1 cfg_rt! { 2 pub(crate) use crate::runtime::spawn_blocking; 3 pub(crate) use crate::task::JoinHandle; 4 } 5 6 cfg_not_rt! { 7 use std::fmt; 8 use std::future::Future; 9 use std::pin::Pin; 10 use std::task::{Context, Poll}; 11 12 pub(crate) fn spawn_blocking<F, R>(_f: F) -> JoinHandle<R> 13 where 14 F: FnOnce() -> R + Send + 'static, 15 R: Send + 'static, 16 { 17 assert_send_sync::<JoinHandle<std::cell::Cell<()>>>(); 18 panic!("requires the `rt` Tokio feature flag") 19 20 } 21 22 pub(crate) struct JoinHandle<R> { 23 _p: std::marker::PhantomData<R>, 24 } 25 26 unsafe impl<T: Send> Send for JoinHandle<T> {} 27 unsafe impl<T: Send> Sync for JoinHandle<T> {} 28 29 impl<R> Future for JoinHandle<R> { 30 type Output = Result<R, std::io::Error>; 31 32 fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> { 33 unreachable!() 34 } 35 } 36 37 impl<T> fmt::Debug for JoinHandle<T> 38 where 39 T: fmt::Debug, 40 { 41 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { 42 fmt.debug_struct("JoinHandle").finish() 43 } 44 } 45 46 fn assert_send_sync<T: Send + Sync>() { 47 } 48 } 49