Stack overflow in compat layers

[Nemo157]

Minimal repro for futures 0.3.0-alpha.7 provided by @andreasots (https://gist.github.com/andreasots/4ea3982036ad703158ee3ddc11376eee):

#![feature(await_macro, async_await, futures_api)]

use tokio::timer::Delay;
use std::time::Instant;
use futures::prelude::*;
use futures::compat::Future01CompatExt;

fn main() {
    let f = async {
        await!(Delay::new(Instant::now()).compat());
    };
    tokio::run(f.unit_error().boxed().compat());
}

Slightly snipped stack trace (can probably have more unnecessary lines removed):

#42 0x000055555556d669 in <futures_util::compat::compat03to01::CurrentRef as core::task::wake::UnsafeWake>::clone_raw (self=0x1)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat03to01.rs:98
#43 0x000055555556d87a in <core::task::wake::Waker as core::clone::Clone>::clone (self=0x7ffff63fce48) at libcore/task/wake.rs:72
#44 0x000055555556d563 in futures_util::compat::compat01to03::<impl core::convert::From<futures_util::compat::compat01to03::WakerToHandle<'a>> for futures::task_impl::NotifyHandle>::from (handle=...)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat01to03.rs:61
#45 0x000055555556cc23 in <T as core::convert::Into<U>>::into (self=...) at libcore/convert.rs:456
#46 0x00005555555682c8 in futures::task_impl::with_notify::{{closure}}::{{closure}} () at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:497
#47 0x00005555556544db in futures::task_impl::core::BorrowedUnpark::to_owned (self=0x7ffff62012a8) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/core.rs:49
#48 0x000055555564f231 in futures::task_impl::std::BorrowedUnpark::to_owned (self=0x7ffff63fc988) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/std/mod.rs:124
[...]
#20649 0x0000555555652f2f in futures::task_impl::current::{{closure}} (borrowed=0x7ffff63fc980) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:116
#20650 0x0000555555652eaa in futures::task_impl::with (f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:45
#20651 0x0000555555652ef1 in futures::task_impl::current () at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:115
#20652 0x000055555556d669 in <futures_util::compat::compat03to01::CurrentRef as core::task::wake::UnsafeWake>::clone_raw (self=0x1)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat03to01.rs:98
#20653 0x000055555556d87a in <core::task::wake::Waker as core::clone::Clone>::clone (self=0x7ffff63fce48) at libcore/task/wake.rs:72
#20654 0x000055555556d563 in futures_util::compat::compat01to03::<impl core::convert::From<futures_util::compat::compat01to03::WakerToHandle<'a>> for futures::task_impl::NotifyHandle>::from (handle=...)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat01to03.rs:61
#20655 0x000055555556cc23 in <T as core::convert::Into<U>>::into (self=...) at libcore/convert.rs:456
#20656 0x00005555555682c8 in futures::task_impl::with_notify::{{closure}}::{{closure}} () at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:497
#20657 0x00005555556544db in futures::task_impl::core::BorrowedUnpark::to_owned (self=0x7ffff63fc5d8) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/core.rs:49
#20658 0x000055555564f231 in futures::task_impl::std::BorrowedUnpark::to_owned (self=0x7ffff63fc988) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/std/mod.rs:124
#20659 0x0000555555652f2f in futures::task_impl::current::{{closure}} (borrowed=0x7ffff63fc980) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:116
[...]
#20666 0x0000555555569cfb in futures_util::compat::compat01to03::<impl core::future::future::Future for futures_util::compat::compat::Compat<Fut>>::poll::{{closure}} ()
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat01to03.rs:26
#20667 0x000055555556b6cc in futures::task_impl::std::set (task=0x7ffff63fc980, f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/std/mod.rs:78
#20668 0x0000555555568247 in futures::task_impl::with_notify::{{closure}} (task=0x7ffff63fcfe0) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:505
#20669 0x00005555555683b8 in futures::task_impl::with (f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:45
#20670 0x000055555556817b in futures::task_impl::with_notify (notify=0x7ffff63fcad8, id=0, f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:496
#20671 0x000055555556aa8e in futures_util::compat::compat01to03::<impl core::future::future::Future for futures_util::compat::compat::Compat<Fut>>::poll (self=..., lw=0x7ffff63fce48)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat01to03.rs:25
[...]
#20682 0x0000555555569ab1 in futures_util::compat::compat03to01::<impl futures::future::Future for futures_util::compat::compat::Compat<Fut>>::poll::{{closure}} (inner=..., lw=0x7ffff63fce48)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat03to01.rs:21
#20683 0x0000555555569c4c in futures_util::compat::compat03to01::with_context (compat=0x7ffff6a21088, f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat03to01.rs:122
#20684 0x000055555556aab3 in futures_util::compat::compat03to01::<impl futures::future::Future for futures_util::compat::compat::Compat<Fut>>::poll (self=0x7ffff6a21088)
    at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.7/src/compat/compat03to01.rs:21
#20685 0x0000555555651205 in <alloc::boxed::Box<F> as futures::future::Future>::poll (self=0x7ffff6a540c8) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/future/mod.rs:113
#20686 0x00005555555eef13 in <futures::task_impl::Spawn<T>>::poll_future_notify::{{closure}} (f=0x7ffff6a540c8) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:314
#20687 0x00005555555ef1d0 in <futures::task_impl::Spawn<T>>::enter::{{closure}} () at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:388
#20688 0x00005555555da34c in futures::task_impl::std::set (task=0x7ffff63fcfe0, f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/std/mod.rs:78
#20689 0x00005555555ef04b in <futures::task_impl::Spawn<T>>::enter (self=0x7ffff6a540a0, unpark=..., f=...) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:388
#20690 0x00005555555eee7a in <futures::task_impl::Spawn<T>>::poll_future_notify (self=0x7ffff6a540a0, notify=0x7ffff63fd9e8, id=140737331413120) at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/futures-0.1.24/src/task_impl/mod.rs:314
#20691 0x00005555555cd065 in tokio_threadpool::task::Task::run::{{closure}} () at /home/andreas/.cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/tokio-threadpool-0.1.7/src/task/mod.rs:127

The issue appears to be because CurrentRef delays getting the task until it's needed it waits too long and the task's waker has already been replaced with a NotifyWaker that tries to use the CurrentRef, making a loop. Removing CurrentRef and producing a CurrentOwned straight away when needed fixes it. I assume CurentRef is there because CurrentOwned can be expensive with the Arc and accessing task::current, maybe there's an alternative optimization that could be done and will be safe against task::current being changed under it?

cc @seanmonstar since you introduced CurrentRef

[tikue]

@Nemo157 do you have a diff of the workaround I could use until this is fixed?

[Nemo157]

@tikue it was just deleting CurrentRef and changing places that used it to use CurrentOwned instead, I didn't keep the code around. #1286 looks like it's probably a better solution, you could try that out.