Mismatched pop_error_scope call: no error scope for this thr

Error message

Mismatched pop_error_scope call: no error scope for this thread. Error scopes are thread-local.

What it means

pop_error_scope panics when the thread-local error scope count is 0 (no matching push) or when scopes are popped out of order. Error scopes in the web backend are tracked per thread, so popping from a different thread than the push, or an extra/mismatched pop, is a programming error rather than a GPU error.

Source

Thrown at wgpu/src/backend/webgpu.rs:2780

        let index = self.error_scope_count.get();
        self.error_scope_count.set(
            index
                .checked_add(1)
                .expect("Greater than 2^32 nested error scopes"),
        );
        self.inner.push_error_scope(match filter {
            crate::ErrorFilter::OutOfMemory => webgpu_sys::GpuErrorFilter::OutOfMemory,
            crate::ErrorFilter::Validation => webgpu_sys::GpuErrorFilter::Validation,
            crate::ErrorFilter::Internal => webgpu_sys::GpuErrorFilter::Internal,
        });
        index
    }

    fn pop_error_scope(&self, index: u32) -> Pin<Box<dyn dispatch::PopErrorScopeFuture>> {
        let current_scope_count = self.error_scope_count.get();
        let is_panicking = crate::util::is_panicking();
        if current_scope_count == 0 && !is_panicking {
            panic!("Mismatched pop_error_scope call: no error scope for this thread. Error scopes are thread-local.");
        }
        if index + 1 != current_scope_count && !is_panicking {
            panic!(
                "Mismatched pop_error_scope call: error scopes must be popped in reverse order."
            );
        }
        // Decrement the error scope count. We've asserted that the current
        // size is `index + 1` above.
        self.error_scope_count.set(index);

        let error_promise = self.inner.pop_error_scope();
        Box::pin(MakeSendFuture::new(
            wasm_bindgen_futures::JsFuture::from(error_promise),
            future_pop_error_scope,
        ))
    }

    unsafe fn start_graphics_debugger_capture(&self) {

View on GitHub (pinned to 3e11ff59bf)

Solutions

Ensure every pop_error_scope is called on the same thread as its matching push_error_scope; in async code, await the returned future rather than hopping threads.
Balance push/pop pairs in RAII-style helpers or guaranteed control flow so counts never go negative or out of order.
Pop scopes in reverse order (LIFO) when nesting error scopes.

Example fix

// before
let handle = device.push_error_scope(wgpu::ErrorFilter::Validation);
spawn(async move { let err = handle.pop().await; }); // different thread: panics
// after
let handle = device.push_error_scope(wgpu::ErrorFilter::Validation);
let err = handle.pop().await; // same thread, awaited in order

Defensive patterns

Strategy: try-catch

Validate before calling

// before popping, ensure the current scope exists (app-level counter mirrored from push calls)
assert!(active_error_scopes.get() > 0, "no error scope to pop on this thread");

Try / catch

// wgpu's pop_error_scope returns a future resolving to Result, but this panic is synchronous;
// prevent it structurally with an RAII guard:
struct ErrorScope<'a> { device: &'a wgpu::Device }
impl<'a> ErrorScope<'a> {
    async fn pop(self) -> Option<wgpu::Error> { self.device.pop_error_scope().await }
}
impl Drop for ErrorScope<'_> { /* ensure balanced push/pop per thread */ }

Prevention

Always push and pop error scopes on the same thread; never move the pop future across threads/tasks.
Use an RAII guard or explicit counter so pushes and pops stay balanced and LIFO.
Avoid early returns between push and pop that unbalance the scope stack.

When it happens

Trigger: Calling device.pop_error_scope without a preceding push_error_scope on the same thread; pushing on the main thread and popping inside an async callback/worker or wasm task that runs on another thread context; popping two scopes in the wrong order.

Common situations: Awaiting pop_error_scope across an async runtime boundary (spawned task) instead of the pushing thread; forgetting a push after early-return code paths; over-popping in nested scope helpers.

Related errors

AI-assisted analysis of gfx-rs/wgpu@3e11ff59bf (2026-09-03). Data as JSON: /api/errors/ff3be7851d3d5bb0. Report an issue: GitHub.