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Fix race condition on attach and mouse track on warp

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I tried running the wayland devdraw implementation on Sway 1.10,
wlroots 0.18 and encountered the error:

	xdg_surface#13: error 3: xdg_surface has never been configured

According to https://wayland.app/protocols/xdg-shell#xdg_surface ,
a client must commit a surface without a buffer, *wait* for the first
configure request from the compositor, ack it, and *only then* can
it proceed to attach a buffer to the surface and tell wayland to display it.

This was caused by the following sequence of events:

1. devdraw starts, enters gfx_main
2. `gfx_main` calls `gfx_started`, which spawns the `serveproc` thread
3. `gfx_main` enters `wl_display_dispatch`, flushing any buffered requests to
   the compositor, and enters `wl_display_poll()` to wait for incoming messages
4. `serveproc` calls `rpc_attach`, sets up the surface, and buffers a commit.

The race is between #3 and #4. If #3 happens first, the buffered commit
just sits there until `rpc_flush` is called, which calls `wl_display_flush()`,
but at that point a buffer is attached too quickly for the configure to happen.

This commit fixes the race by adding a `configured` field to the WaylandClient
and using it to guard `rpc_flush`.

In addition, I found that mouse warping, at least in sway, would move
the cursor but future mouse presses would register at the old location
until I moved the mouse. So I added a call to gfx_mousetrack to the end
of `rpc_setmouse`.
This commit is contained in:
David Arroyo 2024-11-28 16:30:25 +01:00
parent a3cbe3483f
commit 6dffdd6b08
1 changed files with 24 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

17
src/cmd/devdraw/wayland.c
View file

@ -65,6 +65,9 @@ struct WaylandClient {
struct xdg_surface *xdg_surface;
struct xdg_toplevel *xdg_toplevel;
// Initial configure call is complete
int configured;
// A callback when wl_surface is ready for the next frame.
// Currently this is not used for drawing,
// but as a hack for implementing key repeat
@ -368,10 +371,11 @@ static const struct wl_buffer_listener wl_buffer_listener = {
static void xdg_surface_configure(void *data, struct xdg_surface *xdg_surface, uint32_t serial) {
DEBUG("xdg_surface_configure\n");
const Client* c = data;
const WaylandClient *wl = c->view;
WaylandClient *wl = (WaylandClient*) c->view;
qlock(&wayland_lock);
xdg_surface_ack_configure(wl->xdg_surface, serial);
wl->configured = 1;
qunlock(&wayland_lock);
DEBUG("xdg_surface_configure: returned\n");
@ -981,7 +985,15 @@ static void rpc_setmouse(Client *c, Point p) {
wl_surface_commit(wl->wl_surface);
zwp_locked_pointer_v1_destroy(lock);
wl->mouse_x = wl_fixed_to_int(x) * wl_output_scale_factor;
wl->mouse_y = wl_fixed_to_int(y) * wl_output_scale_factor;
int mx = wl->mouse_x;
int my = wl->mouse_y;
int mb = wl->buttons;
qunlock(&wayland_lock);
gfx_mousetrack(c, mx, my, mb, nsec()/1000000);
}
static void rpc_topwin(Client*) {
@ -1017,6 +1029,7 @@ static void rpc_flush(Client *c, Rectangle r) {
WaylandClient *wl = (WaylandClient*) c->view;
qlock(&wayland_lock);
if (wl->configured) {
int w = Dx(wl->memimage->r);
int h = Dy(wl->memimage->r);
WaylandBuffer *b = get_xrgb8888_buffer(w, h);
@ -1025,6 +1038,7 @@ static void rpc_flush(Client *c, Rectangle r) {
wl_surface_damage_buffer(wl->wl_surface, r.min.x, r.min.y, Dx(r), Dy(r));
wl_surface_commit(wl->wl_surface);
wl_display_flush(wl_display);
}
qunlock(&wayland_lock);
}
@ -1091,6 +1105,7 @@ Memimage *rpc_attach(Client *c, char *label, char *winsize) {
c->displaydpi = 110 * wl_output_scale_factor;
wl_surface_set_buffer_scale(wl->wl_surface, wl_output_scale_factor);
wl_surface_commit(wl->wl_surface);
wl_display_flush(wl_display);
qunlock(&wayland_lock);
return wl->memimage;