how to trap keypress inside a command?

[elbrandt]

Hi,
Fantastic library, well written and feature packed. Thanks for your work.
We're using CliLocalTerminalSession with a LoopScheduler. One of the commands we've implemented, we'd like the command to run in a loop 'until the user presses a key' to end the command and return to the menu.

When we implement this in our command's lambda using the select() function, they way we typically would in a regular command line app, I find that we're in a race condition with a thread running the same select() command in an instance of the LinuxKeyboard class. So, I think either we're doing it wrong, or this "run command until key is pressed" use case isn't supported in this library.
Is there a relatively pain-free way to do what we want? Can we somehow temporarily pause the scheduler within our command?
I can elaborate more on the use case if this question is unclear.
Thanks again for an excellent library.
-Eric.

[daniele77]

Hi @elbrandt
first of all, thank you very much for using our library.
If you like it, please consider donating using the heart icon on top of this page :-)

Supposing you're on a Linux machine, you can try something like this:

#include <thread>
#include <atomic>
#include <termios.h>
#include <unistd.h>

...
    
menu->Insert(
        "cycle",
        [](std::ostream& out)
        { 
            out << "Press any key to stop the cycle\n";
             std::atomic<bool> stop(false);
             std::thread servant([&]()
            {
                while (!stop)
                {
                    out << "Cycling...\n";
                    std::this_thread::sleep_for(std::chrono::seconds(1));
                }
            });

            struct termios t;
            constexpr tcflag_t ICANON_FLAG = ICANON;
            constexpr tcflag_t ECHO_FLAG = ECHO;                    
            // get current setup
            tcgetattr(STDIN_FILENO, &t);
            // disable canonic input and echo
            t.c_lflag &= ~(ICANON_FLAG | ECHO_FLAG);
            // update new settings...
            tcsetattr(STDIN_FILENO, TCSANOW, &t);                    

            getchar();

             stop = true;
             servant.join();
        },
        "Start a cycle in another thread until any key is pressed"
);

I've tested the code and everything works.
Of course, this solution cannot work on remote consoles, but since you're using CliLocalTerminalSession , this should not represent a problem for your use case.

[elbrandt]

Thanks! We'll try this out ASAP. I appreciate the versatility of your library to accommodate this.

[daniele77]

I've just committed a fix that should enable user keyboard handling on Linux platform as well (commit 17dafd8).
It's the issue #239.
Now you can use std::cin and std::getline inside command handlers (local session only, of course).
Please, see if this solves your problem.