Bearpi开发板之HarmonyOS互斥锁

互斥锁的概念

1、互斥锁又称互斥型信号量，是一种特殊的二值性信号量，用于实现对共享资源的独占式处理。 2、任意时刻互斥锁的状态只有两种：开锁或闭锁。 3、当有任务持有时，互斥锁处于闭锁状态，这个任务获得该互斥锁的所有权。 4、当该任务释放时，该互斥锁被开锁，任务失去该互斥锁的所有权。 5、当一个任务持有互斥锁时，其他任务将不能再对该互斥锁进行开锁或持有。 6、多任务环境下往往存在多个任务竞争同一共享资源的应用场景，互斥锁可被用于对共享资源的保护从而实现独占式访问。 另外，互斥锁可以解决信号量存在的优先级翻转问题。

运作原理

• 多任务环境下会存在多个任务访问同一公共资源的场景，而有些公共资源是非共享的，需要任务进行独占式处理。互斥锁怎样来避免这种冲突呢？
• 用互斥锁处理非共享资源的同步访问时，如果有任务访问该资源，则互斥锁为加锁状态。此时其他任务如果想访问这个公共资源则会被阻塞，直到互斥锁被持有该锁的任务释放后，其他任务才能重新访问该公共资源，此时互斥锁再次上锁，如此确保同一时刻只有一个任务正在访问这个公共资源，保证了公共资源操作的完整性。

cmsis_os2的API互斥锁接口简介

• 创建互斥锁：osMutexId_t osMutexNew (const osMutexAttr_t *attr);
• 获取互斥锁：osStatus_t osMutexAcquire (osMutexId_t mutex_id, uint32_t timeout);
• 释放互斥锁：osStatus_t osMutexRelease (osMutexId_t mutex_id);
• 删除互斥锁：osStatus_t osMutexDelete (osMutexId_t mutex_id);

创建高中低优先级共3个任务和一个互斥对象

#include 
#include 
#include "ohos_init.h"
#include 
#include "cmsis_os2.h"
#include "wifiiot_gpio.h"
#include "wifiiot_gpio_ex.h"




void hi_thread(void *p)
{
 
  osDelay(100);
  while(1)
  {
    osMutexAcquire(p,osWaitForever);
     printf("hi thread\n");
    osDelay(300);
    osMutexRelease(p);
  }
}

void mid_thread(void *p)
{
   (void)p;
  osDelay(100);
  while(1)
  {
    printf("mid thread\n");
    osDelay(100);
  }
}


void low_thread(void *p)
{
  
  while(1)
  {
    osMutexAcquire(p,osWaitForever);
    printf("low thread\n");
    osDelay(300);
    osMutexRelease(p);
  }
}




void my_led_example(void)
{
    GpioInit();
    IoSetFunc(WIFI_IOT_IO_NAME_GPIO_2,WIFI_IOT_IO_FUNC_GPIO_2_GPIO);
    GpioSetDir(WIFI_IOT_IO_NAME_GPIO_2,WIFI_IOT_GPIO_DIR_OUT);
    
    osThreadAttr_t attr;
    attr.attr_bits = 0;
    attr.cb_mem = NULL;
    attr.cb_size = 0;
    attr.stack_mem = NULL;
    attr.stack_size = 1024;
    attr.priority = 25;

    static osMutexId_t mutex;
    mutex = osMutexNew(NULL);
    if (mutex == NULL)
    {
       printf("Falied to create mutex!\n");
    }

   osThreadId_t id = osThreadNew(hi_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create hi_thread!\n");
   }
      attr.priority = 24;

    id = osThreadNew(mid_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create mid_thread!\n");
   }

    attr.priority = 23;

    id = osThreadNew(low_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create low_thread!\n");
   }
}
SYS_RUN(my_led_example);

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扩展实验代码

#include 
#include 
#include "ohos_init.h"
#include 
#include "cmsis_os2.h"
#include "wifiiot_gpio.h"
#include "wifiiot_gpio_ex.h"




void hi_thread(void *p)
{
 
    osDelay(100U);
    osStatus_t status;
    while (1)
    {
        // try to acquire mutex
      
        status = osMutexAcquire(p, osWaitForever);
        printf("hi_thread is runing.\r\n");
        if(status != osOK)
        {
           printf("hi thread acquire mutex failed\r\n");
        }
        else
        {
            printf("hi thread acquire mutex success\r\n");
        }
        
        printf("hi thread block 3s\n");
        osDelay(300U);
        printf("hi thread osMutexRelease is called\n");
        status = osMutexRelease(p);
        if(status != osOK)
        {
            printf("hi thread release mutex failed\r\n");
        }
        else
        {
           printf("hi thread release mutex success\r\n");
        }
    }
}

void mid_thread(void *p)
{
   (void)p;
  osDelay(100);
  while(1)
  {
    printf("mid thread\n");
    osDelay(100);
  }
}


void low_thread(void *p)
{
  osStatus_t status;
  while (1)
  {
    status = osMutexAcquire(p, osWaitForever);
    printf("low_thread is runing.\r\n");
    if(status != osOK)
    {
        printf("lo tread acquire mutex failed\r\n");
    }
    else
    {
       printf("lo thread acquire mutex success\r\n");
    }
    // block mutex for 3s
    printf("lo thread block 3s\n");
    osDelay(300U);
    printf("lo thread osMutexRelease is called\n");
    status = osMutexRelease(p);
    if(status != osOK)
    {
      printf("lo thread release mutex failed\r\n");
    }
    else
    {
      printf("lo thread release mutex success\r\n");
    }
  }

}




void my_led_example(void)
{
    GpioInit();
    IoSetFunc(WIFI_IOT_IO_NAME_GPIO_2,WIFI_IOT_IO_FUNC_GPIO_2_GPIO);
    GpioSetDir(WIFI_IOT_IO_NAME_GPIO_2,WIFI_IOT_GPIO_DIR_OUT);
    
    osThreadAttr_t attr;
    attr.attr_bits = 0;
    attr.cb_mem = NULL;
    attr.cb_size = 0;
    attr.stack_mem = NULL;
    attr.stack_size = 1024;
    attr.priority = 25;

    static osMutexId_t mutex;
    mutex = osMutexNew(NULL);
    if (mutex == NULL)
    {
       printf("Falied to create mutex!\n");
    }

   osThreadId_t id = osThreadNew(hi_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create hi_thread!\n");
   }
      attr.priority = 24;

    id = osThreadNew(mid_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create mid_thread!\n");
   }

    attr.priority = 23;

    id = osThreadNew(low_thread,mutex,&attr);
   if(id == NULL)
   {
        printf("Falied to create low_thread!\n");
   }
}
SYS_RUN(my_led_example);

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