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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:
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。
- /**
- ****************************************************
- * File Name : main.c
- * Description : Main program body
- ****************************************************
- ** This notice applies to any and all portions of this file
- * that are not between comment pairs USER CODE BEGIN and
- * USER CODE END. Other portions of this file, whether
- * inserted by the user or by software development tools
- * are owned by their respective copyright owners.
- *
- * COPYRIGHT(c) 2017 STMicroelectronics
- *
- * Redistribution and use in source and binary forms, with or without modification,
- * are permitted provided that the following conditions are met:
- * 1. Redistributions of source code must retain the above copyright notice,
- * this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright notice,
- * this list of conditions and the following disclaimer in the documentation
- * and/or other materials provided with the distribution.
- * 3. Neither the name of STMicroelectronics nor the names of its contributors
- * may be used to endorse or promote products derived from this software
- * without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
- * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
- * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
- * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- ****************************************************
- */
- /* Includes ------------------------------------------------------------------*/
- #include "main.h"
- #include "STM32f1xx_hal.h"
- #include "usart.h"
- #include "gpio.h"
- /* USER CODE BEGIN Includes */
- #include "rtthread.h"
- #include "string.h"
- /* USER CODE END Includes */
- /* Private variables ---------------------------------------------------------*/
- /* USER CODE BEGIN PV */
- /* Private variables ---------------------------------------------------------*/
- /* USER CODE END PV */
- /* Private function prototypes -----------------------------------------------*/
- void SystemClock_Config(void);
- /* USER CODE BEGIN PFP */
- /* Private function prototypes -----------------------------------------------*/
- /* USER CODE END PFP */
- /* USER CODE BEGIN 0 */
- //重映射串口1到rt_kprintf
- void rt_hw_console_output(const char *str)
- {
- /* empty console output */
- char aa='\r';
- rt_enter_critical();
- while(*str!='\0')
- {
- if(*str=='\n')
- {
- HAL_UART_Transmit(&huart1, (uint8_t *)&aa, 1, 10);
- }
- HAL_UART_Transmit(&huart1, (uint8_t *)(str++), 1, 10);
- }
-
- rt_exit_critical();
- }
- void rt_hw_us_delay(int us)
- {
- rt_uint32_t delta;
- /* 获得延时经过的tick数 */
- us = us * (SysTick->LOAD/(1000000/RT_TICK_PER_SECOND));
- /* 获得当前时间 */
- delta = SysTick->VAL;
- /* 循环获得当前时间,直到达到指定的时间后退出循环 */
- while (delta - SysTick->VAL< us);
- }
- void rt_hw_ms_delay(int ms)
- {
- int i=0,j=0;
- for(j=0;j<ms;j++)
- {
- for (i=0;i<2;i++)
- rt_hw_us_delay(500);
- }
- }
- /*
- * 程序清单:信号量作为锁实现资源互斥访问。
- *
- */
- /* 指向线程控制块的指针 */
- static rt_thread_t tid = RT_NULL;
- struct rt_semaphore sem;
- char str[11];
- /* 线程1入口 */
- void thread1_entry(void* parameter)
- {
- while(1)
- {
- rt_sem_take(&sem, RT_WAITING_FOREVER);
- strcpy(str,"gokit demo");
- rt_kprintf("thread1: %s\n",str);
- rt_sem_release(&sem);
- }
- }
- /* 线程2入口 */
- void thread2_entry(void* parameter)
- {
- while(1)
- {
- rt_sem_take(&sem, RT_WAITING_FOREVER);
- strcpy(str,"Gokit Demo");
- rt_kprintf("thread2: %s\n",str);
- rt_sem_release(&sem);
- }
- }
- /* 线程3入口 */
- void thread3_entry(void* parameter)
- {
- while(1)
- {
- rt_sem_take(&sem, RT_WAITING_FOREVER);
- strcpy(str,"GOKIT DEMO");
- rt_kprintf("thread3: %s\n",str);
- rt_sem_release(&sem);
- }
- }
- /* USER CODE END 0 */
- int main(void)
- {
- /* USER CODE BEGIN 1 */
- /* USER CODE END 1 */
- /* MCU Configuration----------------------------------------------------------*/
- // /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
- // HAL_Init();
