【一起来玩RTOS系列】之RT-Thread 信号量用于线程同步
信号量
信号量是一种轻型的用于解决线程间同步问题的内核对象，线程可以获取或释放它，从而达到同步或互斥的目的。信号量就像一把钥匙，把一段临界区给锁住，只允许有钥匙的线程进行访问：线程拿到了钥匙，才允许它进入临界区；而离开后把钥匙传递给排队在后面的等待线程，让后续线程依次进入临界区。
信号量工作示意图如图 信号量工作示意图 所示，每个信号量对象都有一个信号量值和一个线程等待队列，信号量的值对应了信号量对象的实例数目、资源数目，假如信号量值为5，则表示共有5个信号量实例（资源）可以被使用，当信号量实例数目为零时，再申请该信号量的线程就会被挂起在该信号量的等待队列上，等待可用的信号量实例（资源）。
RT-Thread信号量相关接口
初始化信号量
对于静态信号量对象，它的内存空间在编译时期就被编译器分配出来，放在数据段或ZI段上，此时使用信号量就不再需要使用rt_sem_create接口来创建它，而只需在使用前对它进行初始化即可。初始化信号量对象可使用下面的函数接口：
rt_err_t rt_sem_init (rt_sem_t sem, const char* name, rt_uint32_t value, rt_uint8_t flag);
当调用这个函数时，系统将对这个semaphore对象进行初始化，然后初始化IPC对象以及与semaphore相关的部分。在初始化信号量指定的参数中，信号量标志参数决定了当信号量不可用时，多个线程等待的方式。当选择FIFO方式时，那么等待线程队列将按照先进先出的方式排队，先进入的线程将先获得等待的信号量；当选择PRIO（优先级等待）方式时，等待线程队列将按照优先级进行排队，优先级高的等待线程将先获得等待的信号量。
参数描述
sem信号量对象的句柄；
name信号量名称；
value信号量初始值；
flag信号量标志。
#define RT_IPC_FLAG_FIFO 0x00 /* IPC参数采用FIFO方式*/
#define RT_IPC_FLAG_PRIO 0x01 /* IPC参数采用优先级方式*/
函数返回
RT_EOK
获取信号量
线程通过获取信号量来获得信号量资源实例，当信号量值大于零时，线程将获得信号量，并且相应的信号量值都会减1，获取信号量使用下面的函数接口：
rt_err_t rt_sem_take (rt_sem_t sem, rt_int32_t time);
在调用这个函数时，如果信号量的值等于零，那么说明当前信号量资源实例不可用，申请该信号量的线程将根据time参数的情况选择直接返回、或挂起等待一段时间、或永久等待，直到其他线程或中断释放该信号量。如果在参数time指定的时间内依然得不到信号量，线程将超时返回，返回值是-RT_ETIMEOUT。
函数参数
参数描述
sem信号量对象的句柄；
time指定的等待时间，单位是操作系统时钟节拍（OS Tick）。
函数返回
成功获得信号量返回RT_EOK；超时依然未获得信号量返回-RT_ETIMEOUT；其他错误返回-RT_ERROR。
无等待获取信号量
当用户不想在申请的信号量上挂起线程进行等待时，可以使用无等待方式获取信号量，无等待获取信号量使用下面的函数接口：
rt_err_t rt_sem_trytake(rt_sem_t sem);
这个函数与rt_sem_take(sem, 0) 的作用相同，即当线程申请的信号量资源实例不可用的时候，它不会等待在该信号量上，而是直接返回-RT_ETIMEOUT。
函数参数
参数描述
sem信号量对象的句柄。
函数返回
成功获取信号量返回RT_EOK；否则返回RT_ETIMEOUT。
释放信号量
当线程完成资源的访问后，应尽快释放它持有的信号量，使得其他线程能获得该信号量。释放信号量使用下面的函数接口：
rt_err_t rt_sem_release(rt_sem_t sem);
当信号量的值等于零时，并且有线程等待这个信号量时，将唤醒等待在该信号量线程队列中的第一个线程，由它获取信号量。否则将把信号量的值加一。
函数参数
参数描述
sem信号量对象的句柄。
函数返回
RT_EOK
下面在机智云Gokit开发板上演示如何初始化一个信号量，并使用信号量来进行任务同步的例子，程序中创建2个线程，低优先级线程1发送信号量，高优先级线程2等待信号量后翻转Gokit上的红色LED。
/**
****************************************************
* 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：创建2个线程，低优先级线程1发送信号量，高优先级线程2等待信号量后翻转Gokit上的红色LED。
*/
/* 指向线程控制块的指针 */
static rt_thread_t tid1 = RT_NULL;
static rt_thread_t tid2 = RT_NULL;
/* 信号量控制块 */
struct rt_semaphore sem;
/* 线程1入口 */
static void thread1_entry(void* parameter)
{
while (1)
{
rt_kprintf("low thread release a sem.\n");
rt_sem_release(&sem);
rt_thread_delay(1000);
}
}
/* 线程2入口 */
static void thread2_entry(void* parameter)
{
while (1)
{
rt_sem_take(&sem, RT_WAITING_FOREVER);//永久等待信号量
rt_kprintf("high thread take sem.\n");
LED1_Toggle();
LED2_Toggle();
LED3_Toggle();
LED4_Toggle();
}
}
/* 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 */
/* 初始化信号量 */
rt_sem_init(&sem , "sem", 0, RT_IPC_FLAG_FIFO);//初始化信号量
/* 创建线程1 */
tid1 = rt_thread_create("tid1",
thread1_entry, /* 线程入口是thread1_entry */
RT_NULL, /* 入口参数是RT_NULL */
512,
3, //优先级
20);
if (tid1 != RT_NULL)
rt_thread_startup(tid1);
/* 创建线程2 */
tid2 = rt_thread_create("tid2",
thread2_entry,/* 线程入口是thread2_entry */
RT_NULL, /* 入口参数是RT_NULL */
512,
2,//优先级
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 */
/**
* @briefThis function is executed in case of error occurrence.
* @paramNone
* @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***/
串口助手现象如下：
每隔1s，LED翻转状态：
源码下载：
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