mysql - 多线程访问MySQL错误

Question

我写了一个简单的多线程C程序来访问MySQL，除了当 我在每个线程函数中添加 usleep() 或 sleep() 函数。 我在 main 方法中创建了两个 pthread，

int main(){
        mysql_library_init(0,NULL,NULL);
        printf("Hello world!\n");
        init_pool(&p,100);
        pthread_t producer;
        pthread_t consumer_1;
        pthread_t consumer_2;
        pthread_create(&producer,NULL,produce_fun,NULL);
        pthread_create(&consumer_1,NULL,consume_fun,NULL);
        pthread_create(&consumer_2,NULL,consume_fun,NULL);
        mysql_library_end();
}



   void * produce_fun(void *arg){
    pthread_detach(pthread_self());
    //procedure
    while(1){
        usleep(500000);
        printf("producer...\n");
        produce(&p,cnt++);
    }
    pthread_exit(NULL);
}

void * consume_fun(void *arg){
    pthread_detach(pthread_self());
    MYSQL db;
    MYSQL *ptr_db=mysql_init(&db);
    mysql_real_connect();

    //procedure
    while(1){
        usleep(1000000);
        printf("consumer...");
        int item=consume(&p);
        addRecord_d(ptr_db,"test",item);
    }
    mysql_thread_end();
    pthread_exit(NULL);
}

void addRecord_d(MYSQL *ptr_db,const char *t_name,int item){
    char query_buffer[100];
    sprintf(query_buffer,"insert into %s values(0,%d)",t_name,item);
//pthread_mutex_lock(&db_t_lock);
    int ret=mysql_query(ptr_db,query_buffer);
    if(ret){
        fprintf(stderr,"%s%s\n","cannot add record to ",t_name);
        return;
    }

    unsigned long long update_id=mysql_insert_id(ptr_db);
//    pthread_mutex_unlock(&db_t_lock);
    printf("add record (%llu,%d) ok.",update_id,item);
}

程序输出错误如下:

[Thread debugging using libthread_db enabled]
[New Thread 0xb7ae3b70 (LWP 7712)]
Hello world!
[New Thread 0xb72d6b70 (LWP 7713)]
[New Thread 0xb6ad5b70 (LWP 7714)]
[New Thread 0xb62d4b70 (LWP 7715)]
[Thread 0xb7ae3b70 (LWP 7712) exited]
producer...
producer...
consumer...consumer...add record (31441,0) ok.add record (31442,1) ok.producer...
producer...
consumer...consumer...add record (31443,2) ok.add record (31444,3) ok.producer...
producer...
consumer...consumer...add record (31445,4) ok.add record (31446,5) ok.producer...
producer...
consumer...consumer...add record (31447,6) ok.add record (31448,7) ok.producer...
Error in my_thread_global_end(): 2 threads didn't exit
[Thread 0xb72d6b70 (LWP 7713) exited]
[Thread 0xb6ad5b70 (LWP 7714) exited]
[Thread 0xb62d4b70 (LWP 7715) exited]

Program exited normally.

当我在函数addRecord_d中添加pthread_mutex_lock时，错误仍然存​​在。 那么到底问题出在哪里呢？

Answer 1

问题是您太早调用 mysql_library_end() (尤其是线程中的 usleep() )。可以完成主线程并让其他线程继续工作，但不建议这样做。添加 pthread_join() 的解决方案是最好的。您还可以消除 mysql_library_end()，它会起作用。