gui: XWayland fallback when the Wayland window is never mapped
On Sway 1.12 + Qt 6.9 (Guix, NVIDIA) Qt-Wayland deadlocks before mapping: WAYLAND_DEBUG shows the client completes xdg_toplevel setup but never sends the initial wl_surface.commit, so the compositor never sends configure and the surface never maps — the event loop runs, the app prints its startup notice, and no window ever appears. This reproduces with a bare PySide6 QLabel, so it is a toolkit/compositor bug, not ours; no Qt env knob (fractional-scale disable, scale pinning) unblocks it, while the same window maps instantly on XWayland. Fix: a map watchdog on Wayland platforms. An event filter LATCHES the first Expose on the toplevel QWindow (sampling isExposed() at a deadline would misfire: a healthy hidden window — other workspace, scratchpad, locker — reads unexposed ~100 ms after frame callbacks stop). If no expose ever arrived after 4 s, re-exec the same process with QT_QPA_PLATFORM=xcb. Safety rails: a sentinel env var (VAPTVUPT_XCB_FALLBACK_DONE) makes a second fallback impossible even if '-platform wayland' argv (which outranks the env override) brings the child up on Wayland again; execve failure is caught and degrades to the no-fallback message; frozen bundles reuse argv as-is (PyInstaller sets argv[0] to the exe); DISPLAY-unset systems just get an honest notice; VAPTVUPT_NO_XCB_FALLBACK=1 opts out. Verified live: wayland launch relaunches at 4 s and the window appears in the sway tree (title 'VaptVupt 5.0.0', visible, tiled) — first time the GUI is actually on screen on this machine; latch flips true where expose events exist (offscreen); sentinel path stays wayland with no exec; selftest OK.
This commit is contained in:
Cristian Cezar Moisés
parent
92488d47b9
commit
95d9a8279b
1 changed files with 62 additions and 2 deletions
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@ -23,7 +23,7 @@ try:
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QTextEdit, QProgressBar, QTabWidget, QFrame, QCheckBox,
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QSpinBox, QMessageBox, QStatusBar, QScrollArea
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)
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from PySide6.QtCore import Qt, Signal, QObject, QThread, QTimer
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from PySide6.QtCore import Qt, Signal, QObject, QThread, QTimer, QEvent
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from PySide6.QtGui import QPalette, QColor, QIcon, QPixmap
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QT_BINDING = "PySide6"
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except ImportError:
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@ -34,7 +34,7 @@ except ImportError:
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QTextEdit, QProgressBar, QTabWidget, QFrame, QCheckBox,
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QSpinBox, QMessageBox, QStatusBar, QScrollArea
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)
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from PyQt6.QtCore import Qt, pyqtSignal as Signal, QObject, QThread, QTimer
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from PyQt6.QtCore import Qt, pyqtSignal as Signal, QObject, QThread, QTimer, QEvent
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from PyQt6.QtGui import QPalette, QColor, QIcon, QPixmap
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QT_BINDING = "PyQt6"
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except ImportError:
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@ -931,6 +931,66 @@ def main():
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win.raise_()
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win.activateWindow()
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# Wayland map watchdog. On some compositor/toolkit combos (seen live on
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# Sway 1.12 + Qt 6.9: a handshake deadlock where Qt never sends the initial
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# wl_surface.commit, so the compositor never sends configure) the event
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# loop runs but the window NEVER maps — the app looks "started" yet nothing
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# appears. In that state no Expose event is ever delivered, so LATCH the
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# first expose; do NOT sample isExposed() at the deadline (a healthy window
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# that is merely hidden — other workspace, scratchpad, locker — reads
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# unexposed ~100 ms after frame callbacks stop and would misfire). If no
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# expose ever arrived, relaunch this same process on XWayland (xcb), which
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# is unaffected. The sentinel env var prevents any relaunch loop (e.g.
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# "-platform wayland" in argv outranks the env override and would come up
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# wayland again). Nothing auto-starts jobs before the deadline, so the exec
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# cannot interrupt real work. Opt out with VAPTVUPT_NO_XCB_FALLBACK=1.
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if app.platformName().startswith("wayland"):
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class _ExposeLatch(QObject):
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exposed_once = False
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def eventFilter(self, obj, ev):
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if ev.type() == QEvent.Type.Expose and obj.isExposed():
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self.exposed_once = True
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return False
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latch = _ExposeLatch()
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handle = win.windowHandle()
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if handle is not None:
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handle.installEventFilter(latch)
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def _wayland_map_check():
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if latch.exposed_once or (handle is not None and handle.isExposed()):
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return
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can_fallback = (os.environ.get("DISPLAY")
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and sys.executable
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and os.environ.get("VAPTVUPT_NO_XCB_FALLBACK") != "1"
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and os.environ.get("VAPTVUPT_XCB_FALLBACK_DONE") != "1")
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if sys.stderr is not None:
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try:
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sys.stderr.write(
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"Window was not exposed within 4 s (the compositor may "
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"never have mapped it); "
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+ ("relaunching on XWayland (xcb)...\n" if can_fallback
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else "leaving the Wayland window as-is (no X11 "
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"fallback: DISPLAY unset, opted out, or "
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"already tried).\n"))
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sys.stderr.flush()
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except OSError:
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pass
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if can_fallback:
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env = dict(os.environ, QT_QPA_PLATFORM="xcb",
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VAPTVUPT_XCB_FALLBACK_DONE="1")
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argv = (list(sys.argv) if getattr(sys, "frozen", False)
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else [sys.executable] + sys.argv)
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try:
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os.execve(sys.executable, argv, env)
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except OSError as exc:
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if sys.stderr is not None:
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try:
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sys.stderr.write(f"XWayland relaunch failed ({exc});"
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" window will not appear.\n")
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sys.stderr.flush()
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except OSError:
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pass
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QTimer.singleShot(4000, _wayland_map_check)
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# A GUI blocks the launching shell, so a working launch otherwise looks like
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# a "stuck" terminal. Emit one line to stderr so it's unambiguous. Guarded:
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# PyInstaller --windowed sets sys.stderr to None (any write would raise and
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