sched/semaphore: add support to customize semaphore max allowed value

Curernt implementation default semaphore max allowed value to SEM_VALUE_MAX.
  In some cases, user may want to change this, so provide a function to do this: sem_setmaxvalue

Signed-off-by: Chengdong Wang <wangchengdong@lixiang.com>

Documentation/reference/user/05_counting_semaphore.rst

@@ -108,6 +108,11 @@ result.
 Semaphore does not support priority inheritance by default. If you need to
 use a semaphore as a mutex you need to change its default behavior.
 
+Each semaphore is assigned a default maximum value defined by SEM_VALUE_MAX.
+If ``CONFIG_CUSTOM_SEMAPHORE_MAXVALUE`` is enabled, applications may override this limit.
+In such cases, the function ``nxsem_setmaxvalue()`` can be used to specify a custom maximum value
+for an individual semaphore.
+
 In user space, it is recommended to use pthread_mutex instead of
 semaphore for resource protection
 

include/nuttx/semaphore.h

@@ -412,6 +412,27 @@ int nxsem_post_slow(FAR sem_t *sem);
 
 int nxsem_get_value(FAR sem_t *sem, FAR int *sval);
 
+#ifdef CONFIG_CUSTOM_SEMAPHORE_MAXVALUE
+/****************************************************************************
+ * Name:  nxsem_setmaxvalue
+ *
+ * Description:
+ *   This function sets the maximum allowed value for a specific semaphore.
+ *
+ * Input Parameters:
+ *   sem - Semaphore descriptor
+ *   maxvalue - The maximum allowed value
+ *
+ * Returned Value:
+ *   This is an internal OS interface and should not be used by applications.
+ *   It follows the NuttX internal error return policy:  Zero (OK) is
+ *   returned on success.  A negated errno value is returned on failure.
+ *
+ ****************************************************************************/
+
+int nxsem_setmaxvalue(FAR sem_t *sem, int32_t maxvalue);
+#endif
+
 /****************************************************************************
  * Name: nxsem_open
  *

include/semaphore.h

@@ -123,6 +123,10 @@ struct sem_s
 
   dq_queue_t waitlist;
 
+#ifdef CONFIG_CUSTOM_SEMAPHORE_MAXVALUE
+  int32_t maxvalue;
+#endif
+
 #ifdef CONFIG_PRIORITY_INHERITANCE
 #  if CONFIG_SEM_PREALLOCHOLDERS > 0
   FAR struct semholder_s *hhead; /* List of holders of semaphore counts */

libs/libc/semaphore/CMakeLists.txt

@@ -36,6 +36,10 @@ if(CONFIG_FS_NAMED_SEMAPHORES)
   list(APPEND SRCS sem_open.c sem_close.c sem_unlink.c)
 endif()
 
+if(CONFIG_CUSTOM_SEMAPHORE_MAXVALUE)
+  list(APPEND SRCS sem_setmaxvalue.c)
+endif()
+
 if(CONFIG_PRIORITY_PROTECT)
   list(APPEND SRCS sem_getprioceiling.c sem_setprioceiling.c)
 endif()

libs/libc/semaphore/Make.defs

@@ -30,6 +30,10 @@ ifeq ($(CONFIG_FS_NAMED_SEMAPHORES),y)
 CSRCS += sem_open.c sem_close.c sem_unlink.c
 endif
 
+ifeq ($(CONFIG_CUSTOM_SEMAPHORE_MAXVALUE),y)
+CSRCS += sem_setmaxvalue.c
+endif
+
 ifeq ($(CONFIG_PRIORITY_PROTECT),y)
 CSRCS += sem_getprioceiling.c sem_setprioceiling.c
 endif

libs/libc/semaphore/sem_init.c

@@ -72,6 +72,10 @@ int nxsem_init(FAR sem_t *sem, int pshared, int32_t value)
 
   sem->val.semcount = (int32_t)value;
 
+#ifdef CONFIG_CUSTOM_SEMAPHORE_MAXVALUE
+  sem->maxvalue = SEM_VALUE_MAX;
+#endif
+
   /* Initialize semaphore wait list */
 
   dq_init(&sem->waitlist);

libs/libc/semaphore/sem_setmaxvalue.c

@@ -0,0 +1,66 @@
+/****************************************************************************
+ * libs/libc/semaphore/sem_setmaxvalue.c
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/trace.h>
+
+#include <nuttx/semaphore.h>
+
+#ifdef CONFIG_CUSTOM_SEMAPHORE_MAXVALUE
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: nxsem_setmaxvalue
+ *
+ * Description:
+ *  Set sem max allowed value
+ *
+ * Input Parameters:
+ *   sem     - Semaphore object
+ *   delay   - Max allowed semaphore value.
+ *
+ * Returned Value:
+ *   This is an internal OS interface and should not be used by applications.
+ *   It follows the NuttX internal error return policy:  Zero (OK) is
+ *   returned on success.  A negated errno value is returned on failure.
+ *
+ ****************************************************************************/
+
+int nxsem_setmaxvalue(FAR sem_t *sem, int32_t maxvalue)
+{
+  if (sem != NULL)
+    {
+      sem->maxvalue = maxvalue;
+      return OK;
+    }
+
+  return -EINVAL;
+}
+
+#endif /* CONFIG_PRIORITY_INHERITANCE */

sched/Kconfig

@@ -2027,3 +2027,10 @@ config COREDUMP
 		The memory state embeds a snapshot of all segments mapped in the
 		memory space of the program. The CPU state contains register values
 		when the core dump has been generated.
+
+config CUSTOM_SEMAPHORE_MAXVALUE
+	bool "Custom max value for semaphores"
+	default n
+	---help---
+		Enable to support custom max value for semaphores.
+		When this option is enabled, the max value of a semaphore can be set

sched/semaphore/sem_post.c

@@ -125,7 +125,11 @@ int nxsem_post_slow(FAR sem_t *sem)
       sem_count = atomic_read(NXSEM_COUNT(sem));
       do
         {
+#ifdef CONFIG_CUSTOM_SEMAPHORE_MAXVALUE
+          if (sem_count >= sem->maxvalue)
+#else
           if (sem_count >= SEM_VALUE_MAX)
+#endif
             {
               leave_critical_section(flags);
               return -EOVERFLOW;