Mac/Metal: After alt-tab, `get_current_texture` locks for exactly one second

[emilk]

Description

When alt-tabbing between applications I notice that sometimes (often, not always) the wgpu app will wait a full second before showing up after being hidden.

Repro steps

1. On Mac, run cargo r -p wgpu-example-02-hello-window.
2. Use cmd-tab to switch to any other application that covers your entire screen (and more importantly: covers the wgpu-example).
3. Use cmd-tab to switch back to the wgpu-example
4. Observe that it takes exactly one second for the wgpu-example to show up

Expected vs observed behavior

Instant switching

Extra materials

Here's a screenshot of the stack trace after I added some extra profiling scopes:

What is blocking is MetalLayerRef::next_drawable.

Platform

macOS Tahoe 26.0.1
wgpu 27.0.0

Related issues

• surface.get_current_texture blocks for the duration of fullscreen animation on macOS #5613 maybe?

[Wumpf]

Repros for me on Sequoia 15.7.1

out of curiosity I tried it against

• [metal] Use raw-window-metal to do layer creation #6210

delay is still there

[Wumpf]

@madsmtm you've previously went very deep on surfaces/layers for our Metal backend; do you happen to have any intuition or background knowledge about this issue?