Strange behavior of grab() about python-evdev HOT 3 CLOSED

Take this with a grain of salt - I think this happens because your terminal receives a key press event (1), but never the corresponding key release (2) event. The same would happen even if you wrote your program in C:

#include <stdio.h>
#include <fcntl.h>
#include <linux/input.h>
#include <poll.h>

int main(int argc, char *argv[])
{
    int fd = open("/dev/input/event2", O_RDONLY | O_NONBLOCK);

    struct pollfd fds = {fd, POLLIN, POLLIN};
    struct input_event event;

    char cmd[50];
    sprintf(cmd, "sleep 5 && kill %d &", (int)getpid());
    system(cmd); // just in case

    while (poll(&fds, 1, -1)) {
        int n = read(fd, &event, sizeof(event));

        if (event.type == EV_KEY) {
            if ((event.code == KEY_LEFTCTRL) && (event.value == 1))
                ioctl(fd, EVIOCGRAB, 1);
            if ((event.code == KEY_LEFTCTRL) && (event.value == 0))
                ioctl(fd, EVIOCGRAB, 0);
        }

    return 0;
}

You can inject a few events into the input stream to prevent this:

ui = UInput()
for ev in dev.read_loop():
    if ev.code == KEY_LEFTCTRL and ev.value == 1:
        ui.write_event(ev)
        ui.write(EV_KEY, KEY_LEFTCTRL, 0)
        ui.syn
        dev.grab()
    ...

from python-evdev.

Actually, that is what I did in the first place, just removed the ui stuff for the sake of clarity in the example.

You see, the odd thing is, the ungrab command seems to be executed all right: ”Ungrab“ is printed and if you try to ungrab it again (e.g. after the loop), you get an error (which means the device is already ungrabbed). I believe, the problem is in the grab/ungrab itself. The release event is also caught (just printing all the events proves it).

I will try to follow your advice though. Thanks a lot for fast and useful comments!

from python-evdev.

Thanks a million!

Even though I don't get why injecting a 'release' event right after a 'press' one would help, it did :-)

Thanks for assistance, and thanks for the module, great work that saved my day.

from python-evdev.