- // /* USER CODE BEGIN Init */
- // /* USER CODE END Init */
- // /* Configure the system clock */
- // SystemClock_Config();
- // /* USER CODE BEGIN SysInit */
- // /* USER CODE END SysInit */
- // /* Initialize all configured peripherals */
- // MX_GPIO_Init();
- // MX_USART1_UART_Init();
- /* USER CODE BEGIN 2 */
-
- rt_sem_init(&sem, "sem", 1, RT_IPC_FLAG_FIFO);//初始化信号量,初值为1
- /* 创建线程1 */
- tid = rt_thread_create("thread1",
- thread1_entry, /* 线程入口是thread_entry */
- RT_NULL, /* 入口参数是RT_NULL */
- 512, //堆栈大小
- 2, //优先级
- 20);//时间片
- if (tid != RT_NULL)
- rt_thread_startup(tid);
-
- /* 创建线程2 */
- tid = rt_thread_create("thread2",
- thread2_entry, /* 线程入口是thread_entry */
- RT_NULL, /* 入口参数是RT_NULL */
- 512, //堆栈大小
- 2, //优先级
- 20);//时间片
- if (tid != RT_NULL)
- rt_thread_startup(tid);
-
- /* 创建线程3 */
- tid = rt_thread_create("thread3",
- thread3_entry, /* 线程入口是thread_entry */
- RT_NULL, /* 入口参数是RT_NULL */
- 512, //堆栈大小
- 2, //优先级
- 20);//时间片
- if (tid != RT_NULL)
- rt_thread_startup(tid);
-
- printf("\r\n机智云 只为智能硬件而生\r\n");
- printf("Gizwits Smart Cloud for Smart Products\r\n");
- printf("链接|增值|开放|中立|安全|自有|自由|生态\r\n");
- printf("www.gizwits.com\r\n");
- printf("\r\nGokit RT-Thread Demo\r\n\r\n");
-
- return 0;
-
-
- /* USER CODE END 2 */
- /* Infinite loop */
- /* USER CODE BEGIN WHILE */
- // while (1)
- // {
- /* USER CODE END WHILE */
- /* USER CODE BEGIN 3 */
- //
- // }
- /* USER CODE END 3 */
- }
- /** System Clock Configuration
- */
- void SystemClock_Config(void)
- {
- RCC_OscInitTypeDef RCC_OscInitStruct;
- RCC_ClkInitTypeDef RCC_ClkInitStruct;
- /**Initializes the CPU, AHB and APB busses clocks
- */
- RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
- RCC_OscInitStruct.HSEState = RCC_HSE_ON;
- RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
- RCC_OscInitStruct.HSIState = RCC_HSI_ON;
- RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
- RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
- RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
- if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
- {
- _Error_Handler(__FILE__, __LINE__);
- }
- /**Initializes the CPU, AHB and APB busses clocks
- */
- RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
- |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
- RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
- RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
- RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
- RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
- if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
- {
- _Error_Handler(__FILE__, __LINE__);
- }
- /**Configure the Systick interrupt time
- */
- HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
- /**Configure the Systick
- */
- HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
- /* SysTick_IRQn interrupt configuration */
- HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
- }
- /* USER CODE BEGIN 4 */
- /* USER CODE END 4 */
- /**
- * @brief This function is executed in case of error occurrence.
- * @param None
- * @retval None
- */
- void _Error_Handler(char * file, int line)
- {
- /* USER CODE BEGIN Error_Handler_Debug */
- /* User can add his own implementation to report the HAL error return state */
- while(1)
- {
- }
- /* USER CODE END Error_Handler_Debug */
- }
- #ifdef USE_FULL_ASSERT
- /**
- * @brief Reports the name of the source file and the source line number
- * where the assert_param error has occurred.
- * @param file: pointer to the source file name
- * @param line: assert_param error line source number
- * @retval None
- */
- void assert_failed(uint8_t* file, uint32_t line)
- {
- /* USER CODE BEGIN 6 */
- /* User can add his own implementation to report the file name and line number,
- ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
- /* USER CODE END 6 */
- }
- #endif
- /**
- * @}
- */
- /**
- * @}
- */
- /**************** (C) COPYRIGHT STMicroelectronics ****END OF FILE***/
复制代码
串口打印信息如下:
源码下载:
Gokit_RT-Thread.zip
(8.7 MB, 下载次数: 1, 售价: 1 金钱)
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