Allow overriding Instance::new#9606
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Pull request overview
Adds an opt-in mechanism (gated on the custom cfg) to override Instance::new with a user-registered factory function, primarily so a custom backend (e.g. wgpu-native) can intercept instance creation in third-party code and the wgpu test suite. A new BackendOptions::skip_custom_backend_library flag lets a specific call site bypass the override, and wgpu-info gains a regression test that compares a custom-backend report against the wgpu-core report.
Changes:
- New global
set_instance_factory+INSTANCE_FACTORYatomic inwgpu/src/api/instance.rs, consulted fromInstance::newunlessskip_custom_backend_libraryis set. - New
BackendOptions::skip_custom_backend_libraryfield plusWGPU_NO_CUSTOM_BACKENDenv var handling inwgpu-types, with knock-on updates indeno_webgpu,tests/src/init.rs, andwgpu-info. - New
custom_backend_matches_wgpu_coretest inwgpu-info/src/tests.rsand small robustness changes intests/tests/wgpu-gpu/{device,mem_leaks}.rssogenerate_reportreturningNonedoesn't fail.
Reviewed changes
Copilot reviewed 10 out of 10 changed files in this pull request and generated 6 comments.
Show a summary per file
| File | Description |
|---|---|
| wgpu/src/api/instance.rs | Adds set_instance_factory and dispatch through it from Instance::new. |
| wgpu-types/src/backend.rs | Adds skip_custom_backend_library field with env-var handling in from_env_or_default (but not with_env). |
| wgpu-info/src/report.rs | GpuReport::generate now takes a skip_custom flag. |
| wgpu-info/src/cli.rs | Updates CLI caller to pass false. |
| wgpu-info/src/tests.rs | New test comparing custom-backend vs wgpu-core reports. |
| tests/src/init.rs | Explicitly initializes the new field to false. |
| tests/tests/wgpu-gpu/device.rs | Tolerates generate_report returning None for custom backends. |
| tests/tests/wgpu-gpu/mem_leaks.rs | Same: early-return when no report is available. |
| deno_webgpu/lib.rs | Sets skip_custom_backend_library: true (deno does not want overrides). |
| CHANGELOG.md | Documents the new feature. |
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| /// If false and the `custom` feature is enabled for wgpu, and if an override | ||
| /// instance factory was setup, wgpu will return a custom instance created from | ||
| /// that factory. | ||
| /// | ||
| /// Noop on wgpu-core. |
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| static INSTANCE_FACTORY: core::sync::atomic::AtomicUsize = core::sync::atomic::AtomicUsize::new(0); | ||
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| /// Register a factory that can intercept [`Instance::new`] for custom backends. | ||
| /// | ||
| /// The factory receives the [`InstanceDescriptor`] and returns `Ok(Instance)` to | ||
| /// take ownership of the request, or `Err(desc)` to fall through to the built-in backend. | ||
| /// | ||
| /// Only the first call takes effect; subsequent calls are ignored. | ||
| /// | ||
| /// This can be safely called from a constructor. | ||
| #[cfg(custom)] | ||
| pub fn set_instance_factory(f: fn(InstanceDescriptor) -> Result<Instance, InstanceDescriptor>) { | ||
| // 0 is the sentinel for "not set"; fn pointers are never null. | ||
| let _ = INSTANCE_FACTORY.compare_exchange( | ||
| 0, | ||
| f as usize, | ||
| core::sync::atomic::Ordering::Release, | ||
| core::sync::atomic::Ordering::Relaxed, | ||
| ); | ||
| } |
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| let dir = std::env::temp_dir(); | ||
| let a_path = dir.join(format!("wgpu-info-{label}-custom.json")); | ||
| let b_path = dir.join(format!("wgpu-info-{label}-core.json")); | ||
| fs::write(&a_path, a).unwrap(); | ||
| fs::write(&b_path, b).unwrap(); | ||
| let out = Command::new("diff") | ||
| .args(["-u", "--label", "with-custom", "--label", "without-custom"]) | ||
| .args([&a_path, &b_path]) | ||
| .output() | ||
| .unwrap(); | ||
| String::from_utf8(out.stdout).unwrap() |
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Connections
Closes #9595
Split out from #9570.
Description
This is mainly useful for experimentation. It lets you change the behavior of
Instance::new, though users ofInstance::newcan still opt-out of this change.It lets you override the behavior of
Instance::newto return a custom instance (one that doesn't necessarily use webgpu or wgpu-core).My use case is for running wgpu's tests on an external backend (see gfx-rs/wgpu-native#594) but it can also be used to force other libraries or apps to use your own backend, if there isn't a more convenient way.
This shouldn't be a security issue because A. it only affects wgpu, so deno and Firefox are unaffected, and B. it requires a specific function to be called before the instance is created.
Testing
Tested in gfx-rs/wgpu-native#594. That PR has a test which ensures that the custom instance is actually used.
Squash or Rebase?
Squash
Checklist
wgpumay be affected behaviorally.CHANGELOG.mdentries for the user-facing effects of this change are present.