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[经验分享] 【一起来玩RTOS系列】之RT-Thread 信号量作为锁用于临界区访问

发表于 2017-12-2 13:24:44 | 显示全部楼层 |阅读模式
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锁,单一的锁常应用于多个线程间对同一临界区的访问。信号量在作为锁来使用时,通常应将信号量资源实例初始化成1,代表系统默认有一个资源可用。当线程需要访问临界资源时,它需要先获得这个资源锁。当这个线程成功获得资源锁时,其他打算访问临界区的线程将被挂起在该信号量上,这是因为其他线程在试图获取这个锁时,这个锁已经被锁上(信号量值是0)。当获得信号量的线程处理完毕,退出临界区时,它将会释放信号量并把锁解开,而挂起在锁上的第一个等待线程将被唤醒从而获得临界区的访问权。

因为信号量的值始终在1和0之间变动,所以这类锁也叫做二值信号量,如图所示:

rt_binary_semaphore (1).png

接下来在机智云gokit开发板上创建和使用信号量作为锁实现资源的互斥访问,程序中创建初始值为1的信号量,三个相同优先级的线程等待获取信号量并使用同一个缓冲区,然后打印字符串。

  1. /**
  2.   ****************************************************
  3.   * File Name          : main.c
  4.   * Description        : Main program body
  5.   ****************************************************
  6.   ** This notice applies to any and all portions of this file
  7.   * that are not between comment pairs USER CODE BEGIN and
  8.   * USER CODE END. Other portions of this file, whether
  9.   * inserted by the user or by software development tools
  10.   * are owned by their respective copyright owners.
  11.   *
  12.   * COPYRIGHT(c) 2017 STMicroelectronics
  13.   *
  14.   * Redistribution and use in source and binary forms, with or without modification,
  15.   * are permitted provided that the following conditions are met:
  16.   *   1. Redistributions of source code must retain the above copyright notice,
  17.   *      this list of conditions and the following disclaimer.
  18.   *   2. Redistributions in binary form must reproduce the above copyright notice,
  19.   *      this list of conditions and the following disclaimer in the documentation
  20.   *      and/or other materials provided with the distribution.
  21.   *   3. Neither the name of STMicroelectronics nor the names of its contributors
  22.   *      may be used to endorse or promote products derived from this software
  23.   *      without specific prior written permission.
  24.   *
  25.   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  26.   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27.   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  28.   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  29.   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30.   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  31.   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  32.   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  33.   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  34.   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  35.   *
  36.   ****************************************************
  37.   */
  38. /* Includes ------------------------------------------------------------------*/
  39. #include "main.h"
  40. #include "STM32f1xx_hal.h"
  41. #include "usart.h"
  42. #include "gpio.h"

  43. /* USER CODE BEGIN Includes */
  44. #include "rtthread.h"
  45. #include "string.h"
  46. /* USER CODE END Includes */

  47. /* Private variables ---------------------------------------------------------*/

  48. /* USER CODE BEGIN PV */
  49. /* Private variables ---------------------------------------------------------*/

  50. /* USER CODE END PV */

  51. /* Private function prototypes -----------------------------------------------*/
  52. void SystemClock_Config(void);

  53. /* USER CODE BEGIN PFP */
  54. /* Private function prototypes -----------------------------------------------*/

  55. /* USER CODE END PFP */

  56. /* USER CODE BEGIN 0 */
  57. //重映射串口1到rt_kprintf
  58. void rt_hw_console_output(const char *str)
  59. {
  60.     /* empty console output */
  61.         char aa='\r';
  62.           rt_enter_critical();

  63.                 while(*str!='\0')
  64.                 {
  65.                         if(*str=='\n')
  66.                         {
  67.                                 HAL_UART_Transmit(&huart1, (uint8_t *)&aa, 1, 10);
  68.                         }
  69.                                 HAL_UART_Transmit(&huart1, (uint8_t *)(str++), 1, 10);
  70.                 }
  71.                
  72.                 rt_exit_critical();
  73. }

