创建线程时丢失成员数据

Question

我发现很难解释这个问题,所以我会发布代码并解释会发生什么,然后问如何让它做我想做的事情.首先,我在子进程中创建一个线程:

pid_t childpid = fork();

if(childpid == -1){
  cout << "Failed to fork." << endl;   
}
else if(childpid == 0){     
  //request threads
  pthread_t p1, p2, p3;          

  struct arg_struct args1, args2, args3;

  args1.name = "data Joe Smith";
  args1.num_req = n;
  args1.buff_size = b;
  pthread_create(&p1, NULL, &mythreadfunc, (void *)&args1);   
}

这是struct arg_struct:

struct arg_struct{
    string name;
    int num_req;
    int curr_value;
    int buff_size;
};

而且 mythreadfunc:

void *mythreadfunc(void *arguments){ 
    struct arg_struct *args = (struct arg_struct *)arguments;
    string local_name = args->name;     
    int local_num_req = args->num_req;
    //request new thread
    RequestChannel chan("control", RequestChannel::CLIENT_SIDE);
    cout << "done." << endl;
    string reply1 = chan.send_request("newthread");

    cout << "Reply to request 'newthread' is " << reply1 << "'" << endl;

    RequestChannel chan2(reply1, RequestChannel::CLIENT_SIDE); 

    cout<<"local_name:  "<<local_name<<endl;    //returns incorrect value***
    cout<<"local_num_req:  "<<local_num_req<<endl;  //returns incorrect value***

    //close up all channels
    string reply2 = chan2.send_request("quit");
    cout << "Reply to request 'quit' is '" << reply2 << "'" << endl;
    string reply3 = chan.send_request("quit");
    cout << "Reply to request 'quit is '"<< reply3 << "'" << endl;
}

在利用两条线local_name和local_num_req有问题.我编译得很好,但这两个变量似乎每次都存储不同的东西.有时候它可以正常工作,有时候它们会保存垃圾值,程序永远不会执行它们(或者后续的任何内容).我尝试使用args->name没有局部变量的原始名称(即),但问题是相同的.我最好的猜测是我args_struct处理错误的变量,但我不知道为什么它只会失败部分时间.

我怎样才能拥有正确的变量值mythreadfunc？

Answer 1

在堆上为新线程创建参数,它在调用函数中超出范围,因此不适用于您的线程:

struct arg_struct *arg1 = new arg_struct;

args1->num_req = n;
// etc...

pthread_create(&p1, NULL, &mythreadfunc, (void *) args1);