【一起来玩RTOS系列】之RT-Thread 通过调度锁保护代码

bigfanofloT · 发表于 2017-11-25 13:27:58

调度器锁

同中断锁一样把调度器锁住也能让当前运行的任务不被换出，直到调度器解锁。但和中断锁有一点不相同的是，对调度器上锁，系统依然能响应外部中断，中断服务例程依然能进行相应的响应。所以在使用调度器上锁的方式进行任务同步时，需要考虑好任务访问的临界资源是否会被中断服务例程所修改，如果可能会被修改，那么将不适合采用此种方式进行同步。RT-Thread提供的调度锁操作API为：

void rt_enter_critical(void); /* 进入临界区*/

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调用这个函数后，调度器将被上锁。在锁住调度器期间，系统依然响应中断，如果中断唤醒了更高优先级的线程，调度器并不会立刻执行它，直到调用解锁调度器函数时才会尝试进行下一次调度。

void rt_exit_critical(void); /* 退出临界区*/

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当系统退出临界区的时候，系统会计算当前是否有更高优先级的线程就绪，如果有比当前线程更高优先级的线程就绪，将切换到这个高优先级线程中执行；如果无更高优先级线程就绪，将继续执行当前任务。

注： rt_enter_critical/rt_exit_critical可以多次嵌套调用，但每调用一次rt_enter_critical就必须相对应地调用一次rt_exit_critical退出操作，嵌套的最大深度是65535。

使用场合

调度器锁能够方便地使用于一些线程与线程间同步的场合，由于轻型，它不会对系统中断响应造成负担；但它的缺陷也很明显，就是它不能被用于中断与线程间的同步或通知，并且如果执行调度器锁的时间过长，会对系统的实时性造成影响（因为使用了调度器锁后，系统将不再具备优先级的关系，直到它脱离了调度器锁的状态）。

下面在机智云 gokit上验证如何通过调度锁保护代码，程序创建2个不同优先级的线程，线程1的优先级比线程2高，低优先级线程会执行一段耗时比较长的代码：
(1)若不启用调度锁，即注释掉rt_enter_critical和rt_exit_critical这2行代码，则会发现线程2会被线程1打断，字符串被修改为gokit demo而不是期望打印的Gokit Demo，说明线程2被线程1打断;
(2)若启用调度锁，即不注释掉rt_enter_critical和rt_exit_critical这2行代码，则会发现线程2打印的是期望的Gokit Demo，说明线程2没有被线程1打断，调度锁起到了保护临界代码的作用；

/**
****************************************************
* 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：通过调度锁保护临界区代码
*线程1的优先级比线程2高，低优先级线程会执行一段耗时比较长的代码；
*(1)若不启用调度锁，即注释掉rt_enter_critical和rt_exit_critical这2行代码，
*则会发现线程2会被线程1打断，字符串被修改为gokit demo而不是期望打印的Gokit Demo，说明线程2被线程1打断;
*(2)若启用调度锁，即不注释掉rt_enter_critical和rt_exit_critical这2行代码，
*则会发现线程2打印的是期望的Gokit Demo，说明线程2没有被线程1打断，调度锁起到了保护临界代码的作用；
*/
/* 指向线程控制块的指针 */
static rt_thread_t tid1 = RT_NULL;
static rt_thread_t tid2 = RT_NULL;
char str[]="GOKIT DEMO";
/* 线程1入口 */
static void thread1_entry(void* parameter)
{
/* 高优先级线程1开始运行，会修改str内容 */
while(1)
{
strcpy(str,"gokit demo");
rt_kprintf("thread1: %s\n",str);
rt_thread_delay(1000);
}
}
/* 线程2入口 */
static void thread2_entry(void* parameter)
{
/* 调度器上锁，上锁后，将不再切换到其他线程，仅响应中断 */
rt_enter_critical();
strcpy(str,"Gokit Demo");
/*低优先级线程2执行耗时有点长的代码*/
rt_hw_ms_delay(4000);
rt_kprintf("thread2: %s\n",str);
/* 调度器解锁 */
rt_exit_critical();
}
/* 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 */
/* 创建线程1 */
tid1 = rt_thread_create("t1",
thread1_entry,
RT_NULL,
512,
2,
20);
if (tid1 != RT_NULL)
rt_thread_startup(tid1);
/* 创建线程2 */
tid2 = rt_thread_create("t2",
thread2_entry,
RT_NULL,
512,
3,
20);
if (tid2 != RT_NULL)
rt_thread_startup(tid2);
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***/

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源码下载：

Gokit_RT-Thread.zip (8.7 MB, 下载次数: 2, 售价: 1 金钱)