linux下使用gdb调试多线程——以条件变量为例_多线程条件变量如何调试-优快云博客

本文链接：https://blog.youkuaiyun.com/PinkFriday/article/details/80392665

多线程的调试比较麻烦，在linux下我们可以使用gdb来对多线程进行调试。gdb基本的使用不做介绍了。这里说一下使用gdb调试多线程的几种常用的辅助命令：

1. info threads: 显示当前可调试的线程，gdb会给每一个线程分配一个ID，ID前面带“*”的表示是当前被调试的线程

2. thread ID：调试目标ID指定的线程

3. set scheduler-locking [off | on | step]: 调试多线程时，默认除了被调试线程在执行外，其他线程也在执行，如果希望其他线程不执行的话，可以使用on这个选项。step的意思是在单步执行的时候，只有当前线程会执行。

下面使用一个代码实例，来说明如何调试多线程。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <pthread.h>
#include <assert.h>

typedef struct worker
{
	void *(*process)(void *arg);
	void *arg;
	struct worker *next;
	
}CThread_worker;

typedef struct 
{
	pthread_mutex_t queue_lock;
	pthread_cond_t queue_ready;

	CThread_worker *queue_head;

	int shutdown;
	pthread_t *threadid;
	int max_thread_num;
	int cur_queue_size;
}CThread_pool;


static CThread_pool *pool = NULL;
int pool_add_worker(void*(*process)(void *arg), void *arg)
{
	CThread_worker *newworker = (CThread_worker *) malloc(sizeof(CThread_worker));
	newworker->process = process;
	newworker->arg = arg;
	newworker->next = NULL;

	pthread_mutex_lock(&(pool->queue_lock));

	CThread_worker *member = pool->queue_head;
	if (member != NULL)  
    {  
        while (member->next != NULL)  
            member = member->next;  
        member->next = newworker;  
    }  
    else  
    {  
        pool->queue_head = newworker;  
    }  
  
    assert (pool->queue_head != NULL);  
  
    pool->cur_queue_size++;  
    pthread_mutex_unlock (&(pool->queue_lock));  
    pthread_cond_signal (&(pool->queue_ready));  
    return 0;  
}



void *thread_routine(void *arg);



void pool_init(int max_thread_num)
{
	pool = (CThread_pool *) malloc(sizeof(CThread_pool));
	pthread_mutex_init(&(pool->queue_lock), NULL);
	pthread_cond_init(&(pool->queue_ready), NULL);

	pool->queue_head = NULL;

	pool->max_thread_num = max_thread_num;
	pool->cur_queue_size = 0;
	pool->shutdown = 0;
	
	pool->threadid = (pthread_t *)malloc(max_thread_num * sizeof(pthread_t));

	for(int i = 0; i < max_thread_num; i++)
	{
		pthread_create(&(pool->threadid[i]), NULL, thread_routine, NULL);

	}

}


void *thread_routine(void *arg)
{
	printf("starting thread %ld \n", pthread_self());
	while(1)
	{
		pthread_mutex_lock (&(pool->queue_lock));  
		while(pool->cur_queue_size == 0 && !pool->shutdown)
		{
			pthread_cond_wait(&(pool->queue_ready), &(pool->queue_lock));
		}      
	    /*等待队列长度减去1，并取出链表中的头元素*/
	    if(pool->cur_queue_size != 0 && pool->queue_head != NULL) 
	    {
	    	pool->cur_queue_size--;  
		    CThread_worker *worker = pool->queue_head;  
		    pool->queue_head = worker->next;  
		    pthread_mutex_unlock (&(pool->queue_lock));  

		    /*调用回调函数，执行任务*/  
		    (*(worker->process)) (worker->arg);  
		    free (worker);  
		    worker = NULL; 
	    } 
	   
	}
	
}



void *  
myprocess (void *arg)  
{  
    printf ("threadid is %ld, working on task %d\n", pthread_self (),*(int *) arg);  
    sleep (1);/*休息一秒，延长任务的执行时间*/  
    return NULL;  
} 

int main()
{
	pool_init(3);
	 /*连续向池中投入10个任务*/  
    int *workingnum = (int *) malloc (sizeof (int) * 10);  
    int i;  
    for (i = 0; i < 10; i++)  
    {  
        workingnum[i] = i;  
        pool_add_worker (myprocess, &workingnum[i]);  
    }  
    /*等待所有任务完成*/  
    sleep (10);  
    /*销毁线程池*/  
    //pool_destroy ();  
  
    free (workingnum);  
    return 0;  
}

这里的代码参考的网上对于线程池的实现，主线程往队列中添加任务，线程池中的线程在条件变量下等待通知，如果有任务，被唤醒去执行任务。

这里注意生成可执行程序test时要加-g选项

启动gdb：gdb ./test