  74. void rt_hw_us_delay(int us)
  75. {
  76.     rt_uint32_t delta;

  77.     /* 获得延时经过的tick数 */
  78.     us = us * (SysTick->LOAD/(1000000/RT_TICK_PER_SECOND));

  79.     /* 获得当前时间 */
  80.     delta = SysTick->VAL;

  81.     /* 循环获得当前时间,直到达到指定的时间后退出循环 */
  82.     while (delta - SysTick->VAL< us);
  83. }

  84. void rt_hw_ms_delay(int ms)
  85. {
  86.         int i=0,j=0;
  87.         for(j=0;j<ms;j++)
  88.         {
  89.                 for (i=0;i<2;i++)
  90.                 rt_hw_us_delay(500);
  91.         }
  92. }

  93. /*
  94. * 程序清单:信号量作为锁实现资源互斥访问。
  95. *
  96. */

  97. /* 指向线程控制块的指针 */
  98. static rt_thread_t tid = RT_NULL;

  99. struct rt_semaphore sem;

  100. char str[11];
  101. /* 线程1入口 */
  102. void thread1_entry(void* parameter)
  103. {

  104.     while(1)
  105.     {
  106.                         rt_sem_take(&sem, RT_WAITING_FOREVER);
  107.                         strcpy(str,"gokit demo");
  108.                         rt_kprintf("thread1: %s\n",str);       
  109.                         rt_sem_release(&sem);                               
  110.     }

  111. }
  112. /* 线程2入口 */
  113. void thread2_entry(void* parameter)
  114. {

  115.     while(1)
  116.     {
  117.                         rt_sem_take(&sem, RT_WAITING_FOREVER);
  118.                         strcpy(str,"Gokit Demo");
  119.                         rt_kprintf("thread2: %s\n",str);       
  120.                         rt_sem_release(&sem);                               
  121.     }

  122. }
  123. /* 线程3入口 */
  124. void thread3_entry(void* parameter)
  125. {

  126.     while(1)
  127.     {
  128.                         rt_sem_take(&sem, RT_WAITING_FOREVER);
  129.                         strcpy(str,"GOKIT DEMO");
  130.                         rt_kprintf("thread3: %s\n",str);       
  131.                         rt_sem_release(&sem);       
  132.     }

  133. }
  134. /* USER CODE END 0 */

  135. int main(void)
  136. {

  137.   /* USER CODE BEGIN 1 */

  138.   /* USER CODE END 1 */

  139.   /* MCU Configuration----------------------------------------------------------*/

  140. //  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  141. //  HAL_Init();

  142. //  /* USER CODE BEGIN Init */

  143. //  /* USER CODE END Init */

  144. //  /* Configure the system clock */
  145. //  SystemClock_Config();

  146. //  /* USER CODE BEGIN SysInit */

  147. //  /* USER CODE END SysInit */

  148. //  /* Initialize all configured peripherals */
  149. //  MX_GPIO_Init();
  150. //  MX_USART1_UART_Init();

  151.   /* USER CODE BEGIN 2 */
  152.        
  153.         rt_sem_init(&sem, "sem",   1,    RT_IPC_FLAG_FIFO);//初始化信号量,初值为1

