{"record":{"id":"0c5680f09d8348d0","repo":"crossbeam-rs/crossbeam","slug":"failed-to-spawn-scoped-thread","errorCode":null,"errorMessage":"failed to spawn scoped thread","messagePattern":"failed to spawn scoped thread","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"crossbeam-utils/src/thread.rs","lineNumber":266,"sourceCode":"    ///     let handle = s.spawn(|_| {\n    ///         println!(\"A child thread is running\");\n    ///         42\n    ///     });\n    ///\n    ///     // Join the thread and retrieve its result.\n    ///     let res = handle.join().unwrap();\n    ///     assert_eq!(res, 42);\n    /// }).unwrap();\n    /// ```\n    pub fn spawn<'scope, F, T>(&'scope self, f: F) -> ScopedJoinHandle<'scope, T>\n    where\n        F: FnOnce(&Scope<'env>) -> T,\n        F: Send + 'env,\n        T: Send + 'env,\n    {\n        self.builder()\n            .spawn(f)\n            .expect(\"failed to spawn scoped thread\")\n    }\n\n    /// Creates a builder that can configure a thread before spawning.\n    ///\n    /// # Examples\n    ///\n    /// ```\n    /// use crossbeam_utils::thread;\n    ///\n    /// thread::scope(|s| {\n    ///     s.builder()\n    ///         .spawn(|_| println!(\"A child thread is running\"))\n    ///         .unwrap();\n    /// }).unwrap();\n    /// ```\n    pub fn builder<'scope>(&'scope self) -> ScopedThreadBuilder<'scope, 'env> {\n        ScopedThreadBuilder {\n            scope: self,","sourceCodeStart":248,"sourceCodeEnd":284,"githubUrl":"https://github.com/crossbeam-rs/crossbeam/blob/38dacb462261fcd64edcb308aed9cbf95c8c82c3/crossbeam-utils/src/thread.rs#L248-L284","documentation":"`Scope::spawn` delegates to `std::thread::Builder::spawn_scoped` and `.expect(...)`s the result, so any OS-level failure to create the underlying thread (e.g. resource exhaustion) panics with this message. The scope guarantees safety, but thread creation itself can still fail.","triggerScenarios":"Calling `scope.spawn(f)` when the OS cannot create a thread: hit the process/thread limit (RLIMIT_NPROC, cgroup pids.max), out of memory for the stack, invalid configured stack size, or permission restrictions on thread creation.","commonSituations":"Spawning thousands of scoped threads in a loop and exhausting `ulimit -u`; running in a container with a low pids limit; setting an invalid `stack_size` via `Scope::builder()`; CI runners with restrictive rlimits.","solutions":["Use `scope.builder().spawn(f)` and handle the returned `io::Result` instead of the infallible `scope.spawn`","Raise thread limits (`ulimit -u`, container pids.max) or reduce concurrent thread count with a worker pool/semaphore","Check available memory and fix any invalid `stack_size` configured on the builder"],"exampleFix":"// before\nscope.spawn(|s| worker(s)); // panics on resource exhaustion\n\n// after\nmatch scope.builder().spawn(|s| worker(s)) {\n    Ok(handle) => { /* ... */ }\n    Err(e) => eprintln!(\"skipping worker: {e}\"),\n}","handlingStrategy":"fallback","validationCode":"// pre-check before spawning\nlet limits = rlimit::Resource::NPROC.get()?;\nif active_threads as u64 >= limits.0 { return Err(ThreadLimitReached); }","typeGuard":null,"tryCatchPattern":"match scope.builder().spawn(|s| work(s)) {\n    Ok(h) => handles.push(h),\n    Err(e) => log::warn!(\"spawn failed: {e}\"), // degrade gracefully\n}","preventionTips":["Use scope.builder().spawn() when spawn failure is plausible","Bound concurrency with a worker pool instead of unbounded spawning","Check ulimit -u / container pids.max in constrained environments","Validate custom stack_size values passed to the builder"],"tags":["rust","crossbeam-utils","threads","panic","spawn"],"backgroundTag":"thread-interrupted","analyzedSha":"38dacb462261fcd64edcb308aed9cbf95c8c82c3","analyzedAt":"2026-09-13T03:24:01.537Z","contentChangedAt":"2026-09-13T03:24:01.537Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}