************************************/
+
+int down_write_trylock(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: down_write
+ *
+ * Description:
+ *   Acquire a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void down_write(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: up_write
+ *
+ * Description:
+ *   Unlock a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void up_write(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: init_rwsem
+ *
+ * Description:
+ *   Initialize a read-write-lock object, setting its initial state.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   It follows the NuttX internal error return policy: Zero (OK) is
+ *   returned on success. A negated errno value is returned on failure.
+ *
+ ****************************************************************************/
+
+int init_rwsem(FAR rw_semaphore_t *rwsem);
+
+/****************************************************************************
+ * Name: destroy_rwsem
+ *
+ * Description:
+ *   Destroy a read-write-lock object, freeing any resources associated with
+ *   it.
+ *
+ * Input Parameters:
+ *   rwsem - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void destroy_rwsem(FAR rw_semaphore_t *rwsem);
+
+#endif  /* __INCLUDE_NUTTX_RWSEM_H */

sched/semaphore/Make.defs

@@ -22,7 +22,7 @@
 
 CSRCS += sem_destroy.c sem_wait.c sem_trywait.c sem_tickwait.c
 CSRCS += sem_timedwait.c sem_clockwait.c sem_timeout.c sem_post.c
-CSRCS += sem_recover.c sem_reset.c sem_waitirq.c
+CSRCS += sem_recover.c sem_reset.c sem_waitirq.c sem_rw.c
 
 ifeq ($(CONFIG_PRIORITY_INHERITANCE),y)
 CSRCS += sem_initialize.c sem_holder.c sem_setprotocol.c

sched/semaphore/sem_rw.c

@@ -0,0 +1,297 @@
+/****************************************************************************
+ * sched/semaphore/sem_rw.c
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/rwsem.h>
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static inline void up_wait(FAR rw_semaphore_t *rwsem)
+{
+  int i;
+
+  for (i = 0; i < rwsem->waiter; i++)
+    {
+      /* If there are some waiter for unlock, then post the lock wait queue.
+       */
+
+      nxsem_post(&rwsem->waiting);
+    }
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: down_read_trylock
+ *
+ * Description:
+ *   Acquire a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   Return 1 if successful, 0 if failed
+ *
+ ****************************************************************************/
+
+int down_read_trylock(FAR rw_semaphore_t *rwsem)
+{
+  nxmutex_lock(&rwsem->protected);
+
+  if (rwsem->writer > 0)
+    {
+      nxmutex_unlock(&rwsem->protected);
+      return 0;
+    }
+
+  /* In a scenario where there is no write lock, we just need to make the
+   * read base +1.
+   */
+
+  rwsem->reader++;
+
+  nxmutex_unlock(&rwsem->protected);
+
+  return 1;
+}
+
+/****************************************************************************
+ * Name: down_read
+ *
+ * Description:
+ *   Acquire a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void down_read(FAR rw_semaphore_t *rwsem)
+{
+  /* we have to check if there is a write-lock scenario, if there is then we
+   * block and wait for the write-lock to be unlocked.
+   */
+
+  nxmutex_lock(&rwsem->protected);
+
+  while (rwsem->writer > 0)
+    {
+      rwsem->waiter++;
+      nxmutex_unlock(&rwsem->protected);
+      nxsem_wait(&rwsem->waiting);
+      nxmutex_lock(&rwsem->protected);
+      rwsem->waiter--;
+    }
+
+  /* In a scenario where there is no write lock, we just need to make the
+   * read base +1.
+   */
+
+  rwsem->reader++;
+
+  nxmutex_unlock(&rwsem->protected);
+}
+
+/****************************************************************************
+ * Name: up_read
+ *
+ * Description:
+ *   Unlock a read lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void up_read(FAR rw_semaphore_t *rwsem)
+{
+  nxmutex_lock(&rwsem->protected);
+
+  DEBUGASSERT(rwsem->reader > 0);
+
+  rwsem->reader--;
+
+  if (rwsem->waiter > 0)
+    {
+      up_wait(rwsem);
+    }
+
+  nxmutex_unlock(&rwsem->protected);
+}
+
+/****************************************************************************
+ * Name: down_write_trylock
+ *
+ * Description:
+ *   Acquire a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   Return 1 if successful, 0 if failed
+ *
+ ****************************************************************************/
+
+int down_write_trylock(FAR rw_semaphore_t *rwsem)
+{
+  nxmutex_lock(&rwsem->protected);
+
+  if (rwsem->writer > 0 || rwsem->reader > 0)
+    {
+      nxmutex_unlock(&rwsem->protected);
+      return 0;
+    }
+
+  /* The check passes, then we just need the writer reference + 1 */
+
+  rwsem->writer++;
+
+  nxmutex_unlock(&rwsem->protected);
+
+  return 1;
+}
+
+/****************************************************************************
+ * Name: down_write
+ *
+ * Description:
+ *   Acquire a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void down_write(FAR rw_semaphore_t *rwsem)
+{
+  nxmutex_lock(&rwsem->protected);
+
+  while (rwsem->reader > 0 || rwsem->writer > 0)
+    {
+      rwsem->waiter++;
+      nxmutex_unlock(&rwsem->protected);
+      nxsem_wait(&rwsem->waiting);
+      nxmutex_lock(&rwsem->protected);
+      rwsem->waiter--;
+    }
+
+  /* The check passes, then we just need the writer reference + 1 */
+
+  rwsem->writer++;
+
+  nxmutex_unlock(&rwsem->protected);
+}
+
+/****************************************************************************
+ * Name: up_write
+ *
+ * Description:
+ *   Unlock a write lock on a read-write-lock object.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void up_write(FAR rw_semaphore_t *rwsem)
+{
+  nxmutex_lock(&rwsem->protected);
+
+  DEBUGASSERT(rwsem->writer > 0);
+
+  rwsem->writer--;
+
+  up_wait(rwsem);
+
+  nxmutex_unlock(&rwsem->protected);
+}
+
+/****************************************************************************
+ * Name: init_rwsem
+ *
+ * Description:
+ *   Initialize a read-write-lock object, setting its initial state.
+ *
+ * Input Parameters:
+ *   rwsem  - Pointer to the read-write-lock descriptor.
+ *
+ * Returned Value:
+ *   It follows the NuttX internal error return policy: Zero (OK) is
+ *   returned on success. A negated errno value is returned on failure.
+ *
+ ****************************************************************************/
+
+int init_rwsem(FAR rw_semaphore_t *rwsem)
+{
+  int ret;
+
+  /* Initialize structure information */
+
+  ret = nxmutex_init(&rwsem->protected);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  ret = nxsem_init(&rwsem->waiting, 0, 0);
+  if (ret < 0)
+    {
+      nxmutex_destroy(&rwsem->protected);
+      return ret;
+    }
+
+  rwsem->reader = 0;
+  rwsem->writer = 0;
+  rwsem->waiter = 0;
+
+  return OK;
+}
+
+/****************************************************************************
+ * Name: destroy_rwsem
+ *
+ * Description:
+ *   Destroy a read-write-lock object, freeing any resources associated with
+ *   it.
+ *
+ * Input Parameters:
+ *   rwsem - Pointer to the read-write-lock descriptor.
+ *
+ ****************************************************************************/
+
+void destroy_rwsem(FAR rw_semaphore_t *rwsem)
+{
+  /* Need to check if there is still an unlocked or waiting state */
+
+  DEBUGASSERT(rwsem->waiter == 0 && rwsem->reader == 0 &&
+              rwsem->writer == 0);
+
+  nxmutex_destroy(&rwsem->protected);
+  nxsem_destroy(&rwsem->waiting);
+}