rust async_runtime_error ai_generated true

Cannot start a runtime from within a runtime. This happens because a function attempted to block the current thread while the thread is being used to drive asynchronous tasks.

ID: rust/rust-tokio-runtime-shutdown

Also available as: JSON · Markdown
85%Fix Rate
88%Confidence
50Evidence
2023-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1 active — — —

Root Cause

Nested tokio runtimes are not allowed. Calling block_on inside an async context causes this panic.

generic

Workarounds

  1. 90% success Use tokio::spawn instead of block_on for nested async calls 
    // Instead of: runtime.block_on(future)
// Use: tokio::spawn(async { future.await })

    Sources: https://tokio.rs/tokio/tutorial/spawning

  2. 85% success Use Handle::current() with spawn_blocking for sync-in-async bridges 
    let handle = tokio::runtime::Handle::current();
std::thread::spawn(move || {
    handle.block_on(async_function())
}).join().unwrap();

    Sources: https://docs.rs/tokio/latest/tokio/runtime/struct.Handle.html

Dead Ends

Common approaches that don't work:

  1. Create a new Runtime::new() inside the async function 95% fail

    This is exactly what causes the error; nesting runtimes is forbidden

  2. Use std::thread::spawn to run another runtime 55% fail

    While technically works, it defeats the purpose of async and introduces complex synchronization

Error Chain

Leads to:
Preceded by:
Frequently confused with: