Overview

This is a repro for a memory/resource leak using the metal backend of wgpu 0.19. This was not present in version 0.18.

The example is a hybrid of the learn-wgpu for Buffers and Indices and Wgpu without a window. It uses wgpu to render a pentagon and then write it to a PNG file (without opening a window). Then the program attempts to perform this action several hundred times in a loop.

When running on an M1 mac using the metal backend, this worked fine with wgpu 0.18. But starting in 0.19.0 (and through 0.19.3) this crashes with the backtrace shown below.

System specs

These are the specs of the machine that demonstrates this repro:

Chip: Apple M1 Pro macOS: Sonoma 14.4.1 Memory 32 GB

Instructions

Run the repro with:

RUST_BACKTRACE=1 cargo run

Result

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Context leak detected, msgtracer returned -1
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thread 'main' panicked at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/foreign-types-shared-0.3.1/src/lib.rs:72:9:
assertion failed: !ptr.is_null()
stack backtrace:
   0: rust_begin_unwind
             at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:645:5
   1: core::panicking::panic_fmt
             at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/panicking.rs:72:14
   2: core::panicking::panic
             at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/panicking.rs:144:5
   3: foreign_types_shared::ForeignTypeRef::from_ptr
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/foreign-types-shared-0.3.1/src/lib.rs:72:9
   4: <metal::commandqueue::CommandQueue as core::ops::deref::Deref>::deref
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/metal-0.27.0/src/commandqueue.rs:13:1
   5: wgpu_hal::metal::command::<impl wgpu_hal::CommandEncoder<wgpu_hal::metal::Api> for wgpu_hal::metal::CommandEncoder>::begin_encoding::{{closure}}
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-hal-0.19.3/src/metal/command.rs:179:17
   6: objc::rc::autorelease::autoreleasepool
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/objc-0.2.7/src/rc/autorelease.rs:29:5
   7: wgpu_hal::metal::command::<impl wgpu_hal::CommandEncoder<wgpu_hal::metal::Api> for wgpu_hal::metal::CommandEncoder>::begin_encoding
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-hal-0.19.3/src/metal/command.rs:175:19
   8: wgpu_core::device::queue::PendingWrites<A>::activate
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-core-0.19.3/src/device/queue.rs:265:17
   9: wgpu_core::device::resource::Device<A>::new
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-core-0.19.3/src/device/resource.rs:230:9
  10: wgpu_core::instance::Adapter<A>::create_device_and_queue_from_hal
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-core-0.19.3/src/instance.rs:306:29
  11: wgpu_core::instance::Adapter<A>::create_device_and_queue
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-core-0.19.3/src/instance.rs:381:9
  12: wgpu_core::instance::<impl wgpu_core::global::Global<G>>::adapter_request_device
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-core-0.19.3/src/instance.rs:1084:23
  13: <wgpu::backend::wgpu_core::ContextWgpuCore as wgpu::context::Context>::adapter_request_device
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-0.19.3/src/backend/wgpu_core.rs:587:44
  14: <T as wgpu::context::DynContext>::adapter_request_device
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-0.19.3/src/context.rs:2019:22
  15: wgpu::Adapter::request_device
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-0.19.3/src/lib.rs:2119:22
  16: wgpu_memory_repro::State::new::{{closure}}
             at ./src/main.rs:103:31
  17: wgpu_memory_repro::run::{{closure}}
             at ./src/main.rs:300:34
  18: pollster::block_on
             at /Users/jonmmease/.cargo/registry/src/index.crates.io-6f17d22bba15001f/pollster-0.3.0/src/lib.rs:128:15
  19: wgpu_memory_repro::main
             at ./src/main.rs:309:9
  20: core::ops::function::FnOnce::call_once
             at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

The Context leak detected, msgtracer returned -1 line looks significant.

Run with 0.18

To run with 0.18, swap comments in Cargo.toml from

#wgpu = {version = "=0.18.0", default-features = false, features = ["wgsl"]}
wgpu = {version = "=0.19.3", default-features = false, features = ["wgsl", "metal"]}

to

wgpu = {version = "=0.18.0", default-features = false, features = ["wgsl"]}
#wgpu = {version = "=0.19.3", default-features = false, features = ["wgsl", "metal"]}

Then in main.rs, swap comments from

        // // wgpu 0.18
        // let device_descriptor = wgpu::DeviceDescriptor {
        //     label: None,
        //     features: wgpu::Features::empty(),
        //     limits: wgpu::Limits::default(),
        // };

        // wgpu 0.19.3
        let device_descriptor = wgpu::DeviceDescriptor {
            label: None,
            required_features: wgpu::Features::empty(),
            required_limits: wgpu::Limits::default(),
        };

to

        // wgpu 0.18
        let device_descriptor = wgpu::DeviceDescriptor {
            label: None,
            features: wgpu::Features::empty(),
            limits: wgpu::Limits::default(),
        };

        // // wgpu 0.19.3
        // let device_descriptor = wgpu::DeviceDescriptor {
        //     label: None,
        //     required_features: wgpu::Features::empty(),
        //     required_limits: wgpu::Limits::default(),
        // };

Then run as above. In this case, the program completes successfully.