C++ 结束与主线程分离的线程

Question

I have problem with ending detached thread:

void fun_5(int sock_connect)    
{
    unsigned char buff2[76] = {0x01 ,0x01 ,0x02 ,0x02 ,0x00 ,0x4a ,0x31 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x04 ,0x00 ,0x00 ,0x50 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x50 ,0x4c ,0x4d ,0x4f ,0x4d ,0x49 ,0x46 ,0x41 ,0x58 ,0x20 ,0x20 ,0x4e ,0x52 ,0x20 ,0x41 ,0x00 ,0x34 ,0x41 ,0x50 ,0x3c ,0x32 ,0x31 ,0x3e ,0x35 ,0x46 ,0x2e ,0x52 ,0x32 ,0x31 ,0x30 ,0x2f ,0x31 ,0x35 ,0x2f ,0x31 ,0x32 ,0x31 ,0x35 ,0x3a ,0x31 ,0x31 ,0x3a ,0x30 ,0x36 ,0x00 ,0xff ,0xef};
while(thfive)
    {   
            if((send( sock_connect, buff2, sizeof(buff2), MSG_NOSIGNAL ) ) <= 0 )
            {
                close(sock_connect);
                break;
            }
            sleep(5);
    }

}       

This thread sends bytes in every 5 sec when client which connect to server(my program) sends specified sequence of bytes("start"), and it should stop sending when client sends other sequence("stop").

while(thfive) <<- thfive is true when client sends "start", and its false when client sends "stop"

But when client sends "start" after "stop" in less then 5 sec, thread running all the time. Because of that this solution is not the best. There is option to checking condition even when thread sleep? Or how I can kill this detached thread from main thread?

It works in detached thread, because in the same time, program doing other functions. I have more threads like this in the same time ( which sends bytes every 1.5 sec, 10 sec etc). I'm still a novice in programming, and the first time I use multitasking.

Thanks.

Edit 1: My OS is Linux.

Answer 1

When you let the thread run while thfive is true, you must take care. The compiler might optimize the loop so that it only checks thfive at the entry of the loop. thfive does not change inside the loop, so the compiler might think it is not necessary to check thfive every time the loop continues.

Starting with C++11 you should use std::atomic<bool> as type for thfive, see also this SO question .

You might also consider creating an event and signal that event if the worker thread shall terminate. But how to do this depends on the platform you are using. For Windows for example also the socket API can be used event based, so the thread could use one function call to wait for the terminate event or a socket event in parallel (no need to poll).