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Audit mid-flight waitIdleForShutdown sites for bounded semantics #14

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opened 2026-04-18 15:28:17 +00:00 by a73x · 0 comments
a73x commented 2026-04-18 15:28:17 +00:00 (Migrated from git.a73x.sh)
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[claude 2026-04-18] Opened as follow-up to ab6c92f0 (Vulkan bounded waits).

The bounded-waits work migrated all 14 deviceWaitIdle / queueWaitIdle
sites to vk_sync.waitIdleForShutdown (which wraps vkd.deviceWaitIdle
with an unbounded wait and swallows errors to a log line). This
preserved existing behavior while satisfying the grep gate.

However, five of those sites are mid-flight or hot-ish paths — not
shutdown drains — where the driver could wedge exactly the way
ab6c92f0 documented:

  • src/main.zig (scale_pending arm, formerly :424) — before rebuildFaceForScale
  • src/main.zig (resize arm, grid-changed branch, formerly :462) — before recreateSwapchain
  • src/main.zig (resize arm, grid-unchanged branch, formerly :479) — before recreateSwapchain
  • src/main.zig (OutOfDateKHR arm in drawCells catch, formerly :681) — before recreateSwapchain
  • src/renderer.zig uploadAtlas — formerly queueWaitIdle on graphics_queue (one-shot init/capture path; widening to deviceWaitIdle silently swallows DeviceLost during initial atlas upload)

All wait unbounded while the driver may be wedged. If the hang mode
from ab6c92f0 fires during a resize, scale change, or initial atlas
upload, we'll freeze again with the same symptoms.

Scope of this ticket:

  1. Implement vk_sync.waitIdleBounded (currently a @compileError stub).
    The fence-based emulation: submit a no-op to the graphics queue,
    wait on its fence with a timeout. Return error.VkWaitTimeout on
    timeout.
  2. Migrate the four mid-flight main.zig sites from waitIdleForShutdown
    to waitIdleBounded; handle the new timeout error in each caller.
  3. Restore error propagation in uploadAtlas (currently vk_sync.waitIdleForShutdown(self.vkd, self.device); — needs a queue-bounded helper or equivalent fence-based pattern to surface DeviceLost during init).
  4. Keep the ten remaining shutdown/init/bench sites as
    waitIdleForShutdown — those are correct as-is.

Priority: low. The NVIDIA 595 driver flake observed on 2026-04-18
was a fence-wait wedge in drawCells, not a resize/scale wedge.
Resize/scale/init paths have not been observed to hang. File so the
work isn't lost.

Migrated from git-collab issue 0e342b6e65577b240fa92a8b633511a4fa41bf59.

Original author: a73x dev@a73x.sh.

[claude 2026-04-18] Opened as follow-up to ab6c92f0 (Vulkan bounded waits). The bounded-waits work migrated all 14 deviceWaitIdle / queueWaitIdle sites to vk_sync.waitIdleForShutdown (which wraps vkd.deviceWaitIdle with an unbounded wait and swallows errors to a log line). This preserved existing behavior while satisfying the grep gate. However, five of those sites are mid-flight or hot-ish paths — not shutdown drains — where the driver could wedge exactly the way ab6c92f0 documented: - src/main.zig (scale_pending arm, formerly :424) — before rebuildFaceForScale - src/main.zig (resize arm, grid-changed branch, formerly :462) — before recreateSwapchain - src/main.zig (resize arm, grid-unchanged branch, formerly :479) — before recreateSwapchain - src/main.zig (OutOfDateKHR arm in drawCells catch, formerly :681) — before recreateSwapchain - src/renderer.zig uploadAtlas — formerly queueWaitIdle on graphics_queue (one-shot init/capture path; widening to deviceWaitIdle silently swallows DeviceLost during initial atlas upload) All wait unbounded while the driver may be wedged. If the hang mode from ab6c92f0 fires during a resize, scale change, or initial atlas upload, we'll freeze again with the same symptoms. Scope of this ticket: 1. Implement vk_sync.waitIdleBounded (currently a @compileError stub). The fence-based emulation: submit a no-op to the graphics queue, wait on its fence with a timeout. Return error.VkWaitTimeout on timeout. 2. Migrate the four mid-flight main.zig sites from waitIdleForShutdown to waitIdleBounded; handle the new timeout error in each caller. 3. Restore error propagation in uploadAtlas (currently `vk_sync.waitIdleForShutdown(self.vkd, self.device);` — needs a queue-bounded helper or equivalent fence-based pattern to surface DeviceLost during init). 4. Keep the ten remaining shutdown/init/bench sites as waitIdleForShutdown — those are correct as-is. Priority: low. The NVIDIA 595 driver flake observed on 2026-04-18 was a fence-wait wedge in drawCells, not a resize/scale wedge. Resize/scale/init paths have not been observed to hang. File so the work isn't lost. --- Migrated from git-collab issue `0e342b6e65577b240fa92a8b633511a4fa41bf59`. Original author: a73x <dev@a73x.sh>.
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a73x/waystty#14
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