aos multithreading and mutex lock

乘简

aos multithreading and mutex lock [Copy link]

 

First, let’s look at a piece of code:

#include <stdlib.h>
#include <string.h>
#include <aos/aos.h>
#include "aos/cli.h"
#include "main.h"
#include "app_init.h"
#include <drv/timer.h>

#define TAG "app"

volatile int n=0;
csi_timer_t g1_timer;//定义变量
static void g1_handler(csi_timer_t *timer_handle, void *arg)
{
	printf("%d\r\n",n);
	n=0;//为什么这句会时不时不执行呢？
	//printf("%d\r\n",n);
}

void my_test(void)
{
	csi_timer_init(&g1_timer, 0);//初始化定时器
	csi_timer_attach_callback(&g1_timer, g1_handler, NULL);//绑定回调函数
	csi_timer_start(&g1_timer, 1000000);//1000000每秒定时，单位为us，时间到自动执行回调函数
	while(1){
		n++;
	}
	csi_timer_stop(&g1_timer);
	csi_timer_detach_callback(&g1_timer);
	csi_timer_uninit(&g1_timer);
}

int main(void)
{
    board_yoc_init();
    LOGD(TAG, "%s\n", aos_get_app_version());
	my_test();
    return 0;
}

That is, the cumulative number of outputs n per second is executed as:

32767548
65535098
32767548
65535098
32767548
65535098
32767548
65535098
32767548
65535098
32767548
65535098
32767548
65535098

From the execution results, it seems that n=0; in the timer callback function is occasionally not executed. In fact, the reason is that the sentence n++; in the main function cannot be executed by one instruction, but requires three instructions.

1) Take the value of n and put it into the register,

2) Add 1 to the register.

3) Store the value after adding 1 into n,

Then these three instructions may be interrupted by the timer, and then unexpected problems may occur. . .

The correct approach is to look at the following code

/*
 * Copyright (C) 2019-2020 Alibaba Group Holding Limited
 */


#include <stdlib.h>
#include <string.h>
#include <aos/aos.h>
#include "aos/cli.h"
#include "main.h"
#include "app_init.h"
#include <drv/timer.h>

#define TAG "app"

static aos_mutex_t test_mutex;

volatile int n=0;
csi_timer_t g1_timer;//定义变量
static void g1_handler(csi_timer_t *timer_handle, void *arg)
{
	printf("%d\r\n",n);
	aos_mutex_lock(&test_mutex, AOS_WAIT_FOREVER);
	n=0;
	aos_mutex_unlock(&test_mutex);
}

void my_test(void)
{
	csi_timer_init(&g1_timer, 0);//初始化定时器
	csi_timer_attach_callback(&g1_timer, g1_handler, NULL);//绑定回调函数
	csi_timer_start(&g1_timer, 1000000);//1000000每秒定时，单位为us，时间到自动执行回调函数
	while(1){
		aos_mutex_lock(&test_mutex, AOS_WAIT_FOREVER);
		n++;
		aos_mutex_unlock(&test_mutex);
	}
	csi_timer_stop(&g1_timer);
	csi_timer_detach_callback(&g1_timer);
	csi_timer_uninit(&g1_timer);
}

int main(void)
{
    board_yoc_init();
    LOGD(TAG, "%s\n", aos_get_app_version());
	aos_mutex_new(&test_mutex);
	my_test();
    return 0;
}

Execution Result:

668735
668682
668711
668711
668711
668711
668710
668711
668712
668711
668711
668711
668711
668711

Although the program execution is slow, I can get the correct result. Thanks to the technical staff of Pingtou Ge's work order system for patiently answering my questions. . .

The following article is a good understanding of multithreading and resource preemption

Multiple threads are "fighting" for the same resource. How can we keep them in check?

Jacktang

Thank you for sharing

May I ask the original poster, under what circumstances will this aos multithreading and mutex phenomenon occur? Are there other ways to deal with it?

乘简

Jacktang posted on 2022-6-15 07:08 Thank you for sharing. May I ask the OP, under what circumstances will this aos multithreading and mutex phenomenon occur? Are there other ways to deal with it?

In fact, there are definitely methods, such as:

/*
 * Copyright (C) 2019-2020 Alibaba Group Holding Limited
 */


#include <stdlib.h>
#include <string.h>
#include <aos/aos.h>
#include "aos/cli.h"
#include "main.h"
#include "app_init.h"
#include <drv/timer.h>

#define TAG "app"

volatile int n=0,s=0;
csi_timer_t g1_timer;//定义变量
static void g1_handler(csi_timer_t *timer_handle, void *arg)
{
	printf("%d\r\n",n);
	s=1;
}

void my_test(void)
{
	csi_timer_init(&g1_timer, 0);//初始化定时器
	csi_timer_attach_callback(&g1_timer, g1_handler, NULL);//绑定回调函数
	csi_timer_start(&g1_timer, 1000000);//1000000每秒定时，单位为us，时间到自动执行回调函数
	while(1){
		if(s){
			s=0;
			n=1;
		}
		else n++;
	}
	csi_timer_stop(&g1_timer);
	csi_timer_detach_callback(&g1_timer);
	csi_timer_uninit(&g1_timer);
}

int main(void)
{
    board_yoc_init();
    LOGD(TAG, "%s\n", aos_get_app_version());
    my_test();
    return 0;
}