一、任務間通信
- 互斥量
概述
互斥量又稱互斥鎖，一般用於共享資源的互斥排他性訪問保護。
互斥量在任意時刻處於且僅會處於解鎖或鎖定狀態，當一個任務獲取到一把鎖後（互斥量鎖定），其他任務再嘗試獲得這把鎖時會失敗或進入阻塞狀態，當該任務釋放持有的鎖時（互斥量解鎖），會喚醒一個正阻塞等待此互斥量的任務，被喚醒的任務將會獲取這把鎖。
在多任務運行環境中，有些共享資源不具有多線程可重入性，對於這類不希望被多任務同時訪問的資源（臨界資源），可以採用互斥量來進行保護，後面的編程實例章節會演示這一編程範式。
API講解
編程實例
1、在tos_config.h中，配置互斥量組件開關TOS_CFG_MUTEX_EN：
#define TOS_CFG_MUTEX_EN 1u
2、編寫main.c示例代碼：
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "usart.h"
#include "gpio.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "cmsis_os.h"
#include "stdio.h"
#include "tos_k.h"
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
#define STK_SIZE_TASK_WRITER 512
#define STK_SIZE_TASK_READER 512
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
k_stack_t stack_task_writer[STK_SIZE_TASK_WRITER];
k_stack_t stack_task_reader[STK_SIZE_TASK_READER];
k_task_t task_writer;
k_task_t task_reader;
extern void entry_task_writer(void *arg);
extern void entry_task_reader(void *arg);
k_mutex_t critical_resource_locker;
// 一片臨界區內存
static uint32_t critical_resource[3];
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
static void write_critical_resource(int salt)
{
size_t i = 0;
// 此函數每次向共享內存中按遞增順序寫入三個無符號整數
printf("writting critical resource:\n");
for (i = 0; i < 3; ++i) {
printf("%d\t", salt + i);
critical_resource[i] = salt + i;
}
printf("\n");
}
void entry_task_writer(void *arg)
{
size_t salt = 0;
k_err_t err;
while (K_TRUE) {
// 在向臨界區寫入數據之前，先嚐試獲取臨界區保護鎖
err = tos_mutex_pend(&critical_resource_locker);
if (err == K_ERR_NONE) {
// 成功獲取鎖之後，向臨界區寫入數據
write_critical_resource(salt);
// 寫完數據後，釋放互斥鎖
tos_mutex_post(&critical_resource_locker);
}
tos_task_delay(1000);
++salt;
}
}
static void read_critical_resource(void)
{
size_t i = 0;
// 從臨界區讀取數據
printf("reading critical resource:\n");
for (i = 0; i < 3; ++i) {
printf("%d\t", critical_resource[i]);
}
printf("\n");
}
void entry_task_reader(void *arg)
{
k_err_t err;
while (K_TRUE) {
// 讀取臨界區數據之前，先嚐試獲取臨界區保護鎖
err = tos_mutex_pend(&critical_resource_locker);
if (err == K_ERR_NONE) {
// 成功獲取鎖之後，從臨界區讀取數據
read_critical_resource();
// 讀取數據完畢後，釋放互斥鎖
tos_mutex_post(&critical_resource_locker);
}
tos_task_delay(1000);
}
}
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
/* USER CODE BEGIN PV */
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* @brief The application entry point.
* @retval int
*/
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 */
tos_knl_init();
// 創建臨界區保護互斥鎖
tos_mutex_create(&critical_resource_locker);
(void)tos_task_create(&task_writer, "writer", entry_task_writer, NULL,
4, stack_task_writer, STK_SIZE_TASK_WRITER, 0);
(void)tos_task_create(&task_reader, "reader", entry_task_reader, NULL,
4, stack_task_reader, STK_SIZE_TASK_READER, 0);
tos_knl_start();
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
3、運行效果：
源碼鏈接：Git