Reproduce X11 bug where the second KeyRelease event is missing if two grabbed keys are released in quick succession.

grabtest.c

// grabtest tries to reproduce an X11 bug where, when two keys grabbed using
// XGrabKey are held down and then quickly released, the second KeyRelease
// event never makes it to the event queue.
//
// make LDFLAGS=-lX11\ -lXtst grabtest

#include <unistd.h>
#include <stdio.h>
#include <assert.h>
#include <X11/Xlib.h>
#include <X11/keysym.h>
#include <X11/extensions/XTest.h>

#define LEN(X) (sizeof(X) / sizeof(X[0]))
#define PRESS 1
#define RELEASE 0

Display *dpy;
Window root;
int screen;

void
read_n_key_events(int n)
{
	for (int i = 0; i < n; i++) {
		XEvent ev;
		XMaskEvent(dpy, KeyPressMask|KeyReleaseMask, &ev);
		KeySym keysym = XLookupKeysym(&ev.xkey, 0);
		int ispress = ev.type == KeyPress;
		printf("%s %s\n",  ispress ? "press" : "release", XKeysymToString(keysym));
	}
}

int
main()
{
	dpy = XOpenDisplay(NULL);
	assert(dpy);
	root = DefaultRootWindow(dpy);
	screen = DefaultScreen(dpy);

	XSelectInput(dpy, root, KeyPressMask|KeyReleaseMask);

	KeySym keysyms[] = {XK_d, XK_f};

	// Grab keys.
	unsigned modifiers = 0;
	for (int i = 0; i < LEN(keysyms); i++) {
		KeyCode keycode = XKeysymToKeycode(dpy, keysyms[i]);
		int ok = XGrabKey(dpy, keycode, modifiers, root, True, GrabModeAsync, GrabModeAsync);
		assert(ok);
		XKeyboardControl ctrl = {.key=keycode, .auto_repeat_mode=AutoRepeatModeOff};
		XChangeKeyboardControl(dpy, KBKey|KBAutoRepeatMode, &ctrl);
	}

	// Hold keys d and f, then quickly release them.
	KeyCode d = XKeysymToKeycode(dpy, XK_d);
	KeyCode f = XKeysymToKeycode(dpy, XK_f);
	XTestFakeKeyEvent(dpy, d, PRESS, CurrentTime);
	XTestFakeKeyEvent(dpy, f, PRESS, CurrentTime);
	XTestFakeKeyEvent(dpy, d, RELEASE, CurrentTime);
	XFlush(dpy);
	read_n_key_events(3);
	XTestFakeKeyEvent(dpy, f, RELEASE, CurrentTime);
	XFlush(dpy);
	read_n_key_events(1);

	// Clean up.
	for (int i = 0; i < LEN(keysyms); i++) {
		KeyCode keycode = XKeysymToKeycode(dpy, keysyms[i]);
		XKeyboardControl ctrl = {.key=keycode, .auto_repeat_mode=AutoRepeatModeDefault};
		XChangeKeyboardControl(dpy, KBKey|KBAutoRepeatMode, &ctrl);
		XUngrabKey(dpy, keycode, modifiers, root);
	}
	XFlush(dpy);
}

Did you ever find a solution to this issue? im currently having this with an app im developing, and i cannot find a solution

No, sadly. I think this GNOME mailing list post is also referring to the same issue, and that's the only other reference to it that I've seen. I looked through my notes for torbiak/ptrkeys but don't see much else about it except for this commit message. I guess I didn't file a bug or anything.