官方文档参考

107 Access by Multiple Tasks

[[FreeRTOS_Mastering_the_FreeRTOS_Real_Time_Kernel-A_Hands-On_Tutorial_Guide.pdf#page=133&selection=0,3,2,24|FreeRTOS_Mastering_the_FreeRTOS_Real_Time_Kernel-A_Hands-On_Tutorial_Guide, page 133]]

消息队列的多进单出

多个任务共享一个消息队列进行读写操作。

使用时，对不不同任务的优先级设置十分重要。

示例代码

#include <stdio.h>
#include <inttypes.h>
#include "sdkconfig.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_chip_info.h"
#include "esp_flash.h"
#include "esp_system.h"
#include "freertos/queue.h"

void sender_task_1(void *pvPara)
{
    QueueHandle_t QHandle = (QueueHandle_t)pvPara;

    int numToSend = 1;

    while (true) {
        xQueueSendToBack(QHandle, &numToSend, 0); 
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

void sender_task_2(void *pvPara)
{
    QueueHandle_t QHandle = (QueueHandle_t)pvPara;

    int numToSend = 2;

    while (true) {
        xQueueSendToBack(QHandle, &numToSend, 0); 
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

void receiver_task(void *pvPara)
{
    QueueHandle_t QHandle = (QueueHandle_t)pvPara;

    int numToReceive = 0;

    while (true) {
        xQueueReceive(QHandle, &numToReceive, portMAX_DELAY);
        printf("[RECEIVER]: %d\n", numToReceive);
        vTaskDelay(100 / portTICK_PERIOD_MS);
    }
}

void app_main(void)
{
    QueueHandle_t QHandle = xQueueCreate(5, sizeof(int));

    if (QHandle) {
        xTaskCreate(sender_task_1, "Sender Task 1", 2048, (void *)QHandle, 2, NULL);
        xTaskCreate(sender_task_2, "Sender Task 2", 2048, (void *)QHandle, 1, NULL);
        xTaskCreate(receiver_task, "Receiver Task", 2048, (void *)QHandle, 3, NULL);
    } else {
        printf("[MAIN]: Do not have enough memory to create a queue.\n");
    }
}

代码中可以看到任务设置了不同的优先级：

• Sender Task 1 的优先级是 2
• Sender Task 2 的优先级是1
• 而接收任务的优先级是 3，高于发送任务

此代码运行于单核和多核 CPU 是有区别的，单核会看出明显的优先级区别；而多核，仍然会看到1和2交替输出。