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rust.uncancelled_tasks

Stability Medium

Detects spawned tasks that are never cancelled, leading to resource leaks and runaway processes.

Why It Matters

Uncancelled tasks:

Leak resources - Tasks run forever
Consume memory - Accumulating state
Prevent shutdown - Graceful termination fails

Example

// ❌ Before (task never cancelled)
let _handle = tokio::spawn(background_work());
// handle ignored, no way to cancel

// ✅ After (with cancellation)
use tokio_util::sync::CancellationToken;

let token = CancellationToken::new();
let cloned = token.clone();
let handle = tokio::spawn(async move {
    loop {
        tokio::select! {
            _ = cloned.cancelled() => break,
            _ = do_work() => {}
        }
    }
});

// When shutting down:
token.cancel();
handle.await?;

What Unfault Detects

Spawned tasks with ignored handles
Missing cancellation tokens
Tasks without shutdown paths