  154. /* 创建线程1 */
  155.     tid = rt_thread_create("thread1",
  156.         thread1_entry, /* 线程入口是thread_entry */
  157.         RT_NULL, /* 入口参数是RT_NULL */
  158.         512, //堆栈大小
  159.                                 2, //优先级
  160.                                 20);//时间片
  161.     if (tid != RT_NULL)
  162.         rt_thread_startup(tid);
  163.                
  164.                 /* 创建线程2 */
  165.     tid = rt_thread_create("thread2",
  166.         thread2_entry, /* 线程入口是thread_entry */
  167.         RT_NULL, /* 入口参数是RT_NULL */
  168.         512, //堆栈大小
  169.                                 2, //优先级
  170.                                 20);//时间片
  171.     if (tid != RT_NULL)
  172.         rt_thread_startup(tid);
  173.                
  174.                 /* 创建线程3 */
  175.     tid = rt_thread_create("thread3",
  176.         thread3_entry, /* 线程入口是thread_entry */
  177.         RT_NULL, /* 入口参数是RT_NULL */
  178.         512, //堆栈大小
  179.                                 2, //优先级
  180.                                 20);//时间片
  181.     if (tid != RT_NULL)
  182.         rt_thread_startup(tid);
  183.                
  184.         printf("\r\n机智云  只为智能硬件而生\r\n");
  185.         printf("Gizwits Smart Cloud for Smart Products\r\n");
  186.         printf("链接|增值|开放|中立|安全|自有|自由|生态\r\n");
  187.         printf("www.gizwits.com\r\n");
  188.         printf("\r\nGokit RT-Thread Demo\r\n\r\n");
  189.        
  190.         return 0;
  191.        
  192.        


  193.   /* USER CODE END 2 */

  194.   /* Infinite loop */
  195.   /* USER CODE BEGIN WHILE */
  196. //  while (1)
  197. //  {
  198.   /* USER CODE END WHILE */

  199.   /* USER CODE BEGIN 3 */
  200. //               
  201. //  }
  202.   /* USER CODE END 3 */

  203. }

  204. /** System Clock Configuration
  205. */
  206. void SystemClock_Config(void)
  207. {

  208.   RCC_OscInitTypeDef RCC_OscInitStruct;
  209.   RCC_ClkInitTypeDef RCC_ClkInitStruct;

  210.     /**Initializes the CPU, AHB and APB busses clocks
  211.     */
  212.   RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  213.   RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  214.   RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  215.   RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  216.   RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  217.   RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  218.   RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  219.   if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  220.   {
  221.     _Error_Handler(__FILE__, __LINE__);
  222.   }

  223.     /**Initializes the CPU, AHB and APB busses clocks
  224.     */
  225.   RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
  226.                               |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  227.   RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  228.   RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  229.   RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
  230.   RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  231.   if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  232.   {
  233.     _Error_Handler(__FILE__, __LINE__);
  234.   }

  235.     /**Configure the Systick interrupt time
  236.     */
  237.   HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);

  238.     /**Configure the Systick
  239.     */
  240.   HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

  241.   /* SysTick_IRQn interrupt configuration */
  242.   HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
  243. }

  244. /* USER CODE BEGIN 4 */

  245. /* USER CODE END 4 */

  246. /**
  247.   * @brief  This function is executed in case of error occurrence.
  248.   * @param  None
  249.   * @retval None
  250.   */
  251. void _Error_Handler(char * file, int line)
  252. {
  253.   /* USER CODE BEGIN Error_Handler_Debug */
  254.   /* User can add his own implementation to report the HAL error return state */
  255.   while(1)
  256.   {
  257.   }
  258.   /* USER CODE END Error_Handler_Debug */
  259. }

  260. #ifdef USE_FULL_ASSERT

  261. /**
  262.    * @brief Reports the name of the source file and the source line number
  263.    * where the assert_param error has occurred.
  264.    * @param file: pointer to the source file name
  265.    * @param line: assert_param error line source number
  266.    * @retval None
  267.    */
  268. void assert_failed(uint8_t* file, uint32_t line)
  269. {
  270.   /* USER CODE BEGIN 6 */
  271.   /* User can add his own implementation to report the file name and line number,
  272.     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  273.   /* USER CODE END 6 */

  274. }

  275. #endif

  276. /**
  277.   * @}
  278.   */

  279. /**
  280.   * @}
  281. */

  282. /**************** (C) COPYRIGHT STMicroelectronics ****END OF FILE***/
复制代码

串口打印信息如下:
搜狗截图20171202131842.png

源码下载:
Gokit_RT-Thread.zip (8.7 MB, 下载次数: 0, 售价: 1 金钱)
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