"""Let a background thread run Python only while the render thread waits on vsync. With plugin rendering moved to Vegas's prefetch thread (DisplayManager.offscreen, #630) the render thread no longer stops for it, but it still shares the GIL with it. The render thread spends most of each refresh inside SwapOnVSync, which releases the GIL, and needs it back the moment the swap returns. If the prefetch thread is running Python right then, the render thread waits: up to the switch interval (5ms) behind bytecode, and for as long as a C call that keeps the GIL takes. On hdpi that showed up as frames 2-5 refreshes late while a group was being prepared. The gate turns that around. The display manager opens it just before each swap, with a deadline shortly ahead of the refresh the swap will return on, and closes it when the swap returns. A thread inside ``gate.yielding()`` checks it on every Python and C call through a profile hook, and once the window has closed it parks -- blocked on a condition, GIL released -- until the next swap opens it. The render thread then finds the GIL free when its refresh arrives, and the background work runs in time the render thread was only spending waiting. Parking a thread is only safe if nothing the render thread needs is stuck behind it, so it is never parked: * while it holds a lock registered with ``guard()`` (the Vegas buffers and caches the render thread also takes); * inside logging, threading, importlib or the cache, all of which take locks the render thread can take too; * when there is no render loop to protect -- no swap for ``STALE_SECONDS``, as on a static screen or a stalled frame. And a parked thread is never held more than ``MAX_WAIT_SECONDS`` at a time, so whatever the gate gets wrong costs a frame, not a freeze. The render thread itself is never gated, whatever it calls. The prefetch thread is not the only one that competes. Once an hour the sports plugins refresh their schedules together, about twenty ESPN chunk-fetch threads at once (hdpi, 2026-09-24), and the render thread queued behind all of them for a 1.9s freeze. So Vegas also makes its gate the *active* one, and code that runs background fetches wraps them in the module-level ``yielding()``, which uses the active gate if there is one and does nothing otherwise: ``espn_dates``' chunk fetches and the background data service's workers. Only worth enabling on a binding whose SwapOnVSync releases the GIL (see scripts/build_rgbmatrix_nogil.sh). With one that keeps it, the window never lets the background thread run and it only makes progress in the timeouts. """ from __future__ import annotations import math import sys import threading import time from collections import deque from contextlib import nullcontext from typing import Any, Callable, ContextManager, Deque, List, Optional #: Park background threads this long before the refresh a swap will return on, #: so a short C call already under way has finished by then. MARGIN_SECONDS = 0.002 #: The longest a background thread is parked in one go. MAX_WAIT_SECONDS = 0.05 #: No swap for this long means there is no render loop running to protect. STALE_SECONDS = 0.05 #: Swaps needed before the refresh period is trusted enough to open a window. MIN_SAMPLES = 8 #: Parking with any of these on the stack could hold a lock the render #: thread takes: logging handler locks, Condition and Event internals, the #: module import locks, and the disk and memory cache locks. _UNSAFE_PATHS = ( "logging", "threading.py", "importlib", "cache", ) def _unsafe(frame: Any, base: Any) -> bool: """True if a frame above ``base`` comes from somewhere parking could deadlock. ``base`` is the frame that entered ``yielding()``; what lies below it (the thread's own bootstrap in threading.py) holds nothing. """ while frame is not None and frame is not base: filename = frame.f_code.co_filename for part in _UNSAFE_PATHS: if part in filename: return True frame = frame.f_back return False def swap_releases_gil() -> Optional[bool]: """Whether the loaded rgbmatrix binding releases the GIL, or None if none is loaded. The rebuilt binding links PyEval_SaveThread and the stock one never does. The same test as src.common.frame_timing.binding_releases_gil (#629); one of the two goes once both have landed. """ module = sys.modules.get("rgbmatrix.core") path = getattr(module, "__file__", None) if not path: return None try: with open(path, "rb") as handle: return b"PyEval_SaveThread" in handle.read() except OSError: return None def _held(lock: Any) -> bool: """Is ``lock`` held? RLocks report this thread's ownership; plain locks, anyone's.""" is_owned = getattr(lock, "_is_owned", None) if is_owned is not None: return is_owned() return lock.locked() class RenderGate: """Opened by the render thread around each swap; honoured by background threads.""" def __init__(self, clock: Callable[[], float] = time.monotonic): self.clock = clock self._cond = threading.Condition() self._generation = 0 self._open_until = 0.0 self._last_return: Optional[float] = None self._periods: Deque[float] = deque(maxlen=64) self._period: Optional[float] = None self._guarded: List[Any] = [] self._local = threading.local() self._render_ident: Optional[int] = None #: How often, and for how long in all, background threads were parked. self.parks = 0 self.parked_seconds = 0.0 def guard(self, *locks: Any) -> None: """Never park a thread while it holds (or, for a plain Lock, anyone holds) these.""" self._guarded.extend(lock for lock in locks if lock is not None) # -- render thread ----------------------------------------------------- def refresh_period(self) -> Optional[float]: """The panel's refresh period from recent swaps, or None until known. The 10th percentile of the gaps between swap returns, each divided by the hold: a late frame only ever lengthens a gap, so the low end is the panel's own period. """ return self._period def before_swap(self, hold: int) -> None: """The render thread is about to block in SwapOnVSync: open the window.""" hold = max(1, int(hold)) period = self._period now = self.clock() last = self._last_return if period and last is not None and now - last < STALE_SECONDS: # The swap returns on the first refresh boundary after both the # current frame's hold is up and this frame has been handed over; # boundaries fall a whole period apart from the last return. refreshes = max(hold, math.ceil((now - last) / period)) open_until = last + refreshes * period - MARGIN_SECONDS else: open_until = 0.0 # no rhythm to predict from: leave threads be with self._cond: self._open_until = open_until self._generation += 1 self._cond.notify_all() def after_swap(self, hold: int) -> None: """The swap returned and the render thread needs the GIL: close the window.""" now = self.clock() self._open_until = 0.0 if self._render_ident is None: # The first thread to swap is the render loop. A plugin pushing a # live refresh from its update thread swaps too, but must not take # over its exemption. self._render_ident = threading.get_ident() last = self._last_return if last is not None and now - last < STALE_SECONDS: self._periods.append((now - last) / max(1, int(hold))) if len(self._periods) >= MIN_SAMPLES: ordered = sorted(self._periods) self._period = ordered[len(ordered) // 10] self._last_return = now # -- background threads ------------------------------------------------ def _should_park(self, frame: Any, now: float) -> bool: if now < self._open_until: return False # inside the window last = self._last_return if last is None or now - last > STALE_SECONDS or self._period is None: return False # no render loop to protect for lock in self._guarded: if _held(lock): return False return not _unsafe(frame, getattr(self._local, "base", None)) def _hook(self, frame: Any, _event: str, _arg: Any) -> None: now = self.clock() if not self._should_park(frame, now): return generation = self._generation with self._cond: self._cond.wait_for(lambda: self._generation != generation, timeout=MAX_WAIT_SECONDS) self.parks += 1 self.parked_seconds += self.clock() - now def yielding(self) -> "_Yielding": """``with gate.yielding():`` runs the block giving way to the render thread.""" return _Yielding(self) class _Yielding: """Installs a gate's profile hook on the thread for the length of a block.""" def __init__(self, gate: RenderGate): self.gate = gate self._previous: Any = None self._previous_base: Any = None self._skipped = False def __enter__(self) -> RenderGate: gate = self.gate # pylint: disable=protected-access if threading.get_ident() == gate._render_ident: self._skipped = True # parking the render thread parks the display return gate local = gate._local self._previous_base = getattr(local, "base", None) if self._previous_base is None: # Nested blocks keep the outermost frame, so everything the thread # entered since it first gave way is still checked for locks. local.base = sys._getframe(1) self._previous = sys.getprofile() sys.setprofile(gate._hook) return gate def __exit__(self, *_exc: Any) -> None: if self._skipped: return sys.setprofile(self._previous) self.gate._local.base = self._previous_base # pylint: disable=protected-access #: The gate of the Vegas run in progress, if any; see the module docstring. _active: Optional[RenderGate] = None def set_active(gate: Optional[RenderGate]) -> None: """Make ``gate`` the one ``yielding()`` uses (None: no gate, run freely).""" global _active # pylint: disable=global-statement _active = gate def active() -> Optional[RenderGate]: """The gate ``yielding()`` currently uses, if any.""" return _active def yielding() -> ContextManager[Any]: """``with render_gate.yielding():`` gives way to the render thread while a Vegas run has a gate, and does nothing otherwise. For background work that does not know whether Vegas is running.""" gate = _active return gate.yielding() if gate is not None else nullcontext()