c - Linux C : segfault error 4 in libmysqlclient. so.18.0.0

Question

我正在尝试使用以下代码实现多线程 tcp 服务器。

int main(int argc , char *argv[])
{
    int socket_desc , client_sock , c , *new_sock;
    struct sockaddr_in server , client;

    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }
    puts("Socket created");

    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 8888 );

    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        //print the error message
        perror("bind failed. Error");
        return 1;
    }
    puts("bind done");

    //Listen
    listen(socket_desc , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);

    while( (client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
        puts("Connection accepted");

        pthread_t sniffer_thread;
        new_sock = malloc(1);
        *new_sock = client_sock;

        if( pthread_create( &sniffer_thread , NULL ,  connection_handler , (void*) new_sock) < 0)
        {
            perror("could not create thread");
            return 1;
        }

        //Now join the thread , so that we dont terminate before the thread
        //pthread_join( sniffer_thread , NULL);
        puts("Handler assigned");
    }

    if (client_sock < 0)
    {
        perror("accept failed");
        return 1;
    }

    return 0;
}

/*
 * This will handle connection for each client
 * */
void *connection_handler(void *socket_desc)
{
    //Get the socket descriptor
    int newsockfd = *(int*)socket_desc;
    int read_size;
    char *message , buffer[2000];
    int n;
    struct auth details;
    char* reply;

    char cmd[100] = {0};    
    //Receive a message from client
    while( (read_size = recv(newsockfd , buffer , 2000 , 0)) > 0 )
    {
        printf("Incoming data: %s", buffer);

        if(parseData(cmd, buffer, "/", "-"))      /* If received data is compliant */
        {   
            details = authenticate(cmd);
            if (details.verified)                   // If said user can execute this command. 
            {
                reply = execute(cmd);                // Execute.
                n = write(newsockfd, reply, strlen(reply));
                if (n < 0) { error("ERROR writing to socket"); }

                free(reply);
                reply = NULL;

            }
            else                                        // Authentication failed.
            {
                n = write(newsockfd, details.error_msg, strlen(details.error_msg));
                if (n < 0) { error("ERROR writing to socket"); }
                else{
                    if(debug) printf("sent: %s\n", details.error_msg);
                }
            }
        }
    }


    if(read_size == 0)
    {
        puts("Client disconnected");
        fflush(stdout);
    }
    else if(read_size == -1)
    {
        perror("recv failed");
    }

    //Free the socket pointer
    free(socket_desc);

    return 0;
}

authenticate 函数定义在一个实现文件中:

struct auth authenticate(const char* const command)
{
    struct auth data;
    char* db_pwd;
    char* perm;
    char* username = "testUser";
    char query[200] = {0};

    data.verified = FALSE;
    data.error_msg = "";

    printf("in auth\n");
    MYSQL_ROW row;
    snprintf(query, 200, "SELECT password FROM userlist WHERE user='%s'", username);
    if ((row = mysql_fetch_row(run_query(query))))      // if user is on list
    {
        db_pwd = row[0];

        if(!strcmp(db_pwd, password))
        {
            if (!(strcmp(command, "test")))
            {
                 data.verified = TRUE;
            }
        }
    }
    return data;
}

我有一个该程序(主要)的工作单线程版本，具有相同的实现文件，段错误仅发生在多线程版本中。

• 我的代码是不是做错了什么？
• 我应该如何进行调试？

如有任何想法，我们将不胜感激。

Answer 1

阅读 MySQL C API 的文档, 特别是 § 23.8.12 C API Threaded Function Descriptions它在内部使用到 mysqld 服务器进程的套接字连接，因此您必须序列化所有 MySQL 函数。

因此，定义您的全局互斥体，并保护所有使用该互斥体执行 mysql 调用的函数(从请求到获取所有回复行)。更好的是，设计您的应用程序，以便只有一个线程(通常是主线程)使用 mysql 函数。

编译所有警告和调试信息 (gcc -Wall -g)。使用调试器 (gdb)，或许还可以使用 valgrind

如果不熟悉mutexes ，您可能想阅读 pthread tutorial