Re: Multithreading in GR blocks

[Marcus Müller]

Hi Moses,

ah sorry, I was misreading your code!
Looking at this yes, classical socket programming problem:

Looks like your ListenLoop probably simply hangs on `accept`; that's
because the socket is in blocking mode by default.

So, you'd "simply" do the following:

1. prepare your socket as done in Setup(), but make it non-blocking.
2. in your ListenLoop use `select()`, which blocks, on the socket fd
3. When select() returns:
a.
 try to accept(). That can either work instantly (then, select()
finished because there was a connection ready to be accepted), or fail
instantly (because select() finished for any other reason, e.g. the
socket being closed)
b. check whether the socket is still open && !m_bFinished

Or don't. Honestly, writing another TCP socket acceptor in 2020 does
sound like a somewhat tedious thing to do ;) Look at GNU Radio's
gr-network in-tree component, it should have everything you need.

Best regards,
Marcus

On 13.04.20 19:21, Moses Browne Mwakyanjala wrote:
> Hi Marcus,
> I was trying to emulate how the ZMQ block handles multithreading.
> Basically, the ZMQ block overrides the stop() function and joins the
> threads. This is the same thing I tried to do to stop the receive and
> listen threads. Is there any other way of doing this?
> 
> bool
> 
> TCPServer::stop()
> 
> {
> 
> m_bFinished=true;
> 
> m_ReceiveThread->join();
> 
> m_ListenThread->join();
> 
> returntrue;
> 
> }
> 
> Regards,
> 
> Moses.
> 
> 
> On Mon, Apr 13, 2020 at 7:11 PM Marcus Müller <address@hidden
> <mailto:address@hidden>> wrote:
> 
>     Hi Moses,
> 
>     your code doesn't show how your GNU Radio block's stop() function would
>     tell your TCP Server thread that it's time to shut down, so I presume
>     that doesn't happen – that would explain why the flow graph can't ever
>     shut down!
> 
>     Best regards,
>     Marcus
> 
>     On 13.04.20 18:54, Moses Browne Mwakyanjala wrote:
>     > Hello everyone,
>     > I have created a TCP/IP block by adapting the ZMQ message pub block.
>     > Both blocks make use of boost multithreading. The TCP/IP block is used
>     > by a standalone C++ program. To run the gnuradio topblock, the C++
>     > program calls tb->start() function. To stop the topblock, the
>     > functions tb->stop() and tb->wait() are called.However, the program
>     > "hangs" when tb->stop() is called. This suggests there is something
>     > wrong with the way I use boost multithreading. 
>     > All help is appreciated.
>     >
>     > Regards,
>     > Moses. 
>